EFFECT OF THE (10(1)OVER-BAR0) CRYSTAL ORIENTATION ON THE OPTICAL GAIN OF WURTZITE GAN-ALGAN QUANTUM-WELL LASERS

We analyze the valence subband structures of (10 (1) over bar 0)-orien ted wurtzite (WZ) GaN-AlGaN quantum wells (QW's) using the multiband e ffective-mass theory and calculate the optical gain taking into accoun t the subband structure modification due to the crystal orientation ef fect and the pseudomorphic strain which is anisotropic in the QW plane , We show that, for the (10 (1) over bar 0) GaN/AlGaN QW, the two topm ost 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 dispersio n of the (10 (1) over bar 0) QW: also becomes anisotropic, giving a re duced band-edge density-of-states in comparison with the (0001) QW. Mo reover, states constituting the topmost valence subband at the Gamma p oint and along k'(x) are predominantly \Y'>-like. A combination of the reduced band-edge density-of-states and the existence of the preferre d symmetry at the valence band maximum contributes to an improvement o f the y'-polarized TE optical gain. A comparison of the QW's of both o rientations reveals that the (10 (1) over bar 0) QW is capable of achi eving lower transparency current densities. Thus, the (10 (1) over bar 0) QW could be useful in improving the threshold performance of WZ Ga N-based QW lasers.