Low-defect-density ZnO homoepitaxial films grown by low-temperature ALD

We report atomic layer deposition (ALD) of ZnO thin films on O-polar surface crystalline ZnO substrates at the relatively low temperatures of 120, 150, and 200 °C. The as-grown ZnO films are studied with aberration-corrected transmission electron microscopy and diffraction contrast, photoluminescence (PL), and surface photovoltage (SPV) spectroscopy. We find that the homoepitaxial films have a monocrystalline structure with the density of basal stacking faults comparable to that of the substrate ( ∼1011 cm−2) and that the stacking faults can induce high lattice strain due to their interaction with the inversion domain boundaries. The narrow excitonic PL linewidth (2 meV at 8 K) and the sharp SPV bandgap transition confirm the high quality of the ZnO films. Despite similarities in the film properties, the growth temperature has an effect on the density and spatial distribution of intrinsic defects. Our results demonstrate a considerable potential of ALD ZnO homoepitaxy for fabricating high-quality ZnO nanostructures and attaining viable p-type ZnO.