Study of Low-Efficiency Droop in Semipolar ( $20\bar{2}\bar{1}$) InGaN Light-Emitting Diodes by Time-Resolved Photoluminescence

The superior low-efficiency droop performance of semipolar (
$20\bar{2}\bar{1}$
) InGaN light-emitting diodes (LEDs) makes it a hot candidate for efficient solid-state lighting and full-color displays. To unveil the mystery of this low droop and high efficiency, the emission dynamics of semipolar (
$20\bar{2}\bar{1}$
) LEDs is investigated by time-resolved and steady-state photoluminescence (PL) measurements. Much smaller carrier lifetimes (radiative and nonradiative lifetime) were obtained from semipolar (
$20\bar{2}\bar{1}$
) InGaN QWs compared with those on the
$c$
-plane samples, possibly due to the reduced quantum-confined Stark effects and smaller indium fluctuation on semipolar InGaN samples. The experimental findings indicate a much reduced excess carrier density in semipolar (
$20\bar{2}\bar{1}$
) InGaN LEDs, which will impact the device performance. Based on this, a modified ABC equation with weak phase-space-filling (PSF) effect was used to model the droop characteristics of semipolar (
$20\bar{2}\bar{1}$
) LEDs.