JP2003195238A - Reflective multi-layer film for semiconductor spatial light modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element capable of improving the utilization efficiency of light and performing a high-speed operation and a low voltage operation in a spatial light modulator used in an optical information processing technique. <P>SOLUTION: To obtain a reflective multi-layer film, a first material of a low impurity content and a second material of the low impurity content whose refractive index is different from that of the first material are alternately laminated along an appropriate first crystal axis direction. An electro-optical effect is induced by an electric field applied from an optional crystal axis direction including the first crystal axis direction, and an optical refractive index to light made incident from the first crystal axis direction is changed. Since the electro-optical effect is induced by the electric field applied from the optional direction of the element and the optical refractive index to the light made incident from the first crystal axis direction is changed, the interference conditions of the reflective multi-layer film are destroyed, the reflection spectrum is changed by applied voltage and the reflectance is changed at a certain specified wavelength. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing type spatial light modulator, which is an important component of an optical information processing system for performing high-speed high-speed processing, and a reflection type spatial light modulator represented by a projection display. It is related to the control of the reflection spectrum of a reflective multilayer film for the purpose of application to, and in particular, it is possible to easily achieve high speed, stabilization of device operation, high light utilization efficiency, and expansion of the optical frequency range that can be modulated. The present invention relates to the structural design of a simple semiconductor reflective multilayer film.

[0002]

2. Description of the Related Art A spatial light modulator is an element having a function of modulating spatial intensity distribution and phase distribution of light and putting two-dimensional parallel information on the light. This spatial light modulator, in particular, an optical writing type spatial light modulator capable of writing and reading two-dimensional parallel information by light is one of the key devices in an optical arithmetic system and an optical information processing system. .

Various methods have been proposed for the modulation method of this spatial light modulator, but it is considered that the use of a semiconductor is most suitable for enabling a high-speed response. A device made of a semiconductor has a well-established technique for manufacturing, and many compound semiconductors are particularly convenient because they have excellent characteristics as an optical material. Therefore, a reflective spatial light modulator using a compound semiconductor as a reflective multilayer film has been proposed and actually manufactured.

As such a reflection type spatial light modulator, there is one using a reflective multilayer film and using the Franz-Keldesh effect in the bulk or the quantum Stark effect in the multiple quantum well. Considering shifting the absorption edge by simply using the Franz-Keldysh effect in the bulk without using the multiple quantum well, the range in which the absorption edge is displaced by voltage application is narrow and the modulation degree is small. Further, since the absorption edge as steep as that obtained by the multiple quantum well cannot be obtained, sufficient absorption edge control cannot be performed. For the above reasons, the quantum Stark effect using multiple quantum wells is often used in the absorption edge control layer of the reflective spatial light modulator (see Patent Documents 1, 2, and 3). Hereinafter, a conventional reflection-type spatial light modulator, which is currently in trial manufacture or produced and uses the quantum Stark effect in a multiple quantum well, will be described. FIG. 4 is a side view showing the configuration of a conventional reflective spatial light modulator.

This reflective spatial light modulator has a lower electrode 40.
6, a high-reflection multilayer film 402, a multi-quantum well light absorption control layer (hereinafter simply referred to as “multi-quantum well layer”) 403, and a low-reflection multi-layer film 404 are provided from the bottom to the top between the semiconductor substrate 401 on which 6 is formed and the upper electrode 405. It is configured to be sequentially laminated. Here, the reflectance of the low-reflection multilayer film 404 is 10% to 2
0%, the reflectance of the highly reflective multilayer film 402 is almost 100%
Is.

The light incident from the side of the upper electrode 405 is repeatedly reflected between the low reflection multilayer film 404 and the high reflection multilayer film 402, and the reflected light 40 from the low reflection multilayer film 404 side.
8 is emitted. When no voltage is applied between the upper electrode 405 and the lower electrode 406, the multiple quantum well layer 40
There is almost no absorption at 3, and it works as a resonator with a high Q value as a whole. As a result, most of the incident light is reflected, and the reflected light 408 is obtained with high reflectance.

Next, when a voltage is applied between the upper electrode 405 and the lower electrode 406, the effective band gap of the multiple quantum well layer 403 changes, and the absorption edge of the exciton absorption peak shifts to the long wavelength side. When the exciton absorption peak of the multiple quantum well is set on the short wavelength side near the resonance wavelength of the resonator, the exciton absorption peak overlaps the resonance wavelength. That is, the multiple quantum well layer 403 works as a light absorption layer. Therefore, the Q value of the resonator is lowered and the reflectance is lowered. Since the shift amount of the exciton absorption peak is controlled by the magnitude of the applied voltage, the reflected light 4
The intensity of 08 can be changed. Based on the above operation principle, the reflectance can be controlled by changing the applied voltage.

[0008]

[Patent Document 1] JP-A-5-501923

[Patent Document 2] JP-A-5-506518

[Patent Document 3] JP-A-5-273504

[0009]

However, the above configuration has a problem. First, the technical problems of the reflective spatial light modulator will be described. As described above, when the method of inducing the change of the reflectance by changing the absorption edge of the material by utilizing the quantum Stark effect and utilizing the absorption of light, the loss of light is large because the absorption of light is large. And it also generates heat. On the contrary, if the light absorption amount is reduced in order to improve the light utilization efficiency, the change amount of the reflectance decreases, and a high contrast ratio cannot be obtained.

There is also a problem in terms of materials. Among the compound semiconductors, GaAs and InP are used as the substrate as a material which has a good lattice match with the substrate and other materials, is relatively stable in terms of heat, and has excellent crystallinity in crystal growth. , Al, In) As and (Ga, Al, I)
n) P-based III-V group compound semiconductors. However, the absorption edges of these typical materials are all in the infrared light region, and since the absorption is large in the visible light region, the light utilization efficiency is extremely reduced. That is, it is impossible to control the absorption edge in the visible light region using these materials. In order to adapt the reflection-type spatial light modulator with absorption edge control to the visible light region, the constituent material system must be fundamentally changed.

Further, the reflective spatial light modulator using the above-mentioned light absorption layer has a problem in manufacturing. In this structure, it is necessary to form a light absorption layer having a film thickness corresponding to the cavity length, and since each semiconductor layer forming the multiple quantum well layer 403 is extremely thin, a large number of semiconductor layers must be stacked. . Therefore, it takes a huge number of man-hours to manufacture the device. Further, when the multiple quantum well 403 is formed between the layer of the low reflection multilayer film 404 and the high reflection multilayer film layer 404 as described above, high fabrication accuracy is required to form a resonator including the multiple quantum well 403. Therefore, the film thickness and the impurity concentration must be controlled with high accuracy.

The use of the absorption edge control layer requires the thickness of each semiconductor layer to exactly match the design value when manufacturing the resonator structure, as well as the utilization efficiency of light and the number of manufacturing steps. And by no means the preferred method. Furthermore, most of the materials suitable for controlling the absorption edge cannot be used in the visible light region. However, so far,
Since it has been considered difficult to change the reflection spectra themselves of the high-reflection multilayer film 402 and the low-reflection multilayer film 404, the above-mentioned modulation method using the absorption edge control layer has become mainstream.

The present invention has been made in view of the above problems, and an object of the present invention is to solve the problems of the conventional techniques as described above, and also to provide high-speed response and high utilization in visible light. It is an object of the present invention to realize a reflective multilayer film for a spatial light modulator that simultaneously achieves efficiency and low voltage driving.

[0014]

In order to achieve this object, the present invention proposes a reflective multilayer film having two types of constructions.

The reflective multilayer film of the first structure is composed of three parts. That is, it is a first reflective multilayer film layer and a third reflective multilayer film layer and a second reflective multilayer film layer sandwiched between them and acting as a refractive index changing layer. The first reflective multilayer film layer is in contact with the p-type compound semiconductor substrate which is in contact with the first electrode, and the first compound semiconductor layer and the first compound semiconductor layer have different refractive indices and bandgap energies. It has a structure in which p-type impurities are added to the compound semiconductor layer and the compound semiconductor layer is alternately laminated to have a film thickness of ¼ of the target wavelength.
The second reflective multilayer film layer has an extremely low content of impurities, and one of the two types of compound semiconductor layers forming the first reflective multilayer film and the above-mentioned two types of compound semiconductor layers. It is configured by alternately stacking a third compound semiconductor layer having a bandgap energy lower than either bandgap energy of the compound semiconductor layer and having a different refractive index. At this time, the film thickness of the third compound semiconductor layer may be made extremely thin, such as 0.5 to 4 atomic layers, and the film thickness of the first or second compound semiconductor layer may be arbitrary. Furthermore, the film thickness of the second reflective multilayer film layer as a whole may be set to a value larger than 0 and not more than 3/4 of the target wavelength. The third reflective multilayer film layer is in contact with the second electrode, and the first compound semiconductor layer and the first compound semiconductor layer have different refractive indices and bandgap energies.
Each of the compound semiconductor layers to which an n-type impurity is added is alternately laminated to have a film thickness of ¼ of the target wavelength.

At this time, the compound semiconductor layers adjacent to the first reflective multilayer film layer and the second reflective multilayer film layer are compound semiconductor layers having different refractive indexes and bandgap energies, and the third reflective multilayer film. The compound semiconductor layers corresponding to the layer and the adjacent portion of the second reflective multilayer film are also compound semiconductor layers having different refractive indexes and band gap energies. Further, as long as this condition is satisfied, any one of the compound semiconductor layers forming the first reflective multilayer film or any one of the compound semiconductor layers forming the third reflective multilayer film. May have a film thickness other than a quarter of the target wavelength, and the arrangement of the p-type impurity added portion and the n-type impurity added portion may be reversed. Good. Furthermore, the second reflective multilayer film may be formed of a short period superlattice in which the first or second compound semiconductor layers are alternately laminated in units of several atomic layers.

The first, second, and third reflective multilayer films are sequentially laminated, and the quantum Stark effect that occurs in the second reflective multilayer film layer by applying an electric field is not absorbed but controlled as an absorption peak. It is used as a means for changing the refractive index according to the change of the coefficient, thereby causing the shape change of the reflection spectrum and controlling the reflectance. The reflective multilayer film having the first configuration of the present invention is configured by the above structure.

The second type of reflective multilayer film contains almost no impurities and is formed by taking electrodes in an arbitrary direction with respect to a multilayer film composed of two types of materials having different refractive indexes and band gap energies. ing. In this case, a change in the refractive index due to the electro-optic effect and an increase in the working optical path length due to multiple reflection within the multilayer film are used. The reflectance changes by changing the phase state of the incident light in each layer of the reflective multilayer film, and by changing the interference conditions for the innumerable reflected light components that would otherwise interfere in the reflective multilayer film depending on the applied electric field. Control is realized.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is the second material containing a small amount of impurities and the first material containing a small amount of impurities, and the first material having a different refractive index. Are alternately laminated along the proper first crystal axis direction, and an electro-optical effect is induced by an electric field applied from an arbitrary crystal axis direction including the first crystal axis direction. The reflective multi-layer film is characterized in that the optical refractive index with respect to the light incident from the element changes, and the electro-optic effect is induced by the electric field applied from any direction of the element, and the incident from the first crystal axis direction. By changing the optical refractive index of the reflected light, the interference condition of the reflective multilayer film is broken, the reflection spectrum is changed by the applied voltage, and the reflectance is changed at a specific wavelength.

According to a second aspect of the present invention, the first semiconductor layer having a relatively small amount of impurities and the first semiconductor layer have a different refractive index and bandgap energy, and the amount of impurities is relatively small. The electro-optical effect is induced by the electric field applied in the stacking direction on the semiconductor multilayer film layer in which the second semiconductor layers are alternately stacked, and the light is incident in the stacking direction of the multilayer film.
This is a reflective multilayer film characterized by a change in the optical refractive index with respect to light that travels and is reflected. By applying an electric field in the stacking direction, the electro-optical effect is efficiently induced, and the reflectance changes at low voltage. Has the effect of realizing.

According to a third aspect of the present invention, the semiconductor of the first semiconductor layer is Al _y Ga _1-y P (1 ≧ y> 0.
5), and the semiconductor of the second semiconductor layer is Ga _x Al _1-x
3. P (1 ≧ x> 0.5).
The reflective multilayer film described above is used, and as the reflective multilayer film, Al _y Ga _1-y P (1 ≧ y> 0.5) and Ga _x Al _{1-x are used.}
Using a compound semiconductor such as P (1 ≧ x> 0.5), it has the effect of controlling the reflectance in the near-infrared light to visible light region.

FIG. 1 shows an embodiment of the present invention.
3 to FIG. 3 will be described.

(Embodiment 1) FIG. 1 is a sectional view of a reflective multilayer film for modulating reflected light intensity according to a first embodiment of the present invention. In Figure 1, p-GaP substrate with a p-type impurity is doped 101, 102 _{p-Al y Ga 1-y} P layer p-type impurity-doped, 103 p-Ga of the p-type impurity-doped _x Al _1-x P layer, where x is in the range represented by the following formula (1) and y is in the range represented by the following formula (2). 1 ≧ x> 0.5 ………… (1) 1 ≧ y> 0.5 ………… (2)

[0024] 104 _{p-Al y} Ga _1-y begins with P layer 102, p-Al _y Ga ending in _1-y P layer 102 p-G
_{a x Al 1-x P /} Al y Ga 1-y P multilayer film 105 is very low _{i-Ga x Al 1-x} P layer and 10 ¹⁵ ~10 ¹⁶ cm ^-3 carrier concentration of impurities, 106 is the I-Ga _x
As with the Al _1-x P layer 105, the impurity carrier concentration is 1
I-In _z Ga _1-z P is extremely low at 0 ¹⁵ to 10 ¹⁶ cm ^-3
In the layer, z is in the range represented by the following formula (3). 1 ≧ z> 0 ……………… (3)

107 has an extremely low impurity carrier concentration.
I-Ga_xAl_1-xUsing the P layer 105 as a barrier layer,
I-In with extremely low carrier concentration of impurities_zGa_1-z
I-Ga configured to use the P layer 106 as a well layer_x
Al_1-xP / In_zGa_1-zIt is a P multiple quantum well layer.
In addition, this i-Ga_xAl_1-xP / In_zGa_1-zP many
The quantum well layer 107 has its effective band gap energy.
Is less than the energy corresponding to the wavelength of the incident light 113.
Small size, and multiple quantum well fabrication
Sometimes i-Ga_xAl_1-xP layer 105 and i-In_zGa
_1-zThe dislocation due to the difference in lattice constant between the P layer 106 and
Each film thickness is set so that such problems do not occur. example
For example, assuming that the incident light 113 is a He-Ne laser, i-
Ga_xAl _1-xX = 1 for the P layer 105, i-In
If z = 1 is assumed for the GaP layer 106, He-N
e Laser wavelength λ = 632.8 nm (= 1.95e
V), the film thickness of the i-GaP layer 105 is 20 to 1
The film thickness of the i-InP layer 106 is set to an arbitrary value between 00Å
Should be less than 10Å.

Reference numeral 108 denotes n-A doped with n-type impurities.
l_yGa_1-yP layer, 109 was doped with n-type impurities
n-Ga_xAl_1-xIn the P layer, 110 is n-Al_yGa
_1-yStarting at the P layer 108, n-Ga_xAl_1-xP layer 10
N-Ga ending with 9_xAl_1-xP / Al_yGa_1-yP many
A layer film, 111 is a lower electrode, and 112 is an upper electrode. p
-Al_yGa_1-yP layer 102, p-Ga_xAl_1-xP layer
103, n-Al_yGa _1-yP layer 108, n-Ga_xA
l_1-xEach of the P layers 109 is a semiconductor that forms a reflective multilayer film.
Body layers, and their thickness is 1/4 of the target wavelength
To be set. Further, the upper electrode 112 has a cylindrical shape.
Or a transparent electrode, n-Ga_xAl_1-xP / Al_yG
a_1-yAt the top of the P multilayer film 110, the incident light 113
And the emitted light 114 is not blocked or absorbed and penetrates into the multilayer film.
Make the structure accessible. The shape of the lower electrode 111 is arbitrary
Is. The lower electrode 111 has a p-type impurity concentration of 10
²⁰cm^-3Degree p⁺⁺-May be GaP, upper electrode
N-Ga under 112_xAl _1-xThe P layer 109 is an n-type impurity
Material concentration is 10²⁰cm^-3Degree n⁺⁺-Ga_xAl_1-xAt P
It may be. An optical intensity modulation counter configured as described above.
The operation of the multilayer film will be described with reference to FIG.
To do.

First, the characteristics of light reflection / transmission in the multilayer film in the absence of voltage application will be described. p-Ga _x Al _{1-x
P / Al y Ga 1-y} P multilayer film 104 and the n-Ga _x Al
In _{1-x P / Al y Ga} 1-y P multilayer film 110, the reflectance changes with respect to a light of a wavelength of the multilayer film, i.e. the shape of the reflection spectrum has a plurality of peaks and valleys, the most reflection peak in the vicinity of the target wavelength It has a high efficiency and acts as a simple mirror for the target wavelength. The peak near the target wavelength has a width depending on the refractive index difference between the two types of materials.
Now, the i-Ga _x Al _1-x P layer 105 and the i-In _z Ga layer are formed.
_If the total thickness of the _1-z P layer 106 and the _1-z P layer 106 is 1/4 of the effective target wavelength, the i-Ga _x Al _1-x P layer 105 and the i-In
_{Since the z} Ga _{1 -z} P layer 106 is merely an arbitrary layer in the reflective multilayer film, it does not affect the shape of the reflection spectrum. However, when the total film thickness is between 0 and 3/4 of the effective target wavelength, a valley appears in the main peak near the target wavelength in the reflection spectrum. Further, the position and the depth of the valley can be uniquely determined by arbitrarily setting the total film thickness.

Next, a reverse voltage is applied between the upper electrode 112 and the lower electrode 111 to the pn junction of the entire device. Because the _{p-Ga x Al 1-x} P / Al y Ga 1-y P multilayer film 104 includes a relatively large number of p-type impurity, the resistance at this site is low, n-Ga _x Al _{1 -x} P
/ Al _y Ga _1-y for P is the same in the multilayer film 110, most of the applied reverse voltage i-Ga _x Al
_{The 1-x} P / In _z Ga _{1- z} P multiple quantum well layer 107. By applying this reverse voltage, the above-mentioned i-Ga _x
The absorption edge of the Al _1-x P / In _z Ga _1-z P multiple quantum well layer 107 shifts to the long wavelength side due to the quantum Stark effect. At the same time as the shift of the absorption edge at this time, i-Ga _x A
The effective refractive index of the l _{1 -x} P / In _z Ga _{1 -z} P multiple quantum well layer 107 as a whole also changes greatly.

A change in the film thickness of any one of the two materials constituting the reflective multilayer film, that is, a change in the effective optical length, has a great influence on the reflection spectrum.
As described above, when the absorption edge shifts due to the quantum Stark effect and the effective refractive index changes at the same time, it is equivalent to a change in the effective optical length. Since the change of the effective optical length has a great influence on the reflection spectrum, the shape of the reflection spectrum is largely changed by applying the reverse voltage. At this time,
The part of the reflection spectrum that has a valley or a sharp rise as described above is susceptible to changes, so
Incident light 113 corresponding to the wavelength of that portion changes its intensity to become reflected light 114. This intensity change is i-Ga _x A
The _1-x P / In _z Ga _1-z P multiple quantum well layer 107 is proportional to the change amount of the refractive index, and the change amount of the refractive index depends on the applied voltage. As described above, it becomes possible to control the intensity of the reflected light according to the change of the applied voltage. As a specific modulation degree at this time, when the voltage applied to the pn junction is 15 V, the reflectance changes from 0.1% to 30%. The amount of change is 30%, and the modulation transfer function MTF is 0.99.

In the above embodiment, the p-type region and the n-type region are
Operates only by changing the direction of the reverse voltage even if the arrangement of
The principle is the same. Furthermore, p-Ga_xAl_1-xP /
Al _yGa_1-yP multilayer film layer 104 and n-Ga_xAl_1-x
P / Al_yGa_1-yIn the P multilayer film 110, basically
Has no restrictions on the start and end layers.

Further, i-Ga _x Al _1-x P / In _z Ga
_{In the 1-z} P multiple quantum well layer 107, i-In _z Ga
The band gap energy of the _1-z P layer 106 is Ga.
Any semiconductor material may be used as long as it is smaller than the bandgap energy of P bulk and does not exceed the film thickness limitation for the above-mentioned lattice mismatch, and may be a binary, ternary, or quaternary mixed crystal.

Further, i-Ga_xAl_1-xP / In_zG
a_1-zThe P-multiple quantum well layer 107 has a high concentration of impurities added.
A single semiconductor material with added pn junction
Therefore, it is not necessary to make multiple quantum wells.
Therefore, the number of steps for manufacturing is reduced and it is easy to manufacture. Na
As a single semiconductor material having a pn junction, In
_zGa_1-zP (1 ≧ z> 0), In_zAl_1-zP (1 ≧
z> 0), GaAs_zP _1-z(1 ≧ z> 0), AlAs
_zP_1-z(1 ≧ z> 0).

(Second Embodiment) FIG. 2 is a cross-sectional view of a reflective multilayer film for modulating the intensity of reflected light in the second embodiment of the present invention. In FIG. 2, p-GaP substrate with a p-type impurity is doped 201, 202 _{p-Al y Ga 1-y} P layer p-type impurity-doped, 203 p-Ga of the p-type impurity-doped _{In the x} Al _1-x P layer, x and y are in the ranges of the formulas (1) and (2) described in the first embodiment, respectively. 204 p-Al _y start with Ga _1-y P layer 202, p-Al _y Ga ending in _1-y P layer 203 p-Ga _{x
Al 1-x P / Al y} Ga 1-y P multilayer film, 205 a carrier concentration of impurity is extremely low, 10 ¹⁵ ~10 ¹⁶ cm ^-3 i
-Ga _x Al _1-x P layer, 206 is the above-mentioned i-Ga _x Al
_{Like the 1- xP} layer 205, the impurity carrier concentration is 10 ¹⁵
Is extremely low _{i-Al y Ga 1-y} P layer to 10 ¹⁶ cm ^-3. 207 is an i-, which has an extremely low carrier concentration of impurities.
And Ga _x Al _1-x P layer 205, which is also a short-period superlattice layer formed by alternately laminating a very low _{i-Al y Ga 1-y} P layer 206 is a carrier concentration of impurities. The short period superlattice layer 207 has a short period multiple quantum well structure in which a plurality of atomic layers are stacked. In this embodiment, i-Ga _x A
film thickness m atomic layers of l _1-x P layer 205, i-Al _y Ga
The thickness of the _1-y P layer 206 is an n-atom layer, and the _1-y P layer 206 is laminated so that each film thickness _satisfies the condition of the following expression (4). m + n = 14 (4) However, m and n are odd numbers. In addition, this i-Ga _x A
The total thickness of _{l 1-x P / Al y} Ga 1- y P short-period superlattice layer 207 is greater than 0, to be less than or equal to 3/4 of the target wavelength.

Reference numeral 208 is an n-A doped with an n-type impurity.
l _y Ga _1-y P layer, 209 is a _{n-Ga x Al 1-x} P layer n-type impurity is doped, 210 n-Al _y Ga
Starting with the _1-y P layer 208, the n-Ga _x Al _1-x P layer 20
_{N-Ga x Al 1-x} P / Al y Ga 1-y P multilayer film ending with 9, the lower electrode 211, 212 denotes an upper electrode.
_{p-Al y Ga 1-y} P layer _{202, p-Ga x Al 1} -x P
Layer _{203, n-Al y Ga 1} -y P layer 208, n-Ga _x
The Al _1-x P layers 209 are semiconductor layers forming the reflective multilayer films, respectively, and the film thicknesses thereof are set to be ¼ of the target wavelength. The upper electrode 212 is cylindrical, or transparent _{electrode, n-Ga x Al 1- x} P / Al y
At the top of the Ga _{1 -y} P multilayer film 210, incident light 21
3 and the emitted light 214 are allowed to enter the multilayer film without being blocked and absorbed. The shape of the lower electrode 211 is arbitrary. The lower electrode 211 has a p-type impurity concentration of 1
0 ²⁰ cm ^-3 of about may be a p ^++-GAP, the _{n-Ga x Al 1-x} P layer 209 is n-type impurity concentration immediately below the upper electrode 10 ²⁰ cm ^-3 of about n ⁺⁺ - It may be Ga _x Al _1-x P. The operation of the reflective multilayer film for light intensity modulation configured as described above will be described with reference to FIG. In this structure, only the part relating to the refractive index changing layer is different from the first embodiment, and other characteristics are the same as those of the first embodiment.

Corresponding to this refractive index changing layer, each film
Be laminated so that the thickness meets the condition of the above formula (4)
Configured i-Ga_xAl_1-xP / Al_yGa_1-yP short
In the periodic superlattice layer 207, it is indirectly transferred as a bulk.
Despite being a transfer type semiconductor, it is short on the atomic order.
Since the periodic structure is formed, it is not a direct transition semiconductor.
Behaves or has a higher refractive index than the bulk
It has been reported that it has the characteristic of becoming harder. [A
ppl. Phys. Lett. , Vol. 62, No
1, p81-83 Asahi et al. ]this child
Therefore, even if the rate of change of the refractive index is the same, the change
The quantity will inevitably be large. In addition, i-Ga _xAl_1-xP
/ Al_yGa_1-yIn the P short period superlattice layer 207,
The nonlinear changes in optical properties due to the applied field
Can be expected to occur. This i-Ga_xAl_1-xP /
Al_yGa_1-yIn the P short period superlattice layer 207,
If a large change in refractive index occurs, even in the first embodiment
As mentioned, within the main peak in the reflection spectrum
The valley portion existing in the
It is possible to move and control the reflectance intensity.

Also in this case, the arrangement of the p-type region and the n-type region can be interchanged freely, and p-Ga _x Al _{1-x
P / Al y Ga 1-y} P multilayer film 204 and the n-Ga _x Al
In _{1-x P / Al y Ga} 1-y P multilayer film 210, there is no limitation of the initiation layer and the end layer basically.

(Third Embodiment) FIG. 3 is a schematic view of a reflective multilayer film for modulating reflected light intensity according to a third embodiment of the present invention. In FIG. 3, 301 is a GaP substrate containing almost no impurities, and 302 is an impurity concentration of 10 ¹⁶ cm.
^-3 extremely low _{i-Al y Ga 1-y} P layer, 303 is also extremely low _{i-Ga x Al 1-x} P layer impurity concentration, x respectively for y of the aforementioned formula (1) And the range is specified by the equation (2). 304 is i-
Al _y Ga _1-y P layer 302 and i-Ga _x Al _1-x P layer 3
And 03 <100> formed by laminating in the direction of the crystal axis _{307 Ga x Al 1- x P /} Al y Ga 1-y
P is a multilayer film layer. A lower electrode 305 has an arbitrary shape. On the other hand, although 306 is an upper electrode, the upper electrode 306 is a cylindrical type or a transparent electrode, and n-Ga _x A
In the top of the _{l 1-x P / Al y} Ga 1-y P multilayer film 304, incident light 313 and output light 314 is a structure forward to once again enters the multilayer film without being blocked and absorbed. 307 to 311 represent the orientations of crystal axes, and are 3 and 3, respectively.
07 is the <001> crystal axis, 308 is the <100> crystal axis,
309 is a <010> crystal axis, 310 is a <110> crystal axis, and 311 is a (outer 1) crystal axis. Further, 312 is a (001) plane.

[Outer 1]

[0038] If there is no voltage applied between the lower electrode 305 and upper electrode _{306, Ga x Al 1-x} P / Al y G
The a _1-y P multilayer film 304 acts as a reflective multilayer film. When a voltage is applied between the lower electrode 305 and the upper transparent electrode _{306, Ga x Al 1-x} P / Al y Ga 1-y P multilayer film 3
The electro-optic effect is induced with respect to the light that is parallel to the <001> crystal axis 307 of 04. The electric field component of the light traveling in the crystal is divided into two orthogonal direction components. In the case of the present embodiment, these two directions are <110 shown in FIG.
> Crystal axis 310 direction and (outer 1) crystal axis 311 direction. For example, considering the case where light passes through the i-Ga _x Al _1-x P layer 303, the refractive index in the <110> crystal axis 310 direction is as in the following formula (5). Here refractive index ^{_{= n o -1 / 2n o 3}} γ 41 E ............ (5), n o is _{i-Ga x} Al _1-x refractive index in the absence of applied voltage P layer 303, E Is the magnitude of the electric field applied to this layer, and γ ₄₁ is the electrooptic constant of the zinc blende type crystal. Further, the refractive index in the (outer 1) crystal axis 311 direction is expressed by the following equation (6). Refractive index _{= n o + 1 / 2n o} 3 γ 41 E ............ (6)

Immediately after the light passes through the i-Ga _x Al _1-x P layer 303, these two types of components that have undergone a change in the refractive index merge. On the other hand, it is reflected at the end face of the _{i-Ga x Al 1-x} P layer 303, light returning into the _{i-Ga x Al 1-x} P layer 303 is subjected again refractive index change as described above. _{Here, i-Ga x Al 1-} x when considering incoming light from the end surface of the P layer 303, the light is next _{i-Al y} Ga _1-y
A phase shift occurs due to a change in the refractive index in the P layer 302, and the phase does not necessarily match the phase of the light reflected by the end surface of the i-Ga _x Al _1-x P layer 303.

In this way, when the electro-optic effect is induced
The refractive index and the amount of change in refractive index with respect to these two axes are different.
And the phase state of the incident light 311 is Ga_xAl_1-xP / Al
_yGa _1-yWhile the P multilayer film 304 is multiply reflected,
Going away. Due to this shift, the reflection condition is broken and the reflection multilayer
The function as a film is lost and the reflection spectrum changes. Chi
By the way, the voltage applied to the lower electrode 305 and the upper electrode 306 is
The phase difference Γ between the two optical axes generated with respect to the pressure V is
If expressed, it becomes like the following formula (7).         Γ = (2π / λ) (l / d) n_o ³γ₄₁V ………… (7) Where λ is the wavelength of light.

The optical path length l of the incident light 311 depends on the number of times of multiple reflections repeated. The more the number of multiple reflections, the longer the optical path length. Therefore, the greater the number of multiple reflections, the greater the phase shift. Shows. Also, the side electrode 3
Since the phase difference Γ also changes depending on the magnitude of the voltage applied to 05, the reflection spectrum can be controlled by the applied voltage.

[0042]

As described in the foregoing, in the present invention, transparent in the visible light region _{Ga x Al 1-x P /} Al y Ga
A semiconductor reflective spatial light modulator usable in the visible light region is realized by selecting the _1-yP multilayer film as a material.
In addition, a reflective spatial light modulator by controlling the applied electric field was realized by devising a structure that can utilize the refractive index change of the reflective multilayer film itself, which was conventionally difficult, and does not require a resonator structure. Also, the time and effort for manufacturing can be saved at the same time.

Further, since it is also a voltage control type reflection type spatial light modulator, there is only a substrate and an electrode under the reflection multilayer film, and there is room to enable stacking with a pin photodiode or the like. Yes, it is possible to provide more additional functions.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a reflective spatial light modulator according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a reflective spatial light modulator according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a reflective spatial light modulator according to a third embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a configuration of a reflective spatial light modulator according to a conventional technique.

[Explanation of symbols]

101 p-GaP substrate _{102 p-Al y Ga 1-} y P layer _{103 p-Ga x Al 1-} x P layer _{104 p-Ga x Al 1-} x P / Al y Ga 1-y P multilayer film 105 i- Ga _x Al _1-x P layer 106 i-In _z Ga _1-z P layer 107 i-Ga _x Al _1-x P / In _z Ga _1-z P multiple quantum well layer 108 n-Ga _x Al _{1-x P / Al y Ga 1-y} P multilayer _{film, 109 n-Ga x Al 1} -x P layer 111 and 211 lower electrode 112, 212 upper electrode

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H079 AA02 AA12 BA01 BA04 CA02                       DA16 EA28 EB06 GA05 HA12                       HA15 HA16

Claims (3)

[Claims] 1. A first material having a small content of impurities and a second material having a different refractive index from each other and having a small content of impurities are alternately arranged along an appropriate first crystal axis direction. And an electro-optical effect is induced by an electric field applied from any crystal axis direction including the first crystal axis direction.
A reflective multi-layer film, wherein the optical refractive index with respect to light incident from the crystal axis direction of is changed. 2. A first semiconductor layer having a relatively small amount of impurities and a second semiconductor layer having a relatively small amount of impurities, which have different refractive indices and bandgap energies, are alternately laminated. An electro-optical effect is induced in the laminated semiconductor multilayer film layer by an electric field applied in the stacking direction, and the optical refractive index for light incident, advancing, or reflected in the stacking direction of the multilayer film changes. . 3. The semiconductor of the first semiconductor layer is Al _y Ga.
_1-y P (1 ≧ y> 0.5) and the semiconductor of the second semiconductor layer is Ga _x Al _1-x P (1 ≧ x> 0.5). The reflective multilayer film described.