The effect of biaxial strain on the valence bands in (101̄0)-GaN/AlGaN quantum wells (QWs) is theoretically investigated, using the sp3 tight-binding method. The effective mass around the valence band edge in unstrained (101̄0) QWs is reduced to about 1/2 that of (0001) QWs. Under compressive strain, the subband non-parabolicity near the band edge is further reduced due to heavy-hole/light-hole splitting. The optical matrix elements of [112̄0] polarization in these QWs are twice as large as those in (0001) QWs. The reduced effective mass and large optical matrix elements in the (101̄0) QWs are an advantage for short-wavelength laser diodes based on wurtzite GaN.

We analyze theoretically optical gains in vertical-cavity surface-emitting lasers (VCSELs) for various crystal orientations. The calculation based on the multiband effective-mass theory takes into account the effects of anisotropy and nonparabolicity on the valence subband dispersion. It is found that in VCSELs employing InGaAs/InP strained quantum wells (QWs) with non-(001) orientations except (111), the polarization in the QW plane can be controlled and high gains are obtained. In particular, the gains in VCSELs with (NN1)-oriented (N≥2) strained QWs are markedly higher than those in the equivalent (001) lasers.

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Optical gains in wurtzite–GaN strained quantum-well (QW) lasers are estimated theoretically for various crystallographic directions. The calculation of the valence subbands is based on the k⋅p theory, where deformation potentials are determined by a semiempirical tight-binding method. It is found that the gains in GaN strained QW lasers with non-(0001) orientations, particularly around the (101̄5) orientation, are markedly high and anisotropic, unlike those in (0001)-oriented lasers.

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