The present invention relates to a gallium nitride (GaN) based light-emitting diode (LED), and particularly to a GaN-based flip-chip LED with double reflective layers on its side and a fabrication method thereof.
With the improvement of power GaN-based LEDs in efficiency, it is clear that GaN-based LEDs are to be a viable replacement for conventional light sources. However, semiconductor light sources are limited in light-emission efficiency and production cost, which makes their wide application problematic. Nowadays, the methods to improve the light-emission efficiency of LEDs generally include: patterned substrate, transparent substrate, Distributed Bragg Reflector (DBR) structure, surface patterning, flip-chip, chip bonding, and laser lift-off techniques. Chinese patent application 200410095820.X discloses a flip-chip light-emitting device and a method for fabricating the same. The flip-chip light-emitting device includes a substrate, an n-type layer, an active layer, a p-type layer, an ohmic contact layer of tin oxide doped with at least one of: antimony, fluorine, phosphorus and arsenic, and a reflective layer of a reflective material. By using the conductive oxide electrode structure with low surface resistivity and high carrier concentration, current-voltage characteristics and durability can be improved. However, the invention uses a single metal layer as the light-emitting reflective layer, which still absorbs some of the light and limits light emission; moreover, the single metal layer is only on the bottom of the chip, i.e., none on the side, therefore, the light-reflection rate of the reflective layer is limited.
To solve the problems above, an objective of the present invention is to provide a double-reflective-layer GaN-based flip-chip LED with both a DBR and a metal reflective layer on its side and a fabrication method thereof.
The present invention provides a gallium nitride (GaN) based flip-chip light-emitting diode (LED) with double reflective layers on its side, including:
a sapphire substrate;
a buffer layer and an epitaxial layer formed on the sapphire substrate, the epitaxial layer including an N-GaN layer, a multiple-quantum-well layer and a P-GaN layer;
a transparent conductive layer formed on the P-GaN layer;
a distributed Bragg reflector (DBR) formed over a side of the epitaxial layer and the transparent conductive layer;
a metal reflective layer of an Al—Ag alloy formed on the DBR;
a P-type ohmic contact electrode of a Ti—Au alloy formed on the transparent conductive layer; and
an N-type ohmic contact electrode of an Ni—Au alloy formed on the exposed N-GaN layer,
wherein the P-type ohmic contact electrode and the N-type ohmic contact electrode are bonded to a Si heat dissipation substrate through a Ni—Au alloy metal conductive layer and a Au ball bonder.
The present invention also provides a fabrication method for a gallium nitride (GaN) based flip-chip light-emitting diode (LED) with double reflective layers on its side, including:
1) forming a buffer layer and an epitaxial layer on a sapphire substrate, the epitaxial layer including an N-GaN layer, a multiple-quantum-well layer and a P-GaN layer;
2) forming a transparent conductive layer on the P-GaN layer;
3) mask etching a portion of the mesa with the transparent conductive layer such that the N-GaN layer is exposed;
4) cutting the epitaxial layer and the transparent conductive layer such that the epitaxial layer and the transparent conductive layer have a sloping side;
5) forming a distributed Bragg reflector (DBR) over the side of the epitaxial layer and the transparent conductive layer, the DBR including alternating layers with a high refractive index and with a low refractive index;
6) forming a metal reflective layer on the DBR;
7) forming a P-type ohmic contact electrode on the transparent conductive layer;
8) forming an N-type ohmic contact electrode on the exposed N-GaN layer, thereby finishing fabrication of a GaN-based LED s;
9) providing a heat dissipation substrate, and forming a metal conductive layer and a ball bonder on the heat dissipation substrate for eutectic soldering;
10) soldering the GaN-based LED substrate to the heat dissipation substrate; and
11) thinning and polishing the sapphire substrate, and dicing to obtain separate LED chips.
In the present invention, the material of the transparent conductive layer may be any at least one of: ITO, ZnO, In-doped ZnO, Al-doped ZnO and Ga-doped ZnO; the material of the N-type ohmic contact electrode may be any at least one of: Ni—Au, Cr—Pt—Au and Ti—Al—Ti—Au; the material of the P-type ohmic contact electrode may be any at least one of: Ti—Au, Pt—Au and Ti—Al—Ti—Au; the material of the layer with a high refractive index in the DBR may be any at least one of: TiO, TiO2, Ti3O5, Ti2O3, Ta2O5 and ZrO2; the material of the layer with a low refractive index in the DBR may be any at least one of: SiO2, SiNx and Al2O3; the material of the metal reflective layer may be any at least one of: Al and Ag; the material of the metal conductive layer may be any at least one of: Al, Au and Ni; the material of the ball bonder may be Au or an Au alloy; the GaN-based LED substrate may be bonded to the heat dissipation substrate by eutectic soldering or fusion bonding.
The technical solution of the present invention has the advantages that: by arranging a double reflection structure including a DBR and a metal reflective layer on the sloping side of the LED chip, the good reflectivity of the reflective layers can be fully utilized, thereby improving the light-emission efficiency of the LED.
The reference numerals used in the accompanying drawings include:
The present invention will be further described hereinafter with reference to the embodiments and the accompanying drawings.
A fabrication method for a GaN-based flip-chip LED with double reflective layers on its side includes the following steps:
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The embodiments above are for descriptive purpose only, and should not be interpreted as limiting the scope of the present invention. A variety of alternations and variations can be made by those skilled in the art without departing from the scope of the invention. Therefore, all the equivalent technical solutions fall within the scope of the invention, which is defined by the claims.
Number | Date | Country | Kind |
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201010200860.1 | Jun 2010 | CN | national |