JPH0964407A - Semiconductor light receiving element - Google Patents

Abstract

(57) Abstract: In a semiconductor light receiving element for line monitoring of a fiber network for optical communication, for a light of wavelength 1.65 μm,
The purpose is to obtain high quantum efficiency, low dark current, and high current multiplication factor. A semiconductor light receiving element of the present invention comprises an InP buffer layer, an n-InAsP buffer layer, and an InP buffer layer on an InP substrate.
Strained InGaAs light absorption layer 4 having a wavelength of 1.85 μm and InG having a wavelength changed from 1.85 μm to 1.67 μm
aAs linear step layer 5 and InGaAs intermediate layer 6
And an n-InP multiplication layer 7 and an InP window layer 8. The 1.65 μm light incident from the window layer 8 side is distorted by I
It is absorbed in the nGaAs light absorption layer 4 and becomes a carrier by photoelectric conversion to flow to an external circuit. InP and strain In
Generation of dark current caused by lattice mismatch with GaAs can be suppressed to a low level by sandwiching an InAsP layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element used for optical measurement and optical communication, and more particularly to a semiconductor light receiving element for line monitoring of a fiber network for optical communication.

[0002]

2. Description of the Related Art Optical fibers are currently used as optical communication lines. As a maintenance management method for such an installed optical fiber network, OTDE (Optical Ti)
There is a meDomain Reflectometer). OTDR is a device to check the breaking point of the installed optical fiber, and its basic principle is to monitor the Rayleigh scattered light generated when the pulsed light incident on the fiber propagates in the fiber and When the break point occurs, Rayleigh scattered light does not return. The position of the breaking point can be accurately known by converting the time until the Rayleigh scattered light disappears into a distance. However, in this case, the communication line must be connected to the OTDR device, which causes a problem that the communication line is temporarily cut off. Therefore, in order to solve this problem, a method is conceivable in which light in the wavelength range of 1.65 μm different from the transmission wavelength of 1.3 μm or 1.55 μm in optical communication is used and the line is constantly monitored while using the communication line. ing.

Avalanche photodiodes (hereinafter referred to as APDs) are widely used as semiconductor light receiving elements used in such a system for constant monitoring. Since the element itself has an amplifying function, the APD is widely used for optical measurement and optical communication as a highly sensitive light receiving element. Above all, InP / InGaAs is used as a material of a semiconductor light receiving element for a wavelength band of 1.3 μm or 1.55 μm used for large-capacity long-distance optical communication. FIG. 4 shows one conventional example of a semiconductor light receiving element using these materials.

FIG. 5 is a sectional view showing a conventional example of an APD using InGaAs. On the n ⁺ -InP substrate 1, the carrier concentration is 1E15 to 2E16 cm ^-3 and the layer thickness is 1 to ³ μm.
m n-InP buffer layer 2 and carrier concentration 1E14 to 1
E16 cm ^-3 and layer thickness of 1-5 μm n ⁻ −In _0.53 Ga
_0.47 As light absorption layer 17 and carrier concentration 1E15 to 1E
N-InGaAs with a thickness of 16 cm ^-3 and a layer thickness of 0.3-1 μm
P intermediate layer 6 and carrier concentration 2E16 to 4E16 cm ^-3
And an n ⁺ -InP multiplication layer 7 having a layer thickness of 0.8 to 4 μm, a carrier concentration of 1E15 to 8E15 cm ^−3, and a layer thickness of 1 to 2 μm.
m n ⁺ -InP window layer 8 and a p ⁺ -InP region 10 having a carrier concentration of 1E17 to 1E20 cm ^-3 as a light receiving portion are selectively formed by Zn diffusion diffusion in an epitaxial crystal grown by a vapor phase growth method. Further, a guard ring 9 is formed by a Be ion implantation method so as to surround the light receiving portion. By applying a reverse bias to the APD using InGaAs, the light absorption layer of InGaAs
A depletion layer spreads in the light absorption layer 17. At this time InGaAs
The wavelength corresponding to the bandgap energy of the layer 17 is 1.
When light of 67 μm or less, for example, 1.3 μm, is incident, carriers are generated by the photoelectric effect in the depleted light absorption layer 17. The generated carriers are accelerated to the saturation speed by the internal electric field of 20 to 100 kV / cm in the depletion layer and flow to the external circuit as a current.

The problem here is that, in the conventional example shown in FIG. 5, since the light absorption layer 17 is made of n ^-- InGaAs, the wavelength at the absorption edge is 1.67 μm, which is not suitable for optical communication transmission. The light of 1.3 μm or 1.55 μm used does not cause a problem in sensitivity, but the wavelength for continuous monitoring is 1.65 μm.
Since m falls near the absorption edge, the sensitivity is low and the quantum efficiency is about 20%. A second conventional example has been proposed in order to solve such a problem and receive light of a longer wavelength.

A second conventional example is shown in FIG. n ⁺ -InP
After the n ⁺ -InP buffer layer 2 is grown on the substrate 1, the n ⁻ -InAs / GaAs superlattice light absorption layer 18 having a thickness of 1.5 to 2 μm and the n ⁻ -InGaAsP having a thickness of 0.1 μm are formed.
A crystal obtained by sequentially growing the layer 6, the n ⁺ -InP multiplication layer 7 having a thickness of 1.5 μm, and the p-InP layer 19 having a thickness of 1 μm was subjected to mesa etching, and then used as a p-side electrode 13. The light receiving element is formed by depositing TiPtAu and AuGeNi as the n-side electrode 15, respectively. In this way, by forming the light absorption layer into a superlattice layer structure of InAs and GaAs, the wavelength at the absorption edge can be expanded to 3.2 μm.

However, the problem here is that in the case of the second conventional example, a lattice mismatch occurs at the interface because of the formation of a superlattice of InAs and GaAs on the InP substrate. Dark current is generated due to the lattice defects. The dark current causes noise, which lowers the sensitivity.

[0008]

[Problems to be Solved by the Invention] The above-mentioned conventional AP
In D, due to the formation of InAs and GaAs superlattice on InP, a lattice mismatch occurs at the interface, and a dark current occurs due to the lattice defect. This dark current causes noise, which lowers the sensitivity.

Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide a light receiving element for line monitoring of a fiber network for optical communication.
It is to obtain high quantum efficiency, low dark current, and high current multiplication factor for light having a wavelength of 1.65 μm.

[0010]

In order to achieve the above object, according to a basic aspect of the present invention, a first conductivity type InAsP layer and a first conductivity type In _{0.57 are} formed on a first conductivity type InP substrate.
Ga _0.43 As light absorption layer (λ = 1.85 μm), a first-conductivity-type InP multiplication layer, and a first-conductivity-type InP window layer are sequentially formed in the heteroepitaxial layer structure, and in the window layer or the multiplication layer. A structure in which a second conductivity type InP region is partially provided in the layer, a second conductivity type electrode formed on the second conductivity type InP region provided in the window layer, and the first conductivity type InP substrate There is provided a semiconductor light receiving element having the first conductivity type electrode formed thereon.

First conductivity type In _0.57 in the above basic embodiment
The layer thickness of the Ga _0.43 As light absorbing layer is 2 μm to 5 μm.

The first conductivity type I in the above-mentioned basic mode
A layer whose composition is continuously changed from a wavelength of 1.85 μm to 1.67 μm is interposed between the n _0.57 Ga _0.43 As light absorption layer and the first conductivity type InP multiplication layer.

[0013]

In the present invention, the n-InAsP buffer layer is provided on the substrate side with the strained n-InGaAs light absorption layer interposed, and the wavelength of 1.85 μm to 1.67 μm is provided on the multiplication layer and window layer sides.
N-InGaAs linear step layer changed to n
By using the heteroepitaxial layer structure in which the -InGaAs intermediate layer is formed, it is possible to shift the absorption edge to the ultra-high frequency side, suppress lattice mismatch, and reduce noise. As a result, the semiconductor light receiving element of the present invention exhibits high sensitivity at long wavelengths, and high multiplication factor can be obtained.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in more detail with reference to the embodiments shown in the accompanying drawings. Embodiment 1 FIG. 1 shows a first embodiment of the semiconductor light receiving element of the present invention.

On the surface of the n ⁺ -InP substrate 1, a carrier concentration of 1E15 to 2E16 cm ^-3 and a layer thickness of 1 to ³ μm are preferable by the vapor phase growth method. This time, the carrier concentration is 1E15.
cm ⁻³ and layer thickness 2 μm, n ⁺ -InP buffer layer 2, and carrier concentration 1E15 to 2E16c for relaxing lattice mismatch.
m ⁻³ and a layer thickness of 1 to ³ μm are preferable, and this time, an n-InAsP buffer layer 3 having a carrier concentration of 1E15 cm ⁻³ and a layer thickness of 2 μm, and an absorption edge wavelength λ = 1.8 as a long wavelength light absorption layer.
5 μm, carrier concentration 1E15 to 5E15 cm ⁻³ and layer thickness ^{3 to 4} μm are preferable.
cm ⁻³ and strain 4 μm thick n ⁻ −InGaAs (λ =
(1.85 μm) After growing the light absorption layer 4, the absorption edge wavelength is changed from 1.85 μm to 1.6 to relieve the lattice mismatch.
Carrier concentration 3E15 ~ 1E
16 cm ⁻³ and a layer thickness of 0.03 to 0.5 μm are preferable,
This time, carrier concentration is 1E16cm ^-3 and layer thickness is 0.5μm
Strained n-InGaAs linear step layer 5 is grown, and then the carrier concentration is preferably 3E15 to 1E16 cm ⁻³ and the layer thickness is 0.03 to 0.5 μm. This time, the n is the carrier concentration is 1E16 cm ⁻³ and the layer thickness is 0.5 μm. -InG
The aAsP intermediate layer 6 is grown, and thereafter, a carrier concentration of 1E16 to 4E16 cm ^-3 and a layer thickness of 0.
5 to 3 μm is preferable, this time carrier concentration is 3E16c
An n ⁺ -InP multiplication layer 7 having a thickness of m ⁻³ and a layer thickness of 1.4 μm is grown. Finally, as the window layer, the carrier concentration is 2E15 to 6E.
Preferably 15cm ^-3 and a layer thickness 1 to 2 [mu] m, ⁿ of the carrier concentration 5E15 cm ^-3 and the layer thickness 1.4μm this time - -I
The nP window layer 8 is grown.

A mask is grown on the surface of the epitaxial wafer thus grown by the CVD method, and the guard ring 9 is formed by the ion implantation method of Be, for example. Next, a window of a diffusion mask is opened so as to overlap with the guard ring 9, and a p ⁺ region 10 of 1E17 to 1E20 cm ^-3 corresponding to a light receiving portion is selectively formed by, for example, Zn diffusion diffusion. Thereafter, an insulating film 11 such as a SiN _x film or a SiO ₂ film is grown on the surface side by a usual method, and then a part of the insulating film 11 on the p ⁺ region 10 is perforated to form a p-side contact electrode. After forming 12 by, for example, a vapor deposition method, heat treatment is performed. A p-side electrode 13 is formed so as to cover the p-side contact electrode.

Subsequently, after the n-side contact electrode 14 is formed on the back surface of the n ⁺ -InP substrate 1 by, for example, the vapor deposition method,
Heat treatment is performed, and finally the n-side electrode 15 is formed so as to cover the n-contact electrode 14.

Strained InGaAs manufactured in this way
The spectral sensitivity characteristics of -APD are shown in FIG. When a light of 1.65 μm is incident on this APD, the light is p ⁺ from the window layer 8 side.
After entering the diffusion region 10 and passing through the multiplication layer 7, the intermediate layer 6, and the strained InGaAs linear step layer 5, the strain n
-It is absorbed by the InGaAs light absorption layer 4. The carriers generated by the light absorbed here are the p-side electrode 13
It is accelerated by an electric field applied between the n-side electrode 15 and the n-side electrode 15, flows into the p-side electrode 13, and is discharged to an external circuit to become a photocurrent.

By adopting such a structure, 1.6
It is possible to absorb light of 5 μm with high efficiency of 70% or more. Further, the strained n ^-- InGaAs light absorption layer 4 and n
⁺ -InP substrate 1 and n-InP buffer layer 2 and n-I
Since the lattice mismatch can be suppressed by sandwiching the nAsP buffer layer 3 between them, a low dark current characteristic of 100 nA or less can be obtained.

FIG. 4 shows the relationship between the x value of In _x Ga _1-x As and the dark current. From this, it can be seen that if x = 0.57 is exceeded, the dark current becomes high, and it cannot be used as an OTDR.

[0021] In addition, distortion ⁿ by the above-mentioned effect - -InG
The carriers generated in the aAs light absorption layer 4 are n ⁺ -In
A high multiplication factor of 30 times or more can be obtained by the electric field applied to the P multiplication layer 7.

In the present invention, the InGaAsP-based heteroepitaxial layer is used, but such characteristics could not be obtained with other material-based heteroepitaxial layers.

The above effects are obtained by the CVD method, the MOCVD method, the MBE method, in addition to the epitaxial wafer by the vapor phase growth method.
The same effect can be obtained in the epitaxial wafer by the ALE method. Second Embodiment: FIG. 3 shows a second embodiment of the semiconductor light receiving element of the present invention.

The carrier concentration is preferably 1E15 to 2E16 cm ^-3 and the layer thickness is 1 to ³ μm on the back surface of the n ⁺ -InP substrate 1 by the vapor phase growth method. This time, the carrier concentration is 1E15c.
m ⁻³ and a layer thickness of 2 μm, the n-InP buffer layer 2, and a carrier concentration of 1E15 to 2E16 cm ⁻³ for relaxing the lattice mismatch.
Also, the layer thickness is preferably 1 to 3 μm, and the carrier concentration is 1 this time.
N-InAsP buffer layer 3 having E15 cm ⁻³ and a layer thickness of 2 μm
And an absorption edge wavelength λ = 1.85μ as a long wavelength light absorption layer
m, carrier concentration is 1E15 to 5E15 cm ^-3 and layer thickness is 3
~ 4μm is preferable, this time carrier concentration 3E15cm
^-3 and a strain of 4 μm in thickness n ⁻ −InGaAs (λ = 1.
(85 μm) After growing the light absorption layer 4, the absorption edge wavelength is changed from 1.85 μm to 1.67 μ to relieve the lattice mismatch.
The carrier concentration is changed from 3E15 to 1E16 in order.
cm ^-3 and a layer thickness 0.03~0.5μm preferably, after this time grown strained n-InGaAs linear step layer 5 having a carrier concentration 1E16 cm ^-3 and a layer thickness 0.5 [mu] m, carrier concentration 3E15～1E16cm ^{- 3} and a layer thickness of 0.03 to 0.5 μm are preferable, and this time, n-InGaAs having a carrier concentration of 1E16 cm ⁻³ and a layer thickness of 0.5 μm.
A P intermediate layer 6 is grown, and then a carrier concentration of 1E16 to 4E16 cm ⁻³ and a layer thickness of 0.5 to ³ μm is used as a multiplication layer.
This time, the n ⁺ -InP multiplication layer 7 having a carrier concentration of 3E16 cm ^-3 and a layer thickness of 1.4 μm is grown this time. Finally, as the window layer, the carrier concentration is 2E15 to 6E15 cm ^-3.
Also, the layer thickness is preferably 1 to 2 μm, and the carrier concentration is 5 this time.
N ⁻ −InP window layer 8 having E15 cm ⁻³ and a layer thickness of 1.4 μm
Grow.

A mask is grown on the back surface of the epitaxial wafer thus grown by the CVD method, and the guard ring 9 is formed by the ion implantation method of Be, for example. Then, a window of a diffusion mask is opened so as to overlap the guard ring 9, and a p ⁺ region 1 of 1E17 to 1E20 cm ^-3 corresponding to a light receiving portion is formed by sealing diffusion of Zn, for example.
0 is selectively formed. After that, an insulating film 11 is grown on the back surface side by a usual method, and then a part of the insulating film 11 on the p ⁺ region 10 is perforated to form a p-side contact electrode 12.
Is formed by, for example, a vapor deposition method, and then heat treatment is performed. P-side electrode 13 so as to cover the p-side contact electrode
To form

Subsequently, the surface of the n ⁺ -InP substrate 1 is chemically etched to form a radius of 120 μm to 1 μm.
A lens having a convex shape of 50 μm is formed. An antireflection film 16 is formed on the surface of this lens. The n-side contact electrode 14 is formed on the surface of the n ⁺ -InP substrate 1 so as to surround the lens.
Is formed by, for example, a vapor deposition method, then heat treatment is performed, and finally the n-side electrode 15 is formed so as to cover the n-contact electrode 14.

Back-illuminated type strain I manufactured in this way
When light enters the 1.65μm to nGaAs-AP, after light passes through the n ⁺ -InP substrate 1, InP buffer layer 2, n-InAsP buffer layer 3 from the surface of the lens, distortion n ^- -
It is absorbed by the InGaAs light absorption layer 4. The carriers generated by the light absorbed here are n-InGaA.
s linear step layer 5, n-InGaAsP intermediate layer 6,
n ⁺ -InP multiplication layer 7, n ^-- InP window layer 8, P ⁺ -I
The current flows from the p-side electrode 13 to the external circuit through the nP layer 10.

By adopting such a structure, 1.6
It is possible to absorb light of 5 μm with high efficiency of 70% or more. Further, the strained n ^-- InGaAs light absorption layer 4 and n
⁺ -InP substrate 1 and n-InP buffer layer 2 and n-I
Since the lattice mismatch can be suppressed by sandwiching the nAsP buffer layer 3, a low dark current characteristic of 100 nA or less can be obtained.

[0029] In addition, distortion ⁿ by the above-mentioned effect - -InG
The carriers generated in the aAs light absorption layer 4 are n ⁺ -In
A high multiplication factor of 30 times or more can be obtained by the electric field applied to the P multiplication layer 7.

The above effects are obtained by the CVD method, the MOCVD method, the MBE method, in addition to the epitaxial wafer by the vapor phase growth method.
The same effect can be obtained in the epitaxial wafer by the ALE method.

[0031]

As described above, according to the present invention,
Light of 1.65 μm can be absorbed with high efficiency of 70% or more in the strained n ⁻ -InGaAs light absorption layer. Further, since lattice mismatch can be suppressed, low dark current characteristics of 100 nA or less can be obtained. In addition, strain n ⁻ −InG
The carriers generated in the aAs light absorption layer 4 are n ⁺ -In
Due to the charges applied to the P multiplication layer 7, a high multiplication factor of 30 times or more can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor light receiving element according to a first embodiment of the present invention.

FIG. 2 is a sensitivity distribution of the semiconductor light receiving element according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a semiconductor light receiving element according to a second embodiment of the present invention.

FIG. 4 is a graph showing a value of x and dark current characteristics of In _x Ga _1-x As.

FIG. 5 is a sectional view of a semiconductor light receiving element showing a conventional example.

FIG. 6 is a sectional view of a semiconductor light receiving element showing another conventional example.

[Explanation of symbols]

1 n ⁺ -InP substrate 2 n-InP buffer layer 3 n ^-- InAsP buffer layer 4 Strain n ^--In _0.57 Ga _0.43 As light absorption layer 5 n-InGaAs linear step layer 6 n-InGaAsP intermediate layer 7 n ⁺ -InP Multiplier layer 8 n ⁻ -InP window layer 9 Guard ring 10 p ⁺ region 11 Insulating film 12 p-side contact electrode 13 p-side electrode 14 n-side contact electrode 15 n-side electrode 16 antireflection film 17 n-In _0.57 Ga _0.43 As Light absorption layer 18 n-InAs / GaAs superlattice light absorption layer 19 p ⁺ -InP layer

Claims (6)

[Claims] 1. A first conductivity type InAsP layer, a first conductivity type In _0.57 Ga _0.43 As light absorption layer (λ = 1.85 μm), and a first conductivity type InP multiplication layer on a first conductivity type InP substrate. Layer and a first conductivity type InP window layer are sequentially formed, a structure in which a second conductivity type InP region is partially provided in the window layer or the multiplication layer, and in the window layer 2. A semiconductor light receiving element, comprising: a second conductivity type electrode formed on the second conductivity type InP region provided on the first conductivity type electrode; and a first conductivity type electrode formed on the first conductivity type InP substrate. 2. The semiconductor light receiving element according to claim 1, wherein the first conductivity type In _0.57 Ga _0.43 As light absorption layer has a layer thickness of 2 μm to 5 μm. 3. The first conductivity type In _0.57 Ga _0.43 As light absorption layer and the first conductivity type InP multiplication layer have a wavelength of 1.
2. The semiconductor light receiving element according to claim 1, wherein a structure is provided in which a layer whose composition is continuously changed from 85 μm to 1.67 μm is interposed. 4. A first conductivity type InP buffer layer is provided on a first conductivity type InP substrate, and a first conductivity type InAsP buffer layer is provided on the first conductivity type InP buffer layer. Type I
a first conductivity type InGaAs light absorption layer is provided on the nAsP buffer layer, and a first conductivity type strained linear step InGaAs layer is provided on the first conductivity type InGaAs light absorption layer;
The first conductivity type strained linear step InGaAs layer has a first conductivity type InGaAsP intermediate layer, and the first conductivity type InGaAsP intermediate layer has a first conductivity type InP multiplication layer. First conductivity type I on the InP multiplication layer
an nP window layer, a second conductivity type region on the InP window layer, the second conductivity type region and the first conductivity type InP
A semiconductor light-receiving element characterized by having electrodes under a substrate. 5. The semiconductor light receiving element according to claim 4, wherein the first-conductivity-type InGaAs light absorption layer is an In _0.57 Ga _0.43 As layer. 6. A strain linear step I of the first conductivity type.
The nGaAs layer is In _0.57 Ga _0.43 As to In _0.53 Ga
A semiconductor light receiving element comprising a strained linear step layer that changes to _0.47 As.