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We investigate a strongly anisotropically strained M-plane GaN film by photoluminescence spectroscopy. The spectra are dominated by the lowest-energy free-exciton transition, but the second lowest one is also detectable even at low temperatures. Rotating the linear polarization of the excitation results in a systematic change of the intensity ratio between these two transitions. We analyze this observation with the help of 6 × 6 k·p calculations and associated rate equation models. This analysis shows that the pronounced excitation polarization anisotropy for this M-plane GaN film originates from a competition between hole relaxation and exciton recombination. [ABSTRACT FROM AUTHOR]

Using reflectance spectroscopy, the in-plane polarization behavior of unstrained C- and A-plane GaN films is experimentally investigated. While no in-plane polarization anisotropy is observed for all three band-gap related excitons (A, B, and C) in unstrained C-plane GaN films, the A exciton is completely linearly polarized perpendicular to the c axis in unstrained A-plane GaN films. However, the B and C excitons are only partially polarized. This observation is in excellent agreement with results based on band-structure calculations using the Bir-Pikus Hamiltonian for the wurtzite crystal structure. [ABSTRACT FROM AUTHOR]