JPH11177119A - Photodiode and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photodiode provided with high light sensitivity in a short wavelength band below 400 nm as well simultaneously with the light sensitivity of the long wavelength band of an Si photodiode and provide a manufacturing method. SOLUTION: In this photodiode provided with a p-n junction, the p-n junction is formed from the silicon substrate 1 of a first conducting type and the group III nitride (Alx Iny Ga1-x-y N, wherein 0<=x, y<=1 and 0<=x+y<=1) layer 2b of a second conducting type and the light sensitivity on a long wavelength side by a light carrier generated in a depletion layer on a silicon side and the light sensitivity on a short wavelength side by the light carrier generated in the depletion layer on a group III nitride layer side are provided together. A buffer layer is denoted by 2a, and respective electrodes are denoted by 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is silicon (Si) III-nitride on the substrate _{(Al x In y Ga 1-} xy N) layer relates photodiode of pn junction type stacked, particularly Si photodiode The present invention relates to a photodiode having high photosensitivity even in a wavelength region of 400 nm or less in which photosensitivity decreases.

[0002]

2. Description of the Related Art Al _x In _y Ga _1-xy N (where 0 ≦ x, y
≦ 1, 0 ≦ x + y ≦ 1) blue light emitting diode (LE
D) has begun to be used as a light source for analytical instruments and medical instruments. Correspondingly, a light receiving element having photosensitivity even in a short wavelength region is required. As a general light receiving element, a photodiode is used.

[0003] Photodiodes include silicon (Si) photodiodes and gallium phosphide (GaP) corresponding to the wavelength range.
Photodiodes and gallium arsenide (GaAs) photodiodes are commercially available, and when detecting a relatively wide wavelength range from infrared light to infrared light, a pn junction type
Si photodiodes are used. A pn junction type Si photodiode is simple, inexpensive, and widely used.

[0004]

The light sensitivity and detection wavelength range of a pn junction type photodiode basically depend on the light absorption coefficient α of the material. The long wavelength limit of light sensitivity is determined by the optical gap of the material, while the short wavelength limit is determined by a balance between the light penetration length (1 / α) and the distance from the light receiving surface to the depletion layer. Narrow optical gap material such as Si (Si optical gap is 1.1e at room temperature
In a photodiode using V), in order to have light receiving sensitivity up to a short wavelength region, the light penetration length is short, so a pn junction is formed at a shallow position from the light receiving surface, and the depletion layer is extended to near the light receiving surface. There is a need. FIG. 7 is a graph of the spectral sensitivity of a conventional pn junction type Si photodiode for wide area photometry. As described above, even for a Si photodiode in which the pn junction is formed at a position shallow from the light-receiving surface for wide-range photometry from ultraviolet to visible light, the light-receiving sensitivity characteristic is 400 nm.
There is a drop in the following short wavelength side, and there is a problem when applied to wide area photometry.

The composition of the Al _x In _y Ga _1-xy N-based material can be controlled so that an arbitrary optical gap can be obtained in a wide range from 1.9 eV of InN to 6.2 eV of AlN. It has become possible to confirm from the epitaxially grown layer on the sapphire substrate that valence electrons can be controlled by adding the impurity. But Si
A photodetection semiconductor device using such a group III nitride as a substrate and having light sensitivity in a wide wavelength range from an ultraviolet region to an infrared region has not been realized yet.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photodiode suitable for wide-area photometry, which has high photosensitivity in a short wavelength region of 400 nm or less as well as a long wavelength region of a Si photodiode. It is.

[0007]

In order to achieve the above object, in a photodiode having a pn junction and performing photodetection by photocarriers generated in a depletion layer formed by the pn junction, the photodiode comprises: from the silicon substrate and the group III nitride of the second conductivity type of a first conductivity type _{(Al x in y Ga 1-} x- y N, provided that 0 ≦ x, y ≦ 1,0 ≦ x + y ≦ 1) and the layer Become
The light sensitivity on the long wavelength side due to the photocarriers generated in the depletion layer on the silicon side and the light sensitivity on the short wavelength side due to the photocarriers generated in the depletion layer on the group III nitride layer side shall be provided.

In a photodiode having a pn junction and performing photodetection by photocarriers generated in a depletion layer formed by the pn junction, a photodiode of a second conductivity type formed on a surface of a silicon substrate of a first conductivity type A first pn junction comprising a first conductive layer and a first conductive type silicon layer on the second conductive type silicon layer.
Group III nitride (Al _x In _y Ga _1-xy N, where 0 ≦ x, y
≦ 1, 0 ≦ x + y ≦ 1) layer and a second pn junction composed of a second conductivity type group III nitride layer, and a longer wavelength side due to photocarriers generated in a depletion layer of the silicon pn junction. And the photosensitivity on the short wavelength side due to photocarriers generated in the depletion layer of the group III nitride layer pn junction.

Preferably, a low-temperature buffer layer made of a group III nitride is interposed between the silicon substrate and the group III nitride layer. In the above method for manufacturing a photodiode, the group III nitride layer is preferably formed by molecular beam epitaxy. According to the present invention, since the group III nitride layer is formed on the Si substrate to form a hetero pn junction with Si, depletion layers are formed on both sides of the group III nitride and Si. II
Short-wavelength light incident from the Group I nitride side generates photocarriers in the Group III nitride depletion layer, and longer wavelength light transmits through the Group III nitride layer to generate photocarriers in the Si depletion layer. generate. Therefore, light sensitivity over a wavelength range in which both semiconductors have high light sensitivity can be realized by one junction.

Also, a pn junction made of Si and a group III nitride
In a tandem photodiode in which pn junctions are connected in series, longer-wavelength light passes through the group III nitride layer and reaches the pn junction of Si. The photodiode can realize light sensitivity over a wavelength range in which both semiconductors have high light sensitivity. Also, by changing the composition of Al _x In _y Ga _{1 -xy} N according to the application, the rising wavelength of the photosensitivity in the vicinity of 400 nm can be changed. X = 0 for GaN
When y is increased, the wavelength can be shifted to the longer wavelength side, and when y = 0, the wavelength can be shifted to the shorter wavelength side by increasing y.

Further, since a thin low-temperature buffer layer is formed on a Si substrate and then a group III nitride layer having a controlled conductivity type is formed, the crystallinity of the nitride layer is good and the life of photocarriers is long and the photodiode has a long life. Can be expected to have high light sensitivity.
This low temperature buffer layer is generally formed at 400 to 600 ° C. If there is no buffer layer, grain growth may occur in the group III nitride layer.However, although the buffer layer itself has poor crystallinity, it is a layer with good so-called "wettability". Thereby, grain growth in the group III nitride layer is suppressed.

Further, since each of the above-mentioned group III nitride layers is formed by molecular beam epitaxy (MBE), the composition and the controllability of the addition of impurities are good, and good crystallinity and optimization of photosensitivity can be performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An n-type GaN (Al _x In _y Ga
X = y = 0) in _1-xy N is formed and n-type GaN / p-type Si
A hetero pn junction consisting of FIG. 1 relates to the present invention.
FIG. 3 is a perspective view of an n-type GaN / p-type Si hetero pn junction photodiode. The layer configuration will be described according to the manufacturing process.

A p-type Si (1,1,1) having a carrier concentration of 10 ¹⁷ cm ^-3 .
1) A surface wafer was used as the substrate 1 of the first conductivity type. First, after cleaning the Si substrate with hydrofluoric acid, the substrate temperature was reduced to 8 in vacuum.
The temperature was set to 00 ° C., and preheating was performed for 1 minute to clean the surface. The following GaN layers were formed by molecular beam epitaxy (MBE). By lowering the substrate temperature to 500 ° C. and simultaneously irradiating Ga from the effusion cell and nitrogen radicals from the radical source, a low-temperature buffer layer 2a made of GaN and having a thickness of 1.2 nm was formed. Thereafter, the supply of Ga was stopped by closing the shutter of the effusion cell, and the substrate temperature was rapidly increased to 800 ° C. Then, the n-type GaN layer (the second conductivity type group III nitride layer 2b) is formed by simultaneously irradiating Ga and Si as a donor with nitrogen radicals, thereby forming an n-type GaN / p-type Si hetero pn junction. Was prepared. The layer thickness of the n-type GaN layer is 1 μm, and the carrier concentration is 1 × 10 ¹⁸ cm ⁻³ .

A group III nitride-side electrode 3 and a substrate-side electrode 4 were formed as ohmic electrodes at the n-type GaN / p-type Si hetero pn junction, respectively, to produce a photodiode. For electrode material, n-type GaN is Ti (50 nm thick)
/ Al (thickness 300nm), Si for Ti (thickness 100nm) / N
i (thickness: 400 nm) / Au (thickness: 300 nm). Both of these electrodes were formed by sputtering. In order to use the n-type GaN side as the light receiving surface, the GaN side electrode 3 was patterned in a square ring shape surrounding the light receiving surface, and the entire back surface of the Si substrate was used as the electrode surface.

On the other hand, sapphire is formed by a similar stratification method.
The n-type GaN was formed on a (0,0,0,1) plane substrate and the photocurrent was measured. For the measurement, a pair of ohmic electrodes were formed on the n-type GaN surface at intervals of 1 mm, and light was irradiated between the electrodes while a voltage of 5 V was applied between the electrodes. FIG. 2 is a graph showing the wavelength dependence of the irradiation light of the photocurrent of the n-type GaN layer on the sapphire substrate. It can be seen that the photocurrent sharply increases above the optical gap of GaN, that is, in the short wavelength region where the photosensitivity of the Si photodiode decreases.

FIG. 3 is a graph showing the wavelength dependence of the light sensitivity of the n-type GaN / p-type Si hetero pn junction photodiode according to the present invention. In the hetero pn junction structure, a large amount of interface states are formed at the interface between n-type GaN and p-type Si due to the lattice mismatch between GaN and Si.
Although no sharp rise in light sensitivity is observed above the optical gap, the light sensitivity in the long wavelength region is comparable to that of the Si photodiode, and the light sensitivity in the short wavelength region below 400 nm is shown in FIG. Obviously, the sensitivity is much higher than that of the Si photodiode. Example 2 A p-type GaN / n-type Si hetero pn junction photodiode having the opposite conductivity type in Example 1 was produced. Fig. 1
And the first conductivity type is n-type.

An n-type (1,1,1) having a carrier concentration of 10 ¹⁷ cm ^-3
The method for forming a group III nitride layer using a planar Si substrate is described in Example 1.
In the same manner as described above, p-type GaN was formed on a Si substrate. After the formation of the buffer layer, the substrate temperature was set to 720 ° C., and Ga, Mg as an acceptor, and nitrogen radicals were simultaneously irradiated to form p-type GaN. The layer thickness was 1 μm.
Similarly, a window was opened in the group III nitride side electrode.

In the same manner as in Example 1, a p-type GaN layer was formed on a sapphire substrate, and the photocurrent was evaluated. FIG. 4 is a graph showing the wavelength dependence of the irradiation light of the photocurrent of the p-type GaN layer on the sapphire substrate. Compared to the characteristics of n-type GaN shown in FIG. 2, the photocurrent in the long wavelength region is larger. However, similar to n-type GaN, the light sensitivity is larger than the optical gap of GaN, that is, the light sensitivity of the Si photodiode. It can be seen that the photocurrent sharply increases in the decreasing short wavelength region.

Also in this pn heterojunction photodiode, similar to the light sensitivity characteristic shown in FIG.
It was confirmed that the sensitivity was high in a short wavelength range. Example 3 As a photodiode having another layer configuration, a tandem photodiode in which a pn junction made of GaN was further formed on a pn junction made of Si was manufactured.

FIG. 5 is a perspective view of a tandem photodiode according to the present invention. The layer configuration will be described according to the manufacturing process. First, B was diffused into the n-type (1,1,1) plane Si substrate 1 by thermal diffusion, and a region about 1 μm from the surface was formed as a p-type layer (second conductivity type Si layer 1a). Then, a low-temperature buffer layer 2a having a thickness of 1.2 nm and an n-type GaN layer (first conductivity type group III nitride layer 2b) doped with Si are formed to a thickness of 1 μm under the same conditions as in Example 1 by MBE. Then, a p-type GaN layer (second conductivity type group III nitride layer 2c) doped with Mg was formed thereon to a thickness of 1 μm. After that, Ni (200
nm) / Au (300 nm) by sputtering,
After opening the window by patterning, in a nitrogen atmosphere 4
Heat treatment at 00 ° C for 10 minutes to form ohmic contact III
A group nitride side electrode 3 was obtained. On the other hand, on the Si side, a Ti / Ni / Au layer was formed by sputtering, and this was used as an ohmic substrate-side electrode 4.

FIG. 6 is a graph showing the wavelength dependence of the light sensitivity of the tandem photodiode according to the present invention. It can be seen that the adoption of the tandem type improves the photosensitivity of the photodiode in the wavelength region of 400 nm or less as compared with the Si photodiode by about four times.

[0023]

According to the present invention, in a photodiode having a pn junction and performing photodetection by photocarriers generated in a depletion layer formed by the pn junction, the pn junction is silicon of the first conductivity type. substrate and the group III nitride of the second conductivity type _{(Al x in y Ga 1-} xy N, provided that 0 ≦ x, y ≦ 1,0 ≦ x
+ Y.ltoreq.1) layer, and the light sensitivity on the long wavelength side due to the photocarriers generated in the depletion layer on the silicon side and the light sensitivity on the short wavelength side due to the photocarriers generated in the depletion layer on the group III nitride layer side. In the long wavelength region, the photosensitivity of the silicon photodiode is maintained, and in the short wavelength region, the sensitivity is higher than that of a silicon photodiode having a pn junction of only silicon caused by the group III nitride layer. Light sensitivity over a wide wavelength range can be obtained.

Also, the second conductive type silicon substrate
A tandem photodiode is formed by further laminating a first-conductivity-type III-nitride layer and a second-conductivity-type III-nitride on the first-conductivity-type silicon layer to form a tandem-type photodiode. By the same action as above, silicon
Both the pn junction and the group III nitride pn junction have high photosensitivity over a wavelength range where photosensitivity is high.

Further, since the group III nitride layer is formed on the Si substrate by MBE, the crystallinity is good, the control of the addition of impurities to the group III nitride is ensured, and the characteristics are good. A photodiode can be obtained. Further, the photodiode according to the present invention having a wide photosensitivity wavelength range has a wide range of application as a light receiving element of various optical devices requiring a spectroscope and other spectroscopic functions.

[Brief description of the drawings]

FIG. 1 is a perspective view of an n-type GaN / p-type Si hetero pn junction photodiode according to the present invention.

FIG. 2 is a graph showing wavelength dependence of irradiation light of photocurrent of an n-type GaN layer on a sapphire substrate.

FIG. 3 is a graph showing the wavelength dependence of the optical sensitivity of an n-type GaN / p-type Si hetero pn junction photodiode according to the present invention.

FIG. 4 is a graph showing wavelength dependence of irradiation light of photocurrent of a p-type GaN layer on a sapphire substrate.

FIG. 5 is a perspective view of a tandem photodiode according to the present invention.

FIG. 6 is a graph showing the wavelength dependence of light sensitivity of a tandem photodiode according to the present invention.

FIG. 7 is a graph of the spectral sensitivity of a conventional pn junction type Si photodiode for wide area photometry.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st conductivity type board | substrate (Si substrate) 1a 2nd conductivity type Si layer 2a Buffer layer 2b 2nd conductivity type group III nitride layer 2c 1st conductivity type group III nitride layer () 3 Group III nitride layer side electrode 4 Si substrate side electrode

Claims (4)

[Claims] 1. A photodiode having a pn junction and performing photodetection by photocarriers generated in a depletion layer formed by the pn junction, wherein the pn junction is a silicon substrate of a first conductivity type and a second conductivity type. Group III nitrides (Al _x In _y Ga _1-xy
N, provided that 0 ≦ x, y ≦ 1, 0 ≦ x + y ≦ 1) layers, and the photosensitivity on the long wavelength side due to the photocarriers generated in the depletion layer on the silicon side and the depletion on the group III nitride layer side A photodiode having both light sensitivity on the short wavelength side due to photocarriers generated in a layer. 2. A photodiode having a pn junction and performing photodetection by photocarriers generated in a depletion layer formed by the pn junction, wherein the second conductivity type formed on the surface of the first conductivity type silicon substrate is provided. A first pn junction made of a silicon layer of the first conductivity type, and
Group III nitride (Al _x In _y Ga _1-xy N, where 0 ≦ x, y
≦ 1, 0 ≦ x + y ≦ 1) layer and a second pn junction composed of a second conductivity type group III nitride layer, and a longer wavelength side due to photocarriers generated in a depletion layer of the silicon pn junction. A photodiode characterized by having both the above-mentioned photosensitivity and the photosensitivity on the short wavelength side due to photocarriers generated in the depletion layer of the group III nitride layer pn junction. 3. The photodiode according to claim 1, wherein a low-temperature buffer layer made of a group III nitride is interposed between the silicon substrate and the group III nitride layer. 4. The method for manufacturing a photodiode according to claim 1, wherein said group III nitride layer is formed by molecular beam epitaxy.