Absorption coefficient of wurtzite GaN calculated from an empirical tight binding model

The linear absorption coefficient for polarizations parallel and perpendicular to the c-axis of wurtzite GaN is calculated by integrating the momentum matrix element over the full Brillouin zone using a fundamental numerical technique. The energy band structure and wave functions required for this calculation are obtained using an sp3d5–sp3 empirical tight-binding method (ETBM) that includes the spin–orbit and up to second-nearest-neighbor interactions. The model reproduces the selection rules expected from symmetry considerations.