Abstract
Correlation between the quality of bulk ZnO substrates and the properties of homoepitaxial ZnO films grown by metalorganic vapor phase epitaxy (MOVPE) has been investigated. Two kinds of commercial wafers grown by different methods have been employed for the investigation. One of them exhibited (i) mosaic structure revealed by xray diffraction (XRD), and (ii) room-temperature photoluminescence (PL) featured by strong LO phonon replicas of free exciton emission. This reflects a dominant phonon scattering by defects, and/or emissions from impurities or defects. The other substrate showed (i) fine single crystal from XRD, and (ii) free exciton emission from the PL data at room temperature. PL peak position of the homoepitaxial film on the former substrate was lower than that of the free exciton emission. For the homoepitaxial film on the latter, (i) the PL peak at room temperature appeared at the energy position of free exciton emission, and (ii) the surface morphology was smoother than that of the film on the former substrate. We found that crystal quality of substrates significantly influenced the ZnO homoepitaxial films, and therefore it is a key to choose a high quality bulk ZnO substrate for homoepitaxial growth to make high quality epilayers contributing to conductivity control and device applications.
