Growth mechanism of ZnO low-temperature homoepitaxy

The authors report on the growth mechanism of ZnO films at the low growth temperature of 500 oCusinghomoepitaxy,whosetemperatureisunavailabletoobtainhigh-qualityZnOfilmsinheteroepitaxy. One typical set of ZnO films were grown on (0001) ZnO substrates by molecular-beam epitaxy: a standard structure without buffer and two buffered structures with high-temperature (HT) homobuffer and low-temperature (LT) homobuffer. As a result, the LT homobuffered structure had the outstanding material properties: the surface roughness is 0.9 nm, the full width at half maximum of x-ray rocking curve is 13 arcsec, and the emission linewdith of donor-bound excitons is 2.4 meV. In terms of the theoretical interpretation of the experimentally obtained electron mobilities, it was found that the LT homobuffered structure less suffers from the dislocation scattering and the ionized-impurity scattering, compared to the HT homobuffered structure. It is proposed that in the ZnO low-temperature homoepitaxy, the LT homobuffer plays a key role in suppressing the outdiffusion of contaminants and inducing the complete termination of dislocations in the homointerface, which result in the formation of smooth wetting layer on the homointerface.