Injection current‐dependent quantum efficiency of InGaN‐based light‐emitting diodes on sapphire and GaN substrates

Abstract

AbstractWe studied the nonthermal mechanism of quantum efficiency (QE) roll‐off in InGaN‐based multiple‐quantum‐well LEDs on sapphire and bulk GaN substrates with In content ranging from 1% to 28%. Both the efficiency evolution and peak energy shift appear to be strongly dependent on the In content, but nearly independent of the dislocation density in the active region. The QE of the green LED peaks at a current density as low as 1.4 A/cm2, and decreases dramatically as current is increased, whereas the UV LED has a nearly constant QE at currents up to 1 kA/cm2. In contrast to minimal current‐induced peak shift and spectral broadening in the near‐UV and UV LED, the green LED has a monotonic peak blueshift of a total amount of ∼110 meV and a spectral broadening by a factor of 2. These results lead to a conclusion that carrier delocalization followed by nonradiative recombination at misfit defects is the major nonthermal mechanism of the efficiency roll‐off in InGaN‐based visible LEDs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)