Characteristics of InGaN light-emitting diodes on GaN substrates with low threading dislocation densities

InGaN light-emitting diodes (LEDs) on GaN substrates with low threading dislocation densities (TDDs) were fabricated, and the characteristics of the LEDs were compared with those on sapphire substrates. LEDs with 3 nm-thick-quantum-wells (QWs) grown on GaN as well as on sapphire substrates showed a decrease of the external quantum efficiency (EQE) With increasing forward current, indicating that carrier localization is in play in both cases. The decrease in the EQE was, however, suppressed in LEDs grown on GaN substrates by adopting thicker QWs. The LED with 5 nm-thick-QWs on GaN substrate mounted p-side down and molded with epoxy showed EQE as high as 26% at 125 A/cm(2). Cathodo luminescence (CL) observations revealed the formation of dark areas related to TDDs, and the dark areas deteriorated the EQE of the LED on the sapphire substrate. (c) 2007 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.