Zinc oxide crystals were grown by CVT contactless technique and thermally annealed in the air, nitrogen or oxygen atmospheres, or zinc or arsenic vapours. Wide ranges of annealing times and temperatures were applied. The variety of morphology and quality of the crystal surfece was investigated by AFM and XRD. It was found, that thermal annealing in the air, nitrogen, oxygen and zinc resulted in similar evolution of the crystal surface, although there are observed differences in the rate of the changes. The annealing in zinc vapour resulted in smooth morphology and stabilization of colour of the crystal, which was dependent on the pressure of the zinc vapour. The obtained roughness (RMS) was typically lower than 1 nm. The annealing in arsenic vapour leads to degradation of the crystal surface. The improvement of the surface was not observed in case of thermal annealing of the rough ZnO surfaces obtained by ALE homoepitaxy on the smooth CVT as-grown ZnO surfaces.

This work was supported by Ministry of Education and Science under grant No. 3 T0A 051 28.