Optical polarization properties of M-plane GaN films investigated by transmittance anisotropy spectroscopy

The authors investigate the in-plane optical polarization properties of [11¯00]-oriented (M-plane) GaN films on γ-LiAlO2(100) substrates by transmittance anisotropy spectroscopy (TAS). This technique is sensitive to the difference in the transmittance between light polarized parallel and perpendicular to the c axis of GaN, which for M-plane GaN lies in the film plane. The TAS spectrum exhibits a clear resonance in the vicinity of the fundamental bandgap. Simulations demonstrate that this resonance directly reflects the polarization-dependent shift of the bandgap. The zero crossings of the differential TAS spectrum are shown to be a measure for the polarization-dependent transition energies.