Impact of oxygen source parameters on homoepitaxial ZnO films grown at low-temperature on Zn-polar substrates

ZnO thin films were epitaxially grown on Zn-polar (0 0 0 1) ZnO substrates by plasma-assisted molecular beam epitaxy at a low temperature of 610 °C. The influence of Zn/O ratio on the epitaxial growth of ZnO was investigated. By optimizing the Zn/O ratio, a surface root mean square roughness of 0.277 nm with one or two monolayer height steps was achieved at a low growth temperature by growing on ZnO substrates with 0.5° miscut angle toward the [11¯00] axis. Electrostatic ion trapping of the oxygen plasma was found crucial to deflect etching oxygen species at an oxygen flow rate of two standard cubic centimeters per minute, resulting in fewer surface defects and a longer photoluminescence (PL) lifetime of 217 ps. The impact of oxygen source gas purity was studied by high resolution X-ray diffraction and time-resolved photoluminescence (TRPL) measurements of resultant epilayers and higher gas purity was found necessary to reduce non-radiative centers.

► ZnO homoepitaxial films were directly grown on Zn-polar ZnO substrates by PAMBE.
► Atomically flat surface was achieved with monolayer height steps at low growth temperature.
► The impact of oxygen flux, deflection of oxygen plasma species, and oxygen purity was studied.
► Photoluminescence (PL) lifetime of 217 ps was achieved by optimizing the oxygen conditions.