JPS63158882A - Semicoductor optical memory - Google Patents

Abstract

PURPOSE:To conduct operation at high speed by changing the bias state of a p-n junction in a unijunction-transistor including a thin-film semiconductor layer having quantum well structure in an emitter region by trigger beams, switching the state to a conductive state from a nonconductive state and generating the breaching of exaction absorption. CONSTITUTION:A semiconductor optical memory has a unijunction-transistor having first and second base electrodes, 11, 12 and an emitter electrode 13 consisting of a metallic layer formed to an emitter region 14, a bias-voltage supply means giving each of the emitter electrode 13 and the first base electrode 11 and the second base electrode 12 predetermined potential VE, VB and GND and biassing the unijunction-transistor to the state of high impedance, and a trigger-beam applying means lowering the potential of a base region just under the emitter region 14 and bringing the unijunction-transistor to a conductive state. Accordingly, the base region in the unijunction-transistor biassed under a high resistance state is irradiated with trigger beams, and switched to the conductive state, thus acquiring the semiconductor optical memory, which has small light intensity and can be operated at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor optical memory required in image processing, optical computers, and the like.

[Conventional technology]

The light transmittance is changed by a minute trigger light,
Semiconductor optical memory, which has the ability to maintain this state even after the trigger light disappears, is an indispensable key device in constructing future optical exchange and parallel optical information processing systems. An example of a device having such a function is the 5EED (Self-Electro-Optic-X effect device).
- Optic Effect Device) is known. 5EED stands for Applied Physics Letters.
s), Vol. 45, pp. 13 to 15, 1984, bistable to transmitted light is achieved by utilizing changes in exciton absorption in multiple quantum wells due to an applied electric field. It is something that gives rise to characteristics. The product of light intensity (Ps) and response time (τ, ) required for switching is ~4 fJ/μm
It is 2. There is a trade-off relationship between reducing light intensity and shortening response time. The light receiving area S of 5EED is 10μm
Assuming that X is 10ttm, 40mW is required as Ps to obtain r,=10ns. This value is too large when considering integration.

Also, the ratio of the transmitted light intensity at "H" and "L" is 1:
The extinction ratio is about 0.6, which cannot be said to be good.

[Problem that the invention seeks to solve]

The 5EED, which is the conventional semiconductor optical memory described above, has the disadvantage that it is not suitable for integration because it cannot simultaneously reduce the light intensity required for switching and shorten the response time, and its extinction ratio is also poor.

An object of the present invention is to provide a semiconductor optical memory that requires low light intensity for switching and can operate at high speed. Another object of the present invention is to provide a semiconductor memory with improved extinction ratio.

[Means for solving problems]

The semiconductor optical memory of the present invention includes an emitter region including a thin film semiconductor layer having a quantum well structure, a base region that is in contact with the emitter region, and a first metal layer formed on the base region with the emitter-base junction in between. ．． Second
a unijunction transistor including a base electrode and an emitter electrode made of a metal layer formed in the emitter region, and a predetermined potential is applied to each of the emitter electrode, the first base electrode, and the second base electrode. bias voltage supply means for biasing the unijunction transistor to a high impedance state; and trigger light irradiation means for lowering a base region potential directly below the emitter region to bring the unijunction transistor into a conductive state. It consists of

[Effect]

By irradiating the base region of a unijunction transistor biased to a high resistance state with trigger light and switching it to a conductive state, free carriers are supplied to the thin film semiconductor layer of the quantum well structure. The absorption coefficient for light decreases. This state is maintained even if the irradiation of the trigger light is stopped.

〔Example〕

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

FIG. 1 is a schematic cross-sectional view of a semiconductor chip showing the main parts of an embodiment of the present invention.

This embodiment includes an emitter region 14 including a thin film semiconductor layer 15 having a quantum well structure, a base region 16 that is in contact with the emitter region 14, and a base region 1 with an emitter-base junction in between.
The first . A unijunction transistor including an emitter electrode 13 made of a second base electrode 11, 12 and a metal layer formed in an emitter region 14; Bias voltage supply means biases the unijunction transistor to a high impedance state by applying a predetermined potential V, , V, , GND to each of the unijunction transistors; and trigger light 19 irradiation means for bringing the light into conduction. That is, the base region 16 has a thickness of 0.
．． 2μm high resistance n-GaAs layer (Fe doped)
The thin film semiconductor layer 15 consists of a multiple quantum well in which undoped GaAs and Aeo, 3(ia) (1,7As) are alternately stacked with a thickness of 5 nm.
s and Ae O-'3GaO-7^S are p-type, and the background carrier concentration is N= I
It was m-'. The number of laminated layers is 100, and the total thickness of this portion is 1 μm. 17 is p-Ae
. , 3Gao, 7As layer (thickness 0.5 μm, N=
I x 1018 cm-'), 18 is a p-GaAs layer (thickness 0.1) tm for ohmic contact, N
= 5X 1018 cm-').

Mesa etching is performed in a circular shape up to the base region 16 with a size of 60 μmφ. Note that the semi-insulating GaAs substrate 10
A window is selectively etched into a circular shape from the back side,
The transmittance may be improved.

Next, the operation of this embodiment will be explained.

FIG. 2 is a voltage-current characteristic diagram of the embodiment shown in FIG.
FIG. 3 is an absorption characteristic diagram showing absorption coefficients before and after exciton absorption bleaching in FIG.

A predetermined bias voltage is supplied to the second base electrode 12.
The electric field directed toward the first base electrode 11 from the base region 16
Suppose that it is occurring inside. Potential V directly below the emitter region 14
When the emitter voltage Vt is VE<VC, the pn junction is slightly biased in the reverse direction and is in a high impedance state. When Vi>Vc, the pn junction is biased in the forward direction and holes are injected. As a result, the conductivity between the emitter region 14 and the first base electrode 11 is modulated by a positive feedback effect, and the base-to-base current increases, showing a negative resistance as shown in FIG. 2. In FIG. 2, V=V, A voltage is set at the point , and the emitter region 14 is irradiated with incident light of a predetermined wavelength. When the trigger light is applied to the base region 16 from the first base electrode 11, the conductivity of this portion increases.

As a result, Vc decreases, and when Vi:>Vc is reached, the state shifts to a low impedance state and current begins to rapidly flow into the emitter region 14. (2) If 1 is brought close to the on-voltage in the range vE<Vc, the trigger light intensity required to shift to the low impedance state can be reduced as much as desired in principle. When the emitter is slightly biased in the opposite direction and in a high impedance state, the light absorption of the thin film semiconductor layer 15 is as shown by the curve (a) in FIG. This corresponds to exciton absorption due to position. By keeping the thickness of the thin film below the de Broglie wavelength, significant exciton absorption can be seen even at room temperature.

The wavelength of the incident light is made to almost match the exciton wavelength, and the trigger light creates a non-conducting state 1! When the state changes from (=high impedance state m> to a conductive state (=low impedance state) and a current suddenly flows into the thin film semiconductor layer 15, light absorption becomes as shown in the curve (b) in Figure 3. The reason why the absorption coefficient decreases due to current injection is that free carriers are supplied to the thin film semiconductor layer 15, and exciton absorption is weakened (bleaching) due to the accompanying screening effect, etc., Physical, Review Letters (
Physical Review Letters) magazine,
As described in Vol. 17, pp. 2433-2436, 1984, it has been confirmed that bleaching of exciton absorption in GaAs-^e GaAs occurs at lps or less. The reason why the absorption coefficient does not completely fall to zero even after bleaching in Fig. 3(b) is due to the effect of band gap shrinkage, etc., but it is still 1:
0.4, a larger absorption coefficient ratio than the conventional example, resulting in conduction.

The difference in transmittance when non-conducting can also be enhanced somewhat.

Furthermore, the trigger sensitivity can be improved over 5EED by keeping the bias voltage sufficiently close to the on-voltage. Therefore, even if it is assumed that there is a trade-off relationship between reducing the light intensity and shortening the response time, miniaturization can be achieved without increasing the intensity of the trigger light very much.

〔Effect of the invention〕

As explained above, the present invention uses a trigger light to change the bias state of the pn junction of a unijunction transistor including a thin film semiconductor layer with a quantum well structure in the emitter region to switch from a non-conducting state to a conducting state, thereby generating exciters. Since it causes absorption bleaching, it is possible to reduce the light intensity required for switching semiconductor optical memories, thereby achieving high-speed operation. From a different perspective, this means that a semiconductor optical memory suitable for integration can be realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a semiconductor chip showing the main parts of an embodiment of the present invention, FIG. 2 is a voltage-current characteristic diagram of the embodiment of FIG. 1, and FIG. 3 is a GaAs-klo-5GaO ,7
Curve (a) is an absorption characteristic diagram showing the absorption coefficient before and after exciton absorption bleaching at a temperature of 15K in an As multiple quantum well.
is before bleaching, and curve (b) is in the bleached state. DESCRIPTION OF SYMBOLS 10... Semi-insulating GaAs substrate, 11... First base electrode, 12... Second base electrode, 13... Emitter electrode, 14... Emitter region, 15... Thin film semiconductor Layer, 16--Base region, 17.''p
A1! O,5GJI0.7As layer, 1.8-p-Ga
As layer, 19-) Loga light. The leopard man's mouth

Claims (2)

[Claims] (1) An emitter region including a thin film semiconductor layer having a quantum well structure, a base region that is in contact with the emitter region, and first and second metal layers each formed on the base region with the emitter-base junction in between. A unijunction transistor includes a base electrode and an emitter electrode made of a metal layer formed in the emitter region, and a predetermined potential is applied to each of the emitter electrode, the first base electrode, and the second base electrode. bias voltage supply means for biasing the unijunction transistor to a high impedance state; and trigger light irradiation means for lowering the potential of a base region immediately below the emitter region to bring the unijunction transistor into a conductive state. A semiconductor optical memory characterized by: (2) The semiconductor optical memory according to claim (1), wherein the thin film semiconductor layer maintains a light transmittance for incident light having an exciton absorption wavelength.