High-performance GaN-based light-emitting diodes on patterned sapphire substrate with a novel hybrid Ag mirror and atomic layer deposition-TiO2/Al2O3 distributed Bragg reflector backside reflector

Abstract

GaN-based light-emitting diodes (LED) on a patterned sapphire substrate with a novel hybrid atomic layer deposition (ALD)-TiO 2 Al 2 O 3 distributed Bragg reflector (DBR) and Ag mirror have been proposed and fabricated. Due to the excellent thickness uniformity of ALD for the proposed reflector, high reflectivity over 99.3% at an incident angle of 5 deg has been achieved. It was also found that the reflectivity of a backside reflector with an Ag mirror slightly depends on incident light wavelength and incident angle. Moreover, because of the good adhesion between TiO 2 /Al 2 O 3 DBR and the Ag mirror, the fabrication process was simplified and reliable. With a 60 mA current injection, an enhancement of 5.2%, 8.9%, and 47.1% in light output power (LOP) at the 460 nm wavelength was realized for the proposed LED with Ag mirror and 3-pair ALD-TiO 2 Al 2 O 3 DBR as compared with a LED with a traditional Ag mirror and 3-pair TiO 2 /SiO 2 DBR, with Al mirror and 3-pair ALD-TiO 2 Al 2 O 3 DBR, and without backside reflector, respectively. This result shows that the ALD-TiO 2 /Al 2 O 3 DBR can be used to enhance the LOP greatly and improve adhesion between the sapphire substrate and the metallic mirror, and thus is very promising for fabricating high performance GaN-based LEDs.