An AlGaN tunnel junction light emitting diode operating at 255 nm

Abstract

We report on the demonstration of high-performance tunnel junction deep ultraviolet (UV) light-emitting diodes (LEDs) by using plasma- assisted molecular beam epitaxy. The device heterostructure was grown under slightly Ga-rich conditions to promote the formation of nanoscale clusters in the active region. The device operates at 255 nm with a maximum external quantum efficiency of 7.2% and wall-plug of 4%, which are nearly one to two orders of magnitude higher than those of previously reported tunnel junction devices operating at this wavelength. The devices exhibit highly stable emission, with a nearly constant emission peak with increasing current, due to the strong charge carrier confinement related to the presence of Ga-rich nanoclusters. Efficiency droop, however, is observed at relatively low current densities. Detailed temperature-dependent measurements suggest that the presence of efficiency droop of deep UV LEDs is largely due to electron overflow.