Photonic properties of ZnO epilayers

摘要

The characterization by various experimental techniques of homoepitaxial growth and photonic properties of ZnO epilayers was exhaustively analyzed. The photonic properties of ZnO as promising material for the realization of polariton lasers were investigated by angular dependent reflection spectroscopy. The fitting of the polariton dispersion curve with the experimental results provided us information about the longitudinal-transverse exciton-polariton splitting and damping constants. In addition, the valence band symmetry was examined by angular resolved magneto-optical photoluminescence. From our theoretical and experimental results we extracted evidence that the topmost A valence band possesses Γ_7 symmetry. Micro-Raman spectroscopy revealed even in homoepitaxially grown samples the existence of compressive or tensile strain which varied not only in the ZnO layers but also in the templates. In contrast, the untreated substrates were uniformly strained. Sporadically crystal perturbations culminating in the formation of separated growth domains were observed. Additionally, resonant Raman scattering was performed, showing a strong enhancement of the 2E_1(LO) mode for resonant excitation of the I_8 bound exciton complex. We suggest that the resonant Raman scattering led to a longer lifetime of the resonantly excited phonon mode due to a strong exciton-phonon interaction.