Atomic layer deposition growth of epitaxial zinc oxide

In this work the basic characteristics of ZnO, atomic layer deposition (ALD) and epitaxial ZnO growth by ALD are presented, followed by the experimental results of the epitaxial growth of ZnO on GaN template by 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), atomic force microscope (AFM), X-ray diffraction (XRD), photoluminescence (PL) measurements and positron annihilation spectroscopy. The ZnO fims were confrmed epitaxial, and the film quality was found to improve with increasing deposition temperature in the vicinity of the threshold temperature of two dimensional growth. Contrary to previous reports, high-temperature annealing did not enhance the film properties but rather damaged the film. 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.