JPH10333193A - Photo-refractive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photo-refractive device capable of applying a uniform external electric field and ensuring enhanced performance by forming a pair of electrodes along a pair of opposite edge faces of a semiconductor crystal producing a photo-refractive effect when an external electric field is applied. SOLUTION: This photo-refractive device has a semiconductor crystal 1 producing a photo-refractive effect when an external electric field is applied and a pair of electrodes 3 formed along a pair of opposite edge faces of the crystal 1. The crystal 1 is an AlGaAs/GaAs multilayered film having a multiple quantum well structure and an insulating protective film 5 of SiO2 is formed on the top of the crystal 1. The electrodes 3 are formed by vapor-depositing gold on a pair of opposite edge faces 2 of the crystal 1 and the protective film 5. The crystal 1 and the electrodes 3 are formed on a glass substrate 6. The opposite electrode faces 4 of the electrodes 3 are parallel to each other and have mirror image relation with the crystal 1 in-between.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photorefractive element made of a semiconductor crystal exhibiting a photorefractive effect by applying an external electric field.

[0002]

2. Description of the Related Art In recent years, electrical image processing technology has become mainstream due to the dramatic progress of computer image processing technology and semiconductor technology. However, rate limiting by parallel / serial conversion and LSI (Large Scale Integrated Circuit) Due to bandwidth limitations due to wiring delays, etc., the limit to speeding up with only electrical image processing technology is beginning to appear, and new optical information processing that actively takes advantage of new nonlinear optical phenomena, taking advantage of the massive parallelism inherent in light Research on is active. Above all, a significant suggestion has been made about the application of the generation of a phase conjugate wave by two-wave mixing and four-wave mixing, which is an interference phenomenon of light waves caused by the photorefractive effect, to optical information processing.

Materials having a photorefractive effect include paraelectric materials such as BSO (Bi ₁₂ SiO ₂₀ ) and Ga
Compound semiconductors such as As and ferroelectrics such as LiNbO ₃ and BaTiO ₃ are known. However, among applications to optical information processing, applications requiring real-time processing or high-speed processing require a minimum response in the photorefractive effect. A short time is required. The minimum response time is, for example, on the order of milliseconds for BSO (Bi ₁₂ SiO ₂₀ ) as a paraelectric substance, whereas it is as short as 10 microseconds for a bulk GaAs compound semiconductor. is there.

As described above, in order for a compound semiconductor such as GaAs, which can be applied to real-time processing or high-speed processing, to exhibit a photorefractive effect, a semiconductor crystal must be applied with 10 kV
/ Cm strong electric field needs to be applied. Conventional G
In a photorefractive element using a compound semiconductor such as aAs, a pair of electrodes for applying a high voltage is formed on a surface of a semiconductor crystal as shown in FIG. Some structures were arranged side by side.

[0005]

When a semiconductor crystal of a compound semiconductor such as GaAs is used as a photorefractive element, it is ideal that the photorefractive effect has a uniform characteristic over the entire region of the semiconductor crystal through which incident light passes. However, in the photorefractive element having the above-described conventional electrode structure, it is difficult to generate a uniform electric field over the entire region of the semiconductor crystal, which is one of the factors that hinders the improvement of the performance of the photorefractive effect. Was. In fact, the diffraction efficiency, which is one of the performance indicators of the photorefractive effect, is as low as 2-3% in the case of GaAs having the above-mentioned conventional electrode structure, whereas the above-mentioned BSO is 25%, for example. Compound semiconductors such as GaAs
While it is excellent in high-speed response that can be applied to real-time processing and high-speed processing, it has been desired to improve performance for realizing characteristics similar to those of the aforementioned BSO. The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor crystal exhibiting a photorefractive effect by applying an external electric field to a more uniform external electric field than that of the conventional electrode structure. It is an object of the present invention to provide a photorefractive element which can be applied and has high performance.

[0006]

A first feature of a photorefractive element according to the present invention for achieving this object is to apply an external electric field as described in claim 1 of the claims. Thus, the semiconductor device has a semiconductor crystal exhibiting a photorefractive effect and a pair of electrodes formed along a pair of opposed end faces of the semiconductor crystal.

According to a second feature of the invention, as described in claim 2 of the claims, in addition to the first feature of the invention, opposing electrode surfaces of the pair of electrodes are parallel to each other. And a mirror image relationship with respect to the semiconductor crystal.

[0008] The third characteristic configuration is, as described in claim 3 of the claims, in addition to the above-mentioned first or second characteristic configuration, in which the semiconductor crystal has a quantum well structure by a laminated structure. Wherein the electrode surfaces of the pair of electrodes are formed perpendicular to the stacked surface of the semiconductor crystal.

[0009] The fourth feature of the present invention, in addition to the above-mentioned first, second or third feature of the present invention, further includes a predetermined feature on the surface of the semiconductor crystal. The point is that an insulating protective film that transmits light in a wavelength range is formed.

The operation will be described below. According to the first characteristic configuration, in the semiconductor crystal located between the pair of electrodes, the direction of an external electric field generated by applying a predetermined voltage between the electrodes is described in the column of the related art, Or Figure 3
In the case of the conventional electrode structure shown in the above, while the difference greatly in the vicinity of the electrode and the center of the semiconductor crystal, the same direction or substantially the same direction at any position between the pair of electrodes, The electric field intensity distribution becomes more uniform. As a result, since a more uniform external electric field is generated in the semiconductor crystal as compared with the conventional electrode structure, the characteristics of the photorefractive effect generated by the external electric field can be made uniform.

According to the second characteristic configuration, the external electric field in the semiconductor crystal can be made uniform, and the performance of the photorefractive effect can be improved.

The semiconductor crystal is, for example, A
It has been pointed out that in the case of a compound semiconductor that forms a quantum well structure by a laminated structure such as an lGaAs / GaAs quantum well structure compound semiconductor, the minimum response time can be shortened to the order of microseconds or less. In general, there are cases where an external electric field is applied parallel to the stacking surface of the stacked structure forming the quantum well structure, and cases where an external electric field is applied vertically. The latter case has a feature that the photorefractive effect appears only for a moment when the polarity of the electric field is reversed when an alternating electric field is applied, and is not suitable for applications in which the photorefractive effect is used continuously. On the other hand, in the former case, a photorefractive effect is continuously exhibited by application of an electrostatic field, and an amplifying effect can be expected in an application for outputting a phase conjugate wave. It is preferable to apply an external electric field parallel to. According to the third characteristic configuration, since a uniform external electric field is generated in parallel with the lamination plane, continuous photorefractive effect can be exhibited and the minimum response time can be shortened by the quantum well structure. . Further, the performance of the photorefractive effect can be improved as compared with the case where the above-described conventional electrode structure and quantum well structure are combined.

In order for the semiconductor crystal to exhibit the photorefractive effect effectively, it is required that the semiconductor crystal has a high resistance state in which free electrons hardly exist in the semiconductor crystal. According to this, while the insulating protective film allows external incident light to penetrate into the semiconductor crystal, it is possible to prevent penetration of components such as moisture that inhibit the high resistance state, thereby preventing performance degradation. Further, by forming a part of the electrode over the upper surface of the insulating protective film, the effect of preventing intrusion of moisture or the like can be improved. At this time, the external electric field is distorted by the electrode part. Since the electric field is formed exclusively in the insulating protective film,
As a result, a uniform external electric field can be obtained in the semiconductor crystal due to the presence of the insulating protective film, and the performance of the photorefractive effect and the reliability can be improved at the same time.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a photorefractive element according to the present invention (hereinafter referred to as the element of the present invention) will be described below with reference to the drawings.

As shown in FIG. 1, the device according to the present invention comprises SiO 2
A semiconductor crystal 1 of an AlGaAs / GaAs multilayer film having a multiple quantum well structure in which _two insulating protective films 5 are formed on the upper surface, and a pair of opposite end surfaces 2 of the semiconductor crystal 1 and the insulating protective film 5 are coated with gold. This is a structure in which electrodes 3 formed by vapor deposition are formed on a glass substrate 6. The opposing electrode surfaces 4 of the pair of electrodes 3 are parallel to each other and have a mirror image relationship with the semiconductor crystal 1 interposed therebetween.

The manufacturing process of the device of the present invention will be described with reference to the process chart shown in FIG. In step 1, the semiconductor crystal 1 is formed by growing an AlGaAs / GaAs multilayer film on the GaAs substrate 7 by MBE (Molecular Beam Epitaxy) or MOCVD (Metal Organic Chemical Vapor Deposition). The thickness of the semiconductor crystal 1 is about 2 μ.

In step 2, an insulating protective film 5 of SiO ₂ is formed on the semiconductor crystal 1 by thermal CVD or sputtering.

In step 3, the insulating protective film 5 is patterned by ordinary photolithography using a resist.

In step 4, the semiconductor crystal 1 is subjected to the GaAs etching by plasma etching or vapor phase etching using the insulating protective film 5 patterned in step 3 as a mask.
The substrate 7 is etched. Note that the pair of opposed end faces 2 formed by the etching in this step is the G
It is formed substantially perpendicular to the aAs substrate. The distance between the pair of end faces 2 is 2 mm.

In step 5, a resist 8 is applied to the entire surface of the GaAs substrate 7 and the semiconductor crystal 1 formed in step 4 and the insulating protection film 5, and then a part of the insulating protection film 5 and other electrodes are applied. A resist patterning is performed to remove the resist 8 except for a portion where no resist is formed.

In step 6, gold as an electrode metal 9 is deposited on the entire surface.

In step 7, when the resist 8 patterned in step 5 is removed by a lift-off process, the electrode metal 9 that has been in contact with the resist 8 is simultaneously removed, and the electrode metal 9 is patterned. Electrode 3
Is formed.

In step 8, the back surface of the photorefractive element completed in step 7 is polished, and the glass substrate 6 is polished.
The photorefractive element shown in FIG.

The distance (2 mm) between the pair of end faces 2 is the distance between the pair of electrodes 3. The voltage to be applied between the electrodes is 2 kV to obtain a predetermined electric field (10 kV / cm). Is done. The applied voltage needs to be adjusted accordingly if the inter-electrode interval changes, but the inter-electrode interval is determined by the beam diameter incident on the photorefractive element.

The oscillation wavelength of the laser light source of the incident light used in the device of the present invention is determined in accordance with the sensitivity range of AlGaAs / GaAs, and is about 800 nm to 1500 nm. Transmits incident light in the wavelength range.

Hereinafter, another embodiment will be described. In the present embodiment, the semiconductor crystal 1 is an AlGaAs / GaAs multilayer compound semiconductor having a multiple quantum well structure. However, the semiconductor crystal 1 does not necessarily have to have a multiple quantum well structure.
It does not have to be lGaAs / GaAs compound semiconductor. The same improvement effect can be expected if the semiconductor crystal exhibits a photorefractive effect by applying an external electric field.

Regarding the processing of the end face 2 of the semiconductor crystal 1, it is preferable that the end face 2 is formed substantially perpendicular to the GaAs substrate, and that it can be further processed vertically.
It does not have to be strictly vertical. Further, the opposing electrode surfaces 4 of the pair of electrodes 3, that is, the end surfaces 2.
May be parallel to each other, and the mirror image relationship may not be strict with the semiconductor crystal 1 interposed therebetween. The cross-sectional shape of the semiconductor crystal 1 is not necessarily a symmetrical rectangular shape.
May be trapezoidal or inverted trapezoidal depending on the etching method. Even in such a case,
The uniformity of the external electric field is greatly improved as compared with the conventional electrode structure shown in FIG.

The method for manufacturing the element of the present invention does not necessarily have to be the processing method shown in the above steps 1 to 8. Also,
The insulating protective film 5 does not necessarily have to be a SiO ₂ film as long as it has insulating properties, can prevent moisture and the like from entering, and can transmit light in a predetermined wavelength range. Further, in step 8, the photorefractive element completed in step 7 may be provided on an insulating substrate other than a glass substrate. In addition, the insulating substrate only needs to be able to transmit light in a predetermined wavelength range or reflect light in the wavelength range on its surface.

[0029]

As described above, according to the present invention,
A more uniform external electric field can be applied to a semiconductor crystal that exhibits a photorefractive effect by applying an external electric field than that of the conventional electrode structure described in the section of the conventional technology, thereby improving the performance of the photorefractive effect. Can be achieved.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a photorefractive element according to the present invention.

FIG. 2 is a manufacturing process diagram of the photorefractive element according to the present invention.

FIG. 3 is a longitudinal sectional view of a photorefractive element having a conventional electrode structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor crystal 2 End surface 3 Electrode 4 Electrode surface 5 Insulating protective film 6 Glass substrate 7 GaAs substrate 8 Resist 9 Metal for electrode

Claims (4)

[Claims] 1. A semiconductor crystal (1) exhibiting a photorefractive effect by applying an external electric field, and a pair of electrodes formed along a pair of opposite end faces (2) of the semiconductor crystal (1). (3) A photorefractive element comprising: 2. The photorefractive element according to claim 1, wherein opposing electrode surfaces of said pair of electrodes are parallel to each other, and have a mirror image relationship with respect to said semiconductor crystal. 3. The semiconductor crystal (1) is a compound semiconductor forming a quantum well structure by a laminated structure, wherein the electrode surfaces (4) of the pair of electrodes (3) are arranged with respect to a laminated surface of the semiconductor crystal. The photorefractive element according to claim 1, wherein the photorefractive element is formed vertically. 4. The photorefractive element according to claim 1, wherein an insulating protective film for transmitting light in a predetermined wavelength range is formed on a surface of said semiconductor crystal.