JP6983554B2 - Optical deflection element and display device - Google Patents

Description

The present invention relates to a light deflection element and a display device.

A prototype display device in which minute LEDs (Light Emitting Diodes) are arranged side by side has been prototyped. LED displays in which LEDs are arranged are attracting attention as high-quality display devices characterized by high-speed moving image responsiveness, color reproducibility, and a wide viewing angle. In 2012, a high-definition television (HDTV) LED display was reported, and in 2016, a tile-type display in which multiple LED displays were unitized and placed side by side was also prototyped.

In order to develop from these two-dimensional video display devices and further realize a three-dimensional display device, it is necessary to construct a display in which a large number of pixels are arranged. In particular, if the required number of pixels is simply calculated for the display method using integral 3D, which is being developed as a natural 3D image display method without wearing 3D glasses, 60 viewpoints in the horizontal direction are assumed. Assuming 60 viewpoints in the vertical direction and a stereoscopic resolution of HD, the number of pixels is 60 × 60 × HD × RGB (RGB: red, green, blue). This enormous number of pixels is actually 225 times as many as that of Super Hi-Vision, which is a television with the largest number of pixels.

An observer who directly looks at this integral three-dimensional display device will directly look at the light rays emitted from the display. Therefore, it is desirable that the fine light source constituting each pixel is an LED instead of a laser diode (LD).

As a prior study of producing multiple colors from this one LED element pixel, in an LED made of indium gallium nitride (InGaN) formed on the C surface of a sapphire substrate, pulse width modulation in which the voltage value of the applied voltage is changed is used. It has been reported that the emission color can be changed in the blue-green region. (See, for example, Non-Patent Document 1).

Further, in a display device using LEDs, an LED display device that outputs the three primary colors of red, green, and blue from one InGaAlN-LED has already been proposed as a method for reducing the arrangement of a huge number of pixels (for example, non-patent documents). 2).

As described above, the LED having InGaAlN as a basic structure can emit light of all three primary colors of red, green and blue with one element.

According to this LED method, since light of three colors of red, green, and blue can be emitted from one pixel, the number of pixels constituting the display can be reduced to one-third of the conventional one.
Further, an integral type stereoscopic display device that combines fine red, blue, and green LEDs and an optical lens has also been proposed (see, for example, Patent Document 1).

On the other hand, there has also been proposed a method of substantially increasing the number of light rays emitted from a display device by incorporating a time-division display technique by deflecting the light rays emitted from the LED. According to this method, the number of light rays emitted from the display can be increased without increasing the number of pixels of the display device. Proposal to realize an integral three-dimensional display device by changing the direction of the light beam emitted from the LED by using the piezo effect (reverse piezoelectric effect) in GaN-LED, which is the base material of the LED. (See, for example, Patent Document 2).

A method of separately manufacturing a light source such as an LED and a deflection element and individually combining them to deflect light has already been widely put into practical use. As this deflection method, a technique for rotating a mechanical mirror such as a galvanometer or a polygon mirror (polyhedral mirror) has been widely used for a long time. This mechanical deflection technology has recently been developed as a MEMS (Micro Electro Mechanical System) technology.

Further, an optical deflection element using an electro-optic effect (EO effect) as a non-mechanical deflection element such as MEMS has also been developed. The EO effect is an effect in which the refractive index changes in proportion to the electric field, and is also called the Pockels effect.

Typical EO materials include, for example, lithium niobate LiNbO ₃ (LN) single crystal and lead zirconate titanate lead La ₂ O ₃ / PbZrO ₃ / PbTiO ₃ (PLZT) ceramics. An EO optical deflection element in which a prism-shaped electrode is formed on the (001) plane of an LN crystal or PLZT has also been developed (see, for example, Non-Patent Documents 3 and 4).

Further, a light deflection element using a potassium tantalate potassium niobate KTa _1-x Nb _X O ₃ (KTN) crystal has also been put into practical use (see, for example, Patent Document 3). This light deflection element has a structure in which a KTN crystal is sandwiched between electrodes from above and below, and a voltage is applied between the electrodes to deflect light. At that time, in addition to the above-mentioned EO effect, the deflection angle is increased by trapping the electrons injected from the electrodes in the crystal defects in the KTN crystal and using the effect of the space charge in the crystal (the effect of the space charge in the crystal is used). For example, see Non-Patent Document 5).

Further, attempts have been made to realize deflection of the light output from the optical waveguide by changing the wavelength of the light incident on the optical waveguide. Generally, in the vicinity of the cutoff wavelength λc in the optical waveguide, the deflection angle can be increased by the wavelength change of the input light. In the optical waveguide structure of a semiconductor using gallium arsenide (GaAs), a deflection angle of about 50 ° has been reported in the wavelength range of 952 to 989 nm (see, for example, Non-Patent Document 6). Since the structure of the deflection element using this semiconductor follows the structure of the surface emitting laser, it is expected that an optical switch or the like will be realized by a compact element combining the semiconductor laser and the deflection element in the future. In this method, deflection is realized by changing the wavelength of the light source.

On the other hand, attempts are being made to utilize the EO effect of a semiconductor as a phase modulator that modulates light. In particular, wurtzite-type crystal materials such as InGaAlN, which is the main material for LEDs, have a higher refractive index modulation rate due to the EO effect than those with a zinc flash structure such as indium gallium arsenide arsenide (InGaAsP). It is known (see, for example, Patent Documents 4, 5 and 6).

Japanese Patent No. 6095686 Japanese Patent No. 6010417 Patent No. 5565910 Public Relations Japanese Patent No. 4494257 Japanese Unexamined Patent Publication No. 11-21040 Japanese Patent No. 5227351

T. Azuhata, T. Homma, Y. Ishizuka, and S. Chichibu. Jpn. J. Appl. Phys (2003) L497-498. H. S. El-Ghoroury, M. Yeh, J. C. Chen, X. Li, and C. Chuang: AIP Advances 6 (2016) 075316. Y. Ninomiya, IEEE J. Quantum Electron. QE-9 (1973) 791. Q.Ye, Z.Dong, R. Qu, and Z. Fang, Optics Express, Vol.15, No.25 (2007) 16943. Koichiro Nakamura, Yuzo Sasaki NTT Technical Journal (December 2007) 56-59. X.Gu, T. Shimada, A. Matsutani, and F. Koyama, IEEE Photonics Journal Vol.4, No5 (2012) 1712-1719.

_{Bulk-type inorganics such as LiNbO 3} (LN) crystals due to electro-optic (EO) effect and KTN crystals due to the combined effect of space charge effect and EO effect due to electron injection, instead of the mechanical deflection function by MEMS of the optical deflection element. Deflection elements using materials have been developed. In principle, the former is capable of high-speed response of GHz or higher, but the drive voltage of the deflection element is as high as 400 to 1 KV or higher, and the latter is about 100 to 300 V, which does not require as high voltage as the former, but the response speed. Decreases below 100 KHz. In all of these bulk types, since the light source and the deflection element are structurally separated, it is an issue to reduce the size of the light deflection element including the light source.

Further, although the light deflection element using the KTN crystal has a feature that the deflection angle can be made larger than that of the LN crystal due to the space charge effect, it is necessary to reduce the size of the light deflection element including the above-mentioned light source. Since the deflection operation occurs only near the phase transition temperature of the KTN crystal, precise temperature control is indispensable.

When the stereoscopic display device is realized, the observer who directly looks at the display device will directly look at the light rays emitted from the display. Therefore, it is desirable that the fine light source constituting each pixel is an LED instead of a laser diode (LD). It is possible to control the deflection of the light beam emitted from the pixel by emitting light from the LED, and by configuring the LED and the deflection element on the same substrate and forming the pixel with a structure that integrates the LED light source and the deflection element. It becomes.

The most effective method is considered to be a proposal in which each pixel of the display device is composed of LEDs and the direction of light rays emitted from the LEDs is deflected by a time-division display technique. To date, the applicant has proposed direction control of an element using the inverse piezoelectric effect of InGaAlN, but the response speed of the inverse piezoelectric effect is at most about 1 kHz, so that a faster response can be achieved. There is a demand for a deflection method that has (see Patent Document 2).

Furthermore, while indium gallium nitride aluminum InGaAlN-based LEDs can cover the entire RGB region of visible light from outside, aluminum gallium phosphorus (AlGaP: green to red), aluminum gallium indium phosphorus (AlGaInP: yellow to red), The light emitting region such as aluminum gallium arsenide (AlGaAs: red to near infrared) and their mixed crystal system is limited.

Further, regarding the light deflection method, regardless of the EO effect, in the method of changing the emission wavelength of the light source, the wavelength of light shifts according to the light deflection angle. At that time, if the wavelength changes depending on the deflection angle, there is a problem that the color of the display changes according to the viewing angle of the display when considering display applications and the like.

In the light deflection method based on the EO effect, light deflection is possible without changing the emission wavelength. Among them, the indium gallium nitride aluminum (InGaAlN) -based crystal structure has hexagonal crystal symmetry, and wurtzite-type crystals. Since it has a structure, it is known that it has stronger ionicity than the zinc flash structure type of AlGaP, AlGaInP, and AlGaAs, and has a large refractive index modulation factor due to the EO effect, which is suitable for this method.

Therefore, based on these, the present application is characterized in that the light source portion of the InGaAlN-based LED and the deflection portion of the same material as the LED are structurally integrally formed on the same substrate, and light emission and light emission from the LED light source unit. It is an object of the present invention to provide an optical deflection element capable of realizing a deflection unit for deflecting a light source on the same substrate, and a display device using the optical deflection element.

The optical deflection element of the embodiment of the present invention includes a sapphire substrate, an n-type layer using GaxAl1-xN (0 <x≤1) provided on the C surface of the sapphire substrate as a base material, and the n-type layer. A quantum well layer composed of InyGa1-yN (0 <y ≦ 1) or a multi-layered pair of InyGa1-yN (0 <y ≦ 1) and a barrier layer (GaN), which is an active layer laminated in the above. A quantum well, a p-type layer using GaxAl1-xN (0 <x≤1) laminated on the quantum well layer or the multiple quantum well as a base material, the n-type layer, the quantum well layer, and the p. A first voltage application portion that causes the first region to function as a light emitting diode portion by applying a forward bias first voltage to the first region of the laminated body of the mold layer, and the first region of the laminated body. light emission of the light emitting diode than is provided in the second region of the inside of the diode in the direction of light propagation, polarized light emission of the light emitting diode to emit luminescence pre Symbol polarized further in a particular direction deflection Including part.

According to the present invention, since the emission direction is deflected by a simple configuration in which a voltage is applied between the electrodes provided on the light emitting element, the light deflection element can be miniaturized.

According to the first aspect of the present invention, since the InGaAlN-based semiconductor material is used to function as a light emitting element and a deflection element, both light emission and deflection in the emission direction can be performed.

According to the second aspect of the present invention or the third aspect of the present invention or the fourth aspect of the present invention, a light beam is used by utilizing diffraction and interference of light in a structure having a simple structure in which a wire grid polarizing element provided on a light emitting element is used as an electrode. Since the emission direction of the light emitting element can be specified, it is possible to facilitate miniaturization and high density of the light emitting element.

According to the fifth aspect of the present invention, the light emitting element can be polarized by using a metal cladding provided on the light emitting element, and the emission direction of the light ray can be specified by the electrode provided on the light emitting element.

According to the sixth aspect of the present invention, since the direction of the light rays from each pixel is specified by the emission direction specifying unit using the interference of light, the definition is higher than that of the stereoscopic image display device using a lens. can do. Further, since one light emitting element functions as pixels corresponding to a plurality of emission directions, the number of light emitting elements mounted on the stereoscopic image display device can be reduced.

It is a perspective view which shows the light deflection element 100 of Embodiment 1. FIG. It is a figure which shows the cross section of AA of FIG. It is a figure which shows the relationship between the boundary surface of FIG. 2 and the incident light. It is a figure which shows the distribution of the refractive index in the depth direction. It is a figure which shows the wavelength dependence of the refractive index of a sapphire substrate and GaN. It is a dispersion curve of a three-layer structure slab type optical waveguide of a GaN core in TE1 and TM1 modes when calculated at n _Air = 1.00, n _GaN = 2.47, n _{Al2O3 = 1.78 and a peak wavelength of 458 nm for a blue LED.} It is a figure which shows the light deflection element 100A of the modification of Embodiment 1. It is a figure which shows the light deflection element 100B of the modification of Embodiment 1. FIG. It is a figure which shows the light deflection element 200 of Embodiment 2. It is a figure which shows the display device of the integral three-dimensional system of Embodiment 3.

Hereinafter, embodiments to which the optical deflection element and the display device of the present invention are applied will be described.

<Embodiment 1>
FIG. 1 is a perspective view showing the light deflection element 100 of the first embodiment. FIG. 2 is a diagram showing a cross section taken along the line AA of FIG. Further, FIG. 3 is a diagram showing the relationship between the boundary surface of FIG. 2 and the incident light. In FIGS. 1 and 2, an XYZ coordinate system is defined. In the following, for convenience of explanation, the Z-axis positive direction side is referred to as the upper side and the Z-axis negative direction side is referred to as the lower side with respect to the reference position, but it does not indicate a universal vertical relationship.

The optical deflection element 100 includes a sapphire substrate 101, a GaN layer 102, an n-GaN layer 110, an MQW layer 120, a GaN layer 130, a p-GaN layer 140, an n-type electrode 150, a p-type electrode 160, a light-shielding film 170, and an insulating layer. Includes 171, wire grid modulator 180, bias voltage sources 190A, 190B.

In the sapphire (Al ₂ O ₃ ) substrate 101, the (0001) plane, which is the sapphire C plane, is parallel to the XY plane and is located on the positive side of the Z axis, and the GaN layer 102 is laminated on the (0001) plane. ..

The GaN layer 102 is an undoped gallium nitride layer and is provided on the (0001) plane of the sapphire substrate 101. The GaN layer 102 is, for example, a MOCVD (Metal Organic Chemical Vapor Deposition) method (or Metal Organic Vapor Phase Epitaxy: MOVPE) using hydrogen as a carrier gas, TMG (trimethylgallium) as a Ga source, and ammonia as a nitrogen source. It is laminated on the sapphire substrate 101 by a crystal growth method composed of (nominal name).

The n-GaN layer 110 is provided on the GaN layer 102. The n-GaN layer 110 is an n-type gallium nitride layer, and as an example, it grows by a MOCVD method in which silicon (Si) is doped with _{silane (SiH 4).} The n-GaN layer 110 may contain aluminum, and in this case, it is _{regarded as a layer using gallium nitride aluminum (Ga x} Al _1-x N (0 <x ≦ 1)) as a base material. Can be done.

The MQW layer 120 is a _{multiple quantum well (MQW) composed of indium gallium nitride (In y} Ga _1-y N (0 <y ≦ 1)), and is above the n-GaN layer 110. It is provided in. The MQW layer 120 is provided in a region above the n-GaN layer 110 that avoids the end on the negative direction side of the X-axis. The MQW layer 120 is laminated on the n-GaN layer 110 by the MOCVD method.

More specifically, the GaN layer 102, the n-GaN layer 110, and the MQW layer 120 can be formed as follows. The GaN layer 102, the n-GaN layer 110, and the MQW layer 120 are sequentially placed on the sapphire substrate 101 by, for example, a film forming method such as an MBE (molecular beam epitaxy) method or a MOCVD (metalorganic chemical vapor deposition) method. It can be laminated and formed.

More specifically, the n-GaN layer 110 is formed by growing a crystal composed of GaN doped with Si, which is an n-type impurity, via an undoped GaN layer 102. Further, the n-GaN layer 110 may be formed in a two-layer structure of, for example, an n-type contact layer made of GaN and an n-type clad layer made of AlGaN.

The MQW layer 120 is provided between the n-GaN layer 110, the undoped GaN layer 130, and the p-type semiconductor layer 140, and is formed by laminating, for example, InGaN on the n-GaN layer 110. It is also possible to form an active layer composed of InGaN as the MQW layer 120 to form a double heterostructure. Further, as the MQW layer 120, for example, a quantum well structure in which a barrier layer composed of undoped GaN and a well layer composed of undoped InN or InGaN are alternately laminated, preferably an active layer having a multiple quantum well structure, is used. It may be formed.

The p-type semiconductor layer 140 is formed by growing a crystal composed of GaN doped with Mg, which is a p-type impurity, on the MQW layer 120 or the undoped GaN layer 130 formed on the MQW layer 120. As an example, it can be produced by doping magnesium (Mg) by the MOCVD method and performing heat treatment in a nitrogen atmosphere. Similar to the n-GaN layer 110, the p-type semiconductor layer 140 may also be formed into a two-layer structure of, for example, a p-type clad layer made of GaN and a p-type contact layer made of AlGaN.

Further, the p-GaN layer 140 may contain aluminum, and in this case, it is _{formed as a layer using gallium nitride aluminum (Ga x} Al _1-x N (0 <x ≦ 1)) as a base material. be able to.

The n-type electrode 150 is one of a pair of electrodes for applying an electric field to the LED region 50A (p-GaN 140, GaN layer 130, MQW layer 120, n-GaN layer 110), and is a bias voltage source 190A. It is connected to the negative electrode of. The LED region 50A is an example of the light emitting diode portion. The n-type electrode 150 is provided at the end of the region above the n-GaN layer 110 on the negative direction side of the X-axis. The MQW layer 120, the GaN layer 130, and the p-GaN layer 140 are not provided in the region where the n-type electrode 150 is provided.

The p-type electrode 160 is one of a pair of electrodes for applying an electric field to the LED region 50A, and is connected to a positive electrode of the bias voltage source 190A. By arranging the p-type electrode 160 in this way and applying a forward bias from the bias voltage source 190A between the p-type electrode 160 and the n-type electrode 150, the GaN layer 102, the n-GaN layer 110, and the MQW layer 120 are applied. , The current flows in the LED region 50A of the GaN layer 130 and the p-GaN layer 140.

The MQW layer 120 is provided between the p-GaN layer 140 and the GaN layer 130 and the n-type GaN layer 110, and is a carrier that is transported via the p-GaN layer 140, and the n-type semiconductor layer 110. It emits light when it recombines with electrons, which are carriers transported via. At that time, due to the relationship between the carrier mobility and the recombination time in the p-GaN layer 140 and the n-type GaN layer 110, the region directly below the contact surface between the p-type electrode 160 and the p-GaN 140 and the LED region 50 in the vicinity thereof are present. Only the MQW layer region 120A in the portion surrounded by the light emits light, and does not emit light in the other regions.

The light-shielding film 170 is provided in the region between the p-type electrode 160 and the wire grid polarizing element 180 on the upper surface of the p-GaN layer 140. The insulating layer 171 is provided between the light-shielding film 170 and the p-GaN layer 140, and insulates the light-shielding film 170 from the p-GaN layer 140.

The wire-grid polymerase 180 is formed on the upper surface of the p-GaN layer 140 on the upper surface region of the p-GaN layer 140 in the positive direction of the X-axis in a plan view from the LED region 50A. As a manufacturing method, a combination of a metal vapor deposition method and photolithography is generally used, and the material of the wire grid polarizing element 180 has a structure extending in a fine line shape in the Y-axis direction, and is made of aluminum, gold, or silver. It is composed of a metal such as or a solid solution thereof, has a plurality of metal wires, and the wires are arranged in parallel with each other. The Y-axis positive end (the portion surrounded by the broken line in FIG. 1) of the plurality of wires of the wire grid modulator 180 is connected to the negative electrode of the bias voltage source 190B.

The wire grid polarizing element 180 transmits the TM polarized light component of the light incident on the grid from the GaN layer into the air by forming a fine metal grid (slit shape) on the surface of the p-GaN layer 140. On the other hand, the TE polarizing component is reflected on the GaN laminated film (GaN layer 102, n-GaN layer 110, MQW layer 120, GaN layer 130, p-GaN layer 140) side or partially absorbed by a metal to be a polarizing element. Functions as. In the following, the GaN laminated film (GaN layer 102, n-GaN layer 110, MQW layer 120, GaN layer 130, p-GaN layer 140) will be referred to as GaN laminated film 102 to 140.

Further, in the bias voltage source 190B, a bias voltage is applied between the n-type electrode 150 and the wire grid polarizing element 180, at which time the wire grid polarizing element also functions as an electrode in addition to the polarizing element. That is, of the light emitted in the LED region 50A, the wire grid splitter polarizes the TM light, and further applies an electric field to the wire grid splitter 180 to deflect the light in the positive direction of the Z axis in the emission angle direction according to the applied voltage. It can be carried out.

The bias voltage source 190A is a DC power source connected between the p-type electrode 160 and the n-type electrode 150 so as to apply a forward bias to the p-GaN layer 140 and the n-GaN layer 110. That is, the positive electrode of the DC power supply is connected to the p-type electrode 160, and the negative electrode is connected to the n-type electrode 150. The bias voltage source 190A can also perform forward bias pulse width modulation or pulse high modulation when changing the output light intensity of the LED or changing the emission color.

The bias voltage source 190B is a variable DC power source in which the positive electrode is connected to the n-type electrode 150 and the negative terminal is connected to the wire grid modulator 180, and the output voltage can be changed.

As described above, the optical deflection element 100 includes a p-type layer (p-GaN layer 140) and an n-type layer (n-GaN layer 110) using _{Ga x} Al _{1-x N (0 <x ≦ 1) as a base material.} ), In particular, an LED structure incorporating a multiple quantum well (MQW layer 120) in which a pair _{of In y} Ga _1-y N (0 <y ≦ 1) and a barrier layer (GaN) is multi-layered as an active layer. It has a basic structure. Here, in FIG. 2, as an example, y = 0.2, and the composition of the MQW layer 120 is MQW in _{which 10 layers of an In 0.2} Ga _0.8 N active layer having a thickness of 4 nm and a barrier layer having a thickness of 11 nm are laminated. This is an example of a structure incorporating the layer 120.

In the LED region 50A, the light emitted from the MQW layer region 120A of the portion surrounded by 50A among the MQW layers 120 of _{In y} Ga _{1-y N (0 <y ≦ 1) is TE (MQW layer 120).} It has both components of TM (light having an electric field vector in the Y-axis direction parallel to) and TM (light having an electric field vector in the Z-axis direction perpendicular to the MQW layer 120). This is in contrast to the gallium nitride laser diode (GaN-LD) formed on the C-plane of the sapphire substrate, which radiates only the TE mode.

For example, the TE of the LED region 50A, which is a gallium nitride LED (GaN-LED) formed by the n-GaN layer 110, the MQW layer 120, the GaN layer 130, and the p-GaN layer 140 formed on the C surface of the sapphire substrate 101. The difference in the intensity ratio of the polarization between the mode and the TM mode is about 30% at the maximum at the peak wavelength of 458 nm of the blue LED.

For the light emitted by the MQW layer 120, the GaN laminated film (102 to 140) including the MQW layer 120 can be regarded as an optical waveguide by providing the light-shielding film 170, and the p-GaN layer 140 and the air on the upper side can be regarded as an optical waveguide. Total internal reflection is performed at the interface between the layer and the interface between the GaN layer 102 and the sapphire substrate 101. FIG. 3 is a diagram showing the relationship between the boundary surface of the optical waveguide and the incident light, and is an enlarged view of the light propagation region of FIG. 2B. Assuming that the angle formed by the vertical direction of the boundary surface and the incident light is θ, the following equations (1) and (2) are obtained _{for the critical angles θ 1} and θ _{2 at each interface according to the Snell law.}

Now, for example, for the peak wavelength 458nm of blue LED, refractive index _n Air = 1.00 in the air, the refractive index _n GaN = 2.47 in in GaN multilayer films 102 to 140, of in the sapphire substrate 101 Assuming that the refractive index n _{Al2O3 = 1.78, the critical angle θ 1} at the interface between the air layer and the p-GaN layer 140 and _{the critical angle θ 2} at the interface between the GaN layer 102 and the sapphire substrate 101 are According to the equations (1) and (2), θ ₁ = 23.9 ° and θ ₂ = 46.1 °.

Therefore, the optical waveguide (GaN layer 102, n-GaN layer 110, MQW layer 120, GaN layer 130, p-GaN layer 140) of light emitted from the LED region 50A in the positive direction of the X-axis to the upper and lower boundary surfaces. If the incident angle θ _{satisfies the condition θ> θ 2} , the light emitted from the MQW layer 120 due to the difference in refractive index between the p-GaN layer 140 and air or between the GaN layer 102 and the sapphire substrate 101 will be emitted. It propagates in the positive direction of the X-axis while totally reflecting in the optical waveguide.

That is, if the light-shielding film 170 as shown in FIG. 1 is provided in the vicinity of the p-type electrode 160 on the positive direction side of the X-axis _{, the condition of θ> θ 2} can always be satisfied, so that the air layer and the p-GaN layer 140 can be satisfied. Light emission can be suppressed from the interface with the air layer, and almost no light is output in the Y-axis direction, so that the GaN laminated films 102 to 140 can be propagated as an optical waveguide.

On the other hand, in the configurations of FIGS. 1 and 2, the thickness of the GaN laminated film 102 to 140 including the MQW layer 120, that is, the thickness of the optical waveguide is a, the wave number in vacuum is k, and the upper and lower boundary surfaces of the GaN laminated film 102 to 140. The following equations (3) and (4) hold, where θ is the angle of incidence on.

In the formula (3), a is the total thickness _{of the GaN laminated films 102 to 140, φ Air} is the phase change due to total internal reflection at the interface between the GaN laminated films 102 to 140 and the air, and φ _Al2O3 is the GaN laminated film. The phase change due to total reflection at the interface between the films 102 to 140 and the sapphire substrate 101, m is an integer of 0 or more (0, 1, 2, ...), And β represents the propagation constant.

FIG. 4 is a diagram showing the distribution of the refractive index of the sapphire substrate 101 and the GaN laminated film 102 to 140 in the depth (thickness) direction. The depth of 0 μm is the position of the boundary between the sapphire substrate 101 and the GaN layer 102.

As shown in FIG. 4, the refractive index of the sapphire substrate 101 is 1.78, and the refractive index of the GaN laminated films 102 to 140 is 2.47. The GaN laminated films 102 to 140 include the MQW layer 120, and the refractive index of the MQW layer 120 is slightly higher than that of the GaN layer 102, the n-GaN layer 110, the GaN layer 130, and the p-GaN layer 140. It is about 2.5.

Such a device structure can be treated as a slab-type optical waveguide having a three-layer structure in which air is a clad layer, GaN laminated films 102 to 140 functioning as an optical waveguide are a core layer, and a sapphire substrate 101 is a clad layer. Analysis of general asymmetric TE-mode and TM-mode slab-type optical waveguides can be applied. That is, the light-shielding film 170 in FIG. 2 can prevent the radiation mode to the upper surface (front surface) and the radiation mode to the sapphire substrate 101 from occurring, and the GaN stacking is performed in the section where the light-shielding film 170 exists in the X-axis direction. The light propagating in the film is a multimode propagating light having a discrete solution including a plurality of propagating lights satisfying the following equation (5).

Further, in the equation (3), since _{the values of the phase change φ Air} and the phase change φ _Al2O3 are different between the TE mode and the TM mode, the dispersion curve in the waveguide analysis is also different between the TE1 and the TM1.

FIG. 5 is a diagram showing the wavelength dependence of the refractive indexes of the sapphire substrate 101 and the GaN laminated films 102 to 140. As shown in FIG. 5, the refractive index of the GaN laminated films 102 to 140 is about 2.55 at a wavelength of 400 nm, gradually decreases with increasing wavelength, and becomes about 2.35 at 900 nm. Further, the refractive index of the sapphire substrate 101 is about 1.78 at a wavelength of 400 nm, and it tends to decrease very slowly with increasing wavelength, but it is almost constant.

FIG. 6 shows a three-layer structure slab of GaN laminated films 102 to 140 in TE1 and TM1 calculated at a peak wavelength of 458 nm for a blue LED with _{n Air} = 1.00, n _GaN = 2.47, and n _{Al2O3 = 1.78.} It is a dispersion curve of a type optical wave guide.

In FIG. 6, the horizontal axis represents a V parameter (also referred to as a normalized frequency), and the vertical axis represents a normalized propagation constant b (normalized propagation constant). FIG. 6 shows the characteristics of modes 0 to 5 (m = 0 to 5) in the TE mode and the TM mode.

As shown in FIG. 6, the dispersion curve is different in each mode of TE and TM, reflecting the three-layer structure in which the refractive index is asymmetric. Further, the propagation constant β can be analytically obtained from the equation (5) and the bV characteristic. Further, from the ratio of β and the wave number k, the equivalent refractive index n _eq (also referred to as equivalent index or effective index) can be obtained as in the following equation (6).

Next, a wire-grid polymerase 180 (see FIGS. 1 and 2) will be described. The wire grid polarizing element 180 has a plurality of metal wires arranged on the surface of the p-GaN layer 140 at a pitch Λ (μm). The plurality of wires extend in the Y-axis direction and are arranged in parallel at a pitch Λ (μm) in the X-axis direction.

In the wire grid polarizing element 180, by forming a fine metal grid (slit shape) on the surface of the p-GaN layer 140, the TM mode component incident on the grid from the GaN layer is transmitted to the air. , The TE polarizing component is reflected (partially absorbed) to the GaN layer to function as a polarizing element. That is, in the light (TE mode) that vibrates in the wire extension direction (Y-axis direction), the electric field vibration direction of the light coincides with the wire extension direction, so that the electrons in the metal of the wire transfer Joule heat due to the movement of the electric field. It is generated and the light is absorbed by the metal. Further, the light that is not absorbed by the metal is reflected by the metal on the GaN side. On the other hand, for light (TM mode) having an electric field orthogonal to the metal of the wire in the extension direction, light absorption is small and transmitted because the distance that electrons can move in the metal is limited. That is, since the wire grid polarizing element 180 functions as a diffraction grating, the TM mode can transmit between the wires. Therefore, in the wire grid polarizing element 180, only the light in the TM mode can be extracted to the outside among the light propagating in the TM mode and the TE mode propagating inside the GaN laminated films 102 to 140.

The light rays that pass through the wire grid polarizing element 180 and are taken out to the outside are given by the following equation (7), where α is the angle formed by the light rays emitted and the direction perpendicular to the boundary surface.

When applying a reverse bias voltage from the bias voltage source 190B between the wire grid polarizer 180 and the LED region 50A n-type electrode 150 in the form of proportional equivalent refractive index _{n eq} of TM mode to the applied voltage, variable Can be made to. In the equation (7), λ ₀ is the peak wavelength (center wavelength) of the light emission in the LED region 50A, and is always a constant value regardless of the value of the reverse bias voltage. The pitch Λ of the wire grid polarizing element 180 may be appropriately set under the condition that sinα> 0 is satisfied in the equation (7). By changing the applied voltage according to the direction of the light rays output from the LED region 50A, it is possible to control the angle α formed between the XZ plane and the vertical direction of the light rays.

In FIG. 2, the reason why the EO effect derived from the GaN crystal structure is exhibited is that the GaN crystal structure is a hexagonal crystal structure with low symmetry, and the crystals of the TM mode GaN laminated films 102 to 140 are exhibited. The EO effect derived from the fact that the structure does not contain central symmetry is exhibited. That is, when an electric field is applied to a crystal structure having such low symmetry and no centrosymmetry, a change in the refractive index proportional to the electric field, that is, an electro-optic (EO) effect due to the Pockels effect occurs.

Further, such a large change in the refractive index is enhanced particularly in the LED having the quantum well of InN. The horizontal (a-axis) lattice constant of the GaN crystal is 0.3189 nm, and the lattice constant of the InN crystal in the same direction is 0.3548 nm. Therefore, there is an 11% lattice mismatch between the two. Due to this lattice mismatch, the in-plane compressive strain is further increased and the pocketless effect is enhanced.

However, a large EO effect derived from the MQW layer 120 in the GaN laminated films 102 to 140 formed on the C surface of the sapphire substrate 101 cannot be expected in the TM mode.

That is, regarding the refractive index modulation effect in the MQW layer 120, TE polarized light is modulated, but TM polarized light is hardly modulated. In order to avoid this, instead of crystal growth of GaN on the C plane of the sapphire substrate 101, it is most effective to form MQW formed on a semi-polar substrate which is a substrate tilted by about 45 ° from the C plane. be. Alternatively, instead of growing GaN, the basic structure is such that a p-type layer and an n-type layer using _{Ga x} Al _1-x N (0 <x ≦ 1), which is a solid solution of AlN, as a base material are laminated, and particularly an active layer. It is also effective to have a structure incorporating an MQW of In _y Ga _{1-y N (0 <y ≦ 1).} In GaN, the transition (optical selectivity) allowed between the valence band Top and the bottom of the conductor is perpendicular to the electric field vector and the C axis of the GaN crystal, whereas in AlN, the electric field vector and the GaN crystal. This is because it is parallel to the C axis of.

This is the main cause, and in AlN, the light of the electric field vector parallel to the C axis can also be modulated. Since it is considered that the band structure of MQW also follows the band structure of GaN and AlN which are the parent materials, an LED whose base material is _{Ga x} Al _{1-x N (0 <x ≦ 1) containing Al instead of GaN is used.} It is effective for TM mode modulation.

As described above, according to the first embodiment, since the LED region 50A and the wire grid polarizing element 180 can be formed on the same substrate (sapphire substrate 101), it is possible to realize a compact optical deflection element 100. In the first embodiment, for the light modulator and the light deflector, the light source (LED region 50A) and the light modulation unit (EO modulation unit 50C having the wire grid modulator 180 as an electrode) are integrated to achieve compact light deflection. The element 100 can be realized. At that time, by combining the polarization plane of the light source (LED region 50A) and the polarization plane of the EO modulation unit 50C (modulation unit having the wire grid modulator 180 as an electrode), the modulation and light deflection of the light source can be realized. The EO modulation unit 50C is an example of a deflection unit. The deflecting unit acts as a deflector and deflects by changing the refractive index as a modulator.

Since the optical deflection element 100 uses an electro-optic effect (EO effect) capable of high-speed modulation of GHz or higher as the phase modulation of light, high-speed optical deflection control is possible. By using the light deflection element 100 for each pixel of the display unit of the integral stereoscopic display device, it is possible to realize a significant reduction in the number of pixels required for stereoscopic display by time-division display.

FIG. 7 is a diagram showing a light deflection element 100A of a modification of the first embodiment. The optical deflection element 100A includes a sapphire substrate 101, a GaN layer 102, an n-GaN layer 110, an MQW layer 120, a GaN layer 130, a p-GaN layer 140, an n-type electrode 150, a p-type electrode 160A, a light-shielding film 170A, and a wire grid. Includes a extruder 180A and bias voltage sources 190A, 190B.

The optical deflection element 100A includes a ring-shaped wire grid polarizing element 180A instead of the wire grid polarizing element 180 of the optical deflection element 100 shown in FIGS. 1 and 2. Along with this, the p-type electrode 160 and the light-shielding film 170 shown in FIGS. 1 and 2 have been changed to the p-type electrode 160A and the light-shielding film 170A. In FIG. 7, the insulating layer corresponding to the insulating layer 171 is omitted.

The wire grid polarizing element 180A has a plurality of wires arranged concentrically and an electrode 180A1. Further, the light-shielding film 170A has a base portion 170A1 extending from the outside to the center of the plurality of wires in a plan view, and a central portion 170A2 covering the center of the plurality of wires (the inner portion of the wire having the smallest diameter). Further, the p-type electrode 160A is provided on the upper side of the light-shielding film 170A and has a base portion 160A1 extending from the outside to the center of the plurality of wires in a plan view and a center portion 160A2. The base 160A1 and the center 160A2 are located on the base 170A1 and the center 170A2, respectively.

Similar to the optical deflection element 100 shown in FIGS. 1 and 2, such an optical deflection element 100A applies a reverse bias voltage from the bias voltage source 190B between the entire wire grid polarizing element 180A and the n-type electrode 150. do. An electric field is applied from the bias voltage source 190B to the wire grid polarizing element 180A via one electrode 180A1. The electrode 180A1 is a linear electrode provided from the center of a plurality of wires of the wire grid polarizing element 180A toward the outside in the radial direction.

The light generated in the LED region 50A is diffracted by the wire grid polarizing element 180A and can be taken out in the Z-axis direction. Further, since the wire grid polarizing element 180A has a shape that surrounds the LED region 50A from the periphery in a plan view, it is possible to form a varifocal lens with the entire wire grid polarizing element 180A. Therefore, the extracted light is beam-converged on the beam 100A1 as shown in FIG.

FIG. 8 is a diagram showing a light deflection element 100B of a modification of the first embodiment. The optical deflection element 100B is obtained by changing the wire grid polarizing element 180A of the optical deflection element 100A shown in FIG. 7 to the wire grid polarizing element 180B.

The wire grid polarizing element 180B has a plurality of wires arranged concentrically and eight electrodes 180B1 to 180B8. The electrodes 180B1 to 180B8 are formed by arranging eight electrodes 180A1 shown in FIG. 7 at equal angular intervals. A variable voltage is applied to the electrodes 180B1 to 180B8 independently of the bias voltage source 190B.

The wire grid polarizing element 180B is regarded as a plurality of electrodes divided into eight in the circumferential direction to enable the divided drive. Propagation light in the GaN laminated films 102 to 140 under the eight electrodes 180B1 to 180B8 by providing a voltage difference applied to the voltage applied to the wire from each of the electrodes 180B1 to 180B8 by the split drive of the electrodes 180B1 to 180B8. By having different phase distributions in the concentric circle direction, the elevation angle and the azimuth angle of the beam 100B1 can be controlled.

Such a wire grid polarizing element 180B can also be regarded as an optical phased array having eight openings. However, in order to realize the operation as an optical phased array, it is necessary that the entire opening is within the coherence length defined by the spectral width of the light emission of the LED region 50A. In the case of a general LED, the coherence length is about 20 μm. The coherence length can be extended by enhancing the light confinement effect in the LED. The optical phased array operation enables direction control of the optical beam and convergence / divergence operation.

<Embodiment 2>
FIG. 9 is a diagram showing the light deflection element 200 of the second embodiment. In the stacking direction in the same direction of the MQW layer 120 to have an electric field component, a structure capable of light deflected by the TE mode using the electro-optical constant r _13.

In order to have such an electric field component, the optical deflection element 200 includes a sapphire substrate 101, a GaN layer 102, an n-GaN layer 110, an MQW layer 120, a GaN layer 130, a p-GaN layer 140, and an n-type electrode 150. It includes a p-type electrode 160, a light-shielding film 170, an insulating layer 171 and a metal cladding 280, a bias voltage source 190A, 290B1, 290B2, and p-type electrodes 290C1 and 290C2.

The metal cladding 280 is a metal film having a rectangular shape in a plan view, and is directly formed on the upper surface of the p-GaN layer 140 of the optical waveguide of the GaN laminated films 102 to 140. The position of the metal cladding 280 in the X-axis direction is a position adjacent to the positive direction side of the p-type electrode 160. P-type electrodes 290C1 and 290C2 are provided on the X-axis positive direction side of the metal cladding 280. The metal cladding 280 is made of, for example, a metal thin film such as Al, Au, or Ag, and Al having a particularly large imaginary portion having a complex dielectric constant is effective. As a manufacturing method, for example, it is formed by a vapor deposition method.

The p-type electrodes 290C1 and 290C2 are provided on the upper surface of the p-GaN layer 140 of the optical waveguide of the GaN laminated films 102 to 140 on the X-axis positive direction side of the metal cladding 280. The p-type electrode 290C1 is provided at the end of the upper surface of the p-GaN layer 140 on the positive Y-axis side, and the p-type electrode 290C2 is located on the negative Y-axis side of the upper surface of the p-GaN layer 140. It is provided at the end. Further, a reverse bias voltage is applied to the p-type electrode 290C1 by the bias voltage source 290B1 to the n-type electrode 150, and a variable reverse bias voltage is applied to the p-type electrode 290C2 by the bias voltage source 290B2.

In the optical deflection elements 100, 100A, and 100B shown in FIGS. 1, 2, 7, and 8, the TM mode light is taken out to the outside, and the GaN laminated films 102 to 140 formed on the C-plane substrate of the sapphire substrate 101. Although it was difficult to express a large EO coefficient in the MQW layer 120 of InGaN, according to this structure, since the TE mode can be used, the electro-optic constant r ₁₃ = 20 (pm / V) even in the light emitting region of visible light. ) It is possible to develop a large electro-optic effect.

In particular, the TM mode is absorbed by using the metal cladding 280 in which the metal is directly formed on the upper surface of the p-GaN layer 140, and the TE mode is transmitted in the positive direction of the X axis inside the GaN laminated films 102 to 140. Can be done. The light in TE mode is emitted from the end face on the positive direction side of the X axis.

According to this structure, since the electromagnetic field distribution in the TM mode permeates into the metal of the metal cladding 280, the propagation loss in the TM mode is large, and only the TE mode permeates. That is, the metal behaves as a dielectric having a negative dielectric constant and a large loss with respect to light in TM mode. As a result, in the waveguide region sandwiched between the two p-type electrodes 290C1 and 290C2, the bias voltage of the bias voltage source 290B2 is varied to efficiently deflect the TE mode light as shown by the arrow. Since the direction radiated from the end face on the positive direction side of the X axis can be controlled in the XY plane, it is possible to form a large optical deflection element 200 having _{an electro-optical constant r 13 by using an inexpensive C-plane sapphire substrate.} It will be possible.

<Embodiment 3>
FIG. 10 is a diagram showing the integral stereoscopic display device (stereoscopic image display device) 300 of the third embodiment. The display device 300 shown in FIG. 10 is an integral three-dimensional display device using any one of the light deflection elements 100, 100A, 100B, and 200 of the first and second embodiments. In the display device 300 of FIG. 10, any one of the optical deflection elements 100, 100A, 100B, and 200 is arranged in each pixel. In FIGS. 10A and 10B, the light radiated from each of the plurality of optical deflection elements 100, 100A, 100B, and 200 is time-divisioned and displayed in a time-division manner to the user of the display device 300. Provides stereoscopic images.

According to such a configuration, the stereoscopic image display device 300 switches and outputs an image signal corresponding to two or more emission directions for each pixel in a time-division manner by the light emission control unit, and outputs the light emission of the pixel. Controls light emission. Further, the stereoscopic image display device 300 specifies the emission direction of the light rays from each pixel. At this time, the stereoscopic image display device 300 is provided as each pixel in synchronization with the timing at which the light emission control unit switches the image signal to be output to each pixel corresponding to two or more emission directions by controlling the emission direction. It deflects the emission direction of the light emitting element. As a result, the stereoscopic image display device 300 displays the stereoscopic image of the integral photography method.

Therefore, since the directions of the light rays from each pixel are specified in two or more emission directions, the stereoscopic image can be made high-definition as compared with the stereoscopic image display device using a conventional lens. Further, since one light emitting element functions as a pixel corresponding to a plurality of emission directions by the time division method, the number of light emitting elements mounted on the stereoscopic image display device 300 can be reduced.

When the stereoscopic display device is realized, the observer who directly looks at the display device will directly look at the light rays emitted from the display. Therefore, as a fine light source constituting each pixel, it can be realized by using an LED instead of a laser diode (LD).

It is possible to display a stereoscopic image by controlling the direction and shape of the light beam emitted from the pixel by time-division display because the structure is integrated with the LED light source and the deflection element by forming the pixel. Become.

The light deflection elements 100, 100A, 100B, and 200 can be generally applied to devices that require light beam forming and direction control. For example, it is suitable for a light source for a projector, an optical switch, a connector used for spatial optical interconclusion, an illumination light source that does not require a diffuser, and the like.

Although the optical deflection element and the display device according to the exemplary embodiment of the present invention have been described above, the present invention is not limited to the specifically disclosed embodiments and is within the scope of claims. Various modifications and changes are possible without deviating from.

50A LED region 50B Optical propagation region 50C Optical modulation region 100, 100A, 100B, 200 Optical deflection element 101 Sapphire substrate 102 to 140 GaN laminated film
102 GaN layer

110 n-GaN layer 120 MQW layer 120A MQW layer light emitting region 130 GaN layer 140 p-GaN layer 150 n-type electrode 160 p-type electrode 160A p-type electrode 160A1 base 160A2 center 170 light-shielding film 170A light-shielding film 170A1 base 170A2 center 171 Insulation layer 180 Wire grid splitter 180A, 180B Wire grid splitter 180A1, 180B1 to 180B8 Electrodes 190A, 190B Bias voltage source 300 Display device

Claims (6)

With a sapphire board,
_{An n-type layer using Ga x} Al _1-x N (0 <x ≦ 1) as a base material provided on the C surface of the sapphire substrate, and
An active layer stacked on the n-type _{layer, In y Ga 1-y N} (0 <y ≦ 1) quantum well layer composed of or _{In y Ga 1-y N (} 0 <y ≦ 1) and Multiple quantum wells with multiple barrier layer (GaN) pairs,
A p-type layer whose base material is _{Ga x} Al _1-x N (0 <x ≦ 1) laminated on the quantum well layer or the multiple quantum wells.
By applying a forward-biased first voltage to the first region of the n-type layer, the quantum well layer, and the p-type layer laminate, a first voltage application that causes the first region to function as a light emitting diode portion. Department and
The out of the laminate than said first region is provided in the second area in the direction in which light emission of the light emitting diode to light propagating in the diode, polarized light emission of the light emitting diode unit, prior to further SL polarization A light deflection element that includes a deflection section that emits light emitted in a specific direction. The deflection portion is a wire grid deflector having a plurality of metal wires provided at predetermined intervals inside the p-type layer or on the opposite side of the p-type layer from the quantum well layer in the second region. can be,
A second voltage application unit that applies a second voltage in the direction opposite to the first voltage to the n-type layer is further included between the wire grid polarizing element and the n-type layer.
The wire grid polarizing element removes the TE polarization component of the light emission, polarizes the TM polarization component of the light emission, and further applies a voltage to the second voltage application portion to deflect the TM polarization component. The light deflecting element according to claim 1, wherein the light emission is emitted from the wire grid polarizing element in a specific external direction. The deflection portion is a wire grid deflector having a plurality of metal wires provided at predetermined intervals inside the p-type layer or on the opposite side of the p-type layer from the quantum well layer in the second region. can be,
A second voltage application unit that applies a second voltage in the direction opposite to the first voltage to the n-type layer is further included between the wire grid polarizing element and the n-type layer.
The plurality of metal wires of the wire grid polarizing element are a plurality of circumferential wires arranged concentrically.
It said second voltage applying unit, by applying the second voltage to the circumferential plurality of wires, according to claim 1, wherein focusing the light beam of the light emission is emitted to the outside from the wire grid polarizer Light deflection element. The second voltage application unit is provided with a plurality of circumferential wires at predetermined angles, has a plurality of electrodes extending in the radial direction, and individually applies a second voltage to each electrode. The light deflection element according to claim 3, wherein the shape, the emission direction, and the emission angle of the light beam emitted from the wire grid polarizing element to the outside are controlled. The deflection portion is a thin-film metal cladding provided on the p-type layer in the second region.
The TM polarization component of the emission is removed by the metal cladding, the TE polarization component of the emission is propagated in the diode, and the TE polarization component is further deflected and specified by two p-type electrodes. The light deflection element according to claim 1, wherein the light emission is emitted in the direction of. An integral photography type stereoscopic image display device including a display panel in which the optical deflection elements according to any one of claims 1 to 5 are arranged in a two-dimensional array as pixels.
Image signals corresponding to two or more emission directions displayed by the stereoscopic image display device are switched and output for each of the pixels in a time-divided manner, and light emission and non-emission in the emission direction from the pixels are controlled. A featured stereoscopic image display device.

Images