Optical and structural characteristics of ZnO films grown on (0 0 0 1) sapphire substrates by ALD using DEZn and N₂O

Zinc oxide (ZnO) films were grown at 600 °C on (0 0 0 1) sapphire substrates by atomic layer deposition (ALD) using diethylzinc (DEZn) and nitrous oxide (N₂O) as source precursors. In some cases, low-temperature (LT) ZnO buffer layers were employed along with post-annealing or buffer-layer annealing for the optimization of ZnO growth. Based on the θ to 2θ X-ray diffraction (XRD) data, the as-grown ZnO films exhibit a preferred orientation with 〈0 0 0 1〉_ZnO being parallel to the 〈0 0 0 1〉_sapphire. Both post-annealing and buffer-layer annealing were found to be very helpful for improving the optical properties of the ZnO films. Room temperature (RT) photoluminescence (PL) spectra of the ZnO films show strong near-band edge (NBE) emissions with completely quenched defect luminescence. The best ZnO films were achieved with a sharp neutral donor excitonic (D^oX) emission as well as phonon replicas of free A-excitons in the 10 K PL spectrum.