Strain effects on the polarized optical properties of InGaN with different In compositions

Strain effects on the polarized optical properties of c-plane and m-plane In_xGa_1 - xN were discussed for different In compositions (x=0, 0.05, 0.10, 0.15) by analyzing the relative oscillator strength (ROS) and energy level splitting of the three transitions related to the top three valence bands (VBs). The ROS was calculated by applying the effective-mass Hamiltonian based on k \cdotp perturbation theory. For c-plane In_xGa_1-xN, it was found that the ROS of \left| X \right\rangle and \left| Y \right\rangle-like states were superposed with each other. Especially, under compressive strain, they dominated in the top VB whose energy level also went up with strain, while the ROS of the \left| Z \right\rangle-like state decreased in the second band. For m-plane In_xGa_1-xN under compressive strain, the top three VBs were dominated by \left| X \right\rangle, \left| Z \right\rangle, and \left| Y \right\rangle-like states, respectively, which led to nearly linearly-polarized light emissions. For the top VB, ROS difference between \left| X \right\rangle and \left| Z \right\rangle-like states became larger with compressive strain. It was also found that such tendencies were more evident in layers with higher In compositions. As a result, there would be more TE modes in total emissions from both c-plane and m-plane InGaN with compressive strain and In content, leading to a larger polarization degree. Experimental results of luminescence from InGaN/GaN quantum wells (QWs) showed good coincidence with our calculations.