Laser spike annealing for GaN LEDs
View Patent ↗Methods of performing laser spike annealing (LSA) in forming gallium nitride (GaN) light-emitting diodes (LEDs) as well as GaN LEDs formed using LSA are disclosed. An exemplary method includes forming atop a substrate a GaN multilayer structure having a n-GaN layer and a p-GaN layer that sandwich an active layer. The method also includes performing LSA by scanning a laser beam over the p-GaN layer. The method further includes forming a transparent conducting layer atop the GaN multilayer structure, and adding a p-contact to the transparent conducting layer and a n-contact to the n-GaN layer. The resultant GaN LEDs have enhanced output power, lower turn-on voltage and reduced series resistance.
1. A method of forming a gallium nitride (GaN) light-emitting diode (LED), comprising:
forming atop a substrate a GaN multilayer structure having a n-GaN layer and a p-GaN layer that sandwich an active layer, wherein the p-GaN layer includes dopants bound to hydrogen;
performing laser spike annealing (LSA) through at least the p-GaN layer by scanning a laser beam over the p-GaN layer, thereby breaking the hydrogen bonds and activating the dopants therein;
forming a transparent conducting layer atop the GaN multilayer structure; and
adding a p-contact to the transparent conducting layer and a n-contact to the n-GaN layer.
2. The method of claim 1 , further comprising performing the LSA through the transparent conducting layer.
3. The method of claim 2 , further comprising performing LSA of the p-contact.
4. The method of claim 3 , further comprising performing LSA of the n-contact.
5. The method of claim 3 , wherein the p-contact has a p-contact resistance, and said performing of LSA of the p-contact results in the p-contact resistance being in a range from about 4×10 −4 ohm-cm 2 to about 1×10 −5 ohm-cm 2 .
6. The method of claim 4 , further comprising:
forming a ledge in the GaN multilayer structure and transparent conducting layer to expose the n-GaN layer; and
forming the n-contact on the exposed GaN layer.
7. The method of claim 1 , wherein the LSA has a maximum anneal temperature T AM in the range from about 900° C. to about 1,500° C.
8. The method of claim 7 , wherein the scanning of the laser beam is conducted so that the laser beam has a dwell time from about 10 μs to about 10 ms.
9. The method of claim 7 , wherein the laser beam has a line-type beam shape with an aspect ratio of about 100:1.
10. The method of claim 1 , wherein the p-GaN layer has an activated dopant concentration after LSA in the range from about 5×10 17 cm −3 to about 5×10 18 cm −3 .
11. The method of claim 1 , further comprising forming the active layer to comprise a multiple quantum well structure.
12. The method of claim 1 , wherein the dopants consist of Mg.
13. The method of claim 1 , wherein the transparent contact layer includes indium tin oxide (ITO).
14. The method of claim 1 , wherein the n-contact includes at least one of Ti/Au, Ni/Au or Ti/Al.
15. The method of claim 1 , wherein the p-contact includes at least one of Ni/Au and Cr/Au.
16. The method of claim 1 , wherein the p-GaN layer has a contact resistance, and wherein the total contact resistance is reduced by about 60% by performing said laser spike annealing.
17. The method of claim 1 , wherein the laser spike annealing reaches through the GaN multilayer structure.