JPH02189984A - Avalanche photodiode - Google Patents

Abstract

PURPOSE:To enhance sensitivity by making valence band discontinuity amount in the band discontinuous part of an oblique type periodic structure larger than a conduction band discontinuity amount. CONSTITUTION:A semiconductor material in which conduction band discontinuity DELTAEv is increased larger than conduction band discontinuity DELTAEc in an oblique type periodic structure such as InGaAs, GaAsSb/InP is selected. Thus, since large DELTAEv is provided so that hole carrier generated by an incident light is obtained excessively by DELTAEv in the valance electrons discontinuity part, ionization more easily occurs. On the contrary, since electron carrier loses small DELTAEc or by DELTAEc of energy in a conduction band discontinuity part, ionization scarcely occurs. Thus, sensitivity can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-sensitivity light-receiving element used in optical communications and the like.

[Conventional technology]

InP as a light receiving element for optical communication in the wavelength range of 1 to 1.6 μm
/InGaAs heterojunction type avalanche photodiodes (hereinafter abbreviated as APD) are being put into practical use. A cross-sectional view of the structure of this heterojunction APD is shown in FIG. In the figure, 1' is < ], OO> oriented InP substrate, 2 is InP buffer layer, 3 is In 0.5SG ao,
47A S light absorption layer, 3' is InGaAs
P intermediate layer, 4' is InP avalanche multiplication layer, 5 is p
+ conductive region, 6 is a surface protective film, 7.8 is each p-side electrode,
This is the n-side electrode. The incident light is I no, 53G a
0347A S The hole carriers, which are absorbed by the light absorption layer and generate photocarriers, are injected into the InP avalanche multiplication layer 4', causing avalanche multiplication. A
In order to increase the sensitivity of PD, it is desirable that the hole ionization rate β and the electron ionization rate α be significantly different (β)α or α)β). 4' is β/α-L-2, and there is a limit to increasing the sensitivity.

[Problem to be solved by the invention]

In order to achieve high sensitivity of APD, it is necessary to artificially control the ionization rate ratio, and F. Capasso (F.
Capasso) is eye 1~repurui 1 hellanxion on electrochiheises (TEEETran)
s Electron Devices), E D
-Volume 30, pages 381-390 (1983), using a semiconductor periodic structure whose forbidden band width changes periodically as an avalanche multiplication layer, ionization is achieved by increasing the energy of electrons by ΔEc at the conduction band discontinuity ΔEc. We are proposing ways to make this more likely to occur. That is, a periodic structure is provided so that α)β is satisfied. However, in the InGaAsP long-wavelength material, which currently has the most complete crystal growth technology, β>α in most of the InGaAsP composition range, so their proposal (α)β) cannot be applied to the InGaAsP system. do not have. Therefore, the object of the present invention is to provide a highly sensitive APD that satisfies β)α.

[Means to solve the problem]

The present invention provides an avalanche photodiode including a semiconductor layer consisting of one layer or multiple layers including at least a semiconductor layer in which an avalanche multiplication region that participates in carrier multiplication (avalanche multiplication layer) is formed, and the avalanche photodiode is provided with an avalanche photodiode. The multiplication layer is a semiconductor layer whose forbidden band width gradually changes in the layer thickness direction.<1. ], ], > Consists of a tilted periodic structure in which the forbidden band width is periodically changed by laminating multiple layers in the crystal orientation, and the amount of valence band discontinuity at the band discontinuity of the tilted periodic structure is the conduction band. The configuration is characterized by being larger than the discontinuous amount.

[Effect]

The operation and principle of the present invention will be explained using FIG. 1 (a) and FIG. 3. FIG. 1 (a) is a band diagram of the avalanche multiplication region of the present invention. Semiconductor materials with band discontinuity △Ev larger than conduction band discontinuity △Ec, such as InGaAs series, GaAsSb/I
Select nP system. By having a large ΔEv, hole carriers generated by light incidence gain energy in excess of ΔEv in the valence electron discontinuity, making ionization more likely to occur. On the other hand, electron carriers have a small ΔEc at the conduction band discontinuity, or lose energy by 8 Ec, so that ionization becomes difficult to occur. That is, the structure of the present invention has the function of promoting β)α.

Furthermore < 11. Ionization of electron carriers can be suppressed by making photocarriers travel in the <111> direction using a crystal with a <111> orientation.

That is, FIG. 3 shows a general energy band diagram of a compound semiconductor, and <111. When electron carriers are accelerated in the > direction (L direction), many of the electron carriers are The ionization phenomenon of electrons occurs under the condition that both energy and momentum are equal before and after ionization, but when the electron transitions to the L valley, this law of conservation no longer holds, and the ionization is unlikely to occur.In other words, if electrons travel in the <111> direction, there is a function to suppress α, and β)α
encourage

Due to the above two effects, the present invention can be expected to achieve β) and α, and can achieve high sensitivity.

〔Example〕

An avalanche multiplication region with a band structure as shown in Figure 1 (a) was realized using an InGaAsP system lattice-matched to InP. That is, InGaAsP, which has the narrowest forbidden band width,
The composition was gradually changed from O,4°As to InP, which has the widest forbidden band width, and the forbidden band width was changed in a gradient manner. △
E■ is about 0.4 eV. 700℃ on <111> orientation n+-InP substrate 1 by hydride VPE method.
and n-InP buffer layer (thickness ~1 μm)2. n--
InGaAs light absorption layer (thickness ~2 μm, carrier concentration ~
5 x 1015cm-') 3, period is 800~1
000-person graded periodic structure (5 periods) avalanche multiplication layer (carrier concentration ~3-1016 cm-3) 4,102
A surface layer 5' was laminated. A mask was created on this wafer completed by VER using a conventional exposure technique, and a p'' conductive region 5 was selectively formed through the mask by thermal diffusion of Zn.The area of the p+ conductive region was approximately 100 μm.
Corresponds to φ. The surface protection film 6 is a SiNx film (thickness: 2000 mm) formed by plasma CVD. p-side electrode 7.
The n-side electrode 8 is made of AuZn made by a normal vapor deposition method,
It is AuGe. The APD is completed as shown in step 2.
Wavelength 06371m from the window opened on the p-side electrode side of
, , 55 μrn of light is incident on each p+ conductive region 5.
Photocarriers were generated in the n-InGaAs layer 3, and electrons and holes were injected into the p+1 junction front. As a result, when the ionization rate of electrons and the ionization rate of holes were measured and the ratio thereof was estimated, β/α=10 was realized.

〔Effect of the invention〕

Since the β/α ratio of the conventional InP/InGaA,s heterojunction APD was about 2, the β/αz10 of the present invention is clearly effective. As a result, higher sensitivity can be achieved than in the past.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) do not show one embodiment of the present invention.
(a) is a band diagram, and (b) is a structural sectional view. FIG. 2 is an energy band diagram of a conventional example, and FIG. 3 is an energy band diagram of a compound semiconductor crystal. In the figure, ], 1'...substrate, 2... buffer layer, 3... light absorption layer, 3'... intermediate layer, 4, 4'... avalanche multiplication layer, 5... p゛Conductive region, 5'...Surface layer, 6
. . . surface protective film, 7 . . . p-side electrode, 8 . . . rl-side electrode.

Claims (1)

[Claims] In an avalanche photodiode, the avalanche photodiode includes a semiconductor layer consisting of one or more layers including at least a semiconductor layer (avalanche multiplication layer) in which an avalanche multiplication region that participates in carrier multiplication is formed, wherein the avalanche multiplication layer is ,
A semiconductor layer whose forbidden band width gradually changes in the layer thickness direction is
111> Consists of a tilted periodic structure in which the forbidden band width is periodically changed by laminating multiple layers in the crystal orientation, and the amount of valence band discontinuity at the band discontinuity of the tilted periodic structure is the amount of conduction band discontinuity. Avalanche photodiode is characterized by being larger than the .