Step-flow growth of homoepitaxial ZnO thin layers by halide vapor phase epitaxy using ZnCl2 and H2O source gases

The surface morphology of homoepitaxial (0 0 0 1)ZnO thin layers grown by halide vapor phase epitaxy (HVPE) using ZnCl2 and H2O source gases was investigated. Atomic force microscopy (AFM) observations showed that high temperature growth at 1000 °C with a low input H2O/ZnCl2 (VI/II) partial pressure ratio of 20 strongly promoted step-flow growth. X-ray diffraction (XRD) analyses revealed the crystalline quality of the homoepitaxial ZnO layer grown at 1000 °C with input VI/II ratio of 20 is comparable to that of bulk ZnO substrates. Under a constant input partial pressure of ZnCl2, the growth rate of ZnO is constant within the temperature range 700-900 °C, and the growth rate decreases above 900 °C due to the shift of thermodynamic equilibrium of the growth reaction.