JP3369778B2 - Semiconductor reflective multilayer film and reflective spatial light modulator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied 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 space typified by a projection type display. The present invention relates to a semiconductor reflective multilayer film for application to an optical modulator and the like and a reflective spatial light modulator provided with the semiconductor reflective multilayer film. Particularly, it is easy to increase speed, stabilize element operation, and improve light utilization efficiency. The present invention relates to a structural design of a semiconductor reflective multilayer film that can be used in the above.

[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, particularly an optical writing type spatial light modulator capable of writing and reading two-dimensional parallel information by light, is one of the key devices of an optical arithmetic system and an optical information processing system. is there.

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.
Semiconductor devices have a well-established technology for manufacturing, and many compound semiconductors are particularly convenient because they have excellent characteristics as optical materials. Therefore, a reflective spatial light modulator using a compound semiconductor as a reflective multilayer film has been proposed and is actually manufactured.

As such a reflective spatial light modulator,
There is one using a reflective multilayer film and using the Franz-Keldesh effect in the bulk and the quantum Stark effect in multiple quantum wells.

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.

[0007] The following are currently in trial production or production,
A reflective spatial light modulator using the quantum Stark effect in a multiple quantum well will be described with reference to FIG. This device has a structure in which a high reflection multilayer film layer 602, a multiple quantum well light absorption control layer 603, and a low reflection multilayer film layer 604 are sequentially stacked between a semiconductor substrate 601 having a lower electrode 606 formed thereon and an upper electrode 605. ing. Here, the reflectance of the low-reflection multilayer film layer 604 is about 10% to 20%, and the reflectance of the high-reflection multilayer film layer 602 is almost 100%.

Incident light 607 from the upper electrode 605 side
Repeats reflection between the low-reflection multilayer film layer 604 and the high-reflection multilayer film layer 602, and is emitted as reflected light 608 from the low-reflection multilayer film layer 604 side. Between electrodes 605 and 60
In the state in which no voltage is applied between 6, the multiple quantum well layer 6
There is almost no absorption at 03, 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 608 is obtained with high reflectance.

Next, when a voltage is applied between the electrodes 605 and 606, the effective band gap of the multiple quantum well layer 603 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 603 functions as a light absorption layer. Therefore, the Q value of the resonator is lowered and the reflectance is lowered. Since the shift amount of this exciton absorption peak is controlled by the magnitude of the applied voltage, the intensity of the reflected light 608 can be changed by the voltage. Based on the above operation principle, the reflectance can be controlled by changing the applied voltage.

[0010]

However, the above configuration has some problems. First, the technical problems of the reflective spatial light modulator will be described. As described above, when the method of changing the absorption edge of the material using the quantum Stark effect is used, the usable wavelength is limited to the vicinity of the absorption edge. Further, the material that can be used for the above purpose of use must be a direct transition type semiconductor with a sharp rise of the absorption edge. As a material that is a direct transition type semiconductor, has a lattice match with the substrate and other materials, is relatively stable in terms of heat, and has excellent crystallinity in crystal growth, GaAs and InP are used as the substrate. And (Ga, Al, In) As system and (Ga, A)
l, In) P-based III-V group compound semiconductors. However, the absorption edges of these typical materials are all in the infrared light region, and the absorption is large in the visible light region, which not only extremely reduces the light utilization efficiency, but also in the visible light region using these. Absorption edge control is not possible. In order to adapt the reflection-type spatial light modulator with absorption edge control to the visible light region, the material system to be constructed must be fundamentally changed.

Further, the reflective spatial light modulator utilizing the above-mentioned light absorbing layer has a problem in manufacturing.
In this structure, it is necessary to form a thick multiple quantum well light absorption layer, and since each semiconductor layer forming the multiple quantum well layer 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.
Furthermore, when a multi-quantum well light absorption layer is formed between the low-reflection film layer and the high-reflection film layer as described above, high fabrication accuracy is required in order to produce a resonator including the multi-quantum well. The thickness and impurity concentration must be controlled with high precision (Journal of Crystal Growth 107 (1991) 860-866 No.
See rth Holland).

The use of the absorption edge control layer is not only necessary when the thickness of each semiconductor layer is made to exactly match the design value at the time of manufacturing the resonator structure, but also considering the utilization efficiency of light and the number of man-hours until manufacturing. Not the preferred method, but so far,
Since it has been considered difficult to change the reflection spectrum itself of the reflective multilayer film, the above-mentioned modulation method using the absorption edge control layer has become mainstream.

The present invention solves the problems of the prior art and provides a semiconductor reflective multilayer film that simultaneously achieves high-speed response, high utilization efficiency in visible light, and low voltage driving, and a semiconductor reflective multilayer film. Another object of the present invention is to provide a reflective spatial light modulator.

[0014]

In order to achieve the above-mentioned object, the present invention has a reflective multilayer film having two types of constructions.

As shown in FIG. 1, the first structure comprises three parts, that is, a first reflective multilayer film layer ML1, a second reflective multilayer film layer ML2, and a third reflective multilayer film layer ML3. Has been done. The first reflective multilayer film layer ML1 is in contact with the p-type compound semiconductor substrate BP in contact with the first electrode E1, and the first compound semiconductor layer SL1 and the first compound semiconductor layer SL1 have a refractive index and a bandgap energy. The second compound semiconductor layer SL2 having a different wavelength and p-type impurities added to the second compound semiconductor layer SL2 are alternately laminated to have a film thickness of ¼ of the target wavelength. Second reflective multilayer film layer ML2
Includes a large amount of p-type impurities, and includes the first reflective multilayer film M.
A third compound semiconductor layer ML3 having the same refractive index and bandgap energy in either one of the two types of compound semiconductor layers forming L1, and the compound semiconductor layer M.
The fourth compound semiconductor layer SL4 is formed by adding a large amount of n-type impurities to a compound semiconductor having a refractive index of L3 and a bandgap energy. The second reflective multilayer film layer ML2 is composed of two kinds of compound semiconductor layers having the same refractive index and bandgap energy but different kinds of impurities, but the total film thickness thereof is 0.
It may be set to a larger value and 3/4 or less of the target wavelength. The third reflective multilayer film layer ML3 includes the second electrode E2.
In contact with the first compound semiconductor layer SL1 and the first compound semiconductor layer SL1 have a refractive index and a bandgap energy different from each other.
It has a structure in which type impurities are added alternately so as to have a film thickness of ¼ of the target wavelength. At this time, the first reflective multilayer film layer ML1 and the second reflective multilayer film layer M
The compound semiconductor layers corresponding to the adjacent portions of L2 are compound semiconductor layers having different refractive indices and band gap energies, and the compound semiconductor layers corresponding to the adjacent portions of the third reflective multilayer film layer ML3 and the second reflective multilayer film layer ML2. Both are made of compound semiconductor layers having different refractive indexes and band gap energies. If this condition is satisfied, the second reflective multilayer film layer ML2 may be composed of two kinds of compound semiconductors having different refractive indexes and band gaps, or the first reflective multilayer film layer ML1. Any one of the compound semiconductor layers or the one of the compound semiconductor layers forming the third reflective multilayer film layer ML3 has a film thickness other than a quarter of the target wavelength. It may be. Furthermore, the arrangement of the part to which the p-type impurity is added and the part to which the n-type impurity is added may be reversed.

These first, second and third reflective multilayer films M
By laminating L1, ML2, and ML3 sequentially, the semiconductor reflective multilayer film of the first configuration of the present invention is formed.

In the semiconductor reflective multilayer film having the second structure of the present invention, as shown in FIG. 2, a large amount of n-type impurities are added on the p-type compound semiconductor substrate BP in contact with the first electrode E1. The first compound semiconductor layer SL1 and the first compound semiconductor layer SL1 have different refractive indices and band gap energies, and the second compound semiconductor layer S containing a large amount of p-type impurities.
L2 and L2 are alternately laminated so as to have a film thickness of ¼ of the target wavelength to form the reflective multilayer film layer ML, and the second electrode E
2 is provided so as to be in contact with the uppermost part of the reflective multilayer film layer ML. The hetero band structure of the first compound semiconductor layer SL1 and the second compound semiconductor layer SL2 has a second conduction band bottom of the first compound semiconductor layer SL1 even if p-type and n-type impurities are not added. Compound semiconductor layer SL2
Is located energetically below the bottom of the conduction band, and at the same time the top of the valence band of the first compound semiconductor layer SL1 is above the top of the valence band of the second compound semiconductor layer SL2. . In this structure, a large amount of p-type and n-type impurities are added, so that the first compound semiconductor layer SL
The hetero band structure is such that the bottom of the conduction band 1 and the top of the valence band of the second compound semiconductor layer SL2 are close to the Fermi level.

[0018]

The semiconductor reflective multilayer film having the above-mentioned two kinds of structures is the first
There is no absorption edge control layer between the electrode E1 and the compound semiconductor substrate in contact with the second electrode E2, and the reflective multilayer film structure allows direct reflectance control by the applied voltage.
That is, a layer such as a pn junction that causes a change in the refractive index distribution due to a change in applied voltage is provided at an arbitrary portion of the reflective multilayer film, and the multiple reflection effect of the reflective multilayer film is utilized to form the reflective multilayer film. There are two types: a method of changing the reflection spectrum itself and a method of changing the material properties of the element itself by using a hetero-band structure peculiar to the material and changing the function itself as a reflective multilayer film.

In the case of the reaction body reflection multilayer film of the first structure, if no voltage is applied, the first reflection multilayer film layer ML1 and the second reflection multilayer film layer are formed.
In the reflective multilayer film layer ML2, the reflectance change of the multilayer film with respect to the light wavelength, that is, the shape of the reflection spectrum has a plurality of peaks and valleys, and the peak near the target wavelength has the highest reflectivity and is a simple mirror for the target wavelength. Work as. Now, assuming that the layer thickness of the second reflective multilayer film layer ML2 is a quarter of the target wavelength, the second reflective multilayer film layer ML2 functions equivalent to any semiconductor layer that constitutes the reflective multilayer film. It does not affect the shape of the reflection spectrum. When the layer thickness of the second reflective multilayer film layer ML2 is between 0 and 3/4 of the 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.

By the way, a depletion layer having an extremely low carrier concentration is naturally formed between the two compound semiconductor layers forming the second reflective multilayer film layer ML2. For this reason,
The distribution of the refractive index is equivalent to that a compound semiconductor layer containing no impurities is inserted between the p ⁺ type compound semiconductor layer and the n ⁺ type compound semiconductor layer. The thickness of this depletion layer is 4n
very thin. In this depletion layer, the difference in refractive index between the p ⁺ type compound semiconductor layer and the n ⁺ type compound semiconductor layer is about 10%, and the second reflective multilayer film layer ML2
When setting the layer thickness, the effect of the depletion layer should be taken into consideration, and the thickness of the target wavelength should be determined.

When a reverse voltage is applied to the pn junction between the first electrode E1 and the second electrode E2, the depletion layer width increases and reaches about 20 nm at a voltage of 10 to 20V. When the width of the depletion layer increases, the effective optical length of the second reflective multilayer film changes, and at the same time, the periodic structure of the reflective multilayer film locally collapses. 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 sharp rising portion of the valley or peak in the above-mentioned reflection spectrum is easily affected by the change, so that the reflectance with respect to the incident light corresponding to the wavelength of that portion changes greatly. As described above, it becomes possible to control the intensity of the reflected light according to the change of the applied voltage.

Also in the case of the semiconductor reflective multilayer film having the second structure, the reflective multilayer film layer ML has the first compound semiconductor layer SL1 and the second compound semiconductor layer SL1 in order to maximize the reflectance at the target wavelength. The thickness of the layer SL2 is designed to be ¼ of the target wavelength. The hetero band structure of this multilayer film is a structure called Type II, in which the conduction band bottom of the second compound semiconductor layer SL2 is above the conduction band bottom of the first compound semiconductor layer SL1 and The top of the valence band of the second compound semiconductor layer SL2 is above the top of the valence band of the first compound semiconductor layer SL1.

When a large amount of p-type impurities are added to the second compound semiconductor layer SL2 and a large amount of n-type impurities are added to the first compound semiconductor layer SL1, the first compound semiconductor layer SL1 is formed.
The bottom of the conduction band and the top of the valence band of the second compound semiconductor layer SL2 approach the Fermi level.

When a voltage is applied to this highly reflective multilayer film ML,
The carriers doped in the first compound semiconductor layer SL1 and the second compound semiconductor layer SL2 try to move according to the direction of the electric field, but the second compound semiconductor layer S
The holes in L2 are blocked by the valence band barrier of the first compound semiconductor layer SL1 and the electrons in the first compound semiconductor layer SL1 are blocked by the conduction band barrier of the second compound semiconductor layer SL2. The carriers are biased in opposite directions. As described above, there are as many places where the distribution of the impurity concentration in each region is largely different as many as the number of cycles of the multilayer film. The change in the impurity concentration distribution causes a change in the refractive index through the plasma effect, and the multiple reflection is performed in a form in which the deviation of the reflection condition of the reflective multilayer film corresponding to the change is superimposed, and the reflection spectrum changes. .

When a larger voltage is applied to the semiconductor reflective multilayer film of the second structure, the first compound semiconductor layer S
The electrons, which are the minority carriers in the second compound semiconductor layer SL2 that were blocked by the valence band barrier of L1, pass through the barrier due to the tunnel effect. In addition, the conduction band barrier of the second compound semiconductor layer SL2 acts as a forward bias for the applied electric field, so that it does not act as a barrier against electrons tunneling through the valence band barrier of the first compound semiconductor layer SL1. I won't. As a result, a current starts to flow in the entire device. In this way, when current starts flowing in the hetero band structure of Type II, the original optical characteristics of the material change,
The refractive index also changes greatly. As a result, the reflection spectrum also changes greatly, and the reflectance can be controlled by the applied voltage.

The method of modulating the light intensity by the semiconductor reflective multilayer film according to the present invention has been described above. In either of the two types of semiconductor reflective multilayer films having the above-described structures, a reflective multilayer film is produced by using two types of materials that are transparent in the visible light region, that is, have a large bandgap energy, and the pn is formed inside the reflective multilayer film. By providing a junction, a change in the refractive index due to voltage application is locally caused to change the reflection spectrum of the multilayer film.

Since the semiconductor multilayer film and the reflection type spatial light modulator according to the present invention do not include the absorption edge control layer, it is not necessary to use the direct transition type semiconductor, and the band gap energy is not required because the transparent region is used. Any large material will do. From this, it is possible to use an indirect transition type semiconductor material, and it is also possible to use it even if the wavelength is not near the absorption edge as in the modulation method of the absorption edge control type, and there is an advantage that the application range of the wavelength is wide.

Further, the semiconductor reflective multilayer film and the reflective spatial light modulator according to the present invention modulate the reflection spectrum itself of the reflective multilayer film using the transparent region to reflect from near total reflection to near transmissive reflection. It is possible to perform modulation up to the rate, the degree of modulation is large, and the light intensity can be modulated without using a light absorption layer, so that high utilization efficiency of light is realized. Moreover, since the multiple quantum well layer is not used in the fabrication, strict design and control of the film thickness are not required, and the light intensity modulation can be realized by the element having a relatively simple structure. Furthermore, the rate of change in reflectance may be considered to be nsec or less, and high-speed operability can be secured.

As described above, according to the semiconductor reflective multilayer film and the reflective spatial light modulator of the present invention, high-speed response and simplicity of device fabrication can be achieved at the same time, and the light intensity with respect to light in the visible light region can be achieved. Modulation can be achieved.

[0030]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a schematic sectional view of a reflective spatial light modulator according to the first embodiment of the present invention (corresponding to claim 1).

In FIG. 3, 101 corresponds to BP in FIG.
P-GaP substrate doped with a p-type impurity
Is a p-type doped with a p-type impurity corresponding to SL1 in FIG.
-Al_yGa_1-yP layer, 103 corresponds to SL2 in FIG.
P-Ga doped with p-type impurities_xAl_1-xIn P layer
Yes, x is in the range of formula (1) and y is in the range of formula (2).         1 ≧ x> 0.5 (1)         1 ≧ y> 0.5 (2) 104 is a first reflective multilayer film layer corresponding to ML1 in FIG.
Yes, p-Al_yGa_{1- y}Starting at the P layer 102, p-A
l_yGa_1-yP-Ga ending at P layer 102_xAl _1-xP
/ Al_yGa_1-yIt is a P multilayer film. 105 is SL of FIG.
The carrier concentration of the p-type impurity corresponding to 3 is 10¹⁹-10
²⁰cm^-3And extremely high p⁺-Ga_xAl_{1- x}P layer, 10
6 is the carrier concentration of the n-type impurity corresponding to SL4 in FIG.
Is 10¹⁹-10²⁰cm^-3And extremely high n⁺-Ga_xAl
_1-xP layer, and by these, the second reflective multilayer film of FIG.
ML2 is configured. 107 corresponds to SL5 in FIG.
n-Al doped with n-type impurities_yGa_1-yP layer, 1
08 corresponds to SL6 in FIG. n-type impurity doped
N-Ga_xAl_1-xP layer, and 109 in FIG.
The third reflective multilayer film layer corresponding to L3 is n-Al._y
Ga_1-yStarting with the P layer 107, n-Ga_xAl_1-xP layer
N-Ga ending with 108_xAl_1-xP / Al_yGa_1-y
It is a P multilayer film. Reference numeral 110 is a lower battery corresponding to E1 in FIG.
The electrode 111 is an upper electrode corresponding to E2 in FIG.

[0032] _{p-Al y Ga 1-y} P layer 102, p-Ga
_x Al _1-x P layer _{103, n-Al y Ga 1} -y P layer 10
7. The n-Ga _x Al _1-x P layer 108 is a semiconductor layer forming a reflective multilayer film, and its film thickness is set to be 1/4 of the target wavelength. Also, the upper electrode 1
Reference numeral 11 denotes a cylindrical or transparent electrode, n-Ga _x Al _1-
In the top of the _{x P / Al y Ga 1-} y P multilayer film 109, incident light 112 and output light 113 is a structure forward to once again enters the multilayer film without being blocked and absorbed. The shape of the lower electrode 110 is arbitrary. In addition, the lower electrode 110
Is p ^{+ +} -GaP having a p-type impurity concentration of about 10 ²⁰ cm ^-3.
Or n-Ga _x Al _1-x P directly under the upper electrode
The layer 108 is made of n ⁺⁺ having an n-type impurity concentration of about 10 ²⁰ cm ^−3.
It may be —Ga _x Al _{1- x} P.

Reflective spatial light modulation constructed as described above
Please refer to FIG. 3 for the semiconductor reflective multilayer film in the container.
The operation will be described. First, in the state where no voltage is applied
The characteristics of light reflection / transmission in the multilayer film will be described. p-G
a_xAl_1-xP / Al_yGa _1-yP multilayer film 104 and
n-Ga_xAl_1-xP / Al_yGa_1-yP multilayer film 109
Then, the reflectance change of the multilayer film with respect to the light wavelength,
The shape of the emissive spectrum has multiple peaks and valleys.
The peak near the target wavelength has the highest reflectance,
Acts as a simple mirror for the target wavelength. The purpose
The peak near the wavelength depends on the refractive index difference between the two materials.
Has a certain width. Now p⁺-Ga_xAl_1-xWith P layer 105
n + -Ga_xAl_1-xEffective sum of film thickness with P layer 106
If it is a quarter of the target wavelength, p⁺-Ga_xAl_1-xP
Layers 105 and n⁺-Ga_xAl_1-xThe P layer 106 is a semiconductor
Reflective because it is only one arbitrary layer in the reflective multilayer
It has almost no effect on the shape of the spectrum. In that case
If the film thickness of the meter is between 0 and 3/4 of the effective target wavelength
The main peak near the target wavelength in the reflection spectrum.
A valley appears in Ku. Also, its position and the depth of the valley
Is uniquely set by arbitrarily setting the total film thickness.
I can decide.

By the way, p⁺-Ga_xAl_1-xP layer 10
5 and n⁺-Ga_xAl_1-xCarry between the P layer 106
A is exhausted, carrier concentration is 10¹⁶cm^-3Extremely below
Low i-Ga_xAl_1-xThe P layer is made naturally. this
Therefore, the distribution of the refractive index is p⁺-Ga_xAl_1-xP layer 10
5 and n⁺-Ga_xAl_1-xImpurities are formed between the P layer 106 and
Ga not included_xAl_1-xEquivalent to inserting P layer
become. This carrier concentration is extremely low
The layer, that is, the depletion layer has a carrier concentration of 10 ¹⁹~ 1
0²⁰cm^-3Very thin at 4 nm in pn junction
Yes. In addition, the decrease in the refractive index due to the plasma effect is 10
¹⁹-10²⁰cm^-3Carrier concentration is about 10%
Is. Therefore, p⁺-Ga_xAl_1-xWith P layer 105
n⁺-Ga _xAl_1-xSet the total film thickness with P layer 106
In consideration of the effect of this depletion layer,
It suffices to decide how many times the target wavelength should be used.

Next, a reverse voltage is applied to the pn junction between the upper electrode 111 and the lower electrode 110. By applying this reverse voltage, the width of the depletion layer is increased and reaches about 20 nm at a voltage of 10 to 20V. Of the two materials forming the semiconductor reflective multilayer film, a change in the film thickness of any one layer, that is, a change in the effective optical length has a great influence on the reflection spectrum. As described above, when the width of the depletion layer increases, the effective optical length changes, and at the same time, the periodic structure of the reflective multilayer film also collapses locally. 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, since the portion of the reflection spectrum having the above-mentioned valley or sharp rising edge is easily affected by the change, the incident light 112 corresponding to the wavelength of the portion.
Changes its intensity to become reflected light 113. This change in intensity is proportional to the depletion layer width, and the depletion layer width is proportional to the square root of 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 applied voltage to the pn junction is 15V,
The reflectance varies from 0.1% to 30%. The amount of change is 30%, and the modulation transfer function MTF is 0.99.

In the above embodiment, even if the arrangements of the p-type and p ⁺ -type regions and the n-type and n ⁺ -types are exchanged, the operation principle remains the same except that the reverse voltage direction is changed. ).

Further, the p ⁺ -Ga _x Al _1-x P layer 105 and the n ⁺ -Ga _x Al _1-x P layer 106 are respectively p ⁺
-Al _y Ga _1-y replaced by a P layer and _{^{n + -Al y Ga 1-y}} P _{layer, p-Ga x Al 1-} x P / Al y Ga 1-y P
The multilayer film 104 is terminated with a p-Ga _x Al _1-x P layer, and n
_{-Gax Al 1-x P / Al} y Ga 1-y P multilayer film 109 have a structure to start with _{n-Ga x Al 1-x} P layer, the same operation principle (claim 3 corresponds).

Also in this case, the p-type and p ⁺ -type regions can be replaced with the n-type and n ⁺ -type regions (corresponding to claim 4).

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic sectional view of a reflection type optical modulator according to the second embodiment of the present invention (corresponding to claim 8).

In FIG. 4, 201 corresponds to BP in FIG.
202. p-GaP substrate doped with p-type impurities
Is a p-type doped with a p-type impurity corresponding to SL1 in FIG.
-Al_yGa_1-yP layer, 203 corresponds to SL2 in FIG.
P-Ga doped with p-type impurities_xAl_1-xIn P layer
And subscripts x and y are the above-mentioned formula (1) and formula, respectively.
Within the range of (2). 204 corresponds to ML1 in FIG.
The first reflective multilayer film layer, p-Al_yGa_1-yP layer 2
Starting with 02, p-Al_yGa_1-yEnds with P layer 202
p-Ga_xAl_1-xP / Al_yGa_1-yP multilayer film
It 205 is a p-type impurity carrier corresponding to SL3 in FIG.
Rear concentration is 10¹⁹-10²⁰cm^-3And extremely high p⁺-G
a_xAl_1-xP layer, 206 is n corresponding to SL4 in FIG.
Carrier concentration of type impurities is 10¹⁹-10²⁰cm^-3And extremely
High n⁺-Al_yGa_1-yP layer,
The second reflective multilayer film layer ML2 of FIG. 1 is configured. 207
Is an n-type impurity-doped n corresponding to SL5 in FIG.
-Ga_xAl_1-xP layer, 208 corresponds to SL6 in FIG.
N-Al doped with n-type impurities_yGa_1-yIn P layer
Yes, 209 is a third reflective multilayer corresponding to ML3 in FIG.
Membrane layer, n-Ga _xAl_1-xStarting with P-layer 207,
n-Ga_xAl_1-xN-Ga ending at P layer 207_xAl
_1-xP / Al_yGa_1-yIt is a P multilayer film. 210 is shown in FIG.
The lower electrode corresponding to E1 of FIG. 1, 211 corresponds to E2 of FIG.
Is the upper electrode. The upper electrode 211 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 209, incident light 212
And the emitted light 213 is not blocked and absorbed, and
Make a structure that can penetrate into. The shape of the lower electrode 210 is
It is optional. In addition, also in the present embodiment, the same as in the first embodiment.
The configuration can be changed in various ways (claims
9、10、11、12)).

Next, the operation of this embodiment will be described.
Also in the case of the present embodiment, as in the case of the first embodiment,
P ⁺ -Ga _x Al _1-x P layer 205 and n ⁺ by voltage application
-Al is _y Ga _1-y P layer reflectance modulation using the depletion layer changes in 206, but significantly different from, not to make a pn junction in one of the material constituting the multilayer film, By making a hetero pn junction, a depletion layer is formed across both materials. Since the carrier is depleted in the depletion layer portion, the refractive index is different, and the periodic structure of the refractive index in this portion locally collapses. Further, since it is a hetero pn junction, its resistance value is higher than that of the homo pn junction, and the voltage is more likely to be concentrated and applied to this portion as compared with the case of the first embodiment. Of course, also in this case, the effective optical length is changed as in the case of the first embodiment. A local deviation of the periodic structure and a local deviation of the effective optical length occur at this location at the same time, and as a result, the reflection spectrum shape changes as the applied voltage changes, as in the first embodiment.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a schematic sectional view of a reflective spatial light modulator according to the third embodiment of the present invention (corresponding to claim 13).

In FIG. 5, reference numeral 301 denotes a p-GaP substrate doped with a p-type impurity corresponding to BP in FIG. 2, and 302.
Indicates that the n-type impurity corresponding to SL1 in FIG.
N ⁺ -A highly doped with 0 ¹⁹ to 10 ²⁰ cm ^-3
l _y Ga _1-y P layer, 303 is equivalent to SL2 in FIG. 2 p
Is a p ⁺ -Ga _x Al _{1 -x} P layer in which the type impurities are extremely highly doped with a carrier concentration of 10 ¹⁹ to 10 ²⁰ cm ^-3 , and x
And y are the same as the ranges shown in the above formula (1) and formula (2), respectively. 304 is n ⁺ -Al
_y Ga _1-y P layer 302 and p ⁺ -Ga _x Al _1-x P layer 30
Corresponds 3 and a in the reflective multilayer film ML in FIG. 2 of alternately laminated _{^{p + -Ga x Al 1-x}} P / n + -Al y Ga 1-y is P multilayer film, 305 of FIG. 2 A lower electrode corresponding to E1 and an upper electrode 306 corresponding to E1 in FIG. The upper electrode 316 is a cylindrical type or a transparent electrode, and is p ⁺ −
_{Ga x Al 1-x P /} n + -Al y Ga 1-y P multilayer film 30
4, the incident light 307 and the outgoing light 308
Is not blocked and absorbed so that it can enter the multilayer film. The shape of the lower electrode 305 is arbitrary.

Next, the operation of this embodiment will be described.
P in this embodiment⁺-Ga_xAl _1-xP / n⁺-Al
_yGa_1-yThe P multilayer film layer 304 has the maximum reflectance at the target wavelength.
Each semiconductor layer 302 and 303 has a
The film thickness is designed to be one quarter of the target wavelength. Well
The hetero band structure of this multilayer film is called Type II.
The structure is exposed, and a schematic diagram of the band structure is shown.
6 shows. Of the hetero band structure called Type II
Characteristic is Ga_xAl_1-xBottom of conduction band 403 of P layer 401
But Al_yGa_1-yFrom the bottom 405 of the conduction band of the P layer 402
Is also on top and Ga_xAl_1-xCharge of P layer 401
The top 404 of the baby band is Al_yGa_1-yValence electron of P layer 402
The point is above the top 406 of the band. One like this
Both the conduction band bottom and the valence band top of the other material are the other material.
Is above the bottom of the conduction band and the top of the valence band
It is a characteristic of the hetero band structure called Type II.
It

When a large amount of p-type impurities is added to the Ga _x Al _1-x P layer 401 and a large amount of n-type impurities is added to the Al _y Ga _1-y P layer 402, the Ga _x Al _1-x P valence band is obtained. Top 40
4 approaches the Fermi level 409, and the Al _y Ga _1-y P conduction band bottom 405 also approaches the Fermi level 409. The degree of this approach becomes larger or smaller depending on the doping amount. In the case of this embodiment, the doping amount is carrier concentration of 10 ¹⁹ to
Since it is as high as 10 ²⁰ cm ⁻³ , the distance between the top of the Ga _x Al _1-x P valence band 404 and the Fermi level 409 of the bottom of the Al _y Ga _1-y P conduction band 405 is close to several meV.

When a voltage is applied to this highly reflective multilayer film, p⁺
-Ga_xAl_1-xP layer 401 and n⁺-Al_yGa
_1-yCarriers doped in the P layer 402 have an electric field
Try to move according to the direction of, but p⁺-Ga_xAl
_1-xThe holes which are the majority carriers in the P layer 401 are n⁺−
Al_yGa_1-yIn the valence band barrier 408 of the P layer 402, n
⁺-Al_yGa_1-yThe electrons that are the majority carriers in the P layer are
p⁺-Ga_xAl_1-xBlocked by P conduction band barrier 407,
These carriers are biased in opposite directions.
In this way, the distribution of the impurity concentration in each region is
There are as many places as the number of cycles of the multilayer film, which is very different from the previous one
It will be. From this change in the impurity concentration distribution, the plasma effect
A change in the refractive index occurs through the fruit, and the reaction corresponding to the change occurs.
Multiple reflections can be achieved by superimposing the deviation of the reflection conditions of the reflective multilayer film.
And a change in the reflectance spectrum occurs.

FIG. 7 shows a heteroband structure in the case where a still higher voltage is applied. At this time, n ⁺ -Al _y G
The electrons, which were the minority carriers in the p ⁺ -Ga _x Al _{1 -x} P layer 501 and were blocked by the valence band barrier 504 of the a _{1 -y} P layer 502, passed through the barrier due to the tunnel effect, and the tunnel current 507. Occurs. In addition, p ⁺ -Ga _x Al
The conduction band barrier 503 of the _1-x P layer 501 has an applied electric field 506.
There for the action of the forward bias, n ⁺ -Al _y Ga
_For the electrons tunneling through the valence band barrier 504 of the _1-y P layer 502, the effect as a barrier is lost. As a result, a current starts to flow in the entire device. Like this Ty
When a current flows in the peII heteroband structure, the original optical characteristics of the material change greatly in phase conversion, and the refractive index also changes significantly. As a result, the reflection spectrum also changes greatly, and the reflectance can be controlled by the applied voltage.

[0048]

As described above, according to the present invention,
Transparent in the visible light region _{Ga x Al 1-x P /} Al y Ga 1-y
A semiconductor reflective spatial light modulator usable in the visible light region can be realized by selecting the P multilayer film as a material. In addition, a reflective spatial light modulator that does not use optical absorption control has been realized by adopting a configuration that can utilize the change in the refractive index of the reflective multilayer film itself, which has been considered difficult in the past. I can omit it.

Since it is also a voltage-controlled reflective spatial light modulator, there is only a substrate and electrodes below the reflective multilayer film.
There is room for stacking with a pin photodiode or the like, and more additional functions can be provided.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a reflective spatial light modulator for explaining the concept of the present invention.

FIG. 2 is a schematic sectional view of another reflective spatial light modulator for explaining the concept of the present invention.

FIG. 3 is a schematic sectional view of a reflective spatial light modulator according to the first embodiment of the present invention.

FIG. 4 is a schematic sectional view of a reflective spatial light modulator according to a second embodiment of the present invention.

FIG. 5 is a schematic sectional view of a reflective spatial light modulator according to a third embodiment of the present invention.

FIG. 6 is a schematic diagram showing a hetero band structure of a multilayer film in a third embodiment.

FIG. 7 is a schematic diagram showing a hetero band structure when a voltage is applied to the multilayer film in the third embodiment.

FIG. 8 is a schematic sectional view of a reflective spatial light modulator in a conventional example.

[Explanation of symbols]

BP semiconductor substrate E1 First electrode E2 Second electrode ML reflective multilayer film ML1 First reflective multilayer film layer ML2 second reflective multilayer film layer ML3 Third reflective multilayer film layer SL1 first semiconductor layer SL2 Second semiconductor layer SL3 Third semiconductor layer SL4 Fourth semiconductor layer SL5 Fifth semiconductor layer SL6 Sixth semiconductor layer

─────────────────────────────────────────────────── ─── Continued Front Page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/015 503 G02F 1/29

Claims (18)

(57) [Claims] 1. A first semiconductor layer containing a p-type impurity and a second semiconductor layer containing a p-type impurity and having a refractive index and bandgap energy different from each other.
Starting from the first semiconductor layer and alternately terminating at the first semiconductor layer, the first reflective multilayer film layers and the second semiconductor layer are made of a material having the same refractive index and the same bandgap energy as that of the second semiconductor layer. The third semiconductor layer containing a larger amount of p-type impurities than the semiconductor layer and a material having the same refractive index and bandgap energy as those of the second semiconductor layer and having a p-type impurity concentration comparable to that of the third semiconductor layer. And a fourth semiconductor layer containing a large amount of n-type impurities are stacked, and the total film thickness of the third semiconductor layer and the fourth semiconductor layer is larger than 0 and the second semiconductor layer A second reflective multilayer film having a thickness of 3 times or less; a fifth semiconductor layer containing n-type impurities and having the same refractive index and bandgap energy as the first semiconductor layer; Same as the second semiconductor layer A sixth semiconductor layer of which having a rate and the band gap energy starting from the fifth semiconductor layer,
A semiconductor reflective multilayer film having a structure in which a third reflective multilayer film layer that is alternately stacked so as to terminate at a sixth semiconductor layer is stacked. 2. A first semiconductor layer containing an n-type impurity and a second semiconductor layer containing an n-type impurity and having a refractive index and bandgap energy different from each other.
Starting from the first semiconductor layer and alternately terminating at the first semiconductor layer, the first reflective multilayer film layers and the second semiconductor layer are made of a material having the same refractive index and the same bandgap energy as that of the second semiconductor layer. The third semiconductor layer containing a larger amount of n-type impurities than the semiconductor layer and a material having the same refractive index and bandgap energy as those of the second semiconductor layer and comparable to the n-type impurity concentration of the third semiconductor layer. And a fourth semiconductor layer containing a large amount of p-type impurities are stacked, and the total film thickness of the third semiconductor layer and the fourth semiconductor layer is greater than 0 and the second semiconductor layer A second reflective multilayer film layer having a thickness of 3 times or less, a fifth semiconductor layer containing p-type impurities and having the same refractive index and bandgap energy as the first semiconductor layer, and p-type impurities Same as the second semiconductor layer A sixth semiconductor layer of which having a rate and the band gap energy starting from the fifth semiconductor layer,
A semiconductor reflective multilayer film having a structure in which a third reflective multilayer film layer that is alternately stacked so as to terminate at a sixth semiconductor layer is stacked. 3. A first semiconductor layer containing a p-type impurity and a second semiconductor layer containing a p-type impurity and having a refractive index and a bandgap energy different from each other.
Starting from the first semiconductor layer and terminating alternately at the second semiconductor layer, the first reflective multilayer film layers and the first semiconductor layer having the same refractive index and the same bandgap energy as those of the first reflective multilayer film layer. The third semiconductor layer containing a larger amount of p-type impurities than the semiconductor layer and the material having the same refractive index and bandgap energy as those of the first semiconductor layer and comparable to the p-type impurity concentration of the third semiconductor layer. A fourth semiconductor layer containing a large amount of n-type impurities is stacked, and the total film thickness of the third semiconductor layer and the fourth semiconductor layer is larger than 0 and the first semiconductor layer A second reflective multilayer film having a thickness of 3 times or less; a fifth semiconductor layer containing n-type impurities and having the same refractive index and bandgap energy as the first semiconductor layer; Same as the second semiconductor layer A sixth semiconductor layer of which having a rate and the band gap energy starting from the sixth semiconductor layer,
A semiconductor reflective multilayer film having a structure in which a third reflective multilayer film layer that is alternately stacked so as to terminate at a sixth semiconductor layer is stacked. 4. A first semiconductor layer containing an n-type impurity and a second semiconductor layer containing an n-type impurity and having a refractive index and bandgap energy different from each other.
Starting from the first semiconductor layer and terminating alternately at the second semiconductor layer, the first reflective multilayer film layers and the first semiconductor layer having the same refractive index and the same bandgap energy as those of the first reflective multilayer film layer. The third semiconductor layer containing a larger amount of n-type impurities than the semiconductor layer, and the material having the same refractive index and bandgap energy as those of the first semiconductor layer and comparable to the n-type impurity concentration of the third semiconductor layer. A fourth semiconductor layer containing a large amount of p-type impurities is stacked, and the total film thickness of the third semiconductor layer and the fourth semiconductor layer is greater than 0 and the first semiconductor layer A second reflective multilayer film layer having a thickness of 3 times or less, a fifth semiconductor layer containing p-type impurities and having the same refractive index and bandgap energy as the first semiconductor layer, and p-type impurities Same as the second semiconductor layer A sixth semiconductor layer of which having a rate and the band gap energy starting from the sixth semiconductor layer,
A semiconductor reflective multilayer film having a structure in which a third reflective multilayer film layer that is alternately stacked so as to terminate at a sixth semiconductor layer is stacked. 5. Except for any one of the first semiconductor layers in the first reflective multilayer film layer, the other films have the same thickness or any one of the second semiconductor layers. Except for any one of the fifth semiconductor layers in the third reflective multi-layer film, the other film thicknesses are equal or other than the sixth semiconductor layer. A structure having the same film thickness except for one of the arbitrary ones.
5. The semiconductor reflective multilayer film according to any one of 4 to 4. 6. 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). 6. The semiconductor reflective multilayer film according to any one of 5 to 5. 7. The semiconductor reflective multilayer film according to claim 1, further comprising a first reflective multilayer film layer laminated on the semiconductor substrate, and the first reflective multilayer film layer being in contact with the semiconductor substrate. A reflective spatial light modulator having a structure in which electrodes are stacked and a second electrode is stacked in contact with a third reflective multilayer film layer. 8. A first semiconductor layer containing a p-type impurity and a second semiconductor layer containing a p-type impurity and having a refractive index and a bandgap energy different from each other.
Starting from the first semiconductor layer and alternately terminating at the first semiconductor layer, the first reflective multilayer film layers and the second semiconductor layer are made of a material having the same refractive index and the same bandgap energy as that of the second semiconductor layer. The third semiconductor layer containing a larger amount of p-type impurities than the semiconductor layer and the material having the same refractive index and bandgap energy as those of the first semiconductor layer and comparable to the p-type impurity concentration of the third semiconductor layer. And a fourth semiconductor layer containing a large amount of n-type impurity, and a fifth reflective multilayer film layer including n-type impurity and having the same refractive index and bandgap energy as the second semiconductor layer. A semiconductor layer and a sixth semiconductor layer containing an n-type impurity and having the same refractive index and bandgap energy as the first semiconductor layer are started from the fifth semiconductor layer and terminated at the fifth semiconductor layer. Third reflective multilayer film and the semiconductor reflective multilayer film having a stacked structure in which each other by laminating. 9. A first semiconductor layer containing an n-type impurity and a second semiconductor layer containing an n-type impurity and having a refractive index and a bandgap energy different from each other.
Starting from the first semiconductor layer and alternately terminating at the first semiconductor layer, the first reflective multilayer film layers and the second semiconductor layer are made of a material having the same refractive index and the same bandgap energy as that of the second semiconductor layer. The third semiconductor layer containing a larger amount of n-type impurities than the semiconductor layer, and the material having the same refractive index and bandgap energy as those of the first semiconductor layer and comparable to the n-type impurity concentration of the third semiconductor layer. A second reflective multilayer film layer in which a fourth semiconductor layer containing a large amount of p-type impurities is stacked, and a fifth reflective multilayer film layer containing p-type impurities and having the same refractive index and bandgap energy as the second semiconductor layer. The semiconductor layer and the sixth semiconductor layer containing p-type impurities and having the same refractive index and bandgap energy as those of the first semiconductor layer start from the fifth semiconductor layer and end with the fifth semiconductor layer. The third reflective multi-layer coating layer and the reflective multilayer film, wherein the laminated structure of the laminated on. 10. Except for any one of the first semiconductor layers in the first reflective multilayer film, any other one having the same film thickness or any one of the second semiconductor layers is formed. Except for any one of the fifth semiconductor layers in the third reflective multi-layer film, the other film thicknesses are equal or other than the sixth semiconductor layer. 10. The semiconductor reflective multilayer film according to claim 8, which has a structure having the same film thickness other than any one. 11. The semiconductor of the first semiconductor layer is Al _y Ga.
9. _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). 11. The semiconductor reflective multilayer film according to any one of 1 to 10. 12. A semiconductor reflective multilayer film according to claim 8, further comprising a first reflective multilayer film layer laminated on the semiconductor substrate, the first reflective multilayer film layer being in contact with the semiconductor substrate. The electrode is laminated and contacts the second reflective multilayer film to form the second
Reflective spatial light modulator having a structure in which the above electrodes are laminated. 13. A first semiconductor layer containing a large amount of n-type impurities and a second semiconductor layer containing a large amount of p-type impurities and having a different refractive index and band gap energy are alternately formed. A semiconductor reflective multilayer film having a laminated structure. 14. A hetero band structure of a semiconductor of a first semiconductor layer and a semiconductor of a second semiconductor layer, wherein a conduction band bottom of a semiconductor of the first semiconductor layer is a conduction band of a semiconductor of the second semiconductor layer. The structure is located energetically below the bottom of the band, and the top of the valence band of the semiconductor of the first semiconductor layer is below the top of the valence band of the semiconductor of the second semiconductor layer. 14. The semiconductor reflective multilayer film according to claim 13, wherein: 15. An electric field is applied parallel to the stacking direction of each layer, so that the top of the valence band of the semiconductor of the second semiconductor layer is above the bottom of the conduction band of the semiconductor of the first semiconductor layer. 15. The semiconductor reflective multilayer film according to claim 13 or 14, which is a multilayer film that is located or changes to a state close thereto. 16. The semiconductor of the first semiconductor layer is Al _y Ga.
14. _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). 16. The semiconductor reflective multilayer film according to any one of 1 to 15. 17. The semiconductor reflective multilayer film according to claim 13, further comprising a lowest semiconductor layer of the semiconductor reflective multilayer film, which is laminated on a semiconductor substrate. A reflective spatial light modulator having a structure in which a first electrode is laminated in contact with a substrate, and a second electrode is laminated in contact with an uppermost second semiconductor layer of the semiconductor reflective multilayer film. 18. The reflective spatial light modulator according to claim 7, 12 or 17, wherein the semiconductor substrate is p-GaP.