Efficiency retention at high current injection levels in m -plane InGaN light emitting diodes

Abstract

We report the internal quantum efficiency (IQE) and external quantum efficiency (EQE) of <i>m</i>-plane InGaN-based LEDs and <i>c</i>-plane LEDs emitting at 400 nm. According to excitation density dependent photoluminescence (PL) measurements, the IQE values for the <i>m</i>-plane LEDs are approximately 70% higher than that for <i>c</i>-plane reference LEDs with the same structure (multiple-quantum well active region with 3nm In_0.01Ga_0.99N barriers) and similar emission wavelength (400nm) albeit on sapphire substrate. Electroluminescence (EL) measurements reveal that the external quantum efficiency (EQE) from both LEDs shows negligible droop under electrical injection due to the employment of thin In_0.01Ga_0.99N barriers, <i>i.e.</i> coupled quantum wells, in the active regions. However, with increasing current, the EL intensity of the <i>m</i>-plane LEDs increases more rapidly than that of the <i>c</i>-plane LEDs, with the EL intensity reaching its peak value at ~240 Acm^-2 for the <i>m</i>-plane LEDs and ~420 Acm^-2 for the <i>c</i>-plane LEDs. Consistent with the IQE values obtained from the PL measurements, the m-plane LEDs exhibit ~ 60% higher EQE values than the <i>c</i>-plane counterparts. It is also worth to mention that increasing the emission wavelength (from 400 nm to 435 nm) for the <i>m</i>-plane LEDs does not affect the efficiency retention at high injection levels.