JPH0682859B2 - Static induction type semiconductor photodetector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photodetector having a high speed and high sensitivity based on the principle of an electrostatic induction transistor, and particularly for long wavelength optical communication because the long wavelength sensitivity is improved. It is used as a high-speed, high-sensitivity photodetector.

[Prior art]

As a conventional photodetector, an electrostatic induction phototransistor is particularly close to the present invention.

For example, Jpn. Pat. Appln. KOKAI Publication No. 62-18752 "Semiconductor photoelectric conversion device") In the static induction phototransistor, a pin diode distributed around the gate is used as a photodetector. Taking the n-channel as an example, holes among the electron-hole pairs generated by light are accumulated in the p ⁺ gate region, which causes a change in the gate potential, which causes the potential barrier height in the channel to be modulated. Therefore, the amplified current flowing between the source and drain is modulated by this gate potential change.
The optical amplification degree is very high, and the weaker the incident light intensity is, the higher the weaker the incident light intensity is, which is the opposite characteristic of the conventional bipolar phototransistor. The maximum optical amplification G _max is approximately Is represented by. Where n _S is the impurity density of the n ⁺ source region,
P _G impurity density of the p ⁺ gate region, D _m is the electron diffusion constant, D _p is the hole diffusion constant, W _G is the effective thickness of the potential barrier, L _P is the hole diffusion length, q Is the unit charge amount, K is the Boltzmann constant, T is the absolute temperature, V _biGS is the diffusion potential of the gate diode between the source and the source, and V _biG ^* _S is the height of the potential barrier height peak viewed from the source. An example of the general structure is shown in FIG. The p ⁺ region 62 diffused in the n ⁻ or p ⁻ high resistance layer 61 formed on the n ⁺ substrate 60 is a gate region, and the n ⁺ region 67 is a source region. The n ⁺ substrate 60 is the drain region. Reference numerals 64 and 65 denote a gate region and a source electrode, respectively. 63 is an insulator. The light penetrating by the incident light hν is mainly the electrons in the n ⁻ high resistance layer 61.
Generates hole pairs. Since the holes are accumulated in the p ⁺ gate region 62, an amplified signal is obtained between the main electrodes 65 and 66. The dimensions between the p ⁺ gates 62, the impurity density, and the dimensions of the n ⁻ layer 61 and the impurity density are selected so that a potential barrier is formed in the n ⁻ high resistance layer. In the conventional structure, the forbidden band width of the semiconductor in the high resistance layer region n ^- 61 and the p ⁺ gate region 62 and the n ⁺ substrate
The band gaps of the semiconductors forming 60 are all the same. That is, almost all regions are often formed of the same semiconductor. There are some examples of static induction transistors in which a heterojunction is provided in the gate region or the source region. In this case, when formed in a wider bandgap than the semiconductor gate region 62 in the semiconductor of the channel region, the gate 62 and channel n ^- heterojunction occurs in the bonding interface 61. If only the gate is formed of a semiconductor having a wide band gap and the other regions are made of the same semiconductor, the current amplification factor increases in a form integrated by the potential difference at the heterojunction interface. That is, the potential difference at the hetero interface comes into the content of the exponential term of the equation (1). Further, the current amplification factor increases even if a semiconductor having a wide band gap is used for the source region.
In FIG. 2, when the part of the n ⁺ substrate 60 is formed by the p ⁺ region, it becomes an electrostatic induction type photothyristor. Even if the n ⁺ region 67 is used as the drain region and the n ⁺ substrate 60 is used as the source region, it operates as a static induction transistor.

[Problems to be solved by the invention]

However, the present inventor has found an electrostatic induction type photodetector with higher speed and higher sensitivity.

[Means to be Solved by the Invention]

By using a semiconductor with a narrower bandgap than the gate and drain regions in the high-resistance layer region between the gate and drain, long-wavelength sensitivity is increased, and a photodetector with increased optical amplification of the static induction transistor Become. Further, since a stronger electric field can be generated with the same thickness and the same voltage in the semiconductor portion having the narrower forbidden band width than in the case where the conventional forbidden band width is formed, an avalanche electric field is applied. As long as you choose dimensions, voltage, impurity density, etc.
Light is received at high speed and with high sensitivity at D, and signal amplification is further performed at the electrostatic induction transistor section. Further, the structure of the present invention has sufficiently high sensitivity and high speed even if the electric field strength is not so high as to give an avalanche electric field.

[Action]

As mentioned above, the gate of the conventional static induction phototransistor
If the high resistance layer portion between the drains is formed of a semiconductor having a narrow band gap, a strong electric field is easily generated between the gate and the drain. When an avalanche electric field is reached, carriers multiplied by collisional ionization of carriers travel in a strong electric field. Taking the case of an n-channel static induction transistor as an example, the multiplied holes are accumulated in the p ⁺ gate region, and the multiplied electrons are partly at the heterojunction interface between the high resistance layer and the anode region. Accumulated. holes stored in p ⁺ gate region in order to positively charge the p ⁺ gate region, will be the gate of the static induction transistor is forward biased, the potential barrier in the channel is reduced. Along with this, electrons are injected from the n ⁺ source region to the high resistance channel region, and holes as an optical signal multiplied by the avalanche electric field amplify a larger number of electrons to cause a gap between the source and drain. The signal output is obtained.

〔Example〕

 FIG. 1 shows an embodiment of the present invention.

Region 21 indicates a drain or anode region, which is a main electrode region formed as an n ⁺ region or p ⁺ region, and n ⁺
If it is a region, it operates as a static induction phototransistor,
If it is in the p ⁺ region, it operates as an electrostatic induction photothyristor. For example, n ⁺ InP or p ⁺ InP is used as the material.
The region 20 is a drain or anode electrode, and the electrode material is an alloy such as Au-Ge-Ni for n ⁺ InP and Au-Zn-Ni for p ⁺ InP. The region 22 is a high resistance layer formed of a semiconductor having a small forbidden band width, which is a feature of the present invention. For example, InGaAs is used. The region 24 is also a high resistance layer, but is a semiconductor layer different from the region 22 and having a wider forbidden band than the region 22. For example, n ^- InP is used. p ⁺ region 25
Acts as a gate of an electrostatic induction phototransistor or an electrostatic induction photothyristor, and is formed of, for example, p ⁺ InP. The n ⁺ region 28 acts as the source region of the static induction phototransistor or the cathode region of the static induction photothyristor, and is formed of, for example, n ⁺ InP. Region 26 is an insulating optical antireflection coating. The region 27 is a gate electrode, and is formed of, for example, Au-Zn-Ni for p ⁺ InP. The region 29 is an electrode of the n ⁺ region 28, and is formed of Au-Ge-Ni for n ⁺ InP, for example. The light hν enters from the surface of the p ⁺ gate region. The high resistance layer regions 24 and 22 correspond to the i layer portion of the p-i-n diode formed between the p ⁺ gate region 25 and the n ⁺ region 28 or between the p ⁺ gate region 25 and the high impurity density region 21. . The high resistance layer regions 24 and 22 are gate electrodes 27.
The dimensions and the impurity density are selected so that the voltage is almost depleted by the voltage applied between the one main electrode 29 and the other main electrode 20. Further, a potential barrier is formed in a part of the high resistance layer portions 24 and 22 sandwiched by the p ⁺ gate 25 as viewed from the n ⁺ region 28, and its height is between the voltage of the gate electrode 27 and the n ⁺ electrode 29 and the electrode 20. The size and impurity density between the p ⁺ gate regions 25 and the thickness of the high resistance layers 22 and 24 are selected so as to be changed by the electrostatic induction effect due to the voltage of. Other regions 24, 25 as the high resistance layer region 22,
By using a semiconductor having a narrower band gap than 21 and 28, the sensitivity in the long wavelength region of the wavelength of light incident from the surface is increased. Since a strong electric field is more likely to occur, p ⁺ (25) n
^{- (24) n - (22} ) n + or p ⁺ (21) dimensioned to avalanche electric field is generated in the region of 22 between the static an impurity density and the like are distributed around avalanche photodiode of the gate if selected An inductive photodetector will be formed.
An optical signal received at high speed and with high sensitivity by the avalanche diode formed between the p ⁺ gate 25 and the high impurity density region 21 is extracted from between the main electrodes 29 and 20 as a further amplified signal. Electron-hole pairs are generated in the almost depleted high resistance layer regions 22 and 24, of which holes are p ⁺ gate regions.
N ⁺ region accumulated in gate 25 by the electrostatic induction effect of gate 25
The height of the potential barrier generated near 28 changes. A p-type semiconductor may be used instead of the high resistance region 24. If the p-type region is completely depleted, the operation is equivalent to that of the static induction phototransistor, but if the p-type region has a neutral region remaining, it becomes a bipolar phototransistor. When the substrate 21 is p ⁺ type, it becomes a photothyristor.
Alternatively, the entire high resistance layer region 24 or a part near the region 22 may be formed of a semiconductor (for example, n ⁻ InGaAs) having a narrow bandgap like the high resistance layer region 22. The high impurity density region 21 has the same conductivity type as the gate region 25 (in the example of FIG. 1,
In the case of p ⁺ ), the embodiment of FIG. 1 operates as an electrostatic induction photothyristor. In this case, the hetero interface between the region 21 and the region 22 having a narrow forbidden band is a region where electrons among electron holes generated by light are accumulated. More holes are amplified by this accumulation of electrons and more holes are transferred from p ⁺ region 21 to region 22.
Will be injected into. Although InP-InGaAs is shown as an example of the semiconductor forming each part, the present invention is not limited to this, and other binary systems such as GaAs-GaAlAs and GaAs-InGaAsP,
A combination of ternary and quaternary compound semiconductors may be used.
Although the planar gate structure is shown in the embodiment of the present invention, the gate may have a buried gate, a cut gate, a MOS (MIS) gate, a hetero gate, or a Schottky gate.

〔The invention's effect〕

The electrostatic induction photodetector according to the present invention is mainly characterized by using a semiconductor having a narrow forbidden band between the gate and the drain or the gate and the anode. Has increased long wavelength sensitivity. Furthermore, since it becomes easy to increase the electric field strength in this region, if the avalanche electric field strength is reached, light can be received at high speed and high sensitivity by the avalanche diode between the gate and drain or the gate and anode. Higher speed and higher sensitivity than the electric induction type photodetector.

The present invention provides a photodetector for long-wavelength optical communication that is easy to manufacture using a conventional manufacturing method such as a MOCVD method, an optical CVD method, an optical epitaxial method, and a molecular layer epitaxial method, and has high speed and high sensitivity. Therefore, it has high industrial value.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows an example of a sectional structure of a conventional static induction photodetector. 20 …… Main electrode that serves as drain or anode, 21 ……
n ⁺ or p ⁺ high impurity density region, 22 …… high resistance layer with a narrower band gap than other regions, 24 …… high resistance layer, 25
...... Gate diffusion region, 28 …… Source or cathode region, 29 …… Source or cathode electrode, 26 …… Insulating optical antireflection film, 27 …… Gate electrode.

Claims (1)

[Claims] 1. A semiconductor substrate having a second high resistance layer and a first high resistance layer having a band gap smaller than that of the substrate in this order, and a heterojunction provided between each region. A first conductivity type high impurity density gate diffusion region formed in the first high resistance layer, and a second diffusion layer formed in the first high resistance layer sandwiched by the gate diffusion region. A first main electrode region formed of a high impurity density region of a conductivity type opposite to the gate diffusion region and a first main surface on which the gate and the first main electrode region are formed are provided on the opposite side. A second main electrode region formed of a first or second conductivity type high impurity density region forming a junction surface with the second high resistance layer, and a second main electrode region formed on the first and second main electrode regions. An insulating property formed on the first high resistance layer including the first and second electrodes and the gate diffusion region; An optical antireflection film and a gate electrode formed on the gate diffusion region, and only the semiconductor forming the second high resistance layer has a forbidden band width smaller than the forbidden band width of the semiconductor in other regions. Formed by a semiconductor which has a size of each part so that an avalanche electric field is easily generated by a voltage applied to the second main electrode region and the gate region,
And in the first high resistance layer or in the first and second high resistance layers, the voltage between the gate diffusion region and the first main electrode region and the voltage between the gate diffusion region and the second main electrode region. A potential barrier is formed by the voltage so that the first and second high resistance layer regions are almost depleted, and the height of the potential barrier is changed by the potentials of the gate diffusion region and the second main electrode region. The electrostatic induction photodetector is characterized in that the majority carriers flowing between the first and second main electrodes are controlled by the height of the potential barrier.