Effect of growth temperature on the epitaxial growth of ZnO on GaN by ALD

•High quality epitaxial ZnO films were grown on GaN template by ALD.•Smooth surface morphology was achieved above the threshold temperature of 2D growth.•The film quality was found to improve with increasing deposition temperature.•Only separate Zn-vacancies were observed in the films.

We report on the epitaxial growth of ZnO on GaN template by atomic layer deposition (ALD). Diethylzinc (DEZn) and water vapour (H2O) were used as precursors. The structure and the quality of the grown ZnO layers were studied with scanning electron microscope (SEM), X-ray diffraction (XRD), photoluminescence (PL) measurements and positron annihilation spectroscopy. The ZnO films were confirmed epitaxial, and the film quality was found to improve with increasing deposition temperature in the vicinity of the threshold temperature of two dimensional growth. We conclude that high quality ZnO thin films can be grown by ALD. Interestingly only separate Zn-vacancies were observed in the films, although ZnO thin films typically contain fairly high density of surface pits and vacancy clusters.