关键词: GaN, polarization degree, m-plane, relative oscillator strength

Abstract: Strain effects on the polarized optical properties of $c$-plane and $m$-plane In$_x$Ga$_{1 - x}$N 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$ \cdot$p perturbation theory. For $c$-plane In$_x$Ga$_{1-x}$N, 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$_x$Ga$_{1-x}$N 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.

Key words: GaN, polarization degree, m-plane, relative oscillator strength