JP2010186873A - White light emitting device and manufacturing method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white light emitting element having almost no color unevenness. <P>SOLUTION: The white light emitting element includes: a semiconductor layer 104 which has an n-type semiconductor layer 101, a p-type semiconductor layer 103, and a light-emitting layer 102 sandwiched between the n-type semiconductor layer 101 and the p-type semiconductor layer 103 so as to generate light and in which one of the main faces is a light-emitting face; a phosphor containing layer 114 containing a phosphor, which absorbs light generated by the light-emitting layer 102 so as to emit a fluorescence, and provided on the face, facing the light-emitting face, of the main faces of the semiconductor layer; and a reflecting layer 115 provided on the face, facing the face provided with the semiconductor layer 104, of the faces of the phosphor containing layer 114. Irregularities are formed on an interface between the reflecting layer 115 and the phosphor containing layer 114. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a white light emitting device and a method for manufacturing the same.

In recent years, a white light emitting element using a light emitting diode (LED) has been actively researched in order to reduce power consumption of a white light source such as a lighting fixture or a backlight light source of a liquid crystal display device. Among them, in particular, light emitting diodes using wide band gap semiconductors such as nitride semiconductors can radiate ultraviolet light or blue light, and thus are actively developed as light sources for white light emitting elements that emit white light. ing. A configuration for realizing a white light emitting element using a light emitting diode that emits ultraviolet light (hereinafter referred to as “ultraviolet light emitting diode”) or a light emitting diode that emits blue light (hereinafter referred to as “blue light emitting diode”). As for, the structure of (1)-(3) shown below is mainly mentioned.
(1) Configuration combining blue light emitting diode and yellow phosphor (2) Configuration combining ultraviolet light emitting diode and blue, green and red phosphors (3) Configuration combining blue, green and red light emitting diodes In the configurations (1) to (3), the configuration (3) has a relatively high cost and tends to have poor color mixing. Therefore, at present, the blue light-emitting diode and the yellow phosphor as in (1) are combined with the light-emitting diode and the phosphor as in (1) and (2). Development of a combined white light emitting device is in progress. As a white light emitting element combining such phosphors, for example, the shape of a white light emitting element as disclosed in Patent Documents 1 to 3 has been proposed.

  FIG. 7 is a cross-sectional view showing a conventional white light emitting device. For example, in Patent Documents 2 and 3, a method for forming a phosphor-containing layer (or a phosphor film made of a phosphor) mainly containing a phosphor on the light emitting diode 2010 using a semiconductor technique such as coating, vapor deposition, or sputtering. Has been proposed.

  A white light emitting element 2020 shown in FIG. 7 includes a substrate 2005, an epitaxial layer 2004 formed on the substrate 2005, and a phosphor-containing layer 2003 formed on the back surface of the substrate 2005. The epitaxial layer 2004 is composed of a plurality of semiconductor layers, and a part of the upper portion of the epitaxial layer 2004 is removed. A first electrode 2001 is formed on a portion of the epitaxial layer 2004 from which the upper portion is removed, and a second electrode 2002 is formed on the other portion. By cutting the wafer 2000 at a predetermined position, a white light emitting element having the cut surface 2006 as a side surface is formed.

  Blue light is emitted from the light emitting layer in the epitaxial layer 2004. Part of this blue light is absorbed by the phosphor-containing layer 2003, and the phosphor-containing layer 2003 generates yellow light.

According to this configuration and the manufacturing method, since the phosphor-containing layer 2003 is collectively formed on the wafer before being divided into individual light emitting diodes using semiconductor technology, the manufacturing cost for forming the phosphor can be reduced. Can do. In addition, since the phosphor-containing layer 2003 can be uniformly formed on a plurality of white light emitting elements at the same time, color variations among the white light emitting elements can be reduced.
JP 2002-118293 A JP 2005-332857 A JP 2005-332858 A

  In the conventional white light emitting element 2020, the phosphor-containing layer 2003 is formed using semiconductor technology. Therefore, the phosphor-containing layer 2003 is formed only on the upper and lower surfaces of the wafer 2000, and in the white light emitting element 2020 after cutting, the phosphor-containing layer 2003 is not formed on the side surface. Further, in the conventional white light emitting element 2020, the phosphor-containing layer 2003, the epitaxial layer 2004, and the substrate 2005 are each composed of layers having different refractive indexes. For this reason, a part of the light generated in the light emitting layer in the epitaxial layer 2004 is totally reflected at the interface between these layers and propagates in the epitaxial layer 2004 or the substrate 2005 to form the phosphor-containing layer 2003. The light is emitted from the side surface of the white light emitting element 2020 that is not. Thus, since the light emitted from the side surface of the white light emitting element 2020 does not pass through the phosphor-containing layer 2003, the light emitted from the side surface of the white light emitting element 2020 is different in color from the light emitted from the upper or lower direction. A defect, that is, a problem that color unevenness occurs depending on the irradiation direction occurs.

  An object of the present invention is to provide a white light emitting device with less color unevenness.

  In view of the above technical problem, the first white light emitting element of the present invention is sandwiched between an n-type semiconductor layer, a p-type semiconductor layer, the n-type semiconductor layer, and the p-type semiconductor layer, and generates light. A semiconductor layer having one of the main surfaces serving as a light emitting surface, and a phosphor that absorbs light generated by the light emitting layer and emits fluorescence. A phosphor-containing layer provided on a surface facing the light emitting surface, and a reflective layer provided on a surface of the phosphor-containing layer facing the surface provided with the semiconductor layer. Unevenness is formed at the interface between the reflective layer and the phosphor-containing layer.

  According to this configuration, since the interface between the reflective layer and the phosphor-containing layer is an uneven surface, the light generated in the light emitting portion repeats multiple reflections between the semiconductor layer and the reflective layer, and then the light of the semiconductor layer. The light exits from the exit surface. Thereby, since the light produced | generated by the light emitting layer passes a fluorescent substance containing layer in multiple times, even if it makes a fluorescent substance containing layer thin, light can be converted into fluorescent light with high efficiency. Therefore, a thinner white light emitting element can be realized. In addition, since the interface between the reflective layer and the phosphor-containing layer is an uneven surface, the component emitted from the side surface of the semiconductor layer is reduced in the light generated in the light-emitting layer and the fluorescent light converted in the phosphor-containing layer. Thus, the light can be emitted mainly from the light exit surface. Thereby, a white light emitting element with little color unevenness can be realized. In addition, since such a structure is realizable without performing special patterning, it can be manufactured at low cost.

  Concavities and convexities may be formed on the surface of the semiconductor layer that faces the light emitting surface. By adopting this configuration, reflection at the interface between the semiconductor layer and the phosphor-containing layer can be reduced, so that a white light-emitting element with less color unevenness can be realized.

  Further, when the wavelength of light generated by the light emitting layer is λ and the refractive index of the semiconductor layer is n, it is preferable that the average interval of the irregularities on the surface of the light emitting layer facing the light emitting surface is λ / n or more. .

  Irregularities may be formed on the light emitting surface of the semiconductor layer.

  The irregularities formed on the light emitting surface may have a periodic structure.

  The semiconductor layer may be made of a nitride semiconductor.

  The phosphor-containing layer may contain a dielectric.

  The dielectric is preferably made of at least one oxide of Ti, Nb, Ta, W, Zn, Y, and Ce. According to this configuration, the refractive index of the phosphor-containing layer can be brought close to the refractive index of the semiconductor layer, and reflection at the interface can be reduced, thereby realizing a white light emitting element with higher efficiency and less color unevenness. It becomes possible to do.

  The reflective layer has a configuration in which a dielectric layer and a metal layer are laminated in order from the side facing the phosphor-containing layer, and the refractive index of the dielectric layer is the semiconductor layer and the phosphor. The refractive index is preferably smaller than the refractive index of the containing layer.

  You may further provide the metal board | substrate provided on the surface facing the surface in which the said fluorescent substance content layer was provided among the surfaces of the said reflection layer.

The method for manufacturing a white light emitting device of the present invention includes a semiconductor layer having an n-type semiconductor layer, a p-type semiconductor layer, and a light-emitting layer sandwiched between the n-type semiconductor layer and the p-type semiconductor layer on a first substrate. And forming a second substrate on the second surface of the main surface of the semiconductor layer opposite to the first surface on which the first substrate is provided via an adhesive layer A step (b) of attaching,
After the step (b), after removing the first substrate, the step (c) of forming irregularities on the exposed first surface of the semiconductor layer, and on the first surface of the semiconductor layer And a step (d) of sequentially forming a phosphor-containing layer including a phosphor that absorbs light generated by the light-emitting layer and emits fluorescence, and a reflective layer.

  According to this method, a white light emitting element can be manufactured at low cost.

  The semiconductor layer is made of a nitride semiconductor, and in the step (c), if irregularities are formed on the first surface by wet etching, it is not necessary to form a mask or the like, and the semiconductor layer can be manufactured at low cost. Unevenness can be formed on the surface.

  According to the white light emitting element of the present invention, it is possible to reduce propagation in the lateral direction while totally reflecting light generated in the light emitting layer at the interface between the semiconductor layer or the substrate and the phosphor-containing layer. Therefore, it is possible to provide a white light-emitting element with little color unevenness in the radiation direction. Further, by disposing the phosphor-containing layer between the semiconductor layer and the reflective film, light propagating in the direction from the light emitting layer toward the reflective film passes through the phosphor-containing layer at least twice. Thereby, since the light produced | generated by the light emitting layer can be efficiently converted into fluorescent light by a fluorescent substance containing layer, a fluorescent substance containing layer can be made thin and size reduction of a white light emitting element is realizable. Moreover, according to the manufacturing method of a white light emitting element, a white light emitting element can be formed at low cost.

  Hereinafter, a semiconductor light emitting device and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
-Structure of white light emitting element-
FIG. 1A is a schematic plan view of a white light emitting device according to the first embodiment of the present invention as viewed from above, and FIG. 1B is a cross-sectional view of the white light emitting device shown in FIG. It is sectional drawing in the II line. Hereinafter, the direction from the support substrate 116 toward the light emission surface will be described as “upward”.

  The white light emitting element 100 of the present embodiment includes a support substrate 116, a reflective layer 115 provided on one of the main surfaces of the support substrate 116 (upper surface in FIG. 1B), and an upper surface of the reflective layer 115. Provided phosphor-containing layer 114, semiconductor layer 104 provided on the upper surface of phosphor-containing layer 114, transparent electrode 111 provided on the upper surface of semiconductor layer 104, and provided on the upper surface of transparent electrode 111 The p-type electrode 112 and the n-type electrode 113 provided on part of the semiconductor layer 104 are provided. The transparent electrode 111 is provided to diffuse the current injected from the p-type electrode 112 over the entire surface of the semiconductor layer 104.

  The semiconductor layer 104 includes an n-type semiconductor layer 101, a light emitting layer 102, and a p-type semiconductor layer 103 in the order of proximity to the phosphor-containing layer 114. A part of the upper portion of the n-type semiconductor layer 101, the light emitting layer 102, and the p-type semiconductor layer 103 is removed by etching or the like, and an n-type electrode 113 is provided so as to be in ohmic contact with the exposed surface of the n-type semiconductor layer 101. It has been.

  In the white light emitting device 100 described above, the support substrate 116 is a metal-plated substrate (substrate manufactured by a plating method) made of, for example, Au, Cu, Ni, and the n-type semiconductor layer 101 is doped with, for example, Si. It is an n-type nitride semiconductor layer made of GaN having a thickness of, for example, about 2000 nm. The light emitting layer 102 has, for example, a multiple quantum well structure composed of, for example, an InGaN layer and a GaN layer, adjusted so as to exhibit blue light emission centered at a wavelength of 470 nm. The p-type semiconductor layer 103 is a p-type nitride semiconductor layer made of, for example, GaN having a thickness of about 200 nm doped with Mg.

  The n-type electrode 113 is composed of a metal multilayer film made of, for example, Ti, Al, Ni, Au, or the like. The p-type electrode 112 is composed of a metal multilayer film made of, for example, Ti, Al, Ni, Au or the like. The p-type electrode 112 is in contact with a part of the transparent electrode 111.

The transparent electrode 111 is made of, for example, ITO (Indium Tin Oxide), ZnO doped with Al or Ga, TiO ₂ doped with Nb (niobium), Ni / Au, or the like (laminated film of Ni film and Au film). And is formed so as to be in contact with the upper surface of the p-type semiconductor layer 103. The upper surface of the transparent electrode 111 serves as a light emitting surface 120 that emits light generated in the semiconductor layer 104.

  In the white light emitting device 100 of the present embodiment, light generated in the light emitting layer 102 is below the surface of the semiconductor layer 104 facing the surface on which the transparent electrode 111 is provided (the surface on the light emitting surface 120 side). A phosphor-containing layer 114 containing a material that absorbs and generates fluorescent light that is a complementary color is provided, and light generated in the light-emitting layer 102 and generated in the phosphor-containing layer 114 under the phosphor-containing layer 114. A reflective layer 115 having a high reflectance with respect to the fluorescent light is provided.

  According to this configuration, after the light emitted in the direction from the light emitting layer 102 toward the phosphor-containing layer 114 passes through the phosphor-containing layer 114, the light can be reflected again to the phosphor-containing layer 114. it can. Therefore, a part of the light that was not absorbed by the phosphor-containing layer 114 when it first passed through the phosphor-containing layer 114 can be absorbed by the phosphor-containing layer 114, and (light emission) in the phosphor-containing layer 114 The conversion efficiency from the light generated in layer 102 to fluorescent light can be greatly improved.

  Examples of the phosphor contained in the phosphor-containing layer 114 include YAG (Yttrium Aluminum Garnet) and sialon phosphor. Further, as the material of the reflective layer 115, for example, a metal such as Al or Ag is used.

  Furthermore, in the white light emitting device 100 of the present embodiment, irregularities having a predetermined size and interval are formed at the interface between the semiconductor layer 104 and the phosphor-containing layer 114. In other words, a surface closer to the phosphor-containing layer 114 in the main surface of the semiconductor layer 104 and a surface closer to the semiconductor layer 104 in the main surface of the phosphor-containing layer 114 have a predetermined size, Spacing irregularities are formed. Further, irregularities having a predetermined size and interval are formed at the interface between the phosphor-containing layer 114 and the reflective layer 115. In other words, the main surface of the phosphor-containing layer 114 closer to the reflective layer 115 and the surface of the reflective layer 115 closer to the phosphor-containing layer 114 have a predetermined size and spacing. Asperities are formed. The effect of this configuration will be described later. The unevenness formed on the interface between the semiconductor layer 104 and the phosphor-containing layer 114 and the uneven reflection surface 121 may be, for example, a wavy shape with a sawtooth cross section, or a recess and a protrusion are two-dimensional. It may have a shape formed alternately. Alternatively, the interface between the semiconductor layer 104 and the phosphor-containing layer 114 and the concavo-convex cross section formed on the concavo-convex reflective surface 121 may be rectangular wave-shaped. Moreover, although this unevenness | corrugation may have a structure where a recessed part and a convex part are repeated periodically, you may have a structure where the recessed part and the convex part are provided irregularly. However, it is most preferable if the unevenness having a sawtooth cross section is formed in a two-dimensional manner, because the uneven reflection surface 121 is composed of a slope not parallel to the light emitting surface.

  The average spacing of the irregularities formed at the interface between the phosphor-containing layer 114 and the reflective layer 115 (irregular reflective surface 121) is generated in the light emitting layer 102, with the refractive index of the semiconductor layer 104 (n-type semiconductor layer 101) being n. When the wavelength of light is λ, it is preferable to make it larger than λ / n. Moreover, it is preferable that the average of the height difference of a recessed part and a convex part is about 50 nm-2000 nm. Furthermore, for the phosphor-containing layer 114, a material is selected so that the refractive index of the phosphor-containing layer 114 is equal to or smaller than the refractive index of the semiconductor layer 104 in consideration of the difference in refractive index with the semiconductor layer 104. It is preferable. Thus, when light enters the phosphor-containing layer 114 from the semiconductor layer 104, the amount of light reflected at the interface between the semiconductor layer 104 and the phosphor-containing layer 114 can be reduced. The amount of light incident on the containing layer 114 can be increased.

-Operation of white light emitting element-
Hereinafter, the operation of the white light emitting device of this embodiment will be described focusing on the function of the irregularities formed at the interface between the phosphor-containing layer 114 and the reflective layer 115.

  FIG. 2A is an enlarged cross-sectional view showing a part 125 in the vicinity of the reflective layer 115 in the white light emitting element according to this embodiment, and FIG. It is a figure which shows the reflection intensity of the incident light. The vertical axis of FIG. 2B represents the intensity of reflected light with respect to the intensity of incident light (that is, (reflected light intensity) / (incident light intensity)), and the horizontal axis represents the incident angle of light.

  As shown in FIG. 1B, light generated in the light emitting layer 102 in the semiconductor layer 104 is evenly emitted from the light emitting point in all directions at 360 °. At this time, the light emitted in the direction from the light emitting layer 102 to the transparent electrode 111, that is, the direction from the light emitting layer 102 to the light emitting surface 120, the interface between the transparent electrode 111 and the p-type semiconductor layer 103, and the transparent The light 141 a having an incident angle on the upper surface of the electrode 111 that is equal to or smaller than the critical angle is emitted to the outside of the white light emitting element 100 as it is. The light emitted here is, for example, blue light.

  On the other hand, the light 141 b incident on the light emitting surface 120 at a critical angle or more is totally reflected by the light emitting surface 120 toward the support substrate 116. Since the phosphor-containing layer 114 and the reflective layer 115 are provided between the semiconductor layer 104 and the support substrate 116, the light totally reflected by the light emitting surface 120 passes through the phosphor-containing layer 114 and is reflected by the reflective layer. 115 is incident. At this time, the light 141 b is incident on the phosphor-containing layer 114 with almost no reflection due to the unevenness of the interface between the semiconductor layer 104 and the phosphor-containing layer 114. Here, the reason why reflection at the interface between the semiconductor layer 104 and the phosphor-containing layer 114 is suppressed is due to a light diffusion effect or the like. Next, a part of the light 141 b is converted into fluorescent light when passing through the phosphor-containing layer 114.

  The light 141b incident on the reflective layer 115 is reflected in the direction toward the semiconductor layer 104 by the upper surface of the reflective layer 115, passes through the phosphor-containing layer 114 again, and is guided to the light emitting surface (shown in FIG. 1B). Light 141c, 141d). Also at this time, part of the blue light component of the light is converted into fluorescent light by the phosphor-containing layer 114. Note that when the light 141 b is reflected by the reflective layer 115, the light is reflected by so-called Lambertian reflection that reflects in various directions by the uneven reflection surface 121 of the reflective layer 115.

Hereinafter, the function of the uneven reflection surface 121 will be described more specifically with reference to FIGS. In the white light emitting device 100 of the present embodiment, the uniform light incident on the uneven reflection surface 121 is reflected in various directions. At this time, the intensity distribution of the reflected light does not depend on the incident angle, and as shown in FIG. 2B, the normal direction of the reflecting surface is the largest, and Lambert's proportional to the cosine of the angle formed with respect to the normal line. The distribution follows the cosine law. At this time, for example, the semiconductor layer 104 is made of GaN and the transparent electrode 111 is made of a TiO ₂ -based material so that the refractive index of the semiconductor layer 104 and the transparent electrode 111 is 2.5, and the refractive index outside the white light emitting device 100 is 1. .5 (assuming that it is molded with a transparent resin), the critical angle of the light exit surface 120 is 36.9 degrees. Light 141c having a critical angle or less is extracted from the light exit surface 120 to the outside. On the other hand, the light 141d whose incident angle is greater than or equal to the critical angle is again totally reflected in the direction of the reflective layer 115 on the light exit surface 120, but is again reflected in various directions by the reflective film having the uneven surface, and the same as above. Most of the light is extracted from the light emitting surface 120 to the outside.

  As for the light 141e radiated in the direction from the light emitting layer 102 toward the support substrate 116, the light incident on the reflective layer 115 is reflected in various directions on the uneven reflective surface 121 as described above. Most of the light 141e incident on the reflective layer 115 becomes light 141f incident on the light exit surface 120 at an angle smaller than the critical angle, and is extracted from the light exit surface 120 to the outside. On the other hand, the light 141g whose incident angle is greater than or equal to the critical angle is totally reflected again in the direction toward the reflective layer 115 on the light emitting surface 120, and is reflected again in various directions by the reflective layer 115 having an uneven surface. Then, most of the light 141 g is extracted from the light emitting surface 120 to the outside of the white light emitting element 100, and the rest is reflected again in the direction toward the reflective layer 115. As described above, the light generated in the semiconductor layer 104 is only reflected between the light emitting surface 120 and the concave / convex reflecting surface 121 a plurality of times, and most of the light is not propagated in the side surface direction to the outside. It is taken out. Therefore, light emission from the side surface of the white light emitting element 100 is suppressed.

  Here, in the white light emitting element of the present embodiment, the phosphor-containing layer 114 is sandwiched between the light emitting surface 120 and the reflective layer 115 having an uneven surface. Thereby, most of the fluorescent light generated by the phosphor-containing layer 114 is also emitted from the light emitting surface 120 due to the effect of the concave and convex reflection surface 121 as in the case of blue light. Therefore, since both the light generated in the semiconductor layer 104 and the fluorescent light are emitted from the same light emitting surface 120, a white light emitting element with little color unevenness can be realized.

  At this time, the light generated in the semiconductor layer 104 repeats multiple reflections between the light emitting surface 120 and the reflective layer 115, so that the conversion efficiency from blue light to fluorescent light is improved in the phosphor-containing layer 114. Since the conversion efficiency to fluorescent light is proportional to the thickness of the phosphor-containing layer, when the reflective layer 115 having irregularities is not provided, the phosphor-containing layer is thickened in order to improve the conversion efficiency to fluorescent light. There is a need to. On the other hand, in the white light emitting device 100 of the present embodiment, as described above, the light generated in the semiconductor layer 104 is emitted after passing through the phosphor-containing layer 114 a plurality of times. Even if the thickness is reduced, conversion efficiency sufficient to generate white light can be achieved, and a white light-emitting element in which a thinner phosphor-containing layer is integrated with a semiconductor layer can be realized.

  Note that the interval between the irregularities formed at the interface between the phosphor-containing layer 114 and the reflective layer 115 is preferably larger than λ / n, but the above-described effect is exhibited even when the interval between the irregularities is λ / n or less. It is possible.

  Further, in the white light emitting device 100 of the present embodiment, the reflectance of the interface between the semiconductor layer 104 and the phosphor-containing layer 114 is reduced, and the intensity distribution of reflected light in the reflective layer 115 is Lambertian reflection. It is preferable to design.

  In the above description, the material is selected so that the refractive index of the phosphor-containing layer 114 is smaller than the refractive index of the semiconductor layer 104. However, the combination of the materials of the phosphor-containing layer 114 and the semiconductor layer 104 is not limited to this. Not exclusively. However, in order to suppress reflection at the interface between the phosphor-containing layer 114 and the semiconductor layer 104, the refractive indexes of the phosphor-containing layer 114 and the semiconductor layer 104 are preferably close.

  Further, although the reflective layer 115 is a metal layer, it is not limited to this. For example, the reflective layer 115 may have a structure in which a dielectric layer and a metal layer are stacked in order from the side closer to the phosphor-containing layer 114. In this case, the refractive index of the dielectric layer is preferably smaller than the refractive index of the semiconductor layer 104. For example, the refractive index of the dielectric layer is preferably smaller than 1.8 and more preferably smaller than 1.5 with respect to the refractive index of 2.5 of the semiconductor layer 104. The critical angle of light incident on the reflective layer 115 is determined by the refractive index difference between the semiconductor layer and the dielectric layer. Therefore, with the above-described configuration, light incident on the reflective layer 115 that is incident at an angle larger than the critical angle can be totally reflected without being attenuated. The luminous efficiency of the element can be improved.

  In the above description, the semiconductor layer 104 emits blue light. However, the semiconductor layer 104 may emit violet light, ultraviolet light, or the like. In this case, as the phosphor contained in the phosphor-containing layer 114, a material that converts violet light or ultraviolet light into visible light such as yellow light may be used.

  Further, in the white light emitting device 100 of the present embodiment, the n-type electrode 113 is provided so as to be in direct contact with the n-type semiconductor layer 101, but when viewed from the semiconductor layer 104, the phosphor-containing layer 114 side, that is, the support substrate 116. An n-type electrode 113 may be provided on the lower surface of the substrate.

  In the above description, “unevenness is formed at the interface between the phosphor-containing layer 114 and the reflective layer 115”, but this is uneven when viewed from the height between the recess and the protrusion. This includes the case where only the concave portion or only the convex portion is formed on the main surface of the phosphor-containing layer 114.

  In the white light emitting device 100 of the present embodiment, the light emitting surface is formed on the p-type semiconductor layer 103 side when viewed from the light emitting layer 102. However, the arrangement of the p-type semiconductor layer 103 and the n-type semiconductor layer 101 is switched. Thus, it is also possible to emit light from the n-type semiconductor layer 101 side. In this case, if the unevenness is formed at the interface between the p-type semiconductor layer 103 and the reflective layer 115, the above-described effect can be obtained.

-White light emitting device manufacturing method-
FIGS. 3A to 3D and FIGS. 4A to 4E are cross-sectional views illustrating manufacturing steps of the white light emitting device according to the first embodiment.

First, in the process shown in FIG. 3A, for example, a Si substrate having a <111> plane orientation, a sapphire substrate having a <0001> plane orientation, or a 6H-SiC substrate having a <0001> plane orientation. A buffer layer (not shown) such as ALN (aluminum nitride) or a GaN layer grown at a low temperature is formed on the main surface of a certain first substrate 150 by epitaxial growth using MOCVD (Metal Organic Chemical Vapor Deposition). The semiconductor layer 104 is formed with a gap therebetween. Specifically, the n-type semiconductor layer 101 made of, for example, n-type GaN, an In _x Ga _1-x N well layer, and a GaN barrier layer are alternately and repeatedly deposited on the buffer layer a plurality of times. A semiconductor layer 104 is formed by sequentially laminating a light emitting layer 102 having a multiple quantum well structure and a p-type semiconductor layer 103 made of a P-type GaN layer.

  Next, in the step shown in FIG. 3B, the transparent electrode 111, the p-type electrode 112, and the n-type electrode 113 are formed. Specifically, a part of the semiconductor layer 104 is selectively removed using a photolithography technique and dry etching, and a part of the n-type semiconductor layer 101 is exposed. Subsequently, a transparent electrode 111 made of, for example, ITO is selectively formed on a part of the upper surface of the p-type semiconductor layer 103 by using photolithography and vacuum evaporation, and then annealed in an oxygen atmosphere. Thereafter, the p-type electrode 112 is selectively formed on a part of the upper surface of the transparent electrode 111 by photolithography and vacuum deposition, while the n-type electrode 113 is selectively formed on a part of the exposed n-type semiconductor layer 101. To form.

  Next, in the step shown in FIG. 3C, an adhesive layer 151 is formed by coating so as to cover the transparent electrode 111, the p-type electrode 112, and the n-type electrode 113. The second substrate 152 is bonded. At this time, the second substrate 152 is bonded so that the transparent electrode 111, the p-type electrode 112, and the n-type electrode 113 face the second substrate 152. The second substrate 152 is made of, for example, sapphire. In addition, as the adhesive constituting the adhesive layer 151, for example, a silicone resin or the like that is resistant to a strong alkaline solution such as potassium hydroxide (KOH) can be used. The silicone resin can be removed later with a predetermined release agent.

  Next, in the step shown in FIG. 3D, the first substrate 150 is removed to expose one main surface of the n-type semiconductor layer 101 (a surface facing the surface on which the light emitting layer 102 is formed). In this step, if the first substrate 150 is a silicon substrate, the substrate can be removed by wet etching using a mixed solution of hydrofluoric acid and nitric acid, for example. Alternatively, if the first substrate 150 is a sapphire substrate, the substrate can be removed by a laser lift-off method. Note that the white light emitting element being manufactured at the end of this step is referred to as a substrate 190 for convenience.

Subsequently, in the step shown in FIG. 4A, the n-type semiconductor layer 101 is wet-etched using a PEC (Photo-electrochemical) etching method using a potassium hydroxide (KOH) aqueous solution and ultraviolet light irradiation in combination. Unevenness is formed on the main surface of the n-type semiconductor layer 101 exposed in the step. Specifically, the substrate 190 is immersed in a container 153 containing a KOH aqueous solution 154, and wet etching of the n-type semiconductor layer 101 is performed in a state where ultraviolet light is irradiated. For example, at this time, the concentration of the aqueous KOH solution is 45%, the temperature is room temperature, and the irradiation intensity of ultraviolet light is 10 mW / cm ² .

  Since the etching of the semiconductor by this PEC etching has anisotropy with respect to the plane orientation, the {1-10-1} plane which is a kind of crystal orientation plane of the n-type semiconductor layer 101 and one of the semipolar planes is And exposed by this etching (in the expression of the plane orientation, “−1” indicates one bar). Thereby, the uneven | corrugated surface 155 which has the slope comprised by the {1-10-1} surface can be formed.

Next, in the step shown in FIG. 4B, a phosphor-containing layer 114 containing, for example, YAG, sialon phosphor, etc., and Al, Ag, or an alloy thereof are formed on the uneven surface 155 by using an electron beam evaporation method. The reflective layer 115 made of is sequentially formed. The thickness of the phosphor-containing layer 114 is, for example, about 1 to 100 μm and adjusted so that the emitted light becomes white. The reflective layer 115 has a thickness of 10 to 1000 nm, for example. Thus, by forming the uneven surface 155 in the semiconductor layer 104 in advance, the uneven surface (uneven reflection surface 121) can be easily formed at the interface between the phosphor-containing layer 114 and the reflection layer 115. Further, since the phosphor-containing layer 114 does not require patterning or the like and can be formed on the entire surface of the semiconductor layer 104, the semiconductor layer 104 and the phosphor-containing layer 114 can be integrated at a low cost. It becomes. A dielectric layer made of, for example, SiO ₂ or SiN may be inserted between the phosphor-containing layer 114 and the reflective layer 115 made of metal.

  The phosphor-containing layer 114 may contain a dielectric. According to this configuration, since the refractive index of the phosphor-containing layer 114 can be controlled by the dielectric material, it is possible to realize a white light-emitting element with higher efficiency and less color unevenness. In this case, the dielectric is composed of at least one oxide of Ti (titanium), Nb (niobium), Ta (tantalum), W (tungsten), Zn (zinc), Y (yttrium), and Ce (cerium). It is preferable. According to this configuration, the refractive index of the phosphor-containing layer 114 can be made close to the refractive index of the semiconductor layer 104, and reflection at the interface between the two layers can be reduced, so that the efficiency is high and the color unevenness is small. A white light emitting element can be realized.

  Next, in the step shown in FIG. 4C, a support substrate 116 made of a conductive material is formed on the upper surface of the reflective layer 115 (the surface far from the phosphor-containing layer 114). At this time, the material constituting the support substrate 116 is preferably a material having excellent heat dissipation, and for example, a metal material such as Ni, Cu, or Au is formed by electrolytic plating or electroless plating. preferable. Among them, in particular, in order to form the support substrate 116 at a low cost, it is desirable that the support substrate 116 be made of Cu formed by electrolytic plating.

  Next, in a step shown in FIG. 4D, the second substrate 152 is separated from the white light emitting element being manufactured by removing the adhesive layer 151 using a peeling solution for the adhesive layer 151.

  Finally, in the step shown in FIG. 4E, the wafer is divided into chips by dicing using a blade 156 to form a white light emitting element.

  Through the above steps, a white light-emitting element with less color unevenness in which a semiconductor layer including a light-emitting layer and a phosphor-containing layer are integrated can be manufactured at low cost. In particular, according to the above-described method, an uneven surface can be easily formed at the interface between the phosphor-containing layer 114 and the reflective layer 115, so that the cost of the white light emitting element can be reduced.

  In the step shown in FIG. 4A, the uneven surface is formed using wet etching, but the uneven surface can also be formed using dry etching.

(Second Embodiment)
FIG. 5 is a cross-sectional view showing a configuration of a white light emitting element according to the second embodiment of the present invention.
Since the structure of the white light emitting element of this embodiment is almost the same as the structure of the white light emitting element of Embodiment 1, portions having the same functions and configurations are denoted by the same reference numerals as in FIG. The description is omitted or simplified. Hereinafter, the white light emitting device of this embodiment will be described in detail.

-Structure of white light emitting element-
As shown in FIG. 5, the white light emitting device 200 of the present embodiment includes a support substrate 116, a reflective layer 115 provided on one of the main surfaces of the support substrate 116 (upper surface in FIG. 5), and the reflective layer 115. Of the phosphor-containing layer 114 provided on the upper surface of the semiconductor layer 204, the semiconductor layer 204 provided on the upper surface of the phosphor-containing layer 114, the transparent electrode 211 provided on the upper surface of the semiconductor layer 204, and the transparent electrode 211 A p-type electrode 112 provided on the upper surface and an n-type electrode 113 provided on a part of the semiconductor layer 204 are provided. Similarly to the white light emitting device 100 according to the first embodiment, also in the white light emitting device 200 of the present embodiment, the interface between the semiconductor layer 204 and the phosphor containing layer 114, the phosphor containing layer 114 and the reflecting layer 115. Concavities and convexities are formed on the interface between the reflective layer 115 and the support substrate 116.

  The semiconductor layer 204 is composed of an n-type semiconductor layer 101, a light emitting layer 102, and a p-type semiconductor layer 203 in the order closer to the phosphor-containing layer 114. A part of the upper part of the n-type semiconductor layer 101, the light emitting layer 102, and the p-type semiconductor layer 203 is removed by etching or the like, and an n-type electrode 113 is provided so as to be in ohmic contact with the exposed surface of the n-type semiconductor layer 101. It has been. The p-type electrode 112 is provided on the transparent electrode 211 so as to be electrically connected to the transparent electrode 211.

  The support substrate 116 is a metal-plated substrate made of, for example, Au, Cu, Ni or the like, and the n-type semiconductor layer 101 is an n-type nitride semiconductor layer made of, for example, GaN doped with Si, for example, having a thickness of about 2000 nm. It is. The light emitting layer 102 has, for example, a multiple quantum well structure composed of, for example, an InGaN layer and a GaN layer, adjusted so as to exhibit blue light emission centered at a wavelength of 470 nm. The p-type semiconductor layer 203 is a p-type nitride semiconductor layer made of, for example, GaN having a thickness of about 200 nm doped with Mg.

The transparent electrode 111 is made of, for example, ITO (Indium Tin Oxide), ZnO doped with Al or Ga, TiO ₂ doped with Nb (niobium), Ni / Au, or the like (laminated film of Ni film and Au film). And is formed so as to be in contact with the upper surface of the p-type semiconductor layer 103. The thickness of the transparent electrode 111 is, for example, about 5 nm to 500 nm.

  The feature of the white light emitting device 200 of the present embodiment is that fine irregularities are formed on the interface between the p-type semiconductor layer 203 and the transparent electrode 211 and on the upper surface of the transparent electrode 211 (the main surface far from the p-type semiconductor layer 203). That is to be formed. The upper surface of the transparent electrode 211 is an uneven light emitting surface 220. As an example of the unevenness, columnar recesses having a horizontal cross-section diameter of about 500 nm may be provided on the upper surface of the p-type semiconductor layer 203 in a two-dimensional manner with a period of about 1 μm. The depth of the columnar recess may be about 150 nm, for example.

  The unevenness of the upper surface of the p-type semiconductor layer 203 can be realized by removing a part of the upper portion of the p-type semiconductor layer 203 by, for example, a photolithography technique and dry etching.

-Operation of white light emitting element-
Subsequently, the operation of the white light emitting element 200 of the present embodiment will be described focusing on the function of the uneven light emitting surface 220 formed on the upper surface of the transparent electrode 211.

  FIG. 6A is an enlarged cross-sectional view showing a part of the transparent electrode 111 according to the first embodiment, and FIG. 6B is a cross-sectional view of the transparent electrode 211 in the white light emitting device according to the second embodiment. It is sectional drawing which expands and shows a part of (c), (c) is a figure which shows the relationship between the unevenness | corrugation formed in the transparent electrode, and the light transmittance. Note that “p” shown in FIG. 6B indicates the period of the unevenness, and “h” indicates the distance from the concave portion to the convex portion, that is, the height of the concave and convex portions.

  Light generated in the light emitting layer 102 in the semiconductor layer 204 is evenly emitted from the light emitting point in all directions of 360 °. At this time, the light emitted from the light emitting layer 102 toward the transparent electrode 211, that is, the light emitted from the light emitting layer 102 toward the uneven light emitting surface 220, and the transparent electrode 211 and the p-type semiconductor layer 203 are transparent. The light 241 a having an incident angle on the upper surface of the electrode 211 that is equal to or smaller than the critical angle is emitted to the outside of the white light emitting element 200 as it is.

  The light 241b incident on the light emitting surface at a critical angle or more is totally reflected in the direction toward the support substrate 116 on the flat light emitting surface (see FIG. 6A). On the other hand, since the uneven light emitting surface 220 is scattered and diffracted by the unevenness formed on the surface, the uneven light emitting surface 220 transmits a part 241b ′ of the incident light at a critical angle or more (FIG. 6B). )reference). In addition, the light reflected in the direction toward the support substrate 116 on the uneven light emission surface 220 passes through the phosphor-containing layer 114 and enters the reflective layer 115.

  The light incident on the reflection layer 115 is Lambert-reflected in the direction toward the semiconductor layer 204 by the uneven reflection surface 121 of the reflection layer 115, passes through the phosphor-containing layer 114 again, and enters the uneven light emission surface 220. At this time, the intensity distribution of the light incident on the concave / convex light exit surface 220 shows a Lambertian distribution with respect to the incident angle, but the angular distribution of the light transmittance on the concave / convex light exit surface 220 has characteristics almost equal to the Lambert distribution. . Therefore, almost all of the light 241 c having an incident angle smaller than the critical angle and the light 241 d ′ having an incident angle larger than the critical angle are mostly emitted from the uneven light emitting surface 220 to the outside of the white light emitting element 200. This effect is the same for the light emitted from the light emitting point toward the support substrate 116.

  Thus, the luminous efficiency of the white light emitting element can be improved by using the concave / convex light emitting surface 220 having a concave / convex shape as the light emitting surface. Furthermore, at the light emitting point, the light 241a and 241b ′ emitted outside without passing through the phosphor-containing layer 114 and the radiation angle characteristics of the light emitted outside through the phosphor-containing layer 114 are almost equal. Are equal. Therefore, according to the white light emitting device 200 of the present embodiment, it is possible to further reduce the color unevenness of the emitted light.

The above effect will be described more specifically with reference to FIGS. FIG. 6C shows the result of calculating the incident angle dependence of the transmittance on the light exit surface in the white light emitting device shown in FIGS. 6A and 6B. Here, for simplicity, the refractive indexes of the semiconductor layers 104 and 204 and the transparent electrode 111 are set to the same n ₁ = 2.5, and the unevenness is formed only on the uppermost surface.

The refractive index outside the white light emitting elements 100 and 200 was set to n ₂ = 1.5 (assumed to be molded with a transparent resin). The wavelength of light incident on the light exit surface was 470 nm.

  As shown in FIG. 6C, when the unevenness is not formed on the light exit surface, the light is totally reflected at an incident angle larger than the critical angle, so that the light transmittance is zero. On the other hand, in the case of the concavo-convex light emitting surface 220, it can be seen that light is transmitted even when the incident angle of light is greater than or equal to the critical angle, and the angular dependence of transmittance is close to a Lambertian distribution. As described above, by forming irregularities on the light emitting surface, it becomes possible to take out light having an incident angle equal to or larger than the critical angle to the outside of the white light emitting element 200, so that the light emission efficiency of the white light emitting element is greatly improved. be able to. Furthermore, since it is possible to match the transmittance distribution of the light emitted from the light emitting layer 102 in the direction toward the light exit surface with the uneven light exit surface 220 and the distribution of light reflected by the uneven reflective surface 121, A white light emitting element with less color unevenness can be realized.

  The present invention can be applied, for example, as a backlight light source for various display devices or a white light emitting element for illumination, and is very useful.

(A) is a schematic plan view when the white light emitting element according to the first embodiment of the present invention is viewed from above, and (b) is a line II-II shown in (a) of the white light emitting element. FIG. (A) is sectional drawing which expands and shows a part of reflective film vicinity in the white light emitting element which concerns on 1st Embodiment, (b) is the light which injected into the uneven | corrugated reflective surface of the said white light emitting element. It is a figure which shows the reflection intensity of. (A)-(d) is sectional drawing which shows the manufacturing process of the white light emitting element which concerns on 1st Embodiment. (A)-(e) is sectional drawing which shows the manufacturing process of the white light emitting element which concerns on 1st Embodiment. It is sectional drawing which shows the structure of the white light emitting element which concerns on the 2nd Embodiment of this invention. (A) is sectional drawing which expands and shows a part of transparent electrode which concerns on 1st Embodiment, (b) is a part of transparent electrode in the white light emitting element which concerns on 2nd Embodiment. It is sectional drawing which expands and is shown, (c) is a figure which shows the relationship between the unevenness | corrugation formed in the transparent electrode, and the light transmittance. It is sectional drawing which shows the conventional white light emitting element.

100, 200 White light-emitting element 101 n-type semiconductor layer 102 light-emitting layer 103, 203 p-type semiconductor layer 104, 204 semiconductor layer 111 transparent electrode 112 p-type electrode 113 n-type electrode 114 phosphor-containing layer 115 reflective layer 116 support substrate 120 light Outgoing surface 121 Irregular reflection surface 125 Parts 141a, 141b, 141c, 141d, 141e, 141f, 141g near the reflection layer Light 150 First substrate 151 Adhesive layer 152 Second substrate 153 Container 154 KOH aqueous solution 155 Irregular surface 156 Blade 190 Substrate 211 Transparent electrode 220 Uneven light exit surface 241a, 241b, 241b ′, 241c, 241d ′ Light

Claims (12)

An n-type semiconductor layer, a p-type semiconductor layer, a light-emitting layer that generates light and is sandwiched between the n-type semiconductor layer and the p-type semiconductor layer, and one of the main surfaces is a light emitting surface. A semiconductor layer,
Including a phosphor that emits fluorescence by absorbing light generated by the light emitting layer, and a phosphor-containing layer provided on a surface of the main surface of the semiconductor layer that faces the light emitting surface;
A reflective layer provided on the surface of the phosphor-containing layer facing the surface on which the semiconductor layer is provided;
A white light emitting device in which irregularities are formed at an interface between the reflective layer and the phosphor-containing layer. The white light emitting device according to claim 1,
The white light emitting element by which the unevenness | corrugation is formed in the surface facing the said light-projection surface among the surfaces of the said semiconductor layer. The white light emitting device according to claim 2,
When the wavelength of light generated by the light emitting layer is λ and the refractive index of the semiconductor layer is n,
The white light emitting element whose average space | interval of the said unevenness | corrugation in the surface facing the light-projection surface of the said light emitting layer is more than (lambda) / n. In the white light emitting element as described in any one of Claims 1-3,
A white light emitting element in which irregularities are formed on the light emitting surface of the semiconductor layer. The white light emitting device according to claim 4,
The unevenness formed on the light emitting surface is a white light emitting device having a periodic structure. In the white light emitting element as described in any one of Claims 1-4,
A white light emitting device in which the semiconductor layer is made of a nitride semiconductor. In the white light emitting element as described in any one of Claims 1-6,
The white light emitting element in which the said fluorescent substance content layer contains a dielectric material. In the white light emitting element according to claim 7,
The white light emitting element in which the dielectric is made of at least one oxide of Ti, Nb, Ta, W, Zn, Y, and Ce. In the white light emitting element according to any one of claims 1 to 8,
The reflective layer has a configuration in which a dielectric layer and a metal layer are laminated in order from the side facing the phosphor-containing layer,
The white light emitting element in which the refractive index of the said dielectric material layer is smaller than the refractive index of the said semiconductor layer and the said fluorescent substance content layer. In the white light emitting element according to any one of claims 1 to 9,
The white light emitting element further provided with the metal substrate provided on the surface facing the surface in which the said fluorescent substance content layer was provided among the surfaces of the said reflection layer. Forming a semiconductor layer having a n-type semiconductor layer, a p-type semiconductor layer, and a light emitting layer sandwiched between the n-type semiconductor layer and the p-type semiconductor layer on a first substrate;
A step (b) of attaching a second substrate via an adhesive layer on a second surface of the main surface of the semiconductor layer opposite to the first surface on which the first substrate is provided;
After the step (b), after removing the first substrate, the step (c) of forming irregularities on the exposed first surface of the semiconductor layer;
A step (d) of sequentially forming, on the first surface of the semiconductor layer, a phosphor-containing layer including a phosphor that absorbs light generated by the light-emitting layer and emits fluorescence, and a reflective layer; A method for manufacturing a white light emitting element. In the manufacturing method of the white light emitting element according to claim 11,
The semiconductor layer is made of a nitride semiconductor;
In the step (c), a method for manufacturing a white light emitting element, wherein irregularities are formed on the first surface by wet etching.

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