Morphology evolution of a-plane ZnO films on r-plane sapphire with growth by pulsed laser deposition

In this study, the morphology evolution of epitaxial a-plane ZnO on r-plane sapphire at low and high temperatures with growth by pulsed laser deposition (PLD) are presented. Examination of the surfaces of ZnO films during growth was done with in situ reflection high energy electron diffraction, and atomic force microscopy was used to examine the surface morphology of the corresponding films after growth. For initial growth, it was observed that (1 × 2) reconstruction on ZnO grown at 750 °C (HT-ZnO) occurred with step-flow growth, while ZnO grown at 450 °C (LT-ZnO) exhibited island growth mode. For thick films both HT- and LT-ZnO surfaces eventually develop into stripe morphology. Significant change of surface morphology during cooling had also been observed.