JP2003298188A - Distributed bragg reflector, surface emission laser element, surface emission laser array, optical interconnection system and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed Bragg reflector having a low electric resistance and a high reflectance. <P>SOLUTION: In the distributed Bragg reflector (DBR), a first semiconductor layer 1 having a large refractive index and a second semiconductor layer 2 having a small refractive index are formed alternately, and a material layer 3 having a refractive index between those of the first semiconductor layer 1 and the second semiconductor layer 2 is provided between the first semiconductor layer 1 and the second semiconductor layer 2. The distributed Bragg reflector has a design reflection wavelength longer than 1.1 μm and the material layer 3 has a thickness in the range of 5-50 nm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed Bragg reflector, a surface emitting laser device, a surface emitting laser array, an optical interconnection system and an optical communication system.

[0002]

2. Description of the Related Art Conventionally, a distributed Bragg reflector (DBR) having a reflection band in the 0.85 μm band to 0.98 μm band is known as a resonator mirror of a surface emitting laser device. Further, a surface emitting laser of the same wavelength band using this is known.

The distributed Bragg reflector is constructed by alternately laminating materials having different refractive indexes to have a thickness of ¼ optical wavelength, and utilizes multiple reflection of light waves at the interface. It is possible to obtain a high reflectance.

Further, the surface emitting laser element is suitable as a light source for optical interconnection and image processing systems because it has a low oscillation threshold current, can operate at high speed, and is easily secondary-integrated. ,Attention has been paid. In the surface emitting laser element, since the region where the optical gain is generated is only a part of the resonance region and the resonator length is short,
A resonator mirror having a high reflectance of 99.9% or more is required, and a distributed Bragg reflector is suitable as this resonator mirror. Examples of the material of the distributed Bragg reflector include semiconductor materials and dielectric materials. Particularly, the distributed Bragg reflector made of a semiconductor material can be energized and is suitable for application to a laser element such as a surface emitting laser. ing.

Conventionally, as such a surface emitting laser device, devices of 0.85 μm band and 0.98 μm band made of AlGaAs based material using GaAs as a substrate are known. In this material system, semiconductor distribution made of AlGaAs material is known. Bragg reflectors are used as resonator mirrors.

The distributed Bragg reflector made of an AlGaAs material is composed of two types of AlGaAs layers having different Al compositions, a semiconductor layer having a large Al composition (for example, an AlAs layer) is used as a low refractive index layer, and a high refractive index layer. As A
A semiconductor layer having a small l composition (for example, a GaAs layer) is used. In a typical surface emitting laser device, p-type and n-type distributed Bragg reflectors are provided on both sides of the active layer to confine light waves and inject carriers into the active region. Among these two types of distributed Bragg reflectors of the conductive type, the p-type distributed Bragg reflector has a problem in that it has a high electric resistance due to the influence of the hetero interface formed by the semiconductor layers having different Al compositions.

Conventionally, in order to reduce the electric resistance of the p-type distributed Bragg reflector due to the influence of this hetero interface, for example, in a surface emitting laser device in the 0.98 μm band or the like, a reference “Photonics Technology Le” is used.
terts Vol. 2, No. 4, 1990,
p. p. 234-236, Photonics Tec
hnology Letters Vol. 4, N
o. 12, 1992, p. p. 1325-1327 "
As described above, it is known to provide a hetero barrier buffer layer such as a composition gradient layer having an Al composition in between these two kinds of layers constituting the distributed Bragg reflector having different Al compositions.

[0008]

[Problems to be Solved by the Invention]
With AlGaAs-based semiconductor materials, it is very difficult to fabricate a laser that oscillates at a wavelength longer than 1.1 μm on a GaAs substrate because of the problem of lattice distortion of the active layer. Long-wave surface emitting laser devices have not been studied.

Conventionally, as a laser device having a wavelength longer than the 1.1 μm band, a device using an InGaAsP-based material with InP as a substrate has been mainly studied, and a surface emitting laser device using this material system is manufactured. Examples have been reported. Although this material system also has a problem of high resistance due to the hetero interface, the difference in the refractive index between the InGaAsP materials, which are the materials of the distributed Bragg reflector, is originally AlGaAs.
There is a problem that it is difficult to obtain a good quality distributed Bragg reflector due to a material problem such as being very small compared to the system material and having poor thermal conductivity. It is also possible to use a distributed Bragg reflector made of a dielectric material instead of the semiconductor distributed Bragg reflector, but it requires current injection from the lateral direction, which complicates the structure and increases the operating voltage. There is a problem. Further, when InP is used as a substrate, it is difficult to use a selective oxidation process using an Al (Ga) As layer, and it is difficult to obtain a surface-emitting laser device having excellent lateral mode control by an oxidation aperture. There is a problem such as.

Due to the above problems, on the GaAs substrate and the InP substrate, a surface emitting laser element of a practical level in a wavelength range longer than 1.1 μm has not been obtained. In optical communication using quartz fiber, 1.3μ
A surface emitting laser element that oscillates in the m band and the 1.5 μm band is suitable, but conventionally, a surface emitting laser element for practical use for communication has not been obtained.

However, in recent years, as a surface emitting laser device of a long wavelength band on a GaAs substrate, by studying the growth conditions of a high strain crystal, or by studying the active layer material itself,
A surface emitting laser device having a wavelength longer than 1.1 μm on a GaAs substrate has been studied. However, as described above, conventionally, there is no example of a surface emitting laser in this wavelength band on a GaAs substrate, and a detailed study of a distributed Bragg reflector and a compositionally graded layer in a wavelength band longer than 1.1 μm is as follows. Not done yet.

Therefore, according to the prior art, in this wavelength band, a semiconductor distributed Bragg reflector excellent in both electrical characteristics (low electrical resistance) and optical characteristics (high reflectance),
Also, it is difficult to obtain a surface-emitting laser device having excellent characteristics, which uses this as a reflecting mirror.

The present invention provides a distributed Bragg reflector, a surface emitting laser element, a surface emitting laser array, an optical interconnection system, and an optical communication system, which have a low electric resistance and a high reflectance in a long wave band longer than 1.1 μm. It is intended to be provided.

[0014]

In order to achieve the above object, the invention according to claim 1 is such that a first semiconductor layer having a large refractive index and a second semiconductor layer having a small refractive index are alternately arranged. Between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index that are stacked, the refractive index of the first semiconductor layer and the second semiconductor layer are
In the distributed Bragg reflector provided with a material layer having a refractive index value between that of the semiconductor layer and the refractive index of the semiconductor layer, the designed reflection wavelength of the distributed Bragg reflector is a long wave longer than 1.1 μm, Is characterized in that the thickness is in the range of 5 nm to 50 nm.

According to a second aspect of the present invention, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated to form a first semiconductor layer having a large refractive index. A material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the layer and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector, the design reflection wavelength of the distributed Bragg reflector is 1.1 μm.
The wavelength is longer than m, and the material layer has a thickness in the range of 20 nm to 50 nm.

According to a third aspect of the present invention, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated to form a first semiconductor having a large refractive index. A material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the layer and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector, the design reflection wavelength of the distributed Bragg reflector is 1.1 μm.
The wavelength is longer than m, and the material layer has a thickness in the range of 30 nm to 50 nm.

According to a fourth aspect of the invention, in the distributed Bragg reflector according to the second aspect, the first Bragg reflector having a large refractive index and the second semiconductor layer having a small refractive index constituting the distributed Bragg reflector are provided. The semiconductor layer is AlAs, GaAs, or A
It is characterized in that the difference in Al composition between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index, which is formed of 1GaAs mixed crystal, is less than 0.8.

According to a fifth aspect of the present invention, in the distributed Bragg reflector according to the third aspect, the first semiconductor layer has a second semiconductor layer having a small refractive index and the first semiconductor layer having a large refractive index. The semiconductor layer is AlAs, GaAs, or A
It is characterized in that the difference in Al composition between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index, which is formed of 1GaAs mixed crystal, is 0.8 or more.

According to a sixth aspect of the present invention, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated to form a first semiconductor layer having a large refractive index. A material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the layer and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector, the design reflection wavelength of the distributed Bragg reflector is 1.1 μm.
The wavelength is longer than m, and the material layer has a thickness of (50) with respect to the design reflection wavelength λ [μm] of the distributed Bragg reflector.
λ−15) [nm] or less.

According to a seventh aspect of the invention, in the distributed Bragg reflector according to the sixth aspect, the material layer has a thickness of 2
It is characterized by being 0 nm or more.

The invention according to claim 8 is the distributed Bragg reflector according to claim 6, wherein the material layer has a thickness of 3
It is characterized by being 0 nm or more.

The invention according to claim 9 includes an active layer,
In a surface emitting laser device having a resonator mirror, the distributed Bragg reflector according to any one of claims 1 to 8 is used as the resonator mirror.

The invention according to claim 10 is the same as that of claim 9.
In the surface emitting laser device described above, the material of the active layer is Ga.
NAs, GaInAs, GaInNAs, GaAsS
b, GaInAsSb, or GaInNAsSb.

The invention described in claim 11 is the same as that of claim 9.
Alternatively, a surface emitting laser array comprising a plurality of surface emitting laser elements according to claim 10 is arranged.

The invention according to claim 12 is the invention according to claim 9.
An optical interconnection system using the surface emitting laser element according to claim 10 or the surface emitting laser array according to claim 11.

The invention according to claim 13 is the same as the invention according to claim 9.
An optical communication system using the surface emitting laser element according to claim 10 or the surface emitting laser array according to claim 11.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment A distributed Bragg reflector (DB) according to the first embodiment of the present invention.
In R), the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated, and the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are formed. And a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer, the distributed Bragg reflection. The design reflection wavelength of the vessel is 1.
The wavelength is longer than 1 μm, and the material layer has a thickness in the range of 5 nm to 50 nm.

Here, the design reflection wavelength is defined as follows. That is, in FIG. 1, as an example, AlAs /
The DBR reflection spectrum is shown for a stack of 24 pairs of GaAs. Here, the thickness of the AlAs layer and the thickness of the GaAs layer are 93.8 nm and 79.3 nm, respectively, which corresponds to a thickness of 1 / 4n of 1.1 μm. Note that n is a GaAs layer or AlAs at a wavelength of 1.1 μm.
The refractive index of each of the layers. As described above, when the thickness of each layer of the DBR is set to 1 / 4n of a certain wavelength λ, the highest reflectance can be obtained in the widest band in the vicinity of the wavelength λ. In the present invention, this λ is called the design reflection wavelength.

In the first embodiment, the material layer has a design reflection wavelength of 1.1 μm while maintaining a high reflectance.
It has a function of effectively reducing the resistance of the distributed Bragg reflector having a wavelength longer than m.

2 and 3 are views showing an example of the distributed Bragg reflector (DBR) according to the first embodiment of the present invention. In the example of FIGS. 2 and 3, the distributed Bragg reflector (DBR) is
A GaAs layer is used as the first semiconductor layer 1 having a large refractive index, AlAs is used as the second semiconductor layer 2 having a small refractive index, and a composition gradient layer (for example, having a thickness of 30 nm) is used, and an AlAs layer, a composition gradient layer, and a GaAs layer are cyclically and repeatedly laminated. Specifically, in the examples of FIGS. 2 and 3, AlGaAs is used as the composition gradient layer, and the composition gradient layer is formed as a linear composition gradient layer.

In the structure shown in FIGS. 2 and 3, the designed reflection wavelength (λ) of the DBR is 1.3 μm, and the AlAs layer 2 and the GaAs layer 1 each have a wavelength of λ / 4n and a thickness of 111 μm. They are 0.6 nm and 95.2 nm. Here, n is the refractive index of each semiconductor layer with respect to the wavelength of 1.3 μm. The DBRs of FIGS. 2 and 3 are adjusted in thickness such that the optical length of each semiconductor layer corresponding to the optical length of the linear composition gradient layer 3 (thickness is 30 nm) is subtracted from the above thickness. is doing. In addition, each semiconductor layer is made of AlAs.
Layer 2 is 2E18 cm ^-3 , GaAs layer 1 is 1E18c
The p-type doping is performed so that m ⁻³ and the linear composition gradient layer 3 become 2E18 cm ⁻³ .

The resistance values of the distributed Bragg reflectors of FIGS. 2 and 3 are as low as about the bulk resistance value, which is a very low value, and the design reflection wavelength is 1.3 μm, which is 0.8 compared with the conventional value.
Since it has a longer wave than the distributed Bragg reflector in the 5 μm band,
The thickness of the layer forming the DBR was large, the influence of the reduction in reflectance due to the linear composition gradient layer was small, and the optical characteristics were good. As described above, it was possible to obtain a distributed Bragg reflector having a lower resistance and a higher reflectance than the conventional one. Here, a linear composition gradient layer is used as the material layer 3, but the material layer 3 may be a non-linearly changed material, or a plurality of layers having slightly different compositions. It may be configured by.

In the first embodiment of the present invention, the set reflection wavelength of the DBR is 1.1 μm band or more, which is 0.85 μm compared with the conventional one.
The band is set to have a longer wave than the band of 0.98 μm, and the thickness of the material layer is set to a range of 5 nm to 50 nm.

For example, if the reflection wavelength is set to 1.3 μm and a long wave is generated, each layer (first semiconductor layer 1, second semiconductor layer) constituting the DBR is formed.
The thickness of the semiconductor layer 2) is about 1.5 times thicker than that of the conventional 0.85 μm band, and the relative proportion of the thickness of the material layer 3 can be reduced. In addition, the reflection wavelength is 1.5 μm
As the wavelength becomes longer, such as a band, the relative proportion of the thickness of the material layer 3 can be further reduced. As described above, the thickness of each layer (first semiconductor layer 1 and second semiconductor layer 2) constituting the DBR is proportional to the wavelength and increases as the wavelength becomes longer. The influence is reduced, and the influence such as a decrease in reflectance can be reduced.

Further, since the cause of the high resistance is due to the influence of the hetero interface, the thickness of the material layer 3 required for the low resistance is determined by the material system used, not by the wavelength band. Even in the 0.85 μm band, 1.1 μ
Even in a wavelength range longer than m, the material layer thickness required to reduce the electric resistance value to about the bulk resistance value is the same, and the length of the reflection wavelength allows the material layer 3 to have an allowable amount. The thickness is increased. As described above, when the material layer 3 having the same thickness as that of the conventional case is provided, the decrease in the reflectance is small, and when the same amount of decrease in the reflectance value as the conventional case is allowed,
The electric resistance can be made sufficiently low.

Further, the thickness of the material layer 3 is particularly 5 nm to 5 nm.
In the range of 0 nm, the following effects can be obtained.
As an example, FIG. 4 shows the relationship between the reflectance of the DBR in the 0.88 μm band and the 1.3 μm band and the thickness of the material layer (linear composition gradient layer) 3 with respect to the linear composition gradient layer 3 shown in FIG. Has been done.

The designed reflection wavelength of the conventional DBR is set to 0.
The reason why the thickness is set to 88 μm is that characteristics are compared by the material layers forming the same DBR in each band.
This is because As absorbs light having a shorter wavelength than 0.87 μm. In FIG. 4, a GaAs layer is used for the layer having a large refractive index, and an AlAs layer is used for the layer having a small refractive index.

Here, as an example of the semiconductor material of the distributed Bragg reflector, the AlGaAs type semiconductor material is shown. In particular, this material system has the following excellent properties as the material of the distributed Bragg reflector. Because there is. That is, the AlGaAs-based semiconductor material can be crystal-grown on a GaAs substrate that is inexpensive and easily available and is substantially lattice-matched, and has excellent heat dissipation properties as compared with other semiconductor material systems. In addition, Ga that is a binary material that forms a mixed crystal
The refractive index difference between As and AlAs is, for example, 1.3 μm
In the band, it is as large as about 0.5, and a high reflectance can be obtained with a smaller number of laminated pairs than other semiconductor material systems.

Here, in each wavelength band, the number of laminated pairs in which the reflectance value exceeds 99.9% for the first time is 0.88 μm.
There are 18 pairs of bands and 23 pairs of 1.3 μm bands. FIG. 4 shows the relationship between the thickness of the composition gradient layer of the DBR and the reflectance for each wavelength band having the above-mentioned number of pairs.

In the above example, the material layer 3 is a linear composition gradient layer whose composition changes linearly from GaAs to AlAs.
In addition to this, the rate of change of composition may be non-linear, and the composition is not changed continuously but discretely changed.
It may be composed of three or more layers, and
It may be a combination of these.

For example, when a DBR is used as a reflecting mirror of a surface emitting laser device, it is important to use a DBR having a high reflectance to reduce the threshold current of the device, and the influence of the reflectance due to the composition gradient layer is small. Is important.

The following table (Table 1) shows the reflectance values shown in FIG.

[0044]

[Table 1]

As described above, Table 1 shows the reflectance values shown in FIG. 4, but in the 1.3 μm band, there is almost no reduction in reflectance up to a thickness of 5 nm of the composition gradient layer 3. But,
In the 0.88 μm band, a decrease in the reflectance value is beginning to be seen from the thickness of the compositionally graded layer 3 of 5 nm. Since the surface emitting laser element has a short resonator length and the influence of reflection loss due to the mirror is very large, even a slight decrease in the reflectance value has a great influence on the threshold current value.

FIGS. 5 and 6 show an A having a reflection wavelength of 1.3 μm with a linear composition gradient layer having a structure similar to the result of FIG.
Resistivity (dV / dJ: current density J [A / of voltage V [V] near the zero bias of 1As / GaAs DBR
Differential according cm ^2]) is a diagram showing a [Ωcm ^2]. However, the number of stacked pairs is four. 5 is a logarithmic display, and FIG. 6 is a linear display. Further, in FIGS. 5 and 6, the broken line shows the result estimated from the bulk resistance value without considering the influence of band discontinuity. DBR p
Type doping density is 1E18 [cm for each layer
^-3 ].

FIG. 5 shows that the electrical resistivity decreases as the thickness of the compositionally graded layer 3 decreases.
Since the relative proportion of the compositionally graded layer 3 is small in the strip, Table 1
Further, as shown in FIG. 5, if the thickness of the compositionally graded layer is 5 nm, it is possible to reduce the electric resistance by about two digits with almost no influence on the reflectance. If the reflection wavelength is longer, a thicker composition gradient layer can be provided,
The resistance can be reduced without affecting the reflectance. However, if it is thinner than this, the effect of lowering the resistance as shown in FIG. 5 is hardly obtained, so that the thickness of the composition gradient layer is insufficient.

As shown in FIG. 5, the distributed Bragg reflector having no compositionally graded layer (distributed Bragg reflector having a compositionally graded layer having a thickness of 0 nm) has a very high resistivity of 1 Ωcm ² , which is a real problem. When used as a reflecting mirror of a surface emitting laser device, for example, it is difficult to energize the device through a distributed Bragg reflector having 20 pairs or more. In addition, a very high voltage is required to energize. Therefore, it is difficult to apply such a distributed Bragg reflector to a current drive optical device such as a surface emitting laser device. However, when the composition gradient layer having a thickness of 5 nm is provided as described above, it is possible to reduce the electrical resistivity by about two digits as compared with the case where the composition gradient layer is not provided. This facilitates energization of the element and enables oscillation. Furthermore, since the voltage required for energization is also reduced, various problems relating to reliability such as element breakdown and failure are greatly improved. Further, as shown in Table 1, since there is almost no decrease in reflectance, it is possible to obtain oscillation with a low threshold current density.

That is, the thickness of 5 nm can be considered as the lower limit of the thickness of the compositionally graded layer which can reduce the resistance without affecting the reflection characteristics in the long wavelength band. Therefore, it is appropriate that the material layer 3 (composition gradient layer in this example) has a thickness of 5 nm or more.

Furthermore, as the thickness of the compositionally graded layer is increased, the resistivity sharply decreases, and along with this, the operating voltage of the device,
Element heat generation is reduced. Therefore, the temperature at which oscillation can be maintained,
And the resulting output increases.

For example, when the permittivity of the reflectance is set to 99.8%, the thickness of the compositionally graded layer which can be provided in the 0.88 μm band is limited to 20 nm as shown in FIG.
In the 1.3 μm band, the compositionally graded layer can have a thickness of 50 nm. Further, as shown in FIG. 5, the electric resistance value is effectively reduced to 50 nm up to a thickness of 50 nm.
At m, it becomes about 1.05 times the bulk resistance value, and when the thickness exceeds this value, a saturation tendency begins to be exhibited. However, the reflectance starts to decrease rapidly as the thickness of the compositionally graded layer increases,
Since it decreases to 99.8% or less when m or more, it is considered that the range of thickness of the compositionally graded layer that satisfies both of these characteristics at the same time is 50 nm or less as a thickness having a practical meaning.

FIG. 7 shows in detail how the reflectance is reduced. FIG. 7 is a diagram showing a change (| dR / dt |) in the reflectance R with respect to the thickness t of the composition gradient layer. Figure 7
Compared with the tangent line shown in FIG.
It can be seen that the change in reflectance rapidly increases from m or more. The oscillation threshold current of the device starts to increase correspondingly.

As described above, for example, 5 nm or more, 50
Design reflection wavelength provided with a composition gradient layer having a thickness of nm or less
In the distributed Bragg reflector of 3 μm, it is possible to effectively reduce the resistance due to the effect of the hetero interface, and it is possible to obtain a high reflectance at the same time. In a surface emitting laser device using this, it is possible to easily obtain oscillation with a low threshold current under realistic driving conditions.

Further, for example, in order to increase the output of the surface emitting laser, it is necessary to set the mirror reflectance on the light output side to a small value and design it so that the light output can be easily obtained. Further, in order to stably oscillate up to a high output (high injection region), it is necessary to suppress element heat generation and set a high output saturation point due to heat. 5
The DBR provided with the material layer 3 (composition gradient layer in this example) having a relatively large thickness of 0 nm satisfies these conditions and is therefore suitable for high output applications.

In the first embodiment, the thickness of the material layer 3 is appropriately selected in the range of 5 nm to 50 nm according to the purpose, and a DBR having excellent reflection characteristics and electric characteristics can be obtained. .

In the above example (examples of FIGS. 2 and 3),
The second semiconductor layer 2 having a small refractive index was an AlAs layer, and the first semiconductor layer 1 having a large refractive index was a GaAs layer.
In the AlGaAs material, the refractive index becomes smaller as the Al composition increases. Therefore, two kinds of AlG having different Al compositions
Since the DBR can be configured by the aAs layer,
In addition to the above examples, AlGaAs may be used on one or both layers.
The present invention may be applied to DBR using a mixed crystal. However, the greater the difference in refractive index between the two layers that make up the DBR,
Since a high reflectance can be obtained with a small number of laminated pairs, it is desirable that the difference in Al composition between the two types of layers is large in terms of reflection characteristics. The structures of the examples of FIGS. 2 and 3 show combinations in which the difference in refractive index between AlAs and GaAs is the largest. In such a combination having a large difference in Al composition, the amount of discontinuity in the valence band that causes a hetero spike also becomes large, so that good reflection characteristics can be obtained, but there is a problem that the resistance is easily increased.
In other words, it is a combination in which the above-mentioned problems are most serious. In such a case, it is particularly important to provide a material layer having a refractive index value intermediate between a small value and a large value. In this case, in particular, since the valence band discontinuity is large, it is possible to reduce the resistance. It is necessary to provide a material layer having a sufficient thickness between the small and large values. However, the conventional 0.85 μm
This was difficult for a DBR such as an obi. On the other hand, in the distributed Bragg reflector of the present invention, it is possible to obtain a high reflectance and a low resistance value at the same time even when the materials shown in FIGS. 2 and 3 are used.

Second Embodiment A distributed Bragg reflector (DB) according to a second embodiment of the present invention.
In R), the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated, and the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are formed. In the distributed Bragg reflector, a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the distributed Bragg reflector. The design reflection wavelength of the reflector is longer than 1.1 μm, and the material layer is characterized by having a thickness in the range of 20 nm to 50 nm.

Also in this second embodiment, the material layer has a design reflection wavelength of 1.1 μm while keeping the reflectance high.
It has a function of effectively reducing the electric resistance of the distributed Bragg reflector having a wavelength longer than m.

In the second embodiment, the composition gradient layer of the long wavelength band DBR having a design reflection wavelength of 1.1 μm or more has a thickness of 20 nm to 50 nm. Where again
It can be seen from a detailed view of FIG. 5 that the resistivity first sharply decreases with an increase in the thickness of the compositionally graded layer and then gradually approaches the bulk resistivity. In the DBR of FIG. 5, the thickness of the compositionally graded layer where the decrease in resistivity begins to saturate is about 20 nm. When the thickness of the compositionally graded layer is 20 nm, the resistivity is extremely low, which is about double the bulk resistance value. Therefore, as described above, the composition gradient layer having a thickness of 20 nm or more and 50
By setting the thickness in the range of nm or less, it is possible to obtain a DBR whose resistivity is reduced to approximately the bulk.

Third Embodiment A distributed Bragg reflector (DB) according to a third embodiment of the present invention.
In R), the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated, and the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are formed. In the distributed Bragg reflector, a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the distributed Bragg reflector. The design reflection wavelength of the reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 30 nm to 50 nm.

Also in the third embodiment, the material layer has a design reflection wavelength of 1.1 μm while keeping the reflectance high.
It has a function of effectively reducing the electric resistance of the distributed Bragg reflector having a wavelength longer than m.

8 and 9 are views showing an example of a distributed Bragg reflector (DBR) according to the third embodiment of the present invention. In the example of FIGS. 8 and 9, the distributed Bragg reflector (DBR) is
A GaAs layer is used as the first semiconductor layer 1 having a large refractive index, an Al _0.8 Ga _0.2 As layer is used as a second semiconductor layer 2 having a small refractive index, and a composition gradient is used as the material layer 3. A layer (eg, 30 nm thick) is used,
An AlAs layer, a composition gradient layer, and a GaAs layer are periodically and repeatedly laminated. Specifically, in the examples of FIGS. 8 and 9, the composition gradient layer is a parabolic composition gradient layer (for example, A
1 GaAs parabolic composition gradient layer).

Here, the parabolic composition gradient layer is provided so that the valence band side energy is convex downward toward the Al _0.8 Ga _0.2 As layer having a wide band gap.

In the structures shown in FIGS. 8 and 9, the designed reflection wavelength (λ) of the DBR is 1.5 μm, and the Al _0.8 Ga _0.2 As layer and the GaAs layer have λ / 4n for a wavelength of 1.5 μm.
The thickness is 110.8 nm and 125.5 nm, respectively. Here, n is the refractive index of each semiconductor layer for a wavelength of 1.5 μm. The DBRs of FIGS. 8 and 9 have the above-mentioned thicknesses, and thus the above-mentioned parabolic composition gradient layer 3 (having a thickness of 50
The thickness is adjusted so as to reduce the optical length of each semiconductor layer corresponding to the optical length of (nm). Further, here, when the low refractive index layer is, for example, an Al _0.6 Ga _0.4 As layer, it corresponds to an example of an eighth embodiment described later. in this case,
The λ / 4n thickness of the Al _0.6 Ga _0.4 As layer for 1.5 μm is 121.7 nm.

The semiconductor layer is an Al _0.8 Ga _0.2 As layer,
5E1 for each of the GaAs layer and the parabolic composition gradient layer
The p-type doping is uniformly performed so as to be 7 cm ⁻³ .

The doping density of the distributed Bragg reflector shown in FIG. 8 is 5E17 cm ^-3, which is a lower value than that of the conventional distributed Bragg reflector, but the resistance value is 50 nm, which is thicker than that of the conventional distributed Bragg reflector. It was lowered to about the value of the bulk, and a low value was obtained. In addition, by setting the doping density low, it is possible to obtain a distributed Bragg reflector with less light absorption between valence bands and less absorption loss. Further, since the designed reflection wavelength is 1.5 μm, which is a much longer wave than the conventional distributed Bragg reflector in the 0.85 μm band, it is easy to provide a very thick parabolic composition gradient layer of 50 nm while keeping the reflectance high. be able to. As a result, the optical characteristics are also good. As described above, it is possible to obtain a distributed Bragg reflector having a lower resistance and a higher reflectance than the conventional one.

Here, the parabolic composition gradient layer is used as the material layer 3, but the material layer 3 may be another one. Also, the design reflection wavelength of the DBR is 1.5
It may be other than μm, and the Al composition of the low refractive index layer may be another value. Further, the doping density may be different for each semiconductor layer.

In the third embodiment, the thickness of the composition gradient layer in the long wavelength band DBR having a design reflection wavelength of 1.1 μm or more is set to 30 nm to 50 nm. When the thickness of the compositionally graded layer is increased as shown in FIG. 5, the resistivity of the DBR rapidly decreases to a certain thickness. The thickness of the compositionally graded layer in which this rapid decrease in resistivity is observed is also related to the DBR doping density. For example, FIG. 10 shows AlAs / G of FIG.
In aAs DBR, the doping concentration of each layer is 7E
It is a figure showing the result when it was set to 17 cm ^-3 . Figure 10
When the doping density is low, the composition gradient layer whose resistivity is rapidly reduced to about bulk resistivity is as thick as about 30 nm. It is changing linearly. Especially p-type DB
In R, in addition to free carrier absorption, light absorption increases when the hole density (doping density) increases due to light absorption between valence bands, which causes an increase in oscillation threshold current in a laser device or the like. In terms of optical characteristics, it is preferable that the carrier density is low. Further, since absorption between valence bands becomes remarkable for long wavelength light, especially in the wavelength band of 1.1 μm or more,
It is important to keep absorption losses low. Furthermore, it is difficult to reduce the absorption loss in the conventional DBR including the layer having the doping density exceeding 1E18 cm ^-3 .

For this reason, either the first semiconductor layer (having a large refractive index) and the second semiconductor layer (having a small refractive index) or the material layer (composition gradient layer) constituting the DBR, Or, the doping density of all layers is intentionally lowered (1E1
8 cm ^-3 or less). However, in the DBR with the doping density reduced in this way, the spread of the depletion layer becomes large, so that the effect of the hetero interface becomes more remarkable and the electric resistance tends to increase. For example, if you set the doping density a little lower for this reason,
To alleviate the influence of the hetero interface and reduce the resistance value, a thicker composition gradient layer is necessary, and referring to the results of FIG. 10, the effect is particularly remarkable from the thickness of 30 nm or more. If the doping density is further reduced, a thicker composition gradient layer is required.
By providing the composition gradient layer having a thickness within the above range of m, 50 nm, etc., it becomes possible to effectively reduce the influence of the hetero interface. The same can be said when the layer forming the DBR is made of AlGaAs in addition to AlAs.

FIG. 11 shows Al _0.8 Ga _0.2 As / GaAs.
11 is a diagram in which the resistance value of the 4-pair DBR is calculated in the same manner as in FIG. 10. In FIG. 11, the doping density of each layer is further set to 5E17 cm ⁻³ , but in this case as well, it can be seen that the resistivity becomes approximately the same as the bulk resistivity when the compositionally graded layer has a thickness of 30 nm or more. For example, for the reasons described above, the first semiconductor layer (having a high refractive index) forming the DBR,
In the DBR in which the doping density of any one of the second semiconductor layer (having a small refractive index) or the material layer (gradient composition layer) or all layers is set smaller than that of the conventional one (1E18 cm ⁻³ or less), The thickness of the compositionally graded layer of 30 nm is the thickness at the boundary where the electrical resistivity begins to saturate. Therefore, in the case where the doping density of at least one layer constituting the DBR is 1E18 cm ⁻³ or less, the composition gradient layer having a thickness in the range of 30 nm to 50 nm is used to effectively increase the resistance value as described above. Can be reduced to

Of course, the above range of the thickness of the compositionally graded layer is a thickness that can effectively reduce the resistance even in a DBR having a higher doping density, and all layers including the DBR have a thickness of 1E18 cm ^-3 or more. It may be used when it is doped with. But especially 1E18
cm ⁻³ or less doping density, and 30 nm to 50 n
By appropriately selecting these in the range of the thickness of the composition gradient layer of m, both the absorption loss and the electric resistance can be simultaneously reduced.

Further, by using the distributed Bragg reflector of the third embodiment as a reflector mirror of a surface emitting laser device, a surface emitting laser device having excellent device characteristics can be obtained. In addition, as described above, 30 nm to 5 nm
The thickness of the compositionally graded layer of 0 nm is 0.85 μm compared with the conventional one.
It is difficult to provide a DBR used in a band or the like, and it becomes possible to provide a DBR in the long wavelength band having a wavelength of 1.1 μm or more, which is the object of the present invention, for the first time without deteriorating optical characteristics. Is.

Fourth Embodiment A distributed Bragg reflector according to a fourth embodiment of the present invention is the distributed Bragg reflector according to claim 2, wherein the second semiconductor constituting the distributed Bragg reflector has a small refractive index. The first semiconductor layer having a large refractive index with the layer is formed of AlAs, GaAs, or AlGaAs mixed crystal, and the first semiconductor layer having a large refractive index is formed.
The difference in Al composition between the second semiconductor layer having a small refractive index and the second semiconductor layer having a small refractive index is less than 0.8.

In the fourth embodiment, in the distributed Bragg reflector made of the AlGaAs semiconductor material, when the difference in Al composition between the semiconductor layers constituting the distributed Bragg reflector is less than 0.8. , It is possible to effectively reduce the electric resistance while keeping the reflectance of the semiconductor distributed Bragg reflector having the designed reflection wavelength in the wavelength band longer than 1.1 μm high.

That is, the AlGaAs mixed crystal semiconductor is A
The valence band energy monotonously decreases with increasing l composition, and the band discontinuity with the GaAs single crystal increases as the AlGaAs mixed crystal with a larger Al composition forms a large potential barrier at the hetero interface, which causes the increase in resistance. Becomes Also,
The decrease in valence band energy is approximately proportional to the Al composition, and the amount of band discontinuity between semiconductor layers having different Al compositions corresponds to the difference in Al composition.

12 and 13 are diagrams showing the electrical resistivity of four pairs of p-type distributed Bragg reflectors having a design reflection wavelength of 1.3 μm, with the thickness of the composition gradient layer being changed. Figure 1
2, in the distributed Bragg reflector, the high refractive index layer is GaAs, and the low refractive index layer is AlAs, Al _0.8 G.
The three types are shown as a _0.2 As and Al _0.6 Ga _0.4 As. Further, the thickness of each semiconductor layer is set to ¼ optical thickness of the design wavelength according to the refractive index of the material. Further, the doping density of the semiconductor layer, for all layers, 5E17 cm ^-3 in Figure 12, 1E18 cm ^-3 in Figure 13
And make it uniform. The doping concentration of 1E18 cm ⁻³ is a typical value used for p-type DBR doping. A distributed Bragg reflector having a larger Al composition in the AlGaAs layer has a higher resistivity in a region where the composition gradient layer is thin, and a thick composition gradient layer is required to reduce the resistance to a bulk level. For example, Al _0.6 Ga
_{With 0.4} As and GaAs, the band discontinuity in the valence band is about 300 meV, and Al _0.8 Ga _0.2 As
And GaAs, the band discontinuity in the valence band is 400
It is about meV.

In the case of the distributed Bragg reflector made of AlAs and GaAs, the thickness of the compositionally graded layer required to effectively reduce the resistivity depends on the doping density, but the results shown in FIGS. Considering together, 20 nm
It is understood that the composition gradient layer having the above thickness may be provided.
When attention is paid to the band discontinuity of the semiconductor material forming the distributed Bragg reflector as described above, when the band discontinuity amount is less than 400 meV, that is, the Al composition difference is less than 0.8, the composition gradient layer is formed. The thickness of 20 nm or more is the thickness that can effectively reduce the resistance.

In addition, the increase in resistance due to band discontinuity actually depends not only on the height and width of the barrier but also on the effective mass of holes as carriers, but the effective mass of heavy holes is
AlGaA normally used as a distributed Bragg reflector
The s, AlGaInP, and GaInAsP-based materials do not differ as much as the effective mass of electrons and the like, and the amount of band discontinuity can be considered as a measure of the resistance of the hetero interface. Therefore, when the band discontinuity in the valence band is less than 400 meV, that is, the Al composition difference is less than 0.8, the compositional gradient layer having a thickness of 20 nm or more is used to more effectively achieve the electrical resistance. It is possible to reduce the rate.

As described above, the upper limit thickness of the compositionally graded layer is selected by taking into consideration the design reflection wavelength of the distributed Bragg reflector and selecting a thickness in a range in which the decrease in reflectance is not remarkable. It is possible to obtain a distributed Bragg reflector having excellent electrical and optical characteristics.

Fifth Embodiment A distributed Bragg reflector according to a fifth embodiment of the present invention is the distributed Bragg reflector according to claim 3, wherein the second semiconductor constituting the distributed Bragg reflector has a small refractive index. The first semiconductor layer having a large refractive index with the layer is formed of AlAs, GaAs, or AlGaAs mixed crystal, and the first semiconductor layer having a large refractive index is formed.
The difference in Al composition between the semiconductor layer of No. 2 and the second semiconductor layer of which the refractive index is small is 0.8 or more.

In the fifth embodiment, in the distributed Bragg reflector made of an AlGaAs semiconductor material, when the difference in Al composition between the semiconductor layers constituting the distributed Bragg reflector is 0.8 or more. , It is possible to effectively reduce the electric resistance while keeping the reflectance of the semiconductor distributed Bragg reflector having the designed reflection wavelength in the wavelength band longer than 1.1 μm high.

That is, the band discontinuity in the valence band is about 500 meV between AlAs and GaAs.
In the case of a distributed Bragg reflector composed of GaAs and GaAs, a thicker composition gradient layer is required (depending on the doping density) to effectively reduce the resistivity. Figure 1
2, when considering the results of FIG. 13 together, it is understood that the composition gradient layer having a thickness of 30 nm or more should be provided. When attention is paid to the band discontinuity of the semiconductor material forming the distributed Bragg reflector, the amount of band discontinuity is 400
In the case of meV or more, the compositionally graded layer having a thickness of 30 nm or more is a thickness that can effectively reduce the resistance.

The Al composition difference and the valence band band discontinuity are
There is the relationship described in the above fourth embodiment, and the valence band discontinuity amount of 400 meV corresponds to the Al composition difference of 0.8 or more. Therefore, when the Al composition difference is 0.8 or more, the thickness of the composition gradient layer of 30 nm or more is the thickness that can effectively reduce the resistance, and by providing the composition gradient layer of this thickness, It is possible to effectively reduce the electric resistivity.

As to the upper limit thickness of the compositionally graded layer, as described above, considering the design reflection wavelength of the distributed Bragg reflector, the thickness is selected within the range in which the decrease in reflectance is not remarkable. It is possible to obtain a distributed Bragg reflector having excellent electrical and optical characteristics.

Sixth Embodiment In a distributed Bragg reflector according to a sixth embodiment of the present invention, first semiconductor layers having a large refractive index and second semiconductor layers having a small refractive index are alternately laminated. A refractive index between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector provided with a material layer that takes a value, the designed reflection wavelength of the distributed Bragg reflector is longer than 1.1 μm, and the material layer has a thickness of
The design reflection wavelength λ [μm] of the distributed Bragg reflector is (50λ−15) [nm] or less.

Also in the sixth embodiment, the material layer has a design reflection wavelength of 1.1 μm while keeping the reflectance high.
It has a function of effectively reducing the resistance of the distributed Bragg reflector having a wavelength longer than m.

FIG. 14 shows the relationship between the composition gradient layer thickness and the reflectance for a distributed Bragg reflector having a design reflection wavelength of 1.1 μm to 1.7 μm. The distributed Bragg reflector uses GaAs as a high refractive index and an AlAs layer as a low refractive index layer. Further, the number of pairs of the distributed Bragg reflector is set to the number of pairs in which the reflectance starts to exceed 99.9% at each wavelength. That is,
18 pairs at 0.88 μm, 22 pairs at 1.1 μm,
23 pairs at 1.3 μm, 23 pairs at 1.5 μm,
At 1.7 μm, there are 24 pairs. Further, FIG. 15 shows the change rate of the reflectance of FIG. 14 with respect to the composition gradient layer thickness (| dR
/ Dt |) is shown. It can be seen from FIG. 14 that the reflectance decreases as the thickness of the composition gradient layer increases. Further, it can be seen from FIG. 15 that the rate of decrease in reflectance rapidly increases from a certain composition gradient layer thickness. Figure 15
In order to make this situation easy to understand, the slope of the change rate is shown by a straight line. That is, the straight line in FIG. 15 is obtained by drawing a tangent line of the rate of change with respect to the thickness at which the reflectance starts to decrease. For example, focusing on a distributed Bragg reflector having a design reflection wavelength of 1.3 μm and looking at FIG. 15, it can be seen that the rate of change in reflectance rapidly increases from the composition gradient layer thickness of 50 nm. In FIG. 14, correspondingly, the reflectance of the distributed Bragg reflector begins to decrease sharply. Therefore, for example, in a surface emitting laser device using this as a reflecting mirror, the oscillation threshold current increases rapidly. Further, as shown in FIG. 15, the thickness of the compositionally graded layer in which the rate of change in reflectance rapidly increases differs depending on the design wavelength band of the semiconductor distributed Bragg reflector. That is, as the distributed Bragg reflector having the longer design reflection wavelength has a larger thickness of each semiconductor layer forming the reflector, the influence on the composition gradient layer having the same thickness is reduced.

As described above, the thickness (threshold thickness) of the compositionally graded layer at which the rate of change starts to increase rapidly depends on the design reflection wavelength of the distributed Bragg reflector. It can be seen that it does not depend on the wavelength so much, and is about 0.09 as shown in FIG.

Further, the threshold thickness for each wavelength shown in FIG. 14 is shown in the following table (Table 2).

[0090]

[Table 2]

From Table 2, there is a substantially linear relationship between the design reflection wavelength and the threshold thickness, and from Table 2, the relationship between the threshold thickness t [nm] and the design reflection wavelength λ [μm] of the distributed Bragg reflector. It can be seen that there is a relation of the following equation (Equation 1) when is obtained.

[0092]

## EQU1 ## t = 50λ-15

Therefore, the distributed Bragg reflector having a design reflection wavelength λ of 1.1 μm or more is provided with a material layer (composition gradient layer) having a thickness of t or less determined by the formula 1 to increase the height. It is possible to obtain a distributed Bragg reflector having a low resistance and maintaining the reflectance. In the above example, the composition gradient layer is a linear composition gradient layer, but a non-linear composition gradient layer may be used as well. Even in this case, similar results and effects can be obtained.

Seventh Embodiment A distributed Bragg reflector according to a seventh embodiment of the present invention is a sixth embodiment.
In the distributed Bragg reflector of the above embodiment, the material layer has a thickness of 20 nm or more.

Also in the embodiment of the seventh embodiment, the material layer effectively reduces the resistance of the distributed Bragg reflector having a designed reflection wavelength longer than 1.1 μm while keeping the reflectance high. It has a function.

As described in the sixth embodiment,
The compositional gradient layer capable of keeping the reflectance of the distributed Bragg reflector high and the design reflection wavelength have a relationship of Mathematical formula 1.

Regarding the electrical characteristics, as described above, the thicker the composition gradient layer, the more the influence of the semiconductor hetero interface can be reduced, and a distributed Bragg reflector having a lower resistance can be obtained. You can Further, the effect of lowering the resistance by the compositionally graded layer is determined by the material of the distributed Bragg reflector, the doping density, and the profile, and is essentially independent of the reflection wavelength band. Therefore, there is a lower limit to the composition gradient layer that can sufficiently obtain the effect of lowering the resistance, and in order to obtain a distributed Bragg reflector having a sufficiently low resistance, it is necessary to provide the composition gradient layer having a certain thickness or more.

For example, in the distributed Bragg reflector uniformly doped to the density of 1E18 cm ^-3 in FIG. 13, when the thickness of the composition gradient layer is less than 20 nm, the resistivity of the distributed Bragg reflector is different from the bulk resistivity. 20 nm, which is an order of magnitude larger
From the above, it can be seen that the resistivity is reduced to the same order as the bulk resistivity. Therefore, in the case of the above-mentioned doping density, it is preferable in terms of electrical characteristics that the compositionally graded layer has a thickness of 20 nm or more. Therefore, from the above results, by selecting the thickness t [nm] of the composition gradient layer in the range of 20 ≦ t ≦ 50λ−15 with respect to the design reflection wavelength λ [μm] of the distributed Bragg reflector, Thus, it is possible to obtain a distributed Bragg reflector having a sufficiently low resistance and excellent characteristics in which a high optical reflectance is maintained.

Eighth Embodiment The distributed Bragg reflector according to the eighth embodiment of the present invention is the sixth embodiment.
In the distributed Bragg reflector of the embodiment of the
It is characterized in that the thickness is 30 nm or more.

Also in the eighth embodiment, the material layer has a design reflection wavelength of 1.1 μm while keeping the reflectance high.
It has a function of effectively reducing the resistance of the distributed Bragg reflector having a wavelength longer than m.

In the semiconductor material, the photoabsorption tends to increase with the increase of the free carriers even for the photons whose energy is smaller than the band gap. In addition, in the p-type semiconductor, the increase of the holes serving as the carriers increases. Accordingly, light absorption due to absorption between valence bands remarkably occurs. Further, the absorption between valence bands increases as the wavelength becomes longer, so that the designed reflection wavelength is 1.
This is a particular problem in distributed Bragg reflectors having a wavelength longer than 1 μm, and their light absorption causes a reduction in the reflectance of the distributed Bragg reflector. Further, in a laser device using this as a reflecting mirror, the threshold current increases due to light absorption,
It causes a decrease in efficiency. Therefore, in terms of reduction of light absorption, it is preferable that the doping density of the semiconductor layer is as low as possible. However, since the depletion layer at the hetero interface increases as the doping density is reduced, the effect of the potential barrier at the interface becomes large, which causes the resistivity to increase.

Therefore, for example, in the semiconductor distributed Bragg reflector whose doping density is reduced for the above-mentioned purpose, a thicker composition gradient layer is required to reduce the resistivity. When such a distributed Bragg reflector is doped to, for example, about 5E17 cm ⁻³ , the result of FIG. 12 shows that the composition gradient layer has a thickness of 3
From 0 nm or more, it can be seen that the resistivity is reduced to the same level as the bulk.

Various combinations are conceivable as the doping density and profile of the semiconductor layer, and the types thereof are enormous. However, a similar tendency is exhibited when the doping density of at least one semiconductor layer is less than 1E18 cm ^-3 . Because the height and barrier thickness of the potential barrier formed at the hetero interface are determined by the doping density of the semiconductor layer in contact with the hetero interface, and the effect of the hetero interface is greater as the doping density is lower than 1E18 cm ^-3. This is also because the electrical characteristics are determined mainly by the hetero interface having a low doping density. The present invention exerts a large action and effect on the semiconductor layer constituting the distributed Bragg reflector, in which at least one semiconductor layer has a doping density of less than 1E18 cm ^-3 .

Further, here, the above-mentioned results of the doping density are shown as an example, but the distributed Bragg reflector doped to the order of 1E17 cm ^-3 shows substantially the same result. Of course, the doping density may be in a range lower than this, and in that case, the resistance is similarly reduced by setting the thickness of the composition gradient layer to 30 nm or more in the range of the sixth embodiment. be able to.

As described above, for the design reflection wavelength λ [μm] of the distributed Bragg reflector, the thickness t [nm] of the material (composition gradient layer) is selected within the range of 30 ≦ t ≦ 50λ−15. Thus, it is possible to obtain a distributed Bragg reflector having an electrically low resistance and an excellent optical characteristic that maintains a high reflectance.

Ninth Embodiment A surface-emission laser device according to the ninth embodiment of the present invention has an active layer and a resonator mirror, and the resonator mirror is formed according to any one of the first to eighth embodiments. It is characterized in that a form of distributed Bragg reflector is used.

The surface-emission laser device of the ninth embodiment operates at low voltage, high efficiency and high output.

That is, in the ninth embodiment, the distributed Bragg reflector according to any one of the first to eighth embodiments is used as the resonator mirror (reflection mirror) of the surface emitting laser device. As the distributed Bragg reflector made of a semiconductor material, one using an AlGaAs material (for example, AlAs / GaAs material) is used as a resonator of a surface emitting laser device because of its reflection characteristics and compatibility with an oxidation process (for current constriction). It has excellent characteristics as a mirror (reflection mirror).

Furthermore, by using the distributed Bragg reflector of the first embodiment, it is possible to achieve 0.8 for conventional optical communication and optical transmission applications.
As compared with the 5 μm band and 0.98 μm band surface emitting lasers, it is possible to obtain a surface emitting laser element for low oscillation threshold current, low power consumption, high power operable optical communication and optical transmission. In particular,
The 1.3 μm band is a zero-dispersion band of a quartz single-mode fiber, and high-speed data communication can be performed by combining it with a surface emitting laser device having this band as an oscillation wavelength. In addition, wavelength 1.5 μm band is wavelength division multiplexing (DWD).
It is an important wavelength band in M), and a surface emitting laser element having excellent characteristics is required in this wavelength band. The surface emitting laser element using the distributed Bragg reflector according to any one of the first to eighth embodiments of the present invention has a low operating voltage and high efficiency, and thus is a surface emitting laser element suitable for these applications. is there.

Tenth Embodiment A surface emitting laser device according to a tenth embodiment of the present invention is the ninth embodiment.
In the surface-emission laser device of the above embodiment, the material of the active layer is GaNAs, GaInAs, GaInNAs, GaA.
It is characterized by being any one of sSb, GaInAsSb, and GaInNAsSb.

The surface emitting laser device of the tenth embodiment operates at low voltage, high efficiency, high output and high temperature.

That is, in the tenth embodiment, the material of the active layer is GaNAs, GaInAs, GaInN.
As, GaAsSb, GaInAsSb, GaInNA
Either of sSb and these materials are GaA
s It is possible to grow crystals on the substrate, reflectivity, thermal conductivity,
AlGaAs with excellent characteristics in terms of process control (crystal growth and selective oxidation of Al (Ga) As mixed crystals)
A DBR made of a system material can be used to obtain a surface emitting laser element that oscillates at a wavelength longer than 1.1 μm. In particular,
High-speed communication and high-speed transmission can be achieved by combining a laser element having a wavelength of 1.3 μm and a quartz single mode laser. Also, 1.5μ, which is important for wavelength division multiplexing
An element having excellent characteristics can be obtained in the m band.

Further, the above-mentioned materials (GaNAs, Ga
InAs, GaInNAs, GaAsSb, GaInA
sSb, GaInNAsSb), especially GaIn
The NAs mixed crystal material is GaAs that serves as a carrier confinement layer.
Since the amount of band discontinuity in the conduction band is large with respect to the layer and the overflow of electrons can be reduced, stable oscillation can be obtained up to a high temperature. As described above, according to the present invention, a surface emitting laser element suitable for optical communication and optical transmission can be obtained. In this way, the active layer is formed of GaInNAs
Then, it is possible to obtain a surface emitting laser device having a wavelength longer than 1.1 μm on the GaAs substrate, including the 1.3 μm band important for quartz single mode fiber communication and the 1.5 μm band important for wavelength multiplexing communication.

FIG. 16 shows the structure of a surface emitting laser device according to the present invention.
It is a figure which shows an example. The surface emitting laser element of FIG.
Oscillation wavelength in 1.3 μm band with InNAs mixed crystal as active layer
Is an element with. That is, the device of FIG.
On the As substrate 11, Al_{0. 8}Ga_0.2As / GaAs
36 pairs n-DBR12, GaAs spacer layer 13,
GaInNAs multiple quantum well active layer 14, GaAs spacer
Source layer 15, Al_{0. 8}Ga_0.2As / GaAs 26P
A p-DBR 17 and p-GaAs contact layer 18 are connected.
The crystal is grown. In addition, of the oscillation light in p-DBR17
The AlAs selective oxidation layer 16 is provided at the position corresponding to the node of the standing wave.
It has been burned.

In the device of FIG. 16, the cylindrical mesa is left, the layers up to the n-DBR 12 are removed by etching, and the AlAs layer 16 is selectively oxidized from the side surface of the etching to provide an oxide confinement structure (current constriction structure). ing. Here, the oxide confinement diameter is 5 so that a single transverse mode oscillation can be obtained.
μm. Then, the etched region is filled with the polyimide film 19, and the light emitting portion 20 at the center of the mesa is formed.
A p-type ohmic electrode 21 is formed in a region other than the above, and an n-type ohmic electrode 22 is formed on the back surface of the substrate 11.

Here, n-DBR12 is Al _0.9 Ga.
It is composed of _0.1 As / GaAs.

As shown in FIG. 17, the p-DBR 17 is constructed by laminating an Al _0.9 Ga _0.1 As layer 31, an AlGaAs composition gradient layer 32, and a GaAs layer 33 in a predetermined number of pairs. Here, Al _0.8 G of p-DBR17
a _0.2 As layer 31 is a layer having a small refractive index (second semiconductor layer),
The GaAs layer 33 corresponds to a layer having a large refractive index (first semiconductor layer). Further, as the material layer, the Al composition is the above two layers 31,
33 was used as the composition gradient layer 32 in which the composition was linearly changed from one composition to the other composition. The composition gradient layer 32 has a thickness of 40.
nm. The p-DBR17 is uniformly doped so that the carrier density is 8E17 cm ^-3 .

The operating voltage and the oscillation threshold current of this surface emitting laser element can be obtained at very low values by using the DBR (distributed Bragg reflector) of the present invention.
In addition, the threshold current density of the device was low and a high efficiency could be obtained, even compared with the device having a doping density of 1E18 cm ^-3 . In addition, element resistance (p-DBR17
The resistance of the element is low, so that the element does not generate much heat, the saturation point of output due to heat is high, and high output can be obtained.
In addition, since the active layer material is GaInNAs, Ga
An oscillation wavelength of 1.3 μm could be obtained on the As substrate.
The device realized a fundamental transverse mode oscillation in the 1.3 μm band and was able to obtain a surface emitting laser device having excellent characteristics for use in optical communication.

That is, the oscillation wavelength of the surface-emission laser device shown in FIG. 16 is longer than 1.1 μm.
By using GaInNAs for 4, the GaAs substrate 1
1.3 μm band, 1,5 μm, which is important for fiber communication
It is possible to obtain a surface emitting laser device having a wavelength longer than 1.1 μm including the band.

Eleventh Embodiment The surface emitting laser array of the eleventh embodiment of the present invention is characterized in that a plurality of surface emitting laser elements of the ninth or tenth embodiment are arranged. There is.

The surface emitting laser array of the eleventh embodiment operates at low voltage, high efficiency, high output and high temperature.

That is, in this eleventh embodiment, a surface emitting laser array can be constructed by arranging a plurality of the surface emitting laser elements of the present invention described above. The distributed Bragg reflector (DBR) of the surface emitting laser device of the present invention described above.
In comparison with conventional 0.85 μm band and 0.98 μm band surface emitting laser elements, the distributed Bragg reflector (DBR) has a lower resistance and the operating voltage of the surface emitting laser element is reduced.
That is, the power consumption and heat generation of the elements are small, and the effect of reducing the power consumption is great when the elements are integrated at high density like an array. Further, there is little interference between elements due to heat generation, and a surface emitting laser array having excellent characteristics and reliability can be obtained.

Twelfth Embodiment Further , an optical interconnection system can be constituted by the surface emitting laser device of the present invention described above or the surface emitting laser array of the present invention described above.

In the optical interconnection system having such a structure, the design reflection wavelength is set to a wavelength longer than 1.1 μm, and the material layer having the thickness larger than the conventional one and the refractive index between the small value and the large value is provided. By using the surface emitting laser device or the surface emitting laser array of the present invention in which a distributed Bragg reflector (DBR) having a small resistance value is used as a resonator, a highly reliable interconnection system capable of high-speed transmission is provided. Can be provided.

That is, as described above, the surface emitting laser element or the surface emitting laser array used in the optical interconnection system of the present invention has the p-type by setting the oscillation wavelength to be longer than 1.1 μm. DBR
The thickness of each layer constituting the
It is thicker than the surface emitting laser device in the 8 μm band. Therefore, without significantly reducing the reflectance, the conventional 0.85 μm,
It is possible to provide a material layer having a thickness larger than that of a surface emitting laser element in the 0.98 μm band and having a refractive index between a small value and a large value between the layers of the DBR, and the resistance value of the DBR is conventionally reduced. Can be smaller than As a result, the operating voltage can be reduced, the heat generation of the element can be reduced, the power consumption can be reduced, and the reliability such as the element life can be improved. Further, since the element resistance is small, the response time of the element is shortened, which is suitable for high speed modulation.

Therefore, in an optical interconnection system using such a surface emitting laser element or a surface emitting laser array, high power modulation is possible with low power consumption and system reliability is high. Furthermore, by setting the oscillation wavelength to be longer than 1.1 μm, it is possible to construct an optical interconnection system using a quartz single mode fiber. Quartz single mode fiber is 1.3μ
The surface-emitting laser device has a characteristic that it has zero dispersion in the m band and the oscillation spectrum width is very narrow. In the interconnection system combining the quartz single mode fiber and the surface emitting laser element of the present invention having a low element resistance and capable of high-speed modulation in the 1.3 µm band, the conventional 0.85 µm band and 0.98 µm band surface emitting lasers are used. The great effect that high-speed transmission is possible, which is difficult with the optical interconnection system using elements, is obtained. In addition, the active layer material (GaNAs, GaInAs,
GaInNAs, GaAsSb, GaInAsSb, G
Among the aInNAsSb), a surface emitting laser device using a GaInNAs quantum well as an active layer is, for example, GaA.
Since the conduction band discontinuity with the s barrier layer is large and the overflow of electrons is small due to the material characteristics, the device operates stably with respect to changes in environmental temperature. In addition, since it is possible to grow crystals on a GaAs substrate, it is possible to use a distributed Bragg reflector made of an AlGaAs mixed crystal, which has excellent reflection characteristics and heat dissipation and has an established oxide confinement process. An excellent laser light source can be used.

From the above, a highly reliable optical interconnection system capable of high-speed transmission can be obtained.

FIG. 18 is a diagram showing a specific example of the optical interconnection system of the present invention. The optical interconnection system in FIG. 18 is configured as a parallel optical interconnection system between devices.

In the interconnection system of FIG. 18, the equipment 1 and the equipment 2 are connected using an optical fiber array. The device 1 on the transmission side includes a one-dimensional surface-emission laser array module using the surface-emission laser array of the present invention described above and a drive circuit for the same. The device 2 on the receiving side includes a photodiode array module and a signal detection circuit.

FIG. 19 shows an outline of the surface emitting laser array module. The surface emitting laser array module in FIG. 19 is configured by mounting a one-dimensional monolithic surface emitting laser array, a microlens array, and a fiber array on a silicon substrate. The surface emitting laser array is provided so as to face the fiber, and is coupled to the quartz single mode fiber mounted in the V groove formed on the silicon substrate through the microlens array. The oscillation wavelength of the surface emitting laser array is in the 1.3 μm band, and a quartz single mode fiber is used.

As in the above optical interconnection system, the quartz single mode fiber and the oscillation wavelength are 1.
High-speed transmission becomes possible by using a surface emitting laser array having a wavelength (1.3 μm) longer than 1 μm. This is because the quartz fiber has zero wavelength dispersion in the 1.3 μm band, and the oscillation spectrum of the surface emitting laser element is narrow, and in particular, the resistance value of the distributed Bragg reflector of the surface emitting laser element of the present invention is high. Is small, and it is largely due to the effect that the response of the element is improved.

Further, the operating voltage was reduced by lowering the resistance of the element, the reliability of the element life etc. was high, and the reliability of the system was also improved. In addition, the power consumption of the device was reduced due to the low resistance of the device, and the power consumption of the system was also reduced. Also,
Due to the low resistance of the element, heat generation was reduced and high output operation was possible. Therefore, an interconnection system with a low code error rate was obtained.

At this time, the above-mentioned active layer material (GaNA
s, GaInAs, GaInNAs, GaAsSb, G
aInAsSb, GaInNAsSb), especially in a surface emitting laser element using a quantum well of GaInNAs mixed crystal as an active layer, the conduction band band discontinuity with the GaAs barrier layer is large and the electron overflow is small in terms of material characteristics. , Stable operation against changes in environmental temperature.

As described above, it is possible to obtain a highly reliable parallel optical interconnection system which consumes less power and can operate at high speed.

In the above-mentioned example, the parallel optical interconnection system has been described as an example. However, in addition to this, a serial transmission system using a single element can be constructed.
Further, it can be applied not only between devices but also between boards, between chips, and interconnection within a chip.

Thirteenth Embodiment Further , an optical communication system can be constituted by the surface emitting laser device of the present invention described above or the surface emitting laser array of the present invention described above.

In the optical communication system having such a configuration, the design reflection wavelength is set to a wavelength longer than 1.1 μm, and the material layer having a thickness larger than the conventional one and a refractive index between a small value and a large value is provided. By using the surface emitting laser device or the surface emitting laser array of the present invention in which a distributed black reflector (DBR) having a small resistance value is a resonator mirror as a light source, device resistance and heat generation are small, and high speed transmission is possible. It is possible to provide a high optical communication system.

That is, as the surface emitting laser element or the surface emitting laser array used in the above-described optical communication system of the present invention, the p-type DBR is obtained by setting the oscillation wavelength to longer than 1.1 μm as described above. The thickness of each layer to be formed is thicker than that of the conventional 0.85 μm and 0.98 μm band surface emitting laser element, and thus, the conventional 0.85 μm and 0.98 μm without significantly reducing the reflectance.
It is possible to provide a material layer having a thickness larger than that of the surface emitting laser element of the μm band and having a refractive index between a small value and a large value between the layers of the DBR, so that the resistance value of the DBR is smaller than that of the conventional one. Can be made smaller. Therefore, the operating voltage can be reduced, and
It is possible to obtain effects such that heat generation of the element can be reduced, power consumption can be reduced, and reliability such as life of the element is improved. Further, since the element resistance is small, the response time of the element is shortened, which is suitable for high speed modulation.

Therefore, in an optical communication system using such a surface emitting laser element or a surface emitting laser array, high power modulation is possible with low power consumption and system reliability is high. Furthermore, by setting the oscillation wavelength to be longer than 1.1 μm, it is possible to construct an optical communication system using a quartz single mode fiber. The quartz single mode fiber has zero dispersion in the 1.3 μm band, and
The surface emitting laser device has a feature that the oscillation spectrum width is very narrow. In the optical communication system combining the quartz single mode fiber and the surface emitting laser element of the present invention having a low element resistance and capable of high-speed modulation in the 1.3 µm band, the conventional 0.85 µm band and 0.98 µm band surface emitting lasers are used. It is possible to obtain a great effect that high-speed communication is possible, which is difficult in the optical communication system using the elements. In addition, the active layer materials (GaNAs, GaInAs, GaInNA) described above are used.
s, GaAsSb, GaInAsSb, GaInNAs
Among the Sb), particularly in a surface emitting laser device using GaInNAs as a quantum well, for example, the band discontinuity of the conduction band is large and the overflow of electrons is small with respect to the GaAs barrier layer, etc. In addition to stable and stable operation, it is possible to use a distributed Bragg reflector made of an AlGaAs mixed crystal, which has excellent reflection characteristics and heat dissipation due to the fact that crystal growth is possible on a GaAs substrate and an oxidation confinement process is established. Therefore, conventional InP
The temperature characteristics of the light source are superior to those of an optical communication system using an end-face type laser using an InGaAsP mixed crystal formed on a substrate. Further, it is possible to easily obtain a surface emitting laser element which is difficult to manufacture with the above-mentioned material system. This surface emitting laser device is easy to form an array and has a high coupling rate with an optical fiber, and is suitable as a light source for an optical communication system using an optical fiber. From the above, by using the surface emitting laser device or the surface emitting laser array of the present invention, a highly reliable optical communication system capable of high speed communication can be obtained.

FIG. 20 is a diagram showing a specific example of the optical communication system of the present invention. The optical communication system of FIG. 20 is an optical LAN.
Configured as a system. The optical LAN system of FIG. 20 is an optical LAN system configured by using the above-described surface emitting laser element or surface emitting laser array element of the present invention. That is, the surface emitting laser device or the surface emitting laser array device of the present invention is used as a light source for optical transmission between the server and the core switch, between the core switch and each switch, and between the switch and each terminal. Is used. In addition, quartz single mode fibers or multimode fibers are used to couple the devices. The physical layer of such an optical LAN is, for example, 10
Gigabit Ethernet (registered trademark) such as 00BASE-LX can be used.

In the optical LAN system of FIG. 20, a surface emitting laser element or a surface emitting laser array having an oscillation wavelength longer than 1.1 μm (1.3 μm) is used as a light source. In this surface emitting laser element, the oscillation wavelength is set to a wavelength longer than 1.1 μm (1.3 μm), so that the thickness of the distributed Bragg reflector is not significantly lowered and the thickness is larger and the refractive index is higher than that of the conventional one. Since a semiconductor layer having a value between small and large can be provided, the conventional 0.85 μm, 0.
As compared with a surface emitting laser device having a distributed Bragg reflector in the 98 μm band, the device resistance can be reduced, the device can respond faster, and an optical communication system capable of high-speed communication can be obtained.

When a quartz single mode fiber is used to connect the devices, high speed communication becomes possible by using a 1.3 μm band surface emitting laser device as a light source. This is because the quartz fiber has zero wavelength dispersion in the 1.3 μm band, and the oscillation spectrum of the surface emitting laser element is narrow, and in particular, the resistance value of the distributed Bragg reflector of the surface emitting laser element of the present invention is high. Is small, and it is largely due to the effect that the response of the element is improved.

Further, since the resistance of the element is lowered, the operating voltage is reduced, the reliability such as the life of the element is improved, and the reliability of the system is improved. In addition, the power consumption of the device was reduced due to the low resistance of the device, and the power consumption of the system was also reduced. In addition, heat generation is reduced due to the low resistance of the element, and high output operation is possible. Therefore, an optical communication system with a low code error rate was obtained. In addition, the above-mentioned active layer material (GaNA
s, GaInAs, GaInNAs, GaAsSb, G
aInAsSb, GaInNAsSb), by using a GaInNAs mixed crystal, the conventional In
Compared to a communication system in the same wavelength band using an end-face type laser using an InGaAsP mixed crystal formed on a P substrate, the temperature characteristics of the light source are excellent, and a temperature control and compensation device is unnecessary. Further, it is possible to easily use the surface emitting laser element which is difficult to manufacture with the above-mentioned material system. This surface emitting laser device
It is easy to form an array, has a high coupling rate with an optical fiber, and is suitable as a light source for an optical communication system using an optical fiber.
As described above, it is possible to obtain a highly reliable optical communication system capable of high-speed communication.

In the above example, a LAN using an optical fiber is shown as an example of the optical communication system, but the optical communication system may be a WAN or the like in addition to this. And WAN may be connected to each other. Also, the terminal is a server, P
The present invention is not limited to C (computer), and is applicable to all optical communication systems including information equipment terminals that perform communication or data transmission / reception via optical fibers, and exchanges and relays that exchange and relay data.

[0145]

As described above, according to the first aspect of the invention, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated, A refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index. In a distributed Bragg reflector provided with a material layer having a thickness of 5 nm, the designed reflection wavelength of the distributed Bragg reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 5 nm to 50 nm. It is possible to provide a distributed Bragg reflector (DBR) having a low electric resistance and a high reflectivity in a long-wave band longer than 1.1 μm. That is, in the long wavelength band DBR having a design reflection wavelength of 1.1 μm or more, the DB is maintained while maintaining a high reflectance.
The electric resistance of R can be reduced.

According to the second and fourth aspects of the present invention, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated, and the refractive index is A material having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer between the large first semiconductor layer and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector provided with a layer, the designed reflection wavelength of the distributed Bragg reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 20 nm to 50 nm. In the long wavelength band DBR of 1.1 μm or more, the electrical resistance of the DBR can be reduced while maintaining a high reflectance.

According to the third and fifth aspects of the present invention, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated, and the refractive index is A material having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer between the large first semiconductor layer and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector provided with a layer, the designed reflection wavelength of the distributed Bragg reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 30 nm to 50 nm. In the long wavelength band DBR of 1.1 μm or more, the electrical resistance of the DBR can be reduced while maintaining a high reflectance.

According to the sixth, seventh and eighth inventions, the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index are alternately laminated. A refractive index between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index. In the distributed Bragg reflector provided with a material layer having a value, the designed reflection wavelength of the distributed Bragg reflector is longer than 1.1 μm, and the material layer has a thickness of the distributed Bragg reflector design. Since the reflection wavelength λ [μm] is (50λ−15) [nm] or less, the design reflection wavelength is 1.1 μm or more in the long wavelength band D.
In the BR, the electrical resistance of the DBR can be reduced while maintaining a high reflectance.

Further, according to the invention of claim 9, in a surface emitting laser device having an active layer and a cavity mirror, the cavity mirror is described in any one of claims 1 to 8. Since the distributed Bragg reflector of is used in the conventional optical communication and optical transmission applications, 0.85 μm band, 0.98 μm
As compared with the m-band surface emitting laser, it is possible to obtain a surface emitting laser device for low oscillation threshold current, low power consumption, high output operation, optical communication, and optical transmission. That is, it is possible to obtain a surface emitting laser device having a low operating voltage and capable of operating with high efficiency and high output.

According to the invention of claim 10, in the surface emitting laser element of claim 9, the material of the active layer is GaNAs, GaInAs, GaInNAs, GaA.
Since it is any one of sSb, GaInAsSb, and GaInNAsSb, it is possible to obtain a surface emitting laser element that oscillates at a wavelength longer than 1.1 μm. Especially wavelength 1.3μ
By combining an m-band laser element and a quartz single mode laser, high speed communication and high speed transmission become possible. That is, it is possible to obtain a surface emitting laser device for communication which has a low operating voltage and can operate with high efficiency, high temperature and high output.

According to the eleventh aspect of the present invention, since the surface emitting laser array is formed by arranging a plurality of the surface emitting laser elements according to the ninth or tenth aspect, the elements are heated by heat generation. It is possible to obtain a surface emitting laser array having excellent characteristics and reliability with little interference. That is, it is possible to obtain a surface emitting laser array for communication which has a low operating voltage and can operate with high efficiency, high temperature and high output.

According to the twelfth aspect of the invention, the surface emitting laser element of the ninth or tenth aspect, or
Since it is an optical interconnection system using the surface emitting laser array according to claim 11, it is possible to obtain an optical interconnection system capable of high-speed transmission and having high reliability.

According to the invention described in claim 13, the surface emitting laser device according to claim 9 or 10, or
Since it is an optical communication system using the surface emitting laser array according to claim 11, it is possible to obtain an optical communication system capable of high-speed communication and having high reliability.

[Brief description of drawings]

FIG. 1 D by stacking 24 pairs of AlAs / GaAs
It is a figure which shows the reflection spectrum of BR.

FIG. 2 is a diagram showing an example of a distributed Bragg reflector (DBR) according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of a distributed Bragg reflector (DBR) according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the reflectance of DBRs in the 0.88 μm band and the 1.3 μm band and the thickness of the material layer (linear composition gradient layer).

5 is an AlAs / GaAs having a reflection wavelength of 1.3 μm with a linear composition gradient layer having a structure similar to that of FIG.
Resistivity (dV / d) near zero bias of DBR
J is a diagram showing a derivative of voltage V [V] by current density J [A / cm ² ]) [Ωcm ² ].

6 is an AlAs / GaAs having a reflection wavelength of 1.3 μm with a linear composition gradient layer having a structure similar to the result of FIG.
Resistivity (dV / d) near zero bias of DBR
J is a diagram showing a derivative of voltage V [V] by current density J [A / cm ² ]) [Ωcm ² ].

FIG. 7 is a diagram showing a change in reflectance R with respect to a film thickness t of a composition gradient layer.

FIG. 8 is a diagram showing an example of a distributed Bragg reflector (DBR) according to a third embodiment of the present invention.

FIG. 9 is a diagram showing an example of a distributed Bragg reflector (DBR) according to a third embodiment of the present invention.

10 is a diagram showing the results when the doping concentration of each layer in the AlAs / GaAs DBR of FIG. 4 is 7E17 cm ⁻³ .

FIG. 11: 4-pair DB of Al _0.8 Ga _0.2 As / GaAs
It is the figure which calculated the electrical resistivity of R similarly to FIG.

FIG. 12: 4 pairs of p with a design reflection wavelength of 1.3 μm
It is the figure which showed the electrical resistivity of the type distributed Bragg reflector by changing the thickness of the composition gradient layer.

FIG. 13: 4 pairs of p with a design reflection wavelength of 1.3 μm
It is the figure which showed the electrical resistivity of the type distributed Bragg reflector by changing the thickness of the composition gradient layer.

FIG. 14 is a diagram showing a relationship between a composition gradient layer thickness and reflectance for a distributed Bragg reflector having a design reflection wavelength of 1.1 μm to 1.7 μm.

15 is a diagram showing a change rate (| dR / dt |) of the reflectance of FIG. 14 with respect to the composition gradient layer thickness.

FIG. 16 is a diagram showing a configuration example of a surface emitting laser element of the present invention.

FIG. 17 is a diagram showing a configuration example of a surface emitting laser element of the present invention.

FIG. 18 is a diagram showing a specific example of the optical interconnection system of the present invention.

FIG. 19 is a diagram showing an outline of a surface emitting laser array module.

FIG. 20 is a diagram showing a specific example of an optical communication system of the present invention.

[Explanation of symbols]

1 1st semiconductor layer 2 2nd semiconductor layer 3 Material layer 11 n-GaAs substrate 12 n-DBR 13 GaAs spacer layer 14 GaInNAs active layer 15 GaAs spacer layer 16 Current narrowing layer 17 P-DBR 18 P-GaAs contact layer 19 polyimide film 20 light emitting part 21 P-side electrode 22 n-side electrode 31 Al _0.9 Ga _0.1 As layer 32 AlGaAs composition gradient layer 33 GaAs layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Takahashi             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Akihiro Ito             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 5F073 AA51 AA65 AB04 AB17 AB27                       AB28 BA02 CA07 CA17 CA20                       CB02 EA23

Claims (13)

[Claims] 1. A first semiconductor layer having a large refractive index and a second semiconductor layer having a small refractive index are alternately laminated, and a first semiconductor layer having a large refractive index and a first semiconductor layer having a small refractive index are laminated. In the distributed Bragg reflector, a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the two Bragg reflectors. A distributed Bragg reflector characterized in that the design reflection wavelength of the Bragg reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 5 nm to 50 nm. 2. A first semiconductor layer having a large refractive index and a second semiconductor layer having a small refractive index are alternately laminated, and a first semiconductor layer having a large refractive index and a first semiconductor layer having a small refractive index are laminated. In the distributed Bragg reflector, a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the two Bragg reflectors. A distributed Bragg reflector characterized in that the design reflection wavelength of the Bragg reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 20 nm to 50 nm. 3. A first semiconductor layer having a large refractive index and a second semiconductor layer having a small refractive index are alternately stacked, and a first semiconductor layer having a large refractive index and a first semiconductor layer having a small refractive index are laminated. In the distributed Bragg reflector, a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the two Bragg reflectors. A distributed Bragg reflector characterized in that the design reflection wavelength of the Bragg reflector is longer than 1.1 μm, and the material layer has a thickness in the range of 30 nm to 50 nm. 4. The distributed Bragg reflector according to claim 2, wherein the second semiconductor layer having a small refractive index and the first semiconductor layer having a large refractive index which form the distributed Bragg reflector are made of Al.
Made of As, GaAs, or AlGaAs mixed crystal,
A distributed Bragg reflector characterized in that the difference in Al composition between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index is less than 0.8. 5. The distributed Bragg reflector according to claim 3, wherein the second semiconductor layer having a small refractive index and the first semiconductor layer having a large refractive index which form the distributed Bragg reflector are made of Al.
Made of As, GaAs, or AlGaAs mixed crystal,
A distributed Bragg reflector characterized in that the difference in Al composition between the first semiconductor layer having a large refractive index and the second semiconductor layer having a small refractive index is 0.8 or more. 6. A first semiconductor layer having a large refractive index and a second semiconductor layer having a small refractive index are alternately stacked, and a first semiconductor layer having a large refractive index and a first semiconductor layer having a small refractive index are laminated. In the distributed Bragg reflector, a material layer having a refractive index value between the refractive index of the first semiconductor layer and the refractive index of the second semiconductor layer is provided between the two Bragg reflectors. The design reflection wavelength of the Bragg reflector is longer than 1.1 μm, and the thickness of the material layer is the design reflection wavelength λ of the distributed Bragg reflector.
A distributed Bragg reflector characterized in that it is (50λ-15) [nm] or less with respect to [μm]. 7. The distributed Bragg reflector according to claim 6, wherein the material layer has a thickness of 20 nm or more. 8. The distributed Bragg reflector according to claim 6, wherein the material layer has a thickness of 30 nm or more. 9. A surface emitting laser device having an active layer and a cavity mirror, wherein the distributed Bragg reflector according to any one of claims 1 to 8 is used for the cavity mirror. Characteristic surface emitting laser device. 10. The surface emitting laser device according to claim 9, wherein the material of the active layer is GaNAs, GaInAs, Ga.
InNAs, GaAsSb, GaInAsSb, GaI
A surface-emitting laser device characterized by being one of nNAsSb. 11. A surface emitting laser array comprising a plurality of surface emitting laser elements according to claim 9 or 10. 12. An optical interconnection system comprising the surface emitting laser element according to claim 9 or 10, or the surface emitting laser array according to claim 11. 13. An optical communication system using the surface emitting laser device according to claim 9 or 10, or the surface emitting laser array according to claim 11.