Characterising the degree of polarisation anisotropy in an a-plane GaN film

We have performed a thorough characterisation of an a-plane GaN film, using X-ray diffraction reciprocal space mapping, k•p theory and polarised photoluminescence spectroscopy Within the plane of the film and along the growth direction, the strain was found to be compressive and tensile respectively. The relative oscillator strength of the transitions involving the topmost valence bands has been calculated as a function of strain. We find that using the experimentally determined strain values as input parameters to the theoretical model, results in good agreement between the predicted relative oscillator strengths and the degree of optical polarisation anisotropy measured in the low temperature photoluminescence spectroscopy.