JPS63187671A - 1.3mum-range semiconductor photodetector - Google Patents

Abstract

PURPOSE:To reduce dark currents, and to improve frequency characteristics by keeping the forbidden band width Eg of a first semiconductor layer as an optical absorption layer within a range of 0.80<=Eg<=0.95eV. CONSTITUTION:A semiconductor substrate 2 consisting of N-type InP, a buffer layer 3 composed of N-type InP and an InGaAsP optical absorption layer 11 having forbidden band width of 0.90eV are formed onto an N-type electrode 1, an N-type InP window layer 5, an surface protective film 6 made up of SiO2, a P-type light-receiving region 8 shaped into the window layer 5 through Zn diffusion and a P-type electrode 9 are formed onto the layer 11, and a P-type guard ring 7 is shaped into the window layer 5. Accordingly, InGaAsP, forbidden band width of which is kept within a range to 0.95eV (1.3mum) from 0.80eV (a wavelength of 1.55mum), is used as the optical absorption layer, thus eliminating the need for the formation of an intermediate layer, then acquiring a photodetector having excellent high-speed response characteristics with high yield through a simple manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a semiconductor light receiving element for a 1.3-band wavelength.

[Conventional technology]

Currently, the photodetector for 1-band optical communication is made of fnP semiconductor (14).The forbidden band 1L is used as the light absorption layer.
I n Ga As or I n of V70.7+eV
A semiconductor photodetector using GaASP has a maximum optical wavelength of 1
．． It has sensitivity up to 7-wavelength range, and is sensitive to optical fiber light In
It can be widely used in optical communication systems using wavelengths in the 1.3-band and 1.55-μm bands with low loss.

FIG. 1 shows an example of a conventional light-receiving device for l-band optical communication. In Fig. 1, (I) 1, n-side electric
) is, for example, an n-type half ? , one-piece board, (
3) is, for example, a buffer layer made of n-type InP, (4)
) is, for example, n-type InG at about 0.7:+eV in the forbidden band.
The light absorption layer (5) made of aAs is, for example, n-type [n
A window layer made of P, (6) is a surface protective film made of SiO□, etc. provided on the surface of the window layer, and (8) is, for example, a Z
A P-type light-receiving region is provided in the window layer (5) by diffusion of n, etc., (9) is a p(!III electrode), and (7) is a △1]D (avalanche photodiode). )
When used as a window layer (5), a guard ring consisting of a P wall region is provided in the window layer (5). In this structure, a VOn-type InGaAs layer with a forbidden band width of about 0.75 e is used as the light absorption layer, so that the device according to this example has a wavelength of 1.1 to
It has good sensitivity in a wide wavelength range of 1.7-
- It can be widely used as a light-receiving element for optical communication in the band.

In addition, since the device according to this example has the p-n junction in the InP window layer (5), which has a relatively large forbidden band of approximately 1.34 eV, leakage at the p-n junction occurs when a bias voltage is applied. The current is kept extremely small, resulting in an excellent light-receiving element with low dark current and low noise.

However, the light receiving element having this structure has drawbacks as shown in FIG. That is, 1.34 eV in the forbidden band
of InP window layer (5) and 0.75 eV of InGa in the forbidden band.
At the heterojunction surface with the As light absorption layer (4), a discontinuity of ΔEv occurs in the valence band. This ΔEv acts as an energy barrier for holes among the electron-hole pairs generated during light irradiation and prevents the drift of the genuine tag, resulting in a problem that the high-speed operation of the device is significantly impaired. Furthermore, in the manufacturing process of a device having this structure, it is necessary to grow an InP window layer on the 1nGaAs light absorption layer during crystal growth. In this case, as a crystal growth method, for example, the liquid phase epitaxial growth method (
LPE? ), it is possible to add In to the melt for lnP growth.
Since GaAs is easily melted by 1 volume, 1 volume is easily melted during the growth of the lnP window layer.
A so-called "meltback" problem occurs in which the nGaAs light absorption layer begins to melt, making it difficult to control the 719 layer, and has the disadvantage that the crystallinity of the I n P / I nGaΔS interface is significantly reduced.

FIG. 3 shows an example of a semiconductor light receiving element devised to solve the above problem. In the same figure, θ0
) is provided between the light absorption layer (4) and the window layer (5) in FIG. 1, for example, in the forbidden zone 1. This is an intermediate layer made of IeV InGaAsP. By providing an intermediate JV 01l), the discontinuity ΔEv of the valence band, which was a problem in the device structure of FIG.
A light-receiving element capable of high-speed operation at Hz or higher is realized. Furthermore, since In,GaAsP acts as an anti-meltback layer, the influence of "meltback" during crystal growth described above is significantly reduced.

[Problems to be Solved by the Invention] However, it has been found that the element structure shown in FIG. 3 has a problem in the manufacturing process. That is, InGa
Variations in the thickness and impurity concentration of the AsP intermediate layer 00) have a large effect on the characteristics of the device. For example, inappropriate thickness and impurity concentration cause a decrease in the sensitivity of the device and an increase in dark current.

Therefore, in order to manufacture elements with good characteristics at a high yield, it is necessary to optimize the thickness and impurity concentration of the intermediate layer and to improve the uniformity. However, it is extremely difficult to manufacture an element under such conditions. Furthermore, in order to manufacture a 1.3-band light receiving element, there is no need to complicate the manufacturing process by using a semiconductor layer with a narrow forbidden band 1, such as InGaAs, as the light absorption layer.

The present invention has been made in view of the above points, and has the following features:
．． It is an object of the present invention to provide a structure of a semiconductor light-receiving element that has practically good sensitivity in the 3-band wavelength region, has a small dark current, has good frequency characteristics, and can be manufactured with a high yield through simple steps.

[Means for Solving the Problems] In order to achieve the above object, the 1, 3-band semiconductor photodetector according to the present invention includes a first semiconductor layer which is a light absorption layer, and a layer on the first semiconductor layer. formed adjacent to each other, has a larger forbidden band than that of the first semiconductor layer, and has p-
In a semiconductor light-receiving device comprising a second conductor layer having an n-junction, the forbidden band rl'lE of the first semiconductor layer is
It is characterized in that g is set to 0.80≦Eg≦0.95eV.

[Effect]

Next, the operation of the present invention will be explained with reference to FIG. 4 showing one embodiment.

In Figure 4, (11) is the forbidden band I of 0.90 eV.
nGaAsPAs-like layer. Therefore, when performing crystal growth using the LPE method, unlike InGaAs, InP
No “meltback” problem occurs during window layer growth.I
nGaAs P becomes smaller in the forbidden band as As increases and P decreases. According to experiments, even if As increases and P decreases, the forbidden band is less than about 0.80eν l nGa
It has been shown that the AsP quaternary crystal does not cause a particularly serious meltback problem.
．． When InGaAs with 75eν is used for the light absorption layer, a heterobarrier due to discontinuity in the valence band causes a decrease in response speed, but when the forbidden band becomes 0.80eν or more,
The response speed is improved and the heterobarrier does not have a significant negative effect on the fast response characteristics. FIG. 5 shows that the frequency characteristics of the structural element according to the invention are different from the frequency characteristics of the conventional structural element shown in FIG.

As a result of the above, the forbidden band 11 of the light absorption layer is 0.80e.
V (wavelength 1.55-) to 0.95eV (1,3-
), the third
There is no need to provide an intermediate layer as shown in the figure, and a light receiving element with high yield and excellent high-speed response characteristics can be obtained through a simple manufacturing process.

In addition, in this example, when the bias voltage is set to 5■,
Dark current is 1nA or less, sensitivity is 0.1A/W or more, wavelength 1
．． The new circular wave number for llr+n high-speed modulated light is 50.
0M]lz or more, and it was found that the properties were extremely good.

[Example] The fourth recess is a diagram showing an embodiment of the present invention.

(1) 1. : n-type electrode, (2) is a semiconductor substrate made of n-type 1nP, (3) is a buffer layer made of n-type 1nP, (l l) is a forbidden band tlO, I n G of 90 eν
aΔsP light absorption layer, (5) is an n-type 1nP window layer, (6) is a surface protective film made of SiO2, (8) is a p-type light receiving region provided in the window layer (5) by Zn diffusion, (9 ) is an n-type electrode. (7) is a p-type guard ring provided in the window layer (5).

The present invention is not limited to the above-mentioned embodiments, but can be implemented with various modifications. For example, in the above embodiment, p-n! We have explained the so-called planar type in which the coupling is formed by diffusion of Zn.
A similar effect is expected even if the n P window layer is formed into a mesa type with a two-layer structure of n-type 1nP and p-type I r+ P.

Further, in the above embodiment, the light is applied to the epitaxially grown layer;
Although a structure in which the light is incident from the front is shown, the light may be incident from the n-type 1r+P substrate side. In addition, in this example, the window layer is InP.
However, if the material has a wider forbidden band than the light absorption layer,
There is no problem with materials other than lnP. As the light absorption layer material, there is only a limitation of 0.80 to 0.95 eV in the forbidden band, and InG including superlattice structure etc.
It goes without saying that it is possible to implement this method even in cases other than aAsP.

〔Effect of the invention〕

As explained above, according to the present invention, 1.3μ・:1
Provided is a semiconductor light-receiving element that has practically good sensitivity in the wavelength range of :, has a small ff&'E current, and has good frequency characteristics. In particular, since the element structure is in a cylinder, the present invention has a great effect in that it can be assembled in a simple process with a high yield.

・1. Brief explanation of the drawings No. 16 is a sectional view of main parts showing the structure of a conventional semiconductor photodetector, FIG. 2 is a semiconductor energy band diagram explaining the problems of the photodetector with the structure shown in FIG. Figure 3 is a cross-sectional view of main parts showing the structure of a conventional light-receiving element that is an improvement on the structure shown in Figure 1.
The figure is a cross-sectional view of a main part showing an embodiment of the present invention, and FIG. 5 is a diagram showing frequency characteristics of a positive structural element according to the present invention.

1: n-type, 11den) rabbit, 2: n-type 1n
P group (anti, 3: n-type 1 n P huff layer,
4: n-type 1nGaAs light absorption layer, 5. n-type InP window layer, 6: surface protective film, 7: p-type guard ring, 8: p-type light-receiving area, 9; P-side' break, l
o:r+pear-shaped 1nGaAsP medium

Claims (2)

[Claims] (1) A first semiconductor layer that is a light absorption layer, which is formed adjacent to the first semiconductor layer, has a forbidden band width larger than the forbidden band width of the first semiconductor layer, and has a A semiconductor light-receiving device comprising a second semiconductor layer having a p-n junction in the semiconductor light-receiving device, characterized in that the first semiconductor layer has a forbidden band width Eg of 0.80≦Eg≦0.95 eV. element. (2) The semiconductor light-receiving device according to claim 1, wherein the first semiconductor layer is InGaAsP.