High optical polarization ratio from semipolar (202¯1¯) blue-green InGaN/GaN light-emitting diodes

Abstract

The optical polarization ratio of spontaneous emission was investigated by electroluminescence measurements for semipolar $(20\overline{2}\overline{1})$ InGaN/GaN light-emitting diodes, covering the blue to green spectral range. Devices fabricated on semipolar $(20\overline{2}\overline{1})$ substrates exhibit polarization ratios ranging from 0.46 at 418 nm to 0.67 at 519 nm. These polarization ratios are significantly higher than those reported on semipolar $(20\overline{2}1)$ devices. The valence band energy separation is extracted from spectral measurements and is consistent with the increased polarization ratio and theoretical predictions. Quantum well interdiffusion induced valence band mixing is suggested as a possible explanation for the low experimental value of polarization ratio observed for the $(20\overline{2}1)$ devices.