Photoreflectance spectra of a high-quality ZnO epilayer on the ScAlMgO 4 (0001) substrate grown by laser molecular-beam epitaxy exhibited clear excitonic resonances due to three excitons associated with uppermost valence bands (A, B, and C excitons). The oscillator strengths of the B and C excitons are larger than that of the A exciton. Their broadening was interpreted to be due to the contribution by exciton-polaritons in terms of large longitudinal-transverse splitting of respective excitons. Dependence of the exciton energy on temperature was well fitted assuming the Bose-Einstein statistics giving the Einstein characteristic temperature E of 380 K (33 meV).
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