JP2006059864A - Light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the efficiency to a large solid angle or wide spectrum by reducing dependency on band or on angle of field, and to more efficiently pick up lights radiating from a light emitter in air. <P>SOLUTION: The light emitting surface is made to have a quasi-crystal structure without translational symmetry instead of a cyclic structure with translational symmetry, thereby reducing dependency on band or on angle of field related to the cyclic structure as well as improving the pick-up efficiency of emitted lights in air. The light emitting element has a quasi-crystal structure with translation symmetry on the light emitting surface because a grid structure formed of photonic quasi-crystal without translational symmetry is formed on the light emitting surface of the light emitter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Light emitting elements such as light emitting diodes (LEDs) and organic ELs are expected to be used in a wide range of fields such as displays, displays, and lighting. However, the light emitted from a light emitter is externally reflected by total reflection. Since extraction is limited, a problem has been pointed out that 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.

  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, and 3). The periodic structure formed on the semiconductor surface changes the direction of light inside the semiconductor by the wave number converting action of the periodic structure, and takes out the totally reflected light into the air.

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

  There is a demand for more efficient extraction of light emitted from a light emitter in the air.

  In addition, the light emitting device having a periodic structure on the semiconductor surface described above has a slight relationship between the wavelength and the period, and the periodic structure has a band dependency and a viewing angle dependency. There is a problem that there is a limit to improving it.

  The present invention solves the above-mentioned conventional problems, reduces the band dependency and the viewing angle dependency, improves the efficiency with respect to a wide solid angle and a wide spectrum, and more efficiently emits light emitted from a light emitter in the air. The purpose is to take out.

  The present invention reduces the band dependency and the viewing angle dependency associated with the periodic structure by replacing the light emitting surface configuration with a periodic structure having translational symmetry and a quasicrystal configuration without translational symmetry, Improves the efficiency of extracting emitted light into the air.

  The light-emitting element of the present invention has a structure in which a lattice structure of a photonic quasicrystal having no translational symmetry is formed on the light-emitting surface of the light emitter, so that the structure of the light-emitting surface has no quasicrystal structure. And

  Here, in general, a crystal is a solid in which substances are regularly arranged periodically and has translational symmetry that can fill a space by periodically shifting unit cells.

  On the other hand, the quasicrystal does not have the translational symmetry that the crystal has, and has rotational symmetry (for example, 5, 8, 10, 12) that is not allowed in a crystal having normal translational symmetry. . In the present invention, the quasicrystal is different from that in which the periodicity of the crystal is disturbed by a disturbance or the like, and actively deviates from the periodicity based on a predetermined property such as the above-described rotational symmetry. It has such characteristics.

  The photonic crystal is a solid in which two substances having different refractive indexes are regularly arranged with a period of about the wavelength of light.

  Therefore, the photonic quasicrystal of the present invention has a refractive index quasi-periodic structure having a long-range order and a rotational symmetry without having a translational symmetry with respect to the refractive index on the light emitting surface of the light emitter. it can. 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.

  With the above configuration, the refractive index region constituting the photonic crystal has rotational symmetry that is incompatible with translational symmetry in the light emitting surface of the light emitting device of the present invention.

  In more detail, the configuration of the light-emitting element of the present invention includes a plurality of first regions having a first refractive index on the light-emitting surface of the light emitter, and a second refraction different from the first refractive index. The structure includes a plurality of second regions having a ratio, and these regions are arranged according to a pattern of a quasicrystal to form a lattice structure of a photonic quasicrystal. As a result, the first region and / or the second region have a long-range regularity, a short-range irregularity, and a rotational symmetry that is incompatible with translational symmetry.

  In the first form of the lattice structure, one of the first region and the second region is formed by a semiconductor layer, and the other region is formed by being dispersed in the semiconductor layer. The semiconductor layers forming the first region are arranged according to a quasicrystal pattern so as not to have translational symmetry. Then, this part is an opening or a recess formed in the semiconductor layer, and is arranged at the position of the lattice point of the quasicrystal pattern. Thus, by arranging at the lattice point positions of the quasicrystal pattern, the arrangement of the openings or the recesses on the semiconductor layer becomes the quasicrystal pattern arrangement.

  In the second form of the lattice structure, a quasicrystal pattern is formed on the semiconductor layer, and the first region and the second region are arranged in association with each unit cell constituting the quasicrystal pattern. To do. Since each unit cell of the quasicrystal is a quasicrystal pattern that does not have translational symmetry, the first region and the second region that are arranged in correspondence with this pattern have an arrangement that does not have translational symmetry. . And any one of this 1st area | region and 2nd area | region can be made into the opening part or recessed part formed in the unit cell which comprises the pattern of a quasicrystal.

  In the first and second embodiments described above, the opening or the recess is filled with, for example, air. Since the refractive indexes of the semiconductor layer and air are different, the refractive indexes of the first region and the second region are different, so that a photonic quasicrystal is formed.

  In addition, the arrangement pitch of the openings or the recesses is about a fraction of the emission wavelength λ, for example, 0.2 to 1.6 times, and the aperture is about a fraction of the arrangement pitch, for example, 0.3 to 1.0 times.

  The quasicrystalline pattern can be a Penrose tiling pattern or a square-triangular tiling pattern with 12-fold symmetry. An opening or a recess can be formed by a pentagonal pattern included in a Penrose tiling pattern, and an opening or a recess can be formed by a hexagonal pattern included in a square-triangle tiling pattern.

  In the light emitting device of the present invention, the quasi-periodic structure described above is a structure deviating from a complete periodic structure, and the periodic structure and the aperiodic structure are provided on the same light emitting surface. With the periodic structure, it is possible to obtain a high efficiency equal to or higher than that of the photonic crystal in the light extraction, and it is possible to obtain a broadband property and a wide angle property in the light extraction by the non-periodic structure.

  As described above, according to the present invention, it is possible to reduce the band dependency and the viewing angle dependency and improve the efficiency with respect to a wide solid angle and a wide spectrum.

  Further, the light emitted from the light emitter can be extracted more efficiently in the air.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram for explaining a schematic configuration of a light emitting device of the present invention. Here, a light-emitting element is described as an example using a semiconductor.

  In FIG. 1, a light emitting device 1 is configured to emit light emitted from an active layer 3 in contact with the light emitting portion of an LED including an active layer 3 and cladding layers 2 and 4 sandwiching the active layer 3 above and below. And a light emitting surface 5 to be taken out. The refractive index of each layer is, for example, 3.0 for the active layer 3 and 2.7 for the cladding layers 4 and 5.

  The shape shown in FIG. 1 shows an analysis model of a light emitting element, and when λ is an emission wavelength, for example, the vertical and horizontal dimensions are 8λ, and the thickness of three layers. Is 2λ and the thickness of the active layer 3 is 0.3λ, but the dimensions in the vertical and horizontal directions can be arbitrarily set. 1 shows an example of the layered structure of the active layer and the clad layer in the light emitting portion, it can be a bulk structure as will be described later.

  The light emitting device 1 of the present invention includes a light emitting surface 5 on the upper surface of the clad layer 5 on the upper side of the light emitting portion.

  The light emitting surface 5 is configured by forming a hole (or recess) 6 in a semiconductor layer. Since the hole 6 is filled with air, the light emitting surface 5 is composed of two regions having different refractive indexes of the semiconductor portion region and the air portion region formed by the hole 6. A photonic crystal is configured by repeatedly arranging different regions with a period of about the wavelength of light.

  The shape of the hole 6 can be any shape other than a circle. The holes 6 are arranged on the semiconductor layer according to a pattern of quasicrystals having no translational symmetry. The hole 6 of the present invention is a photonic crystal in which the above-described two different refractive index regions are repeated with a period of the order of the wavelength of light, and a photonic quasicrystal (Quasiperiodic Photonic Crystal: QPC) is obtained by following the pattern of the quasicrystal. ).

  As a pattern for forming the quasicrystal, for example, a Penrose tiling pattern or a 12-fold Symmetric pattern can be used.

  Penrose-type photonic quasicrystals have a five-fold rotational symmetry, square-triangle tiling (12-fold Symmetric) photonic quasicrystals have a 12-fold rotational symmetry, Both have rotational symmetry that is not allowed in ordinary crystals with translational symmetry. Note that rotational symmetry is an indistinguishable property before and after the rotation of the figure, and the five-fold rotational symmetry is that the figures overlap with each other by rotation of 72 ° (= 360 ° / 5) and the rotation is 12-fold symmetrical. The symmetry is that the figures overlap with each other by rotation of 30 ° (= 360 ° / 12). In FIG. 1, the holes 6 are arranged based on 12-fold rotational symmetry.

  The light emitting surface 5 may be configured to use the upper surface portion of the cladding layer 5, or may be configured to form a semiconductor layer above the cladding layer 5. Further, the circular hole 6 can use a laser processing technique for forming a recess in the semiconductor layer by laser light irradiation, or a semiconductor generation technique such as etching the semiconductor layer using a mask.

  The light emitted from the active layer 3 is emitted from the light emitting surface 5 to the outside (air side). At this time, the light-emitting surface 5 of the light-emitting element 1 of the present invention improves the light extraction efficiency from the light-emitting body to the outside by forming a photonic quasicrystal structure on the light-emitting surface. Broadband and wide angle are improved.

  Hereinafter, with reference to FIG. 2, in the light emitting device using the photonic quasicrystal (QPC-LED) according to the present invention, the intensity distribution with respect to the incident angle of light and the simulation result of the radiation power extracted from the light emitting device to the outside Compared with a flat LED (planar LED) and a photonic crystal LED (PC-LED).

  In the simulation, the wavelength is changed in a range where the cell size is 1/10 or less of n (refractive index), and excitation is given to only one point of the Ey component at the central portion in the active layer. In FIG. 2, the wavelength λ = 1.00 μm, the pitch a = 0.6λ, the circular hole diameter 2r / a = 0.66, and the cross-sectional electric field distribution at this time is shown in FIG. The distribution is shown in FIG. 2B, the intensity distribution with respect to the incident angle of light on the light emitting surface is shown in FIG. 2C, and the time variation of the radiation pattern is shown in FIG. 2A to 2D, the left side is a simulation result by a flat LED, the center is a simulation result by a PC-LED, and the right side is a simulation result by the QPC-LED of the present invention.

  As shown in the intensity distribution with respect to the incident angle of light in FIG. 2 (c), in a light emitting element using a flat LED, light in a narrow range within a total reflection angle θ1 = 21.7 ° determined by the refractive index difference between the cladding and air. In contrast, light-emitting elements using PC-LEDs and QPC-LEDs can extract light with a total reflection angle or more.

  In addition, as shown in the radiation pattern of FIG. 2 (d), the light emitting element using the QPC-LED can obtain 1.7 times the output of the light emitting element using the flat LED. On the other hand, an output of 1.2 times can be obtained.

  Next, the change of the radiation power with respect to the circular hole diameter 2r and the pitch a is shown using FIG. Here, an analysis result in which the pitch a is fixed and the emission wavelength λ and the circular hole diameter 2r are changed is shown. Fig. 3 (a) shows the change in the radiation power of the PC-LED standardized by the flat LED with respect to the hole diameter and pitch, and Fig. 3 (b) shows the change in the radiation power of the QPC-LED similarly normalized. Show. In FIG. 3A, a high output is obtained in the range of 2r / a = 0.6 to 0.8 in the PC-LED using the photonic crystal, and the maximum is about 1.5 times that of the planar LED. . On the other hand, FIG. 3B shows that in the QPC-LED using the photonic quasicrystal of the present invention, the highest output 1.8 times can be obtained when 2r = 0.5λ and a = 0.6λ. Yes.

  In FIG. 3, the black circle mark is 2r / a = 0.8, the black square mark is 2r / a = 0.75, the black triangle mark is 2r / a = 0.66, and the white circle mark is 2r / a = 0. 60, white square mark 2r / a = 0.50, white triangle mark 2r / a = 0.40, and x mark 2r / a = 0.33.

  According to the simulation results shown in FIGS. 2 and 3, the efficiency for a wide solid angle and a wide spectrum is improved and the band dependency and the viewing angle dependency are reduced by using the light emitting element of the photonic quasicrystal of the present invention. be able to.

  Next, a comparison between the layer structure and the bulk structure of the light emitter will be described with reference to FIGS.

When the light emitter has a layer structure of an active layer and a clad layer, the light emitted from the active layer undergoes total reflection due to the difference in refractive index between the active layer and the clad layer as shown in FIG. Looking at the influence on the radiation power of the light confined in the active layer without being guided through the cladding layer, the refractive indexes of the active layer, the cladding layer, and air are 3.0, 2.7, and 1.0, respectively. The total reflection angle θ1 at the interface between the cladding layer and air is expressed by the following equation (1).
Sin ⁻¹ (nAir / nClad) = 21.74 ° (1)

Similarly, the total reflection angle θ2 at the interface between the active layer and the clad layer is also expressed by the following equation (2).
Sin ⁻¹ (nClad / nAct) = 64.16 ° (2)

  From the above equation (2), light traveling from the active layer at an incident angle of 64.16 ° or more is confined in the active layer.

  Here, when a bulk structure without an active layer is used, all light is guided to the cladding layer, so that the output is improved in a PC-LED or QPC-LED that can extract light traveling at a total reflection angle or more.

  FIG. 5 shows time-dependent changes in the vertical cross-section electric field distribution and radiation power when there is an active layer and when there is no active layer and a bulk structure in a planar LED and a QPC-LED.

  At this time, when the wavelength λ = 1.00 μm, the QPC pitch a = 0.6λ, and the circular hole diameter 2r / a = 0.66, the light is vertically elongated due to the refractive index when there is an active layer, When there is no active layer, the shape is close to a perfect circle.

  The output without the active layer is 0.9 times that of the planar LED compared with the case of having the active layer, whereas the QPC-LED shows almost no change. This is presumed to capture a large amount of light traveling at a total reflection angle or more for the amount of decrease in the vertical direction.

  As a pattern for forming a photonic quasicrystal for constituting the light emitting device of the present invention, for example, a Penrose-type pattern or a square-triangle tiling pattern is used. Can do. Hereinafter, a pattern example for forming a photonic quasicrystal will be described with reference to FIG.

  FIG. 6A shows a pattern of Penrose tiling (Penrose-type), and FIG. 6B shows a pattern of square-triangle tiling (12-fold Symmetric).

  Penrose tiling (Penrose-type) pattern 11 shown in FIG. 6A has a five-fold rotational symmetry. The Penrose tiling is formed by adjacent diamond-shaped unit cells 12 and 13 having different angles (diamonds having inner angles of 36 ° and 144 ° and diamonds having inner angles of 72 ° and 108 °). By affixing in a plane, a non-periodic pattern having a 5-fold symmetry axis can be formed.

  In order to construct the structure of the photonic quasicrystal using the Penrose-type pattern, various modes can be used.

  For example, in the first aspect, the photonic quasicrystal can be formed by dividing the Penrose tiling pattern into a dodecagonal region 14 and other regions and making the refractive indexes of the two regions different from each other. Here, the different refractive indexes can be formed, for example, by forming holes (openings) or recesses in the decagonal region 14 in the semiconductor plane, and the refractive index portion of the semiconductor and the refractive index portion of air. Different refractive indices can be repeated depending on the case.

  Further, in the second aspect, it can be formed by forming a hole (opening) or a recess at the apex 15 of the lattice structure constituting the Penrose tiling in the plane of the semiconductor. Different refractive indices can be repeated depending on the refractive index portion.

  In the third aspect, the photonic quasicrystal can be formed by making the refractive indexes of the two types of rhombus patterns (unit lattices 12 and 13) constituting the Penrose tiling different from each other. Here, different refractive indexes can be formed, for example, by forming holes (openings) or recesses in one type of rhombus pattern on the semiconductor plane, and the refractive index portion of the semiconductor and the refractive index portion of the air Different refractive indices can be repeated according to the above.

  The square-triangle tiling (12-fold Symmetric) photonic quasicrystal shown in FIG. 6B has 12-fold rotational symmetry.

  Square-triangular tiling is formed by adjacent square and triangular unit cells 22 and 23, and this unit cell is bonded in a plane to form a 12-fold symmetry axis and an aperiodic pattern. Can do.

  In order to construct the structure of the photonic quasicrystal using the pattern of the square-triangle tiling (12-fold Symmetric), various modes can be used.

  For example, in the first embodiment, a photonic quasicrystal can be formed by dividing a square-triangle tiling pattern into a dodecagonal region 24 and other regions and making the refractive indexes of both regions different from each other. . Here, the different refractive indexes can be formed, for example, by forming holes (openings) or recesses in the dodecagonal region 24 in the semiconductor plane, and the refractive index portion of the semiconductor and the refractive index portion of air. Different refractive indices can be repeated depending on the case.

  Further, in the second aspect, it can be formed by forming a hole (opening) or a recess at the apex 25 of the lattice structure constituting the square-triangle tiling in the semiconductor plane, and the refractive index portion of the semiconductor Different refractive indices can be repeated depending on the refractive index portion of the air.

  In the third aspect, the photonic quasicrystal can be formed by making the refractive indexes of the two types of unit cells (square pattern and triangle pattern) constituting the square-triangle tiling different from each other. Here, the different refractive indexes can be formed, for example, by forming holes (openings) or recesses in one unit cell in the semiconductor plane, depending on the refractive index portion of the semiconductor and the refractive index portion of the air. Different refractive indices can be repeated.

  For example, gallium nitride (GaN) or GaInAsP can be used as the semiconductor constituting the light emitting element and the light emitting surface.

  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.

  In the above description, the configuration of the semiconductor LED is described as an example, but the same applies to a configuration in which extraction of light from the light emitting portion is restricted by total reflection at a boundary portion between the light emitting portion and the outside. By applying the light emitting surface having the lattice structure of the photonic quasicrystal of the present invention, the light extraction efficiency can be increased, and the viewing angle dependency can be reduced to obtain a high solid angle. Can do.

  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 schematic structure of the light emitting element of this invention. It is a figure which shows the simulation result of the intensity distribution with respect to the incident angle of light, and the radiation power taken out in the light emitting element by the photonic quasicrystal (QPC-LED) of this invention. It is a figure which shows the change of the radiation power with respect to the circular hole diameter and pitch of the light emitting element of this invention. It is a figure for demonstrating a layer structure and a bulk structure in the light emission part of this invention. It is a figure which shows the time-dependent change of the longitudinal cross-section electric field distribution and radiation power by a layer structure and a bulk structure. It is a figure for demonstrating the example of a pattern which forms a photonic quasicrystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting element 2 ... Cladding layer 3 ... Active layer 4 ... Cladding layer 5 ... Light emitting surface 6 ... Hole 11 ... Pattern 12, 13 ... Unit lattice 14 ... Decagonal region 15 ... Vertex 21 ... Pattern 22, 23 ... Unit Grid 24 ... Dodecagonal area 25 ... Vertex

Claims (13)

  A light-emitting element, wherein a lattice structure of a photonic quasicrystal having no translational symmetry is formed on a light-emitting surface of a light-emitting body. A light-emitting element 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 on a light-emitting surface of a light-emitting body.   A light-emitting element, wherein refractive index regions constituting a photonic crystal are arranged on a light-emitting surface of a light emitter according to a quasi-crystal pattern having no translational symmetry.   The light emitting device according to claim 3, wherein the refractive index region has rotational symmetry that is incompatible with translational symmetry. A plurality of first regions having a first refractive index and a plurality of second regions having a second refractive index different from the first refractive index are formed on a light emitting surface of the light emitter according to a quasicrystal pattern. To form a lattice structure of photonic quasicrystals,
The first region and / or the second region have a long-range regularity, a short-range irregularity, and a rotational symmetry that is incompatible with a translational symmetry. In the lattice structure, one region of the first region or the second region is a semiconductor layer, and the other region of the first region or the second region is a portion that is formed in the semiconductor layer,
6. The light emitting device according to claim 5, wherein the portions are arranged according to a quasicrystal pattern having no translational symmetry. The part is an opening or a recess formed in the semiconductor layer,
The light emitting device according to claim 6, wherein the arrangement position of the openings or the recesses is a position of a lattice point of a quasicrystal pattern.   The lattice structure is characterized in that on the semiconductor layer, the first region and the second region are arranged in association with unit cells constituting a pattern of a quasicrystal having no translational symmetry. 5. The light emitting device according to 5.   9. The light emitting device according to claim 8, wherein one of the first region and the second region is an opening or a recess formed in a unit cell constituting the pattern of the quasicrystal.   The arrangement pitch of the openings or recesses is about 0.2 to 1.6 times the emission wavelength λ, and the aperture is about 0.3 to 1 times the arrangement pitch. 9. The light emitting device according to 9.   11. The light emitting device according to claim 1, wherein the quasicrystal pattern is a Penrose tiling pattern or a square-triangle tiling pattern having 12-fold symmetry.   The light emitting device according to claim 11, wherein the opening or the recess is formed by a dodecagonal pattern included in the Penrose tiling pattern. The light emitting device according to claim 11, wherein the opening or the recess is formed by a hexagonal pattern included in the square-triangle tiling pattern.