JPH05275734A - Phototransistor - Google Patents

Abstract

PURPOSE:To provide a phototransitor which is based on a new principle. CONSTITUTION:A phototransistor which is sensitive to light as a signal input and which outputs a multiplied electric signal toward an external circuit is provided with the following: a semiconductor 11 in which one pair of electrodes composed of an anode 21 and a cathode 22 are installed; an electric-field application means which applies a prescribed electric field into the semiconductor between the pair of electrodes; a light irradiation hv means by which the interference between the anode and the semiconductor is irradiated with light as a signal input; and a cathode means by which holes generated in the anode body by irradiation with the light are injected into the semiconductor and which promotes the injection of electrons into the semiconductor from the cathode. When the anode 21 is irradiated with the light as an input signal to be amplified, the holes are generated and injected into the semiconductor. Then, the electrons are injected from the cathode 22, and an amplified electric signal is output to an external circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phototransistor in which holes are generated by light irradiation and the electron flow is controlled by the holes.

[0002]

2. Description of the Related Art Phototransistors have existed in the past, but
These phototransistors used pnp (npn) junctions. Moreover, there is a drawback that the dark current is considerably increased when operated in the multiplication region.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a phototransistor having a novel structure which solves the drawbacks of the prior art.

[0004]

According to the present invention, in a phototransistor which is sensitive to light as a signal input and outputs an amplified electric signal toward an external circuit, a pair of electrodes consisting of an anode and a cathode is set. Electric field applying means for applying a predetermined electric field between the semiconductor and the semiconductor between the pair of electrodes, a light irradiating means for irradiating the vicinity of the interface between the anode and the semiconductor with light as a signal input, and the anode by this light irradiation. And a cathode means for injecting the generated holes into the semiconductor and promoting electron injection from the cathode into the semiconductor.

[0005]

According to the structure of the present invention, when light as an input signal to be amplified is applied to the anode, holes are generated and injected into the semiconductor. Then, electrons are injected from the cathode, and the amplified electric signal is output to the external circuit.

As described above, the present invention not only improves the drawbacks of the conventional phototransistor and does not require a pnp junction, but also easily causes avalanche multiplication depending on the applied electric field to inject electrons. Can be easily multiplied. Moreover, the semiconductor used can be a high-resistance semiconductor, and the dark current can be suppressed low. The present invention is a phototransistor that has the functions of a so-called avalanche transistor and a photodiode, and the structure that does not particularly require a pn junction makes it possible to realize a phototransistor that is simple and has a low dark current.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is based on an idea completely different from the idea of phototransistors up to now. Conventional phototransistors generate carriers in the base region of the transistor, and pn is generated by the space charge generated in the base.
The junction was forward biased to control the current flowing in the device. In the present invention, light is used to inject holes from the anode into the semiconductor. The basic principle of the phototransistor of the present invention is that the amount of electrons injected from the cathode to the semiconductor is controlled by the amount of holes generated. Further, multiplication can be performed if necessary. The phototransistor having such a concept has never been invented.

The contents of the present invention will be described with reference to specific examples. FIG. 1 is a structural diagram of the most basic embodiment of the phototransistor of the present invention. Semiconductor 1 ₁ , eg GaA
s A pair of electrodes is formed on the wafer, and anode 2 ₁ and cathode 2
_Set to ₂ . The electrode material will be described later, but in this example, AuG having an ohmic junction for both the cathode 2 ₂ and the anode 2 _1.
e / Ni / Au. The anode 2 ₁ is made sufficiently thin so that the interface of the semiconductor 1 ₁ can be efficiently irradiated with light.

A potential barrier is always formed at the interface between the anode 2 ₁ and the semiconductor 1 ₁ regardless of whether the junction is an ohmic junction or a Schottky junction. The height of this barrier depends on the type of junction and the material of the semiconductor 1 ₁ , but is approximately 1 / _one of the bandgap energy of the semiconductor 1 _1.
2 or 2/3. This value determines the limit wavelength at which this phototransistor operates. Semiconductor 1 ₁ is GaAs
In the case of, the band gap energy at room temperature is 1.
It is 43 eV, and the limit wavelength is about 1300 nm to 1700 nm.

Light (hν) is applied to the interface between the anode 2 ₁ and the semiconductor 1 ₁ from the outside. The irradiated light excites holes in the anode 2 ₁ . Since the energy of this hot hole has the same energy as the light energy applied,
If the photon energy of the illuminating light is higher than the previous barrier, hot holes will be injected across the barrier into the semiconductor 1 ₁ . To counter this, electrons are injected from the cathode 2 ₂ . Semiconductor 1 ₁
Since an electric field is applied by the electrodes 2 ₁ , 2 ₂ provided on the upper surface and the power source 4 ₃ to the anode, the injected electrons are carried to the anode 2 ₁ and observed by the ammeter 4 ₁ as a signal current. It

Furthermore, in order to increase the signal current, it is better to cause the avalanche neighbor by a high electric field Te at the immediately before the anode 2 ₁ as shown below. Conditions necessary for this, it semiconductor 1 ₁ is a high-resistance semiconductor as semi-insulating GaAs, also the bias field is that it is a field of more than about 0.5 kV / cm as a mean field. The upper limit is not particularly required to be set, but it is also a feature of the present invention that it operates in a region where the average electric field is low, and further, it is set to 2.5 kV / cm or less in order to clearly distinguish it from other phenomena.

[0012] high resistance semiconductor 1 _1, upon application of a high electric field of this degree, that in the vicinity of the anode 2 ₁ concentration of electric field is generated are known by studies of the present inventors. Anode 2
_The holes injected from ₁ to the semiconductor 1 ₁ travel toward the cathode 2 ₂ . At this time, in order to prevent generation of space charge, the cathode 2
Electrons are injected from ₂ . The cathode 2 ₂ side of the semiconductor 1 ₁ has a high carrier density and the resistance value decreases. Electrodes 2 ₁ , 2 ₂
When a constant bias voltage is applied in between, the electric field in this region decreases. On the contrary, the electric field strength in the vicinity of the anode 2 ₁ is increased accordingly. In this way, so that avalanche multiplication by injection electrons near the anode 2 ₁ occurs. A large number of holes generated by the avalanche multiplication work in exactly the same way as the light-injected holes, and the entire avalanche current is maintained. A current due to light is further added to this, and the current further increases, and this amount becomes the photocurrent gain. This is the basic operation of the phototransistor of the present invention.

FIG. 2 shows the above operation mechanism on an energy band diagram. FIG. 3A is a potential diagram immediately after the electrons 5 ₁ and the holes 5 ₂ are generated from the anode 2 ₁ by the light irradiation (hν), and the holes 5 ₄ among them are injected into the semiconductor 1 ₁ . FIG (b) is avalanche multiplication is induced are injected electrons 5 ₃ for neutralization of a large amount of holes generated by the avalanche multiplication region 5 _5, also the charge from the cathode 2 ₂ by injection The potential diagram of the operating state is drawn.

As can be seen from the above description, the basic operation of the phototransistor according to this embodiment is to apply an electric field to the semiconductor 1 ₁ and irradiate the anode 2 ₁ with light. Further, in the foregoing description, it has been explained as do not interfere especially in the injection of electrons from the cathode 2 _2. However, cathode 2 ₂ and semiconductor 1
_The potential barrier formed at the interface with ₁ may interfere with electron injection. In this case, it may be preferable to irradiate the cathode 2 ₂ with light. That is, in the cathode 2 ₂ as well, as in the case of the anode 2 ₁ , the injection of electrons may be assisted by the light energy.

By this basic operation, the current output can be obtained not only by the light irradiation of the anode 2 ₁ but also by the light irradiation of the cathode 2 _2. This means that the above two kinds of light irradiation perform AND logic. To do. That is, the anode 2 ₁ and the cathode 2 ₂
Are used as blocking electrodes for holes and electrons, respectively, to form a logic gate that multiplies the input light. This is valuable as a simple multiplication and correlator.

By devising the light irradiation means, various types of phototransistors can be constructed as shown in FIGS. For example, in the configuration according to the above description, the semiconductor 1 ₁ has a diode configuration of the anode 2 ₁ and the cathode 2 ₂ , but the anode is divided into _two and a three-pole configuration is applied under another bias. The positive electrode 2 ₃ for injecting holes and the positive electrode 2 ₁ for signal current may be separately operated.
Here, the hole injection anode 2 ₃ has a flat plate shape in FIG. 3, but has a mesh shape in FIG.

FIG. 5 shows an example in which electrodes are formed in the thickness direction of a semiconductor wafer. That is, the anode 2 ₁ is formed on the upper surface of the semiconductor 1 ₁ and the cathode 2 ₂ is formed on the lower surface to form a phototransistor.

As the light irradiation means, the thinned anode may be replaced with a partial electrode such as a mesh pattern. In this case, if the anode 2 ₁ is thick, the light is irradiated only to the electrode interface portion in the peripheral portion of the electrode opening portion, so that the anode 2 ₁ also needs to be thinned.

However, the situation is completely different when the irradiation light has a wavelength longer than the wavelength corresponding to the band gap energy of the semiconductor. The structural drawing in this case is shown in FIG.
It is FIG. In this case, the light hν applied to the semiconductor 1 ₁ from the interval between the anode electrodes 2 ₁ passes through the high-resistance semiconductor 1 ₁ , so that the back surface of the semiconductor 1 ₁ in FIG. 6 and the back surface of the semiconductor 11 in FIG. The light is reflected by 2 ₂ and the interface between the anode 2 ₁ and the semiconductor 1 ₁ is irradiated with light. Therefore, in this case, the anode 2 ₁ may not be particularly thin.

[0020] Furthermore, it may be irradiated from the semiconductor 1 ₁ of the wafer side. This example is shown in FIGS. In the case of this structure, the structure is suitable for a device that controls current by light from a semiconductor laser formed on the same semiconductor wafer. It is also possible to irradiate light from the cathode 2 ₂ side. In this case, either the cathode 2 ₂ is thinned for light transmission, there must be in the mesh electrode shape (10, 11).

The electrodes used in the present invention will be described.
First, regarding the cathode 2 ₂ , when holes are injected into the semiconductor 1 ₁ , electrons that neutralize the holes must be easily injected into the semiconductor 1 ₁ from the cathode 2 ₂ . Therefore, an ohmic bonding material that does not become an electron block is suitable as the cathode material. Such materials include AuGe, AgInG
Examples of the alloy metal include e, AuSn, and the like. Alternatively, a metal electrode via an N ⁺ thin layer may be used.

However, when considering irradiating the cathode with light as described above, in some cases, it is better to use the cathode as an electron blocking electrode, that is, a Schottky electrode to enhance controllability by light. is there. Examples of the metal having the Schottky junction include Au, Al, WSi, T
iPtAu etc. are mentioned.

The same discussion can be made for the anode 2 ₁ .
This is because, as an electrode material suitable for injecting holes from the anode 2 ₁ into the semiconductor 1 ₁ , this has a lower potential barrier for holes. However, conversely, it is also beneficial to sacrifice the limit wavelength and enhance blocking for hole injection to suppress dark current and enhance light controllability. For this purpose, ohmic bonding may be used.

[0024] Stated for dark current, semiconductor 1 ₁ high-resistance semiconductor, particularly if it is semi-insulating, although it is needless to say that the dark current is kept low, the semiconductor 1 ₁
If the substrate is an n-type semiconductor substrate, the cathode 2 ₂ may be a pn junction whose injection state can be controlled by a bias in order to reduce the ohmic current or a Schottky junction. it can.

In order to greatly improve the limit wavelength, and to lower the potential barrier when injecting holes by light irradiation and extend the limit wavelength on the long wavelength side, this pn junction is made a heterojunction. You can also 12 and 13 are structural views of this embodiment, and FIG. 14 is an energy band diagram thereof.

As described above, the long wavelength limit of the phototransistor of the present invention is determined by the size of the potential barrier formed between the anode 2 ₁ and the semiconductor 1 ₁ . Potential barrier to the more band gap energy is small becomes small, it is possible to use a semiconductor material having a smallest possible band gap energy as the semiconductor 1 _1.

[0027] Examples of such attempts, it may be replaced with a semiconductor material having a smaller band gap energy of all of the semiconductor 1 ₁ but 12, as in FIG. 13, another only immediately before the anode 2 _first semiconductor 1 You can also replace it with ₂ . Overall, because it is a semiconductor 1 ₁ with a large band gap energy, it is the fact that dark current is kept low, such as a high resistance semiconductor material are readily available, since merit is large.

[0028] Next, worth mentioning about the resistivity of the semiconductor 1 _1. In the mechanism of the phototransistor of the present invention, holes are injected from the anode 2 ₁ by light irradiation, and the cathode 2 is injected to neutralize the holes.
It is necessary that ₂ electrons be injected. It takes a certain amount of time to neutralize the charge, which is called a dielectric relaxation time. The dielectric relaxation time τ is determined by τ = εε ₀ / σ. Here, ε and ε ₀ are the relative permittivity of the semiconductor _{11 and} the permittivity of vacuum. Further, σ is the conductivity of the semiconductor 1 ₁ .

[0029] Thus, the semiconductor 1 ₁ is too in the case of high resistance, the response speed of the optical transistor becomes extremely slow. Also, increasing the conductivity to obtain responsiveness is
It is meaningless because the means for concentrating the electric field on the anode 2 ₁ applied in the present invention cannot be used. Therefore, the upper limit of the carrier concentration of the semiconductor used in the phototransistor of the present invention is preferably 10 ¹⁴ cm ⁻³ or less. Furthermore, the response speed can be improved by making the transit time of the carrier between the electrodes shorter than the dielectric relaxation time τ. Therefore, the distance between the electrodes is preferably 80 μm or less. The high resistance semiconductor used in the present invention may be semi-insulated,
It is known that the impurities contained for the carrier compensation have no influence. Examples of the semiconductor 1 ₁ which is a semi-insulating is, Cr: GaAs, CrO: GaAs , Fe: In
P etc. are mentioned.

Finally, the negative resistance will be touched upon. In the present invention, it was described that avalanche multiplication occurs when the bias applied between the electrodes 2 ₁ and 2 ₂ is high, but if the conductivity modulation is strong at this time, negative resistance occurs. If it is desired to suppress the occurrence of negative resistance may be Osaere conductivity modulation, as the unit, it is sufficient to increase the carrier density of the semiconductor 1 _1. Alternatively, in order to prevent bias redistribution within the device, a low resistance portion and a thin high resistance portion may be formed between the electrodes 2 ₁ and 2 ₂ , and the high resistance side is the anode side. Even if the conductivity of the high resistance region changes due to the injection of holes from the anode, the negative resistance does not appear because the effect on the whole is small. By suppressing the negative resistance in this manner, a hole injection control type avalanche diode with low noise can be obtained.

The reason for the low noise is that the phonon scattering of electrons is suppressed and the electrons can easily become light energy by forming the structure as in the present invention. In other words, the multiplication factors of electrons and holes in the avalanche region are extremely different, and it can be said that only electrons are multiplied, so that excess noise, which is the main noise of a normal avalanche diode, is less likely to occur.

As described above, the present invention is a phototransistor which is completely different from the conventional ones, has a simple structure, is sensitive to long wavelengths, and is highly sensitive to avalanche. ..

[0033]

According to the present invention, it is possible to realize a device that efficiently controls the current by irradiating it with light, particularly infrared light. In particular, the simple structure and availability of the semi-insulating substrate and compound semiconductor are suitable for application to optical integrated circuits, and can greatly contribute to optical computers using optical integrated circuits that are expected in the future.

[Brief description of drawings]

FIG. 1 is a structural diagram of a phototransistor according to an embodiment of the present invention.

2 is an energy band diagram for FIG. 1,
(A) shows the state immediately after the injection of holes, and (b) shows the operating state.

FIG. 3 is a structural diagram of a phototransistor according to an embodiment of the present invention in which the anode is divided into a hole injecting anode and a current extracting electrode.

FIG. 4 is a structural diagram of a phototransistor according to an embodiment of the present invention in which an anode is divided into a hole injection anode and a current extraction electrode.

FIG. 5 is a structural diagram of a phototransistor according to an embodiment of the present invention in which a pair of electrodes are formed in the thickness direction of a semiconductor wafer.

FIG. 6 is a structural diagram of a phototransistor according to an embodiment of the present invention in which the anode has a mesh shape.

FIG. 7 is a structural diagram of a phototransistor according to an embodiment of the present invention in which the anode has a mesh shape.

FIG. 8 is a structural diagram of a phototransistor of an embodiment of the present invention in which light irradiation is performed from the sidewall of a semiconductor substrate.

FIG. 9 is a structural diagram of a phototransistor of an embodiment of the present invention in which light irradiation is performed from the sidewall of a semiconductor substrate.

FIG. 10 is a structural diagram of a phototransistor according to an embodiment of the present invention in which light irradiation is performed from a cathode.

FIG. 11 is a structural diagram of a phototransistor according to an embodiment of the present invention in which light irradiation is performed from a cathode.

FIG. 12 is a structural diagram of a phototransistor according to an embodiment of the present invention in which a limit wavelength is extended by a heterojunction.

FIG. 13 is a structural diagram of a phototransistor of an embodiment of the present invention in which a limiting wavelength is extended by a heterojunction.

FIG. 14 is an energy band diagram for the phototransistor of the embodiment of FIGS.

[Explanation of symbols]

hν ... Irradiation light, E _O ... Conduction band, E _V ... Valence band, ₁₁ ...
Semiconductor, 1 ₂ ... Semiconductor having band gap energy different from that of semiconductor 1 ₁ , 2 ₁ ... Anode, 2 ₂ ... Cathode, 2 ₃
... hole injection dedicated internal anode, 4 ₁ ... ammeter, 4 ₂ ... semiconductor internal bias power supply, 4 ₃ ... hole injection control power supply, 5 ₁ ...
Excited electron, 5 ₂ ... Excited hole, 5 ₃ ... Injection electron, 5 ₄ ... Injection hole, 5 ₅ ... Avalanche multiplication region.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location 8422-4M H01L 31/10 H (72) Inventor Takashi Iida 1126-1 Nono-cho, Hamamatsu-shi, Shizuoka Hamamatsu Photonics Co., Ltd. (72) Inventor Sadahisa Warashi 1126-1 Nono, Hamamatsu-shi, Shizuoka Prefecture 1 126 Hamamatsu Photonics Co., Ltd. (72) Kenichi Sugimoto 1 126-1 Nono, Hamamatsu-shi, Shizuoka Hamamatsu Photonics Co., Ltd. In-house (72) Inventor Tomoko Suzuki 1 126-1 Nomachi, Hamamatsu City, Shizuoka Prefecture Hamamatsu Photonics Co., Ltd.

Claims (13)

[Claims] 1. A phototransistor which is sensitive to light as a signal input and outputs an amplified electric signal toward an external circuit, wherein a semiconductor having a pair of electrodes consisting of an anode and a cathode is set, An electric field applying means for applying a predetermined electric field in the semiconductor between the electrodes, a light irradiating means for irradiating light as a signal input near the interface between the anode and the semiconductor, and light generated by the anode by this light irradiation. And a cathode means for injecting holes into the semiconductor to promote electron injection from the cathode into the semiconductor. 2. The light irradiating means is configured to irradiate light both near the interface between the anode and the semiconductor and near the interface between the cathode and the semiconductor. Phototransistor. 3. The anode and the cathode each have an electrode that blocks holes and electrons, and separate light is made incident on each of the anode and the cathode, and an AND logic is applied by light input. The phototransistor according to claim 2, which is adapted to be performed. 4. The semiconductor has a carrier concentration of 10 ¹⁴ c.
^{4. The} phototransistor according to claim 1, wherein the phototransistor is a high-resistance semiconductor having m ⁻³ or less. 5. The phototransistor according to claim 4, wherein the high resistance semiconductor is semi-insulating. 6. The high resistance semiconductor is GaAs or I.
The phototransistor according to claim 4, which is a compound semiconductor mainly composed of nP. 7. The electric field generated by the electric field applying means is 0.5.
4. The phototransistor according to claim 1, wherein the phototransistor is configured to have a voltage of not less than kV / cm and not more than 2.5 kV / cm. 8. The method according to claim 1, wherein at least one of the anode and the cathode is an ohmic electrode.
2. The phototransistor according to 2 or 3. 9. The phototransistor according to claim 1, wherein the semiconductor just before the anode is provided with a barrier junction. 10. The phototransistor according to claim 9, wherein the barrier junction is formed of a semiconductor heterojunction. 11. The phototransistor according to claim 1, 2 or 3, wherein the light emitted by the light irradiation means has a wavelength longer than a wavelength corresponding to the bandgap energy of the semiconductor. 12. The phototransistor according to claim 1, further comprising a control electrode for generating holes by light irradiation by the light irradiation means. 13. The phototransistor according to claim 1, wherein the distance between the anode and the cathode is 80 μm or less.