Chemical etching behavior of Pt-patterned (0001) and (000̄1) surfaces of ZnO

The chemical etching mechanism of ZnO (0001) and (000̄1) polar surfaces was experimentally investigated by a scanning electron microscope, and applied to the control of surface morphology. The (0001) and (000̄1) surfaces of ZnO single crystal were periodically patterned using Pt masks, and were etched in HCl solution for 1-6 d. The etched patterns could not exactly reflect the shape of the masks due to side etching on the (0001) surface. With respect to the (000̄1) surface, many hillocks periodically formed with keeping the original square shape. The difference in the etching behavior was caused by the difference in the uppermost surface structure. The (0001) surface was etched at step or kink sites because of the existence of oxygen ions at only the steps or kinks, and therefore the step flow etching occurs. However, the (000̄1) surface is etched not at steps and kinks but at the terraces in which only the oxygen ions exist, and the etching direction is vertical to the crystal surface. After long-duration etching, the pattern changed into a pointed pyramidal shape on the (000̄1) surface.