Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2003-01-27
2004-06-01
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S094000, C257S099000, C257S103000
Reexamination Certificate
active
06744071
ABSTRACT:
FILED OF THE INVENTION
This invention relates to a nitride semiconductor element with a supporting substrate used for a light-emitting device such as a light emitting diode (LED), a laser diode (LD), etc., a photoreceptor such as a solar cell, a photo sensor, etc., an electronic device such as a transistor, a power device, etc., and a method for producing thereof. An attaching structure is employed as one of the methods for producing.
BACKGROUND OF THE INVENTION
A nitride semiconductor is one of desirable candidate direct-band-gap semiconductor materials, however, it is difficult to produce a bulk of its single crystal. Therefore, hetero-epitaxial technology is usually employed to grow GaN on a different material substrate such as sapphire, SiC, etc. by metal-organic chemical vapor deposition (MOCVD) for the present. It was shown that sapphire is a preferable substrate for growing a high efficient light-emitting device of nitride semiconductor because of its stability at high temperature under atmosphere with ammonia in an epitaxial vapor deposition process compared with the other different material substrates. When a sapphire substrate is employed, a process for forming AIGaN layer as a buffer layer on the sapphire substrate at low-temperature around 600° C. is usually employed to grow nitride semiconductor layers thereon. It can improve crystallinity of the nitride semiconductor layers.
Concretely Specifically, a nitride semiconductor element grown on a sapphire substrate is used for a blue LED, a pure-green LED with higher luminance than conventional LEDs, and an LD(laser diode). They are applied for a full-color display; traffic lights; an image scanner; light sources such as a light source for an optical disc, which is media, for example DVD, capable of memorizing a large-capacity of information; a light source for communication; a printer; etc. Further, it is anticipated to apply to an electronic device such as a field-effect transistor (FET).
Related Reference 1
Japanese Patent Laid-Open Publication Toku-Kai No. HEI 9-129932 (1997).
However, sapphire is a low thermal conductivity insulating material. Thus, the structure of nitride semiconductor element is limited. For example, in the case of conductive substrate such as GaAs or GaP, one of electric contact portions (terminals) can be disposed on the top surface of the semiconductor device, another contact portion can be disposed on the bottom. But, both of the electric contact portions of the light-emitting element grown on the sapphire substrate should be disposed on the top surface (the same plane side). Therefore, when an insulating material such as sapphire, etc. is employed as a substrate, it reduce the effective area of light-emission compared with a conductive substrate having the same area of substrate. In addition, when an insulating substrate is employed, it reduces the number of elements (chips) obtained from the same diameter of a wafer.
Further, a nitride semiconductor element with an insulating substrate such as sapphire is used as face-up type or face-down type. These types have both terminals in the same plane side, so that it increases current density locally. Then, it generates heat in the element (chip), so that it accelerates deterioration of the element. In addition, wires are required for both of pn terminals in a wire-bonding process for the terminals, so that it increases chip size. Therefore it reduces yield of chips. Additionally, sapphire has high hardness and a crystal structure with hexagonal system. So that when sapphire is employed as a substrate for growth, it is requires to break into chips by scribing the sapphire substrate. Thus, it requires an additional process compared with the other substrates.
Furthermore, recently, it has been available that an LED capable of emitting in ultra-violet region is in practical use. Generally, ultra-violet region is defined as wavelength of light-emission not more than 400 nm. The band gap of GaN is 365 nm. To shorten the wavelength not more than 365 nm, absorption of GaN of a contact layer, etc. may reduce the outgoing efficiency of the light extremely.
The present invention is devised to solve the above problems, and therefore, is aimed to at providing a high efficient nitride semiconductor element having an opposed terminal structure, whose terminals facing each other, without increasing its voltage, and a method for producing thereof. Further, it is another object to provide a high light-emitting power nitride semiconductor element even in ultra-violet region.
SUMMARY OF THE INVENTION
The nitride semiconductor element of the invention includes, at least a conductive layer, a first terminal, a nitride semiconductor with a light-emitting layer, and a second terminal, from a supporting substrate successively, wherein, the first terminal and a first insulating protect layer are interposed between the conductive layer and a first conductive type nitride semiconductor layer. The nitride semiconductor may include the first conductive type nitride semiconductor layer, the light-emitting layer, and a second conductive type nitride semiconductor layer, which has an asperity portion as a top layer thereof. When the supporting substrate is conductive material, it can provide the nitride semiconductor element with an opposed terminal structure. In addition, when the first terminal is a p-type terminal, it can improve the outgoing efficiency of the light. That is, the second conductive type nitride semiconductor element formed in the second terminal (n-type terminal) side, which is topside of the nitride semiconductor layer, is an n-type nitride semiconductor layer. In other word, the n-type nitride semiconductor layer side is the outgoing surface of the light. An n-type layer in the nitride semiconductor (especially GaN system semiconductor) is of low resistance, so that the size of the n-type terminal, the second terminal, can be downsized. Because downsizing the size of the n-type terminal reduce the area cutting off the light, it can improve the outgoing efficiency of the light. Additionally, the conventional nitride semiconductor element has a structure having both terminals in the same plane side, so that it is required to provide a p-pad terminal for the p-type terminal. When conductive material is employed as the supporting substrate in the invention, die-bonding to a package such as a lead frame with a conductive material can achieve continuity. Therefore the p-pad terminal can be eliminated, it can increase the area of light-emission. In addition, providing the first insulating protect layer can prevent short circuit, etc., so that it can improve yield and reliability. It can also simplify its producing process.
In the nitride semiconductor element of the invention, the first terminal and the first insulating protect layer are in contact with the first conductive type nitride semiconductor layer. The first terminal may be formed on the whole of the first conductive type nitride semiconductor layer, however, it should be appreciated that forming the first terminal partially and covering an opening portion with the first insulating protect layer can adjust the contact area between the first terminal and the first conductive type nitride semiconductor layer. In addition, forming the first terminal in a pattern such as a rectangular shape, lines, a square shape, a grid pattern, dots, a rhombus, a parallelogram, a mesh shape, a striped shape, a ramose shape branching from one into a plurality of branches, etc. can improve the outgoing efficiency of the light. When the first conductive type nitride semiconductor layer can have ohmic contact with the first terminal, either p-type terminal or n-type terminal can be employed as the first conductive type nitride semiconductor layer. The first conductive type nitride semiconductor layer is not restricted either in a single-layer or a multi-layer.
The first terminal includes at least one element selected from the group of. Ag, Rh, Ni, Au, Pd, Ir, Ti, Pt, W, and Al. Concretely, reflectivity of Ag, Al, Rh, Pd, and
Kamada Kazumi
Nonaka Mitsuhiro
Sano Masahiko
Yamamoto Masashi
Nichia Corporation
Prenty Mark V.
Wenderoth , Lind & Ponack, L.L.P.
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