JPH0258877A - Semiconductor photo detector - Google Patents

Abstract

PURPOSE:To shorten the transit time of electron, and enable high speed response by arranging a plurality of intermediate layers whose forbidden bandwidths are mutually different, between a semiconductor substrate and a light absorbing layer. CONSTITUTION:By hydride vapor growth method, intermediate layers composed of In0.92Ga0.08As0.16P0.84 (forbidden bandwidth-1.23eV) 2a, and In0.77Ga0.23As0.64P0.36 (forbidden band width-0.96eV) 2c are grown in order on an N<+>-InP substrate 1. Next, an In0.53Ga0.47As light absorbing layer 3 and an InP cap layer 4 are laminated. Each carrier concentration is about 5X10<15>cm<-3>. A P-type conducting region 5 is formed by thermal diffusion of Zn, and a PN junction front is positioned in the vicinity of the interface between the light absorbing layer 3 and the cap layer 4. Thereby, a semiconductor photo detector wherein transit time of electron carrier is short and the cut off frequency is high can be obtained.

Description

[Detailed description of the invention] (Industrial usage gF> The present invention relates to a high-speed semiconductor light-receiving device.

(Prior Art) As the speed and capacity of optical communication increases, the development of light receiving elements that exhibit high-speed response is progressing. The current optical communication wavelength is 1
, an InP substrate is used as a light-receiving element in the 3u+n band, or the 1.5 μm band, and InP is lattice-matched to InP.
A structure in which O,S3G a 0.47A S is used as a light absorption layer is widely used. The structure of an example is shown in cross section in FIG. 2(a). The semiconductor light receiving element shown in the figure is a photodiode. n--In on the n-type conductive InP substrate 1
P buffer layer 2, n-I nGaAs light absorption layer 3, n-
An epitaxial layer wafer is constituted by the InP cap layer 4, a p-type conductive region 5 is selectively formed on this epitaxial layer wafer, and a surface protection film 6 and an electric 'lf! 7
．． 8 to form a photodiode.

(Problems to be Solved by the Invention) In order to increase the speed of a photodiode, it is effective to reduce the junction capacitance and shorten the travel time of carriers generated by optical excitation. The former problem can be solved by reducing the bonding area. Here, we will discuss improvements to reduce the travel time of carriers. FIG. 2(b) shows a band diadem of a conventional photodiode during operation between A and A' in FIG. 2(a). Of the electron/hole carrier pairs generated in the light absorption layer 3 by the light irradiation, the correct tag travels to the A side, and the electron travels to the A' side. However, when electron carriers are injected into the buffer layer 2, they are prevented from traveling by the barrier 9 formed by the conduction band terminal continuity. This has caused a significant problem in increasing the speed of photodiodes.

(Measures Pi for Solving the Problems) The present invention includes a plurality of semiconductor layers stacked on a semiconductor substrate, and the plurality of semiconductor layers have a light absorption layer and a wide forbidden band width that transmits light. A semiconductor light-receiving device including a cap layer, characterized in that a plurality of intermediate layers having mutually different forbidden band widths are provided between the semiconductor substrate and the light absorption layer.

(Function) The present invention solves the conventional drawbacks by the method described above. For comparison with conventional examples, an InP/InGaAs heterojunction photodiode will be described, but the same applies to Ike's semiconductor material system. As shown in FIG. 1(b), the semiconductor light-receiving device according to the present invention includes a plurality of intermediate layers 2a, 2b, and 2c having different forbidden band widths.
Obstacle g9 to electron carriers generated by photoexcitation is smaller than in the past. Therefore, in the device of the present invention, the transit time of electrons is shortened and high-speed response is possible.

(Example> FIG. 1 is a sectional view showing the structure of an embodiment of the present invention.

This example was produced according to the following steps. n”-I
I was deposited on the nP substrate 1 by hydride vapor phase epitaxy.
n 0.92G ao, oaA So, +bP
0.84 (forbidden band width ~ 1.23e V) 2 aI
n 0.77G a 0.23A S O,64P O
, s6 (gap band width ~ 0.96e V) 2c After sequentially growing the intermediate layer consisting of I n 0.53G a 0
．． 47A S light absorption layer 3-1nP cap layer 4 was laminated. The carrier concentration of each layer was about 5 x 10''cn-3. The p-type conductive region 5 was formed by Zn thermal diffusion, and the pn junction front was located near the interface between the light absorption layer 3 and the cap layer 4. By plasma CVD method, Si
An Nx surface protective film 6 was deposited, and a window was opened in a part of the surface of the p-type conductive region 5 to form an AuZnPIPI electrode 7.

The n-side electrode 8 is made of an AuGe/Ni metal film.

In the photodiode of the embodiment shown in FIG. 1, the transit time of electron carriers can be shortened, so the cutoff frequency can be increased. FIG. 3 shows the frequency characteristics of a photodiode. The solid line in FIG. 3 shows the characteristics of the photodiode of the present invention manufactured in the example, and the dotted line shows the frequency characteristics of the conventional example. In the past, electron carriers were trapped due to the discontinuous conduction band barrier, resulting in deterioration of frequency response, but in the present invention, flat response characteristics were obtained up to about 20 GHz. Although the present invention has been described only with respect to a PIN type photodiode, the same effect can be obtained with a song photodiode such as an avalanche photodiode, for example.

(Effects of the Invention) As described above in detail, according to the present invention, a semiconductor light-receiving element can be obtained in which the travel time of electron carriers is short and the cutoff frequency is high. Therefore, the semiconductor light receiving element of the present invention can operate at high speed.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view showing an embodiment of a semiconductor light-receiving element according to the present invention, FIG. 1(b) is a band diagram of the embodiment, and FIG. 2(a) is a cross-sectional view showing a conventional light-receiving element. 2(b) are band diagrams of the conventional light receiving element, and FIG. 3 is a diagram showing the frequency response characteristics of the embodiment of FIG. 1 and the conventional light receiving element of FIG. 2. 1... Semiconductor substrate, 2a, 2b, 2c... Intermediate layer,
3... Light absorption layer, 4... Cap layer with wide forbidden band width, 5... P1 type conductive region, 6... Surface protective film, 7...
...p-side electrode, 8...n-side electrode, 9...barrier due to conduction band discontinuity.

Claims (1)

[Claims] 1. A plurality of semiconductor layers are stacked on a semiconductor substrate, and the plurality of semiconductor layers include a light absorption layer and a semiconductor cap layer that transmits light and has a wide forbidden band width. 1. A semiconductor light-receiving device characterized in that a plurality of intermediate layers having mutually different forbidden band widths are provided between the semiconductor substrate and the light absorption layer. 2. The semiconductor light-receiving device according to claim 1, wherein the forbidden band width of the plurality of intermediate layers becomes narrower from the semiconductor substrate toward the light absorption layer.