JP2006005171A - Light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element wherein an oxide transparent electrode layer is used as its electrode for light emitting drive, and the internal reflection generated in the boundary surface formed by the oxide transparent electrode layer is suppressed, and resultantly, its light deriving efficiency is made favorable. <P>SOLUTION: The light emitting element 100 has a compound semiconductor layer 50 having a light emitting layer 24 and has an oxide transparent electrode layer 30 laminated on the compound semiconductor layer 50 and for applying a light emitting drive voltage to the light emitting layer 24. The light emitted from the light emitting layer 24 is derived to be transmitted through the oxide transparent electrode layer 30. Between the oxide transparent electrode layer 30 and the compound semiconductor layer 50, intermediate-refractive-index layers 31 are interposed each of which has a refractive-index intermediate between the oxide transparent electrode layer 30 and the compound semiconductor layer 50. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light emitting element.

JP-A-1-225178 JP-A-6-188455 JP-A-8-83927 JP 2001-7399 A JP 2002-43621 A

  Among semiconductor light-emitting elements in which a light-emitting layer portion is formed of a compound semiconductor, those used as light-emitting diode light sources for display and illumination use a metal electrode for applying a driving voltage to the light extraction surface side of the light-emitting layer portion. Form. Since the metal electrode functions as a light shielding body, for example, it is formed so as to cover only the central portion of the main surface of the light emitting layer portion, and light is extracted from the surrounding electrode non-formation region. However, there is no change in that the metal electrode is a light shield, and if the area of the metal electrode is made extremely small, current diffusion in the element surface is hindered, and the amount of light extraction is restricted. . Therefore, the entire surface of the light emitting layer is covered with a transparent and highly conductive ITO (Indium Tin Oxide) electrode layer, and the light extraction efficiency through the ITO electrode layer is improved, and the current diffusion effect is improved. The proposal which aims at simultaneously is disclosed by patent documents 1-5 etc., for example.

  By the way, the ITO layer is transparent to visible light, but has a large refractive index difference from the compound semiconductor constituting the light emitting element chip. Specifically, while the refractive index of ITO is 1.7 to 1.8, most of the III-V compound semiconductors have a refractive index of 3 or more. As a result, at the interface between the ITO layer and the compound semiconductor layer, the total reflection critical angle with respect to the emitted light beam to be extracted becomes small, and the ratio of the emitted light beam that returns to the inside of the element due to interface reflection increases. There's a problem

  An object of the present invention is to provide a light-emitting element that uses an oxide transparent electrode layer as an electrode for driving light emission, suppresses internal reflection at the boundary surface formed by the oxide transparent electrode layer, and thus has high light extraction efficiency. There is to do.

Means for Solving the Problems and Effects of the Invention

  In order to solve the above problems, a light-emitting element of the present invention includes a compound semiconductor layer having a light-emitting layer portion, and an oxide transparent layer that is stacked on the compound semiconductor layer and applies a light-emission driving voltage to the light-emitting layer portion. In a light-emitting device having an electrode layer and extracting light from the light-emitting layer portion in a form of transmitting the oxide transparent electrode layer, the oxide between the oxide transparent electrode layer and the compound semiconductor layer An intermediate refractive index layer having an intermediate refractive index between the transparent electrode layer and the compound semiconductor layer is disposed. In this specification, “refractive index” means the refractive index at the peak wavelength of the luminous flux from the light emitting element chip.

  According to the light emitting device of the present invention, since the intermediate refractive index layer is disposed between the oxide transparent electrode layer and the compound semiconductor layer, it is compared with the conventional device structure in which the oxide transparent electrode layer and the compound semiconductor layer are in direct contact with each other. As a result, the refractive index difference at the boundary surface formed by the oxide transparent electrode layer is reduced. As a result, the total reflection critical angle with respect to the luminous flux to be extracted increases, so that internal reflection at the boundary surface is suppressed, and a light emitting element with good light extraction efficiency is realized.

  When the intermediate refractive index layer is composed of an insulating layer, the oxide transparent electrode layer is electrically connected to the compound semiconductor layer through a conduction penetrating portion formed through the intermediate refractive index layer. The driving voltage can be applied to the light emitting layer by the layer.

  A metal electrode for applying a light emission driving voltage to the light emitting layer portion can be formed on the oxide transparent electrode layer so as to cover a part of its main surface for wire bonding or the like. Since the metal electrode serves as a light shield, the emitted luminous flux is extracted outside in the main surface of the oxide transparent electrode layer with the peripheral region of the metal electrode as a light extraction region. In this case, of the main surface of the compound semiconductor layer, the projection region of the metal electrode is the first region and the other region is the second region, and the intermediate refractive index layer is formed so as to cover the second region. Thus, it is possible to increase the extraction efficiency of the luminous flux from the light extraction region.

  Since the oxide transparent electrode layer has a low sheet resistance, it plays the role of diffusing the drive current supplied from the metal electrode in the plane. When the intermediate refractive index layer formed in the second region is an insulating layer, conductive through-holes penetrating the intermediate refractive index layer are dispersedly formed in the second region, and the oxide transparent electrode layer is formed in the conductive through-holes. It is desirable to conduct with the compound semiconductor layer. Thereby, the current diffused in the plane by the oxide transparent electrode layer can be supplied uniformly to the compound semiconductor layer side having the light emitting layer portion, and the light emitting layer portion can be caused to emit light uniformly in the plane.

  The intermediate refractive index layer made of an insulating layer can also be formed in the first region that forms the region immediately below the metal electrode. In this case, if the conduction through portion is not formed in the first region, the intermediate refractive index layer formed in the first region can function as a current blocking layer. As a result, light emission directly under the metal electrode that prevents light extraction is suppressed, and the detour current is distributed to the light extraction region side, so that more current can be spent on light emission in the light extraction region. As a result, the emission luminance of the entire device including the light extraction efficiency can be increased.

  The oxide transparent electrode layer can be disposed in contact with the compound semiconductor layer in the conductive through portion. In this case, forming a contact layer made of a compound semiconductor having a lower band gap energy than the compound semiconductor forming the metal or the light emitting layer on the outermost surface portion of the compound semiconductor layer reduces the contact resistance with the compound semiconductor layer. It is effective in terms of Since the contact layer functions as an absorption layer for the emitted light beam, it is desirable to selectively form the contact layer in the conductive through portion. Thereby, the contact layer can be excluded from the region of the intermediate refractive index layer that effectively contributes to the light extraction, and the light extraction efficiency of the entire device can be further increased.

  Specifically, the oxide transparent electrode layer can be composed of an ITO layer (Indium-Tin Oxide) or a zinc oxide layer. In this case, the intermediate refractive index layer can be composed of any one of silicon nitride, boron nitride, aluminum nitride, titanium oxide, zirconium oxide, cerium oxide, and tantalum oxide. When the compound semiconductor layer is composed of a III-V group compound semiconductor and ITO is adopted as the material of the oxide transparent electrode layer, an intermediate refractive index layer having a refractive index of 1.9 to 2.5 is used. Is desirable. In addition, when zinc oxide is used as the material of the oxide transparent electrode layer, it is desirable to use an intermediate refractive index layer having a refractive index of 2.1 or more and 2.5 or less. If a material lower than the lower limit of the refractive index range is used for the intermediate refractive index layer, the effect of reducing the refractive index difference from the oxide transparent electrode layer is diminished, and if a higher material is used, the refractive index difference from the compound semiconductor layer is reduced. The effect of reducing the thickness fades. In either case, there is a possibility that the effect of suppressing internal reflection at the boundary between the intermediate refractive index layer and the oxide transparent electrode layer or the compound semiconductor layer is insufficient.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows an embodiment of a light emitting device of the present invention. The light emitting element 100 includes a compound semiconductor layer 50 having a light emitting layer portion 24 and a current diffusion layer 20 formed on the first main surface of the light emitting layer portion 24. The first main surface of the compound semiconductor layer 50 is covered with an oxide transparent electrode layer 30 for applying a light emission driving voltage to the light emitting layer portion. Further, an intermediate refractive index layer 31 having an intermediate refractive index between the oxide transparent electrode layer 30 and the compound semiconductor layer light emitting layer portion 50 is provided between the oxide transparent electrode layer 30 and the compound semiconductor layer 50. ing.

The light emitting layer portion 24 is made of (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1: AlGaInP) or In _x Ga _y Al _1-xy N ( 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1: InGaAlN). In the present embodiment, the active layer 5 made of a non-doped (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 0.55, 0.45 ≦ y ≦ 0.55) mixed crystal is used. , P-type (Al _z Ga _1-z ) _y In _1-y P (where x <z ≦ 1) and n-type (Al _z Ga _1-z ) _y In _1-y P It has a structure sandwiched between n-type clad layers 4 (x <z ≦ 1), and the emission wavelength is changed from yellow-green to red region (emission wavelength (peak emission wavelength)) depending on the composition of the active layer 5 550 nm to 670 nm). The current spreading layer 20 is made of a III-V group compound semiconductor, such as AlGaAs, GaP, or GaInP, that has a larger band gap energy than the active layer 5 (that is, is transparent to the luminous flux). These are epitaxially grown on the element substrate 7 made of GaAs via the GaAs buffer layer 2 by a well-known MOVPE method. The refractive index of the group III-V compound semiconductor (AlGaInP, AlGaAs, GaP, or GaInP) forming the light emitting layer portion 24 and the current spreading layer 20 is 3.2 to 3.5 in the above emission wavelength region.

The oxide transparent electrode layer 30 is made of ITO (refractive index: 1.7 to 1.8) or zinc oxide (refractive index: 2.0). In this embodiment, ITO is adopted. ITO is an indium oxide film doped with tin oxide, and the resistivity can be set to a sufficiently low value of 5 × 10 ⁻⁴ Ω · cm or less by setting the content of tin oxide to 1 to 9 mass%. . The intermediate refractive index layer 31 includes silicon nitride (refractive index: 1.8 to 2.5), boron nitride (refractive index: 2.0), aluminum nitride (refractive index: 2.2), titanium oxide (refractive index: 2.5), zirconium oxide (refractive index: 2.1), cerium oxide (refractive index: 2.2), and tantalum oxide (refractive index: 2.1). In this embodiment, silicon nitride is used. It has been adopted. These are all formed by sputtering or CVD (Chemical Vapor Deposition), and each has a thickness of, for example, not less than 400 nm and not more than 3 μm. As disclosed in Japanese Patent Publication No. 6-85448, the refractive index of silicon nitride can be adjusted in the range of 1.8 to 2.5 depending on the composition ratio of Si and N. FIG. 6 shows the relationship between the Si / N ratio and the refractive index.

  The above-exemplified intermediate refractive index layers 31 are all insulating layers, and the oxide transparent electrode layer 30 is electrically connected to the compound semiconductor layer 50 through a conductive through-hole 31h formed through the intermediate refractive index layer 31. Yes. A metal electrode (for example, an Au electrode) 9 for applying a light emission driving voltage to the light emitting layer portion 24 is formed on the oxide transparent electrode layer 30 so as to cover a part of the main surface thereof for wire bonding or the like. . The element substrate 7 is n-type, and its second main surface is covered with a back electrode 15 made of an Au electrode or the like via a contact layer 16 made of AuGeNi alloy or the like.

  Of the main surface of the compound semiconductor layer 50, the intermediate refractive index layer 31 includes a main body layer portion 31w covering the second region, the projection region of the metal electrode 9 as the first region, and the other region as the second region, The current blocking layer portion 31b covers one region. As shown in FIG.2 and FIG.3, the conduction | electrical_connection penetration part 31h is distributedly formed in the main body layer part 31w which covers a 2nd area | region. On the other hand, no conduction through portion is formed in the current blocking layer portion 31b.

  Returning to FIG. 1, a contact layer 32 made of a compound semiconductor having a band gap energy smaller than that of the compound semiconductor (here, AlGaInP) forming the light emitting layer portion 24 (active layer 5) is formed on the outermost surface portion of the compound semiconductor layer 50. Has been. Specifically, the contact layer 32 is made of GaAs or InGaAs. Since the contact layer 32 acts as an absorption layer for the luminous flux, the contact layer 32 is selectively formed in the conduction through portion 31h (that is, the contact layer 32 is formed between the intermediate refractive index layer 31 and the current diffusion layer 20). The two layers 31 and 20 are in direct contact with each other). FIG. 2 shows an example in which the contact layer 32 (and thus the conductive through-hole 31h) is distributed and formed in the second region by a combination of the first portion 32s surrounding the first region and the second portion 32r extending radially from the first region. It is. FIG. 3 shows an example in which the contact layer 32 (and hence the conductive through-hole 31h) is dispersedly formed in the second region in the form of dots. The contact layer 32 can also be made of metal. In the present embodiment, the current diffusion layer 20 in contact with the contact layer 32 is p-type, and the metal contact layer can be made of, for example, an AuBe alloy (in the case where the current diffusion layer 20 is n-type, the metal contact layer). For example, an AuGeNi alloy).

  The light emitting element 100 emits light at a wavelength corresponding to the band gap energy of the active layer 5 by applying a voltage in the forward direction between the metal electrode 9 and the back electrode 15. The emitted light beam LB passes through the intermediate refractive index layer 31 and the oxide transparent electrode layer 30 and is extracted to the outside from the light extraction area PA that forms the periphery of the metal electrode 9. Since the intermediate refractive index layer 31 having an intermediate refractive index between the oxide transparent electrode layer 30 and the compound semiconductor layer 50 is disposed, the structure in which the oxide transparent electrode layer 30 and the compound semiconductor layer 50 are in direct contact with each other. Compared with the above, the refractive index difference at the boundary surface formed by the oxide transparent electrode layer is reduced and the total reflection critical angle with respect to the emitted light beam LB to be extracted is increased, so that internal reflection at the boundary surface is suppressed, The light extraction efficiency can be improved.

  Since the oxide transparent electrode layer 30 has a low sheet resistance, the driving current supplied from the metal electrode 9 can be uniformly diffused in the plane. Although the intermediate refractive index layer 31 is an insulating layer, since the conductive through portions 31h are dispersedly formed in the main body layer portion 31w corresponding to the light extraction area PA, the intermediate refractive index layer 31 is interposed between the conductive through portions 31h with respect to the light emitting layer portion 24. The light emission drive current can be evenly distributed. On the other hand, the current blocking layer portion 31b located immediately below the metal electrode 9 has no conduction through portion, and light emission immediately below the metal electrode 9 that prevents light extraction is suppressed. Further, since the bypass current is distributed to the light extraction region side, a larger amount of current can be consumed for light emission in the light extraction region with the same drive voltage. Further, since the light-absorbing contact layer 32 is selectively formed in the conduction through portion 31h, there is no absorption loss due to the contact layer 32 in the region where the intermediate refractive index layer 31 is formed, and the light extraction efficiency is further increased. Improvements are being made.

  The light emitting device 100 can cover the periphery of the chip with a mold 60 made of a polymer material. The mold 60 can be made of, for example, an epoxy resin. The refractive index of the epoxy resin is 1.5 to 1.6. When the oxide transparent electrode layer 30 is made of either ITO or zinc oxide, the compound semiconductor layer 50 → intermediate along the extraction path of the luminous flux. The refractive index decreases unidirectionally in the order of the refractive index layer 31 → the oxide transparent electrode layer 30 → the mold 60 → the atmosphere, and a structure capable of effectively suppressing the boundary reflection of the emitted light flux is realized. In particular, when the oxide transparent electrode layer 30 is made of ITO, the refractive index is almost the same as that of the mold 60 made of an epoxy resin, and reflection at the boundary between the oxide transparent electrode layer 30 and the mold 60 hardly occurs. There are advantages.

  Hereinafter, modified examples of the light-emitting element of the present invention will be described (the same reference numerals are given to portions common to the light-emitting element 100 of FIG. 1 and detailed description thereof will be omitted). The light emitting element 200 of FIG. 4 is an example in which an intermediate refractive index layer is formed of a stacked body of a plurality of layers 31a and 32b having different refractive indexes. In this case, it is desirable from the viewpoint of suppressing reflection at the boundary that the plurality of layers are arranged so that the refractive index decreases sequentially from the compound semiconductor layer 50 side toward the oxide transparent electrode layer 30 side. In addition, when the multiple layers 31a and 32b are made of silicon nitride having different Si / N composition ratios in particular, the difference in refractive index between adjacent layers can be further reduced, and the effect of suppressing boundary reflection can be made more remarkable. it can. If the number of layers is increased, the refractive index can be substantially continuously changed in the layer thickness direction.

  The light emitting element 300 in FIG. 5 shows an example in which the main body layer portion 31w of the intermediate refractive index layer 31 is dispersedly formed in the second region in the form of dots (that is, the main body layer portion and the contact layer in FIG. 3). Is equivalent to the reversed formation relationship). When the surface of the scattered main body layer portion 31w is formed in a spherical shape, boundary reflection is less likely to occur, and the light extraction efficiency can be increased.

  In all of the configurations of FIGS. 1, 4 and 5, the GaAs substrate for epitaxial growth of the light emitting layer portion 24 is left as the element substrate 7. However, the GaAs substrate is removed by grinding or etching, and the removed surface is removed. A transparent semiconductor substrate such as a GaP substrate can be bonded together, or the removal surface can be covered with a reflective metal layer. As a result, the luminous flux directed toward the back side of the element can be effectively extracted outside, and the light extraction efficiency of the element can be further improved.

The cross-sectional schematic diagram which shows typically 1st embodiment of the light emitting element of this invention. The top view which shows the 1st example of the formation form of the intermediate refractive index layer in the light emitting element of this invention. The top view which shows the 2nd example of the formation form of the intermediate refractive index layer in the light emitting element of this invention. The cross-sectional schematic diagram which shows typically 2nd embodiment of the light emitting element of this invention. The cross-sectional schematic diagram which shows typically 3rd embodiment of the light emitting element of this invention. The graph which shows the relationship between the refractive index of the silicon nitride which comprises an intermediate | middle refractive index layer, and Si / N composition ratio.

Explanation of symbols

100, 200, 300 Light-emitting element 9 Metal electrode 24 Light-emitting layer part 30 Oxide transparent electrode layer 31 Intermediate refractive index layer 31h Conducting through-hole 32 Contact layer 50 Compound semiconductor layer

Claims (8)

A compound semiconductor layer having a light emitting layer portion; and an oxide transparent electrode layer that is laminated on the compound semiconductor layer and applies a light emission driving voltage to the light emitting layer portion. In the light emitting device in which the oxide transparent electrode layer is taken out in the form of transmitting, between the oxide transparent electrode layer and the compound semiconductor layer, between the oxide transparent electrode layer and the compound semiconductor layer An intermediate refractive index layer having a refractive index of 5 is disposed. The intermediate refractive index layer is an insulating layer, and the transparent oxide electrode layer is electrically connected to the compound semiconductor layer through a conductive through portion formed through the intermediate refractive index layer. Item 2. A light emitting device according to Item 1. A metal electrode for applying a light emission driving voltage to the light emitting layer portion is formed so as to cover a part of the main surface of the oxide transparent electrode layer, and a projection region of the metal electrode is formed on the main surface of the compound semiconductor layer. 3. The light-emitting element according to claim 1, wherein the intermediate refractive index layer is formed so as to cover the second region, with the first region being the first region and the other region being the second region. . The intermediate refractive index layer formed in the second region is an insulating layer, and in the second region, conductive through portions penetrating the intermediate refractive index layer are formed and dispersed in the conductive through portion. 4. The light emitting device according to claim 3, wherein a transparent electrode layer is electrically connected to the compound semiconductor layer. 5. The light emitting device according to claim 4, wherein the intermediate refractive index layer made of the insulating layer is also formed in the first region, and the conductive through portion is not formed in the first region. element. The oxide transparent electrode layer is disposed in contact with the compound semiconductor layer in the conduction penetrating portion, and in order to reduce contact resistance with the compound semiconductor layer, a metal or an 6. The light emitting element according to claim 2, wherein a contact layer made of a compound semiconductor having a band gap energy smaller than that of the compound semiconductor forming the light emitting layer portion is formed. The light emitting device according to claim 6, wherein the contact layer is selectively formed in the conduction through portion. The oxide transparent electrode layer is an ITO layer or a zinc oxide layer, and the intermediate refractive index layer is made of any one of silicon nitride, boron nitride, aluminum nitride, titanium oxide, zirconium oxide, cerium oxide, and tantalum oxide. The light-emitting element according to claim 1.

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