JPH02231775A - Compound semiconductor photodetector - Google Patents

Abstract

PURPOSE:To improve the quantum efficiency, and to obtain sensitivity continuously extending over a wide wavelength range from a short wavelength to a long wavelength by specifying the thickness of an InP cap layer and the depth of a diffusion region. CONSTITUTION:An InGaAs light absorption layer 3 and an InP cap layer 4 are laminated successively onto one conductivity type InP substrate 1 doped in high concentration, and the opposite conductivity type diffusion region 6 reaching from the surface of the InP cap layer 4 to the InGaAs light absorption layer 3 and being doped in high concentration is formed. The thickness of the InP cap layer 4 is brought to 0.1mum or less while the depth of the diffusion region 6 is brought to 0.7mum or less. Accordingly, quantum efficiency is improved, and sensibility is acquired continuously extending over a wide wavelength range from a short wavelength of 0.7-0.8mum to a long wavelength of 1.3mum and 1.55mum.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to provide an InGaAs/InP PIN photodiode with continuous sensitivity over a wide wavelength range from short wavelengths to long wavelengths. on a highly doped InP substrate of one conductivity type. In
In a compound semiconductor light-receiving element, a GaAs light absorption layer and an InP cap layer are sequentially laminated, and a heavily doped diffusion region of the opposite conductivity type is formed, which reaches the InGaAs light absorption layer from the surface of the InP cap layer. {n
The thickness of the P cap layer is set to O. lμm or less, and
The depth of the diffusion region is configured to be 0.7 μm or less. [Industrial field of application] Masaaki Moku. Compound semiconductor photodetector, especially InGaAs/
Regarding InP PIN photodiodes. The optical wavelength bands used for optical communications mainly include: There are three types: ■0.7-0.8μm band. this is. Using an inexpensive semiconductor laser developed for compact discs (CDs),
Used in short-range, medium-low speed optical communication systems. ■1.3μm band. This is a wavelength band in which the material dispersion of optical fibers is close to zero, and is used in long-distance, high-capacity optical communication systems. ■1.55μm band. this is. In the wavelength band where the transmission loss of optical fiber is the smallest. Used in long-distance, high-capacity optical communication systems. Conventional. For the short wavelength band of 0.7 to 0.8 μm, a light receiving element using S+ is used, and for the short wavelength band of 1.3 μm or 1.55 μm.
In the long wavelength band of μm. A photodetector using Ge or InP is used. In recent years, optical multiplex communication, which transmits light with different wavelengths from short to long wavelengths through the same optical fiber, has been put into practical use. A photodetector element that can receive all light from short wavelengths to long wavelengths using the same element is desired. Furthermore, it is desired that light-receiving elements for measurement be capable of continuously obtaining luminosity over a wide wavelength range from short wavelengths to long wavelengths.

[Conventional technology]

(Conventional Example 1) Figure 3 shows the conventional InGaAs/In P P I
It is a diagram showing an N photodiode. In the figure, 11 is an n'-1nP substrate. 12 is thickness 5
~8μm n-1nP buffer layer, 13 is 2-3 thick
μm n--InGaAs light absorption layer. 14 has a thickness of approximately lμ
m n-1nP cap layer, 15 is SiN film, 16 is n
The surface of the -1nP cap layer l4 is n-InGaAs
17 is an anti-reflection film that reaches the light absorption layer 13. 18 and 19 are electrodes.

InGaAs/InP P I with the structure shown in Figure 3
For N photodiodes, 1.3 μm and 1.5
The 5 μm light passes through the n-1nP cap layer 14. Since the light is absorbed by the n--1nGaAs light absorption layer 13, which is almost a depletion region, a large quantum efficiency can be obtained.

However, light of 0.7 to 0.8 um is n-
Photocarriers generated by light are absorbed in the 1nP camp layer 14. The problem is that the quantum efficiency (sensitivity) is poor because it dies while it diffuses into the depletion region. (Conventional Example 2) In order to solve the problems of Conventional Example 1, an InGaAs/InP PIN photodiode shown in FIG. 4 was devised.

In Figure 4. 21 is an n''-1nP substrate, 22 is an n--InP buffer layer with a thickness of 2 to 3 μm, and 23 is a thickness of 2 to 3 μm.
A 3 μm n−1 nGaAs light absorption layer, 24 a SiN film, 25 a p4 diffusion region, 26 an antireflection film, and 27 and 28 electrodes.

The InGaAs/In P P I N photodiode in this example is. InGaAs/In shown in Figure 3
From P P I N photodiode. 0.7~0
．． It absorbs light of 8 μm. It has a structure in which the n-1nP cap layer, which degrades the quantum efficiency for light in this wavelength range, has been removed. Such a structure improves the quantum efficiency for light in the 0.7-0.8 μm band, but the narrow bandgap n
- -The InGaAs light absorption layer 23 is exposed to the surface and the Si
In order to form an interface with the N film 24, the surface state density increases. Dark current increases. A problem arises. [Problems to be Solved by the Invention] The InGaAs/InP P I N photodiode of Conventional Example 1 has an n-InP camp layer of 0.
There is a problem in that it absorbs light of 9 μm or less, resulting in poor quantum efficiency for light in this wavelength band.

In addition, InGa of conventional example 2 which solved the problems of conventional example 1
As/InP PIN photodiode. Since the n--InGaAs light absorption layer with a narrow bandgap becomes the semiconductor surface and forms an interface with the SiN film, the surface state density increases. The problem was that the dark current increased. The present invention is a compound semiconductor photodetector that solves these problems and provides continuous sensitivity over a wide wavelength range from short wavelengths to long wavelengths. Especially InGaAs/
The present invention aims to provide an In P P I N photodiode.

[Means for Solving the Problems] In order to achieve the above object, the light receiving element according to the present invention includes a highly doped InP substrate of one conductivity type.
In a compound semiconductor light-receiving element in which an InGaAs light absorption layer and an InP cap layer are sequentially laminated to form a heavily doped diffusion region of the opposite conductivity type that reaches the InGaAs light absorption layer from the surface of the InP camp layer, the I
The thickness of the nP camp layer is set to 0. In addition to making it 1 μm or less. The depth of the diffusion region is configured to be 0.7 μm or less.

[Effect]

The present invention solves the problems of Conventional Example 1, in which the InP cap layer absorbs light of 0.9 μm or less, resulting in poor quantum efficiency for light in this wavelength range, and. Because the InGaAs light absorption layer with a narrow bandgap becomes the semiconductor surface and forms an interface with the SiN film. The surface state density increases,
Dark current increases. This was done to simultaneously solve the problems of Conventional Example 2, and the point is that I
Even with the nP cap layer attached. The purpose of this study is to elucidate the structural conditions that allow light of 0.9 μm or less to reach the InGaAs light absorption layer. for that. The inventors set the thickness of the InP cap layer to 0.1 μm, 0.2 #m and 0.35, c+m,
The depth of the diffusion region was set to 0.7 μm and 1 μm, respectively.
．． For a total of six types of samples with a thickness of 3 μm, 0.78
, we measured the quantum efficiency of iIm for light. The results are shown in the table below.

(Left below) 7m A: Thickness of InP camp layer (μm) B: Depth of diffusion region (μm) (Impurity concentration I
Values determined by P monitor wafer) From this table. The thinner the InP cap layer is, the more Also.
It can be seen that the shallower the depth of the diffusion region, the greater the quantum efficiency for 0.78 μm light.

If the practical quantum efficiency is 75% or more, the thickness of the InP cap layer should be 0.1 μm or less. This means that the depth of the diffusion region should be 0.7 μm or less.

The present invention was made based on the above findings, and
On a highly doped InP substrate of one conductivity type, I
An nGaAs light absorption layer and an InP cap layer are sequentially laminated. In a compound semiconductor photodetector in which a heavily doped diffusion region of the opposite conductivity type is formed that reaches an InGaAs light absorption layer from the surface of an InP cap layer. In
The thickness of the P cap layer should be 0.1 μm or less. With.
The depth of the diffusion region is configured to be 0.7 μm or less. By configuring it like this. InG that provides continuous sensitivity over a wide wavelength range from short wavelengths of 0.7 to 0.8 μm to long wavelengths of 1.3 μm and 1.55 μm
An aAs/InP PIN photodiode can be obtained.

〔Example〕

Figure 1 is. InGaAs/
FIG. 2 is a diagram showing an InP PIN photodiode.

In Figure 1, 1 is an n''-InP substrate. 2 is an n-InP substrate.
P buffer layer, 3 is n--1nGaAs light absorption layer, 4
is an n-4nP cap layer, 5 is a SiN film, 6 is a p9 diffusion region, and 7 is an antireflection film. 8 and 9 are electrodes.

below. InGaAs/In P P shown in Figure 1
A method for manufacturing an IN photodiode will be explained.

For manufacturing the device. An epitaxial wafer with a double heterostructure of InP/InGaAs/InP grown by the chloride VPE method was used. The growth temperature is 670°C.

n--1nP buffer layer 2 has an impurity concentration of 8×1014e
ll-', thickness 2.5 μn, n--1nG
The aAs light absorption layer 3 has an impurity concentration of 2X I Q ”a++
InP cap layer 4 has an impurity concentration of 6 x 10 cm and a thickness of 0.11 μm.
It is m. Among these, the n-1nP camp layer 4 is.
Because the entire surface is etched by 0.05 μm during device fabrication,
The final thickness in the chip state is 0.06 μm.

After that, a SiN film 5 as a puffy basis film is formed by plasma CVD method, a hole is made for the light receiving part, and a Zn film is formed.
Zn diffusion is performed to form the p0 diffusion region 6 using ZnPz as a source at 500°C. Do this for 7 minutes or less. When this was measured using an InP monitor wafer with an impurity concentration of 1×10 Ithal-' or higher, the diffusion depth of the p diffusion region 6 was found to be . It was 0.7 μm. Next. Deposit SiN by plasma CVD method.
An antireflection film 7 is formed. The antireflection film 7 of this example is as follows:
It is a single layer film with a refractive index of 1.82 and a film thickness of 1200 mm. As a result, a transmittance of 98.7% was obtained for 0.78 μm light. A transmittance of 91.6% is obtained for 1.3 μm light.

lastly. Electrodes 8 such as Ti/Pt/^U and Au/
An electrode 9 of Ge/Ni or the like is formed.

InGaAs/I of this example obtained through the above steps
FIG. 2 shows the dark current characteristics of the nP PIN photodiode. Dark current at normal operating voltage of 5V is approximately 30p
It is A. Conventional InGaAs/In P P I
It is also small compared to an N photodiode.

The dark current increases significantly near the bias voltage of 5V.
This means that the electric field in the n- -1nGaAs light absorption layer is 1
．． It is thought that this is because the voltage is 5×10' V/3 or more, and a tunnel current is generated.

The quantum efficiency is almost constant in the reverse bias voltage region. 0
．． A value of 76% for 78 μm light and 81% for 1.3 μm light was obtained. [Effects of the Invention] According to the present invention, from short wavelengths of 0.7 to 0.8 μm to 1.
InGaAs/In with continuous sensitivity over a wide wavelength range up to long wavelengths of 3 μm and 1.55 μm
A P PIN photodiode can be obtained. 1: n''-1nP substrate 2 = n--1nP bathophore layer 3: n--1nGaAs light absorption layer 4: n-1nP
Cap layer 5: SiN film 6: P diffusion region 7: antireflection film aria pole 9: electrode

Claims (1)

[Claims] An InGaAs light absorption layer (3) and an InP cap layer (4) are sequentially laminated on a highly doped InP substrate (1) of one conductivity type. In a compound semiconductor light-receiving element in which a heavily doped diffusion region (6) of the opposite conductivity type is formed which reaches an InGaAs light absorption layer (3) from the surface. A compound semiconductor light-receiving element characterized in that the thickness of the InP cap layer (4) is 0.1 μm or less, and the depth of the diffusion region (6) is 0.7 μm or less.