Strain effect on optical polarization properties of a ‐plane GaN on r ‐plane sapphire

In this study, the optical polarization properties under varying strains in a-plane GaN were investigated. The valence band (VB) structure for a-plane GaN is derived from the effective-mass Hamiltonian based on k·p perturbation theory. The relative oscillator strength (ROS) calculations of the transitions related to the top three VBs near Γ point are applied to analyzing the optical polarized properties. For a-plane GaN, the main components of the first, the second and the third VBs are |Y 〉-like (y-axis // [100]), |Z 〉-like (z-axis // [0001]) and |X 〉-like (x-axis // [110]) states, respectively. Under small compressive strain along c-axis, the polarization degree increases with compressive strain increasing. According to X-ray diffraction (XRD) scans and Raman backscattering spectra, both the in-plane and out-plane strains were evaluated. Polarized photoluminescence (PL) is employed to obtain the polarization degree. The experimental results of a-plane GaN samples under different strains showed good accordance with our theoretical calculations (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)