Abstract
In this paper, the k.p perturbation theory is adopted to calculate the interband excitonic transition energies and their polarization selection rules in c-plane AlN films, GaxAl1-xN and InxAl1-xN alloys modulated by both isotropic biaxial in-plane strain and varying alloy compositions. It is shown that valence band mixing induced by both strain and alloy composition has a dramatic influence on the optical polarization properties. The calculated results provide both good physical insight into the band structure engineering and helpful instructions in the future design of high efficiency and novel UV-emitters.