JPS6317570A - Phototransistor - Google Patents

Abstract

PURPOSE:To achieve low-voltage photoswitching operation of a phototransistor by a method wherein the mean refractive index of a quantum well structure is set up to exceed those of an emitter layer, base layer and collector layer. CONSTITUTION:A collector layer 2, multiple quantum well layers 3, a base layer 4, an emitter layer 5, and a cap layer 6 are successively crystal-grown on an n-GaAs substrate 1. Next, partial photoetching is done to expose the base layer 4. The layer 3 is shaped into stripes to form a collector layer 7, a base electrode 8 and an emitter electrode 9. At this time, if the film thickness and composition of quantum well and barrier of the multiple quantum well structure 3 are set up so that the mean refractive index of multiple the quantum well structure 3 may exceed those of the collector layer 2, base layer 4 and emitter layer 5, then incident light 10 is led to the multiple quantum structure 3 and output light 11 is obtained. Through these procedures, photoswitching operation is enabled to be performed at low signal voltage making use of the amplification of a transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an original transistor, and particularly to an optical switch used in optical communication or information processing equipment.

This invention relates to a phototransistor having an optical bistable function.

[Conventional technology]

Conventionally, as the original switch for this woodcutter, a device using a semiconductor using the Franz-Keldytsch effect is small and excellent. The Franz-Keldissi gourd effect is an effect in which the absorption edge wavelength shifts to longer wavelengths when an electric field is applied to a semiconductor. As this semiconductor, a waveguide optical switch is being considered that uses a multi-quantum well structure in which layers with different forbidden band widths of s o o tx or less are laminated alternately (1985 IEICE General Conference 83- 4).

[Problem that the invention seeks to solve]

The above-mentioned conventional waveguide optical switch performs switching by applying a relatively high electric field to the waveguide layer and changing the absorption coefficient of the waveguide layer. It had the disadvantage of requiring

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a phototransistor capable of optical switching operation at low voltage.

[Means for solving problems]

The original transistor of the present invention includes a collector layer of a first conductivity type, a quantum well structure including at least one quantum well provided in contact with the collector layer, and a quantum well structure provided in contact with the quantum well structure. The quantum well structure has a structure in which the average refractive index of the quantum well structure is larger than the refractive index of any of the emitter layer, the base layer, and the collector layer.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an original transistor according to an embodiment of the present invention.

In the figure, 1 is an n-GaAs substrate, 2 is a collector layer (n-GaAs
lxcGat-xcAs), thickness is 0.3-3μ
m.

Typically, for example n-AA! 0.4 Ga6. ．． 1A
s, thickness 1.5 μm), 3 is a multiple quantum well structure (kl
X QwGal-XQWA S, O (thickness≦30
0A quantum well and All x (2BGa I
A barrier of As, O<thickness≦300, typically has a thickness of, for example, 100 Ga (a barrier made of 1,6 As is
0 period), 4 is the base layer (p kl
Consisting of I
)5 is the emitter layer (n-AI XEGal-XE
Made of As, the thickness is 0.3-3μm1 typically AI
,,, Ga6.6 As thickness 1.5 μm), 6 is key
ryp layer (n-GaAs).

Here, the average refractive index of the multi-quantum well structure 3 is the collector layer 2. The film thicknesses and compositions of the quantum well and barrier of the multi-quantum well structure 3 are set so that the refractive index is greater than the refractive index of either the base layer 4 or the emitter layer 5. As a result, the incident light 10 is guided into the multi-quantum well structure 3, and the output light 11 is obtained.

Next, the operation of the phototransistor of this example will be explained.

FIG. 2 shows a circuit diagram when this embodiment is operated as a waveguide type optical switch.

When a signal voltage 23 is applied between the pace and the emitter, a pace current 24 (2In) is applied to the pace electrode 8.
flows to At this time, the collector current 25 (EIc) is calculated as IC=βIB using the current amplification factor β of the phototransistor 20.
1). At this time, collector voltage 26 (=V
c) is expressed as VC=V0-)1,1c.--.--(2). In equation (2), ■o is the voltage of the DC power supply 22, and R is the resistance value of the external resistor 21. According to equations (1) and (2), collector voltage 26 (EVc) is VC=V. −RβI, ,−・・(
3). Here, when the signal voltage 23 is changed, the base current z,1 (=IB) changes, and the collector voltage ■c changes (3)
It will change depending on the formula. The magnitude of the signal voltage 23 is roughly around the forbidden band width of the semi-coated body, so it is L5~2v.
It will be about. Further, the DC power supply 22 can apply a relatively large voltage of 5V or more to the collector electrode 7. Therefore, in this embodiment, since the large collector voltage 26 is controlled by the low signal voltage 23, the electric field applied to the multi-quantum well structure 3 changes, and the original switch operation can be performed.

In the above-described operation, an electrical signal is input as the signal, but the original transistor of this embodiment can be controlled by an optical input signal.

Next, this operation will be explained.

The third factor shows the absorption spectrum of the multi-quantum well structure 3. The control signal -5'l:30 is assumed to be light having a wavelength λ0 near the exciton peak of the multi-quantum well structure 3 when the electric field is zero. Furthermore, the controlled light 31 has a wavelength of λ1, which is longer than λ0. First, when the control signal light 30 is zero, the collector current 25 is zero, so a large DC voltage (HVo) is applied to the collector voltage 26 according to equation (2). At this time, the absorption spectrum is shown by the broken line in FIG. 3, and there is a large absorption for the controlled source 31, resulting in an OFF state for the controlled source 'jt31. Next, when the control signal light 30 is incident, it undergoes a large absorption, and this absorption causes a collector current 25 (=Ic) to flow due to the same effect as the base current 24 (=IB).

Then, according to equation (3), the collector voltage 26 (miVc
) decreases and becomes almost zero, resulting in the absorption spectrum of electric field=O shown in FIG. At this time, the control light 31 is in an on state in which absorption is almost zero. Therefore, the controlled light 31 is turned on only when the control signal light 30 is incident, and when the control signal light 30 is not present, the controlled light 31 is turned off.

Next, the optical bistable operation of the optical transistor of this example will be explained. A circuit diagram for this operation is shown in FIG. First, the incident light is the wavelength λ shown in Figure 3.

Let's assume that the light is incident. First, when there is no incident light, the collector current 25 (MiIC) is zero, so the collector voltage 26 (=VC) is approximately equal to the voltage vo of the DC power supply 22, and a large electric field is applied to the multi-quantum well structure 3. It is in a state. Therefore, the absorption spectrum of the multi-quantum well structure 3 is as shown by the broken line in FIG. Next, as the incident light (wavelength λ0) is gradually increased, the collector current 25 increases and the electric field applied to the multi-quantum well structure 3 decreases, so that the absorption coefficient at the wavelength λ0 increases. As the absorption coefficient increases, positive feedback occurs, which further increases the collector current 25. The state of this positive feedback is shown below.

When such positive feedback is applied, absorption increases rapidly, and the intensity of the emitted light becomes almost zero. This change is the A-)B transition in the dependence of the output light intensity on the incident light intensity shown in FIG. Next, when the incident light is decreased from point B, a positive feedback as shown below is applied.

Then, the absorption coefficient decreases rapidly and the output light increases. At this time, the operating point transitions from point 0 to point D in FIG.

As explained above, the optical transistor of this embodiment can perform optical bistable operation. Note that the bias power supply V in Fig. 4
By adjusting B, the operating point when there is no incident light can be adjusted.

Next, a method for manufacturing the original transistor of this embodiment will be briefly described. First, a collector layer 2 is placed on an n-GaAs substrate 1.
Multiple quantum well layer 3. Base layer 4. Emitter layer 5. The cap layer 6 is successively crystal-grown.

The crystal growth method may be any growth method such as molecular beam epitaxy, organometallic vapor phase epitaxy, or the like. Next, base layer 4
Partially photo-etch until exposed. Next, photoetching is performed to process the multiple quantum well layer 3 into stripes. Next, collector electrode 7. Pace electrode8. The emitter electrode 9 is formed to complete the process.

In the embodiment described above, a multiple quantum well structure is used as the quantum well structure, but the quantum well structure is not limited to this, and a single quantum well structure may also be used. Further, in this embodiment, the npn) transistor configuration is used, but the present invention is not limited to this. Further, in this embodiment, the lateral waveguide structure is a high mesa stripe structure, but the present invention is not limited to this, and other waveguide structures 1 such as a buried structure, a ridge waveguide structure, etc. may be used. or,
In this example, klGaAs/GaAs was used as the material, but the material is not limited to this, and other materials such as InGaAsP/
InP-based InGaAlAs/InP-based materials, etc. may also be used.

〔Effect of the invention〕

As explained above, in the present invention, by providing a quantum well structure between the collector and pace of a bipolar transistor, an original transistor capable of optical switching operation at a low signal voltage can be obtained by utilizing the increase in transistor = action t. effective.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a circuit diagram for optical switching operation of an embodiment of the present invention, and FIG. 3 is a characteristic diagram showing the absorption spectrum of a multiple quantum well layer. Fourth
The figure is a circuit diagram for optical bistable operation, and FIG. 5 is an input/output characteristic diagram for optical bistable operation. DESCRIPTION OF SYMBOLS 1... N-GaAs substrate, 2... Collector layer, 3... Multiple quantum well structure, 4...
...Pace layer, 5...Emitter layer, 6...
...Cap layer, 7...Collector electrode, 8.
...Pace electrode, 9...Emitter electrode,
10...Incoming light, 11...Outgoing light, 2
0...Phototransistor, 21...Resistor, 22...DC power supply, 23...Signal voltage, 24...Pace current, 25 ...Collector current, 26...Collector voltage, 30...
... Control signal light, 31 ... Controlled light, 40
・・・・・・Bye Kaya l Takumi 2θ old Y Lance, ri' 2nd Figure 30 Cow 1 signal light 3rd sWJ

Claims (1)

[Claims] A quantum well structure including a collector layer of a first conductivity type, at least one quantum well provided in contact with the collector layer, a base layer provided in contact with the quantum well structure, and a quantum well structure including at least one quantum well provided in contact with the collector layer; A light comprising an emitter layer of a first conductivity type provided in contact with each other, wherein the average refractive index of the quantum well structure is larger than the refractive index of any of the emitter layer, the base layer, and the collector layer. transistor.