On the reduction of efficiency loss in polar c -plane and non-polar m -plane InGaN light emitting diodes

Abstract

We have undertaken a series of experiments in InGaN light emitting diode (LED) structures both on polar (c-plane) and non-polar (m-plane) GaN substrates with and without magnesium doped AlGaN electron blocking layers (EBLs) on the p-side of the p-n junction to shed the much needed light on the carrier injection and transport. The LEDs grown on c-plane bulk GaN substrates without EBL show 40% peak electroluminescence (EL) intensity, while the EL peak intensity of the LEDs grown on m-plane bulk GaN substrates without EBL is 30% of that with EBL. However, optical measurements for internal quantum efficiency (IQE) reveal that the IQE values of LEDs with and without EBL are comparable for both cases, which are in the range of 80-85% for m-plane variety and 50% for c-plane variety. Furthermore, with varying Al composition (15%, 8%, 0%) in the EBL, the EL intensity for both m-pane and c-plane LEDs decrease progressively as the Al composition decreases. When highly conductive and transparent Ga doped ZnO layers are used as the current spreading layers for LEDs, the degradation of the efficiency with injection is significantly reduced to 27% compared to LEDs with semitransparent Ni/Au contacts having 50% efficiency degradation up to the same current density ∼3500 A/cm2. This can be due to presumably the reduction in current filamentation or current crowding. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.