JP2000028973A - Optical modulation element, exposure element, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulation element, an exposure element, and a display device which are driven with a low voltage with a simple constitution and are quickly and stably operated and take visible light through infrared light as the object. SOLUTION: In this optical modulation element, a semiconductor layer 3 made of an n-type semiconductor material is provided on the upper face of a lower transparent electrode 2, and an upper transparent electrode 5 is provided on the upper face of the semiconductor layer 3 with an insulating layer 4 between them, and carrier of the n-type semiconductor layer 3 is depleted by applying such electric field in the vertical direction that the upper transparent electrode 5 is negative and the lower transparent electrode 2 is positive, thus changing at least one of the light reflection factor and the light absorption factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light modulator, and more particularly, to a light modulator capable of modulating, exposing, and displaying light in the infrared to visible wavelength range.

[0002]

2. Description of the Related Art Conventionally, light modulation and light modulation
Elements that control the exposure or display of materials include liquid crystal elements,
LN (lithium niobate: L using the Pockels effect)
iNbO_Three), KDP (potassium phosphate: KH)_TwoPO_Four), A
DP (ammonium phosphate: NH_FourH _TwoPO_Four) Such as electro-optic
Crystals, mainly electro-optics such as PLZT utilizing Kerr effect
Crystals are used. However, the above-mentioned liquid crystal element has low voltage
Although it is an element that can be driven, its response speed is slow,
Large environmental dependency. Furthermore, the main method of liquid crystal elements is
TN type (twisted nematic type), birefringent type, etc. are polarized
The problem that a plate is required and light is absorbed by the polarizing plate
There is.

[0003] As a new light modulating element for solving the above problem, as shown in FIG.
Japanese Patent Application Laid-Open No. Hei 9-179082 discloses a technique in which a voltage is applied by sandwiching a dielectric substance 113 such as PZT or PLZT between transparent electrodes 114 and 115 to perform light modulation. This is because when no voltage is applied between both transparent electrodes, light is transmitted, and when a voltage is applied, electrons are filled in the negative electrode side of the transparent electrode and the electron concentration increases, so that free electrons of the metal are increased. Light modulation is performed using the principle that light is reflected by the transparent electrode on the negative electrode side, as in the case of the optical characteristics of the above. According to this, light modulation becomes possible without using a polarizing plate.

[0004]

In the above-mentioned light modulation, the shorter the wavelength of the target light, the higher the electron concentration required for the light modulation. Therefore, in order to induce an increase in the electron concentration of the light modulation element, it is necessary to increase the number of electrons to be filled. In order to drive at a low voltage, it is necessary to increase the capacitance between the electrodes. The above-mentioned dielectric substance has a very high dielectric constant, for example, PZT, PLZT or the like which is a ceramic-based high dielectric substance. Material. However, it is difficult to form a thin film having a stable dielectric constant with the above materials having a high dielectric constant, and it is also difficult to stably control the electron concentration of the transparent electrode. is there. In recent years, light modulation elements based on the electric field optical effect of a semiconductor and carrier concentration control in a pn junction have been developed. There is nothing to change the light modulation or the light reflectivity.
In addition, an electro-optic crystal can respond faster than a liquid crystal element and has less environmental dependency, but an electro-optic crystal using the Pockels effect has a higher driving voltage. An electro-optic crystal utilizing the Kerr effect can be driven at a relatively low voltage, but requires a very high driving voltage as compared with a liquid crystal element. Further, it is difficult to form a high-definition array using an electro-optic crystal. Further, a polarizing plate is required, and there is a problem that light is absorbed by the polarizing plate.

The present invention has been made in view of the above-mentioned problems in the conventional light modulation element, and has a simple structure, which can operate stably at a low voltage with a high speed and at a high speed from a visible light to a red light. An object is to provide a light modulation element, an exposure element, and a display device for external light.

[0006]

In order to achieve the above object,
The light modulation device according to claim 1, wherein a semiconductor layer is provided on an upper surface of the lower transparent electrode, and an upper transparent electrode is provided on the upper surface of the semiconductor layer via an insulating layer, and the upper transparent electrode and the lower transparent electrode are provided. An electric field for depleting carriers in the semiconductor layer is applied between the first and second layers to change at least one of the light reflectance and the light absorption.

In this light modulation element, at least one of the light absorption and the reflectance is reduced by applying an electric field between the upper transparent electrode and the lower transparent electrode to deplete the carriers in the semiconductor layer. Therefore, when an electric field is applied, the light modulation element transmits the incident light, and when the electric field is not applied, the light modulation element exhibits or modulates the incident light by absorbing or reflecting and not transmitting the incident light.

[0008] Light modulation element according to claim 2, the band gap energy E _g of the semiconductor, _{when 0} the wavelength of the modulated light being lambda, the speed of light in vacuum c, and Planck's constant was h, E _g> hc / λ ₀ [eV].

In this light modulation element, the wavelength λ ₀ of the light to be modulated is longer than the wavelength λ _g of the light absorption edge. Therefore,
Stable light modulation can be performed without using the region below the absorption edge wavelength due to the band gap where the absorptance is always high.

[0010] Light modulation element according to claim 3, the band gap energy E _g of the semiconductor is characterized in that at 2 [eV] or more.

In this light modulating element, light from visible light to infrared light can be modulated stably by setting the band gap energy E _g of the semiconductor to 2 [eV].

According to a fourth aspect of the present invention, the wavelength λ ₀ of the modulated light is smaller than the plasma wavelength λ _{p of the} semiconductor layer.

In this light modulating device, when the wavelength λ _{0 of the} light to be modulated is shorter than the plasma wavelength λ _p of the semiconductor layer in the absence of an electric field, the reflectance is low but the semiconductor layer is free-absorbing. The absorptance increases and the light transmittance decreases.
Further, when the semiconductor layer is depleted by applying an electric field to lower the carrier concentration, the absorptance decreases and the light transmittance increases. Thereby, the light transmittance can be changed.

According to a fifth aspect of the present invention, the wavelength λ ₀ of the modulated light is larger than the plasma wavelength λ _{p of the} semiconductor layer.

In this light modulation element, when the wavelength λ _{0 of the} light to be modulated is longer than the plasma wavelength λ _p of the semiconductor layer in the absence of an electric field, the reflectance is high and the light transmittance is low. When the semiconductor layer is depleted by applying an electric field to lower the carrier concentration, the reflectance decreases and the light transmittance increases. Thereby, the light transmittance can be changed.

The light modulating element according to claim 6 is characterized in that a reverse bias voltage is applied so that the thickness of the depleted layer becomes substantially equal to the thickness of the semiconductor layer.

In this light modulation device, the depletion layer in the semiconductor layer is formed over substantially the entire semiconductor layer, so that the ratio of the depletion layer in the semiconductor layer increases, and the light modulation effect is substantially maximized. Can be demonstrated.

The light modulating element according to claim 7, wherein a plurality of light modulating layers comprising the semiconductor layer and the insulating layer are laminated on the upper surface of the lower transparent electrode, and the upper transparent electrode is formed on the upper surface of the uppermost light modulating layer. It is characterized by having provided.

In this light modulation element, when a voltage is applied between the electrodes, a depletion layer is generated in each of the plurality of semiconductor layers, so that the depletion layer region is expanded, and the light modulation capability is further improved.

In the light modulating element according to the present invention, at least one intermediate transparent electrode is provided between the upper and lower transparent electrodes, the light modulating layer is interposed between the respective electrodes, and the semiconductor layer is An electric field for depleting carriers in the semiconductor layer is applied between the connected intermediate transparent electrode and the intermediate transparent electrode in contact with the insulating layer.

In this light modulating element, the depletion of each semiconductor layer is made more reliable, and the depletion of each semiconductor layer is made more uniform in all regions in the layer.

In a ninth aspect of the present invention, the semiconductor layer is an n-type semiconductor layer.

In this light modulation device, light modulation by depletion and injection of carriers in the n-type semiconductor layer, that is, electrons, becomes possible.

According to a tenth aspect of the present invention, at least one p-type semiconductor layer in which impurities are diffused at a high concentration is provided between the upper and lower transparent electrodes.

In this light modulation device, the electron carriers of the n-type semiconductor layer which move by applying a voltage are recombined at the interface of the p-type semiconductor layer. Therefore, the n-type semiconductor layer can be entirely depleted.

According to an eleventh aspect of the present invention, there is provided an exposure element formed by arranging the light modulation elements according to any one of the first to tenth dimensions one-dimensionally or two-dimensionally.

In this exposure apparatus, the light modulation elements can be made to function as an exposure apparatus by forming them one-dimensionally or two-dimensionally.

According to a twelfth aspect of the present invention, there is provided a display device, wherein the light modulating elements according to any one of the first to tenth aspects are formed in a one-dimensional or two-dimensional array. It is characterized in that a flat light source is provided opposite to the flat light source.

In this display device, the light modulating elements are arranged one-dimensionally or two-dimensionally, and a planar light source is provided so as to face the arranged light modulating elements so that the light modulating element can function as a display device. Can be.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the operation principle of the light modulation device of the present invention will be described. In general, materials rich in free electrons, such as metals, semimetals, and high-concentration impurity semiconductors, have a property of reflecting incident light having a wavelength longer than the plasma wavelength. This is called plasma reflection. The plasma wavelength is calculated as a plasma frequency by the following equation (2).

(Equation 1)

In the equations (1) and (2), ω_pIs a plasm
Frequency, N is carrier concentration, e is electron charge, ε₀Is
Vacuum permittivity, ε_0pIs the optical permittivity, m_0pIs electron optics
Effective mass, λ_pIndicates the plasma wavelength. From the above equation,
When the carrier concentration N is changed, the plasma wavelength λ_pAlso strange
It is understood that That is, the carrier concentration N is increased.
Then, the plasma wavelength λ_pShifts to shorter wavelengths,
Conversely, when the carrier concentration N is reduced, the plasma wavelength
λ _pShifts to the longer wavelength side.

FIG. 1A is a graph showing the relationship between the wavelength λ of incident light and the reflectance when the carrier concentration is set high and low in the above materials.
In FIG. 1 (a), for incident light of wavelength λ ₀ , the reflectivity increases when the carrier concentration is set high, due to the above-mentioned property of the plasma wavelength λ _p , and the incident light is reflected on the material surface. . On the other hand, if the carrier concentration is set low, the reflectance will be low, and the incident light will be introduced into the material.

FIG. 1B is a graph showing the relationship between the wavelength λ of incident light and the absorptance in the semiconductor material. In the conventional semiconductor optical modulator, but the absorption of the light before and after the absorption edge wavelength lambda _g by the band gap is performing optical modulation with the area to be changed, the present invention is, from the infrared light in the visible light region It is characterized in that light modulation is performed at a wavelength. In general,
When the band gap energy of the semiconductor is E _g [eV], the speed of light in vacuum is c [m / s], and the Planck constant is h [Js], the light absorption edge wavelength λ _g [m] is

[0034]

(Equation 2) It is represented by In the present embodiment, since the wavelength λ ₀ of the light to be modulated is longer than λ _g , a semiconductor satisfying the condition of the expression (4) is preferable as the semiconductor material.

(Equation 3)

[0035] If the modulation light to the visible light and infrared light is preferably a band gap energy E _g of the semiconductor is 2 [eV] or more, as preferred specific examples of such a semiconductor material, C, ZnO, SiC, CdS, Ga
P, AlAs, InN, AlN, and the like. FIG.
In (b), for the incident light of wavelength λ ₀ , when the carrier concentration is set high, the absorptance increases, and the incident light introduced into the material is absorbed and not transmitted. On the other hand, when the carrier concentration is set low, the absorptance becomes low, and the introduced incident light is transmitted without being absorbed.

By applying a voltage to the material to change the carrier concentration according to the above-mentioned material characteristics, predetermined incident light,
That is, light transmission or non-transmission (reflection / absorption) light modulation can be performed on the incident light having the wavelength λ ₀ .

However, considering the combination of the light modulation based on the reflectance and the light modulation based on the transmittance, when the electrons are depleted and the light reflectance is lowered, the incident light is transmitted without being absorbed in the material. Therefore, it is necessary to lower the transmittance. Therefore, as shown in FIGS. 2 and 3, the characteristics of the reflectance and the absorptance with respect to the wavelength of the incident light are considered in combination.

First, when the wavelength λ _{0 of the} light to be modulated is shorter than the plasma wavelength λ _p of the n-type semiconductor layer in the absence of an electric field, the reflectance becomes lower regardless of the carrier concentration, Light modulation is performed with a change in absorptivity dominant. When no electric field is applied, the absorptance due to free carrier absorption or the like of the semiconductor layer increases, and the light transmittance decreases. In addition, when an electric field is applied, the n-type semiconductor layer is depleted, the carrier concentration decreases, the absorptance decreases, and the light transmittance increases. Accordingly, the incident light introduced into the material without being reflected is optically modulated by a change in light transmittance in the material. Note that in order to obtain a sufficient change in transmittance, the thickness of the semiconductor layer, the carrier concentration, and the width of the depletion region to be changed may be appropriately selected. In particular, in order to improve the absorptance in the absence of an electric field, it is preferable to make the semiconductor layer sufficiently thick according to the carrier concentration.

Next, when the wavelength λ _{0 of the} light to be modulated is longer than the plasma wavelength λ _p of the n-type semiconductor layer in the absence of an electric field, the light modulation is such that the change in reflectance is dominant. When no electric field is applied, the carrier concentration of the semiconductor layer is high, and the reflectance is high. When an electric field is applied, the n-type semiconductor layer is depleted, the carrier concentration is reduced, and the reflectance is reduced. The absorptance when the reflectivity is small suppresses an increase in the absorptance by making the semiconductor layer thinner. Thereby, the incident light is light-modulated on the material surface by the change in the reflectance. still,
In order to obtain a sufficient transmittance change, the thickness of the semiconductor, the carrier concentration, and the width of the depletion region to be changed may be appropriately selected. In particular, in order to improve the transmittance at the time of depletion, it is preferable to make the semiconductor layer sufficiently thin according to the carrier concentration.

The present invention applies the above principle to a structure in which a transparent electrode, an insulator, and an n-type semiconductor are sequentially laminated as represented by a MOS type semiconductor structure in which the carrier concentration can be easily controlled. This has a great feature in that the laminated structure is configured to directly function as an optical modulation element. According to this laminated structure, the transparent electrode and the insulator are transparent to the target light, only the electron carrier concentration of the n-type semiconductor layer changes the transmittance, and stable light modulation can be achieved with a simple structure. It becomes possible. The specific impurity concentration of the n-type semiconductor is preferably 10 ¹⁸ to 10 ²² [cm ⁻³ ].

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a diagram illustrating a cross-sectional structure of the light modulation device according to the first embodiment of the present invention. In the light modulation device according to the present embodiment, in FIG. 4A, a lower transparent electrode 2 is formed on an upper surface of a transparent substrate 1, and an n-type semiconductor layer 3 is formed on the upper surface of the lower transparent electrode 2 as an impurity-doped semiconductor. Forming
It has a MIS type semiconductor structure in which an insulating layer 4 is disposed on the upper surface of the n-type semiconductor 5 and an upper transparent electrode 5 is formed on the upper surface of the insulating layer. Hereinafter, a set of the n-type semiconductor layer 3 and the insulating layer 4 will be referred to as a light modulation layer a.

In the state of FIG. 4A, donor impurity ions and electrons are uniformly dispersed in the n-type semiconductor layer 3, and the carrier concentration is not reduced. When the light wavelength λ ₀ is longer than the semiconductor plasma wavelength λ _p , the incident light is mainly reflected on the surface and the plasma wavelength λ 0
_When it is shorter than _p , the absorption mainly increases. as a result,
Incident light is not emitted below the transparent substrate 1.

On the other hand, FIG. 4B shows a state in which a reverse bias voltage is applied to the transparent electrodes 2 and 5 of the light modulation device of FIG. 2A. That is, a negative potential of -V is applied to the upper transparent electrode with respect to the lower transparent electrode 2 side. Thereby, the electron carriers in the n-type semiconductor layer 3 move to the lower transparent electrode 2, and a depletion layer in which the electron carriers are deficient is generated. For this reason, the plasma wavelength λ _p of the semiconductor layer 3 shifts to the longer wavelength side, and the surface reflectance of the semiconductor layer 3 or the absorptance in the semiconductor layer 3 decreases, the light transmittance increases, and the semiconductor layer 3 is introduced from above. The incident light passes through the n-type semiconductor layer 3 and is emitted from below the transparent substrate 1. In FIG. 4B, the thickness x _d of the depletion layer is reduced, but it can be set to be substantially equal to the thickness of the n-type semiconductor layer 3 in this case. , The entire n-type semiconductor layer 3 is depleted, and the light modulation characteristics are improved. Further, even if the n-type semiconductor layer 3 is not completely depleted, the absorptance decreases. Further, when the non-depleted region (n-type region) is very thin, the reflection on the surface also decreases. Therefore, the light transmittance can be controlled.

At this time, the thickness x _d of the depletion layer generated in the n-type semiconductor layer 3 is represented by the relationship shown in the equation (5).

(Equation 4) In equation (5), ε _s is the dielectric constant of the depletion layer, V _s is the potential difference of the depletion layer, and N _d is the impurity concentration of the n-type semiconductor layer. Potential V _s of the depletion layer and to increase the voltage applied is high, depletion layer width x _d is increased. This characteristic is obtained at the interface between the insulator and the semiconductor in an inverted state, that is, until hole carriers are injected into the interface. At this time, the depletion layer width x _d becomes
When a voltage is applied such that the voltage spreads to about the thickness of the n-type semiconductor layer, the n-type semiconductor layer is almost completely depleted and electron carriers are no longer spatially present, so that the transmittance of incident light is further increased.

The change in carrier concentration caused by the generation or disappearance of the depletion layer may be considered as a phenomenon similar to, for example, charge / discharge in a capacitor.
Further, a configuration in which a transparent substrate is arranged on the upper transparent electrode 5 may be adopted. Thereby, the light modulation element can be sealed between the transparent substrates, and handling can be facilitated.

Here, the light modulating layer a has a structure in which the polarity of the electrodes connected to each layer is kept as it is and the whole is inverted, that is, the insulating layers 4 and n are formed on the upper surface of the lower transparent electrode 2.
The configuration may be such that the semiconductor layers 3 are stacked in this order.

The upper and lower transparent electrodes and an intermediate transparent electrode to be described later are generally made of a metal which has been made transparent by micronization or a metal compound having conductivity. Alternatively, it can be composed of a very thin translucent film of these metals. The metals include gold, silver,
Palladium, zinc, aluminum and the like can be used, and as the metal compound, indium oxide, zinc oxide,
Aluminum-added zinc oxide (commonly known as AZO) or the like can be used. Specifically, SnO ₂ film (Nesa film), I
A TO film or the like can be given.

When a semiconductor is formed on a transparent electrode as described above, the semiconductor becomes amorphous or polycrystalline. In this case, a general amorphous glass substrate can be used as the transparent electrode. Further, the lower transparent electrode may be omitted, and the lower surface of the n-type semiconductor layer may be used as an electrode.

Further, an insulator such as sapphire,
Alternatively, a semiconductor substrate similar to or similar in lattice constant to the light modulation layer may be used. Further, in this case, the transparent electrode and the transparent substrate may also be used. According to the above substrate, it is possible to form a crystal semiconductor epitaxially on the electrode and the light modulation layer, and a more stable operation can be obtained. As a specific example, a p-type high-concentration impurity semiconductor is epitaxially grown as a substrate-side transparent electrode of the positive electrode. An n-type semiconductor layer is epitaxially grown thereon, or an n-type impurity is diffused,
Alternatively, it is formed by ion implantation. Then, an insulating layer is formed on the n-type semiconductor layer. Finally, a metal compound transparent electrode is formed as an upper transparent electrode of the negative electrode. As the insulating layer, an oxide film, a nitride film, or the like can be used. Further, a ceramic such as a ferroelectric substance can be used. In addition, various materials, forming methods, and the like can be considered, and any material may be used as long as it conforms to the gist of the present invention.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram illustrating a cross-sectional structure of the stacked light modulation element according to the present embodiment. Light modulation element forms a lower transparent electrode 2 on the upper surface of the transparent substrate 1, a light modulation layer a ₁ ~a _m stacking an n-type semiconductor layer 3 and the insulating layer 4 on the upper surface of the lower transparent electrode 2, forming the upper transparent electrode 5 on the upper surface of the insulating layer 4 of the top layer a _m. In the present embodiment, the total number of the light modulation layers is five, but in general, any number of layers can be stacked. The lower transparent electrode 2 and the upper transparent electrode 5
When a reverse bias voltage (−V) is applied between the light modulation layers (a) and (b), each light modulation layer a is polarized, and a depletion layer is generated in each n-type semiconductor layer as shown in FIG. As a result, incident light introduced from above is transmitted through the light modulation layer due to a decrease in reflectance or absorptance and is emitted from the transparent substrate 1.

When the applied voltage is 0 [V], the depletion layer in each semiconductor layer is eliminated, and the absorption or reflectance of the n-type semiconductor layer 3 is increased. 1 is no longer emitted from below. Note that the direction of the incident light may be the opposite direction. According to the present embodiment, by forming the light modulating layers in multiple layers, each light modulating layer can be thinned, and depletion can be efficiently performed. Therefore, the depletion layer region of the entire device can be lengthened with a low applied voltage, and the light modulation capability can be further improved.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram illustrating a cross-sectional structure of the stacked light modulation element according to the present embodiment. This light modulation element has n
All electrodes connected to the mold semiconductor layer are connected to the positive electrode of the power supply, and all electrodes connected to the insulating layer are connected to the negative electrode of the power supply. Therefore, any of the n-type semiconductor layers has a configuration in which electron carriers are extracted and depleted by voltage application.
In this case, the electrode may be a transparent metal compound or a p-type semiconductor, or the electrode may be omitted by using the n-type semiconductor layer as the electrode. In such a configuration, the reflectance or absorptance of the incident light is reduced by applying a voltage, and the transmittance is increased.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing a cross-sectional structure of the light modulation element according to the present embodiment and its interlayer wiring. This light modulating element is formed by laminating a plurality of layers on the lower transparent electrode 2 in the order of the n-type semiconductor layer 3, the insulating layer 4, and the intermediate transparent electrode 7, and configuring the uppermost layer electrode as the upper transparent electrode 5. A power supply (-V) is connected between the electrodes a. Therefore, any of the n-type semiconductor layers has a configuration in which electron carriers are extracted and depleted by voltage application. With such a configuration, light modulation can be performed in accordance with the voltage application, as in the third embodiment.

Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a diagram showing a cross-sectional structure of the light modulation element according to the present embodiment and its interlayer wiring. This light modulation element is provided with a p-type semiconductor layer 8 in which impurities are diffused at a high concentration, instead of the intermediate transparent electrode in the fourth embodiment. Since the p-type semiconductor layer 8 has a very high electric conductivity, it acts like an electrode, and the inside of the layer is uniformly conductive. And
The lower transparent electrode 2 is connected to the positive electrode of the power source, and the upper transparent electrode 5
Is connected to the negative electrode of the power supply. According to the above configuration, the electron carriers of the n-type semiconductor layer that move by applying a voltage are recombined at the interface of the p-type semiconductor layer 8. Therefore, the n-type semiconductor layer 3 can be entirely depleted.

With such a configuration in which the p-type semiconductor layer 8 is provided, the depletion layer of each n-type semiconductor layer 3 is more reliably formed, and the depletion of each n-type semiconductor layer 3 is reduced within the layer. It can be made more uniform in all regions.

Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG. 9 shows a light modulation unit 90 configured by arranging light modulation elements one-dimensionally or two-dimensionally. In the present embodiment, the driving of the light modulation elements of the light modulation unit 90 can be controlled by the driving unit 91 all at once, or every predetermined number of blocks, or independently. Accordingly, the light modulation element can function as the exposure element 92 that can perform one-dimensional or two-dimensional light modulation.

Further, in a system in which each light modulation element is drive-controlled for each block or independently, multi-gradation display can be performed by area gradation. Further, the drive system of the drive unit 91 when the light modulation elements are two-dimensionally arranged may be simple matrix drive or active matrix drive. In the case of simple matrix driving, the configuration can be simplified, and in the case of active matrix driving, a large contrast ratio can be obtained.

According to the above arrangement, the reflectivity and the absorptance of the one-dimensionally or two-dimensionally arranged light modulation elements can be set according to the voltage application state, so that an exposure element which can operate at high speed can be simplified. It can be provided in a configuration.

Next, a seventh embodiment of the present invention will be described with reference to FIG. FIG. 10 shows a configuration of a display device 94 in which a flat light source 93 is arranged to face the configuration of the exposure element 92 in the sixth embodiment. The display device 94 in the present embodiment has a plane light source 93 disposed opposite to the light modulation section 90 of the exposure element 92, and the light from the plane light source 93 is one-dimensionally or two-dimensionally arranged. Is displayed via the. When the light modulator 90 is formed as a one-dimensional array, the planar light source 93 may be a linear light source.

The flat light source 93 is composed of, for example, an infrared light source 93a as a light source and a light guide plate 93b. Infrared source 93
a from the light guide plate 93b is guided to the surface of the light guide plate 93b.
Light emitted from the surface a is incident on the exposure element 90. Then, an arbitrary pattern can be displayed by selectively transmitting or not transmitting (reflecting / absorbing) the light through the light modulation unit according to the application state of the inter-electrode voltage of each exposure element. As described above, an exposure element is formed by a light modulation section in which a plurality of light modulation elements are combined, and a plane light source is arranged on one side of the exposure element to function as a display device.

In the case of a display device, the light to be introduced into each light modulation element is light from a white light source, and the voltage between the electrodes is appropriately adjusted to selectively transmit only light of an arbitrary wavelength component. It is good. This enables high-speed color display with a simple configuration. In addition, by introducing light of a specific wavelength and adjusting the level of the voltage between electrodes or duty control of voltage application, the thickness of a depletion layer in the semiconductor layer or the amount of light transmitted per unit time is changed, and multi-gradation control is performed. It is also possible to do.

In each of the embodiments described above, the light transmittance is reduced when no voltage is applied, and the light transmittance is increased when the reverse bias voltage is applied. It is also possible to make the depletion layer width narrower and further inject carriers to lower the light transmittance. Further, in each of the above embodiments, the case where the incident light is transmitted / non-transmitted (reflected / absorbed) in the light modulation element to modulate the light by changing the light transmittance has been described. An element that modulates the light by changing the light reflectance by reflecting the light in the element may be used, and an element system utilizing the change in the reflected light can be constructed. In each of the embodiments described above, light modulation is mainly performed by carrier control of the n-type semiconductor layer.
That is, light modulation by hole depletion and injection is also possible.

[0063]

According to the light modulation device, the exposure device and the display device of the present invention, since the change in the reflectance and the change in the absorptance according to the change in the carrier concentration of the semiconductor are utilized, the operation can be stably performed at a low operating voltage. Light modulation can be performed, and higher-speed operation can be performed as compared with liquid crystal. Further, since surface light modulation is possible, uniform light modulation can be easily realized, and furthermore, since the structure is simple, it can be provided as an inexpensive product suitable for mass production.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the wavelength λ of incident light and the reflectance and absorptance with respect to the carrier concentration.

FIG. 2 is a graph showing the relationship between the reflectivity and the absorptivity with respect to the carrier concentration when the wavelength of light modulated with respect to the plasma wavelength of the n-type semiconductor layer is short.

FIG. 3 is a graph showing the relationship between the reflectivity and the absorptivity with respect to the carrier concentration when the wavelength of light modulated with respect to the plasma wavelength of the n-type semiconductor layer is a long wavelength.

FIG. 4 is a diagram illustrating an operation principle of the light modulation element according to the embodiment of the present invention.

FIG. 5 is a diagram showing a cross-sectional structure of a stacked optical modulation element according to a second embodiment of the present invention and its interlayer wiring.

FIG. 6 is a diagram showing a cross-sectional structure of a light modulation element according to a third embodiment of the present invention and its interlayer wiring.

FIG. 7 is a diagram showing a cross-sectional structure of an optical modulation device according to a fourth embodiment of the present invention and its interlayer wiring.

FIG. 8 is a diagram showing a cross-sectional structure of a light modulation element according to a fifth embodiment of the present invention and its interlayer wiring.

FIG. 9 is a view showing a configuration of an exposure element according to a sixth embodiment of the present invention.

FIG. 10 is a diagram illustrating a configuration of a display device according to a seventh embodiment of the present invention.

FIG. 11 is a diagram showing one embodiment of a conventional light modulation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Lower transparent electrode 3 N-type semiconductor layer 4 Insulating layer 5 Upper transparent electrode 7 Intermediate transparent electrode 90 Light modulation part 92 Exposure element 93 Flat light source 94 Display device a Light modulation layer

Claims (12)

[Claims] A semiconductor layer is provided on an upper surface of a lower transparent electrode, an upper transparent electrode is provided on an upper surface of the semiconductor layer via an insulating layer, and the semiconductor layer is provided between the upper transparent electrode and the lower transparent electrode. An optical modulator, wherein an electric field for depleting carriers is applied to change at least one of light reflectance and light absorption. 2. The band gap energy E of the semiconductor
_g is the wavelength of the modulated light being lambda _0, when the speed of light in vacuum and c, and Planck's constant is h, according to claim 1, characterized in that the _{E g> hc / λ 0 [} eV] Light modulation element. 3. The bandgap energy E of the semiconductor
_g is not less than 2 [eV].
Or the light modulation element according to claim 2. 4. The light modulation device according to claim 1, wherein a wavelength λ ₀ of the modulated light is smaller than a plasma wavelength λ _{p of the} semiconductor layer. 5. The light modulation device according to claim 1, wherein a wavelength λ ₀ of the modulated light is larger than a plasma wavelength λ _{p of the} semiconductor layer. 6. The method according to claim 1, wherein a reverse bias voltage is applied so that the thickness of the depleted layer is substantially equal to the thickness of the semiconductor layer.
Item 3. The light modulation element according to item 1. 7. A light modulating layer comprising the semiconductor layer and the insulating layer is laminated in a plurality of stages on the upper surface of the lower transparent electrode, and the upper transparent electrode is provided on the upper surface of the uppermost light modulating layer. The light modulation device according to any one of claims 1 to 6. 8. At least one intermediate transparent electrode is provided between the upper and lower transparent electrodes, the light modulating layer is interposed between the respective electrodes, and an intermediate transparent electrode connected to the semiconductor layer is provided. The light modulation device according to claim 7, wherein an electric field for depleting carriers in the semiconductor layer is applied between the intermediate transparent electrode and the intermediate layer. 9. The light modulation device according to claim 1, wherein the semiconductor layer is an n-type semiconductor layer. 10. The light modulation device according to claim 7, wherein at least one p-type semiconductor layer in which impurities are diffused at a high concentration is provided between the upper and lower transparent electrodes. 11. An exposure element, wherein the light modulation elements according to claim 1 are arranged in a one-dimensional or two-dimensional array. 12. A light source according to claim 1, wherein the light modulating elements are arranged one-dimensionally or two-dimensionally, and a planar light source is arranged facing the arranged light modulating elements. A display device, comprising: