Electronic band structure of strained C- and M-plane GaNfilms investigated by polarized photoreflectance spectroscopy

摘要

We investigate the band structure of a strained C-plane GaN(0001) film on 6H-SiC(0001) and a strained M-plane GaN(ll00) film on γ-LiAlO2(100) experimentally by polarized photoreflectance (PPR) spectroscopy and theoretically using the k·p model. Applying 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. These theoretical studies predict a strain-dependent change in the valence band structure for compressively strained M-plane GaN films resulting in a large in-plane polarization anisotropy in comparison to unstrained or compressively strained C-plane GaN films, which is experimentally confirmed by the PPR spectra of the corresponding films. Therefore, it may be possible with M-plane GaN to achieve a lower transparency density in lasers and to naturally fix the polarization direction in surface-emitting lasers.