UNIAXIAL STRAIN EFFECT ON THE ELECTRONIC AND OPTICAL-PROPERTIES OF WURTZITE GAN-ALGAN QUANTUM-WELL LASERS

The valence subband structures of uniaxial-strained wurtzite (WZ) GaN- AlGaN quantum wells (QW's) are calculated using multiband effective-ma ss theory, The optical gain is investigated using a numerical approach in which we account for the subband structure modification and mixing due to the anisotropic strain in the QW plane. We show that the mixin g of the HH and LH bases in the uniaxial-strained (0001) GaN-AlGaN QW decouples \X] and \Y] at the Gamma point, giving two topmost subbands, Y1 and X1, which can be more widely separated than the HH1 and LH1 su bbands in the biaxial-strained (0001) GaN-AlGaN QW, We resolve the sta tes of the subband dispersion in terms of the \X], \Y], and \Z] bases; and show the compositional variation as a function of the in-plane wa vevector. Under uniaxial strain, it is possible to exploit the existen ce of the preferred symmetry at the valence band maximum and the reduc ed band-edge density-of-states due to the, anisotropic in-plane energy dispersion to achieve lower transparency carrier and current densitie s and higher differential gain in comparison with a pseudomorphic biax ial-strained QW. We show that, for a QW laser structure with the optic al cavity along the x axis; uniaxial compressive strain in the y direc tion shows greater improvement than the uniaxial tensile strain in the x direction of the same magnitude. Thus, a suitable uniaxial strain c ould be used to improve the threshold performance of WZ GaN-based QW l asers.