Comparative Study of the Electronic Band Structure of StrainedC-plane andM-plane GaN Films by Polarized Photoreflectance Spectroscopy

Abstract

We have investigated a strained C-plane GaN(0001) film on 6H-SiC(0001) and a strained M-plane GaN(100) film on γ-LiAlO2(100) by polarized photoreflectance spectroscopy, wherein the electric-field vector E of the probe beam is varied in the film plane. In the C-plane film, E always remains perpendicular to the unique c axis of wurtzite GaN, and the spectral features do not change with polarization rotation. In the M-plane film, the orientation of E changes relative to c, and the spectral features are significantly altered. Using the Bir–Pikus Hamiltonian, we calculate the energy and the oscillator strength components of the three transitions at the band gap of GaN as a function of an arbitrary strain in the C plane and the M plane. On its basis, we can explain the origin and the polarization properties of the spectral features in both films.