Structural investigation of ZnO O-polar () surfaces and Schottky interfaces

We report on the atomic structures of bare and metal-coated ZnO O-polar ( 000 1 ¯ ) surfaces as determined by model fitting of surface X-ray diffraction data. O-polar surfaces measured under typical device fabrication conditions are significantly rougher than Zn-polar (0001) surfaces, exhibiting Gaussian-shaped roughness profiles with a width of about 1.5 unit cells, regardless of the existence of a metal over-layer. All samples show a decreased layer distance between the topmost oxygen and zinc layers, consistent with theoretical predictions. Clear differences are observed in the occupations of the topmost oxygen layer in oxidized-metal-coated samples.