Fabrication and Characterization of GaN -Based LEDs Grown on Chemical Wet-Etched Patterned Sapphire Substrates

Characteristics of GaN-based light-emitting diodes (LEDs) grown on the chemical wet-etched patterned sapphire substrates (CWE-PSS) with different crystallography-etched facets were investigated. An improvement of 40% on the overall quantum efficiency was achieved by adopting this CWE-PSS scheme. A Monte Carlo ray-tracing method was employed to derive the optimized condition of sapphire etching time, and the calculated result demonstrated the same trend with real device measurement. Adopting the CWE-PSS in LEDs could not only improve the epitaxial quality but also increase the extraction quantum efficiency due to crystallography-etched facets efficiently scattering the guided light to enter the escape cone on the top of device surfaces. Finally, we observed better aging behaviors of CWE-PSS LEDs, which could be due to the reduction of threading dislocations of the epitaxial layers.