JPH02303073A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain a photodetector of low noise, high sensitivity, and high speed, by forming, in order, a layer whose forbidden bandwidth is smaller than that of a multiplying layer and a layer whose forbidden bandwidth is larger than that of the multiplying layer, on the light incidence side, and making the width of a depletion layer be the whole region of the small forbidden bandwidth layer and a region reaching a part of the multiplying layer. CONSTITUTION:From the surface of a layer 36 to a substrate 31, a conical stand is etched, and an SiNx film 37 is stuck on the surface; a P-type electrode 38 is formed on the whole surface of the rear of the substrate 31; a ring-shaped N-type electrode 39 is formed on the upper surface of the layer 36. While projecting light from a light receiving window inside the electrode 39, a backward voltage is applied between the electrodes 38, 39. Layers 32-35 turn to depletion layers, and the greater part of light absorption is executed by the layer 35. The layers 32, 33 act as multiplying layers. The layer 36 turns to a window layer for transmitting light, and the layer 31 turns to a transmitting layer for the component which has not been subjected to light absorption. The layer 34 acts as a relaxation layer for adjusting electric field intensity distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor light receiving device IVt used in optical communications, and particularly to a device having a structure suitable for high sensitivity and high speed.

C. Prior Art] An example of the AjlGaSb avalanche photodiode is published by IEE, International Electronics Devices Meeting 88. (198
8th year) pp. 487-490 (IEEE, IEDM
88 (1988) Yen, 487-490). This conventional device is an n-type 0aSb
n3 on the board! :1Ga5b%, low carrier concentration, n-type and p-type iGat-8sb (x40.05) layer stacked in a single structure, the signal light is p-type A.
irradiated from the fi G a S b layer side, p and n
It is absorbed by the AQGaSb layer or the n-type GaSbM layer and generates electron-hole pairs. Electrons and holes are caused by the electric field applied between the electrodes, respectively, to the substrate side and the PA Q GaSb
It is possible to move laterally and cause a multiplication effect within the n-type A n GaSb layer. As a result, it is possible to amplify high-speed signals, and it is intended to be used for long-distance transmission.

[Problem to be solved by the invention]

In the conventional device described above, the region to which an electric field is applied, called the depletion layer, is only the n-type AΩGaSb layer that has a multiplication effect, and the layer on the surface where the optical signal is incident and the layer on the substrate side have a depleted bandgap. It has a value that is the same as or very close to the forbidden band width of the layer. As a result, in the wavelength range of 1 to 1.6 μm used in optical communications, not only the depletion layer but also the
p-type A Q, which is a region with high carrier concentration other than region b
Light absorption also occurs in the xGaz-xsb (x 40-05 ) layer, generating electron-hole pairs. Also, p and n
When the A Q GaSb layer of the mold is thin, the GaSb layer also absorbs light and generates electron-hole pairs.

As a result, the conventional device has the following problems.

■Mixing of electrons and holes occurs due to light absorption in the multiplication layer, and holes and electrons are simultaneously generated in the multiplication layer from adjacent regions of the GaB and p-type AQ GaSb multiplication layers. (mixed injection).

The ionization rate ratio decreases and noise increases.

■A region to which no electric field is applied, excluding the region very close to the multiplication layer, i.e., the p-type A n GaSb layer and the GaSb layer.
Efficiency is low because light absorbed by most of the layer is not converted into an electrical signal.

■p-type ^Q GaSb and GaS with no electric field applied
Among the electrons and holes generated in b, those in the vicinity of the multiplication layer enter the depletion layer and are converted into electrical signals, but it takes time to reach the depletion layer, reducing the response speed. .

The present invention solves the above problems and provides a low-noise, high-sensitivity, high-speed light receiving device.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

■At least two layers are formed in order on the side of the light incident direction when viewed from the A Q GaSb layer (multiplier layer) that has a multiplication effect, one with a smaller band gap and the other with a larger band gap than the multiplier layer. However, the depletion layer has a structure whose width is the entire region of the layer with a small forbidden band width and a region extending to at least a part of the multiplication layer.

■In addition to the above (■), at least one layer with a wider forbidden band width than the layer with a smaller forbidden band width in (2) is formed on the side opposite to the direction of light incidence when viewed from the multiplication layer, and the depletion layer is A structure whose width is a region extending to at least a part of a layer multiplication layer with a small forbidden band width.

The above configuration will be explained using FIG. 1 and FIG. 2. In FIG. 1, l is a substrate, 2 is a multiplication layer, 3 is a layer with a smaller forbidden band width than 2, and 4 is a layer with a larger forbidden band width.

Furthermore, in FIG. 1, the light is incident from the surface 5.

Here, the depletion layer is at least the entire thickness of the layer 3 with a small forbidden band and the vicinity of the layer 3 of the multiplication layer 2.

Note that the substrate 1 may have any composition, and if light is to be incident from the substrate side, the first layers 2 to 4 are formed so as to be reversed.

In the above, there may be a layer between layers 2 and 3, and between layers 3 and 4, the size of which is equal to or larger than the middle of the respective prohibited band widths.

In FIG. 2, 21 is a substrate, and 23 is a multiplication layer.

24 is a layer whose forbidden band width is smaller than that of the multiplication layer 23;

25 is a layer with a large forbidden band width, and 22 is a layer with a larger forbidden band width than the layer 24. In FIG. 1, light is incident from the surface 26 of the layer 25.

When the light is incident from the substrate 21 side.

Layers 22-25 are formed in reverse order. Here, the depletion layer includes at least a region from the upper surface of the layer 24 with a small forbidden band width to the lower surface of the multiplication layer 23.

In the above, there may be a layer between each layer having a size equal to or larger than the middle of each forbidden band width, or the forbidden band width may change continuously.

[Effect]

In the structure of the present invention, the layer with a large forbidden band width located on the light incident side is almost transparent to the signal light and acts as a window layer that transmits the signal light to the layer with a small 1M bandgap width.

A layer with a small width (+t, f-) absorbs signals and acts as a light absorption layer that generates ta atoms and holes. Since the light absorption layer is included in the depletion layer, each of the generated electrons and holes immediately starts to move vJ.

The above configuration differs from the conventional example in the following points.

■Since light absorption does not occur in layers other than the depletion layer, there is no diffusion component with slow response speed.

(2) Due to the presence of the light absorption layer, a small amount of light enters the multiplication layer, so fewer electrons and holes are generated due to light absorption within the multiplication layer, and a decrease in the ionization rate ratio can be prevented.

■Since the forbidden band width of the light absorption layer is small, the light absorption coefficient can be increased, so the light absorption efficiency is higher than conventional ones.

(2) Due to the effect (2) above, the layer thickness can be made thinner than in the past, so the response speed can be increased.

Further, by providing a separate layer with a large forbidden 4'rF width on the side opposite to the light incident side, the following advantages can be obtained. In other words, most of the signal light is absorbed by the light absorption layer, but 100% absorption cannot necessarily be achieved.If the wavelength of the signal light is longer than the wavelength determined by the forbidden width of the multiplication layer,
Light passes through the multiplication layer and eventually reaches the outside of the depletion layer.Similar to the left, if the outer region of the depletion layer is composed of a material with a smaller forbidden band width than the multiplication layer, light absorption occurs. Electrons and holes generated near the depletion layer cause a decrease in response speed. However, in the structure of the present invention, a layer with a large forbidden band iJ exists in the vicinity of the depletion layer or is included in the depletion layer, so light absorption and generation of electron-hole pairs in the vicinity of the depletion layer are prevented. This can eliminate deterioration in response speed.

〔Example〕

<Example 1> This will be explained using FIG. 3. First, in Figure 0 where the crystal structure of Figure (a) was created, 30 is a GaSb substrate (p type, 1
'X I O"cm-"), 31 is ^Q o, a
Gao, 5sbo, *aAso, on (p type, lX1
0"・am""6゜3μm), 32 is A Q o, oa
Gao, 5ysbCP type lXl0"Ql-', 0.5
p m), 33 is A m o, oaGao, ey
S b (n-type 2X10"Ql-', 1.5 μm), 3
4 is A Q o, 1Gao, oaSbo, e7Aso,
oa (n type, lXl0"e1m""g, 0.4 layer m)
, 35 is In5bo, t^so, s (n-type IXIO16
Gm-", 2μm), 36 is AQo, aGa
o, esbo, eIIAso, os (n type, I
0" am - 2 μm), and layers 31 to 36 were all formed by a solution growth method. Note that the forbidden band width is
6 is 1.2 eV, layers 32 and 33 are 0.7 eV, and layer 36 is 1.2 eV. OeV, 1ej35 is 0.3eV.

The above crystal was processed as shown in FIG. 3(b) to form a light receiving device. That is, from the surface of the first layer 36 to the substrate 31, a truncated cone having a diameter of approximately 80 μm is coated, and then the substrate 3
A p-type electrode 38 made of a TiAu layer is formed on the entire surface of the back surface of the layer 1. A ring-shaped n layer of AuGeNiAu is formed on the top surface of the layer 1 36.
Type electrode size 9 (outer diameter 60pm.

A width of 10 μm) was formed.

The inner diameter part of the n-type electrode 39 is a light receiving window, and the electrode 38.3 receives 2 μW of light with a wavelength of 1.55 μm from the inner window.
When a reverse voltage was applied between 9 and 9, a photocurrent of 1.5 μA was obtained at a voltage of 8, a multiplication factor of 40 was obtained at a voltage of 30 V, and a band/multiplying stack of 80 GHz was obtained. Further, the ionization rate ratio calculated from excess noise was 6.0.

In this light receiving device, the depletion layer is in the range of layers 32 to 35,
Most of the absorption of light takes place in layer 35, which acts as a light absorption layer, layers 32 and 33 act as multiplication layers, layer 36 is a window layer that transmits light, and layer 31 is a light absorption layer. This is a permeable layer for components that have not been exposed to heat. Note that kII34 acts as a relaxation layer for adjusting the 1-field intensity distribution.

In the device not according to the present invention, the light absorption layer area/multiplication factor was 65 GHz, and the ionization rate ratio was only 5.0.

<Example 2> In the device shown in Example 1, the manufacturing method for the device without the light transmission layer of layer 31 is the same as that described above, and in the device shown in Example 1, the band multiplication The vehicle capacity is 75 (3
Hz, which is worse than that with a transmission layer 36,
Better results were obtained than with the conventional device IT.

<Example 3> This embodiment will be explained using FIG. 4.

In the figure, 40 is a GaSb substrate (n type, 1×10”c
m-ri, 41 is A no, aGao, esba, es
Aso, os (n type, lX10"cm""ae 2μm
), 42 is In5bo, 1Aso, e (n-type lXl
0"ell""", 2μm), 43 is ^Q o, zGa
o, asbo, 5yAso, oi (n type, 3XlO"l
-8,0,4pm), 44 is A Q o, oaGao,
*tsb (n type.

3.5 μm), 45 is A Q o, aGao, asbo
, asAso, oa (n type, 2 μm) and one layer 41~
45, Zn was thermally diffused from the surface of the zero-order first layer 45 grown by the solution growth method, and the range from the top of the layer 44 to a depth of 0.5 μm was made p-type. This was processed into the shape shown in the same figure (b). Here; 44' is p-type A Q
o, oaGao, e7Sb layer, 45' is p-type A Q oaaGao, esbo*esAso*oa. After forming a hole 46 (40 μm in diameter) by etching from the back surface of the substrate 40 to the first layer 41, a cylindrical mesa etching with a diameter of 80 μm is performed from the surface of the layer 45' to the substrate 40, and a SiNx film is formed on the surface. 47 was applied. Furthermore, an n-type electrode 48 made of AuGeNiAu was formed on the back surface of the substrate 40, and a p-type electrode 49 made of AuZu was formed on the surface of the layer 45'. Wavelength 1.55μm from hole 46
When a reverse voltage was applied from both electrodes while injecting a laser beam with a photoelectric power of 2 μW, good characteristics such as a multiplication factor of 40, a band, a multiplication stack of 80 GHz, and an ionization rate ratio of 6 were obtained at a voltage of 30 V.

<Example 4> In the device having the structure shown in Example 1 and the conventional device F't, the dependence of the operating characteristics on the wavelength of the signal light was investigated.

As a result, the device of the present invention has a wavelength of 1.2 μm to 2.5 μm.
In the range of 1.m or more, the photocurrent at a multiplication factor of 1 is 1.
5-1.4 μA was obtained. Also, the band/intussusception is 78~
The 82 GHz ionization rate was also very constant, ranging from 6 to 5.3. On the other hand, the photocurrent in the conventional device has a wavelength of 1.2
0.3μA at μm, 1.0 at 1.55pm
No photocurrent was generated at μA and wavelength of 2.5 μm.

Moreover, the band/intussusception was 45 to 65 GHz, and the ionization rate ratio was also 4 to 5. As a result, it was found that the structure of the present invention has a wide wavelength range and constant characteristics.

(Effects of the Invention) According to the present invention, a light-receiving element having good characteristics such as high response speed, high sensitivity, and low noise in a wide wavelength range can be obtained.

As a result, by using one device, it can be used for long-distance, large-capacity communication 8 for signals of various wavelengths.

Note that if the structure of the present invention satisfies the combination of bandgap widths other than those shown in the embodiments, I n =G a - A n
-A s -P -S b, etc. can be freely combined. In addition, the pn junction is a multiplication layer A
It goes without saying that it does not need to be in the Qo, osGao, and 5ysb layers, and furthermore, the device may have a planar shape.

[Brief explanation of drawings]

1 and 2 are vertical cross-sectional views of a crystal for explaining the present invention in detail, FIG. 3 is a vertical cross-sectional view of a crystal and a device according to an embodiment of the present invention, and FIG. 4 is a vertical cross-sectional view of a crystal and a device according to an embodiment of the present invention. FIG. 3.24, 34, 42...layer with small forbidden width, 2°23.32,33.44...multiplying layer, 4,22°26
．． 31, 36, 41.45...layer with large prohibited band width,
34.43... Layer that adjusts electric field strength. Figure 1 Figure 3 Ward (a, n (b) Figure 2 A Akira 40 (α) (b) q

Claims (1)

[Claims] 1. At least two layers, a layer with a smaller forbidden band width and a layer with a larger forbidden band width than the multiplication layer, are arranged in order on the light incident side of the multiplication layer mainly composed of AlGaSb. A semiconductor light receiving device characterized in that: 2. The semiconductor light-receiving device according to claim 1, characterized in that a layer having a wider forbidden band width than the multiplication layer is formed on the side opposite to the light incident side of the multiplication layer. 3. A communication system device comprising the light receiving device according to claim 1 or 2. 4. A semiconductor light-receiving device that converts an optical signal into an electrical signal, comprising a light absorption layer that absorbs the optical signal and generates electrons and holes, and a depletion layer including the light absorption layer, and the depletion layer A semiconductor light-receiving device characterized in that it is configured so that optical signals are not absorbed outside the semiconductor light-receiving device. 5. A window layer for transmitting optical signals to the absorption layer on the light incidence side of the depletion layer, and a multiplication layer for multiplying electrons and holes on the side opposite to the light incidence side of the absorption layer. 5. The semiconductor light receiving device according to claim 4, further comprising a semiconductor light receiving device.