JPH02253666A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To prevent edge breakdown and assure high speed response by providing a second semiconductor region in a first semiconductor layer, said second semiconductor region having carrier concentration decreasing from a substrate side to a surface, and providing a large curvature portion of a first PN junction as an optical detection region in said second semiconductor layer. CONSTITUTION:A portion of a PN junction 12 without any curved portion which forms an optical detection region and a multiplication layer 5 having higher carrier concentration are contiguous with each other. Accordingly, avalanche building-up time can be reduced. Further, a large curvature portion of the PN junction 12 is formed in a region 6 where carrier concentration decreases from a semiconductor substrate 1 side to a surface. Accordingly, the curvature of the PN junction 12 can be reduced and a graded junction can be realized. Hereby, edge breakdown can be prevented at the large curvature PN junction 12 portion around the optical detection section, so that an effective guard ring can be formed together with a high speed response.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a Brehner-type semiconductor light-receiving element that is equipped with a guard ring and utilizes an avalanche multiplication phenomenon.

(Prior art) At present, InGaAs/InP-based light receiving elements for long-distance and high-speed optical communications are used, which have sensitivity in the wavelength band of 1 to 1.6 μm, where the transmission loss of optical fibers is low. The development of avalanche photodiodes (APDs) is progressing.

As such an APD, for example, the structure shown in FIG. 5 is known. That is, n-1n on the n-1nP substrate 1
P buffer layer 2, n −1nGaAS light absorption layer 3, n
-1nGaAsP intermediate layer 4, n''-1nP multiplication layer 5
, n--1nP window layer 6 are sequentially grown epitaxially, Cd or the like is selectively diffused to form the P- light receiving part 7, and Be or the like is implanted and then high-temperature annealing is performed to form the P-
A guard ring portion 8 is provided, and a P side electrode 10,
An N-side electrode 11 is provided. In the figure, 9 is an antireflection film, and 12 and 13 are PN junctions, respectively.

lnG absorbs and multiplies light in lnGaAsW
In the case of a As - A P D, when a high electric field is applied, the dark current rapidly increases due to tunnel current. For this reason, the InGaAs light absorption layer 3 is usually made with a low carrier concentration to prevent high electric fields from being applied, and the InP layer 5, which has a wide band gap and is difficult to generate a tunnel current, is used as an avalanche region, which is a region for light absorption and multiplication. The above-mentioned structure is adopted in which the area where the image processing is performed is separated.

However, the InGaAs layer 3 and the InP layer 5 have a heterostructure, and holes generated by light absorption are accumulated in the barrier of the valence band existing at the hetero interface, making it impossible to obtain high-speed response characteristics. For this reason, an InGaAs layer 3 and an InP layer 5 having a composition with an energy gap between the two are formed.
An AsP intermediate layer 4 is inserted.

In addition, in order to realize an APD with low current, high multiplication factor, and good characteristics, it is necessary that uniform avalanche multiplication be performed over the entire light-receiving area, and that voltage breakdown should not occur in areas other than the light-receiving area. It is. Particularly, the part with curvature around the light receiving part where the PN junction is selectively formed (14 in Fig. 5)
, the electric field concentrates and local voltage breakdown (edge breakdown) tends to occur. If a local voltage breakdown occurs,
Since the reverse voltage applied to the PN junction 12 of the light receiving section does not increase, avalanche multiplication does not occur. In order to prevent such local voltage breakdown, a guard ring is provided around the light receiving section.

Generally, it is known that the breakdown voltage of a semiconductor light-receiving element increases as the carrier concentration of the semiconductor layer decreases and the band gap widens. Also, regarding the breakdown voltage at a portion with a large curvature of the PN junction surface, the smaller the curvature, the more
The impurity concentration near the N junction is higher in a graded junction where it changes linearly than in a stepped junction where it changes stepwise.

For this reason, in an APD provided with a guard ring, the PN junction 12 in the light receiving part is a stepped junction, the curvature of the PN junction where the curvature is large is made small, and the PN junction 13 in the guard ring part is a sloped junction. The breakdown voltage at the guard ring part is higher than that at the light receiving part.

(Problems to be Solved by the Invention) Generally, to form a stepped junction, a PN junction is formed in an InF' layer with a high carrier concentration, and to form a graded junction, a PN junction is formed in an InF' layer with a low carrier concentration. It is desirable to form a PN junction within the layer.

However, in the above-mentioned APD, in order to obtain the guard ring effect, it is necessary to form the PN junction 13 of the guard ring part to a position deeper than the portion where the curvature of the PN junction 12 of the light receiving part is large. That is, in order to obtain a sufficient guard ring effect, the 12th surface of the PN junction, which becomes the light receiving section, should be shallower than the 13th surface of the PN junction, which is the guard ring section, and should be n -
The n-1nP layer in the 1nP window layer 6 must be formed as close as possible to the double layer 5. Therefore, since the PN junction 12 of the light receiving section is formed in the n -1nP window layer 6 with a low carrier concentration, the avalanche built up time is long (and it is difficult to obtain high-speed response characteristics).

The layer thickness of the n-1nP multiplication layer 5 is determined by the controllability and uniformity of crystal growth, and the thickness of the n-1nP multiplication layer 5 is determined by the controllability and uniformity of crystal growth.
The depth of the PN junction 12 formed within the PN junction 12 is determined by the controllability of diffusion, so in order to realize an APD that has a sufficient guard ring effect and high-speed response characteristics, controllability of both is important. There was a manufacturing problem in that it was not easy and the yield was low.

The present invention solves the above-mentioned drawbacks, and aims to provide a semiconductor light-receiving element that prevents edge breakdown, provides high-speed response characteristics, is easy to manufacture, and has a high yield.

[Structure of the Invention] (Means for Solving the Problems) The semiconductor light receiving element of the present invention is a semiconductor in which a light receiving region having a PN junction is selectively formed in a semiconductor, and a guard ring is provided around the light receiving region. The light-receiving element has a second semiconductor region in which the carrier concentration decreases from the substrate side to the surface in the first semiconductor layer, and the portion of the first PN junction that is the light-receiving region has a large curvature. A semiconductor light-receiving element characterized in that it is provided within a conductor layer of the semiconductor light-receiving element.

(Function) According to the present invention, since the uncurved portion of the PN junction forming the light receiving region is in contact with the multiplication layer with high carrier concentration, avalanche build-up time can be reduced and excellent high-speed response characteristics can be achieved.

Further, according to the present invention, a large portion of the curvature of the PN junction is
Since it is formed in a region where the carrier concentration decreases from the semiconductor substrate side to the surface, the curvature of the PN junction can be reduced and a sloped junction can be realized. Therefore, edge breakdown can be prevented in a portion of the PN junction with a large curvature around the light receiving portion, and an effective guard ring can be formed.

Furthermore, the thickness of the multiplication layer is controlled during the diffusion process.
Compared to epitaxial growth, there is a greater degree of freedom in film thickness control, and it is possible to realize a semiconductor light-receiving element that is easy to control and has a high production yield.

(Embodiment) FIG. 1 shows the structure of an embodiment of the semiconductor light receiving element of the present invention.

On the n''-1nP substrate 1, an n-1nP buffer layer 2, n
-1nGaAs light absorption layer 3, n-InGaAs
The P intermediate layer 4 and the n''-1nP multiplication layer 5ζ are sequentially epitaxially grown, a part of the n-1nP multiplication layer 5 is removed in a donut shape, and the carrier concentration is increased from the substrate to the surface using S102 etc. as a mask. The n-1nP layer 6 is selectively grown so that the light-receiving portion 7 is formed by the selective diffusion method from the multiplication layer 5 to the n-1nP layer 6. 6, and further provided with an antireflection film 9, an n-side electrode 10, and an n-side electrode 11. In the figure, 12 indicates a PN junction.

Next, a method for manufacturing the above semiconductor light receiving element will be explained.

First, on an n''-1nP substrate 1, an n-1nP buffer layer 2, an n-InGaAs light absorption layer 3, an n-InG
The aAsP intermediate layer 4 and the n''-1nP multiplication layer 5 are sequentially epitaxially grown by vapor phase epitaxy (VPE, etc.).Next, SiO2, etc. are deposited and removed by photoetching in a donut shape. Then n”-1
A part of the nP multiplication layer 5 is removed by etching with B r CH30H or the like. The SiO2 eaves created by side etching of the n-1nP multiplication layer 5 are further 5i0
2 is overetched and removed. Next, by the VPE method, n-1nP is applied to the etched portion of the n''-InP multiplication layer 5 so that the carrier concentration decreases continuously or stepwise from the substrate surface to the wafer surface.
Layer 6 is selectively grown. After this, the S i O2 mask is removed.

Next, a SiN selective diffusion mask is deposited by P-CVD or the like, and patterned into a circular shape by photoetching so as to include the n-1nP layer 6. Then, by chemical dry etching method (CDE method) etc., SiN is
Etch the membrane in a circular shape. Using this SiN film or the like as a mask, a p-type impurity such as cadmium (Cd) is selectively diffused by a sealed tube method or the like to form a PN junction 12.

In order to create a guard ring effect in a large part of the curvature of the PN junction 12 in the light receiving part, after removing the SiN film, it was heated in a phosphine atmosphere (1010000pp, 7500C,
Annealing is performed for 60 minutes, and the n-In2 layer 6 is injected and diffused.

After that, a SiN 2 film 9 is deposited to form an antireflection film, and then the SiN 2 film 9 at the p-side electrode extraction portion is removed. Electrode metal is deposited using vacuum evaporation technology, patterned using photoetching technology, and unnecessary electrode metal is removed to form a p-side electrode.

Next, after polishing the back surface of the InP substrate 1, by vacuum evaporation,
An n-side electrode 11 is formed. Finally, heat treatment is performed to form an ohmic electrode, and the semiconductor light-receiving element is completed.

The relationship between carrier concentration, layer thickness, and diffusion profile in this example is shown in FIGS. 2 and 3. The PN junction of the light receiving section (FIG. 1A) is a stepped junction, as shown in FIG. 2. Further, the PN junction of the guard ring portion (FIG. 1B) is an inclined type junction, as shown in FIG. 3.

In the above embodiment, InGaAsP and InP-based compound semiconductors were explained, but AIGaAsSb, GaAs
It is also possible to realize this in Regarding conductivity type,
A structure opposite to that of the embodiment is also possible.

FIG. 4 shows another embodiment of the invention. In the example in Figure 1,
After forming the PN junction 12 that forms the light receiving part by selective diffusion method,
Although the guard ring was formed by applying heat treatment and performing intrusion diffusion, in this example, the guard ring was further formed by an ion implantation method to make the guard ring more effective.

[Effects of the Invention] According to the present invention, it is possible to obtain a semiconductor light-receiving element that has high-speed response characteristics, is hard to cause edge break-down, is easy to manufacture, and has a high yield.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor photodetector according to an embodiment of the present invention;
FIG. 2 is a carrier concentration profile of the light receiving part of the present invention, FIG. 3 is a carrier concentration profile of the guard ring part of the present invention, FIG. 4 is a cross-sectional view of another embodiment of the present invention, and FIG. FIG. 2 is a cross-sectional view of a conventional semiconductor light receiving element.

Claims (1)

[Claims] In a semiconductor light-receiving element in which a light-receiving region having a PN junction is selectively formed in a semiconductor and a guard ring is provided around the light-receiving region, the carrier concentration in the first semiconductor layer decreases from the substrate side to the surface. 1. A semiconductor light-receiving element having a second semiconductor region having a second semiconductor layer, wherein a portion of a first PN junction which is a light-receiving region has a large curvature is provided in the second semiconductor layer.