JPH04129278A - Semiconductor photodetector and substrate for semiconductor photodetector - Google Patents

Abstract

PURPOSE:To maintain an excellent optical power linearity even against an optical intensity of 10mW or more by increasing in thickness an InP cap layer and reducing its resistance value. CONSTITUTION:An InP buffer layer 12 is formed on an InP substrate 10, and an InGaAs light absorption layer 4 is formed thereon. Further, an InP cap layer 16 is formed, its thickness is ranged from 3.5 to 10mum, and formed thicker than that in prior art. An impurity diffused layer 18 is formed in depth in contact with an InGaAs light absorption layer 14 in its photodetecting region. Thus, since the layer 16 is made thick to reduce its resistance value, an excellent optical power linearity can be maintained even for an optical intensity of 10mW or more.

Description

[Detailed Description of the Invention] [Summary] Regarding a semiconductor light receiving element used for measuring light intensity and a semiconductor light receiving element substrate used for manufacturing the semiconductor light receiving element, we have developed an optical technology that is excellent even for light intensities of 10 mW or more. The purpose of the present invention is to provide a semiconductor light-receiving device and a substrate for a semiconductor light-receiving device having high linearity, and an InP semiconductor substrate,
An InGaAs light absorption layer formed on the InP semiconductor substrate and an InGaAs light absorption layer formed on the InGaAs light absorption layer.
In a semiconductor light receiving element having a P-'r double layer and an impurity diffusion layer formed in a light receiving region of the InP cap layer, the thickness of the InP cap layer is within a range of 3.5 μm to 10 μm. Configure.

[Industrial Field of Application] The present invention relates to a semiconductor light-receiving element used for measuring light intensity and a semiconductor light-receiving element substrate used for manufacturing the semiconductor light-receiving element.

As optical communications have become more sophisticated in recent years, accurate light intensity measurement over a wide range is required in the field of optical measurement. Therefore, it is required to improve the optical power linearity (linearity between the optical intensity of incident light and the output photocurrent) of semiconductor light receiving elements used for optical measurement.

[Conventional technology] A conventional semiconductor light receiving element will be explained using FIG. 4.

Approximately 1 μm thick on the approximately 200 μm thick n-InP substrate 10
An n-InP buffer layer 12 with a thickness of n
- About 2 μm thick n-In on the InP buffer layer 12
A GaAsnGaAs light absorption layer is formed on top. n-InGa
A 1 μm thick n-InP cap layer 16 is formed on the AsnGaAs light absorption layer. n-InP? r Yap layer 1
+ is p in the light-receiving region of 6. The impurity diffusion layer 18 is n-InGaAs light absorption N1.
It is formed to a depth that touches 4.

n −I n P ”r A SiN layer 20 is formed on the YAP layer 16, and a ring-shaped P-side electrode 22 is formed in contact with the p+ impurity diffusion layer 18 via this SiN layer 20. n-side The electrode 24 is formed on the lower surface of the n+InP substrate 10.

The incident light irradiated onto the light receiving area inside the p-side electrode 22 is n-I.
The light is absorbed by the nGaAs light absorption layer 14 and a photocurrent is generated. This photocurrent is measured to determine the intensity of the irradiated light.

[Problem to be solved by the invention] However, although conventional semiconductor photodetectors have sufficient optical power linearity up to a light intensity of about 2 mW, in recent years there has been a demand for measuring light intensities of 10 mW or more. However, there is a problem in that satisfactory optical power linearity cannot be maintained for such high-intensity light.

An object of the present invention is to provide a semiconductor light-receiving device and a substrate for a semiconductor light-receiving device, which have excellent optical power linearity even at a light intensity of 10 mW or more.

[Means for Solving the Problems] The above object is to provide an InP semiconductor substrate, an InGaAs light absorption layer formed on the InP semiconductor substrate, and the InP semiconductor substrate.
an InP cap layer formed on the GaAs light absorption layer;
In the semiconductor light receiving element having an impurity diffusion layer formed in the light receiving region of the InP-q YAP layer, the InP
This is achieved by a semiconductor light-receiving element characterized in that the thickness of each layer is within the range of 3.5 μm to 10 μm.

[Function] According to the present invention, since the InP4 YAP layer is made thicker and the resistance value is lowered, excellent optical power linearity can be maintained even with a light intensity of 10 mW or more.

[Example] A semiconductor light receiving element according to an example of the present invention will be described with reference to FIG. Components that are the same as those of the conventional semiconductor light-receiving device shown in FIG. 4 are designated by the same reference numerals, and description thereof will be omitted or simplified.

On an n-InP substrate 10 with a thickness of about 200 μm and an impurity concentration of 4×10 18 cm 3 + , an impurity layer with a thickness of about 1 μm is formed.
-3+ An n-InP buffer layer 12 with a blunt concentration of 1×10 cm is formed. This n+-InP buffer layer 1 and layer 2 have a thickness of 2 μm and an impurity concentration of 3×1016 −
3 n-InGaAs light absorption layers m14 are formed. n-InGaAs light absorption layer 14
On top is a layer with a thickness of about 4 μm and an impurity concentration of 6 x 1015 cm.
This embodiment, in which the n-InP cap layer 16 is formed, is characterized in that the n-InP cap layer 16 is formed thicker, at 4 μm, than the conventional one. The impurity concentration is 2×1 in the approximately 1 mm diameter light-receiving region of the n-InP cap layer 16.
The p+ impurity diffusion layer 18 of 018 cm-3 is made of n-InGa.
It is formed to a depth that contacts the As light absorption layer 14.

n-JnP-3 (A SiN layer 20 is formed on the Yap layer 16. This SiN layer 20 is thin by about 1,800 layers in the central light-receiving area, and thicker by about 3,600 layers around the light-receiving area. A ring-shaped Ti contacts the p-type impurity diffusion layer 18 through the opening of the SiN layer 20.
A P-side electrode 22 of -Pt-Au is formed, and n -In
The bottom surface of the P substrate 10 is covered with Au-Ge-Ni nfl.
A ll electrode 24 is formed.

The incident light incident on the light-receiving region passes through the n-InP:' (Yag layer 16 and is absorbed by the n-1nG, aAs light absorption layer 14, and a photocurrent proportional to the light intensity is generated. pfllll from the n-InGaAs light absorption layer 14
It flows to the electrode 22 and the n-side electrode 24.

Therefore, from the n-InGaAs light absorption layer 14, P(Il
The resistance Rp of the path leading to the l electrode 22 is n-1nG a
If the resistance Rn of the path from the As light absorption layer 14 to the nflll electrode 24 is large, the photocurrent will be saturated and the optical power linearity will be limited.

In the case of this embodiment, the n+-InP substrate 10 and the n+-InP
Although the resistance Rn of the buffer layer 12 is as small as approximately 5×10 −2 Ω or less and is not a problem, the resistance Rp of the p-type impurity diffusion layer 18 of the DInP cap layer 16 may become a major problem.

When light with a spot diameter of 300 μm is not incident on the central part of the light receiving area, if the impurity concentration of the P+ impurity diffusion layer 18 of the n-InP cap layer 16 is 2X10'8 cm-3,
The specific resistance is approximately 5×10 −2 Ωcm. As before, n
-If the thickness of the InP-1i cap 16 is 1 μm,
Its spreading resistance is about 100Ω, but if the thickness of the n-rnP cap layer 16 is 4 μm as in the embodiment, the spreading resistance becomes about 25Ω, about 1/4.

FIG. 2 shows the optical power linearity of the semiconductor photodetector according to this example. The horizontal axis is the light intensity [m, W],
The vertical axis is photocurrent [mA]. It can be seen that good optical power linearity can be maintained up to a light intensity of about 12 mW. Incidentally, the optical power linearity of a conventional semiconductor light-receiving element is shown by a broken line in FIG. 2 for comparison. Light intensity is 3m
It can be seen that good optical power linearity cannot be maintained at around W.

A third embodiment of the semiconductor photodetector substrate according to another embodiment of the present invention
This will be explained using figures.

In order to manufacture a semiconductor light-receiving element, the substrate for a semiconductor light-receiving element according to this embodiment has an n+-InP layer 32 that becomes a buffer layer and an n+-InP layer 32 that becomes a light absorption layer on an n+-InP substrate 30.
-InGaAs layer 34 and n-InP serving as a cap layer
This is a semi-finished wafer with a layer 36 formed thereon.

That is, the impurity concentration is 4×1018c with a thickness of about 200 μm.
About 117 −3 on the m−3 n+-InP substrate 30
nIn with + μm thickness and impurity concentration lXl0 cm
P layer 32, about 2. Impurity concentration 3x1016cm with μm thickness
-3 n-InGaAs layer 34 and an nInP layer 36 having a thickness of about 4 μm and an impurity concentration of 6×10 cm 6 .

For this semi-finished semiconductor photodetector substrate, n-In
A P+ impurity diffusion layer is formed in the light receiving region of the P layer 36, and pf
! By forming the II electrode and the n@ electrode, the semiconductor light receiving element shown in FIG. 1 can be realized.

The present invention is not limited to the above embodiments, and various modifications are possible.

For example, in the above embodiment, the thickness of the n-InP cap layer is 4 μm, but for optical power linearity up to a light intensity of about 10 mW, the thickness may be about 3.5 μm, which is thinner than 4 μm. Furthermore, if the n-InP cap layer is made thicker, the resistance Rp becomes smaller and smaller, but it takes a very long time to manufacture a thick n-InP cap layer, and carriers generated in the light absorption layer are not easily scattered. Uke becomes easier. Therefore, considering realistic manufacturing time and response characteristics, n-
The thickness of the InP4 YAP layer is preferably 10 μm or less.

[Effects of the Invention] As described above, according to the present invention, since the InP-3r gap is made thicker and the resistance value is lowered, excellent optical power linearity can be maintained even for a light intensity of 10 mW or more.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a semiconductor light receiving element according to an embodiment of the present invention, FIG. 2 is a graph showing optical power linearity of a semiconductor light receiving element according to an embodiment of the present invention, and FIG. 3 is a graph showing another embodiment of the present invention. FIG. 4 is a cross-sectional view showing a semiconductor light-receiving element substrate according to an embodiment. FIG. 4 is a cross-sectional view showing a conventional semiconductor light-receiving element. In the figure, 10-n+-InP substrate 12...n''-InP buffer layer 14--n-InGaAs light absorption layer 16...n-InP cap layer 18...p+ impurity diffusion layer 20... SiN layer 22...p-side electrode 24...n-side electrode 3O---n+-InP substrate 32=n+-InP layer 34-n-InGaAs layer 36---n-InP layer

Claims (1)

[Claims] 1. An InP semiconductor substrate, an InGaAs light absorption layer formed on the InP semiconductor substrate, an InP cap layer formed on the InGaAs light absorption layer, and the InP
In a semiconductor light-receiving element having an impurity diffusion layer formed in a light-receiving region of a cap layer, the thickness of the InP cap layer is 3.5 μm to 10 μm.
A semiconductor light-receiving element characterized by being within the range of. 2. A substrate for a semiconductor light receiving element having an InP semiconductor substrate, an InGaAs layer formed on the InP semiconductor substrate, and an InP layer formed on the InGaAs layer, in which the thickness of the InP layer is 3.5 μm. 1. A substrate for a semiconductor light-receiving element, characterized in that the thickness is within a range of 10 μm from 1 to 10 μm.