Flip-chip LED and fabrication method thereof
A flip-chip LED and a method for forming the LED are disclosed. The method includes: providing a substrate and depositing on the substrate an epitaxial layer including, from the bottom upward, an n-type GaN layer, a multi-quantum well active layer, and a p-type GaN layer; etching the epitaxial layer to form an array of openings exposing the n-type GaN layer; forming a first metal layer on the p-type GaN layer; annealing the first metal layer to induce self-assembly thereof; etching the p-type GaN layer by using the first metal layer as a mask such that an array of holes formed therein; and depositing a second metal layer over the array of holes, the second metal layer and the first metal layer form a metal reflector layer. The design can result in an improvement in the light extraction efficiency of the LED.
1. A method of forming a flip-chip light-emitting diode (LED), comprising the following steps performed sequentially:
providing a substrate and depositing an epitaxial layer on the substrate, the epitaxial layer comprising, successively from the bottom upward, an n-type gallium nitride layer, a multi-quantum well active layer, and a p-type gallium nitride layer;
etching the epitaxial layer to form an array of openings exposing the underlying n-type gallium nitride layer;
forming a first metal layer on the p-type gallium nitride layer;
annealing the first metal layer to induce self-assembly thereof;
etching the p-type gallium nitride layer by using the first metal layer as a mask, such that an array of holes are formed in the p-type gallium nitride layer; and
depositing a second metal layer over the array of holes, the second metal layer and the first metal layer forming a metal reflector layer.
2. The method of claim 1 , wherein at least one of the first and second metal layers is formed of a multi-layer metal stack.
3. The method of claim 2 , wherein the multi-layer metal stack is a Ni/Ag/Ti/Pt/Au metal stack, a Ni/Al/Ti/Pt/Au metal stack, a Ni/Ag/Ni/Au metal stack, or a Ni/Al/Ti/Au metal stack.
4. The method of claim 3 , wherein the metal reflector layer has a thickness of 0.1 nm-10 nm.
5. The method of claim 1 , wherein the array of holes is formed in the p-type gallium nitride layer by dry-etching the p-type gallium nitride layer.
6. The method of claim 1 , wherein the substrate is a sapphire substrate.
7. A flip-chip light-emitting diode (LED) formed by the method as defined in claim 1 , comprising:
a substrate;
an epitaxial layer on the substrate, the epitaxial layer comprising, successively from the bottom upward, an n-type gallium nitride layer, a multi-quantum well active layer, and a p-type gallium nitride layer, the p-type gallium nitride layer comprising an array of holes formed therein; and
a metal reflector layer on the p-type gallium nitride layer.
8. The flip-chip LED of claim 7 , wherein the metal reflector layer is formed of a multi-layer metal stack.
9. The flip-chip LED of claim 8 , wherein the multi-layer metal stack is a Ni/Ag/Ti/Pt/Au metal stack, a Ni/Al/Ti/Pt/Au metal stack, a Ni/Ag/Ni/Au metal stack, or a Ni/Al/Ti/Au metal stack.
10. The flip-chip LED of claim 8 , wherein the metal reflector layer has a thickness of 0.1 nm-10 nm.