Optical gain and crystal symmetry in III–V nitride lasers

Abstract

Optical gains of bulk GaN and GaN/AlGaN quantum wells (QWs) are calculated in wurtzite (WZ) and zinc-blende (ZB) structures. The physical parameters are extracted by reproducing the band-edge electronic structures from the first-principles band calculations. It is found that the lower crystal symmetry, that is the WZ structure, is preferable for the lower transparent current density in bulk GaN. Although the introduction of QW structures leads to symmetry lowering only in the ZB structure, we cannot find a significant benefit of the ZB QW structure, owing to the weak spin-orbit coupling of the nitrogen atom.