Defect reduction and efficiency improvement of near-ultraviolet emitters via laterally overgrown GaN on a GaN/patterned sapphire template

Abstract

An approach to improve the defect density and internal quantum efficiency of near-ultraviolet emitters was proposed using a combination of epitaxial lateral overgrowth (ELOG) and patterned sapphire substrate (PSS) techniques. Especially, a complementary dot array pattern corresponding to the underlying PSS was used for the ELOG-SiO2 mask design. Based on the transmission-electron-microscopy and etch-pit-density results, the ELOG∕SiO2∕GaN∕PSS structure can reduce the defect density to a level of 105cm−2. The internal quantum efficiency of the InGaN-based ELOG-PSS light-emitting diode (LED) sample showed three times in magnitude as compared with that of the conventional GaN/sapphire one. Under a 20mA injection current, the output powers of ELOG-PSS, PSS, and conventional LED samples were measured to be 3.3, 2.9, and 2.5mW, respectively. The enhanced output power could be due to a combination of the reduction in dislocation density (by ELOG) and improved light extraction efficiency (by PSS). Unlike the previ...