JPS63281480A - Semiconductor photodetector and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce excess noise and dark current, by arranging one or more intermediate layer between a carrier multiplying layer and a window layer, the impurity concentration of said intermediate layer being larger than that of the multiplying layer and the window layer. CONSTITUTION:On N<+> InP substrate 1, the following are grown in order; N<-> InP layer 2, N<-> InGaAs layer 3, N-InP layer 4, N<-> InP layer 5, N-InP layer 6 and N<-> InP layer 7. By applying an SiNx film formed by plasma CVD to a mask, P-type impurity is selectively introduced, and a main junction 8 and a guard ring junction 9 are formed. The positions of the main junction and the guard ring junction are in an N<-> InP layer 7 and N-InP layer 6, respectivety. For a passivation film, a three-layer film 10, i.e., SiNx/PSG/SiO2 is formed. For an antireflection film, SiNx 11 is stuck on a light receiving surface. For a p-type ohmic electrode 12, Au/Pt/Ti is used, and for an N-type ohmic electrode 13, Au/Pd/AuGeNi is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an avalanche photodiode (hereinafter referred to as APD), and particularly to a low-noise APD having an appropriate operating voltage suitable for long wavelength optical communication systems.

[Conventional technology]

In general, in long-wavelength APDs using compound semiconductor materials, light is absorbed in a semiconductor layer with a narrow band gap, and photoexcited carriers are multiplied in a semiconductor layer with a large band gap.
eparated Absorption andMu
] tiplication) structure is adopted.

Furthermore, in order to realize a low-noise APD, it is necessary to increase the ionization coefficient ratio of electrons and holes. The ionization coefficient ratio depends on the maximum electric field strength of the p''n junction, and the lower the maximum electric field strength, the larger the ionization coefficient ratio.

Therefore, in order to realize a low-noise APD, an electric field distribution that reduces the maximum electric field strength is required. That-
As an example, there is an APD having a Lo-Hi-Lo type impurity concentration described in Japanese Patent Publication No. 61-46078 (FIG. 2). Here, 23 is a light absorption layer with a small forbidden band width;
Reference numeral 25 denotes a multiplication layer with a large forbidden band width, and controls the electric field in an intermediate layer 24 having a relatively high impurity concentration to lower the electric field intensity at the interface between the light absorption layer 23 and the intermediate layer 24 facing the main junction.
Interband tunneling current is prevented from occurring in the light absorption layer 23, which has a small bandgap width. Furthermore, since the impurity concentration in the multiplication layer is low, the maximum electric field strength at breakdown is low. However, the APD having the above Lo-H1-Lo impurity concentration distribution has the following problems.

In order to achieve an electric field strength that increases the ionization coefficient ratio, the impurity concentration of the Lo layer must be at least lXl0”■−
An order of 8 is required. However, Journal of Applied Physics Letters, Volume 43, No. 6
No. (1983), pp. 594-596 (J, of A
ppl, Phys, Lett, 43, 6 (19
83) pp. 594-596), when the impurity concentration reached lXl015■-8, diffusion occurred at an abnormally high diffusion rate, making it difficult to control the junction. .

When the controllability of diffusion deteriorates, the distance between the main junction front and the semiconductor layer 25 varies, so the voltage at which the depletion layer reaches the light absorption layer (punch-through voltage) and the breakdown voltage vary greatly. Variations in breakdown voltage result in variations in the APD's operating voltage.

If the distance between the p"n junction and the intermediate layer 24 is too large, the breakdown voltage will exceed 100V, resulting in poor adaptability to optical communication systems. On the other hand, if the distance between the p/n junction and the intermediate layer 24 is too small, If the band gap is too large, the electric field strength at the interface between the light absorption layer 23 and the intermediate layer 24 increases, and the light absorption layer 2 with a small forbidden band width increases.
3, a tunnel current is generated and deteriorates the dark current characteristics.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into account the control of the formation of a junction with a low impurity concentration, and has the problem of deteriorating device performance such as appropriate fluctuations in operating bias voltage and dark current characteristics.

An object of the present invention is to provide an APD with an appropriate operating voltage, low current, and low noise by considering the impurity concentration and the position of the main junction, and a method for manufacturing the same. [Means for solving the problem] The above object is achieved by devising the impurity concentration distribution constituting the APD and controlling the junction position accordingly.

That is, impurities are selectively introduced to form a junction in the semiconductor layer 6 having a relatively high impurity concentration.

The semiconductor layer 6 is in contact with the semiconductor layer 5 having a low impurity concentration.

In this impurity concentration structure, when an impurity of the other conductivity type is introduced from the surface of the semiconductor layer 7, a junction is formed beyond the semiconductor layer 7, which has a large diffusion coefficient, and into the semiconductor layer 6, which has a large impurity concentration and has a slow diffusion rate. Ru.

[Effect]

In FIG. 1, the semiconductor layer 6 having a relatively high impurity concentration operates so that the p'n junction is located within the semiconductor layer 6. The incident light is absorbed by the semiconductor layer 3 having a low impurity concentration, and the generated photoexcited carriers are mainly multiplied by the semiconductor layer 3 having a low impurity concentration. Further, the electric field distribution of the entire APD is controlled by the semiconductor layer 5 having a relatively high impurity concentration.

By using these technical means, the position of the bond can be stably controlled, so that an APD with excellent characteristics can be obtained with good reproducibility.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 In this example, a case where an InP-based material is used will be explained using FIG. 1.

FIG. 1 is a cross-sectional structural diagram of a planar type InGaAs/InPAPD.

First, the manufacturing method will be described.

n+-InP substrate 1'' Second, vapor phase growth method (for example, MBE
method, MOCVD method, hydride or halide VPE
n--InP layer 2 (No = I
x 10”an-8, thickness 0.57zm).

n--InGaAs layer 3 (Nn = I x 10'δ
1 m −', thickness 3 μm), n-102 layer 4 (No.
= 1-5 x 1016an-8゜thickness 1-1.5
μm), n--I n P layer 5 (No=I x 10
15an-8, thickness 0.2-1 pm), n
-InP layer 6 (No = 1 to 5 x 1018an-
8, thickness 0.2-0.4 μm), n--I n P layer 7
(No=I X 10"Qn -8, thickness 2.5
~3.5 μm).

Using the SiNx film formed by plasma CVD as a mask, p-type impurities are selectively introduced to form main junctions 8 and guard ring junctions 9. In forming the p-type impurity region,
Thermal diffusion of Zn or Cd, or ion implantation of Be, Mg, etc., is used. The positions of the main junction and guard ring junction are n--InP layer 7 and n-InP layer 7, respectively.
It is formed in the P layer 6. Next, as a passivation film, S i N x / P S G / S i O
Two- and three-layer films 10 were formed, and S i N x 11 was deposited on the light-receiving surface as an antireflection film.

The p-type ohmic electrode 12 has A u / P t /
Ti.

The n-type ohmic electrode 13 has A u / P d /
AuGeNi was used in each case.

Next, the operation of this element will be described.

Most of the light incident on this device is absorbed within the semiconductor layer 3, which is depleted by the reverse bias voltage, and photoexcited carriers are generated. The generated photoexcited carriers (holes in this case) are injected into the carrier multiplication layer 5 by the drift electric field. Since a high electric field is applied to the multiplication layer 5, carriers injected by secondary ionization are efficiently multiplied.

The multiplied carriers are collected at the main junction and taken out as a photocurrent to an external circuit.

In this embodiment, since the position of the p'n junction can be accurately controlled within ±0.1 μm, an APD with an appropriate operating voltage and low dark current can be realized. Furthermore, since the impurity concentration in the multiplication region is low, the maximum electric field strength at the time of avalanche breakdown is low, and the ionization coefficient ratio can be increased. the result,
Excessive noise accompanying multiplication is reduced, and a low-noise APD can be achieved.

Embodiment 2 Another embodiment will be described in FIG. The difference from FIG. 1 is that there is a forbidden band width (λg=1.3 μm) between semiconductor layers 3 and 4.
The nGaAsP layer is inserted.

The manufacturing method is basically the same as that in Example 1, and n--
InP42. n--InGaAs43゜n--InGa
AsP44. n-I nP45. n--InP46゜n
-InP47. After growing n--InP48, the main junction 49° guard ring 5 is formed using well-known process technology.
0. Passivation film 512 Anti-reflection film 52. p-type ohmic electrode 53. An n-type ohmic electrode 54 is formed.

In Example 2, energy discontinuity (approximately 0.6 V) in the valence band at the hetero interface of InGaAs43 and InP45
In order to alleviate this, the forbidden band width is set to a value between 43 and 45 (
λ, = 4.3 μm) was inserted. By inserting 44, the energy discontinuity at the heterointerface can be reduced to approximately 0.3■, so it is possible to suppress the hole pile-up phenomenon and achieve high-speed response without making the electric field strength at the heterointerface sufficiently high. can.

Therefore, in the second embodiment, an APD with an appropriate bias voltage, low dark current, high speed, and high sensitivity can be realized with good controllability.

The InGaAs/I n P system has been described above, but InA1A in which InP is replaced with InAffiAs
The present invention is also effective for the s-based InA1As system.

Moreover, the essence of the present invention is that materials other than InP-based materials, such as G
When other compound semiconductors such as aSb-based semiconductors are used, the same applies to combinations of m-v group compounds, Ge, and Si.

〔Effect of the invention〕

According to the present invention, it is possible to form a p-n junction with good controllability in a semiconductor layer with a relatively high impurity concentration and a large band gap, and the impurity concentration of the multiplication layer can be reduced, so that the following effects can be achieved. There is.

(1) Since the ionization coefficient ratio in the carrier multiplication layer can be increased, excess noise can be reduced.

(2) Since the electric field strength in the light absorption layer with a small forbidden band width can be controlled to an appropriate value, generation of interband tunneling current can be suppressed, and dark current near the breakdown voltage can be reduced.

(3) Punch-through voltage, breakdown voltage, etc. can be accurately controlled, which improves reproducibility and can be expected to improve yield in factory production.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of a device shown in Example 1 of the present invention, FIG. 2 is a cross-sectional structural diagram of a conventional APD, and FIG.
FIG. 3 is a cross-sectional structural diagram of an element shown in Example 2 of the present invention. l--/n+-InP substrate, 2-n--InP layer, 3-
n-InGaAs light absorption layer, 4-n-I nP electric field relaxation layer, 5-n--I nP multiplication layer, 6-n-I
nP intermediate layer, 7...n--InP window layer, 8...
p-InP (main junction), 9... p--InP (guard ring), 10... passivation film, 11.・・・
・Anti-reflection film, 12... P-type ohmic electrode, 13.
...n-type ohmic electrode, 21-n+ -InP substrate, 22-n--InP layer, 23-n--InGa
As light absorption layer, 24...n-I nP electric field relaxation layer, 25...n--InP multiplication layer, window layer, 26-p-I
nP (main junction), 27... p--InP (guard ring), 28... passivation film, 29... antireflection film, 30... p-type ohmic electrode, 31...
n-type ohmic electrode, 41-n+ -I n P substrate,
42-n--I nP layer, 43-n--I nGaA
s light absorption layer, 44-n --InGaAsP buffer layer (1g = 1.3 pm), 45--n
-I nP electric field relaxation layer, 46-n--I nP multiplication layer, 47- n -I nP intermediate layer, 48-n--
InP window layer, 49-p-InP (main junction), 50...
p--InP (guard ring), 51... passivation film, 52... antireflection film, 53... p-type ohmic electrode, 54... n-type ohmic electrode.

Claims (1)

[Claims] 1. A light absorption layer that absorbs at least light on a substrate having one conductivity type, a multiplication layer that multiplies carriers generated by absorbing light, and a p/n junction (main junction). In a semiconductor light-receiving device configured by laminating a plurality of semiconductor layers including a window layer having A semiconductor light-receiving element characterized by having one or more. 2. The semiconductor light-receiving device according to claim 1, wherein the p/n junction (main junction) is formed within the intermediate layer. 3. The semiconductor light-receiving device according to claim 1, wherein the p/n junction (main junction) is formed in the intermediate layer, and a guard ring junction is provided in the window layer. 4. The impurity concentration of the intermediate layer is 1×10^1^8 cm
^-^3~1x10^1^7cm^-^3, thickness is 0
．． The semiconductor light receiving element according to claim 1, which has a thickness of 1 to 0.4 μm. 5. In a method for manufacturing a semiconductor light-receiving element, which includes various steps of forming a semiconductor on a substrate, including a main junction having a light-receiving function, the semiconductor light-receiving element has one conductivity type, has a low impurity concentration, and multiplies carriers. A method for manufacturing a semiconductor light-receiving element, comprising the step of forming an intermediate layer between the steps of forming a semiconductor layer (multiplier layer) and a light-transmitting semiconductor layer (dense layer). 6. The method of manufacturing a semiconductor light-receiving device according to claim 5, characterized in that the main junction is formed in the intermediate layer, and the guard ring junction for suppressing edge breakdown is formed in the window layer.