Effect of the (1010) crystal orientation on the optical gain of wurtzite GaN-AlGaN quantum-well lasers

Abstract

We analyze the valence subband structures of (101O)-oriented wurtzite (WZ) GaN-AlGaN quantum wells (QW,s) using the multinand effective-mass theory and calculate the optical gain taking into account the subband structure modification due to the crystal orientation effect and the pseudomorphic strain which is anisotropic in the QW plane We show that, for the (1010) GaN/AlGaN QW, the two topmost subbands, Y'1 and X'1, are more widely separated than the HH1 and LH1 subbands in the (0001) GaN-AlGaN QW. The in-plane energy dispersion of the (1010) QW also becomes anisotropic. giving a reduced band-edge density-of-states in comparison with the (0001) QW. Moreover, states contituting the topmost valence subband at the T point and along k'x are predominantly |Y′〉 -like. A combination of the reduced band-edge density-of-states and the existence of the preferred symmetry at the valence band maximum contributes to an improvement of the u′ -polarized TE optical gain. A comparison of the QW's of both orientations reveals that the (1010) QW is capable of achieving lower transparency current densities. Thus, the (1010) QW could be useful in improving the threshold performance of WZ GaN-based QW lasers.