JPH05275741A - Semiconductor element - Google Patents

Abstract

PURPOSE:To provide a semiconductor element wherein it functions as an optical modulation element and an optical storage element and it can be used for an optical computer, an optical neuro-computer and the like. CONSTITUTION:The following are laminated alternately between a first electrode and a second electrode: p-type GaAs semiconductor layers; and n-type Gaps semiconductor layers 2. Then, the following are formed alternately: first p-n junction parts whose change amount of a change in an energy band structure at junction parts of the GaAs semiconductor layers 1, 2 is large and which are step-shaped; and second p-n junction parts whose change in an energy band structure is gently sloped or whose change amount in a change in the energy band structure is small as compared with that in the first p-n junction parts and which are step-shaped. In addition, quantization levels are formed at both the p-type GaAs semiconductor layers 1 and the n-type GaAs semiconductor layers 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device used as an optical computer, an optical neurocomputer, etc. and functioning as an optical modulator and an optical storage device.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional optical threshold device (IEEE, ED-29, No9 (1982) page 1382). In this optical threshold device, the n-type emitter layer 21 made of InP is used.
And a p-type base layer 22 made of InGaAsP and In
N-type collector layer 23 made of GaAsP, n-type cladding layer 24 made of InP, and n made of InGaAsP
A type active layer 25 and a p-type clad layer 26 made of InP are laminated.

In the optical threshold device having the above structure, when the input light is not incident, the p-type clad layer 26 has a positive voltage with respect to the n-type emitter layer 21. It is applied to the value element and kept in the forward blocking state. In this case, the p-type base layer 22 and the n-type collector layer 2
The pn junction formed by 3 and 3 is reverse-biased, and acts as a barrier against the movement of carriers to block the current. In this forward blocking state, when input light having a predetermined input light intensity or more is incident from the n-type emitter layer 21 side,
Light absorption occurs in the p-type base layer 22, and as shown in the energy band diagram of FIG. 5, electrons generated by light absorption drift move into the n-type active layer 25. Then, the electrons recombine with holes in the n-type active layer 25,
Emits light. This light is emitted from the p-type cladding layer 25. In this way, the optical switching operation is performed.

[0004]

However, in the above-mentioned conventional optical switch, the switching speed thereof depends on the transit time of electrons from the p-type base layer 22 to the n-type active layer 25. Then, the base layer 22 and the active layer 25
Since each of the layers interposed between and is made of InGaAsP and InP having a low electron transfer speed, there is a limit to increase the switching speed.

Therefore, conventionally, from the base layer 22 to the active layer 2
A means for shortening the distance to 5 to increase the switching speed is adopted. Specifically, the semiconductor layer between the base layer 22 and the active layer 25 is thinned. However, in this case, since the n-type cladding layer 24 becomes thin,
Another problem arises in that the number of carriers passing through the clad layer 24 increases, the efficiency of carrier confinement in the active layer 25 decreases, and the output light intensity decreases.

The above-mentioned problems are applicable not only to optical switching elements but also to optical nonlinear elements, and there is a demand for speeding up of wavelength nonlinear characteristics.

The present invention has been made in view of the above problems, and provides a semiconductor device capable of increasing a switching operation or a non-linear speed and applicable to an optical computer, an optical neurocomputer, and the like. The purpose is to

[0008]

A semiconductor device according to the present invention is a semiconductor device in which a p-type semiconductor layer and an n-type semiconductor layer are alternately laminated between first and second electrodes. And a first pn junction having a stepwise change in energy band structure at the junction of the second semiconductor layer, and a gentle slope and change amount compared to the first pn junction having an energy band structure change. And second p-n junctions, which are in the form of small steps, are alternately provided, and p
Quantization levels are provided in both the type semiconductor layer and the n-type semiconductor layer.

[0009]

The semiconductor device according to the present invention is constructed by alternately stacking p-type semiconductor layers and n-type semiconductor layers between the first and second electrodes. The first pn junction in which the energy band structure change in the junction between the first and second semiconductor layers changes stepwise and the energy band structure change in comparison with the change in the first pn junction is Second pn that has a gentle slope, or has a step shape in which the amount of change is smaller than the change in the first pn junction.
The joining portions are provided alternately. Quantization levels are formed in both the p-type semiconductor layer and the n-type semiconductor layer.

The change in the energy band structure at the junction between the p-type semiconductor layer and the n-type semiconductor layer is adjusted by adjusting the effective carrier density (value obtained by subtracting the minority carrier density from the majority carrier density) in each semiconductor layer. It can be set as described above. Further, by appropriately setting the layer thicknesses of the p-type semiconductor layer and the n-type semiconductor layer, the quantization level can be formed in both the p-type semiconductor layer and the n-type semiconductor layer.

In the semiconductor device having such a structure, when light is incident from the outside in the stacking direction with a voltage applied between the first and second electrodes, part or all of the external light is emitted from the semiconductor. The light is absorbed in the element, and electrons and holes are generated in the semiconductor element by this light absorption. And
The electrons and holes are confined in the n-type semiconductor layer and the p-type semiconductor layer, respectively.

That is, in the semiconductor element according to the present invention, when external light is incident on the semiconductor element, the larger the light intensity is, the more electrons and holes are generated due to light absorption in the semiconductor element. The occupancy of electrons with respect to the quantization level in the semiconductor layer and the occupancy of holes with respect to the quantization level in the p-type semiconductor layer are both large. Moreover, these electrons and holes are emitted from the n-type semiconductor layer and the p-type, respectively.
In order to be spatially separated and confined in the type semiconductor layer,
Recombination is unlikely to occur. In particular, when the slope of the energy band structure change in the second pn junction is made steep by the voltage applied between the first and second electrodes, the effect of confining electrons and holes is increased, and recombination is further enhanced. Less likely to happen.

Therefore, in the semiconductor device according to the present invention, the incident external light intensity can be stored in the form of the density of electrons and holes generated by absorption. When the recombination of electrons and holes is made difficult to occur and the density of electrons and holes generated by the absorption of light is maintained, the number of vacant levels is reduced, so that the subsequent light absorption becomes difficult to occur. Therefore, thereafter, the ratio of external incident light passing through the semiconductor element increases. That is, when the intensity of the external light incident on the semiconductor element is high or the frequency of incidence of the external light is high, the light transmittance of the semiconductor element gradually increases.

This storage state (that is, the state in which electrons and holes generated by light absorption are spatially confined and separated in the n-type semiconductor layer and the p-type semiconductor layer, respectively) is the n-type semiconductor layer and the p-type semiconductor. The recombination of electrons and holes in the pn junction formed at the interface with the layer gradually returns to the state before light absorption. That is, the electrons and the holes are recombined by the leakage of the electrons to the p-type semiconductor layer side and the leakage of the holes to the n-type semiconductor layer side. The degree of this exudation is greater in the second pn junction having a gentler slope of energy band structure change than in the first pn junction having a stepwise slope of energy band structure change.
In addition, since the degree of this exudation can be controlled by the voltage applied between the first and second electrodes, the storage time can be controlled by appropriately setting the applied voltage.

Considering, for example, optical engagement in which the semiconductor element array of the present invention is interposed between the light emitting element array and the light receiving element array, first, in order to determine the light transmittance of each semiconductor element, each light emitting element is determined. Light is incident on each semiconductor element with an appropriate distribution of the light emission intensity, and then the input light having the emission intensity corresponding to the input distribution is emitted within the time when the light transmittance is stored in each semiconductor element. Light is incident on each semiconductor element from the element. Then, the product of the input light intensity and the light transmittance can be known by measuring the photocurrent value obtained from each light receiving element. In this way, it is possible to perform processing such as product-sum calculation, which is frequently used in neural networks, in parallel and at high speed, and since the optical coupling in this case is variable, the product operation can also be variable. Further, since the light transmittance of the semiconductor element, which means the degree of coupling, is changed by light, it is not necessary to directly apply an electrical control signal from the outside to the semiconductor element, and the light transmittance can be changed in parallel and at high speed. be able to. Furthermore, since the wavelength of the control light can be the same as the wavelength of the input light in order to change the light transmittance of the semiconductor element, only one type of light emitting element is required, and when the wavelengths of the control light and the input light are different, In comparison, the manufacturing is easy and the integration degree is improved.

The difference between the quantum level energy of electrons in the n-type semiconductor layer and the top energy of the valence band, or the quantization level energy of holes in the p-type semiconductor layer and the bottom energy of the conduction band. It is necessary to set the difference between the two smaller than the light energy of the external light.

[0017]

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

FIG. 1 is a schematic view showing an example of a semiconductor device according to the present invention. The semiconductor device according to the present embodiment is the first
And a p-type GaAs semiconductor layer 1 and an n-type GaAs semiconductor layer 2 are alternately and periodically laminated between the second electrodes (not shown). Then, a predetermined voltage can be applied from the power source 5 between the first and second electrodes. Each of the GaAs semiconductor layers 1 and 2 has an effective carrier density of about 10 ¹⁸ cm ^-3 on one side of the layer and an effective carrier density of about 10 ¹⁵ cm ^-3 on the other side of the layer. A density gradient is provided. Therefore, the first
In the pn junction, the carrier density changes from the effective hole density (about 10 ¹⁸ cm ⁻³ ) in the p-type GaAs semiconductor layer 1 to the n-type Ga.
The step density changes to a large step up to the effective electron density in the As semiconductor layer 2 (about 10 ¹⁸ cm ⁻³ ), and the carrier density in the second pn junction is equal to the effective electron density in the n-type GaAs semiconductor layer 2 ( From about 10 ¹⁵ cm ^-3 ) to the p-type GaAs semiconductor layer 1
The effective hole density (about 10 ¹⁵ cm ^-3 ) within the inside gradually changes.

FIG. 2 is a graph showing the energy band structure of the semiconductor device according to this embodiment. In the semiconductor element of the present embodiment, the energy band structure change in the first pn junction 3 has a step-like shape with a large change amount.
In the pn junction 4, the energy band structure change is gradually and continuously changed, or the energy change amount is in a stepwise manner.

In this semiconductor device, the electrons generated in the device are n-type GaA, as schematically shown in FIG. 3 which shows the wave functions of electrons and holes when no bias voltage is applied.
The holes are confined in the s semiconductor layer 2 and the holes are confined in the p-type GaAs semiconductor layer 1. In addition, external light (for example,
Electrons and holes generated when light having a wavelength of about 800 nm) is incident perpendicularly to the layer plane (that is, in the stacking direction of the GaAs semiconductor layers 1 and 2) are also n-type GaA.
It is confined in the s semiconductor layer 2 and the p-type GaAs semiconductor layer 1.

In this state, the wave function of the electrons confined in the n-type GaAs semiconductor layer 2 and the p-type GaA
s In the wave function of holes confined in the semiconductor layer 1, there is little positional overlap between both wave functions when the position coordinates are taken in the stacking direction, and the probability of recombination of electrons and holes is low.

By applying a voltage in the stacking direction of the semiconductor element to make the inclination of the energy band in the second pn junction 4 in the stacking direction gentle as shown in FIG. 4, the inside of the n-type GaAs semiconductor layer 2 is formed. The overlap between the wave function of the electrons confined in the p-type and the wave function of the holes confined in the p-type GaAs semiconductor layer 1 becomes larger than that when no voltage is applied, and the electrons and holes are recombined. The probability increases.

In addition, a voltage is applied in the opposite direction so that the second p
When the inclination of the energy band in the n-junction 4 in the stacking direction is made steep, the wave function of the electron confined in the n-type GaAs semiconductor layer 2 and the wave function of the hole confined in the p-type GaAs semiconductor layer 1 And the probability of recombination of electrons and holes is lower than that in the case where no voltage is applied.

That is, in the semiconductor device according to the present embodiment, when a voltage is applied so that the energy band of the second pn junction 4 becomes steep, the intensity of incident external light is generated by absorption. The time that can be stored in the form of electron and hole densities can be extended. Then, when external light having an arbitrary emission intensity is newly incident as input light within this storage time, the light transmittance corresponding to the stored carrier is multiplied (multiplied) by the input light intensity. It is possible to obtain the output light having the light intensity.

When the semiconductor element according to the present embodiment is arranged, for example, between a light emitting element and a light receiving element, the light transmittance of the semiconductor element according to the present embodiment is continuously controlled by using the control light output from the light emitting element. The light transmittance can be stored for a predetermined time determined by the applied voltage. Then, by inputting the input light having an arbitrary emission intensity from the light emitting element within the predetermined time, the product of the input light intensity and the light transmittance can be obtained.
In this case, by appropriately setting the storage time by the applied voltage, the storage can be automatically reset, and by newly injecting the control light having the corrected emission intensity from the same light emitting element, The light transmittance can be modified. By repeating such operations, it becomes possible to perform processing such as product-sum calculation, which is frequently used in neural networks, in parallel and at high speed, and further, the product calculation can be made variable. Further, in the present embodiment, since the wavelength of the control light for changing the light transmittance of the semiconductor element may be the same as the wavelength of the input light, only one type of light emitting element may be used, and the wavelengths of the control light and the input light may be different. The production is easier and the degree of integration is improved as compared with the case where is different.

[0026]

As described above, in the semiconductor device according to the present invention, the energy band structure change is stepwise.
Of the pn junction and the first pn junction have an energy band structure that changes more gently than the first pn junction, or has a step shape in which the amount of change is smaller than that of the first pn junction. Second pn junctions are alternately provided, and
Since the quantization levels are provided in both the p-type semiconductor layer and the n-type semiconductor layer, it is possible to change the light transmittance of the semiconductor element by the control light output from the light emitting element and to transmit the light transmission. The rate can be maintained for a time determined by the applied voltage. Therefore, by using the semiconductor device according to the present invention, it becomes possible to perform processing such as multiply-add operation, which is frequently used in neural networks, in parallel and at high speed, and it is possible to make the product operation variable. .. Further, since the control light and the input light may have the same wavelength,
It is easy to manufacture and can be highly integrated.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a semiconductor device according to the present invention.

FIG. 2 is a graph showing the energy band structure of the same.

FIG. 3 is a schematic diagram showing wavefunctions of electrons and holes, which are also superimposed on an energy band structure.

FIG. 4 is a schematic diagram showing changes in wave functions of electrons and holes and changes in energy band structure when the voltage is applied.

FIG. 5 is a diagram showing a conventional optical threshold device.

[Explanation of symbols]

 1; p-type GaAs semiconductor layer 2; n-type GaAs semiconductor layer 3, 4; pn junction 5; power supply 21; emitter layer 22; base layer 23; collector layer 24, 26; clad layer 25; active layer

Claims (1)

[Claims] 1. A semiconductor device comprising a p-type semiconductor layer and an n-type semiconductor layer alternately laminated between a first electrode and a second electrode, wherein an energy band at a junction between the first and second semiconductor layers is formed. The first pn junction has a stepwise structural change, and the second pn junction has an energy band structural change that is gentler than the first pn junction and has a stepwise change with a small amount of change. A semiconductor element, wherein pn junctions are alternately provided, and quantization levels are provided in both the p-type semiconductor layer and the n-type semiconductor layer.