| Scope and method of study. The effects of ultrafine finishing processes, such as etching, chemomechanical polishing and mechanical polishing, on the photoluminescence (PL) of single crystal (wurtzite) seeded-chemical-vapor-transport grown bulk ZnO are presented. Spectrally resolved luminescence from (0001)-oriented samples was studied using a conventional PL system for sample temperatures ranging from 0--300 K. PL from each of the prepared surfaces was measured, and changes in the spectral content, temperature dependence and intensity introduced by polishing are assessed. Room temperature PL results are compared to a direct measure of subsurface damage obtained by axial ion channeling.; Results and conclusions. Dominant bound-exciton emission, two-electron satellites, and optical phonon replicas of higher-energy peaks characterize the low-temperature PL for each of the prepared surfaces. The observation of free-exciton emission at 4.2 K for both the etched and chemomechanically polished surfaces demonstrates the high quality of material used for this study. The temperature dependence (0--300 K) of the free-exciton peak for chemomechanically polished ZnO is presented in this study. Room temperature PL results for all of the polished samples are compared to the amount of lattice disorder introduced by polishing, as measured by axial ion channeling, and an overall trend of decreased PL efficiency with increased lattice disorder is observed. The introduction of new low-temperature PL peaks with increased disorder is also observed. Mechanically polished samples are seen to exhibit hot-exciton emission and a donor-acceptor recombination not observed for any of the other surfaces. Each of these new peaks is attributed to near-surface damage introduced by polishing. The effect of hydrogen treatment on the 4.2 K PL of ZnO was also investigated. Relative intensities of the bound-exciton peaks were observed to change with H treatment and the 3.361 eV peak is tentatively assigned as a H-related bound-exciton peak. Room temperature PL spectroscopy is shown to exhibit potential as a sensitive tool for the characterization of subsurface damage in polished ZnO. Results from this study will aid in identifying the processing conditions which show promise for producing high-quality substrates for use in the homoepitaxial growth of ZnO or the heteroepitaxial growth of GaN thin films for use as short wavelength light emitters. |
