JPS5917549B2 - photosensitive semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photosensitive semiconductor device, and particularly to a photodiode improved to have high sensitivity and fast response speed to an incident wavelength range (for example, 9000X), which has been difficult in the past.

Conventionally, for example, the peak wavelength of a GaAs light emitting diode 9
As a light receiving element for 000X, a group III semiconductor such as Ge or Si having a pn junction has been used.

The spectral photoelectric sensitivity of these light-receiving elements is determined by the forbidden band of the material in the long wavelength range and by the surface recombination speed in the short wavelength range, but it is determined by the depth of the p-n junction. It is also considerably influenced by the lifetime of carriers generated by light absorption.

For example, to increase short-wavelength sensitivity, it is necessary to form a pn junction shallowly and to perform surface treatments that reduce the surface recombination rate, and to increase long-wavelength sensitivity, it is necessary to use materials with a long minority carrier lifetime. It is desirable to use it. However, even with these improvements, the spectral characteristics of the pn photodiode are limited to a wavelength range determined by the bandgap and the surface recombination rate. For example, the incident wavelength 900
For 0X, Si has a wide forbidden band and a small absorption coefficient, so the quantum efficiency cannot be increased beyond a certain level.
Since the diffusion distance is long, this becomes a factor that slows down the response speed. On the other hand, since Ge has an extremely large absorption coefficient and is absorbed at a large rate on the surface, the efficiency of photoelectric conversion is significantly reduced due to surface recombination and recombination during diffusion. FIG. 1 is a cross-sectional view showing a conventional p-n junction type Ge photodiode 0, in which an n-type impurity such as Sb is diffused into a p-type Ge substrate 1 to create an n-type diffusion layer 2, and metal electrodes 3 are formed on each of these layers.
and 4 have been added.

In Ge, 63% of the incident light having a wavelength of 900K is absorbed at a depth of 0.4 μ from the surface of the n-type diffusion layer 2 . Therefore, the depth of the n-type diffusion layer 2 needs to be as shallow as possible. However, the depth of the diffusion layer 2 that can be controlled by conventional diffusion is about 0.5 to 1μ, and for the incident light of 9000X, most of the light is absorbed by the n-type diffusion layer 'O2 and regenerated on the surface. The quantum efficiency becomes extremely low due to the effects of coupling and the n-type diffusion layer has a high impurity concentration and short lifetime. On the other hand, with the recent progress in the -V group compound semiconductor technology, a heterojunction light-receiving element has been proposed.

For example, one example of this is a light-receiving element with a wide wavelength range that is formed by a heterojunction of n-type GaAs and p-type Ge. However, because the crystal of GaAs (5'Ge) with hair-hole junction is still incomplete, such a light-receiving element has not been put into practical use.The reason is that in order to improve crystallinity This is because the temperature needs to be raised, and if the temperature is raised, the area near the junction will be doped with n+ due to interdiffusion between GaAs and Ge, making it useless as a light receiving element. There is no light-receiving element that satisfies both quantum efficiency and response speed for the type 9000 incident light.Therefore, there has been a demand for a light-receiving element with high quantum efficiency and fast response speed.

The present invention provides a photosensitive semiconductor device that can significantly improve quantum efficiency, spectral characteristics, and response speed, which were conventionally limited by materials and bonding formation methods.

The apparatus of the present invention will be explained in detail below with reference to the drawings. FIG. 2 is a sectional view showing an embodiment of the device according to the invention, and
This is a light receiving element intended for receiving light from an aAs light emitting diode (peak wavelength 9000λ).

In the figure, 5 is a p-type Ge substrate, 6 is a p-type Ge growth layer,
7 is an n-type diffusion layer, 8 is an n-type GaAs layer, and 9 and 10 are metal electrodes. Next, the steps for manufacturing this device are as follows: Ga-doped p-type Ge with an impurity concentration of 10a "3" is used as the substrate 5, and B-doped p-type Ge6 with an impurity concentration of 1016i-3 is epitaxied to a film thickness of about 2μ. After letting it grow,
In the same epitaxial growth apparatus, an n-type GaAs layer 8 was formed to a thickness of about 2 .mu.m while an n-type diffusion layer 7 was being formed.

Further, on the back surface of the substrate 5, a metal electrode 10 was formed by vapor-depositing AuGe over the entire surface, and on the surface of the GaAs layer 8, an electrode 9 was formed by vapor-depositing and alloying AuGe in the form of dots of 100 μψ. The slices thus obtained are 0.5 rfr! NXO. It was scribed to a size of 5 ml, die-bonded to a TO-18 type header, and a gold wire (not shown) was bonded to the electrode on the upper surface to form an external lead wire. After this, the surface was lightly treated by etching. Next, the specific contents of this device will be explained.

In this device, the Pn junction is formed extremely shallowly inside the Ge. For incident light with a wavelength of 9000λ, the GaAs layer has a wide bandgap, so it is used as a transparent film.
Furthermore, since its refractive index is between that of Ge and air, it also acts as an antireflection film.

Therefore, most of the incident light is absorbed in Ge,
An electron-hole pair is generated. Here, since the Pn junction is formed extremely shallow, most of the carriers are generated in the p-type layer and are not affected by surface recombination, so the efficiency of photoelectric conversion is extremely high. Since it is about 2μ, the response speed is also extremely fast. This shallow n-type layer is made of Ga
It is formed simultaneously during As growth. By the way, in normal diffusion using As or Sb vapor, since the vapor pressure of As or Sb is high, the surface concentration is high and the junction is formed deeply. Precisely lowering the vapor pressure requires more precise temperature control, which is extremely difficult. Compared to the conventional case of using such an element as it is as a diffusion source, the GaAs used in the device of this invention has an appropriate decomposition vapor pressure of As, and is therefore suitable for controlling the vapor pressure as an As diffusion source. Moreover, unlike the case of forming a heterojunction, it is not necessary to improve the crystallinity of the GaAs layer, so the growth temperature can be lowered.
Alternatively, growth can be performed at a lower temperature using a vacuum evaporation method, a molecular beam method, or the like. Because it can grow at such a low temperature and because As is a compound, the diffusion of Ol into Ge can be controlled extremely shallowly. A shallow diffusion layer increases the sheet resistance of this layer, which increases the series resistance of the light-receiving element, which causes a decrease in efficiency and response speed. For this reason, conventionally, shallow Pn
In bonding and shot barrier photodetectors, SnO2
Attempts have been made to arrange conductive transparent electrodes such as , thin Au evaporated films of about 500 λ, or thick Au films in stripes. However, all of these methods have problems. For example, SnO2 film, thin A
The U film has high resistance, and the striped electrode has extremely poor light incidence efficiency. On the other hand, n-type G on n-type Ge7
The aAs layer 8 can be formed relatively thick, and its resistance value can be lowered by adding appropriate impurities at a high concentration, making it extremely convenient as a transparent electrode. We actually created an element with the structure shown in Figure 2, and used a GaAs laser diode to emit pulsed light with a wavelength of 9000λ to the GaAs of the element.
When tested by applying a voltage of 10-odd V to the same element with input from the s side, the response speed was less than 1 ns and the quantum efficiency was 8.
0(f).

On the other hand, when a Si photodiode with a p-1-n junction structure, which is a typical conventional example, was tested using the same GaAs laser diode as above and the same amount of human light, a quantum efficiency of 80% was obtained. It was necessary to apply a reverse bias of 100 V to this photodiode, and the response speed was about 5 ns, which was slower than that of the present invention.
In the above example, an example of an element with high efficiency and fast response speed for incident light of 9000λ was explained using p-type Ge as the substrate and n-type GaAs as the diffusion source and transparent electrode. In the invention, Ge can be replaced with a group semiconductor such as Si, and GaAs can be replaced with GaAsP. Ga
It can be carried out by replacing it with a 1-V group compound such as AlAs or GaSb.

If it is replaced with Ge7/Si, good growth of a GaAs epitaxial layer cannot be expected because the lattice constants of Si and GaAs are different, but in this device, GaAs
Since the s layer is mainly used as a diffusion source for Si and as a transparent electrode, there is no problem. When Si is used, the light-receiving element has high photosensitivity to ultraviolet light. As detailed above, the present invention has an n-type conductive ...-V group compound semiconductor having a forbidden band width larger than the forbidden band width of the group semiconductor on a p-type conductive group semiconductor, forming an n-type diffusion layer in the group semiconductor by the group V element of the compound semiconductor;
This is a photoelectric conversion device characterized by a structure in which a -V group compound semiconductor is used as a transparent electrode that also serves as an antireflection film.

Therefore, according to the device of the present invention, it is possible to create a photodetector element that is highly efficient and has a fast response speed for incident wavelengths whose quantum efficiency and response speed have been limited by conventional materials and structures. It can be realized.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional Pn junction photodiode.
FIG. 2 is a sectional view showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...p-type Ge substrate, 2...n-type diffusion layer, 3, 4...
...Metal electrode, 5...p-type Ge substrate, 6...p-type G
e growth layer, 7... n-type diffusion layer, 8... n-type GaAs
Layer, 9, 10...metal electrode.

Claims (1)

[Claims] 1. An n-type III-V compound semiconductor having a forbidden band width larger than that of the group IV semiconductor is formed on the p-type conductive group IV semiconductor, and the III-V compound semiconductor is formed on the surface of the group IV semiconductor. - A photosensitive semiconductor device, characterized in that a group V element is introduced into a group V compound semiconductor to form an n-type conductive layer, and an electrode is provided on the surface of the group III-V compound semiconductor layer.