Step-flow growth of homoepitaxial ZnO thin films by ultrasonic spray-assisted MOVPE

Homoepitaxial zinc oxide thin films with atomically flat surfaces have successfully been grown on Zn-polar (0 0 0 1) ZnO substrates with the step-flow growth mode by ultrasonic spray-assisted metalorganic vapor phase epitaxy. The surfaces of the grown layers were composed of terraces and steps, where the step height was mainly 0.26 nm originated from half of a c-axis lattice parameter of hexagonal ZnO crystal, at the optimizing growth conditions. The step-flow growth required the higher growth temperature (for example, at 950 °C), while at lower temperatures (for example, at 875 °C) the growth mode was a mixture of layer-by-layer and step-flow growths. In order for the step-flow growth maintaining the monolayer steps, the miscut angles of substrates should be so small that the terrace lengths were about 200 nm or more in our experimental conditions.