Fabrication of ZnO Hexagonal Micropyramids by Using an rf-Magnetron Sputtering Method

We report on fabrication of self-assembled ZnO hexagonal micropyramids grown on a (0001) $Al_2O_3$ substrate by using an rf-magnetron sputtering method from the aspects of thier structural and optical properties. We found that the average size of the hexagonal micropyramids increases with increasing growth temperature. The reflection and the photoluminescence spectra at 10 K demonstrate high-quality optical properties for the total growth layer. Especially, for the growth temperatures of 650 ℃ and 700 ℃, fine structures are observable in the excitonic transitions in the reflection spectra. Furthermore, under high-density excitation conditions, photoluminescence bands originating from bi-exciton formation and from an inelastic scattering process of excitons, the so-called P emission, were observed.