Polarization dependent study of gain anisotropy in semipolar InGaN lasers

The optical gain of single quantum well laser structures on semipolar $(11\overline{2}2)$-GaN in dependence of the optical polarization and the resonator orientation has been studied by variable stripe length method. The c′-$[11\overline{23}]$ resonator shows maximum gain in TE mode, followed by the m-$[1\overline{1}00]$-resonator with extraordinary polarization. The anisotropic gain behaviour is explained by valence sub-band ordering and birefringence of the wurtzite crystal, resulting in a modification of the transition matrix element for stimulated emission. Measurements are accompanied by 6 × 6 k · p band structure calculations and gain analysis.