JPH088455A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To provide a 1mum band photodetector, which is used in a long-distance optical communication, has high-sensitivity and high-speed characteristics and moreover, has a high reliability. CONSTITUTION:In a hole-injected type superlattice APD, a structure, which has a large valence band energy gap and has little conduction band energy gap, is applied as a superlattice multiplying layer 19 and holes only are selectively multiplied. Moreover, a tensile strain is loaded on a multiplying well layer, pileup of the holes is relaxed and the speedup of a semiconductor photodetector is contrived. Or a hole pileup relaxation layer 20 is inserted between a light absorbing layer 13 and an electric field relaxation layer 18 and the speedup of the semiconductor light-receiving device is contrived. A planar structure can be adopted to this device with comparatively ease.

Description

Detailed Description of the Invention

[0001]

The present invention relates to optical communication, optical information processing,
The present invention mainly relates to an avalanche multiplication type semiconductor light receiving element used in optical measurement and the like.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor light receiving element for optical communication in the band of 1 to 1.6 μm, In lattice-matched In on an InP substrate has been used.
PIN type semiconductor light receiving element ("Optical communication element optics", Mr. Yonezu, Engineering Book Co., Ltd., p. 371 (19), which uses a _0.53 Ga _0.47 As layer (hereinafter abbreviated as InGaAs layer) as a light absorbing layer.
83)), an avalanche multiplication type semiconductor light receiving element (Electronic Letters (Electronic)
s Letters), 1984, Volume 20, pp. 65
3-654) is known. In particular, the latter has been put to practical use for long-distance communication because it has an internal gain effect due to the avalanche multiplication effect and a high-speed response.

FIG. 8 is a structural diagram of a typical InGaAs-APD (the avalanche multiplication type semiconductor light receiving element is referred to as AP below).
Abbreviated as D. ). The principle of operation is that among the photocarriers generated in the InGaAs light absorption layer 13, hole carriers are injected into the InP avalanche layer 14 by the electric field. In
Since a high electric field is applied to the P avalanche layer 14, ionization collision occurs, and multiplication characteristics are reached. In this case, it is known that the noise and fast response characteristics, which are important in device characteristics, are governed by the random ionization process of carriers in the multiplication process. Specifically, the greater the difference between the ionization rates of electrons and holes in the InP layer, which is the multiplication layer, the greater the ionization rate ratio becomes (if the ionization rates of electrons and holes are α and β, respectively, α / Electron when β> 1, β / α> 1
At that time, holes should be the main carriers that cause ionization collisions. ), It is desirable in terms of device characteristics.

However, the ionization ratio (α / β or β
/ Α) is determined by the physical properties of the material, and is at most about β / α = 2 for InP. This is largely different from α / β = 20 of Si having a low noise characteristic, and epoch-making technological innovation is required to realize lower noise and high-speed response characteristics.

On the other hand, in recent years, in an avalanche multiplication type semiconductor light receiving element, a superlattice structure is applied to a multiplication layer,
A superlattice APD intended to promote ionization of electrons by conduction band discontinuity energy is studied. In particular, InAlAs
/ InAlGaAs superlattice layer as a multiplication layer superlattice AP
In D, a gain bandwidth product of 120 GHz is reported (IE Photonics Technology Letters (IEEE Photonics Te
chnology Letters) 1933, 5
Vol., Pp 675-677). FIG. 9 shows a typical I
The structural drawing of nAlAs / InAlGaAs superlattice APD is shown. For element formation, first, the n-type InP substrate 1 is formed by the vapor phase growth method.
N ⁺ type InP buffer layer 2, n ⁺ type InAlAs buffer layer 3, n ⁻ type InAlAs / InAlGaAs superlattice multiplication layer 4, p ⁺ type electric field relaxation layer 5, p ⁻ type light absorption layer 6, p ⁻ type InP cap layer 7 and p ⁺ type InGaAs
The contact layers 8 are sequentially stacked. After that, mesas are formed with a Br-based etchant, and SiNx is deposited on the surface as a passivation film 9. Then, an ohmic electrode is vapor-deposited on the n-side 10 and the p-side 11 to complete the process. Incident light 12
Is incident from the surface.

[0006]

As described in the section of the prior art, the conventional superlattice APD aims at promoting the impact ionization of electrons by conduction band discontinuity energy. However, for example, conventional InAlA
In the case of the APD of the s / InAlGaAs superlattice, when the conduction band discontinuity energy is 0.3 eV, the valence band discontinuity energy is also 0.1 eV, which promotes the collision ionization of holes and the positive ionization in the well layer. There is concern about pile-up of holes. In addition, this superlattice APD has a mesa type element structure, and since the multiplication layer to which a strong electric field is applied is exposed at the end surface of the mesa, it is difficult to form a reliable element.

An object of the present invention is to solve the above-mentioned problems in an APD having a structure for injecting holes into a multiplication layer, selectively multiplying only holes by utilizing a superlattice structure, and An object is to provide a highly sensitive and high speed semiconductor light receiving element having a structure and excellent reliability.

[0008]

A semiconductor device according to claim 1 of the present invention is a semiconductor light-receiving device in which a light absorption layer, a multiplication layer and the like are laminated on a semiconductor substrate, and the multiplication layer is a superlattice. It is characterized in that it is formed of a structure and there is almost no difference in conduction band energy of the superlattice structure.

According to a second aspect of the present invention, in the semiconductor light receiving element of the first aspect, the first semiconductor layer forming the multiplication layer is InP and the second semiconductor layer is It is InAlGaAs, and there is almost no difference in conduction band energy between the superlattice structures.

Alternatively, in the semiconductor light receiving element according to claim 3 of the present invention, in the element according to claim 1 or 2, tensile strain is applied to the well layer of the superlattice structure forming the multiplication layer. Is characterized by.

A semiconductor light receiving element according to a fourth aspect of the present invention is the element according to the first, second or third aspect, further comprising an electric field relaxation layer between the light absorption layer and the multiplication layer, A hole pile-up relaxation layer made of InAlGaAs or InGaAsP is inserted between the light absorption layer and the electric field relaxation layer.

[0012]

FIG. 1 is a diagram for explaining the semiconductor light receiving elements according to claims 1 and 2 of the present invention, and shows a band diagram of the superlattice multiplication layer. As a multiplication layer, InP / In _0.5 Al _0.
23 Ga _0.27 As superlattice structure will be described as an example. The APD of the present invention is a hole-injection-type superlattice APD that injects only holes out of the photocarriers generated in the light absorption layer into the multiplication layer. As shown in FIG. 1, the valence band energy difference of the superlattice structure is 0.3 eV, which increases the ionization rate of the injected holes. On the other hand, the electrons generated in the multiplication layer due to the impact ionization of holes do not have energy supply at the hetero interface in the superlattice structure because the conduction band discontinuity energy is almost 0 eV, and thus the ionization rate can be suppressed. I can. That is, the superlattice structure can increase the ionization rate of only holes, and can improve the ionization rate ratio (β / α). Furthermore, in the superlattice APD of the present invention, the planar structure that is essential for obtaining high reliability can be adopted relatively easily.
The reason for this will be described with reference to FIG.

FIG. 2 shows an example of the element structure and electric field strength of the semiconductor light receiving element of the present invention. p ⁺ -InP cap layer 7
The interface between the superlattice multiplication layer 19 and the superlattice multiplication layer 19 is a pn junction, and the depletion layer extends in one direction to the substrate side when an electric field is applied (in the conventional electron injection type superlattice APD, the depletion layer extends from the pn junction to the substrate side and the surface). It extends in both directions.) In this case, p
^A -type double guard ring structure can be applied, and a device having a planar structure can be formed. As a result, exposure of the multiplication layer or the like to which a high electric field is applied can be prevented, and high reliability can be achieved.

Next, the operation of claim 3 of the present invention will be described. The operation of the invention of claim 3 is the same as that of claims 1 and 2 above.
In addition to the action of, there is the following action. FIG. 3 shows claim 3.
FIG. 6 is a diagram for explaining the action of the above, and shows a band diagram of the multiplication layer. As described above, the holes injected into the multiplication layer promote collision ionization due to the valence band energy difference ΔEv at the hetero-interface, but when this transition from the multiplication well layer to the barrier layer, this ΔEv is a barrier. And acts as a cause of pile-up, especially for holes having a large mass. In claim 3 of the present invention, since tensile stress is applied to the multiplication well layer, the ground level of holes traveling perpendicularly to the layer direction becomes a light hole band, and when the hole mass is bulk, Compared to this, Kao et al. Wrote in Journal Applied Physics (J.
Appl. Phys) 57 (1985) p. 5428. ) From this, the valence band energy difference ΔE
Since the pile-up of holes due to v is alleviated, the high speed characteristics are improved.

Next, claim 4 of the present invention will be described. The action of the invention of claim 4 has the following action in addition to the action of claim 1 and 2 or 3 above. FIG. 4 is a diagram for explaining the action of claim 4, and shows band diagrams of the light absorption layer, the electric field relaxation layer, and the superlattice multiplication layer. The device structure of the present invention is a structure in which only holes among the photocarriers generated in the light absorption layer are injected into the multiplication layer as described above.
The valence band energy difference ΔEv at the interface between the nGaAs light absorption layer and the InP electric field relaxation layer is as large as 0.4 eV. here,
The InP electric field relaxation layer is inserted for the purpose of separating the light absorption layer and the superlattice multiplication layer and suppressing the generation of tunnel dark current in the InGaAs light absorption layer. Therefore, the electric field applied to this region is usually as small as 150 kV / cm or less,
In addition, considering that the mass of holes is eight times heavier than that of electrons, pile-up of holes at this interface is a concern.

According to the invention of claim 4, InAl is formed at this interface.
By inserting the GaAs layer or the InGaAs layer 20, this interface has a stepwise band structure, and the pile-up of holes can be relaxed. As a result, high speed characteristics can be improved.

[0017]

EXAMPLES Examples of claims 1 and 2 of the present invention will be described.
This will be described in detail with reference to the drawings.

FIG. 5 is a sectional view of an avalanche multiplication type light receiving element formed according to one embodiment of the present invention. As the structure, first, the n ⁺ type InP buffer layer 2 is 0.3 μm, the n ⁻ type InGaAs light absorption layer 13 is 0.9 μm, and the n ⁺ type InP electric field relaxation layer 18 is 0.1 μm on the InP substrate 1.
, N ⁻ type InP / InAlGaAs superlattice multiplication layer 19
The 0.2 [mu] m, and the n ^- -type InP cap layer 21 is 2.5μm laminated. Here, the above InP / InAlG
The film thicknesses of the barrier layer and the well layer having the aAs superlattice structure are 120 Å and 80 Å, respectively. Then, a p ⁻ -type double guard ring structure 22 is double-implanted with Be (acceleration voltage 110 kV, dose amount 5 × 10 ¹³ cm
^-2 , accelerating voltage of 60 kV, dose of 3 × 10 ¹³ cm ^-2 ), annealing at 700 ° C. for 20 minutes, and p ⁺ type light receiving region 16 at 570 ° C. using Cd ₃ P ₂ as a diffusion source. Cd
It was prepared by diffusion. Further, a SiNx film 9 is deposited on the surface as a passivation film for 1500 angstrom, and AuGe / Ni for the n-side electrode 10 is deposited for 1500
Angstrom, TiPtAu is deposited to 500 angstrom. In addition, the device structure is completed by depositing AuZn as the p-side electrode 11 at 1500 angstrom.

Under the above-described device structure, the ionization of holes is exaggerated by the principle described in the operation, the effective ionization ratio (β / α ratio) is 5, the maximum bandwidth is 15 GHz, the gain bandwidth product is 120 GHz, and We have realized an avalanche multiplication semiconductor photodetector with low noise and high-speed response characteristics with a quantum efficiency of 70%. As a result of the reliability evaluation test, this device had a long life of 100,000 hours or more. The device structure according to the present invention is specifically, MOVPE, MBE, gas source MB.
It can be produced by a crystal growth technique such as E.

The third embodiment of the present invention will be described in detail with reference to the drawings. FIG. 6 is a sectional view of an avalanche multiplication type light receiving element formed according to an embodiment of the present invention. As the structure, first, an n ⁺ type I is formed on the InP substrate 1.
The nP buffer layer 2 has a thickness of 0.3 μm, the n ⁻ -type InGaAs light absorption layer 13 has a thickness of 0.9 μm, and the n ⁺ -type InP electric field relaxation layer 18
Of 0.1 μm, an n ⁻ type InP / InAlGaAs strained superlattice multiplication layer 23 of 0.2 μm, and an n ⁻ type InP cap layer 21 of 2.5 μm. Where InP /
The barrier layer and the well layer having the InAlGaAs strained superlattice structure have film thicknesses of 120 Å and 80 Å, respectively, and a tensile strain of 1.5% is applied to the multiplication well layer. After that, the p ⁻ -type double guard ring structure 22 is double-implanted with Be (acceleration voltage 110 k
V, dose amount 5 × 10 ¹³ cm ⁻² , accelerating voltage 60 kV, dose amount 3 × 10 ¹³ cm ⁻² ) and annealing at 700 ° C. for 20 minutes, and the p ⁺ -type light receiving region 16 is made of Cd ₃ P _2. Was used as a diffusion source at 570 ° C. for Cd diffusion. Further, a SiNx film 9 is formed on the surface as a passivation film.
500 angstrom is deposited, and AuGe / Ni is 1500 angstrom, Ti for the n-side electrode 10.
Deposit 500 angstroms of PtAu. Also, p
The device structure is completed by depositing AuZn as the side electrode 11 at 1500 angstrom.

Under the above-mentioned device structure, the ionization of holes is exaggerated by the principle described in the operation, the effective ionization ratio (β / α ratio) is 5, the maximum bandwidth is 17 GHz, the gain bandwidth product is 125 GHz, and We have realized an avalanche multiplication semiconductor photodetector with low noise and high-speed response characteristics with a quantum efficiency of 70%. As a result of the reliability evaluation test, this device had a long life of 100,000 hours or more. The device structure according to the present invention is specifically, MOVPE, MBE, gas source MB.
It can be produced by a crystal growth technique such as E.

A fourth embodiment of the present invention will be described in detail with reference to the drawings. FIG. 7 is a sectional view of an avalanche multiplication type light receiving element formed according to an embodiment of the present invention. As the structure, first, an n ⁺ type I is formed on the InP substrate 1.
The nP buffer layer 2 has a thickness of 0.3 μm, the n ⁻ type InGaAs light absorption layer 13 has a thickness of 0.9 μm, and the n ⁻ type In _0.75 Ga _0.25 As.
_0.25 P _0.75 hole pile-up relaxation layer 20 is 500 Å, n ⁺ type InP electric field relaxation layer 18 is 0.1 μm
, N ⁻ type InP / InAlGaAs superlattice multiplication layer 19
Of 0.2 .mu.m and n ^-- type InP cap layer 21 of 2.5 .mu.m. Here, the above InP / InAlG
The film thicknesses of the barrier layer and the well layer having the aAs superlattice structure are 120 Å and 80 Å, respectively. Thereafter, the double guard ring structure 22 is double-implanted with Be (acceleration voltage 110 kV, dose amount 5 × 10 ¹³ cm ^-2 ,
Acceleration voltage 60kV, Dose amount 3 × 10 ¹³ cm ^-2 ) and 700
P ⁺ type light receiving region 1 produced by annealing at ℃ for 20 minutes
No. 6 was prepared by Cd diffusion at 570 ° C. using Cd ₃ P ₂ as a diffusion source. Further, a SiNx film 9 is deposited on the surface as a passivation film for 1500 Å,
AuGe / Ni of 1500 Å and TiPtAu of 500 Å are deposited as the n-side electrode 10. Further, as the p-side electrode 11, AuZn 150 is used.
The device structure is completed by depositing 0 angstrom.

Under the above-described device structure, the ionization of holes is exaggerated by the principle described in the operation, and the effective ionization ratio (β / α ratio) is 5, the maximum band is 16 GHz, the gain bandwidth product is 123 GHz, and We have realized an avalanche multiplication semiconductor photodetector with low noise and high-speed response characteristics with a quantum efficiency of 70%. As a result of the reliability evaluation test, this device had a long life of 100,000 hours or more. The device structure according to the present invention is specifically, MOVPE, MBE, gas source MB.
It can be produced by a crystal growth technique such as E.

[0024]

As described above, the semiconductor light receiving device according to the present invention can provide a 1 μm band light receiving device used for long-distance optical communication, which has high sensitivity and high speed characteristics and high reliability. it can.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the operation of claims 1 and 2 of the present invention.

FIG. 2 is a diagram for explaining the operation of claims 1 and 2 of the present invention.

FIG. 3 is a view for explaining the action of claim 3 of the present invention.

FIG. 4 is a view for explaining the action of claim 4 of the present invention.

FIG. 5 is a diagram for explaining an embodiment of claims 1 and 2 of the present invention.

FIG. 6 is a diagram for explaining an embodiment of claim 3 of the present invention.

FIG. 7 is a diagram for explaining an embodiment of claim 4 of the present invention.

FIG. 8 is a structural diagram of a conventional InGaAs APD.

FIG. 9 is a structural diagram of a conventional superlattice APD.

[Explanation of symbols]

1 n type InP substrate 2 n ⁺ type InP buffer layer 3 n ⁺ type InAlAs buffer layer 4 n ⁻ type InAlAs / InAlGaAs superlattice multiplication layer 5 p ⁺ type InP electric field relaxation layer 6 p ⁻ type InGaAs light absorption layer 7 p ⁺ Type InP cap layer 8 p ⁺ type InGaAs contact layer 9 SiNx passivation film 10 n-side ohmic electrode 11 p-side ohmic electrode 12 incident light 13 n ^- type InGaAs light absorption layer 14 n-type InP multiplication layer 15 n-type InP cap layer 16 p ⁺ type light receiving region 17 p ⁺ type guard ring region 18 n ⁺ type InP electric field relaxation layer 19 n ⁻ type InP / InAlGaAs superlattice multiplication layer 20 n ⁻ type In _0.75 Ga _0.25 As _0.25 P _0.75 hole pileup relaxation layer 21 n ⁻ type InP cap layer 22 p ⁻ type double guard ring structure 23 n ⁻ type InP / InAlGa As strained superlattice multiplication layer

Claims (4)

[Claims] 1. A semiconductor light-receiving element having a light absorption layer and a multiplication layer on a semiconductor substrate, wherein the multiplication layer is formed in a superlattice structure, and there is almost no difference in conduction band energy between the superlattice structure. A semiconductor light receiving element characterized by. 2. The first semiconductor layer constituting the multiplication layer is InP
2. The semiconductor light receiving element according to claim 1, wherein the second semiconductor layer is InAlGaAs, and there is almost no difference in conduction band energy between the superlattice structures. 3. The semiconductor light receiving element according to claim 1, wherein tensile strain is applied to the well layer of the superlattice structure forming the multiplication layer. 4. An electric field relaxation layer is provided between the light absorption layer and the multiplication layer, and a hole pile-up relaxation layer made of InAlGaAs or InGaAsP is inserted between the light absorption layer and the electric field relaxation layer. The semiconductor light receiving element according to claim 1, 2 or 3, characterized in that.