JP2001127336A - Electronic avalanche photodiode of absorption/ multiplication separation-type of high gain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture and provide the electronic avalanche photodiode of the absorption/multiplication separation-type of a high gain with the mild condition of a low processing temperature by using a comparatively simple manufacture process from an inexpensive material, and to provide a photodiode with high sensitivity and high response speed which is especially suitable as a device used for an optical communication system. SOLUTION: The electronic avalanche photodiode of the absorption/ multiplication separation-type of a high gain is formed of a substrate, an absorption layer which is formed on the substrate and is formed of amorphous silicon germanium (a-Si1-XgeX:H), a multiplication layer which is formed on the absorption layer and is formed of amorphous silicon (a-Si:H), and an electrode layer which is formed on the multiplication layer and is formed of aluminium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high gain absorption / multiplication separation type avalanche photodiode.

[0002]

BACKGROUND OF THE INVENTION Optical fiber communications is a new trend in the current telecommunications industry and it is anticipated that optical fibers will soon replace electrical cables and become the dominant communications medium.
The optical sensor is responsible for receiving and detecting an optical signal in the optical fiber communication system, the automatic control device, the computer terminal device, and the like. Various types of optical sensors have been developed, but in fields where high speed and high sensitivity are required, such as optical communication, so-called avalanche photodiodes (hereinafter abbreviated as APDs) have been used in the past. Known as one of the sensors.

[Problems to be solved by the invention]

A conventional electron avalanche photodiode is, for example, an absorption / multiplication separation type avalanche photodiode disclosed in 1984 by Capasso. F. in Electronics Letters, Vol. 20, No. 15, pp. 635-637. (SAM
APD, Separate Absorption and Multiplicatio
n) or, in 1991, Ravi Kuchibhotla et al.
ghtwave Technology, Vol. 9, No. 7, pp. 900-905
The avalanche photodiode (PIN) announced on the page
APD). However, they are mostly made of expensive II-VI or III-V materials, which have high material procurement costs and are difficult to obtain. Furthermore, these manufacturing processes, such as molecular beam epitaxy (MB
E, Molecular Beam Epitaxy (LPE), or Liquid Phase Epitaxy (LPE) is rather complicated, and the processing temperature in the manufacturing process of the member is quite high, which may adversely affect the properties of the member.
In view of these drawbacks, an object of the present invention is to find a new substitute, provide a product that can be manufactured at a low temperature, and provide an inexpensive product.

On the other hand, in 1990, JWHong et al.
tions on Electron Devices, Vol. 37, No. 8, 18
The amorphous silicon material disclosed on pages 04 to 1809 has advantages such as being inexpensive and being able to manufacture a large-area material at a relatively low temperature in the manufacturing process. Also, SBHwang et al. Reported on IEEE Transactions on Electron Dev.
The amorphous silicon material disclosed in ices, Vol. 40, No. 4, pages 721 to 726 has advantages such as no lattice mismatch phenomenon, easy modulation of the energy gap, and absorption of long wavelengths. However, up to now, no avalanche photodiode manufactured using an amorphous silicon material has been found. The present invention solves the above-mentioned disadvantages of the conventional avalanche photodiode, and uses relatively inexpensive amorphous silicon as a main material in a simple process under relatively mild conditions (for example, low processing temperature). An object of the present invention is to provide a high-speed, high-sensitivity avalanche photodiode which can be manufactured under a high speed.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a conventional avalanche photodiode and to an avalanche photodiode made of amorphous silicon which solves the problems in its manufacture. Specifically, by separating the absorption layer and the multiplication layer in the conventional avalanche photodiode, dark current (Dark Current) is reduced and the optical gain value is improved. The hole injection type absorption / multiplication separation type avalanche photodiode according to the present invention has a bias voltage of 16 volts (V) and a light irradiation power of 1.
In the case of μW, the optical gain value reaches 686,
Ideal for long distance optical communication applications. Also, in comparison with the high processing temperature of the conventional avalanche photodiode and the complicated manufacturing process and high material procurement cost, the present invention has a simple manufacturing process and a low processing temperature,
In addition, the present invention is advantageous in that it has advantages such as the ability to use low-cost raw materials, and is therefore economically rich.

That is, the present invention relates to a high gain absorption / multiplication separation type avalanche photodiode comprising a substrate and an amorphous silicon germanium (a-Si _{1 -X)} formed on the substrate. An absorption layer made of Ge _X : H), a multiplication layer made of amorphous silicon (a-Si: H) formed on the absorption layer, and an electrode layer formed on the multiplication layer. It is characterized by having. In a preferred embodiment, the substrate is formed by depositing a transparent conductive oxide on a glass plate.
Further, the absorbing layer is intrinsic to the n ⁺ type amorphous silicon (intr
Insic) amorphous silicon germanium is deposited and laminated, and the multiplication layer is formed by depositing and laminating intrinsic amorphous silicon material on n ⁺ type amorphous silicon. You. Further, the transparent conductive oxide is indium-tin-oxide (ITO). The amorphous silicon germanium (a-Si _1-X Ge _X :
The X value of the germanium atom content of H) is 0.48 or less, and by setting the value in this range, a light-receiving element that absorbs infrared light from red light having an absorption peak wavelength of 525 nm to 820 nm can be prepared. . The value of X is preferably from 0.05 to 0.45, particularly preferably from 0.10 to 0.40. The n ⁺ -type amorphous silicon of the absorption layer and the multiplication layer is formed by being laminated on the conductive oxide (ITO) thin film of the substrate and on the amorphous silicon germanium layer of the absorption layer, respectively. You.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The APD of the present invention can be manufactured as follows. A substrate made of a glass plate previously plated with indium tin oxide is cleaned and then cleaned with plasma-enhanced chemical vapor deposition (Plasma-Enhanced CV).
D) Set in the system, and in order, n ⁺ -a-Si: H / ia-Si
_1-X Ge _X : H / n ⁺ -a-Si: H / ia-Si: H / p ⁺ -a-Si: H 5 layers of amorphous silicon layer or amorphous silicon germanium layer,
Form. Finally, an electrode layer of aluminum or the like is formed by plating by thermal evaporation or the like as an electrode. This may be a disc having an area of about 1.8 mm ² . Note that plating here refers to plating in a broad sense in which a metal is deposited and deposited on a workpiece by means including vapor deposition, sputtering, and the like to form a metal thin film layer. FIG. 1 schematically shows the cross section of the detailed laminated structure of the APD of the present invention and the thickness of each layer.

A process for manufacturing an APD device (for example,
In PECVD, the processing temperature, pressure, and load power for high-frequency irradiation can be performed under the following conditions, respectively. (1) When growing ia-Si: H, 250 ° C., 1 Torr, 5 Torr
0Watt (2) When growing ia-Si _1-X Ge _X : H, at 250 ° C.
5 Torr, 40 Watt The growth gases are SiH ₄ (25% in H ₂ ) and SiH ₄ (25%
in H ₂ ) + GeH ₄ (47.8% inH ₂ ) may be used. The thickness of each layer can be controlled by the deposition rate. For example, ia-
The deposition rate of Si _1-X Ge _X : H is preferably 160 ° / min, and the deposition rate of ia-Si: H is preferably about 60 ° / min. Also, n ⁺ -a-Si: H or p ⁺ -
When growing a-Si: H, for example,
This can be performed by a known method using SiH ₄ + PH ₃ or the like.

The reason for using the ia-Si _1-X Ge _X : H material is that an absorption layer is formed by utilizing the characteristics of the low energy gap, thereby absorbing incident light to generate a photocurrent and emitting light. I do. The reason for using ia-Si: H as a multiplication layer is that
The photocurrent is increased by multiplying the avalanche effect by utilizing the characteristics of the high energy gap, and the optical gain value is improved. The present invention modulates the energy gap by changing the X value of ia-Si _1-X Ge _X : H to control the wavelength (particularly, peak wavelength) of light to be absorbed. The range of use can be adjusted as appropriate and adapted to the appropriate wavelength depending on the application and other factors.

The principle of operation of a hole incident type absorption / multiplication separation type electron avalanche photodiode suitable for the present invention will be described below with reference to FIG. First, a negative voltage is applied to the aluminum electrode end, and the indium tin oxide end is grounded. As can be seen from the Poisson equation, most of the bias voltage is applied to ia-Si: H. Then, another part of the bias voltage is applied to the ia-Si _1-X Ge _X : H layer. Incident light enters from the glass substrate side, ia-Si
_1-X Ge _X : Electrons absorbed by the H layer (ie, absorption layer)
Generates hole pairs. Then, these electron-hole pairs are effectively separated by the electric field applied to this layer, ie the holes are attracted to the negative voltage and migrate to the ia-Si: H layer (multiplier layer) . Then, under the influence of the avalanche effect by the large electric field, more electron-hole pairs are generated, and the holes move to the p ⁺ -a-Si: H layer, and at the same time, the electrons are n ⁺ -
Move to a-Si: H layer. After the electron-hole pairs are generated in this way, the injection of the separated holes into the multiplication layer from the absorption layer is the starting point of the electron avalanche phenomenon. It is referred to as an absorption / multiplication separation type avalanche photodiode (SAM APD). As can be seen from the above description, the present invention has the following advantages. (1) Optoelectronic (or optoelectronic) members can be manufactured by a simple manufacturing process and low procurement cost raw materials. In particular, amorphous silicon materials can be used to manufacture large-area optoelectronic members in addition to the low cost. In addition, a plasma-enhanced chemical vapor deposition (eg, PECVD) system can be used in the material growth process. For this reason, since the thin film layer can be grown at a relatively low temperature (250 ° C.), it is possible to avoid adversely affecting the characteristics of the member. (2) The multiplication layer is composed of a-Si: H material with a high energy gap, and most of the electric field is applied to this layer, so the multiplication avalanche effect can be greatly increased and the optical gain value is improved. it can. (3) The absorption layer is made of ia-Si _1-X Ge _X : H material with low energy gap, and only a part of the electric field is applied to this layer, so that dark current can be reduced effectively and thermal interference is avoided. Therefore, it is possible to prevent a photodetection error of the photodiode, and to obtain high sensitivity and high-speed sensitivity characteristics. (4) The energy gap can be easily modulated by changing the X value of ia-Si _{1 -X} Ge _X : H, so that light of different wavelengths can be absorbed, and the light receiving element can be used in various fields. Can be used for applications. Particularly, it is suitable for application to long wavelength optical communication.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an amorphous silicon
n ⁺ -a-Si: H / intrinsic amorphous silicon germanium ia-Si _1-X Ge
_X : H / amorphous silicon n ⁺ -a-Si: H / intrinsic amorphous silicon ia-Si: H /
A layer of amorphous silicon p ⁺ -a-Si: H is grown and formed in sequence on a pre-plated indium tin oxide thin film on a glass substrate.
In addition, the X value of ia-Si _1-X Ge _X : H is set to, for example, 0.3, and
The thickness of the ia-Si _1-X Ge _X : H layer is increased by 7000 ° according to the deposition rate.
To control. Further, the thickness of the ia-Si: H layer is controlled to 420 °. Finally, an aluminum electrode layer is formed as an electrode by thermal evaporation or the like, and the hole incident type absorption / multiplication separation type avalanche photodiode of the present invention is manufactured. FIG. 1 schematically shows a cross-sectional structure of the formed layer. The electron avalanche photodiode was irradiated with light, and it was measured that there was clearly a photocurrent as shown in FIG. At the same time, as shown in FIG. 3B, a comparative experiment was performed on a conventional multiplied electron avalanche photodiode. FIG.
(A) and (b) show a clear difference between the two diodes. In FIG. 3A, the horizontal axis represents the negative bias voltage (V) applied to the aluminum electrode by grounding the ITO, and the vertical axis represents the photocurrent (mA) obtained by irradiating light. The light irradiation power of the parameter is 100, 50, 20, 10, and 5 μW from top to bottom, and FIG. 3B also shows the result (ie, dark current) of 0 μW (no irradiation). The conventional multiplying avalanche photodiode used in the comparative experiment includes p ⁺ -a-Si: H (450 °), ia-Si
_1-X Ge _X : H (7000-11000 °), n ⁺ -a-Si: H (4
00 A) and aluminum (5000 A) were sequentially laminated and formed as electrodes, and a PIN APD was used. FIG. 4 shows the relationship between the light gain value (vertical axis) and the light irradiation power (horizontal axis) obtained by changing the light irradiation power at a negative bias voltage of 16 V and performing irradiation. . In addition,
Optical gain value (G) is a value defined by the following equation _{G = [(I p -I d} ) / q] / (P in / hν). Where I _p is the photocurrent under illumination, I _d
Is dark current, q is electron charge, P _in
Is the incident light power, and hν
Is the energy of the incident radiati
on). FIG. 4 shows that the optical gain value of the present invention (a) is the same as that of the conventional avalanche photodiode (PIN APD:
(b)) It turns out that it is larger. In particular, when the light irradiation power was 1 μW and the negative bias voltage was 16 V, the optical gain value of the present invention reached 686. The hole injection type absorption /
This characteristic of a multiply-separated electron avalanche photodiode is particularly suitable for use in long-distance optical communication.

FIG. 5 shows the relationship between the applied bias voltage and the optical gain value at a light irradiation power of 1 μW. From the figure, it can be seen that as the applied negative bias voltage increases, the corresponding optical gain value also increases. This increase in the negative bias voltage induces a multiplication avalanche effect in the multiplication avalanche layer (ia-Si: H layer), resulting in an increase in photocurrent and an improvement in the optical gain value. FIG. 6 shows the relationship between the applied bias voltage and the dark current. It can be seen that the dark current increases as the applied negative bias voltage increases. Care must be taken because increasing the bias voltage also increases the dark current of the member itself, which may cause a decrease in sensitivity. However, as can be seen from the experimental data of FIG. 6, when the negative bias voltage is 16 V, the dark current is only 25 μA, while the optical gain value is increased to 686 under the conditions of the light irradiation power of 1 μW and the negative bias voltage of 16 V. Therefore, the photodiode of the present invention satisfies conflicting requirements such as a low dark current and a high optical gain value.

By changing the X value of ia-Si _{1 -X} Ge _X : H, the energy gap can be easily modulated and light of different wavelengths can be absorbed. When the X value is changed from 0 to 0.48 from the experiment, the value of the absorption peak wavelength of the spectrum becomes 52
It was found to be between 5 and 820 nm. FIG. 7 shows that X =
It is a figure which shows the intensity | strength of sensitivity and the wavelength of an absorption spectrum in the case of 0.3, and the absorption peak value at this time is 700 nm (red light). FIG. 8 shows the results of a response speed experiment. As shown in the figure, when the negative bias voltage is 14 V and the load resistance is 14 kΩ, the rise time (the response time when light enters) is 143.5 μsec, and the fall time (the response time when the light is cut off) is 385. 5 μsec. Note that the response time is the time required for the voltage change between the 10% point and the 90% point when the difference between the maximum value and the minimum value of the voltage change is 100%.

[0015]

The present invention relates to an avalanche photodiode (APD) formed by separating an absorption layer and a multiplication layer using an amorphous silicon material and an amorphous silicon germanium material. Compared to APD, raw materials can be obtained easily and inexpensively, and can be manufactured by a relatively simple manufacturing process at a particularly low processing temperature.
PDs exhibit effects such as having characteristics such as low dark current and high light absorption gain. Optoelectronics equipment,
It is suitable and useful as a device used for an optical communication system such as an information highway.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a laminated cross section of a high-gain absorption / multiplication separation electron avalanche photodiode (SAM APD) of the present invention.

FIG. 2 is a schematic view showing an energy band and an electric field of a SAM APD according to the present invention and an operation principle thereof.

FIG. 3 is a characteristic curve diagram showing a correlation between a bias voltage and a photocurrent when light irradiation power is used as a parameter;
(A) is an example of a hole incident type SAM APD of the present invention, and (b) is an example of a conventional PIN APD.

FIG. 4 shows a SAM APD (a) of the present invention and a conventional PI
It is a figure which shows the comparison of the optical gain value corresponding to light irradiation power with NAPD (b).

FIG. 5 is a diagram showing a relationship between an optical gain value and a negative bias voltage of the SAM APD of the present invention.

FIG. 6 is a diagram showing a relationship between dark current and negative bias voltage of the SAM APD of the present invention.

FIG. 7 is a graph showing the wavelength of the absorption spectrum and the responsive intensity of the SAM APD of the present invention.

FIG. 8 is a diagram showing a response time of the SAM APD of the present invention at a negative bias voltage of 14V. Note that one horizontal axis is 100 μsec and one vertical axis is 100 mV.

[Explanation of symbols]

1 Aluminum layer 2 p ⁺ -a-Si: H layer 3 ia-Si: H layer 4 n ⁺ -a-Si: H layer 5 ia-Si _1-X Ge _X : H layer 6 Indium tin oxide (ITO) layer 7 Glass layer

Claims (7)

[Claims] 1. An absorption layer comprising a substrate and an amorphous silicon germanium (a-Si _{1 -X} Ge _X : H, wherein X represents the content of germanium atoms) formed on the substrate. And a multiplying layer formed of amorphous silicon (a-Si: H) formed on the absorption layer, and an electrode layer formed on the multiplying layer. Avalanche photodiode with gain absorption / multiplication separation. 2. The substrate according to claim 1, wherein the substrate is formed by depositing a transparent conductive oxide on a glass plate.
2. An avalanche photodiode of the high gain absorption / multiplication separation type described in 1. 3. The high gain absorption according to claim 1, wherein the absorption layer is formed by depositing intrinsic amorphous silicon germanium on n + type amorphous silicon.
/ Multiplication separation electron avalanche photodiode. 4. The high gain absorption according to claim 1, wherein the multiplication layer is formed by depositing intrinsic amorphous silicon on an n + type amorphous silicon material.
/ Multiplication separation electron avalanche photodiode. 5. A high gain absorption / multiplication separation electron avalanche according to claim 2, wherein the transparent conductive oxide is indium-tin-oxide (ITO). Photodiode. 6. An amorphous silicon germanium (a-Si _{1 -X} Ge _X :
The high gain absorption / multiplication according to any one of claims 1 to 5, wherein the X value of the germanium atom content of H) is 0.48 or less and absorbs red light or infrared light having a wavelength of 525 nm to 820 nm. Separate electron avalanche photodiode. 7. A high gain absorption / multiplication separation type electron avalanche photodiode according to claim 1, wherein the electrode layer is made of aluminum.