JP2008311687A - Self-luminous device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively extract light emitted from illuminants into the air. <P>SOLUTION: The self-luminous device 1 includes a first layer, a light emitting layer overlaying the first layer, a second layer overlaying the light emitting layer and an intermediate layer in the second layer. The refractive index of the intermediate layer is made higher than the refractive index of the first layer and the second layer, the surface of the second layer or the surface of a layer overlaying the second layer has a two-dimensional periodic structure, the intermediate layer is provided inside the two-dimensional periodic structure, and a distance between the upper part of the light emitting layer and the bottom part of the two-dimensional periodic structure is 0.1λ-0.3λ or 0.3λ-λ (λ is wavelength in vacuum). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a self-luminous device that emits light spontaneously, such as a light-emitting diode (LED) or an organic EL.

  Self-emitting devices such as light-emitting diodes (LEDs) and organic EL are expected to be used in a wide range of fields such as displays, displays, and lighting. However, the light emitted from the light emitter is externally reflected by total reflection. Therefore, there is a problem that the utilization efficiency of light emitted from the light emitter is low. For example, the efficiency of a light emitting element using a semiconductor such as an LED is said to be 10% or less.

  Therefore, in the above self-luminous device, it is required to extract light emitted from the light emitter more efficiently in the air.

  In order to solve this problem, a method of forming a periodic structure on a semiconductor surface has been proposed (see, for example, Patent Documents 1, 2, 3, and 4). The periodic structure formed on the semiconductor surface changes the direction of the light inside the semiconductor by the wave number conversion action of the periodic structure so that the totally reflected light is taken out into the air. As a result, the extraction efficiency is improved.

US Pat. No. 5,777,924 Japanese Patent Laid-Open No. 10-4209 JP 2004-128445 A JP 2004-3221 A

  As a result of calculating the extraction efficiency by the above-described periodic structure by the three-dimensional light wave simulation, the inventor of the present application is limited by the diffraction efficiency by the periodic structure, and is limited to 1.5 to 2 times. It was confirmed. The inventor of the present application has applied for a three-dimensional light wave simulation as a wave optical simulation method (Japanese Patent Laid-Open No. 2005-69709).

  Further, depending on the machining process for forming the periodic structure, there is a problem that the periodicity of the periodic structure cannot be perfected, and sufficient light extraction efficiency cannot be obtained. There is a problem that a large burden is imposed on the machining process in order to achieve completeness.

  In order to improve this efficiency, a structure in which a diffraction grating is directly formed in the light emitting layer (active layer) is conceivable, and this structure is expected to further improve the efficiency. However, in the structure in which the diffraction grating is formed directly on the light emitting layer, there is a problem that the quality of the light emitting layer itself is remarkably damaged. Therefore, such a structure cannot be actually used.

  An object of the present invention is to solve the above-described conventional problems and to more efficiently extract light emitted from a light emitter in the air.

  Another object of the present invention is to improve the light extraction efficiency without imposing a burden on the processing process.

  Another object of the present invention is to improve the light extraction efficiency even when the periodicity of the periodic structure is insufficient.

  As a result of analyzing the light emission from the self-luminous device by the above-described three-dimensional light wave simulation, the inventor of the present application has a refractive index distribution of each layer such as a semiconductor layer constituting the self-luminous device as a factor related to light extraction. I found out.

  Moreover, when the light emission surface of the self-light-emitting device is a structure provided with a two-dimensional periodic structure, it also discovered that there existed the distance of the shape of the two-dimensional periodic structure, and a light emitting layer and a two-dimensional periodic structure.

  The self-luminous device of the present invention is based on the knowledge obtained from the above simulation, and includes four aspects as a configuration for improving the light extraction efficiency.

  The first aspect of the self-luminous device of the present invention is an aspect in which the light extraction efficiency is improved by the refractive index distribution of each layer constituting the self-luminous device, and the first layer overlaps with the first layer. A light emitting layer and a second layer overlapping on the light emitting layer, wherein the refractive index of the first layer is different from the refractive index of the second layer, and the refractive indexes of both layers sandwiching the light emitting layer are asymmetric. The configuration.

  In the refractive index distribution of the asymmetric layer, the refractive index of the second layer is made higher than the refractive index of the first layer.

  According to the first aspect, by making the refractive index of the layers sandwiching the light emitting layer asymmetric, the light distribution in each layer constituting the self light emitting device is changed to the light distribution by the configuration in which the refractive index is symmetric. In contrast, this light distribution facilitates extraction of light confined in the light emitting layer out of the light emitting layer.

  By making the refractive index of the second layer higher than the refractive index of the first layer, the light extracted from the light emitting layer is guided to the second layer side having a high refractive index, and the light emitting surface on the second layer side To improve the luminous efficiency to be taken out from.

  The first aspect in which the refractive indexes of both layers sandwiching the light emitting layer are asymmetrical is either a configuration in which the light emitting surface of the self-luminous device does not have a two-dimensional periodic structure or a configuration with a two-dimensional periodic structure. This configuration can also be applied.

  The second aspect of the self-luminous device of the present invention is an aspect in which light extraction efficiency is improved by the distance between the light-emitting layer and the two-dimensional periodic structure in a configuration in which the light emitting surface of the self-luminous device has a two-dimensional periodic structure. A first layer, a light emitting layer overlying the first layer, and a second layer overlying the light emitting layer, the surface of the second layer or the layer overlying the second layer When a two-dimensional periodic structure is provided on the surface and λ is a wavelength in vacuum, the distance between the top of the light emitting layer and the bottom of the two-dimensional periodic structure is 0.1λ to 0.3λ or 0.3λ to λ. This distance is the same as or longer than the penetration depth of the disappearing region.

  When the distance between the upper part of the light emitting layer and the bottom part of the two-dimensional periodic structure is as thick as 0.3λ to λ, the extraction efficiency is improved by increasing the extraction of light that freely emits light inside. In addition, when the distance between the top of the light emitting layer and the bottom of the two-dimensional periodic structure is as thin as 0.1λ to 0.3λ, the light extraction is enhanced and the light emission toward the outside is enhanced. To improve the extraction efficiency.

  This second aspect can be combined with the first aspect described above, and the distance between the bottom of the two-dimensional periodic structure formed on the light emitting surface and the upper part of the light emitting layer is 0.1λ to 0.3λ, or 0.3λ to λ. And the refractive index of the first layer is different from the refractive index of the second layer, the refractive indexes of the two layers sandwiching the light emitting layer are asymmetric, and the refractive index of the second layer is the first refractive index. The structure is higher than the refractive index of the body layer.

  The third aspect of the self-luminous device of the present invention improves the light extraction efficiency by the refractive index distribution of the layers constituting the self-luminous device as in the first aspect, and has a multilayer structure including an intermediate layer And a first layer, a light emitting layer overlapping on the first layer, and a second layer overlapping on the light emitting layer, and an intermediate layer is provided in the second layer. A multilayer structure is adopted.

  This intermediate layer is formed of a medium having a refractive index equivalent to that of the light emitting layer and not absorbing light emitted by the light emitting layer. Alternatively, the intermediate layer is formed with a refractive index higher than that of the first layer and the second layer. The thickness of the intermediate layer is, for example, 0.5λ or more when λ is a wavelength in vacuum.

  This third aspect can be combined with the second aspect described above, and a two-dimensional periodic structure is provided in the second layer, and an intermediate layer is provided in the two-dimensional periodic structure. The distance between the bottom of the structure and the top of the light emitting layer is 0.1λ to 0.3λ or 0.3λ to λ.

  The first layer, the second layer, and the intermediate layer are made of AlGaN, and by forming the Al composition ratio of the intermediate layer lower than the Al composition ratio of the first layer and the second layer, The refractive index is set higher than that of the first layer and the second layer.

  In the second and third aspects, the two-dimensional periodic structure may be a close-packed array of circular holes or a close-packed array of conical protrusions. As the conical protrusion close-packed array, for example, a conical protrusion close-packed array and a pyramidal protrusion close-packed array can be used.

  The two-dimensional periodic structure can be formed by a photonic crystal or a photonic quasicrystal.

  Note that the photonic quasicrystal has a refractive index quasi-periodic structure that has long-range order and rotational symmetry without having translational symmetry with respect to the refractive index on the light emitting surface of the light emitter. This configuration can be formed by arranging the refractive index regions constituting the photonic crystal on the light emitting surface of the light emitter according to the pattern of the quasicrystal having no translational symmetry.

  In the first to third aspects, when the first layer and the second layer are semiconductor layers, the first semiconductor layer is n-GaN (or p-GaN), and the light emitting layer is In GaN, the second semiconductor layer can be formed of p-GaN (or n-GaN).

  In the first to third aspects, the second layer can be covered with a resin layer.

  In addition, by using a quasi-periodic structure of a photonic quasicrystal in a two-dimensional periodic structure, it is possible to reduce band dependency and viewing angle dependency, improve efficiency for a wide solid angle and a wide spectrum, and The emitted light can be extracted more efficiently in the air.

  The first layer and the second layer described above can be formed of a semiconductor substrate, a glass substrate, or the like, thereby forming a light emitting diode or an organic EL.

  Furthermore, the fourth aspect of the self-luminous device of the present invention has a two-dimensional periodic structure on the light emitting surface, and the light extraction efficiency is improved by the refractive index distribution of the layers constituting the self-luminous device as in the first aspect. This is an embodiment to improve.

  The fourth aspect includes a first layer, a light emitting layer overlapping on the first layer, and a second layer overlapping on the light emitting layer. The surface of the second layer or the surface of the layer overlapping on the second layer has a two-dimensional periodic structure. The first layer is a low refractive index layer. The refractive index of the first layer is set lower than that of the light emitting layer and is the same as or lower than that of the second layer. The thickness of the low refractive index layer is approximately the same as the light emission intensity of the light emitting layer.

In the fourth aspect, the light emitting layer is InGaN, and the low refractive index layer of the first layer is any one of AlGaN, Al ₂ O ₃ (sapphire), and AlN (aluminum nitride).

  In one configuration of the self-luminous device of the fourth aspect, an InGaN light emitting layer and an AlGaN layer having a two-dimensional periodic structure are sequentially stacked on a sapphire substrate. A layer having one electrode is provided between the sapphire substrate and the light emitting layer, and the other electrode is provided in a part of the AlGaN layer, thereby energizing the light emitting layer.

  Further, the present invention provides a self-luminous device having a two-dimensional periodic structure, wherein the periodicity of the two-dimensional periodic structure provided in the self-luminous device has a period range of ½ period to two periods, and a period deviation within this range. If so, sufficient effects can be achieved.

  As described above, according to the present invention, the light emitted from the light emitter can be extracted more efficiently in the air. Further, the light extraction efficiency can be improved without imposing a burden on the processing process.

  Even if the periodicity of the periodic structure is insufficient, the light extraction efficiency can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the self-luminous device of the present invention will be described using a configuration example in which each layer is formed of a semiconductor layer, such as a light-emitting diode, but a configuration in which each layer is formed of a glass substrate or the like, such as an organic EL. It can also be applied to.

  A first aspect of the present invention will be described with reference to FIG. In FIG. 1, a self-luminous device 1 according to a first aspect is an aspect in which light extraction efficiency is improved by a refractive index distribution of a semiconductor layer, and the first semiconductor layer 2 and the first semiconductor layer 2 are formed on the first semiconductor layer 2. A light emitting layer 3 that overlaps and a second semiconductor layer 4 that overlaps the light emitting layer 3 are provided, the refractive index of the first semiconductor layer 2 is set to a low refractive index, and the refractive index of the second semiconductor layer 4 is set to a high refractive index. The refractive index of the upper and lower semiconductor layers 2 and 4 sandwiching the light emitting layer 3 is configured to be asymmetric.

  The semiconductor layers 2 and 4 and the light emitting layer 3 constitute each layer of the self light emitting device 1. For example, the first semiconductor layer 2 and the second semiconductor layer 4 are formed of an AlGaN cladding layer, and the light emitting layer 3 is formed of InGaN. Here, the refractive index of the light emitting layer 3 is, for example, 2.8, the refractive index of the AlGaN cladding layer of the first semiconductor layer 2 is 2.5, and the refractive index of the AlGaN cladding layer of the second semiconductor layer 4. Is 2.78. The refractive index of the AlGaN cladding layer of the second semiconductor layer 4 can be made high by making the Al composition lower than the Al composition of the AlGaN cladding layer of the first semiconductor layer 2. . Further, when the wavelength λ in light is λ, the thickness of the light emitting layer 3 is 0.2λ.

  Next, a second aspect of the present invention will be described with reference to FIG. In FIG. 2, the self-light-emitting device 1 according to the second aspect is configured so that light is extracted by the distance ds between the light-emitting layer 3 and the two-dimensional periodic structure 10 in a configuration in which the light-emitting surface of the self-light-emitting device 1 includes the two-dimensional periodic structure 10 This is an aspect of improving efficiency. Note that the two-dimensional periodic structure may be provided on the surface of a layer overlapping with the semiconductor layer in addition to being provided in the semiconductor layer. Below, the example which provides a two-dimensional periodic structure in a semiconductor layer is demonstrated.

  The self-luminous device 1 includes a first semiconductor layer 2, a light emitting layer 3 overlying the first semiconductor layer 2, and a second semiconductor layer 4 overlying the light emitting layer 3. When the two-dimensional periodic structure 10 is provided on the surface of the semiconductor layer 4 and λ is a wavelength in vacuum, the distance between the top of the light emitting layer 3 and the bottom of the two-dimensional periodic structure 10 is 0.1λ to 0.3λ, or 0.3λ to Let λ be. This distance ds is the same as or longer than the penetration depth of the disappearing region.

  The semiconductor layers 2 and 4 and the light emitting layer 3 constitute the respective layers of the self light emitting device 1 in the same manner as in the first embodiment. For example, the first semiconductor layer 2 and the second semiconductor layer 4 are clad of AlGaN. The light emitting layer 3 can be formed of InGaN.

  Here, the refractive indexes of the first semiconductor layer 2, the light emitting layer 3, and the second semiconductor layer 4 may be asymmetrical as well as asymmetrical as in the first embodiment. In the asymmetric configuration, the refractive index of the light emitting layer 3 is, for example, 2.8, the refractive index of the AlGaN cladding layer of the first semiconductor layer 2 is 2.5, and the AlGaN cladding layer of the second semiconductor layer 4 is The refractive index is 2.78. In a symmetric configuration, the refractive index of the light emitting layer 3 is 2.8, for example, and the refractive index of the AlGaN cladding layer of the first semiconductor layer 2 and the second semiconductor layer 4 is 2.5.

  The two-dimensional periodic structure 10 included in the second aspect can be configured by, for example, a close-packed array of circular holes or a close-packed array of conical protrusions, and can be formed of a photonic crystal or a photonic quasicrystal. The conical projection close-packed arrangement is a method of arranging the projections of the cone-shaped close-packed, and the cone-shaped body can have any shape, for example, a conical-projection close-packed arrangement or a pyramidal close-packed close-packed array. It can be an array.

  A photonic crystal is formed by repeatedly arranging regions having different refractive indices at a period of about the wavelength of light, and a photonic quasicrystal has two different refractive index regions at a period of about the wavelength of light. In a repeating photonic crystal, an arrangement pattern is formed in accordance with a quasi-crystal pattern, and has a refractive index quasi-periodic structure having a long-range order and a rotational symmetry without having a translational symmetry with respect to a refractive index. As a pattern for forming the quasicrystal, for example, a Penrose tiling pattern or a 12-fold Symmetric pattern can be used.

  By applying a light emitting surface having a lattice structure of a photonic quasicrystal, light extraction efficiency can be increased, and viewing angle dependency can be reduced to obtain a high solid angle.

  FIGS. 2A and 2B show a case where a close-packed circular hole array is used as the two-dimensional periodic structure. FIG. 2A shows the plane of the two-dimensional periodic structure 10 by the close-packed circular hole arrangement, and FIG. 2B shows the side surfaces of the self-luminous device 1 and the two-dimensional periodic structure 10.

  In the self-light-emitting device 1 having a two-dimensional periodic structure with a close-packed circular hole arrangement, circular holes 11 having a hole diameter 2r and a hole depth dh are periodically arranged in the second semiconductor layer 4. The distance between the bottom 12 and the top of the light emitting layer 3 is ds. A lattice constant a (pitch between holes) is provided as a parameter for determining the two-dimensional periodic structure.

According to the result of the three-dimensional lightwave simulation, the light extraction efficiency varies depending on these parameters a, 2r, and dh,
a = λ to 1.5λ
2r = 0.5a-0.6a
dh = 0.5λ to λ
In this case, the light extraction efficiency is maximized.

  FIG. 2C shows a plane of the two-dimensional periodic structure 10 having a conical projection close-packed arrangement, and FIG. 2D shows the side surfaces of the self-luminous device 1 and the two-dimensional periodic structure 10.

  In the following description, the conical protrusion close-packed array is used for explanation. However, the conical protrusion close-packed array is only an example of the conical protrusion close-packed array, and the pyramidal protrusion close-packed array is used as the pyramidal protrusion close-packed array. Also good.

  In the self-light-emitting device 1 having the two-dimensional periodic structure with the close-packed conical protrusions (assuming that the light emitting surface is completely filled with the conical protrusions), the conical protrusions 13 having an angle θ in the second semiconductor layer 4. Are periodically arranged, and the distance between the bottom 14 of the conical protrusion 13 and the top of the light emitting layer 3 is ds. As parameters for determining the two-dimensional periodic structure, a lattice constant a (a pitch between conical protrusions) and an angle θ are provided.

According to the results of the three-dimensional lightwave simulation, the light extraction efficiency varies depending on these parameters a and θ.
a = 0.5λ to λ
θ = 60 ° -65 °
In this case, the light extraction efficiency is maximized.

  The light extraction efficiency is obtained by comparison based on the light extraction amount of a self-luminous device having a planar structure that does not have a two-dimensional periodic structure, as will be described later.

  Further, according to the result of the three-dimensional light wave simulation, the upper part of the light emitting layer 3 and the bottom part of the two-dimensional periodic structure 10 (the bottom part 12 of the close-packed circular holes shown in FIG. 2B, the cone shown in FIG. 2D). The light extraction efficiency is improved by setting the distance ds to the bottom 14) of the close-packed projections to 0.1λ to 0.3λ or 0.3λ to λ.

  When the distance ds is set to 0.3λ to λ and the distance between the top of the light emitting layer and the bottom of the two-dimensional periodic structure is thick, the light emitting layer 3 can improve the extraction of light emitted freely from the light emitting layer, When the distance ds is set to 0.1λ to 0.3λ and the distance between the top of the light emitting layer and the bottom of the two-dimensional periodic structure is thin, the light emission from the light emitting surface is further enhanced along with the removal from the light emitting layer. Thus, the extraction efficiency is improved by changing the light distribution.

  This two-dimensional periodic structure is formed by previously forming protrusions of a two-dimensional periodic structure with a mold or a mold and transferring the protrusion structure to a semiconductor substrate or an organic EL substrate, or by etching such as epitaxial. Can be formed.

  Since the formation of this two-dimensional periodic structure includes a step of cutting the semiconductor layer, the semiconductor layer is cut to the vicinity of the light emitting layer at the bottom, and the distance is determined by ds described above. For this reason, in the configuration in which the distance ds between the top of the light emitting layer and the bottom of the two-dimensional periodic structure is thin, there is a problem that the possibility of damaging the light emitting layer during the manufacturing process is increased.

  In this case, by combining with the structure in which the refractive index of the semiconductor layer of the first embodiment is asymmetric, and adopting a thick structure with a distance ds of 0.3λ to λ, damage to the light emitting layer during this manufacturing process is achieved. Can solve the problem. Note that the light extraction efficiency at this time can maintain F = 3.61 as shown in an example in FIG. 6 to be described later. Here, F represents a ratio based on the light intensity extracted in a configuration that does not have a two-dimensional periodic structure and does not have any of the first to fourth aspects of the present invention.

  The periodicity of the two-dimensional periodic structure can allow a period shift in a period range of ½ period to 2 periods. FIG. 3 is a diagram showing the relationship between the periodicity of the two-dimensional periodic structure and the output.

  3 (a) and 3 (b) are examples in which the two-dimensional periodic structure is a close-packed arrangement of circular holes, and the two-dimensional periodic structure having the specifications shown in FIG. 3 (a) is normalized by a / λ. The intensity (vertical axis) with respect to the pitch (horizontal axis) is shown using d / λ as a parameter. 3 (c) and 3 (d) are examples in which the two-dimensional periodic structure is a close-packed conical protrusion. In the two-dimensional periodic structure having the specification shown in FIG. 3 (c), the standard is a / λ. The intensity (vertical axis) with respect to the converted pitch (horizontal axis) is shown with θ as a parameter.

  As shown in FIGS. 3A to 3D described above, it is confirmed that the output is effectively increased when the pitch a / λ is in the range of 0.5 to 2.0. Therefore, the periodicity of the two-dimensional periodic structure can tolerate a period shift within a period range of 0.5 to 2.0 when expressed by the normalized pitch a / λ.

  FIG. 3E shows the relationship between the shift in periodicity, the scattering property, and the diffractive property of the two-dimensional periodic structure. In FIG. 3 (e), it is confirmed that the output is increased between 1 and 6 with respect to the normalized pitch represented by a / λ (a: lattice constant, λ: wavelength). The degree of the contribution of the diffractive property and the diffraction property is shown.

  According to FIG.3 (e), the periodicity of a two-dimensional periodic structure can accept | permit a period shift within the period range of 1.0-6.0, when expressed with the normalized pitch a / (lambda).

  Next, a third aspect of the present invention will be described with reference to FIG.

  In FIG. 4, the self-luminous device 1 of the third aspect improves the light extraction efficiency by the refractive index distribution of the semiconductor layer constituting the self-luminous device as in the first aspect. It is the aspect which is set as the multilayer structure provided.

  The self-luminous device 1 includes a first semiconductor layer 2, a light emitting layer 3 overlying the first semiconductor layer 2, a second semiconductor layer 4 overlying the light emitting layer 3, and the second semiconductor layer. 4 is a multilayer structure having an intermediate layer 5 in it.

  The first form of the intermediate layer 5 is formed of a medium that has a refractive index close to that of the light emitting layer 3 and does not absorb light emitted by the light emitting layer 3. In the second embodiment, the refractive index of the intermediate layer 5 is formed higher than that of the semiconductor layers 2 and 4. The thickness of the intermediate layer 5 is, for example, 0.5λ or more when λ is a wavelength in vacuum.

  For example, when the refractive index when the semiconductor layers 2 and 4 are made of an AlGaN cladding layer is 2.5 and the refractive index of the light-emitting layer 3 of InGaN is 3.0, the composition of Al in the AlGaN layer 5 is lowered. The refractive index is 2.8.

  Further, this third aspect can be combined with the second aspect described above, and a multilayer in which a two-dimensional periodic structure 10 is provided in a second semiconductor layer and an intermediate layer 5 is provided in the two-dimensional periodic structure 10. The distance between the bottom of the two-dimensional periodic structure and the top of the light emitting layer may be 0.1λ to 0.3λ or 0.3λ to λ.

  4A is a configuration example in which a periodic structure is not formed on a light emitting surface that does not have a two-dimensional periodic structure, and FIG. 4B is a configuration example in which a circular hole close-packed array is provided as a two-dimensional periodic structure. FIG. 4C shows a configuration example provided with a conical protrusion close-packed array as a two-dimensional periodic structure.

  The self-luminous device having a multilayer structure can exhibit the same effect as a thin structure having an asymmetric structure and a strength ds of 0.1λ to 0.3λ. This is because the light guide of the light emitting layer is combined with the second high refractive index semiconductor layer and is strongly diffracted by the grating of the two-dimensional periodic structure.

  Next, a fourth aspect of the present invention will be described with reference to FIG.

  In FIG. 5, the self-light-emitting device 1 of the fourth aspect includes the two-dimensional periodic structure 10 on the light-emitting surface, and the light extraction efficiency by the refractive index distribution of the layers constituting the self-light-emitting device as in the first aspect. This is a mode of improving the quality.

  The self-light-emitting device 1 according to the fourth aspect includes a first layer, a light-emitting layer that overlaps the first layer, and a second layer that overlaps the light-emitting layer. The surface of the second layer or the surface of the layer overlapping on the second layer has a two-dimensional periodic structure. Here, the first layer is a low refractive index layer, and the refractive index is set lower than that of the light emitting layer and the same as or lower than that of the second layer.

  The fourth aspect can take a plurality of forms. Fig.5 (a)-FIG.5 (c) have shown each form of the 4th aspect.

  The first form of the fourth mode shown in FIG. 5A is a configuration in which the low refractive index layer 20 as the first layer is directly provided below the light emitting layer 3.

  In the configuration in which the light emitting layer 3 and the low refractive index layer 20 are directly bonded, when a good bonding property cannot be obtained between them, a semiconductor layer (for example, p-GaN) is formed on the low refractive index layer 20. The light emitting layer 3 may be stacked with another layer such as a layer) interposed therebetween. In this case, one electrode for supplying power to the light emitting layer 3 can be provided in the semiconductor layer sandwiched therebetween. The p-GaN layer can be effectively used as a layer sandwiched between the low refractive index layer 20 and the light emitting layer 3 because the p-GaN layer has a low electrical resistance and can be thin.

  In the second mode of the fourth mode shown in FIG. 5B, the upper two-dimensional periodic structure 10 and the lower semiconductor layer sandwiching the light emitting layer 3 are formed as a single layer 30, and the single lower layer of the light emitting layer 3 is formed. In this configuration, the low refractive index layer 20 is sandwiched in one layer.

  Further, in the third mode of the fourth mode shown in FIG. 5C, the upper two-dimensional periodic structure 10 and the lower semiconductor layer sandwiching the light emitting layer 3 are formed by a single layer 30, and the single layer 30 The low refractive index layer 20 is provided below.

  In the fourth embodiment, the low refractive index layer 20 has a lower refractive index than that of the light emitting layer 3 and has a refractive index equal to or lower than that of other layers constituting the two-dimensional periodic structure or the like.

  The low-refractive index layer 20 of the fourth aspect may be configured with a single refractive index, or may be configured to have a multilayer film structure by sequentially changing the refractive index. The present invention is characterized in that the light emission efficiency can be increased by a simple configuration in which a low refractive index layer is simply provided below the light emitting layer.

  The thickness of the low refractive index layer is suitably about the same length as the light emission wavelength of the light emitting layer. For example, when the refractive index around the light emitting layer is 2.4 and the refractive index of the low refractive index layer is 2.2, the light emitting layer emits light of approximately 0.5 μm, which is the wavelength of the blue LED. At this time, the effect of increasing the luminous efficiency increases as the thickness of the low refractive index layer increases, and saturates at a thickness of about 0.5 μm, which is the same as the wavelength. If the thickness of the low refractive index layer is approximately the same as the wavelength, it can have a certain range of width. For example, even when the thickness is 0.4 μm, the luminous efficiency can be sufficiently increased.

  In addition, the fact that the effect of increasing the luminous efficiency is saturated at the same thickness as the wavelength means that the same effect can be obtained even when the thickness of the low refractive index device is thicker than this. Yes.

  It should be noted that the thickness of the low refractive index layer of the present invention, which is about the same as this wavelength, is several times more than the thickness of the semiconductor layer usually provided below the light emitting layer.

  In addition, when the refractive index of the low refractive index layer is lowered to, for example, about 2.0 to 1.6, the same effect can be obtained in a direction thinner than the same thickness as the wavelength. This is because the degree of light oozing from the light emitting layer to the low refractive index layer decreases due to the large difference in refractive index from the light emitting layer.

Refractive index of about the 2.0 to 1.6 is, Al ₂ O _{3 (sapphire),} to correspond to the refractive index of AlN (aluminum nitride), Al ₂ O _{3 (sapphire),} a low refractive index of the substrate of AlN (aluminum nitride) By using it as a layer, the self-luminous device of the present invention can be constituted.

  Hereinafter, the light extraction efficiency of each structure of the self-luminous device having a planar structure not including the two-dimensional periodic structure is obtained by a three-dimensional light wave simulation with reference to the light intensity in the single-layer structure, with reference to FIG. Show.

  6A is a plan view of a single layer structure, and FIGS. 6B to 6F are side views of the single layer structure. 6C is an asymmetric structure in which the refractive index is varied, FIG. 6D is a symmetrical structure in which the refractive index is equalized, FIG. 6E is a multilayer structure in which an intermediate layer is provided in the second semiconductor layer, and FIG. f) shows the light extraction efficiency F based on the light intensity in the resin coating structure in which the light emitting surface is covered with the resin cover and the single layer structure. In FIG. 6, the refractive index of air facing the light emitting surface is 1.0.

  In the structure with a single layer shown in FIG. 6B, each refractive index of the first semiconductor layer 2, the light emitting layer 3, and the second semiconductor layer 4 is 2.8, and the intensity of light obtained at this time is used as a reference. Set to “1.00”.

  In the asymmetric structure shown in FIG. 6C, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.78. The light extraction efficiency obtained by this structure is “1.14” based on the light intensity of the structure with a single layer.

  In the symmetrical structure shown in FIG. 6D, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.5. The light extraction efficiency obtained by this structure is “1.02” based on the light intensity of the structure of a single layer.

  In the symmetrical structure shown in FIG. 6E, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, the refractive index of the second semiconductor layer 4 is 2.5, and the second semiconductor layer 4 The refractive index of the intermediate layer 5 provided inside is 2.5. The light extraction efficiency obtained by this structure is “1.02” based on the light intensity of the structure of a single layer.

  In the symmetrical structure shown in FIG. 6 (f), the light emitting surface having the structure of the single layer described above is covered with a resin having a refractive index of 1.45. The light extraction efficiency obtained by this structure is “2.74” based on the light intensity of the structure with a single layer.

  Next, with reference to FIGS. 7 and 8, the light extraction efficiency of each structure of the self-luminous device having the two-dimensional periodic structure is the same as that of the planar light-emitting device not having the two-dimensional periodic structure shown in FIG. The case is shown as a reference.

  Here, based on the optimum parameter range obtained as a result of the three-dimensional light wave simulation, in a self-luminous device having a two-dimensional periodic structure with a close-packed circular hole array, a = 1.5λ, 2r = 0.6a, dh = In a self-luminous device having a two-dimensional periodic structure with a conical protrusion close-packed array, λ is a three-dimensional light wave simulation result with a = 0.5λ and θ = 63 °.

  FIG. 7 shows a case of a two-dimensional periodic structure in a close-packed arrangement of circular holes. Based on the light extraction efficiency of a planar structure, the structure of a single layer (FIGS. 7B and 7G) and the refractive index are shown. Asymmetric structure (FIG. 7 (c), FIG. 7 (h)) to be differentiated, symmetrical structure (FIG. 7 (d), FIG. 7 (i)) having the same refractive index, and a multilayer having an intermediate layer in the second semiconductor layer The light extraction efficiencies of the structures (FIGS. 7 (e) and 7 (j)) and the resin-coated structures (FIGS. 7 (f) and 7 (k)) in which the light emitting surface is covered with the resin cover will be compared.

  FIGS. 7B to 7F show the case where the distance ds between the bottom of the two-dimensional periodic structure and the light emitting layer is 0.3λ to λ, and FIGS. 7G to 7B. (K) is a case of a thin configuration in which the distance ds is 0.1λ to 0.3λ. Further, the refractive index of air facing the light emitting surface in FIG.

  First, the case where the distance ds is a thick structure of 0.3λ to λ will be described with reference to FIGS. 7B to 7F.

  In the structure with a single layer shown in FIG. 7B, the refractive index of each of the first semiconductor layer 2, the light emitting layer 3, and the second semiconductor layer 4 is 2.8, and the light obtained by the structure of FIG. When the strength of the material is “1.00” as the standard, “1.72” is obtained.

  In the asymmetric structure shown in FIG. 7C, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.78. The light extraction efficiency obtained by this structure is “2.94” with respect to the light intensity standard of the single-layer structure of FIG.

  In the symmetrical structure shown in FIG. 7D, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.5. The light extraction efficiency obtained by this structure is “1.84” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the multilayer structure shown in FIG. 7E, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, the refractive index of the second semiconductor layer 4 is 2.5, and the second semiconductor layer 4 The refractive index of the intermediate layer 5 provided inside is 2.5. The light extraction efficiency obtained by this structure is “2.20” with respect to the light intensity standard of the single-layer structure of FIG.

  In the symmetrical structure shown in FIG. 7 (f), the light emitting surface having the structure of the single layer described above is covered with a resin having a refractive index of 1.45. The light extraction efficiency obtained by this structure is “3.62” with respect to the light intensity standard of the single layer structure of FIG.

  Next, the case where the distance ds is as thin as 0.1λ to 0.3λ will be described with reference to FIGS. 7 (g) to 7 (k).

  In the structure with a single layer shown in FIG. 7 (g), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 7 (b) is shown in FIG. 6 (b). It is “1.79” with respect to the light intensity standard obtained by the structure.

  In the asymmetric structure shown in FIG. 7 (h), the light extraction efficiency obtained by the configuration having ds of 0.1λ to 0.3λ in the same configuration as in FIG. 7 (c) is the same as that in FIG. 6 (b). It is “3.97” with respect to the intensity standard of the obtained light.

  In the symmetrical structure shown in FIG. 7 (i), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 7 (d) is the structure of FIG. 6 (b). It is “2.24” with respect to the light intensity standard obtained.

  In the multilayer structure shown in FIG. 7 (j), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 7 (e) is the structure of FIG. 6 (b). It is “3.20” with respect to the intensity standard of the obtained light.

  In the symmetrical structure shown in FIG. 7 (k), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 7 (f) is the structure of FIG. 6 (b). “3.64” with respect to the intensity standard of the light obtained.

  Next, FIG. 8 shows a case of a two-dimensional periodic structure having a conical protrusion close-packed arrangement, and a single-layer structure (FIGS. 8B and 8G) based on the light extraction efficiency of the planar structure, Asymmetric structure (FIGS. 8 (c) and 8 (h)) that varies the refractive index, symmetrical structure (FIGS. 8 (d) and 8 (i)) that equalizes the refractive index, and an intermediate layer on the second semiconductor layer The light extraction efficiency in each of the multi-layered structure (FIGS. 8E and 8J) and the resin-coated structure (FIGS. 8F and 8K) that covers the light emitting surface with a resin cover Compare.

  8B to 8F show a thick structure in which the distance ds between the bottom of the two-dimensional periodic structure and the light emitting layer is set to 0.3λ to λ, and FIGS. (K) is a case of a thin configuration in which the distance ds is 0.1λ to 0.3λ. Further, the refractive index of air facing the light emitting surface in FIG.

  First, the case where the distance ds is a thick structure of 0.3λ to λ will be described with reference to FIGS. 8B to 8F.

  In the structure with a single layer shown in FIG. 8B, the refractive index of each of the first semiconductor layer 2, the light emitting layer 3, and the second semiconductor layer 4 is 2.8, and the light obtained by the structure of FIG. It is “2.11” for the strength standard.

  In the asymmetric structure shown in FIG. 8C, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.78. The light extraction efficiency obtained by this structure is “3.61” with respect to the light intensity standard of the single-layer structure of FIG.

  In the symmetrical structure shown in FIG. 8D, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.5. The light extraction efficiency obtained by this structure is “2.24” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the multilayer structure shown in FIG. 8E, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, the refractive index of the second semiconductor layer 4 is 2.5, and the second semiconductor layer 4 The refractive index of the intermediate layer 5 provided inside is 2.5. The light extraction efficiency obtained by this structure is “2.50” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the symmetrical structure shown in FIG. 8 (f), the light emitting surface having the structure of the single layer described above is covered with a resin having a refractive index of 1.45. The light extraction efficiency obtained by this structure is “3.62” with respect to the light intensity standard of the single layer structure of FIG.

  Next, the case where the distance ds is a thin configuration of 0.1λ to 0.3λ will be described with reference to FIGS. 8 (g) to 8 (k).

  In the structure with a single layer shown in FIG. 8 (g), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 8 (b) is shown in FIG. 6 (b). It is “2.19” against the light intensity standard obtained by the structure.

  In the asymmetric structure shown in FIG. 8 (h), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 8 (c) is the same as that in FIG. 6 (b). It is “4.22” with respect to the intensity standard of the light obtained.

  In the symmetric structure shown in FIG. 8 (i), the light extraction efficiency obtained by the structure in which ds is 0.1λ to 0.3λ in the same structure as in FIG. 8 (d) is the structure shown in FIG. 6 (b). It is “3.47” with respect to the light intensity standard obtained.

  In the multilayer structure shown in FIG. 8 (j), the light extraction efficiency obtained by the structure in which ds is 0.1λ to 0.3λ in the same structure as in FIG. 8 (e) is the structure shown in FIG. 6 (b). It is “4.20” with respect to the intensity standard of the obtained light.

  In the symmetrical structure shown in FIG. 8 (k), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 8 (f) is the structure of FIG. 6 (b). It is "3.67" with respect to the intensity standard of the light obtained.

  The simulation results shown in FIGS. 6, 7, and 8 are summarized in Table 1 below.

  In the table above, the numbers in () indicate the ratio when each structure has a plane structure that does not have a two-dimensional periodic structure as a reference “1.00”.

  According to these simulation results, when the resin cover layer is provided, the improvement is 2.74 times as compared with the case of the single layer. Therefore, the effect of the two-dimensional periodic structure when the resin cover layer is provided is about 1.3 times at most. F = 1.5 can be adjusted by adjusting each layer, but in the case of the resin cover layer, only F >> 2.

  Hereinafter, the light extraction efficiency of each structure of a self-luminous device having a planar structure that is not provided with a two-dimensional periodic structure and is covered with a layer such as a resin cover was obtained by a three-dimensional light wave simulation based on the light intensity in the structure of a single layer. A result is shown using the side view of FIG.

  FIG. 9A is a side view of a single layer structure. 9B is an asymmetric structure in which the refractive index is varied, FIG. 9C is a symmetrical structure in which the refractive index is equalized, FIG. 9D is a multilayer structure in which an intermediate layer is provided in the second semiconductor layer, and FIG. e) and FIG. 9 (f) are structures having a refractive index layer below the light emitting layer, FIG. 9 (e) shows a structure in which the low refractive index layer 20 is sandwiched in a single layer, and FIG. A structure in which the low refractive index layer 20 is provided below the first layer 2 is shown, and the light extraction efficiency F is shown when the light intensity in the single-layer structure is set to be “1.00”. In FIG. 9, the refractive index of the resin cover is 1.45.

  In the single-layer structure shown in FIG. 9A, the refractive index of each of the first semiconductor layer 2, the light emitting layer 3, and the second semiconductor layer 4 is 2.8, and the refractive index of the resin cover is 1.45. The intensity of the light obtained in the above is “1.00”, which is the intensity standard.

  In the asymmetric structure shown in FIG. 9B, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.78. The light extraction efficiency obtained by this structure is “0.99” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the symmetrical structure shown in FIG. 9C, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.5. The light extraction efficiency obtained by this structure is “0.99” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the symmetric structure shown in FIG. 9D, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, the refractive index of the second semiconductor layer 4 is 2.5, and the second semiconductor layer 4 The refractive index of the intermediate layer 5 provided inside is 2.5. The light extraction efficiency obtained by this structure is “0.98” with respect to the light intensity standard of the single layer structure of FIG. 9A.

  In the symmetrical structure shown in FIG. 9E, a low refractive index layer 20 having a refractive index of 2.8 or less is sandwiched in a single first semiconductor layer 2 having a refractive index of 2.8. The light extraction efficiency obtained by this structure is “0.94” with respect to the light intensity standard of the single-layer structure of FIG. 9A.

  In the symmetrical structure shown in FIG. 9F, a low refractive index layer 20 having a refractive index of 2.8 or less is provided below the first semiconductor layer 2 having a refractive index of 2.8. The light extraction efficiency obtained by this structure is “0.95” with respect to the light intensity standard of the structure of the single layer in FIG.

  In addition, the light intensity of the structure with a single layer shown in FIG. 9A is shown in FIG. 6 when the light intensity of the structure with the self-luminous device without the resin cover coating of FIG. Since it becomes “2.74” as shown in (f), the light intensity by each of the structures shown in FIGS. 9A to 9F is an intensity obtained by multiplying the above numerical value by “2.74”.

  Next, referring to FIGS. 10 and 11, the light extraction efficiency of each structure of a self-luminous device having a two-dimensional periodic structure and having a covering structure is shown in the plane not having the two-dimensional periodic structure shown in FIG. A case of a self-luminous device having a structure is shown as a reference.

  Here, based on the optimum parameter range obtained as a result of the three-dimensional light wave simulation, in a self-luminous device having a two-dimensional periodic structure with a close-packed circular hole array, a = 1.5λ, 2r = 0.6a, dh = In a self-luminous device having a two-dimensional periodic structure with a conical protrusion close-packed array, λ is a three-dimensional light wave simulation result with a = 0.5λ and θ = 63 °.

  FIG. 10 shows a case of a two-dimensional periodic structure with a close-packed circular hole arrangement, and an asymmetric structure (FIG. 10 (a), FIG. 10 (f)) in which the refractive index is varied based on the light extraction efficiency of the planar structure. Symmetric structure (FIGS. 10B and 10G) having the same refractive index, multilayer structure including an intermediate layer in the second semiconductor layer (FIGS. 10C and 10H), in a single layer Each of a structure having a low refractive index layer 20 sandwiched between them (FIGS. 10D and 10I) and a structure having a refractive index layer below the light emitting layer (FIGS. 10E and 10J) Compare the light extraction efficiency at.

  FIGS. 10A to 10E show a thick structure in which the distance ds between the bottom of the two-dimensional periodic structure and the light emitting layer is 0.3λ to λ. FIGS. (J) is a thin configuration in which the distance ds is 0.1λ to 0.3λ. The refractive index of the resin cover is 1.45.

  First, the case where the distance ds is a thick structure of 0.3λ to λ will be described with reference to FIGS. 10 (a) to 10 (e).

  In the asymmetric structure shown in FIG. 10A, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.78. The light extraction efficiency obtained by this structure is “1.69” with respect to the light intensity standard of the single-layer structure of FIG. 9A.

  In the symmetrical structure shown in FIG. 10B, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.5. The light extraction efficiency obtained by this structure is “1.24” with respect to the light intensity standard of the single-layer structure of FIG. 9A.

  In the multilayer structure shown in FIG. 10C, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, the refractive index of the second semiconductor layer 4 is 2.5, and the second semiconductor layer 4 The refractive index of the intermediate layer 5 provided inside is 2.5. The light extraction efficiency obtained by this structure is “1.37” with respect to the light intensity standard of the single-layer structure of FIG. 9A.

  Further, in the structure of the low refractive index layer shown in FIG. 10D, the first semiconductor layer 2 has a refractive index lower than the refractive index (2.8) of the light emitting layer 3 and equal to the refractive index of the other layers. A low refractive index layer 20 having a low refractive index is provided. The light extraction efficiency obtained by this structure is “1.73” with respect to the light intensity standard of the single-layer structure of FIG. 9A.

  In the structure of the low refractive index layer shown in FIG. 10E, the refractive index below the light emitting layer 3 is lower than the refractive index (2.8) of the light emitting layer 3 and is equal to or lower than the refractive index of the other layers. A low refractive index layer 20 is provided. The light extraction efficiency obtained by this structure is “1.73” with respect to the light intensity standard of the single-layer structure of FIG. 9A.

  Next, the case where the distance ds is a thin configuration of 0.1λ to 0.3λ will be described with reference to FIGS. 10 (f) to 10 (j).

  In the asymmetric structure shown in FIG. 10 (f), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 10 (a) is the same as that in FIG. 9 (a). It is “2.27” with respect to the light intensity standard obtained.

  In the symmetrical structure shown in FIG. 10 (g), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 10 (b) is the structure of FIG. 9 (a). It is “1.60” with respect to the intensity standard of the obtained light.

  In the multilayer structure shown in FIG. 10 (h), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 10 (c) is the structure of FIG. 9 (a). It is “1.83” with respect to the intensity standard of the obtained light.

  In the low refractive index layer structure shown in FIG. 10 (i), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 10 (d) is shown in FIG. 9 (a). It is “1.91” with respect to the intensity standard of light obtained with the structure.

  In the low refractive index layer structure shown in FIG. 10 (j), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 10 (e) is shown in FIG. 9 (a). It is “1.88” with respect to the intensity standard of light obtained with the structure.

  Next, FIG. 11 shows a case of a two-dimensional periodic structure having a conical projection close-packed arrangement, and an asymmetric structure (FIGS. 11A and 11F) in which the refractive index is varied based on the light extraction efficiency of the planar structure. )), A symmetrical structure (FIGS. 11 (b) and 11 (g)) having the same refractive index, a multilayer structure (FIG. 11 (c), FIG. 11 (h)) having an intermediate layer in the second semiconductor layer, A structure in which the low refractive index layer 20 is sandwiched in a single layer (FIGS. 11D and 11I), and a structure having a refractive index layer below the light emitting layer (FIGS. 11E and 11J) The light extraction efficiency in each of the structures is compared.

  FIGS. 11A to 11E show a thick structure in which the distance ds between the bottom of the two-dimensional periodic structure and the light emitting layer is 0.3λ to λ, and FIGS. (J) is a thin configuration in which the distance ds is 0.1λ to 0.3λ. The refractive index of the resin cover is 1.45.

  First, the case where the distance ds is a thick structure of 0.3λ to λ will be described with reference to FIGS. 11 (a) to 11 (e).

  In the asymmetric structure shown in FIG. 11A, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.78. The light extraction efficiency obtained by this structure is “1.96” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the symmetrical structure shown in FIG. 11B, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, and the refractive index of the second semiconductor layer 4 is 2.5. The light extraction efficiency obtained by this structure is “1.47” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the multilayer structure shown in FIG. 11C, the refractive index of the first semiconductor layer 2 is 2.5, the refractive index of the light emitting layer 3 is 2.8, the refractive index of the second semiconductor layer 4 is 2.5, and the second semiconductor layer 4 The refractive index of the intermediate layer 5 provided inside is 2.5. The light extraction efficiency obtained by this structure is “1.58” with respect to the light intensity standard of the single layer structure of FIG. 9A.

  In the structure of the low refractive index layer shown in FIG. 11D, the first semiconductor layer 2 has a refractive index lower than the refractive index (2.8) of the light emitting layer 3 and equal to the refractive index of the other layers. A low refractive index layer 20 having a low refractive index is provided. The light extraction efficiency obtained by this structure is “1.99” with respect to the light intensity standard of the structure of the single layer in FIG.

  In the structure of the low refractive index layer shown in FIG. 11 (e), the refractive index is lower than the refractive index (2.8) of the light emitting layer 3 below the light emitting layer 3 and is equal to or lower than the refractive index of the other layers. A low refractive index layer 20 is provided. The light extraction efficiency obtained by this structure is “1.97” with respect to the light intensity standard of the structure of the single layer in FIG.

  Next, the case where the distance ds is a thin configuration of 0.1λ to 0.3λ will be described with reference to FIGS. 11 (f) to 11 (j).

  In the asymmetric structure shown in FIG. 11 (f), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 11 (a) is the same as that in FIG. 9 (a). It is “2.37” with respect to the intensity standard of the obtained light.

  In the symmetrical structure shown in FIG. 11 (g), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 11 (b) is the structure of FIG. 9 (a). It is “1.95” with respect to the intensity standard of the obtained light.

  In the multilayer structure shown in FIG. 11 (h), the light extraction efficiency obtained by the structure having ds of 0.1λ to 0.3λ in the same structure as in FIG. 11 (c) is the structure of FIG. 9 (a). It is “2.1” with respect to the intensity standard of the obtained light.

  In the low refractive index layer structure shown in FIG. 11 (i), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 11 (d) is shown in FIG. 9 (a). It is “2.21” with respect to the light intensity standard obtained with this structure.

  In the low refractive index layer structure shown in FIG. 11 (j), the light extraction efficiency obtained by the configuration in which ds is 0.1λ to 0.3λ in the same configuration as in FIG. 11 (e) is shown in FIG. 9 (a). It is “2.13” with respect to the intensity standard of light obtained with the structure.

  The simulation results shown in FIGS. 9, 10, and 11 are summarized in Table 2 below.

  In the table above, the numbers in () indicate the ratio when each structure has a plane structure that does not have a two-dimensional periodic structure as a reference “1.00”.

  According to these simulation results, the light extraction efficiency is improved by 1.73 times to 2.13 times even with a simple configuration in which a low refractive index layer is provided below the light emitting layer.

  FIG. 12 shows the above-described FIGS. 6 to 11 together in one figure. 12, one column on the left side of the upper stage shows FIG. 6, second and third columns from the left side of the upper stage show FIG. 7, and two columns on the right side of the upper stage show FIG. In addition, one column on the left side of the lower stage shows FIG. 9, second and third columns from the left side of the upper stage show FIG. 10, and two columns on the right side of the upper stage show FIG.

  The lower part of FIG. 9 to FIG. 11 and FIG. 12 shows the simulation results when the wavelength λ = 400 μm and the refractive index of the light emitting layer is 2.8. On the other hand, FIG. 13 shows simulation results when the wavelength λ = 400 μm and the refractive index of the light emitting layer is 2.4. It is observed that the light extraction efficiency when the refractive index is 2.4 is lower than that when the refractive index is 2.8, but shows a similar tendency.

  Next, a configuration example and a forming method of the fourth aspect of the self-luminous device of the present invention will be described with reference to FIGS.

FIG. 14A is a first configuration example of the fourth aspect of the self-luminous device. In this configuration example, the second layer 10a having a two-dimensional periodic structure is provided above the light emitting layer 3a, and the first low refractive index layer 20a is provided below the light emitting layer 3a with the layer 31 interposed therebetween. The light emitting layer 3a is made of, for example, InGaN, and the first low-refractive index layer 20a can be made of, for example, AlGaN, Al ₂ O ₃ (sapphire), AlN (aluminum nitride), or the like. The second layer 10a can be n-GaN, and the layer 31 can be p-GaN, which can be formed by changing the Al composition of AlGaN.

  The current supply to the light emitting layer 3 a can be performed by the electrode 32 provided on the second layer 10 a and the electrode 33 provided on the layer 31.

  Since n-GaN can be formed thick, use of the second layer 10a can reduce damage to the lower light emitting layer 3a when the two-dimensional periodic structure is formed by cutting. . Further, since p-GaN has a lower electrical resistance than n-GaN, it is easy to supply current to the surface of the light emitting layer 3a.

  FIG. 14B is a second configuration example of the fourth aspect of the self-luminous device. In this configuration example, a second layer 10a having a two-dimensional periodic structure is provided above the light emitting layer 3a, and a low refractive index layer 20a is provided between the first layers 10b and 10c below the light emitting layer 3a. .

The light emitting layer 3a is made of, for example, InGaN, and the first low-refractive index layer 20a can be made of, for example, AlGaN, Al ₂ O ₃ (sapphire), AlN (aluminum nitride), or the like. The first layers 10b and 10c and the second layer 10a can be formed of n-GaN.

  The current supply to the light emitting layer 3a can be performed by the electrode 32 provided on the second layer 10a and the electrode 33 provided on the first layer 10b.

  FIG. 14C is a third configuration example of the fourth aspect of the self-luminous device. In this configuration example, a second layer 10a having a two-dimensional periodic structure is provided above the light emitting layer 3a, and a first layer 10b and a low refractive index layer 20a are provided below the light emitting layer 3a.

The light emitting layer 3a is made of, for example, InGaN, and the first low-refractive index layer 20a can be made of, for example, AlGaN, Al ₂ O ₃ (sapphire), AlN (aluminum nitride), or the like. The first layer 10b and the second layer 10a can be formed of n-GaN.

  The current supply to the light emitting layer 3a can be performed by the electrode 32 provided on the second layer 10a and the electrode 33 provided on the first layer 10b.

  FIG. 15 is a diagram showing a procedure example for forming the fourth aspect of the self-luminous device of the present invention, and shows a configuration example of FIG.

First, an InGaN layer serving as a light emitting layer is formed on an n-GaN layer, and a p-GaN layer and an Al ₂ O ₃ layer (sapphire) are formed above the InGaN layer. Note that the n-GaN layer and the p-GaN layer can be formed by changing the Al composition of AlGaN (FIG. 15A).

The stack formed in FIG. 15A is inverted, and from below, an Al ₂ O ₃ layer (sapphire), a p-GaN layer, an InGaN layer, and an n-GaN layer are formed (FIG. 15B).

  15A is cut from above to form a two-dimensional periodic structure and a plane for the electrode in the n-GaN layer, and a part of the p-GaN layer is exposed (FIG. 15 ( c)).

  An electrode 32 is formed on a plane on the n-GaN layer formed in FIG. 15A, and an electrode 33 is formed on the exposed surface of the p-GaN layer.

  When the emission wavelength of the self-light-emitting device is in the ultraviolet region, the resin cover is decomposed by the ultraviolet light, so that the configuration with the resin cover is not appropriate. Therefore, in the configuration provided with the resin cover, the configuration provided with the two-dimensional periodic structure is effective for improving the light extraction efficiency.

  As a method for forming a hole (opening) or a recess in a semiconductor portion, a laser processing technique for generating a recess by light irradiation or a semiconductor generation technique such as etching a semiconductor layer using a mask can be used.

  According to the simulation result, when the size of the self-luminous device is fixed and the lattice constant a is variable up to 6λ in the conical protrusion periodic structure, the light extraction efficiency decreases to half of the maximum value. This indicates that light scattering at each element and light diffraction due to the periodicity of the photonic crystal contribute to the same extent on the light extraction efficiency.

  In addition, since the dependence of the lattice constant a is small, the photonic crystal greatly contributes to the light extraction efficiency. In addition, if the size of elements and the degree of close-packed arrangement are optimized to such an extent that the structure is local, periodic, and not significantly deviated from the optimal close-packed arrangement, the same effect can be obtained with other surface structures. You can expect to get

  In the above description, each layer constituting the self-luminous device is described as an example using a semiconductor layer. However, the present invention is not limited to the semiconductor layer, but is configured by another composition such as a glass substrate, such as an organic EL. It can also be applied to the self-luminous device.

  The present invention can be applied to semiconductor LEDs, organic EL, white illumination, lights, indicators, LED communication, and the like.

It is a figure for demonstrating the 1st aspect of this invention. It is a figure for demonstrating the 2nd aspect of this invention. It is a figure which shows the relationship between the periodicity of a two-dimensional periodic structure, and an output. It is a figure for demonstrating the 3rd aspect of this invention. It is a figure for demonstrating the 4th aspect of this invention. It is a figure for demonstrating the simulation result of the light extraction efficiency of each structure of the self-light-emitting device of the planar structure which is not provided with the two-dimensional periodic structure of this invention. It is a figure for demonstrating the simulation result of the light extraction efficiency of each structure of the self-light-emitting device provided with the two-dimensional periodic structure of the circular hole close-packed arrangement of this invention. It is a figure for demonstrating the simulation result of the light extraction efficiency of each structure of the self-light-emitting device provided with the two-dimensional periodic structure of the conical protrusion close-packed array of this invention. It is a figure for demonstrating the light extraction efficiency simulation result of each structure of the self-light-emitting device of the planar structure coat | covered with the resin cover of this invention. It is a figure for demonstrating the simulation result of the light extraction efficiency of each structure of the self-light-emitting device which was provided with the two-dimensional periodic structure of the circular hole close-packed arrangement of this invention, and was made into the covering structure. It is a figure for demonstrating the simulation result of the light extraction efficiency of each structure of the self-light-emitting device which was provided with the two-dimensional periodic structure of the conical protrusion close-packed arrangement | sequence of this invention, and was made into the covering structure. It is a figure which shows the list of the simulation result of the self-light-emitting device of this invention. It is a figure which shows the list of the simulation result of the self-light-emitting device of this invention. It is a figure for demonstrating the structural example of the 4th aspect of the self-light-emitting device of this invention. It is a figure for demonstrating the formation method of the structural example of the 4th aspect of the self-light-emitting device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Self-light-emitting device 2 ... 1st semiconductor layer 3, 3a ... Light emitting layer 4 ... 2nd semiconductor layer 5 ... Intermediate | middle layer 6 ... Resin cover 10 ... Two-dimensional periodic structure 10a ... 2nd layer 10b, 10c ... 1st 1 layer 11 ... circular hole 12 ... bottom 13 ... conical protrusion 14 ... bottom 20, 20a ... low refractive index layer 30 ... single layer 31 ... layer 32, 33 ... electrode

Claims (9)

A first layer;
A light emitting layer overlying the first layer;
A second layer overlying the light emitting layer;
An intermediate layer in the second layer,
The refractive index of the intermediate layer is higher than the refractive index of the first layer and the second layer,
The surface of the second layer or the surface of the layer overlapping on the second layer has a two-dimensional periodic structure,
The intermediate layer is provided in the two-dimensional periodic structure, and the distance between the top of the light emitting layer and the bottom of the two-dimensional periodic structure is 0.1λ to 0.3λ, or 0.3λ to λ (λ is a wavelength in a vacuum). A self-luminous device characterized by that.   The self-luminous device according to claim 1, wherein the thickness of the intermediate layer is 0.5λ or more (λ is a wavelength in a vacuum).   The first layer, the second layer, and the intermediate layer are AlGaN, and the composition ratio of Al in the intermediate layer is lower than the composition ratio of Al in the first layer and the second layer. The self-luminous device according to claim 1 or 2.   The self-luminous device according to any one of claims 1 to 3, wherein the two-dimensional periodic structure is a close-packed array of circular holes or a close-packed array of conical protrusions.   The self-luminous device according to any one of claims 1 to 4, wherein the two-dimensional periodic structure is formed of a photonic crystal.   2. The two-dimensional periodic structure is formed of a photonic quasicrystal having a refractive index quasi-periodic structure having a long-range order and a rotational symmetry without having a translational symmetry with respect to a refractive index. The self-luminous device according to any one of 4 to 4.   The first layer is n-GaN, the light emitting layer is In GaN, and the second layer is p-GaN. Self-luminous device.   The self-luminous device according to any one of claims 1 to 7, further comprising a resin layer overlapping the second layer.   The self-luminous device according to claim 1, wherein the periodicity of the two-dimensional periodic structure has a period range of ½ period to 2 periods.

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