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We report on the studies of linearly polarized photoluminescence (PL) in a (0001) oriented ZnO epitaxial film, grown by metal organic chemical vapor deposition on a GaN template. The emission of mixed longitudinal-transverse exciton polariton modes was observed up to 130 K that evidences polaritonic nature of the excitonic spectrum up to this elevated temperature.

In this paper we report on the metal-organic chemical vapour deposition of ZnO layers. We focus on heteroepitaxial growth on c-plane Al 2 O 3 and the influence of the VI/II ratio during growth on the properties of the layers. The layer quality has been investigated by HRXRD, PL and reflectivity measurements. Under optimized growth conditions the photoluminescence is dominated by strong near band edge emission lines with half widths below 4 meV and the excitonic signals are clearly visible in reflectivity measurements. Hall effect measurements indicate an n-type background doping in the 10 17 cm -3 range, and mobilities of more than 100 cm 2 /Vs can be reached. Moreover, a post-growth annealing step is found to improve the quality of the layers grown under suboptimal conditions. The problem of strain will be addressed and a tensile strain can be confirmed in the heteroepitaxial ZnO layers.