JPH07202336A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser having less layer noise easily and with a good yield with reference to the semiconductor laser having an oscillation wavelength in a visible light region. CONSTITUTION:A part of a p-(Al0.6Ga0.4)0.5In0.5P-clad layer of a semiconductor laser is a trapezoidal stripe. A current narrowing layer consists of two layers of an n-Al0.5Ga0.5As layer 7 and an n-GaAs current contricting layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a good noise characteristic and a single transverse mode, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Semiconductor lasers that emit laser light in the visible light range to emit light have applications such as light sources for optical information processing such as laser beam printers and optical disks, and their importance has recently been increasing. Above all, (Al _x Ga _1-x ) _0.5
The In _0.5 P-based material has a wavelength of 0.69 μm by lattice matching with GaAs, which is a good substrate, and changing the composition x.
To 0.56 μm, it is possible to obtain laser oscillation, and therefore, it is drawing attention.

A conventional double-heterostructure lateral mode control type semiconductor laser having an oscillation wavelength in the red region will be described below with reference to FIG. This semiconductor laser is
n-GaAs buffer layer 2, n on n-GaAs substrate 1
-(Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 3, Ga
_0.5 an In _0.5 P active layer _{4, p- (Al 0.6 Ga 0.4} ) 0. 5 I
n _0.5 P clad layer 5, p-Ga _0.5 In _0.5 P layer 6, n
-GaAs current confinement layer 8 and p-GaAs contact layer 9
Is equipped with. A p-side electrode 10 is formed on the contact layer 9.
However, the n-side electrode 11 is formed on the back surface of the substrate 1.

In this semiconductor laser, metalorganic vapor phase epitaxy
A crystal growth technique such as the MOVPE method is used.
Using these crystal growth techniques, on the n-GaAs substrate 1
N-GaAs buffer layer 2, n- (Al_0.6Ga_0.4)
_0.5In_0.5P clad layer 3, Ga0.5In0.5P active layer
4, p- (Al_0.6Ga_0.4)_0.5In_0.5P clad layer 5
And p-Ga_0.5In_0.5The P layer 6 is sequentially deposited. next
P- by photolithography technology and etching technology
Ga_0.5In_0.5P layer 6 and p- (Al_0.6Ga_0.4) _0.5I
n_0.5A part of the P clad layer 5 is etched into a trapezoidal shape.
Forming a striped ridge on the cladding layer 5. That
The n-GaAs current confinement layer 8 is formed by the post MOVPE method or the like.
Selectively deposited on the outside of the stripe, and p-Ga
As contact layer 9 is deposited.

In the structure of such a semiconductor laser, n-
The GaAs current confinement layer 8 can confine the current, and when the p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 5 is trapezoidally etched, the cladding layer 5 outside the striped ridge is formed. By optimizing the thickness and the width of the stripe-shaped ridge, an effective refractive index difference satisfying the condition of the single transverse mode can be provided inside and outside the trapezoidal stripe, and the clad layer 5 of the active layer 4 can be formed. Light can be effectively trapped under the striped ridge. The stripe width is typically about 5 μm.

However, in the above structure, the longitudinal mode tends to be a single mode. Therefore, when used in an optical disc or the like, it causes noise. The noise includes return light induced noise, mode hopping noise, and the like.

Return light induced noise is noise generated when laser light emitted from a semiconductor laser is reflected by a lens, an optical disk or the like and returns to the inside of the resonator of the semiconductor laser. A single longitudinal mode semiconductor laser has strong coherence, and changes in optical output and spectrum (mode hopping) occur depending on the position of a reflecting surface such as a lens or an optical disk surface or the intensity of reflected light, resulting in noise.

Mode-hopping noise occurs especially when the ambient temperature of the semiconductor laser changes. As the temperature changes, when the vertical mode jumps to the next mode, that is, when mode hopping, random oscillation is repeated alternately between the vertical modes, and the optical output level varies between the vertical modes and the optical output fluctuates. Both things result in noise.

When these semiconductor lasers are applied to optical discs, these noises impair sound quality and image quality, so
It becomes a problem.

Therefore, a structure for improving the noise characteristic has been proposed (Japanese Patent Laid-Open No. 62-39084). As shown in FIG. 17, this semiconductor laser has an n-GaAs substrate 201, an internal current confinement layer 203, and a buffer layer 20.
4, n-clad layer 205, active layer 206, p-clad layer 207, p-GaAs layer 208, p electrode 209, n
It consists of electrodes 210. The material forming this semiconductor laser is AlGaAs. In the region B near the end face of the resonator, a bent waveguide structure as shown in FIG.
On the other hand, the region A near the center has a wide stripe width. The current is injected into a desired region of the active layer 206 by the internal current confinement layer 203. Resonator length is about 300 μm, B region length is about 30
μm, width is about 2.5 μm, length of area A is about 240 μm
m, the width is about 8 μm.

This is an attempt to improve the noise characteristics by making the longitudinal mode multimode in the central area A.

[0012]

However, in the case where the internal current confinement layer is provided on the n-GaAs substrate 201 side as in the structure of the conventional example shown in FIG. Overlying in the horizontal direction, it becomes difficult to inject a current into a desired active layer region. Therefore, there arise problems that the transverse mode becomes unstable and the driving current of the semiconductor laser increases.

On the other hand, if the current confinement layer 203 is p-
It is assumed that it is provided on the clad layer 207 side. In this case, since the hetero barrier against holes between the p-clad layer 207 and the p-GaAs layer 208 provided on the p-clad layer 207 for providing the electrode thereon is large, in the A region. The holes injected from the p-electrode 209 spread too much,
There are problems that the driving current of the semiconductor laser rises and that the spread of the injected holes changes with the change of the environmental temperature. In particular, when the structure shown in FIG. 17 is used for the AlGaInP-based material, the influence thereof becomes large because the hetero barrier in the valence band is larger than that of the AlGaAs-based material. For example, in a red semiconductor laser having an oscillation wavelength in the 670 nm band, injected holes spread horizontally in each layer by as much as 50 μm, which increases the drive current and is not practical.

Further, since there is a region A near the center where the stripe width is not controlled and the transverse mode is not controlled, the stable optical output in the transverse mode may be lowered.

An object of the present invention is to solve such problems and to provide a semiconductor laser with low noise and stable transverse mode, and a method for manufacturing the same.

[0016]

A semiconductor laser according to the present invention comprises a semiconductor substrate, an active layer formed on the semiconductor substrate, a pair of clad layers sandwiching the active layer, and a stripe-shaped predetermined pattern of the active layer. A semiconductor laser having a laminated structure having a current confinement layer for injecting a current into a region,
The current confinement layer includes a first current confinement layer formed in a region other than a region corresponding to the predetermined region of the active layer, the current constriction layer having a width greater than a band gap of the active layer. It has a large forbidden band width and a smaller refractive index than the active layer, thereby achieving the above object.

In one embodiment, of the pair of clad layers, the clad layer located above the active layer is
The semiconductor laser has a stripe-shaped ridge extending along the cavity direction, and the first current confinement layer covers a region other than the stripe-shaped ridge on the cladding layer having the stripe-shaped ridge. ing.

In one embodiment, the current confinement layer further comprises a second current confinement layer provided on the first current confinement layer, the second current confinement layer being the active layer. It has a smaller forbidden band width than the forbidden band width.

In one embodiment, the semiconductor substrate is Ga
The cladding layer is made of As, the active layer is made of GaInP, and the pair of cladding layers is made of AlGa.
It is made of InP, and the first current confinement layer is A
lGaAs or AlGaInP, and the second current confinement layer is formed of GaAs.

In one embodiment, the active layer has a multiple quantum well structure or a strained quantum well structure.

A method of manufacturing a semiconductor laser of the present invention is a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the step further including a step of forming a first cladding layer. A step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and a step of selectively etching a part of the film A step of forming a stripe-shaped ridge extending in the cavity direction of the semiconductor laser on the film, thereby forming a second clad layer, and a step of forming a second clad layer on the part of the second clad layer other than the stripe-shaped ridge portion, The first band gap has a larger band gap and a smaller refractive index than the active layer.
A step of forming a semiconductor layer of, and on the first semiconductor layer,
Forming a second semiconductor layer having a forbidden band width smaller than that of the active layer, thereby achieving the above object. .

Another method of manufacturing the semiconductor laser of the present invention is
A method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the method further comprising forming a first clad layer and forming an active layer on the first clad layer. And a step of forming a film to be a second cladding layer on the active layer, and a first band gap having a larger forbidden band and a smaller refractive index than the active layer on the second cladding.
A step of forming a semiconductor layer of, and on the first semiconductor layer,
Forming a second semiconductor layer having a forbidden band width smaller than that of the active layer, and removing the first semiconductor layer and the second semiconductor layer by stripe recess etching The method further includes a step and a step of forming a film to be the third clad layer on the step, whereby the above object can be achieved.

[0023]

According to the semiconductor laser of the present invention, a current is injected into a semiconductor substrate, an active layer formed on the semiconductor substrate, a pair of clad layers sandwiching the active layer, and stripe-shaped predetermined regions of the active layer. A laminated structure having a current confinement layer for reducing the current constriction layer, the current confinement layer being a first current confinement layer formed in a region other than a region corresponding to the predetermined region of the active layer. The current confinement layer has a band gap larger than the band gap of the active layer and a refractive index smaller than that of the active layer. Light leaking to the outside of the ridge increases, self-pulsation occurs, and as a result, the longitudinal mode becomes multimode and the relative noise intensity (RIN) can be lowered.

According to the semiconductor laser of the present invention, of the pair of cladding layers, the cladding layer located above the active layer has a striped ridge extending along the cavity direction of the semiconductor laser. The first current confinement layer covers the region other than the striped ridge on the cladding layer having the striped ridge, so that carriers can be efficiently injected into a desired portion of the active layer. .

According to the semiconductor laser of the present invention, the current confinement layer further comprises a second current confinement layer provided on the first current confinement layer, and the second current confinement layer. Has a forbidden band width smaller than the forbidden band width of the active layer, which enables laser oscillation in a single transverse mode.

According to the semiconductor laser of the present invention, the semiconductor substrate is made of GaAs, the active layer is made of GaInP, and the pair of clad layers is made of AlGaInP. The first
Current confinement layer is AlGaAs or AlGaInP,
Since the second current confinement layer is made of GaAs, a semiconductor laser having low RIN and high lateral mode stability can be obtained.

According to the semiconductor laser of the present invention, the active layer has a multiple quantum well structure or a strained quantum well structure, so that the oscillation efficiency can be increased and the threshold current can be reduced.

According to the method of manufacturing a semiconductor laser of the present invention, there is provided a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the step further comprising forming a first cladding layer. A step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and a step of selectively etching a part of the film. A step of forming a striped ridge extending in the cavity direction of the semiconductor laser on the film, thereby forming a second cladding layer, and a step of forming a second cladding layer on the portion of the second cladding layer other than the striped ridge portion. A step of forming a first semiconductor layer having a larger forbidden band width and a smaller refractive index than the active layer, and a forbidden band width smaller than that of the active layer on the first semiconductor layer. Forming a second semiconductor layer That process and have include, can RIN by its low to produce a high laser of lateral mode stability yield.

Another method of manufacturing a semiconductor laser according to the present invention is a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, which further comprises forming a first cladding layer. A step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and a forbidden band more than the active layer on the second clad. A step of forming a first semiconductor layer having a large width and a small refractive index, and a second step of forming a forbidden band width smaller than that of the active layer on the first semiconductor layer
The step of forming a semiconductor layer, the step of recessing and etching the first semiconductor layer and the second semiconductor layer in a stripe shape, and the step of forming a film to become a third clad layer thereon. And the step of
A semiconductor laser having low IN and high lateral mode stability can be manufactured with high yield.

[0030]

【Example】

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a lateral mode control type red semiconductor laser according to an embodiment of the present invention.

This semiconductor laser, as shown in FIG.
For example, on an n-GaAs substrate 1, an n-GaAs buffer layer
Ga through 2_0.5In_0.5P active layer 4 (thickness 600Å)
N- (Al_0.6Ga_0.4)_0.5In_0.5P clad layer 3
And p- (Al_0.6Ga_0.4) _0.5In_0.5P clad layer 5
It has a double hetero structure sandwiched between. p- (Al_{0. 6}
Ga_0.4)_0.5In_0.5P clad layer 5 (refractive index 3.33
In the upper part of 7), p-Ga_0.5In_0.5P layer 6 (thickness 0.
1 μm) and p-Ga_0.5In_0.5P layer 6 and p-
(Al_0.6Ga_0.4)_0.5In_0.5Part of P clad layer 5
Are processed into a trapezoidal striped ridge. Ku
In the rud layer 5, the thickness of the striped ridge is
1 μm, the thickness except for the striped ridge
It is 0.25 μm. On the p-GaAs contact layer 9 side
Indicates that the p-side electrode 10 is the n-side electrode 1 on the n-GaAs substrate 1 side.
1 is provided.

P- (Al on both sides of the striped ridge
_0.6 Ga _0.4 ) _0.5 In _0.5 P On the clad layer 5, 0.
1 μm n-Al _0.5 Ga _0.5 As current confinement layers 7 and 0.5
A μm n-GaAs current confinement layer 8 is deposited. n
The -Al _0.5 Ga _0.5 As current confinement layer 7 and the n-GaAs current confinement layer 8 have a function of injecting carriers into a desired region of the active layer 4 and a function of controlling a transverse mode of the semiconductor laser. The forbidden band width of the n-Al _0.5 Ga _0.5 As current confinement layer 7 of the present invention is about 2 eV, which is larger than the forbidden band width of the active layer, and the refractive index is 3.38. The forbidden band width of the n-GaAs current constriction layer 8 is smaller than that of the active layer 4, and a part of light generated by recombination of carriers is absorbed by the n-GaAs current constriction layer 8. The width of the striped ridge is about 5
At μm, a large amount of light is absorbed with respect to the higher-order transverse modes higher than the first-order mode, and the waveguide loss increases, so that oscillation in a single transverse mode is possible.

In the present invention, the current confinement layers 7 and 8 are provided on the p-clad layer 5 side. If it is provided on the n-clad layer side. In this case, since the electrons, which are the majority carriers of the n-cladding layer, have a high mobility, the electrons that have passed through the current confinement layer easily spread in the horizontal direction with each layer, so that the effect as the current confinement is weakened and the driving current is reduced. Rise of
Problems such as instability of the transverse mode occur.

The width of the stripe-shaped ridge is such that a sufficient difference in gain between the fundamental transverse mode and the higher-order transverse modes can be obtained, and single transverse mode oscillation of the semiconductor laser is possible. External stripe ridge, that is, the thickness of the current under the p- (Al _{0. 6} Ga _0.4) of the confinement layer 7 _0.5 In _0.5 P cladding layer 5 has become uniform in the resonator direction, a thickness of 0. It is 25 μm. If this thickness is large, the number of carriers leaking out of the striped ridge increases, the drive current increases, leading to a decrease in reliability, and higher-order modes are likely to oscillate, making transverse modes unstable. To become.

In the present embodiment, the stripe-shaped ridge has a trapezoidal sectional shape, but the sectional shape may be rectangular.

FIG. 2 shows the light distribution in the vicinity of the stripe ridge of the semiconductor laser of the present invention of FIG. 1 and the semiconductor laser of the conventional structure of FIG. In the semiconductor laser of the present invention, the amount of light leaking out of the stripe ridge to the outside is larger than in the conventional solid line structure. This is because in the lateral effective refractive index distribution shown in FIG. 3, the effective refractive index difference inside and outside the stripe ridge of the semiconductor laser of the present invention is smaller than that of the conventional structure, and light confinement is small. Is. Light extruded to the outside of the striped ridge undergoes self-pulsation (self-excited oscillation) because there is no gain in this region, and the longitudinal mode becomes multimode. As a result, RIN is -135 dB / Hz
It can be lowered to In the structure without the two current confinement layers as in the present invention, that is, in the conventional structure shown in FIG. 16, RIN is about −120 dB / Hz.

As a method of causing self-pulsation, in the conventional structure shown in FIG. 16, n-GaAs is used.
P- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P below the current confinement layer 8
It is also conceivable to increase the thickness of the cladding layer 5 to increase the amount of light leaking to the outside of the stripe. But,
In this case, the difference in threshold gain between the basic transverse mode and the higher-order transverse mode cannot be made sufficiently large, and the transverse mode may become unstable, which is not practical. In addition, carriers leaking out of the stripe also increase, leading to an increase in driving current, which may reduce reliability.

In the light intensity distribution of FIG. 2, in the semiconductor laser of the present invention, the peak height of the light intensity is smaller than that of the conventional structure. As a result, the instability of the transverse mode due to spatial hole burning can be reduced, and the effect of suppressing the occurrence of kinks in the current-light output characteristics of the semiconductor laser can be obtained.

FIG. 4 shows changes in the threshold gain when the thickness of the n-Al _0.5 Ga _0.5 As current confinement layer 7 is changed. When the thickness is 0 (position of 0 on the horizontal axis), it is the case of the conventional structure of FIG. m = 0 is the basic lateral mode, and m = 1 is the primary mode. In FIG. 4, the mirror loss is 34 cm ⁻¹ and the free carrier loss is 5 cm ⁻¹ . N-A compared to the conventional structure
In the structure having the l _0.5 Ga _0.5 As current confinement layer 7, the difference in threshold gain between the fundamental mode and the primary mode is large, and the stability of the fundamental transverse mode is higher in the present invention than in the conventional structure. I understand. The thicker the n-Al _0.5 Ga _0.5 As current confinement layer 7 is, the larger the difference in threshold gain becomes. However, if the thickness is too thick, the threshold gain for the fundamental mode increases, which makes laser oscillation difficult. Even if it oscillates, the external differential quantum efficiency is reduced and the drive current is increased. In the material constitution of the embodiment of FIG. 1, n-Al _0.5 Ga _0.5
The thickness of the As current confinement layer 7 is preferably 0.3 μm or less.
However, this thickness changes depending on the refractive index of each layer constituting the semiconductor laser, the absorption coefficient for laser light, and the like. It also changes depending on the material of the current constriction layer.

Although the thickness and composition of the current confinement layer vary depending on the semiconductor laser, the semiconductor laser has two current confinement layers for injecting current into stripe-shaped predetermined regions of the active layer. The current confinement layer has a forbidden band width larger than the forbidden band width of the active layer and a refractive index smaller than that of the active layer, and is provided on the first current confinement layer. If the current confinement layer 2 has a forbidden band width smaller than the forbidden band width of the active layer, self-pulsation occurs, the longitudinal mode becomes multimode, and RIN can be lowered.

In the embodiment shown in FIG. 1, the current confinement layer has two layers, but the first current confinement layer closer to the active layer, that is, the n-Al _0.5 Ga _0.5 As current confinement layer 7 has a stripe shape of the active layer. The second current confinement layer, that is, the n-GaAs current confinement layer 8 may be of the same conductivity type as the clad layer having the shape of a striped ridge, as long as it has sufficient ability to inject current into a predetermined region, and p-type conduction. May be That is, the structure shown in FIG. 18 may be used.

Next, a method of manufacturing this semiconductor laser will be described.
This will be described with reference to FIGS. First, MOVPE method, etc.
On the n-GaAs substrate 1 using the crystal growth method of
GaAs buffer layer 2, n- (Al_0.6Ga_0.4)_0.5I
n_0.5P clad layer 3, Ga_{0. Five}In_0.5P active layer 4, p
-(Al_0.6Ga_0.4)_0.5In_0.5P clad layer 5, p-
Ga_0.5In_0.5The P layer 6 is epitaxially grown (Fig.
5). SiO by thermal CVD₂101 is p-Ga_0.5I
n_0.5After depositing on the P layer 6, the photolithography technique
SiO and the etching technique₂101 to stra
Processed into a shape, SiO₂101 as an etching mask
Then p-Ga_0.5In_0.5P layer 6 and p- (Al_{0 .6}G
a_0.4)_0.5In_0.5Etching a part of P clad layer 5
(Fig. 6). SiO₂The width of 101 is about 5 μm.
Then, by using the selective growth technique of the MOVPE method, a current block is
N-Al as a lock layer_0.5Ga_0.5As current constriction layer 7
The n-GaAs current confinement layer 8 is made of SiO.₂Deposited on 101
P- (Al on both sides of the stripe without_0.6Ga
_0.4)_0.5In_0.5Crystal growth on P clad layer 5
(Fig. 7). After that, SiO₂101 is removed and p-Ga
The As contact layer 9 is crystal-grown (FIG. 8). Finally
Cr / Pt / Au is deposited on the p-GaAs contact layer 9.
The p-side electrode 10 is formed by stacking Au on the n-GaAs substrate 1.
/ Ge / Ni is deposited to form the n-side electrode 11 (FIG. 9).
n-Al_0.5Ga_0.5P− (Al under the As current confinement layer 7
_0.6Ga_0.4)_0.5In_0.5The thickness of the P-clad layer 5 is 0.2
It is 5 μm.

With such a manufacturing method, a lateral mode control type red semiconductor laser as shown in FIG. 1 can be manufactured.

N-Al _0.5 Ga _0.5 As of the current blocking layer
The current confinement layer 7 and the n-GaAs current confinement layer 8 are MOVP.
It is desirable to deposit using a selective growth technique such as E method.
The thickness of the n-Al _0.5 Ga _0.5 As current confinement layer 7 is an important factor that determines the transverse mode stability and noise characteristics of the semiconductor laser, and is not caused by etching or the like, but by crystal growth excellent in film thickness controllability. Need to make. In addition, n-Al
_{Since the 0.5} Ga _0.5 As current confinement layer 7 contains Al, it is easy to form an oxide of Al and causes a decrease in reliability. Therefore, it is necessary to avoid exposing it to the atmosphere. Therefore, n-
It is desirable that the Al _0.5 Ga _0.5 As current confinement layer 7 and the n-GaAs current confinement layer 8 are continuously deposited.

Therefore, according to the manufacturing method of the present invention, RI
A semiconductor laser having a low N can be manufactured with a high yield. , P- (Al _0.6 Ga _0.4 ) _0.5 I on both sides of the stripe without depositing SiO ₂ on the SiO ₂ 101.
Crystals are grown on the n _0.5 P clad layer 5 (FIG. 7). In the above embodiment, the material forming the semiconductor laser was specified.
The clad layer is (Al _y Ga _1-y ) _0.5 In _0.5 P and the active layer is (Al _z Ga _1-z ) _0.5 In _0.5 P (where 0 ≦ z ≦ y ≦
Even in the case of 1), a semiconductor laser having a low RIN can be easily manufactured. When a multiple quantum well or a strained multiple quantum well is used for the active layer, the single longitudinal mode property is strong and the noise characteristics tend to deteriorate.
A semiconductor laser having a low IN can be obtained.

In the above embodiment, the material is AlGaIn.
Although the semiconductor laser using P has been described, it goes without saying that the effect of the present invention is great even if other materials are used. III-
Not only the group V semiconductor laser but also the semiconductor laser made of the group II-VI material, the semiconductor laser has at least one layer having a band gap larger than that of the active layer as the current confinement layer, and the layer above the active layer. With a structure having a layer with a small forbidden band width, a semiconductor laser with low RIN can be obtained.

Example 2 Another semiconductor laser according to the present invention will be described with reference to FIG.

This semiconductor laser has an n-GaAs substrate 1
Ga via the n-GaAs buffer layer 2_0.5In_0.5
The P active layer 4 (thickness 600 Å) is replaced with n- (Al_0.6Ga_0.4)
_0.5In_0.5P cladding layer 3 and p- (Al_0.6G
a_0.4)_0.5In_0.5Double hetero sandwiched between P clad layers 5
It has a structure. p- (Al_0.6Ga_0.4)_0.5In_0.5
On the upper portion of the P clad layer 5, p-Ga is formed._0.5In_0.5P E
Pitch stop layer 301 (thickness 0.01 μm)
Ga_0.5In_0.5N is formed on the P etching stop layer 301.
-Al_0.5Ga_0.5As current confinement layer 7 and n-GaAs
The current confinement layer 8 is deposited. Ga_0.5In_0.5P activity
Injecting carriers into predetermined stripe-shaped regions of layer 4
In order to_0.5Ga_0.5As current constriction layer 7 and n-
The GaAs current confinement layer 8 has stripe-shaped openings.
It Striped exposed p-Ga _0.5In_0.5P E
Of the etching stop layer 301 and the n-GaAs current confinement layer 8
The second p- (Al_0.6Ga_0.4)_0.5In_0.5P
A rud layer 302 is deposited, and a p-G layer is formed on the rud layer 302.
a_0.5In_0.5P layer 6 and p-GaAs contact layer 9 are stacked.
Have been piled up. p on the p-GaAs contact layer 9
The side electrode 10 is an n-side electrode 11 on the n-GaAs substrate 1 side.
Is provided.

N-Al _0.5 Ga _0.5 As current confinement layer 7 and n
The -GaAs current confinement layer 8 has a function of injecting carriers into a desired region of the active layer 4 and a function of controlling a lateral mode of the semiconductor laser. N-Al _0.5 Ga _{0.5 of the} present invention
The forbidden band width of the As current constriction layer 7 is about 2 eV, which is larger than the forbidden band width of the active layer, and the refractive index is 3.38. n-GaA
The forbidden band width of the s current constriction layer 8 is smaller than that of the active layer 4, and a part of the light generated by the recombination of carriers is n-GaA.
It is absorbed by the current confinement layer 8. The width of the stripe is such that a sufficient difference in gain between the fundamental transverse mode and the higher-order transverse modes can be obtained, which enables single transverse mode oscillation of the semiconductor laser. When the width of the opened stripe is about 5 μm, the absorption amount of light in the higher-order transverse modes higher than the first-order mode is larger than that in the fundamental mode, and the waveguide loss becomes sufficiently large, so that oscillation in a single transverse mode occurs. If possible.

In the present invention, the current confinement layers 7 and 8 are provided on the p-clad layer 5 side. If it is provided on the n-clad layer side. In this case, since the electrons, which are the majority carriers of the n-cladding layer, have a high mobility, the electrons that have passed through the current confinement layer easily spread in the horizontal direction with each layer, so that the effect as the current confinement is weakened and the driving current is reduced. Rise of
Problems such as instability of the transverse mode occur.

Outside the stripe, that is, the current confinement layer 7
The thickness of the p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 5 below is 0.25 μm. If this thickness is large, the number of carriers leaking out of the stripe will increase, driving current will increase, leading to lower reliability, or higher-order modes will oscillate easily and the transverse modes will become unstable. To do.

FIG. 11 shows the distribution of light in the vicinity of the striped ridge of the semiconductor laser of the present invention of FIG. 10 and the semiconductor laser of the conventional structure of FIG. In the semiconductor laser of the present invention, the amount of light leaking out of the stripe ridge to the outside is larger than in the conventional solid line structure. This is because the effective refractive index difference between the inside and outside of the stripe ridge of the semiconductor laser of the present invention is smaller than that of the conventional structure, and the light confinement is small. Light extruded to the outside of the striped ridge undergoes self-pulsation because there is no gain in this region, and the longitudinal mode becomes multimode. As a result, RIN is -135 dB / H
It can be lowered to z or less. In the structure without the two current confinement layers as in the present invention, that is, in the conventional structure shown in FIG. 16, RIN is about −120 dB / Hz.

In the light intensity distribution of FIG. 11, in the semiconductor laser of the present invention, the peak height of the light intensity is smaller than the peak height of the conventional structure. As a result, the instability of the transverse mode due to spatial hole burning can be reduced, and the effect of suppressing the occurrence of kinks in the current-light output characteristics of the semiconductor laser can be obtained.

Although the thickness and material of the current confinement layer vary depending on the semiconductor laser, the semiconductor laser has two current confinement layers for injecting current into the stripe-shaped predetermined region of the active layer. The current confinement layer has a forbidden band width larger than the forbidden band width of the active layer and a refractive index smaller than that of the active layer, and is provided on the first current confinement layer. If the current confinement layer 2 has a forbidden band width smaller than the forbidden band width of the active layer, self-pulsation occurs, and the longitudinal mode becomes multi-mode.
Can be lowered.

In the embodiment of FIG. 10, two current confinement layers are used.
However, if the first current confinement layer closer to the active layer, that is, the n-Al _0.5 Ga _0.5 As current confinement layer 7 has sufficient ability to inject current into the stripe-shaped predetermined region of the active layer, The second current confinement layer, that is, the n-GaAs current confinement layer 8 may be of the same conductivity type as the clad layer having the shape of a stripe ridge, or may be p-type conduction.

Next, a method of manufacturing this semiconductor laser will be described.
It will be described with reference to FIGS. First, the MOVPE method
On the n-GaAs substrate 1 using a crystal growth method such as
n-GaAs buffer layer 2, n- (Al_0.6Ga_0.4)
_0.5In_0.5P clad layer 3, Ga_0.5In_0.5P active layer
4, p- (Al_0.6Ga_0.4)_0.5In_0.5P clad layer
5, p-Ga_0.5In_0.5P etching stop layer 301, n
-Al_0.5Ga_0.5As current confinement layer 7, n-GaAs current
The constriction layer 8 is epitaxially grown (FIG. 12). Heat CV
SiO by D₂101 is an n-GaAs current confinement layer 8
After deposition on top, photolithography technique and etch
SiO technology₂101 is striped
And SiO₂101 as an etching mask
-GaAs current confinement layer 8 and n-Al_0.5Ga_0.5As
The current confinement layer 7 is etched to form p-Ga _0.5In_0.5P
The etching stop layer 301 is exposed in stripes (see FIG.
13). Width of stripes created by etching
Is about 5 μm. And the selective growth technique of MOVPE method
Exposed p-Ga in stripes_0.5In
_0.5P etching stop layer 301 and n-GaAs current
The second p- (Al_0.6Ga_0.4)_0.5
In_0.5P clad layer 302, p-Ga_0.5In_0.5P layer
6 was deposited, and on top of that, p-GaAs contact was formed.
The crystal of the electrocut layer 9 is grown (FIG. 14). Finally p-Ga
Cr / Pt / Au is deposited on the As contact layer 9 and p
As the side electrode 10, Au / Ge / on the n-GaAs substrate 1
Ni is deposited to form the n-side electrode 11 (FIG. 15). n-A
l_0.5Ga_0.5P− (Al under the As current confinement layer 7_0.6Ga
_0.4)_0.5In_0.5The thickness of the P-clad layer 5 is 0.25 μm
Is.

With such a manufacturing method, a lateral mode control type red semiconductor laser as shown in FIG. 10 can be manufactured.

N-Al _0.5 Ga _0.5 As of the current blocking layer
The current confinement layer 7 and the n-GaAs current confinement layer 8 are MOVP.
It is desirable to deposit using a crystal growth technique such as E method.
The thickness of the n-Al _0.5 Ga _0.5 As current confinement layer 7 is an important factor that determines the noise characteristics and the lateral mode stability of the semiconductor laser, and is a crystal having excellent film thickness controllability rather than etching. It must be made by growth. Also,
Since the n-Al _0.5 Ga _0.5 As current confinement layer 7 contains Al, it is easy to form an oxide of Al and causes a decrease in reliability. Therefore, it is necessary to avoid exposing it to the atmosphere. _{Therefore, n-Al 0. 5 Ga 0.5} As current blocking layer 7 and the n-GaA
It is desirable that the s-current constriction layer 8 be continuously deposited.

Therefore, according to the manufacturing method of the present invention, RI
A semiconductor laser having a low N can be manufactured with a high yield.

[0061] In the above embodiment has been designated a material constituting the semiconductor laser, the cladding layer is _{(Al y Ga 1-y)} 0.5 I
Even when n _0.5 P and the active layer are (Al _z Ga _1-z ) _0.5 In _0.5 P (where 0 ≦ z ≦ y ≦ 1), a semiconductor laser having a low RIN can be easily manufactured. When a multiple quantum well or a strained multiple quantum well is used for the active layer, the single longitudinal mode property is strong and the noise characteristics tend to be deteriorated. However, according to the semiconductor laser of the present invention, a semiconductor laser having a low RIN can be obtained. it can.

In the above embodiment, the material is AlGaIn.
Although the semiconductor laser using P has been described, it goes without saying that the effect of the present invention is great even if other materials are used. III-
Not only the group V semiconductor laser but also the semiconductor laser made of the group II-VI material, the semiconductor laser has at least one layer having a band gap larger than that of the active layer as the current confinement layer, and the layer above the active layer. With a structure having a layer with a small forbidden band width, a semiconductor laser with low RIN can be obtained. For example, a semiconductor laser made of AlGaAs material may have a structure as shown in FIG.

[0063]

According to the semiconductor laser of the present invention, (1) a semiconductor substrate, an active layer formed on the semiconductor substrate, a pair of clad layers sandwiching the active layer, and a stripe shape of the active layer. A laminated structure having a current confinement layer for injecting current into a predetermined region, wherein the current confinement layer is formed in a region other than a region corresponding to the predetermined region in the active layer. A first current confinement layer, the current confinement layer having a forbidden band width larger than the forbidden band width of the active layer and a refractive index smaller than that of the active layer. As a result, the effective refractive index difference between the inside and outside of the striped ridge can be reduced, the amount of light leaking to the outside of the striped ridge increases, self-pulsation occurs, and as a result, the longitudinal mode becomes multimode and the relative noise intensity (RIN ) Lower You can

According to the semiconductor laser of the present invention, (2) of the pair of clad layers, the clad layer located above the active layer is a striped ridge extending along the cavity direction of the semiconductor laser. Has
The first current confinement layer covers the region other than the striped ridge on the clad layer having the striped ridge, and carriers can be efficiently injected into a desired portion of the active layer.

According to the semiconductor laser of the present invention, (3) the current confinement layer further includes a second current confinement layer provided on the first current confinement layer, and the second current confinement layer is provided.
The current confinement layer has a forbidden band width smaller than the forbidden band width of the active layer, which enables laser oscillation in a single transverse mode.

According to the semiconductor laser of the present invention, (4) the semiconductor substrate is made of GaAs, the active layer is made of GaInP, and the pair of cladding layers is made of AlGaInP. And the first current confinement layer is AlGaAs or A
Since 1GaInP and the second current confinement layer are formed of GaAs, a semiconductor laser having low RIN and high lateral mode stability can be obtained.

According to the semiconductor laser of the present invention, (5) the active layer has a multiple quantum well structure or a strained quantum well structure, so that the oscillation efficiency can be increased and the threshold current can be reduced.

According to the method of manufacturing a semiconductor laser of the present invention, (6) a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, wherein the step further comprises the first cladding. A step of forming a layer, a step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and selectively etching a part of the film. Thereby forming a stripe-shaped ridge extending in the cavity direction of the semiconductor laser on the film, thereby forming a second clad layer, and a step of forming a second clad layer in the second clad layer other than the stripe-shaped ridge portion. Forming a first semiconductor layer having a larger forbidden band width and a smaller refractive index than the active layer on the portion; and a forbidden band smaller than the active layer on the first semiconductor layer. A second semiconductor layer having a width Is included, which makes it possible to manufacture a semiconductor laser with low RIN and high lateral mode stability with high yield.

According to another method of manufacturing a semiconductor laser of the present invention, there is provided (7) a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the step further comprising: 1 step of forming a clad layer, a step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and a step of forming the active layer on the second clad layer. Forming a first semiconductor layer having a forbidden band width larger than that of the layer and having a smaller refractive index; and forming a first forbidden band width smaller than that of the active layer on the first semiconductor layer. Two
The step of forming a semiconductor layer, the step of recessing and etching the first semiconductor layer and the second semiconductor layer in a stripe shape, and the step of forming a film to become a third clad layer thereon. And the step of
A semiconductor laser having low IN and high lateral mode stability can be manufactured with high yield.

[Brief description of drawings]

FIG. 1 is a sectional view of a lateral mode control type red semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a diagram showing the intensity distribution of light in the horizontal direction in each layer of the semiconductor laser of the embodiment of the present invention and the semiconductor laser of the conventional structure.

FIG. 3 is a diagram showing the distribution of the effective refractive index in the horizontal direction in each layer of the semiconductor laser of the example of the present invention and the semiconductor laser of the conventional structure.

FIG. 4 is a diagram for explaining the effect of the semiconductor laser of the present invention, showing the relationship between the threshold gain and the thickness of the first current confinement layer.

FIG. 5 is a sectional view showing a first step sequence in the process of manufacturing the semiconductor laser according to the present invention.

FIG. 6 is a sectional view of a second step sequence showing the manufacturing step of the semiconductor laser of the present invention.

FIG. 7 is a sectional view showing a third step sequence in the process of manufacturing the semiconductor laser according to the present invention.

FIG. 8 is a fourth process step sectional view showing a process for manufacturing a semiconductor laser of the present invention.

FIG. 9 is a sectional view showing a fifth step sequence in the process of manufacturing the semiconductor laser according to the present invention.

FIG. 10 is a sectional view of a transverse mode control type red semiconductor laser according to another embodiment of the present invention.

FIG. 11 is a diagram showing the light intensity distribution in the horizontal direction in each layer of the semiconductor laser of another embodiment of the present invention and the semiconductor laser of the conventional structure.

FIG. 12 is a first diagram showing a manufacturing process of a semiconductor laser of the present invention.
Process cross-sectional view

FIG. 13 is a second diagram showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 14 is a third process showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 15 is a fourth view showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 16 is a sectional view of a conventional red semiconductor laser.

FIG. 17 is a top view and a sectional view of another conventional semiconductor laser.

FIG. 18 is a sectional view of a lateral mode control type red semiconductor laser according to another embodiment of the present invention.

FIG. 19 is a sectional view of a lateral mode control type red semiconductor laser according to another embodiment of the present invention.

[Explanation of symbols]

1 n-GaAs substrate 2 n-GaAs buffer layer 3 n- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 4 Ga _0.5 In _0.5 P active layer 5 p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 6 p-Ga _0.5 In _0.5 P layer 7 n-Al _0.5 Ga _0.5 As layer 8 n-GaAs current confinement layer 9 p-GaAs contact layer 10 p-side electrode 11 n-side electrode 101 SiO ₂ 201 n-GaAs substrate 203 internal current confinement Layer 204 n-GaAs buffer layer 205 n-Ga _0.5 Al _0.5 As clad layer 206 Ga _0.86 Al _0.14 As active layer 207 p-Ga _0.5 Al _0.5 As clad layer 208 p-GaAs layer 209 p-electrode 210 n-electrode 301 p-Ga _0.5 In _0.5 P etching stop layer 302 p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 303 p-GaAs Layer 304 n-Al _0.4 Ga _0.6 As cladding layer 305 an active layer 306 p-Al _0.4 Ga _0.6 As cladding layer 307 n-Al _0.35 Ga _0.65 As layer 308 n-GaAs current confinement layer 309 p-Al _0.4 Ga _0.6 As cladding layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoji Ohnaka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A semiconductor substrate, an active layer formed on the semiconductor substrate, a pair of clad layers sandwiching the active layer, and a current confinement layer for injecting a current into a stripe-shaped predetermined region of the active layer. And a first laser current blocking layer formed in a region other than a region corresponding to the predetermined region of the active layer. The semiconductor laser, wherein the current confinement layer has a forbidden band width larger than the forbidden band width of the active layer and a refractive index smaller than that of the active layer. 2. The semiconductor laser according to claim 1, wherein, of the pair of clad layers, a clad layer located above the active layer is a stripe extending along a cavity direction of the semiconductor laser. A semiconductor laser, wherein the first current confinement layer covers a region other than the striped ridge on the cladding layer having the striped ridge. 3. The semiconductor laser according to claim 1, wherein the current confinement layer further comprises a second current confinement layer provided on the first current confinement layer. 2. The semiconductor laser according to claim 2, wherein the current confinement layer 2 has a forbidden band width smaller than the forbidden band width of the active layer. 4. The semiconductor substrate is formed of GaAs, the active layer is formed of GaInP, the pair of clad layers is formed of AlGaInP, and the first current confinement layer is formed. 4. The semiconductor laser according to claim 3, wherein is made of AlGaAs or AlGaInP, and the second current confinement layer is made of GaAs. 5. The semiconductor laser according to claim 1, wherein the active layer has a multiple quantum well structure or a strained quantum well structure. 6. A method of manufacturing a semiconductor laser, including a step of forming a laminated structure on a semiconductor substrate, the step further comprising a step of forming a first clad layer, and a step of forming a first clad layer on the first clad layer. Forming an active layer on the active layer, forming a film to be the second cladding layer on the active layer, and selectively etching a part of the film to extend in the cavity direction of the semiconductor laser. Forming a striped ridge on the film, thereby forming a second clad layer, and forming a second clad layer on the portion other than the striped ridge portion of the second clad layer, and a forbidden band width larger than that of the active layer. Is large, and
A step of forming a first semiconductor layer having a small refractive index, and a step of forming a second semiconductor layer having a band gap smaller than that of the active layer on the first semiconductor layer. Manufacturing method of semiconductor laser including. 7. A method of manufacturing a semiconductor laser, including a step of forming a laminated structure on a semiconductor substrate, the step further comprising the step of forming a first clad layer, and the step of forming a first clad layer on the first clad layer. A step of forming an active layer on the active layer, a step of forming a film to be a second clad layer on the active layer, and a bandgap larger than that of the active layer on the second clad,
And a step of forming a first semiconductor layer having a small refractive index, and a step of forming a second semiconductor layer having a band gap smaller than that of the active layer on the first semiconductor layer. A semiconductor including a step of recessing and etching the first semiconductor layer and the second semiconductor layer in a stripe shape, and a step of forming a film to be a third clad layer thereon. Laser manufacturing method.