Crystal quality of InN thin films grown on ZnO substrate by radio-frequency molecular beam epitaxy

Abstract

The growth of InN on {0001} ZnO substrates by radio-frequency, plasma-assisted, molecular-beam epitaxy (RF-MBE) has been experimentally investigated. The reflection high-energy electron diffraction (RHEED) pattern quickly recovered to a 1×1 streak pattern as the InN growth was started on nitridated ZnO substrates, whereas the RHEED pattern of the ZnO substrate was spotty because of plasma damage induced by nitridation. The full width at half maximum (FWHM) of the (0002) InN rocking curve was estimated to be around 150 arcsec from x-ray diffraction (XRD). Furthermore, we observed a remarkable feature from our experiments; namely, the crystal quality of InN does not seem to depend on the surface polarity of the ZnO substrate, while it is well known that InN growth on GaN has strong polarity dependence. To investigate this tendency, we have also investigated the surface stability of adatoms, In and N, on Zn- and O-face ZnO surfaces using a first-principles technique. From the theoretical study, N adsorption is more stable on ZnO surfaces of both polarities compared with In adsorption. Accordingly, the preferential initiation by N adatoms onto both ZnO surfaces can explain the unique style of InN growth on ZnO substrates.