JP2009038293A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device capable of preventing polarized light emitted by a light emitting element from being disordered. <P>SOLUTION: The light emitting device 1 includes the light emitting element 2 which emits the polarized light 20 whose linear polarized component is not uniform, but deviates, and a mounting base 3 on which the light emitting element is mounted. The light emitting element 2 is constituted of a nitride semiconductor having a nonpolar surface or semi-polar surface as a principal surface. The mounting base has a mounting surface 30 sectioned in a recessed shape and serving also as a reflector 30R, and the mounting surface and the surface of the reflector are made into a metal coating surface 35 to serve as a mirror surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light emitting device, and more particularly to a light emitting device on which a light emitting element that emits polarized light is mounted.

  For example, an optical element (light guide plate) that changes the propagation direction of light incident from a light emitting element and outputs the light is used for a backlight of a liquid crystal display or the like. The light output from the light guide plate is input to the liquid crystal panel via the polarizing plate, and an image can be displayed on the liquid crystal display. Light incident on the light guide plate (hereinafter simply referred to as “incident light”) is scattered inside the light guide plate, and then the scattered light can be uniformly emitted over the entire light emitting surface from which the light is extracted. That is, a reflection pattern is formed on the surface of the reflection surface that reflects incident light inside the light guide plate. The incident light is directed by the reflection pattern and propagates inside the light guide plate, and propagates inside the light guide plate. Light is output from the light emitting surface.

In recent years, there is a tendency to employ light emitting elements that use output light as deflected light. If this type of light-emitting element is used as a light source for a liquid crystal backlight or projector, the light component cut by the polarizing plate is reduced, and the luminous efficiency can be improved. Expectations are made as described.
T. Takeuchi et al., “Japanese Journal of Applied Physics vol.39”, 2000, pages 413-416.

  A light emitting element that emits deflected light is mounted on a package substrate by die bonding, and the mounted light emitting element is molded with a light-transmitting resin. An LED (light emitting diode) is used as the light emitting element. In this type of light emitting element, not only the deflected light is emitted from the surface facing the irradiated surface, but also the deflected light is emitted from the end face and the back face. In order to effectively use such deflected light and improve the light emission efficiency, the package substrate is provided with a reflector surface that reflects the deflected light emitted from the end face and the back face of the light emitting element to the irradiated surface.

  However, the package substrate is made of, for example, ceramics, and the inner surface including the reflector on which the light emitting element of the package substrate is mounted is uneven and rough. For this reason, irregular reflection occurs in the deflected light emitted from the end surface and the back surface of the light emitting element on the inner surface of the package substrate, and the deflected light emitted from the light emitting device is disturbed.

  The present invention has been made to solve the above problems. Accordingly, the present invention is to provide a light emitting device capable of preventing the disturbance of the deflected light emitted from the light emitting element.

  In order to solve the above problems, a first feature of the present invention is that in a light emitting device, a light emitting element that emits polarized light and a light emitting element are mounted, and at least a part of an inner surface on which the light emitting element is mounted is a mirror surface. A certain implementation base. In the light emitting device according to the first feature, the inner surface of the mounting base further includes a mounting surface on which the light emitting element is mounted and a reflector that reflects the polarized light emitted from the light emitting element, and the mounting surface and the reflector are mirror surfaces. It is preferable. In the light emitting device according to the first feature, it is preferable that the mirror surface is a surface in which the inner surface or the mounting surface and the surface roughness of the reflector are set to ¼ or less of the wavelength of the deflected light emitted from the light emitting element. In the light emitting device according to the first feature, the mirror surface is preferably a surface in which the inner surface or the mounting surface and the surface roughness of the reflector are set to 100 nm or less. In the light emitting device according to the first feature, the mirror surface is preferably a metal coating surface. In the light emitting device according to the first feature, the mounting base is preferably made of ceramics, and the metal coating surface is preferably a coating surface of either aluminum or silver. Furthermore, in the light-emitting device according to the first feature, the light-emitting element is formed of a group III nitride semiconductor having a nonpolar plane or a semipolar plane as a main surface, the first conductivity type first semiconductor layer, A light emitting layer on the semiconductor layer and a second semiconductor layer of the second conductivity type on the light emitting layer are preferably provided.

  According to a second aspect of the present invention, in the light emitting device, the light emitting element that emits deflected light and has a mirror end surface, and the light emitting element are mounted, and at least a part of the inner surface on which the light emitting element is mounted is a mirror surface. And a base.

  ADVANTAGE OF THE INVENTION According to this invention, the light-emitting device which can prevent disorder of the deflection | deviation light emitted from the light emitting element can be provided.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic and different from actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained. Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is to arrange the components and the like as follows. Not specific. The technical idea of the present invention can be variously modified within the scope of the claims.

(First embodiment)
In the first embodiment of the present invention, an example in which an LED is used as a light emitting element and the present invention is applied to a light emitting device having a surface mounting structure will be described.

[Configuration of light emitting device]
As shown in FIG. 1, the light-emitting device 1 according to the first embodiment includes a light-emitting element 2 that emits deflected light 20 and has an end surface 2W that is a mirror surface, and the light-emitting element 2, and the light-emitting element 2 is mounted. And a mounting base 3 in which at least a part of the inner surface is a mirror surface. Further, the light emitting device 1 includes a light transmissive resin portion 4 that covers the light emitting element 2 and transmits the deflected light 20 emitted from the light emitting element 2.

[Implementation-based configuration]
The mounting base 3 is a package substrate having a surface type structure in the first embodiment, and includes a mounting surface 30 having a concave cross-sectional shape that also serves as the reflector 30R. The light emitting element 2 is mounted on the bottom surface of the mounting surface 30 of the mounting base 3, and a reflector 30 </ b> R having a tapered surface is formed on the mounting base 3 around the side surface of the mounted light emitting element 2. The mounting surface 30 and the reflector 30R are integrally formed. In the first embodiment, ceramics such as AlN and Al ₂ O ₃ can be practically used for the mounting base 3, and this ceramic is manufactured by a firing method.

  A metal coating surface 35 is disposed on the inner surface on which the light emitting element 2 of the mounting base 3 is mounted, that is, the mounting surface 30 and the reflector 30R, and the metal coating surface 35 is a mirror surface. The light emitting element 1 is electrically and mechanically connected to the mounting surface 30 via the conductive adhesive 6. For example, a silver (Ag) paste can be practically used for the adhesive 6.

  Here, the “mirror surface” refers to reducing irregular reflection of the deflected light 20R emitted from the end surface 2W and the back surface of the light emitting element 1 in addition to the deflected light 20 emitted from the surface facing the irradiated surface of the light emitting element 1. It is used to mean a reflecting surface that does not disturb the polarization characteristics of the deflected light 20. Specifically, if the surface has a surface roughness equal to or less than ¼ of the wavelength of the deflected light 20R emitted from the light emitting element 1, the deflected light 20R that reflects the surface will not be irregularly reflected. For example, when the wavelength of the deflected light 20R emitted from the light emitting element 1 is 400 nm, the surface roughness of the metal coating surface 35 is set to 100 nm or less.

  In the first embodiment, a metal thin film having a high reflectivity of either aluminum (Al) or Ag formed by electrolytic plating can be practically used for the metal coating surface 35. These metal thin films are formed with a film thickness of, for example, several hundred nm to several μm. In addition, other film-forming methods, such as a vapor deposition method and sputtering method, can be used for the film-forming method of a metal thin film.

[Configuration of Light Emitting Element]
The light emitting element 2 is an LED that emits the deflected light 20 in the first embodiment. Here, “polarized light” means that the linearly polarized light component is not uniform (random) but biased, but in the first embodiment, it is not necessary to be 100% linearly polarized light. Therefore, the polarization direction of the deflected light 20 is the direction with the largest linearly polarized light component.

  For example, as illustrated in FIG. 2, the light emitting element 2 according to the first embodiment includes a light emitting unit 220 that generates the deflected light 20 and the deflected light 20 that is mounted on the light emitting unit 220 and is emitted from the light emitting unit 20. And an output unit (substrate) 210 for outputting.

The light emitting unit 220 uses a non-polar plane or a semi-polar plane of a GaN crystal as a crystal growth surface, and includes a first semiconductor layer 221 of the first conductivity type, an active layer 222, and Each of the second conductivity type second semiconductor layers 223 is sequentially stacked in the normal direction of the crystal growth surface. For example, if the crystal growth surface is an m-plane that is a nonpolar plane, the light-emitting element 2 is composed of a group III nitride semiconductor having the m-plane as a main surface. Examples of the group III nitride semiconductor include aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN). A typical group III nitride semiconductor is represented by Al _x In _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). The GaN semiconductor is a group III-V compound semiconductor well known among hexagonal compound semiconductors containing nitrogen.

  The active layer 222 is supplied with carriers of the first conductivity type from the first semiconductor layer 221 and supplied with carriers of the second conductivity type from the second semiconductor layer 223. When the first conductivity type is n-type and the second conductivity type is p-type, the electrons supplied from the first semiconductor layer 221 and the holes supplied from the second semiconductor layer 223 in the active layer 222 are regenerated. Coupling is performed, and the polarized light 20 is emitted from the active layer 222. The active layer 222 may employ, for example, a quantum well structure in which a well layer (well layer) is sandwiched between barrier layers (layer barrier layers) having a larger band gap than the well layer. it can. The quantum well structure includes not only one well layer but a multiplexed quantum well structure, and further includes a quantum well structure in which the active layer 222 has a multiple quantum well (MQW) structure.

  Usually, light extracted from an active layer made of a group III nitride semiconductor having a c-plane which is a polar plane of a GaN crystal as a crystal growth surface is in a randomly polarized (non-polarized) state. On the other hand, a strong polarization state is realized in the light extracted from the active layer 222 formed by using a group III nitride semiconductor whose crystal growth surface is a non-polar surface or semipolar surface such as a-plane, m-plane other than c-plane can do. For example, when the active layer 222 is configured with the m-plane as the main surface, the polarized light 20 containing a large amount of polarized light components parallel to the m-plane, more specifically, the polarized light components in the a-axis direction, is generated from the active layer 222. Can do. Detailed descriptions of the nonpolar plane and the semipolar plane will be described later.

  The light emitting unit 220 is formed by growing on the crystal growth surface of the output unit 210 by crystal growth. That is, as shown in FIG. 2, the light emitting element 2 includes an output unit 210, the output unit 210, the first semiconductor layer 221 on the output unit 210, and the active layer 222 on the first semiconductor layer 221. And a second semiconductor layer 223 on the active layer 222. In the first embodiment, the output unit 210 is composed of, for example, a GaN single crystal substrate. In the case where the main surface that is a non-polar surface is the main surface serving as the crystal growth surface of the output unit 10, the light emitting unit 220 can be formed on this main surface by crystal growth. That is, the light emitting section 220 is composed of GaN having the m plane as the crystal growth principal surface, and the light emitting element 2 is composed of a group III nitride semiconductor grown with the m plane as the crystal growth principal surface. The main surface of the output unit 210 is the same as the crystal growth surface of the light emitting unit 220.

  The light emitting element 2 further includes a first electrode 211 that supplies an operating voltage to the first semiconductor layer 221 and a second electrode 212 that supplies an operating voltage to the second semiconductor layer 223. As shown in FIG. 2, the first electrode 211 is formed on the surface where the second semiconductor layer 223, the active layer 222, and a part of the first semiconductor layer 221 are partially removed by mesa etching and the first semiconductor layer 221 is exposed. Is disposed. The first semiconductor layer 221 and the first electrode 211 are electrically connected. The second electrode 212 is disposed on the second semiconductor layer 223. The second semiconductor layer 223 and the second electrode 212 are electrically connected.

  For example, aluminum (Al) is used for the first electrode 211, and palladium (Pd) -gold (Au) alloy is used for the second electrode 212, for example. The first electrode 211 is ohmically connected to the first semiconductor layer 211, and the second electrode 212 is ohmically connected to the second semiconductor layer 233. A first conductivity type contact layer may be interposed between the first semiconductor layer 221 and the first electrode 211. In addition, a second conductivity type contact layer may be interposed between the second semiconductor layer 223 and the second electrode 212.

  In the light emitting element 2, the surface (back surface) facing the crystal growth surface (main surface or surface) in contact with the first semiconductor layer 221 of the output unit 210 is an output surface 210A. The deflected light 20 emitted from the active layer 222 is output from the output surface 210A to the outside of the light emitting element 2 as output light.

  The end surface 2W of the light emitting element 2 is a mirror surface, similar to the metal coating surface 35 disposed on the mounting surface 30 of the mounting base 3 and the reflector 30R. The end surface 2W is made into a mirror surface by a processing technique such as etching and polishing (for example, chemical mechanical polishing: CMP) after the light emitting element 2 is cut into chips by cleavage.

[Crystal structure of light-emitting element]
The crystal structure of the group cell of III nitride semiconductor constituting the light emitting element 2 can be approximated by a hexagonal crystal structure as shown in FIGS. In the hexagonal crystal structure, the c-axis is a crystal axis along the axial direction of the hexagonal column. The surface (the top surface of the hexagonal column) having the c-axis as a normal line is a c-plane {0001}. When a group III nitride semiconductor crystal is cleaved in two planes parallel to the c-plane, the + c-axis side plane (+ c plane) becomes a crystal plane in which group III atoms are arranged. The plane on the −c axis side (−c plane) is a crystal plane in which nitrogen atoms are arranged. For this reason, the c-plane is called a polar plane because it exhibits different properties on the + c-axis side and the −c-axis side.

  As shown in FIG. 4, four nitrogen atoms are bonded to one group III atom. The four nitrogen atoms are located at the four vertices of a regular tetrahedron with a group III atom arranged in the center. Of these four nitrogen atoms, one nitrogen atom is located in the + c axis direction with respect to the group III atom, and the other three nitrogen atoms are located on the −c axis side with respect to the group III atom. Since it has such a crystal structure, the polarization direction is along the c-axis in the group III nitride semiconductor.

  In the hexagonal crystal structure, each side surface of the hexagonal column is an m-plane {1-100}. A plane passing through a pair of ridge lines that are not adjacent to each other is a-plane {11-20}. The m-plane and the a-plane are crystal planes perpendicular to the c-plane and are orthogonal to the polarization direction, and thus are nonpolar planes, that is, nonpolar planes. Furthermore, since the crystal plane that is inclined with respect to the c-plane (not parallel to the c-plane or perpendicular to it) crosses the polarization direction obliquely, it is a slightly polar plane, that is, a semipolar plane (Semi-polar plane). Specific examples of the semipolar plane include a {10-11} plane shown in FIG. 5A and a {10-13} plane shown in FIG. 5B.

[Light transmissive resin part]
In the light emitting device 1 according to the first embodiment, the light transmissive resin portion 4 shown in FIG. 1 is filled in a recess formed by the mounting surface 30 and the reflector 30R, covers the light emitting element 2, and the light emitting element 2 transmits the deflected light 20 emitted from the front surface 2 and the deflected light 20R emitted from the end surface 2W and the back surface and reflected by the reflector 30R. For the light transmissive resin portion 4, for example, either a silicone resin or an epoxy resin can be used practically. In the first embodiment, the light transmissive resin portion 4 is not limited to these resin materials.

  In the light emitting device 1 according to the first embodiment configured as described above, since the inner surface on which the light emitting element 2 of the mounting base 3 is mounted is a mirror surface, the deflection is emitted from the end surface 2W and the back surface of the light emitting element 2. The irregular reflection of the light 20R can be reduced, and the disturbance of the deflected light 20 can be reduced. Furthermore, in the light emitting device 1 according to the first embodiment, since the end surface 2W of the light emitting element 2 is a mirror surface, the irregular reflection of the deflected light 20R on the end surface 2W can be reduced, and the disturbance of the deflected light 20 is reduced. can do.

(Second Embodiment)
In the second embodiment of the present invention, an example in which the present invention is applied to a light emitting device having a shell-type package structure instead of the light emitting device 1 having the surface mounting structure according to the first embodiment described above will be described. To do.

  As shown in FIG. 6, in the light emitting device 1 according to the second embodiment, the light emitting element 2 that emits the deflected light 20 and the end surface 2W is a mirror surface, and the light emitting element 2 are mounted, and the light emitting element 2 is mounted. And a mounting base 3 whose inner surface is a mirror surface. Further, the light emitting device 1 includes a light transmissive resin portion 4 that covers the light emitting element 2 and transmits the deflected light 20 emitted from the light emitting element 2.

  In the second embodiment, the mounting base 3 is disposed at one end of the lead 31 and is configured integrally with the lead 31. The lead 31 is used as a cathode electrode in the second embodiment. The basic configuration of the mounting base 3 is the same as that of the mounting base 3 of the light emitting device 1 according to the first embodiment described above, and includes a mounting surface 30 having a concave cross-sectional shape that also serves as the reflector 30R. The light emitting element 2 is mounted on the bottom surface of the mounting surface 30 of the mounting base 3, and a reflector 30 </ b> R having a tapered surface is formed on the mounting base 3 around the side surface of the mounted light emitting element 2. On the inner surface on which the light emitting element 2 of the mounting base 3 is mounted, that is, on the mounting surface 30 and the reflector 30R, a metal coating surface 35 is formed as in the mounting base 3 of the light emitting device 1 according to the first embodiment described above. It is arranged.

  A lead 32 is disposed in a region close to the lead 31. The lead 32 is used as an anode electrode, and one end of the lead 32 is not connected with a symbol but is electrically connected to the light emitting element 2 through a wire.

  The light transmissive resin portion 4 covers the mounting base 3 at one end of the lead 31 and one end of the lead 32, and a hemispherical lens portion 42 on the light emitting element 20, that is, a portion that emits the deflected light 20 from the light emitting element 2. Have As the light-transmitting resin portion 4, either a silicone resin or an epoxy resin is practically used as in the light-transmitting resin portion 4 of the light emitting device 1 according to the first embodiment described above. be able to.

  In the light emitting device 1 according to the second embodiment configured as described above, the same effect as that obtained by the light emitting device 1 according to the above-described first embodiment can be obtained.

(Other embodiments)
As described above, the present invention has been described according to the first embodiment and the second embodiment described above. However, the description and the drawings constituting a part of this disclosure do not limit the present invention.

  As described above, the present invention includes various embodiments and the like not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a block diagram of the light-emitting device which concerns on the 1st Embodiment of this invention. It is principal part sectional drawing which shows the structure of the light emitting element of the light-emitting device shown in FIG. FIG. 3 is a crystal structure diagram for explaining a nonpolar plane of a group III nitride semiconductor of the light emitting device shown in FIG. 2. FIG. 3 is a crystal structure diagram illustrating an atomic arrangement of a group III nitride semiconductor of the light emitting device shown in FIG. 2. (A) And (B) is a crystal structure figure explaining the semipolar surface of the group III nitride semiconductor of the light emitting element shown in FIG. It is a block diagram of the light-emitting device which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light-emitting device 2 ... Light-emitting element 20, 20R ... Deflection light 210 ... Output part 210A ... Output surface 211 ... 1st electrode 212 ... 2nd electrode 220 ... Light-emitting part 221 ... 1st semiconductor layer 222 ... Active layer 223 ... 2nd Semiconductor layer 3 ... mounting base 30 ... mounting surface 30R ... reflector 35 ... metal coating surface 4 ... light transmitting resin portion

Claims (6)

A light emitting element that emits polarized light;
A mounting base on which the light emitting element is mounted, and at least a part of the inner surface on which the light emitting element is mounted is a mirror surface;
A light-emitting device comprising: The mounting base inner surface further includes a mounting surface on which the light emitting element is mounted, and a reflector that reflects the deflected light emitted from the light emitting element,
The light emitting device according to claim 1, wherein the mounting surface and the reflector are mirror surfaces.   2. The mirror surface according to claim 1, wherein a surface roughness of the inner surface or the mounting surface and the reflector is set to be equal to or less than a quarter of a wavelength of deflected light emitted from the light emitting element. Item 3. A light emitting device according to Item 2.   The light-emitting device according to any one of claims 1 to 3, wherein the mirror surface is a surface in which a surface roughness of the inner surface or the mounting surface and the reflector is set to 100 nm or less.   The light emitting element is formed of a group III nitride semiconductor having a nonpolar plane or a semipolar plane as a main surface, and includes a first semiconductor layer of a first conductivity type, a light emitting layer on the first semiconductor layer, and the light emitting layer. The light emitting device according to claim 1, further comprising a second semiconductor layer of the second conductivity type. A light emitting element that emits polarized light and has a mirror end surface;
A mounting base on which the light emitting element is mounted, and at least a part of the inner surface on which the light emitting element is mounted is a mirror surface;
A light-emitting device comprising:

Images