JPH05267639A - Photodetector - Google Patents

Abstract

PURPOSE:To enable a photodetector using a phototransistor to obtain a sufficiently high quantum efficiency, namely, a sufficiently high optical gain even when the thickness of its base layer, namely, light receiving layer is extremely small. CONSTITUTION:A resonator structure is formed by respectively forming Bragg reflectors 4 and 5 on the upper and lower surfaces of a heterojunction phototransistor formed by successively piling up an n-type A GaAs layer 1, p-type GaAs layer 2, and n-type A GaAs layer 3 so that the loop section of standing waves of light formed in the resonator by incident light can be positioned to the part of a base layer, namely, the layer 2 working as a light receiving layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving element, and more particularly to a light receiving element using a phototransistor.

[0002]

2. Description of the Related Art In recent years, research on optical semiconductor devices using a combination of a light emitting element and a light receiving element has been actively conducted, and various kinds have been reported so far.

Heterojunction phototransistors are often used as light-receiving elements in such optical semiconductor devices (eg, IEEE Trans. Electron Devices, vo).
l. ED-31, No. 6, 805 (1984)). In this heterojunction phototransistor, the thickness of the base layer, that is, the light receiving layer (light absorbing layer) is usually large to some extent, for example, 200 to 300.
Unless it is increased to about nm, sufficient quantum efficiency (light-carrier conversion efficiency), and thus, sufficient optical gain cannot be obtained.

[0004]

By the way, in a heterojunction phototransistor using, for example, an AlGaAs layer as an emitter layer and a collector layer, when an InGaAs layer, for example, is used as a base layer, that is, a light receiving layer, it is usually used as a substrate. Light having a wavelength transparent to the GaAs substrate can be used as input light, which is convenient for realizing a two-dimensional array of optical semiconductor devices. However, since InGaAs has a lattice mismatch with AlGaAs, when the base layer, that is, the InGaAs layer as the light receiving layer is epitaxially grown on the AlGaAs layer as the collector layer or the emitter layer of the heterojunction phototransistor,
The thickness of this InGaAs layer must be less than or equal to its critical thickness. However, since this critical film thickness is extremely small on the order of 10 to 20 nm, when this InGaAs layer is used as the light receiving layer, there is a problem that sufficient quantum efficiency, and therefore, sufficiently high optical gain cannot be obtained. ..

Therefore, an object of the present invention is to provide a light-receiving element capable of obtaining a sufficient quantum efficiency and thus a sufficiently high optical gain even when the thickness of the base layer, that is, the light-receiving layer is extremely small. ..

[0006]

In order to achieve the above object, a light receiving element according to the present invention comprises an emitter layer (1 or 3), a base layer (2) and a collector layer (3 or 1) which are laminated on each other. A phototransistor having a resonator structure in which an emitter layer (1 or 3) side and a collector layer (3 or 1) side are sandwiched by Bragg reflectors (4, 5), and light formed in the resonator by light incidence. The thicknesses of the emitter layer (1 or 3), the base layer (2), and the collector layer (3 or 1) are selected so that the antinode of the standing wave of is located at the base layer (2). It is a thing.

[0007]

According to the light-receiving element of the present invention constructed as described above, the antinode portion of the standing wave of light formed in the resonator by the incidence of light, that is, the portion of maximum intensity, is the base layer (2). By being located in the part of
That is, even when the thickness of the light-receiving layer is extremely small, sufficient quantum efficiency, that is, sufficiently high optical gain can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are designated by the same reference numerals.

FIG. 1 shows a light receiving element according to the first embodiment of the present invention.

As shown in FIG. 1, the light receiving element according to the first embodiment has an n-type AlGaAs layer 1 and a p-type AlGaAs layer 1 formed thereon.
The n-type AlGaAs layer 1 side and the n-type AlGaAs layer 3 side of the heterojunction phototransistor consisting of the GaAs layer 2 and the n-type AlGaAs layer 3 formed thereon are Bragg reflectors (also called Bragg reflectors or DBRs) 4, 5 It has a resonator structure sandwiched between. In this case, the n-type AlGaAs layers 1 and 3 form an emitter layer or a collector layer, and the p-type GaAs layer 2 forms a base layer.

The Bragg reflectors 4 and 5 are made of, for example, AlAs.
It is preferably formed of an n-type semiconductor multilayer film in which layers and AlGaAs layers are alternately laminated. Further, in this case, the reflectance of the Bragg reflector 5 on the light incident side is preferably selected to be small so that the incident light can be efficiently taken into the heterojunction phototransistor.

In the light receiving element according to the first embodiment,
The total thickness of the n-type AlGaAs layer 1, the p-type GaAs layer 2, and the n-type AlGaAs layer 3, that is, the cavity length is the antinode of the standing wave of light formed in the cavity by the light incident on the light receiving element. Is located so as to be located in the base layer, that is, in the portion of the p-type GaAs layer 2 serving as the light receiving layer. More specifically, when the wavelength of incident light is λ, this resonator length is selected to be (n + 1) / 2 times (n = 1, 2, ...) Of λ,
As a result, the antinode portion of the standing wave of the light formed in the resonator due to the incident light can be positioned at the portion of the p-type GaAs layer 2 as the light receiving layer. A standing wave in the case of n = 1 is schematically shown in the left part of FIG.

According to the first embodiment, the antinode portion of the standing wave of the light formed in the resonator by the light incidence as described above is located in the portion of the p-type GaAs layer 2 as the light receiving layer. With such a configuration, sufficient quantum efficiency and therefore sufficiently high optical gain can be obtained even when the thickness of the p-type GaAs layer 2 is extremely small.

Further, instead of the p-type GaAs layer 2, for example, p-type
In the case of using the InGaAs layer, even if the thickness of the p-type InGaAs layer has to be suppressed to about 10 to 20 nm or less due to the restriction by the critical film thickness, sufficiently high quantum efficiency, and thus sufficiently high optical gain. Can be obtained.

FIG. 2 shows an optical semiconductor device according to the second embodiment of the present invention.

As shown in FIG. 2, in the optical semiconductor device according to the second embodiment, two heterojunction phototransistors HPT1 and HPT2 are arranged in parallel with each other at the cathode of a laser diode LD whose anode is grounded. Connected to opposite polarity. In this case, the collector of the heterojunction phototransistor HPT1 is connected to the cathode of the laser diode LD, and a negative voltage is applied to its emitter by the negative power supply. The emitter of the heterojunction phototransistor HPT2 is connected to the cathode of the laser diode LD and its collector is grounded. A positive voltage may be applied to the collector of the heterojunction phototransistor HPT2 by a positive power source.

In the optical semiconductor device according to the second embodiment configured as described above, according to the optical input 1 to the base of the heterojunction phototransistor HPT1 and the optical input 2 to the base of the heterojunction phototransistor HPT2. An optical output can be obtained from the laser diode LD. That is, the optical input 1 causes the heterojunction phototransistor H
When PT1 is on, a forward current equal to or higher than the threshold current flows through the laser diode LD to cause laser oscillation and an optical output is obtained. When the optical input 2 turns on the heterojunction phototransistor HPT2,
Since the current flows even through the heterojunction phototransistors HPT1 and HPT2, the forward current flowing through the laser diode LD is reduced to the threshold current or less, and the optical output cannot be obtained. In this case, the optical input 1 is a positive input and the optical input 2 is a negative input.

FIG. 3 shows a specific structural example of the optical semiconductor device according to the second embodiment.

As shown in FIG. 3, in this optical semiconductor device, a so-called SDH (Sepa) is formed on the p-type GaAs substrate 11.
laser diode LD consisting of rated double hetero laser and heterojunction phototransistors HPT1 and HPT
2 and are monolithically integrated.

In this case, a striped ridge 11a formed on the surface of the p-type GaAs substrate 11 and extending in one direction.
A p-type AlGaAs layer 12 as a p-type clad layer formed thereon, an active layer 13 formed thereon, for example, an i-type GaAs layer, and a first n-type clad layer formed thereon The n-type AlGaAs layer 14 serves as a resonator of the SDH laser which constitutes the laser diode LD. Reference numeral 15 is a p-type AlGaAs layer as a current blocking layer,
Reference numeral 16 denotes an n-type AlGaAs layer as the second n-type cladding layer. Regarding the SDH laser, for example, 12th IEEE
International Semiconductor Laser Conference, paper
F-1, 78 (1990).

An n-type GaAs layer 17 as a light absorption layer is formed on the n-type AlGaAs layer 16, and a Bragg reflector 4, an n-type AlGaAs layer 1, a p-type GaAs layer 2, and an n-type AlGaAs layer 3 are formed on the n-type GaAs layer 17.
And the Bragg reflector 5 are sequentially formed. In this case, the n-type AlGaAs layer 1, p above the ridge 11a is formed.
-Type GaAs layer 2, n-type AlGaAs layer 3 and Bragg reflector 5
Heterojunction phototransistors HPT1 and HPT2
A groove 18 for separating the is formed. And this groove 1
N-type AlGaAs layer 1 on one side (left side in FIG. 3) of 8 and p-type Ga
The resonator is formed by a structure in which the upper and lower sides of the heterojunction phototransistor HPT1 having the As layer 2 and the n-type AlGaAs layer 3 as the collector layer, the base layer, and the emitter layer are sandwiched by the Bragg reflectors 4 and 5, respectively, and the groove is formed. 18
N-type AlGaAs layer 1, p-type GaAs on the other side (right side in FIG. 3) of
The resonator is formed by a structure in which the upper and lower sides of the heterojunction phototransistor HPT2 having the layer 2 and the n-type AlGaAs layer 3 as the emitter layer, the base layer and the collector layer are sandwiched by the Bragg reflectors 4 and 5, respectively.

In this case, the heterojunction phototransistor HPT1 and the heterojunction phototransistor HPT1 having a structure in which the upper and lower sides of the heterojunction phototransistor HPT1 are sandwiched by the Bragg reflectors 4 and 5, respectively.
The resonator length of the resonator having the structure in which the upper and lower sides of 1 are sandwiched by the Bragg reflectors 4 and 5 is the same as that of the light receiving element according to the first embodiment, and is equal to the wavelength of the incident light (optical input 1 or optical input 2). (N + 1) / 2 times (n = 1, 2, ...) Is selected, whereby the antinode portion of the standing wave of light formed in these resonators upon incidence of light is p as a light receiving layer. Type GaAs
It is intended to be located in part of layer 2. Therefore, even when the thickness of the p-type GaAs layer 2 is extremely small, it is possible to obtain a sufficient quantum efficiency and thus a sufficiently high optical gain. As a result, when this optical semiconductor device is used as a differential optical amplification element as described later, sufficiently good characteristics such as a high optical amplification factor can be obtained. Also, p-type
For example, when a p-type InGaAs layer is used instead of the GaAs layer 2, even if the thickness of the p-type InGaAs layer has to be suppressed to about 10 to 20 nm or less due to the restriction by the critical film thickness,
Similar benefits can be obtained.

In the optical semiconductor device shown in FIG. 3,
A heterojunction phototransistor HPT1 is formed on the laser diode LD via the n-type GaAs layer 17 as a light absorption layer,
Since the HPT2 is stacked, the output light from the laser diode LD is absorbed by the n-type GaAs layer 17, so that the laser diode LD and the heterojunction phototransistors HPT1 and HPT2 are optically independent from each other. .. Further, it can be seen that the parallel division of the light receiving portion is extremely easily realized by the structure in which the heterojunction phototransistors HPT1 and HPT2 are stacked on the laser diode LD as described above. If the reflectance of the Bragg reflector 4 can be set to substantially 100%, the n-type GaAs layer 17 as the light absorption layer need not be provided.
It is possible to make the laser diode LD and the heterojunction phototransistors HPT1 and HPT2 optically independent of each other.

The heterojunction phototransistors HPT1 and HPT2 in the optical semiconductor device shown in FIG. 3 preferably have the p-type GaAs layer 2 as the base layer as the center and the n-type AlGaAs layers 1 and n as the emitter layer or the collector layer. Type
The AlGaAs layer 3 is formed in a structure in which the energy gap and the carrier concentration are completely symmetrical. By forming the heterojunction phototransistors HPT1 and HPT2 in a symmetrical structure with the base layer as the center, the following advantages can be obtained. That is, the heterojunction phototransistor HPT1 for positive input and the heterojunction phototransistor HPT2 for negative input have opposite emitters and collectors. Therefore, the element designs of these heterojunction phototransistors HPT1 and HPT2 are performed separately. In the ideal case, the emitter layer, the base layer and the collector layer of the heterojunction phototransistor HPT1 and the emitter layer, the base layer and the collector layer of the heterojunction phototransistor HPT2 should be formed separately. However, by making the heterojunction phototransistors HPT1 and HPT2 symmetrical with respect to the base layer as described above, even if these heterojunction phototransistors HPT1 and HPT2 are used with their emitters and collectors reversed, they are exactly the same. Since these characteristics can be obtained, these heterojunction phototransistor HP
T1 and HPT2 can be formed without paying attention to the polarity. This greatly simplifies the overall device design and the device formation process.

Further, in these heterojunction phototransistors HPT1 and HPT2, preferably, a p-type GaAs layer 2 as a base layer and an n-type AlGaAs layer 1 and an n-type AlGaAs layer 3 as an emitter layer or a collector layer are used. Between the intrinsic (i-type) GaAs layer and the so-called graded (grad)
ed) An i-type AlGaAs layer is provided. Here, the Al composition of the graded i-type AlGaAs layer is p-type as the base layer.
For example, the value is changed from 0.3 to 0 toward the GaAs layer 2.
In this case, in the i-type GaAs layers provided on both sides of the p-type GaAs layer 2 as the base layer, the carriers generated in the base layer, that is, the p-type GaAs layer 2 as the light-receiving layer due to light absorption efficiently pass the potential slope. This is to enable the driver to drive well. Also, graded i-type AlGaAs
The layer is for suppressing the potential spike caused by the discontinuity of the energy band due to the heterojunction between the p-type GaAs layer 2 and the n-type AlGaAs layer 1 and the n-type AlGaAs layer 3.

Next, a method of manufacturing the optical semiconductor device shown in FIG. 3 will be described.

As shown in FIG. 3, first, the p-type GaAs substrate 11 is formed.
After forming a ridge 11a on the surface of the p-type AlGaAs layer 12, a p-type AlGaAs layer 12 for a laser diode LD is formed on the p-type GaAs substrate 11 by, for example, metal organic chemical vapor deposition (MOCVD).
For example, an active layer 13 composed of an i-type GaAs layer, an n-type AlGaAs layer 1
4. The p-type AlGaAs layer 15 and the n-type AlGaAs layer 16 are sequentially epitaxially grown, and the n-type GaAs layer 17 as a light absorption layer is further epitaxially grown on the n-type AlGaAs layer 16 and then on the n-type GaAs layer 17. Then, the Bragg reflector 4, the n-type AlGaAs layer 1, the p-type GaAs layer 2, the n-type AlGaAs layer 3 and the Bragg reflector 5 are sequentially epitaxially grown. In this case, the p-type AlGaAs layer 12, the active layer 13, and the n-type AlGaAs layer 14 on the ridge 11a are epitaxially grown in a triangular prism shape as a whole. In the heterojunction phototransistors HPT1 and HPT2, the i-type GaAs layer is provided between the p-type GaAs layer 2 as the base layer and the n-type AlGaAs layer 1 and the n-type AlGaAs layer 3 as the emitter layer or the collector layer as described above. When providing a graded i-type AlGaAs layer, the graded i-type Al is formed on the n-type AlGaAs layer 1.
After the GaAs layer and the i-type GaAs layer are sequentially epitaxially grown, the p-type GaAs layer 2 is epitaxially grown on the i-type GaAs layer, and the i-type GaAs layer and the graded i-type AlGaAs layer are further formed on the p-type GaAs layer 2. After epitaxial growth, n-type Al was formed on the graded i-type AlGaAs layer.
The GaAs layer 3 is epitaxially grown.

After that, a resist pattern (not shown) having a predetermined shape is formed on the Bragg reflector 5 by lithography, and the Bragg reflector 5, the n-type AlGaAs layer 3, the p-type GaAs layer 2, and the n-type are used as a mask. A predetermined portion of the type AlGaAs layer 1 is sequentially removed by dry etching such as reactive ion etching (RIE) to form a trench 18 for separating the heterojunction phototransistors HPT1 and HPT2. As a result, the intended optical semiconductor device is completed.

In the optical semiconductor device according to the second embodiment, the SDH is used as the laser diode LD as described above.
By using a laser, many advantages can be obtained as follows. That is, this SDH laser
The threshold current is extremely low, for example, about 1 to 3 mA, and therefore the operating current can be set to an extremely low value of several mA for a laser diode. For this reason, this SDH laser has a very good matching with an electronic device such as a transistor in terms of operating current, and therefore, the heterojunction phototransistor HT integrated with this SDH laser at the same time.
There is no burden on the design of P1 and HTP2, and flexibility in realizing an optical semiconductor device is high. In addition, low power consumption of the optical semiconductor device can be achieved.

The SDH laser is an internal current confinement type laser and can be formed by one epitaxial growth. Therefore, as described above, all the layers for the SDH laser and the layers for the heterojunction phototransistors HTP1 and HTP2 can be grown by one-time epitaxial growth, so that the manufacturing process of the optical semiconductor device is very easy. It's easy.

The optical semiconductor device according to the second embodiment can have the optical input / output characteristics as shown in FIG. 4 by the optical input 1. The optical input / output characteristics shown in FIG. 4 are
The characteristic is similar to the input / output curve (sigmoid function) of a general neuron as shown in FIG. Further, the suppression effect as shown in FIG. 6 can be obtained by the optical input 2. Therefore, the optical semiconductor device according to the second embodiment can be applied as an optical neuro element.

Further, in general, the optical semiconductor device according to the second embodiment can be used as a differential optical amplifier element which operates by the difference in signal strength between the optical input 1 and the optical input 2. .. In this case, it is possible to realize a linear optical amplification element by applying an appropriate bias light. Further, for example, it can be applied as an optical logic element in which the values around the threshold value are binary.

In the optical semiconductor device according to the second embodiment, the heterojunction phototransistor HPT1,
The base layer of HPT2, that is, the light-receiving layer is formed by the p-type GaAs layer 2, and the active layer 13 of the laser diode LD is formed by the i-type.
Since the heterojunction phototransistors HPT1 and HPT2 have the same light reception wavelength and the laser diode LD emission wavelength because they are formed of the GaAs layer, the base layers of the heterojunction phototransistors HPT1 and HPT2 and the laser diode LD are active. By forming the layer 13 from a different semiconductor layer, the heterojunction phototransistor H
It is possible to make the light receiving wavelengths of PT1 and HPT2 different from the light emitting wavelength of the laser diode LD. For example, the base layer of the heterojunction phototransistors HPT1 and HPT2 is formed of a p-type GaInP layer, and the laser diode L
By forming the active layer 13 of D by the i-type GaAs layer as described above, the heterojunction phototransistor HPT
1. It is possible to set the light receiving wavelength of HPT2 to a wavelength in the visible light region and the light emitting wavelength of the laser diode LD to a wavelength in the infrared light region. By thus making the light receiving wavelengths of the heterojunction phototransistors HPT1 and HPT2 different from the light emitting wavelength of the laser diode LD, this optical semiconductor device can be used as a wavelength conversion element. The optical semiconductor device as such a wavelength conversion element,
It can be applied as an optical neuro device with wavelength conversion, a differential optical amplification device, an optical logic device, and the like.

Further, by arranging a plurality of the optical semiconductor devices shown in FIG. 3 on the same p-type GaAs substrate 11 one-dimensionally and separating them from each other, a one-dimensional array of optical semiconductor devices is realized. be able to. And by providing many one-dimensional arrays of this optical semiconductor device in parallel with each other,
Optical input to the heterojunction phototransistors HPT1 and HPT2 of each optical semiconductor device arranged in a one-dimensional array is performed from their end faces, and an optical output is obtained from the end face of the laser diode LD according to these optical inputs. By using the light output as the light input to the one-dimensional array of the optical semiconductor device in the next stage, it is possible to cascade the one-dimensional array of the optical semiconductor devices.

As described above, the optical semiconductor device shown in FIG. 3 satisfies the conditions advantageous for integration in terms of power consumption and manufacturing process, but as it is, it is normally viewed from the direction perpendicular to the substrate surface. Heterojunction phototransistor HP
Optical input to T1 and HPT2, laser diode LD
Since the optical output is obtained from the end face of the optical disc, and the optical input direction and the optical output direction are deviated from each other by 90 °, this is not suitable for the cascade connection. Regarding this point, as described above, cascade connection is possible by inputting light from the end faces of the heterojunction phototransistors HPT1 and HPT2, but the alignment of input light is not always easy and can be realized by this method. Only one-dimensional array is available, and it is difficult to realize a two-dimensional array. Therefore, a third embodiment capable of solving this problem will be described next.

FIG. 7 shows an optical semiconductor device according to the third embodiment of the present invention.

As shown in FIG. 7, in the optical semiconductor device according to the third embodiment, the p-type AlGaAs layer 12, the active layer 13 and the n-type AlGa having a cylindrical shape as a whole are formed.
A so-called vertical cavity surface emitting laser having a resonator structure in which the upper and lower sides of the As layer 14 are sandwiched by the Bragg reflectors 19 and 20 is used as a laser diode LD, and an optical output is extracted downward in FIG. Reference numerals 21 and 22 are n
Shows a type AlGaAs layer. The upper and lower sides of the heterojunction phototransistors HPT1 and HPT2 are the Bragg reflectors 4,
Similar to the optical semiconductor device according to the second embodiment described above, the resonator structure is formed by being sandwiched between the two. Regarding the vertical cavity surface emitting laser, for example, see Technical Digest of Third Optoelectronics Conf.
erence, 13B1-1, 196 (1990), Technical Digest of Th
ird Optoelectronics Conference, 13B1-3, 200 (1990)
And Technical Digest of Third Optoelectronics Conf
erence, 13B1-4, 202 (1990).

According to the optical semiconductor device of the third embodiment, the same advantages as those of the second embodiment can be obtained in the optical semiconductor device using the vertical cavity surface emitting laser as the laser diode LD. Since the light input from the front surface and the light output from the back surface are possible, it is possible to obtain an advantage that not only the one-dimensional array of the optical semiconductor device but also the two-dimensional array can be easily realized. Here, the surface emitting laser used as the laser diode LD can have a threshold current, and hence an operating current, which can be considerably lowered depending on the design, and is also suitable for forming a two-dimensional array of optical semiconductor devices in this respect as well. ..

FIG. 8 shows an optical semiconductor device according to the fourth embodiment of the present invention.

As shown in FIG. 8, in the optical semiconductor device according to the fourth embodiment, two heterojunction phototransistors HPT1 and HPT2 are arranged in parallel to each other and to the cathode of a laser diode LD whose anode is grounded. A memory cell is composed of those connected in opposite polarities. Here, the heterojunction phototransistor H
The collector of PT1 is connected to the cathode of the laser diode LD, and a negative voltage is applied to the emitter of the laser diode LD by a negative power source.
The emitter of T2 is connected to the cathode of the laser diode LD, and its collector is grounded, as in the optical semiconductor device according to the second embodiment.

Unlike the optical semiconductor device according to the second embodiment, the optical semiconductor device according to the fourth embodiment differs from the laser diode LD and the heterojunction phototransistor HPT.
An optical feedback loop is formed between 1 and 1. On the other hand, the laser diode LD and the heterojunction phototransistor HPT2 are optically independent.

In the optical semiconductor device according to the fourth embodiment configured as described above, when the heterojunction phototransistor HPT1 is turned on by the optical input 1, the laser diode LD receives a forward current higher than its threshold current. An optical output is obtained by flowing and becoming an ON state. Then, a part of this optical output is fed back to the heterojunction phototransistor HPT1 through the optical feedback loop, so that the heterojunction phototransistor HPT1 maintains the ON state even after the optical input 1 disappears, and therefore the laser diode LD Also, the light output is maintained by maintaining the ON state. The above is the set, that is, the write and storage operations.

Next, when the heterojunction phototransistor HPT2 is turned on by the optical input 2, a current starts to flow through the heterojunction phototransistors HPT1 and HPT2, so that the forward current flowing through the laser diode LD becomes a threshold value. The laser diode LD is turned off by reducing the current to less than the current, and no optical output can be obtained. This is the reset or erase operation.

As described above, an optical memory operation capable of setting, that is, writing and resetting, that is, erasing by light is realized. That is, according to the optical semiconductor device of the fourth embodiment, it is possible to realize an optical memory that can be set, that is, written and reset, that is, erased by light.

FIG. 9 shows a specific structural example of the optical semiconductor device according to the fourth embodiment described above.

As shown in FIG. 9, in this optical semiconductor device, similar to the optical semiconductor device according to the second embodiment, the p-type semiconductor device is used.
Laser diode LD consisting of SDH laser and heterojunction phototransistors HPT1 and HP on GaAs substrate 11
T2 and monolithically integrated.

In this case, the n-type AlGaAs layer 1, the p-type GaAs layer 2, and the n-type Al of the current stripe portion of the laser diode LD, that is, the portion away from the ridge 1a in plan view.
The GaAs layer 3 and the Bragg reflector 5 have a groove 18 for separating the heterojunction phototransistors HPT1 and HPT2.
Are formed. Then, the n-type AlGaAs layer 1, the p-type GaAs layer 2, and the n-type Al on one side (left side in FIG. 9) of the groove 18 are formed.
The resonator is formed by a structure in which the upper and lower sides of the heterojunction phototransistor HPT1 having the GaAs layer 3 as the collector layer, the base layer, and the emitter layer are sandwiched by the Bragg reflectors 4 and 5, respectively, and the other side of the groove 18 ( Figure 9
(Middle right) n-type AlGaAs layer 1, p-type GaAs layer 2 and n-type AlGa
A resonator is formed by a structure in which the upper and lower sides of the heterojunction phototransistor HPT2 having the As layer 3 as an emitter layer, a base layer, and a collector layer are sandwiched by the Bragg reflectors 4 and 5, respectively.

Further, in this case, the heterojunction phototransistor HPT1 has a structure in which the heterojunction phototransistor HPT1 is directly laminated directly above the laser diode LD, whereby an optical feedback loop is provided between the laser diode LD and the heterojunction phototransistor HPT1. To be formed. On the other hand, the heterojunction phototransistor H
The PT2 is formed at a position away from the laser diode LD by a sufficient distance in plan view, whereby the laser diode LD and the heterojunction phototransistor HPT1 are optically independent.

Resonator length of the structure in which the upper and lower sides of the heterojunction phototransistor HPT1 are sandwiched by the Bragg reflectors 4 and 5, and the resonator length of the resonator in which the upper and lower sides of the heterojunction phototransistor HPT1 are sandwiched by the Bragg reflectors 4 and 5. Are both (n +) of the wavelength of the incident light (optical input 1 or optical input 2) as in the light receiving element according to the first embodiment.
1) / 2 times (n = 1, 2, ...), whereby the antinode portion of the standing wave of light formed in these resonators upon incidence of light is a p-type light receiving layer. It is located in the portion of the GaAs layer 2. Therefore, this p-type GaAs
Even when the thickness of the layer 2 is extremely small, sufficient quantum efficiency, that is, sufficiently high optical gain can be obtained. And thereby, a sufficiently good optical memory characteristic can be obtained. Also, instead of the p-type GaAs layer 2, for example, p
When the type InGaAs layer is used, the same advantage can be obtained even when the thickness of the p-type InGaAs layer has to be suppressed to about 10 to 20 nm or less due to the restriction by the critical film thickness.

Heterojunction phototransistor HPT1,
HPT2 is preferably a heterojunction phototransistor HPT1, HPP in the optical semiconductor device according to the second embodiment.
Similar to T2, the n-type AlGaAs layer 1 and the n-type AlGaAs layer 3 as the emitter layer or the collector layer centering on the p-type GaAs layer 2 as the base layer are formed to have a completely symmetrical structure with respect to the energy gap and the carrier concentration. It Also, these heterojunction phototransistors HPT1 and HPT2
In the above, preferably, an i-type GaAs layer and a graded i-type AlGaAs layer are provided between the p-type GaAs layer 2 as the base layer and the n-type AlGaAs layer 1 and the n-type AlGaAs layer 3 as the emitter layer or the collector layer. The provision thereof is similar to that of the optical semiconductor device according to the second embodiment.

Further, as described in the second embodiment, the heterojunction phototransistors HPT1 and HPT2 are formed by forming the base layers of the heterojunction phototransistors HPT1 and HPT2 and the active layer 3 of the laser diode LD from different semiconductor layers. Light receiving wavelength of HPT2 and laser diode L
It is possible to make the emission wavelength of D different. In this way, the heterojunction phototransistors HPT1 and HPT2
It is possible to realize an optical memory having a wavelength conversion function by making the light receiving wavelength of the laser diode LD and the light emitting wavelength of the laser diode LD different.

To realize a one-dimensional array of optical semiconductor devices by arranging a plurality of optical semiconductor devices according to the fourth embodiment on the same p-type GaAs substrate 11 one-dimensionally and separating them from each other. This is the same as the optical semiconductor device according to the second embodiment.

FIG. 10 shows an optical semiconductor device according to the fifth embodiment of the present invention.

As shown in FIG. 10, in the optical semiconductor device according to the fifth embodiment, the p-type AlGaAs layer 12, the active layer 13 and the n-type Al, which have a cylindrical shape as a whole, are formed.
A so-called vertical cavity surface emitting laser having a cavity structure in which the upper and lower sides of the GaAs layer 14 are sandwiched by the Bragg reflectors 19 and 20 is used as a laser diode LD.
The optical output is extracted downward in FIG. The upper and lower sides of the heterojunction phototransistors HPT1 and HPT2 are sandwiched by the Bragg reflectors 4 and 5 to form resonator structures, respectively, similarly to the optical semiconductor device according to the fourth embodiment described above.

According to the optical semiconductor device of the fifth embodiment, the optical semiconductor device using the vertical cavity surface emitting laser as the laser diode LD has the same advantages as those of the optical semiconductor device of the fourth embodiment. In addition to being capable of performing light input from the front surface and light output from the back surface, it is possible to easily realize not only a one-dimensional array of an optical semiconductor device but also a two-dimensional array. it can.

In the optical semiconductor devices according to the second, third, fourth and fifth embodiments, the negative power source and the heterojunction phototransistor H are usually used.
A load resistance of, for example, about several tens of ohms is provided between it and PT1. Although it is conceivable to provide this load resistance outside the optical semiconductor device, it can be provided monolithically in the optical semiconductor device as follows.

That is, by the Bragg reflector 5 on the n-type AlGaAs layer 3 as the emitter layer of the heterojunction phototransistor HPT1 in the optical semiconductor device according to the second, third, fourth and fifth embodiments. The composition steepness of the hetero interface between the Bragg reflector 5 and the n-type AlGaAs layer 3 is adjusted so that a load resistance having a required resistance value is formed. That is, by incorporating the load resistance in the Bragg reflector 5 itself, the load resistance can be made completely monolithic in the optical semiconductor device. On the other hand, the Bragg reflector 4 on the lower side of the n-type AlGaAs layer 1 is similar to the Bragg reflector 4 and the n-type AlGa.
The hetero interface with the As layer 1 has a graded structure to reduce the resistance as much as possible.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, the vertical relationship between the laser diode LD and the heterojunction phototransistors HPT and HPT2 may be reversed. That is, the laser diode LD may be formed on the heterojunction phototransistors HPT1 and HPT2.

The laser diode LD and the heterojunction phototransistors HPT1 and HPT2 are made of AlGaAs /
It may be formed using a semiconductor heterostructure other than GaAs. Further, instead of the p-type GaAs substrate 1, another compound semiconductor substrate may be used.

As the laser diode LD, for example, a so-called SAN (Self-Aligned Narrow Stripe) laser or the like may be used.

Furthermore, a light emitting diode may be used instead of the laser diode LD.

Further, in the optical semiconductor devices according to the third and fifth embodiments, the p-type GaAs substrate 1 at the light output end is used.
A hole may be formed in 1 by etching, and the light output may be taken out from this hole. By doing so, the emission wavelength of the laser diode LD is changed to the p-type GaAs substrate 1
The active layer 3 of the laser diode LD can be formed of an i-type GaAs layer because it is not necessary to be transparent to 1. Further, a microlens may be directly formed on the light output end face.

Further, in the optical semiconductor device according to the second embodiment, the two heterojunction phototransistors HPT1 and HPT2 are connected in parallel to the cathode of the laser diode LD, but the cathode of the laser diode LD has a positive input. A parallel connection of k (k ≧ 2) heterojunction phototransistors for use in parallel and a parallel connection of the negative input k heterojunction phototransistors may be connected in parallel with each other. .. By doing so, it is possible to realize an optical semiconductor device having k positive input portions and k negative input portions.

[0065]

As described above, according to the present invention,
Even when the thickness of the base layer, that is, the light-receiving layer is extremely small, sufficient quantum efficiency, and thus, sufficiently high optical gain can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a light receiving element according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an optical semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing a structural example of an optical semiconductor device according to a second embodiment of the present invention.

FIG. 4 is a graph showing an example of light input / output characteristics of an optical semiconductor device according to a second embodiment of the present invention.

FIG. 5 is a graph showing input / output characteristics of a general neuron.

FIG. 6 is a graph showing an example of light input / output characteristics when the suppression effect is obtained by the light input 2 in the optical semiconductor device according to the second embodiment of the present invention.

FIG. 7 is a sectional view showing an optical semiconductor device according to a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing an optical semiconductor device according to a fourth embodiment of the present invention.

FIG. 9 is a sectional view showing a structural example of an optical semiconductor device according to a fourth embodiment of the present invention.

FIG. 10 is a sectional view showing an optical semiconductor device according to a fifth embodiment of the present invention.

[Explanation of symbols]

 1, 3, 14, 16 n-type AlGaAs layer 2 p-type GaAs layer 4, 5 Bragg reflector 11 p-type GaAs substrate 12, 15 p-type AlGaAs layer 13 active layer 17 n-type GaAs layer 18 groove HPT1, HPT2 heterojunction phototransistor LD laser diode

Claims (1)

[Claims] 1. A phototransistor comprising an emitter layer, a base layer and a collector layer laminated on each other has a resonator structure in which the emitter layer side and the collector layer side are sandwiched by a Bragg reflector, and the resonator is formed by light incidence. A light-receiving element in which the thicknesses of the emitter layer, the base layer, and the collector layer are selected so that an antinode portion of a standing wave of light formed therein is located at a portion of the base layer.