JP2006128450A - Group iii nitride semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element which reduces the dislocation density of a group III nitride semiconductor, and reflects light coming from a light-emitting layer to head for a board effectively in taking out the light so as to improve light-emitting efficiency. <P>SOLUTION: According to the group III nitride semiconductor light-emitting element, a reflective metal layer 210 made of Al and a reflective mask layer 220 consisting of an SiO<SB>2</SB>film 221 and an SiN film 222 are formed on the board. Using these layers, a third group nitride semiconductor layer is formed on the board by a selective growth method to form the semiconductor light-emitting element. On the semiconductor layer, a transparent conductive film 10 made of an ITO is formed. Light reflected by the reflective metal layer 210 and the reflective mask layer 220 formed on the board is sent outside as output through the transparent conductive film 10. The above structure reduces the dislocation density of the third group nitride semiconductor through the reflective mask layer 220, and enables effective reflection and takeout of light by the reflective metal layer 210 and the reflective mask layer 220. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a group III nitride semiconductor light-emitting device, and more particularly to reduction of the transition density and improvement of light emission efficiency of the light-emitting device.

Conventionally, it is difficult to obtain a GaN substrate for a group III nitride semiconductor light emitting device, and in order to obtain a group III nitride semiconductor light emitting device, a crystal is grown on a different substrate such as a sapphire substrate. For this reason, a very large number of transitions of 10 ⁸ to 10 ¹⁰ cm ⁻² occurred in the group III nitride semiconductor thin film grown on the substrate. Due to this large number of transitions, the device characteristics of the light emitting device using the group III nitride semiconductor are adversely affected. Therefore, various techniques for reducing the dislocation density of the group III nitride semiconductor thin film have been proposed.

  In addition, in order to efficiently extract light emitted from the light emitting element, a technique for improving light emission efficiency by forming a multilayer film having different refractive indexes and reflecting or transmitting light from the light emitting layer has been proposed.

The following are mentioned as these patent documents.
JP 2003-158295 A In JP-A-2001-274521, a mask layer on a substrate is formed and a dislocation density is reduced by a selective growth technique, and a multi-layer film (DBR (Distributed Bragg Reflection) film of a group III nitride semiconductor layer) ) Discloses a configuration for efficiently extracting emitted light.

Patent Document 2 discloses a configuration of a semiconductor laser in which a dielectric multilayer reflecting mirror (DBR) of a striped ZrO ₂ / SiO ₂ film (mask) is provided on a sapphire substrate.

  However, when a multilayer reflective film that reflects light from the light emitting layer is provided, a group III nitride semiconductor needs to be grown thereon, and there is a problem that the material and composition thereof are restricted. In addition, the multilayer reflective film (DBR) exhibits a reflectance close to 100% with respect to light perpendicular to the film, but with respect to light oblique to the reflective film, the reflectance decreases. In particular, when light in various directions is reflected like a light emitting diode, it may not function effectively.

  Furthermore, in order to reduce the dislocation density of the group III nitride semiconductor thin film, it is necessary to form a selective mask layer on the multilayer reflective film and selectively grow it, resulting in a complicated process and a long time for manufacturing. there were.

  The present invention has been made to solve these problems, and its purpose is to reduce the dislocation density of the group III nitride semiconductor thin film and effectively reflect the light from the light emitting layer toward the substrate. An object of the present invention is to provide a light-emitting element with improved light emission efficiency by extracting light.

  The configuration of the invention for solving the above-described problems is as follows.

  The invention according to claim 1 is a group III nitride in which a mask layer partially provided for selective growth of a group III nitride semiconductor on a substrate and a transparent conductive film is provided on the group III nitride semiconductor layer. In a semiconductor light emitting device, a group III nitride semiconductor comprising a reflective metal layer on a substrate, and the mask layer is composed of a multilayer reflective mask layer having different refractive indexes from which a group III nitride semiconductor does not grow It is a light emitting element.

  Here, the light emitting element is a semiconductor light emitting element having a structure in which a semiconductor layer is formed on a substrate, a transparent conductive film is formed on the semiconductor layer, and light is extracted from the transparent conductive film. The semiconductor layer on which the transparent conductive film is formed may be either a p-type semiconductor or an n-type semiconductor. The p-type semiconductor is usually a p-type semiconductor in relation to the p-type treatment, but the uppermost layer may be an n-type semiconductor due to the evolution of manufacturing technology. Even so, the present invention is applicable.

Examples of the substrate include sapphire (Al ₂ O ₃ ), silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga ₂ O ₃ ), gallium phosphide (GaP), and zinc oxide ( ZnO), magnesium oxide (MgO), manganese oxide (MnO), the general formula _{Al x Ga y in 1-xy} N with quaternary represented, ternary, it can be used binary semiconductor.

  Examples of the transparent conductive film include metal oxides. Typically, indium tin oxide (ITO) or zinc oxide (ZnO) is preferably used. Moreover, a metal thin film may be used, for example, Ni / Au or Co / Au is used.

Examples of the multilayer reflective mask layer include metal oxide, metal nitride, and glass, but typically, silicon oxide (SiO, SiO ₂ , Si _x O _y, etc.), silicon nitride (SiN, Si ₂ N ₃ , etc.). , Si _x N _y, etc.), titanium oxide (TiO, TiO ₂ , Ti _x O _y etc.), titanium nitride (TiN, TiN ₂ , Ti _x N _y etc.), tantalum oxide (TaO, TaO ₂ , Ta _x O _y) ), Tantalum nitride (TaN, TaN ₂ , Ta _x N _y ), aluminum oxide (Al ₂ O ₃ , Al _x O _y ) (where x and y are arbitrary integers) or a composite of these. It is a film obtained by periodically laminating a plurality of types of substances. Desirably, it is a film in which two kinds of substances having a large refractive index difference are alternately laminated. The thickness of each film is set to an integral multiple of 1/4 of the wavelength within the multilayer film of the light to be reflected. This multilayer reflective mask layer is also a DBR (distributed bragg reflector).

  The reflective metal layer is optional as long as it is a metal having a high reflectance with respect to the emitted light. Desirably, silver (Ag), aluminum (Al), rhodium (Rh), a silver alloy, an aluminum alloy, an alloy containing silver and aluminum as main components, and the like.

The invention according to claim 2 is the group III nitride semiconductor light emitting device according to claim 1, wherein the reflective mask layer is made of silicon nitride (Si _x N _y ) and silicon dioxide (SiO ₂ ). With this configuration, it can be formed in the same apparatus, and the reflectance of emitted light can be increased.

  According to a third aspect of the present invention, the substrate is any one of gallium nitride (GaN), sapphire, silicon carbide (SiC), and silicon (Si). This is a group III nitride semiconductor light emitting device.

  A fourth aspect of the present invention is the group III nitride semiconductor light emitting device according to the first to third aspects, wherein the reflective metal layer is aluminum (Al).

  By forming the reflective metal layer with aluminium (Al), a layer with high reflectivity can be manufactured at low cost.

  According to the present invention, a reflective metal layer is provided on a substrate, and a multilayer reflective mask layer having partially different reflectivities is formed, so that the material and composition of the multilayer reflective layer is a group III nitride semiconductor. It is not necessary for the layer to grow, and a combination with higher reflectivity can be selected without being restricted by the material and composition. In addition, light from the light emitting layer is reflected by the multilayer reflective mask layer, and light oblique to the reflective mask layer is reflected by the reflective metal layer, and light is efficiently extracted from the transparent conductive film provided on the semiconductor. Furthermore, since the group III nitride semiconductor is selectively grown through the reflective mask layer, a light emitting element in which the dislocation density in the semiconductor is reduced and the light emission efficiency is further improved can be obtained.

Hereinafter, the best mode for carrying out the present invention will be described.
The specific configuration of the group III nitride semiconductor light-emitting device will be described in detail in a later example. However, as shown in FIG. 1, the present invention transmits light to the outside from the transparent conductive film 10 provided on the semiconductor layer. Is output. A reflective mask layer 220 for performing selective growth is formed on the sapphire substrate 101, and a reflective metal layer 210 is formed between the reflective mask layer 220 and the sapphire substrate 101. At least the uppermost portion of the reflective mask layer 220 is formed with a composition that does not allow the group III nitride semiconductor to grow.

  A buffer layer 102 is formed in a portion where the reflective mask layer 220 is not formed, and an n-type contact layer 104, a light emitting layer 106, a p-type cladding layer 107, and a p-type contact layer 108 are sequentially formed on the buffer layer 102. The transparent conductive film 10 is formed on the p-type contact layer 108.

  With the above configuration, light emitted from the light emitting layer 106 in the direction of the transparent conductive film 10 is output to the outside through the transparent conductive film 10 as it is. Further, light emitted from the light emitting layer 106 in a direction substantially perpendicular to the sapphire substrate 101 is reflected by the reflective mask layer 220 and output to the outside through the transparent conductive film 10. Further, the light emitted obliquely from the light emitting layer 106 with respect to the sapphire substrate 101 is reflected by the reflective metal layer 210 formed under the reflective mask layer 220 and similarly output from the transparent conductive film 10 to the outside. In FIG. 1, the reflective metal layer 210 is provided only under the reflective mask layer 220. However, the reflective metal layer 210 may be provided on the entire surface of the substrate as long as the buffer layer or the group III nitride semiconductor is grown. .

As described above, since the reflective metal layer 210 and the reflective mask layer 220 are formed on the sapphire substrate 101, the light in the substrate direction emitted from the light emitting layer 106 is effectively reflected in the direction of the transparent conductive film 10 and output to the outside. Is done. As shown in FIG. 2, the reflective mask layer 220 is composed of a multilayer film in which SiO ₂ films 221 and SiN films 222 are alternately stacked.

  The reflective mask layer 220 functions as a mask layer for selective growth, and can reduce the dislocation density of the group III nitride semiconductor formed thereon.

  The method for forming the transparent conductive film 10 can be sputtering, vacuum deposition, or the like, and is not particularly limited, but is preferably formed by vacuum deposition using an electron beam. The reflective mask layer 220 can be formed by sputtering, vacuum deposition, or the like, and is not particularly limited, but is preferably formed by plasma CVD.

The single quantum well structure and the multiple quantum well structure constituting the light emitting layer have a group III nitride semiconductor Al _y Ga _{1 -yz} In _z N (0 ≦ y <1, 0 <z) containing at least indium (In). Those including a well layer of ≦ 1) are desirable. The structure of the light emitting layer includes, for example, a well layer made of doped or undoped Ga _1-z In _z N (0 ≦ z ≦ 1) and a group III nitride having an arbitrary composition having a larger band gap than the well layer. Examples thereof include a barrier layer made of a physical semiconductor AlGaInN. Preferable examples are a well layer of undoped Ga _1-z In _z N (0 <z ≦ 1) and a barrier layer made of undoped GaN. Here, doping means that a dopant is intentionally included in the source gas and added to the target layer, and undoping does not intentionally add a dopant without including the dopant in the source gas. Means things. Therefore, undoped includes a case where it is naturally doped by diffusing from the adjacent layer.

  Effective methods for crystal growth of group III nitride semiconductor layers include molecular beam vapor phase epitaxy (MBE), metalorganic vapor phase epitaxy (MOVPE), hydride vapor phase epitaxy (HVPE), and liquid phase epitaxy. It is.

The group III nitride semiconductor of each layer constituting the semiconductor element is at least a binary represented by Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). It can be formed of a III-V nitride semiconductor composed of a ternary, ternary or quaternary semiconductor. Some of these group III elements may be replaced by boron (B) and thallium (Tl), and part of nitrogen (N) may be phosphorus (P), arsenic (As), antimony (Sb ) Or bismuth (Bi).

  Further, when forming an n-type layer using these semiconductors, SiGe, Se, Te, C, etc. are added as n-type impurities, and when forming a p-type layer, a p-type impurity is formed. For example, Be, Ca, Sr, Ba, or the like can be added.

  FIG. 1 is a cross-sectional view showing a semiconductor light emitting device 1 of Example 1, and FIG. 2 is a cross-sectional view showing a manufacturing process of a reflective metal layer and a reflective mask layer provided on the substrate.

A reflective metal layer 210 made of aluminum (Al) having a thickness of 500 nm is formed on a sapphire substrate 101 as a light-transmitting substrate having a thickness of 100 μm, and a multilayer made of SiO ₂ film 221 and SiN film 222 on the reflective metal layer 210. The reflection mask layer 220 is formed, and the buffer layer 102 made of aluminum nitride (AlN) and having a thickness of about 20 nm is formed. The reflective metal layer 210, the reflective mask layer 220, and the buffer layer 102 are formed in stripes and have a width of 10 μm and 1 μm, respectively. The width of the reflective metal layer 210 and the reflective mask layer is preferably 2 μm to 40 μm, more preferably 3 μm to 20 μm. The width of the buffer layer is preferably 0.5 μm to 2 μm. The ratio of the two is preferably about 5: 1 to 20: 1. When the ratio of the buffer layer is larger than 5: 1, sufficient reflection cannot be obtained, and when the ratio of the buffer layer is larger than 20: 1. The n-type contact layer 104 takes time to grow.

The reflective mask layer 220 has an SiO ₂ film 221 of 80 nm and an SiN film 222 of 60 nm, and the total thickness of 12 pairs laminated is 1.68 μm. Each film has a thickness of 1 in the medium wavelength with an emission wavelength of 465 nm (the refractive index of SiO ₂ is 1.46, the wavelength in the medium is 320 nm, the refractive index of SiN is 1.94, and the wavelength in the medium is 240 nm). / 4 is set. The number of stacked reflective mask layers 220 is desirably 8 to 20 pairs. Less than 8 pairs is not desirable because the effect of multiple reflection is small and the reflectance is therefore small. Even if there are 20 pairs or more, the effect of multiple reflection is not as great as that of 20 pairs of reflection films, and the entire film thickness of the reflection mask layer 220 is not desirable.

  An n-type contact layer 104 which is a high carrier concentration n + layer having a thickness of about 8.0 μm and made of silicon (Si) -doped GaN is formed thereon. This n-type contact layer is formed by growing on the reflective mask layer 220 in the lateral direction by selective growth from the partially provided buffer layer 102. Thereby, the dislocation density of the n-type contact layer is reduced.

The n-type contact layer 104 has an electron concentration of 5 × 10 ¹⁸ / cm ³ . The higher the electron concentration of this layer, the better, but it can be increased to 2 × 10 ¹⁹ / cm ³ . Then, on the n-type contact layer 104, a light emitting layer 106 having a multiple quantum well structure (MQW) formed by stacking three periods of non-doped GaN having a thickness of 20 nm and non-doped Ga _0.8 In _0.2 N having a thickness of 3 nm is formed. Has been. A p-type cladding layer 107 made of magnesium (Mg) -doped Al _0.15 Ga _0.85 N and having a thickness of about 60 nm is formed on the light emitting layer 106. Further, a p-type contact layer 108 made of magnesium (Mg) -doped GaN having a thickness of about 130 nm is formed on the p-type cladding layer 107. Further, a transparent conductive film 10 made of ITO is formed on the p-type contact layer 108. The thickness of the transparent conductive film 10 is 0.5 μm.

  On the other hand, an n-electrode 140 is formed on the exposed n-type contact layer 104 by etching from the p-type contact layer 108. The n-electrode 140 has a double structure, and a vanadium (V) layer 141 having a thickness of about 18 nm and an aluminum (Al) layer 142 having a thickness of about 1.8 μm are partially exposed from the n-type contact layer 104. It is configured by sequentially laminating the portions. A p-electrode 150 mainly made of gold (Au) having a film thickness of about 1.5 μm is formed on the transparent conductive film facing the n-electrode 140.

  In the light-emitting element 1 manufactured in this way, the external quantum efficiency was improved by about 15% as compared with the light-emitting element formed with a single mask layer without using the reflective metal layer 210 and the reflective mask layer 220.

  Next, a method for manufacturing the reflective metal layer 210 and the reflective mask layer 220 will be briefly described with reference to FIG.

First, as shown in FIG. 2A, after a reflective metal layer 210 made of aluminum (Al) having a thickness of 500 nm is formed on a sapphire substrate by sputtering, the SiO ₂ film 221 is 80 nm and the SiN film 222 is formed by plasma CVD. Twelve pairs were stacked at 60 nm (in the drawing, the number of layers is omitted). A photomask 300 having a width of 10 μm was formed in a stripe shape at an interval of 1 μm thereon, and each layer was removed up to the sapphire substrate 101 by dry etching (FIG. 2B). Next, although omitted in the description of the configuration of the light emitting element, a protective film 223 made of SiO _{2 is} formed by sputtering in order to protect the reflective metal layer made of aluminum (Al), and the upper surface of the reflective mask layer 220 and The protective film on the sapphire substrate 101 was removed, and only the side surfaces of the reflective metal layer 210 and the reflective mask layer 220 were covered. With this configuration, at least aluminum (Al) in the reflective metal layer 210 is protected, and the influence of aluminum (Al) can be eliminated when a group III nitride semiconductor is grown by MOCVD.
Next, as shown in FIG. 2D, a low-temperature grown buffer layer 102 is formed on the sapphire substrate, an n-type contact layer is formed, and each semiconductor layer of the light emitting element is formed.

  The present invention can be used for light emitting devices such as light emitting elements, light emitting element chips, LED lamps, and displays. This is extremely effective in improving the external quantum efficiency of the light emitting device, and the light emission output can be increased if compared with the same input power.

Sectional drawing of the light emitting element concerning the specific Example of this invention. Sectional drawing which shows the structure of the board | substrate and semiconductor layer interface of the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting element 10 ... Transparent electrically conductive film 101 ... Sapphire substrate 102 ... Buffer layer 104 ... N-type contact layer 106 ... Light emitting layer 107 ... P-type cladding layer 108 ... P-type contact layer 140 ... N electrode 150 ... P electrode 210 ... Reflection Metal layer 220 ... Reflective mask layer 221 ... SiO ₂ film 222 ... SiN film 223 ... Protective film 300 ... Phyto mask

Claims (4)

In a group III nitride semiconductor light emitting device in which a mask layer partially provided for selective growth of a group III nitride semiconductor on a substrate and a transparent conductive film is provided on a group III nitride semiconductor layer,
A reflective metal layer on the substrate;
The group III nitride semiconductor light-emitting device, wherein the mask layer is composed of a multilayer reflective mask layer having a different refractive index in which a group III nitride semiconductor does not grow.   2. The group III nitride semiconductor light emitting device according to claim 1, wherein the reflective mask layer is made of silicon nitride (SixNy) and silicon dioxide (SiO2).   The group III nitride semiconductor according to claim 1 or 2, wherein the substrate is one of gallium nitride (GaN), sapphire, silicon carbide (SiC), and silicon (Si). Light emitting element.   4. The group III nitride semiconductor light-emitting device according to claim 1, wherein the reflective metal layer is aluminum (Al).

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