JPH0821726B2 - Semiconductor photodetector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a semiconductor photodetector.
It is used as a light receiver for optical communication.

[Conventional technology]

Conventionally, pin photodiodes, avalanche photodiodes (APDs), etc. have been used as photodetectors for optical communication. In addition, heterojunction phototransistor (HPT), Modulated Barrier Photodiode (MBP), majority carrier camel diode (Majority Carri
er Camel Diode), Triangular Barrier Photodiode (TBP)
Development of new devices such as

Further, a photodetector having a transmission base type transistor having a transmission base of a Schottky barrier junction for generating a photovoltaic as an amplification stage is described in Japanese Patent Application Publication No. 59-500539.

[Problems to be solved by the invention]

The characteristics of the photodetector for optical communication are required to be high speed, high photosensitivity, low noise and the like. The conventionally used pin photodiode has a high S / N ratio but does not have an amplifying function inside, so it is often used in combination with JFET, etc.
Avalanche photodiodes (APDs) each have the problem of high noise. In addition, HPT, MBP,
Majority Carrier Camel Diode (Majo
rity Carrier Camel Diode), TBP, etc.
Although the operation of the conventional bipolar phototransistor is developed, in both cases, the potential distribution in the base is uniform in the plane perpendicular to the plane in which the current flows,
The high frequency gain is determined by the base resistance component. That is, the value of the base resistance in the extremely thin base is a very large value, which limits the high frequency gain.

Further, a photodetector having a transmissive base type transistor having a transmissive base of a Schottky barrier junction that generates a photoelectromotive force in an amplification stage is an excellent photodetector that operates with higher sensitivity and higher speed than any of the above configurations. However, there is room for improvement for higher speed and higher sensitivity.

In the semiconductor photodetector according to the present invention, further improvement in characteristics can be expected over these devices.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention uses an electrostatic induction phototransistor (hereinafter referred to as SIPT) whose gate is formed of a Schottky electrode or a non-uniform base bipolar phototransistor. That is, in the base or the gate channel in the plane perpendicular to the plane through which the current flows, the potential distribution is provided with a non-uniform portion at a constant cycle, and the potential of the portion where the current most easily flows is set to the Schottky electrode junction interface. This is because it is partially controlled by electrostatic induction with the electric potential of. At the same time, as an element structure that forms a high impurity density p ⁺ region instead of the n ⁺ drain region, the electrons in the electron-hole pairs generated by light in the high resistance channel region accumulate at the p ⁺ / i junction interface, It is possible to promote hole injection from the p ⁺ region and to have higher photosensitivity.

[Action]

FIG. 4 shows a schematic cross-sectional structure diagram and potential diagram of a SIPT having a gate formed of a Schottky electrode according to the present invention. FIG. 4 (a) is a schematic sectional view of the unit element structure of the Schottky gate SIPT, and FIG. 4 (b) is FIG. 4 (a).
Potential diagram along AA 'and BB' of Fig. 4 (c) is
FIG. 4 is a potential diagram in the CC ′ direction of FIG. Fourth
In FIG. 5A, 501 is a source region formed of a high impurity density n-type semiconductor, 502 and 504 are high resistance regions formed of an intrinsic semiconductor or a low impurity density n-type semiconductor, and 505.
Is a drain region formed of an n-type semiconductor having a high impurity density, 503 is a channel region formed of an intrinsic semiconductor or an n-type semiconductor having a low impurity density, and 506 is 502, 503, 504.
Is a metal gate electrode forming a Schottky junction with the semiconductor region. 511 is a drain electrode and 512 is a source electrode. The n ⁺ source region 501 is grounded and the n ⁺ drain region 505 is connected to the drain bias voltage via the load resistor R _L 508.
Biased to V _DD 509. 510 is the true gate point G ^* , which is the saddle point of the potential created in the channel. The gate 506 is open, but there is also a biasing circuit.

In FIG. 4 (b), the solid line AA 'is shown in FIG. 4 (a).
The potential along AA 'and the solid line BB' is shown in Fig. 4 (a).
It is a potential diagram along BB 'of. FIG. 4 (b),
In (c), E _CS , E _CG , E _CG ^* , and E _CD represent the energy of the conduction band at the n ⁺ source region 501, the gate Schottky junction surface, the true gate point G ^* , and the n ⁺ drain region 505, respectively. Shows. Also, E _VS , E _VG , E _VG ^* , and E _VD are respectively
The energy of the valence band at the n ⁺ source region 501, the gate Schottky junction surface, the true gate point G ^* , and the n ⁺ drain region 505 is shown. The dotted line in the potential diagram is the potential when the SIPT is illuminated with light.

Now, from the surface of the Schottky gate SIPT shown in FIG. 4 (a), the penetration depth is about the thickness of the high resistance regions 502, 503, and 504, and the energy is equal to or larger than the band gap of the semiconductor forming the Schottky gate SIPT. Let's say that the light of. This incident light generates an electron-hole pair in the high resistance region of the SIPT, the generated electron 522 flows to the n ⁺ drain region by the electric field, and the hole 523 is at the Schottky junction surface with the lowest potential for the hole. Accumulated. Reference numeral 524 in FIG. 4 (c) indicates accumulated holes. The accumulated holes reduce the potential of the Schottky junction surface. As a result, the potential of the true gate point G ^* is also lowered, and the n ⁺ source region 501 to the channel region 503 are reduced.
Electrons are injected through. A current obtained by amplifying the optical signal flows through the above process. The amplification factor in this case can be expressed by the following equation by the ratio of the number of incident photons and the number of changes in the electrons flowing between the source and the drain.

In equation (1), G is the optical gain, ΔJ _L is the change in the current flowing between the source and drain due to the incident light, Pi is the light energy irradiated on the device surface, η is the quantum efficiency, and ν is the incident The frequency of light, h is Planck's constant, and q is the unit charge amount. In Schottky gate SIPT with open gate operation, the maximum optical gain is G _{max in the} limit where the photocurrent generated by light is smaller than the dark current.
Becomes G _max can be approximately expressed by the following equation.

G _max (n _s / p _G ) {(D _n / W _G ) / (D _p / L _p )} ・ exp {(q / kT) (V _biGS −V _biG ^* _S )} (2) (2) ), N ₂ is the electron density in the n ⁺ source region, p _G is the hole density in the gate region, D _n is the electron diffusion constant, D _p is the hole diffusion constant, and L _p is the hole diffusion length. , W _G is the effective channel width, V _biGS is the potential between the Schottky gate junction surface and the n ⁺ source region, and V _biG ^* _S is the potential between the true gate point and the n ⁺ source region. k is the Boltzmann constant,
T is the absolute temperature. Electrons n ⁺ source region are injected into the channel as compared with the potential energy V _Bigs beyond when holes stored in the fourth gate Schottky junction surface as is apparent from FIG diffuse into the n ⁺ source region The potential energy V _biG ^* _S that exceeds the _threshold is quite small. Therefore, the exponential term in the equation (2) shows a considerably large value, and G _max also becomes large. Compared with the conventional bipolar phototransistor in which the base is composed of a single region, in the phototransistor having the SIT gate structure,
The exponential term multiple optical gain of the equation (2) increases.

The dependence of the optical gain G on the incident light energy P _i can be expressed by the following equation.

G = G _max (P _iC / P _i ) ^{1-n η} (3) In formula (3), P _iC is the energy of the entrance hole at which the hole current excited by light becomes equal to the dark current, and n is a constant. It reflects the saturation effect of the gate-source Schottky diode in the region where the incident light intensity is high. η represents the rate of change of the true gate point G ^* with respect to the change of the gate voltage. As is clear from the formula (3), the optical gain G of SIPT tends to increase as the incident light intensity decreases,
It shows completely different characteristics from the conventional bipolar phototransistor and heterojunction phototransistor.

The response speed of the Schottky gate SIPT can be approximately expressed by the rising time constant τ _r of the following equation.

τ _r nkT {C _GS + (1 + μ) C _GD } / {qJ _L (P _i / P _iC )}
(4) In equation (4), C _GS is the gate-n ⁺ source capacitance, C _GD is the gate-n ⁺ drain capacitance, μ is the Schottky gate SIPT voltage amplification factor, and J _L is excited by light. Hole current.
In the SIT gate structure, a high resistance region is sandwiched between the n ⁺ source region and the gate and between the n ⁺ drain region and the gate, and the junction area of the gate can be made smaller, so compared to conventional bipolar phototransistors and the like. Since C _GS and C _GD can be reduced, high speed operation can be realized.

Further, in the SIT structure, the input noise resistance is small because the resistance r _S between the gate and the source is small. Therefore, SIT
The noise is smaller than that of conventional bipolar transistors and FETs. That is, when the SIT structure is applied to a phototransistor, a low noise photodetector can be realized.

Furthermore, by forming the gate with a Schottky junction, it is possible to suppress the accumulation effect of minority carriers found in the pn junction, so that speedup can be realized.

In the SIT gate structure, the gate spacing and the impurity concentration of the channel are selected so that the channel region is completely depleted by the diffusion potential of the Schottky junction between the gate and the channel and the gate bias.

On the other hand, by incorporating the Schottky structure in a part of the base of the conventional bipolar phototransistor having a uniform structure, the optical gain and the response speed are improved. That is, the channel region 503 of FIG.
May be a p-type semiconductor or a low-impurity-density p-type semiconductor (p ⁻ ). The gate interval may be a condition that the channel is not completely depleted. In this case, a neutral region exists in the base or the channel in a part of the portion where the current easily flows, and forms a resistance component in the base or the channel. As a matter of course, the high frequency characteristics are better in the element in which the base or the channel is entirely depleted and the electrostatic induction effect is easily exerted by the potential of the Schottky junction interface.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a cut gate type Schottky gate SIPT according to the present invention. Since the gate junction capacitance can be reduced by using the cut gate, higher speed can be realized. In FIG. 1, 201 is an n ⁺ drain region, 202 and 204 are high resistance regions having a low impurity density i (or n ⁻ , p ⁻ ), and 203 is an i (or n ⁻ , p ⁻ , p) channel region. 205 is an n ⁺ source area. 206 is a metal gate region that forms a Schottky junction. Reference numeral 207 is an insulating layer. Further, 211 is a drain electrode and 212 is a source electrode.

FIG. 2 shows an embodiment of a planar gate type Schottky gate SIPT according to the present invention. In FIG. 2, 301 is an n ⁺ drain region, 302 is a high resistance region having a low impurity density i (or n ⁻ , p ⁻ ), and 305 is an n ⁺ source region. 306 is a metal gate region forming a Schottky junction. Also, 311
Is a drain electrode and 312 is a source electrode.

FIG. 3 shows an embodiment of a structure in which a metal gate region is surrounded by a high impurity region by a buried gate type Schottky gate SIPT and a non-uniform base BPT according to the present invention. By increasing the impurity density around the metal gate region, the potential between the gate and the source can be increased, so that the optical gain can be further increased. In FIG. 3, 401 is an n ⁺ drain region, and 402 and 40.
4 is a high resistance region of low impurity density i (or n ⁻ , p ⁻ ), 4
03 is an i (or n ⁻ , p ⁻ , p) channel region. 40
5 is an n ⁺ source region. 406 is a metal gate region forming a Schottky junction. 407 is a p ⁺ high impurity density region. Further, 411 is a drain electrode, and 412 is a source electrode.

Although the embodiments shown in FIGS. 1 to 3 are all photodetectors using transistors, in FIGS. 1 to 3 the high impurity density p ⁺ is used instead of the n ⁺ drain regions 201, 301 and 401. A device structure that forms a region is also preferable. In this case, the electrostatic induction thyristor type photodetector is used. That is, in this case, since a storage region for electrons of electron-hole pairs generated by light is formed at the p ⁺ -i (n ⁻ , p ⁻ ) junction interface, a positive region from the p ⁺ region is formed. The hole injection is promoted, and the degree of optical amplification becomes larger than that of the transistor structure.

〔The invention's effect〕

The gate according to the present invention is formed of a Schottky electrode.
SIPT can realize a photodetector with higher photosensitivity, lower noise and higher speed than conventional semiconductor photodetectors.

Also, conventional bipolar phototransistor (BPT)
In addition, by introducing the non-uniform base structure having a Schottky junction according to the present invention, characteristics such as photosensitivity and response speed can be improved.

The semiconductor material forming the photodetector of the present invention is not limited to Si, but may be a III-V group compound semiconductor such as GaAs, InP, InSb, or a II-VI group compound semiconductor. Of course. Further, the source channel or the emitter / base portion may be a heterojunction.

The photodetector according to the present invention can be applied to a photodetector for optical communication and the like, and has high industrial utility value.

[Brief description of drawings]

FIG. 1 is an embodiment of a cut gate type Schottky gate SIPT according to the present invention, FIG. 2 is an embodiment of a planar gate type Schottky gate SIPT according to the present invention, and FIG.
Embedded gate type Schottky gate SI according to the present invention
Example of a structure in which the metal gate region is surrounded by a high impurity density region with PT and non-uniform base BPT, FIG. 4 (a)
FIG. 4 is a sectional view of the unit device structure of a buried gate type Schottky gate SIPT according to the present invention, FIG. 4 (b) is a potential diagram along AA ′ and BB ′ of FIG. 4 (a), and FIG. 4 (c). 4) is a potential diagram in the CC ′ direction of FIG. 4 (a). 201, 301, 401 ... n ⁺ drain region, 202, 204, 302, 40
2,404 ...... high resistance region i ^{(or, n -, p -),} 203,403
...... i (or n ^-, p ^-, p) channel region, 205,30
5,405 …… n ⁺ source region, 206,306,406 …… Schottky metal gate region, 211,311,411 …… Drain electrode, 212,312,412 …… Source electrode

Claims (10)

[Claims] 1. A drain region of the first conductivity type, a high resistance region in which a surface adjacent to the drain region and not in contact with the drain region is periodically uneven, and a concave and convex portion of the high resistance region. A metal gate region disposed inside the insulating layer and forming a Schottky junction with the protrusion, and a high resistance channel region provided adjacent to the metal gate region on the protrusion of the high resistance region. A source region of the first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region, a drain electrode provided on a surface exposed portion of the drain region, and a surface exposed portion of the source region An electron-hole pair is generated mainly in the high resistance region by light entering from a region where the source electrode is not provided in the source region. And before By accumulating holes of the electron-hole pair in the Schottky junction, the potential of the high resistance channel region is controlled by the static induction effect of the Schottky junction, and the source region and the drain region are controlled. A semiconductor photodetector characterized in that an amplified current flows between them. 2. A drain region of the first conductivity type, a high resistance region in which a surface adjacent to the drain region and not in contact with the drain region is periodically uneven, and a concave and convex portion of the high resistance region. A metal gate region disposed inside the insulating layer and forming a Schottky junction with the protrusion, and a second conductivity type provided on the protrusion of the high resistance region adjacent to the metal gate region. A channel region, a source region of the first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region, a drain electrode provided on an exposed surface of the drain region, and the source region A source electrode provided in contact with a part of a surface exposed portion of the second conductive type channel region mainly by light entering from a region of the source region where the source electrode is not provided. During ~ Electronic - hole pairs are generated, the electronic -
By accumulating holes of the hole pairs in the Schottky junction, the potential of the channel region of the second conductivity type is controlled by the electrostatic induction effect of the Schottky junction, and the potential of the source region and the A semiconductor photodetector characterized in that an amplified current flows between the drain regions. 3. A drain region of the first conductivity type, a high resistance region adjacent to the drain region, and a surface of the high resistance region opposite to a surface in contact with the drain region are discontinuous and periodic. A metal gate region provided to form a Schottky junction, and a first conductivity type source region buried in a part of the high resistance region sandwiched by the metal gate region and a surface exposed portion of the drain region. A source electrode provided in contact with a part of the exposed surface of the source region and a source electrode provided in contact with a part of the exposed surface of the source region. An electron-hole pair is generated in the high resistance region,
By accumulating holes of the electron-hole pairs in the Schottky junction, the potential of the high resistance region is controlled by the electrostatic induction effect of the Schottky junction, and the source region and the drain region are controlled. A semiconductor photodetector characterized in that an amplified current flows between them. 4. A drain region of the first conductivity type, a high resistance region adjacent to the drain region, and discontinuously and periodically provided in the high resistance region so as to divide the high resistance region into two parts. A metal gate region forming a Schottky junction, a second conductivity type high impurity density region provided around the metal gate region, a second conductivity type high impurity density region, and the high resistance. A high resistance channel region adjacent to the region and sandwiched between the metal gate regions, and a source region of a first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region, A drain electrode provided on the exposed surface of the drain region; and a source electrode provided in contact with a portion of the exposed surface of the source region, wherein the source electrode is provided on the source region. Electrons-hole pairs are generated mainly in the high-resistance channel region by light entering from the non-existing region, and holes of the electron-hole pairs are accumulated in the Schottky junction, thereby increasing the high resistance. A semiconductor photodetector, wherein a potential of a channel region is controlled by an electrostatic induction effect of the Schottky junction, and an amplified current flows between the source region and the drain region. 5. A drain region of the first conductivity type, a high resistance region adjacent to the drain region, and discontinuously and periodically provided in the high resistance region so as to divide the high resistance region into two parts. A metal gate region forming a Schottky junction, a second conductivity type high impurity density region provided around the metal gate region, a second conductivity type high impurity density region, and the high resistance. A second conductivity type channel region adjacent to the region and sandwiched between the metal gate regions, and a first conductivity type channel region in contact with the high resistance region and opposite to the drain region. A source region, a drain electrode provided on a surface exposed portion of the drain region, and a source electrode provided in contact with a part of a surface exposed portion of the source region, the source electrode of the source region Electrons-hole pairs are generated mainly in the channel region of the second conductivity type due to light penetrating from the non-shielded region, and holes of the electron-hole pairs are accumulated in the Schottky junction. As a result, the potential of the channel region of the second conductivity type is controlled by the electrostatic induction effect of the Schottky junction, and the amplified current flows between the source region and the drain region. Semiconductor photodetector. 6. A drain region of the first conductivity type, a high resistance region in which a surface adjacent to the drain region and not in contact with the drain region is periodically uneven, and a concave and convex portion of the high resistance region. A metal gate region disposed inside the insulating layer and forming a Schottky junction with the protrusion, and a high resistance channel region provided adjacent to the metal gate region on the protrusion of the high resistance region. A source region of a conductivity type opposite to the first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region; a drain electrode provided on a surface exposed portion of the drain region; The source electrode is provided in contact with a part of the surface exposed portion of the region, and the light mainly entering in the high resistance region is caused by light entering from a region in the source region where the source electrode is not provided. Positive When a pair is generated and holes of the electron-hole pair are accumulated in the Schottky junction, the potential of the high resistance channel region is controlled by the electrostatic induction effect of the Schottky junction, A semiconductor photodetector, wherein amplified current flows between a source region and the drain region. 7. A drain region of the first conductivity type, a high resistance region in which a surface adjacent to the drain region and not in contact with the drain region is periodically uneven, and a concave portion of the high resistance region which is uneven. A metal gate region disposed inside the insulating layer and forming a Schottky junction with the protrusion, and a second conductivity type provided on the protrusion of the high resistance region adjacent to the metal gate region. Channel region, a source region of a conductivity type opposite to the first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region, and a drain electrode provided on a surface exposed portion of the drain region. And a source electrode provided in contact with a part of the exposed surface of the source region, the light mainly entering the second region due to light penetrating from a region where the source electrode is not provided in the source region. Conductive type Electron-hole pairs are generated in the channel region, and holes of the electron-hole pairs are accumulated in the Schottky junction, so that the potential of the channel region of the second conductivity type changes to the shot region. A semiconductor photodetector, wherein an amplified current flows between the source region and the drain region, which is controlled by an electrostatic induction effect of a key junction. 8. A drain region of the first conductivity type, a high resistance region adjacent to the drain region, and a surface of the high resistance region opposite to a surface in contact with the drain region are discontinuous and periodic. A metal gate region provided to form a Schottky junction, and a source region and a drain region of a conductivity type opposite to the first conductivity type buried in a part of the high resistance region sandwiched between the metal gate regions. A source electrode provided in contact with a part of the surface exposed portion of the source region, the source electrode provided in contact with a part of the surface exposed portion of the source region, and penetrates from the region where the source electrode is not provided in the source region. The light that is generated mainly causes electrons in the high resistance region.
A hole pair is generated and holes of the electron-hole pair are accumulated in the Schottky junction, whereby the potential of the high resistance region is controlled by the electrostatic induction effect of the Schottky junction, A semiconductor photodetector, wherein an amplified current flows between the source region and the drain region. 9. A drain region of the first conductivity type, a high resistance region adjacent to the drain region, and discontinuously and periodically provided in the high resistance region and arranged to divide the high resistance region into two parts. A metal gate region forming a Schottky junction, a second conductivity type high impurity density region provided around the metal gate region, a second conductivity type high impurity density region, and the high resistance. A high resistance channel region adjacent to the region and sandwiched between the metal gate regions, and a conductivity type opposite to the first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region. Of the source region, a drain electrode provided on a surface exposed portion of the drain region, and a source electrode provided in contact with a part of the surface exposed portion of the source region. Electrons-hole pairs are generated mainly in the high resistance channel region by light entering from a region where no electrode is provided, and holes of the electron-hole pairs are accumulated in the Schottky junction. With this, the potential of the high resistance channel region is controlled by the electrostatic induction effect of the Schottky junction, and the amplified current flows between the source region and the drain region. 10. A drain region of the first conductivity type, a high resistance region adjacent to the drain region, and discontinuously and periodically provided in the high resistance region so as to divide the high resistance region into two parts. A metal gate region forming a Schottky junction, a second conductivity type high impurity density region provided around the metal gate region, a second conductivity type high impurity density region, and the high resistance. A second conductivity type channel region adjacent to the region and sandwiched between the metal gate regions, and the first conductivity type disposed on the opposite side of the drain region in contact with the high resistance region. A source region having a conductivity type opposite to that of the source region; a drain electrode provided on a surface exposed portion of the drain region; and a source electrode provided in contact with a part of the surface exposed portion of the source region. It said source by light entering from provided non region of the electrode, electrons mainly in the second in the channel region of conductivity type - hole pairs are generated, the electronic -
By accumulating holes of the hole pairs in the Schottky junction, the potential of the channel region of the second conductivity type is controlled by the electrostatic induction effect of the Schottky junction, and the potential of the source region and the A semiconductor photodetector characterized in that an amplified current flows between the drain regions.