Homoepitaxial growth of dense ZnO(0 0 0 1) and ZnO (112¯0) films via MOVPE on selected ZnO substrates

Deposition via metalorganic vapor phase epitaxy of a low-temperature (480 °C) layer followed by a high-temperature (800 °C) densification step was employed for the growth of each ∼200 nm thick, contiguous ZnO(0 0 0 1) layer on a ZnO(0 0 0 1)-oriented substrate. Multiple iterations of this process resulted in films as thick as 2 μm. Ultra-high-purity (UHP) O2 served as the principal source of atomic oxygen; however, nitrous oxide (N2O) and nitrogen dioxide (NO2) were also investigated as potential oxygen sources in the pure state as well as in mixtures with oxygen produced in the chamber and for nitrogen doping of the growing (0 0 0 1) films. Carbon and hydrogen, derived from the decomposition of the diethylzinc precursor, and N were incorporated into the films primarily during the low-temperature step. Films grown using N2O+O2 contained an average of 5×1017 cm−3 atomic nitrogen; films using NO2+O2 had an average nitrogen concentration of 9×1019 cm−3. The low-temperature growths on ZnO(0 0 0 1) using O2 and N2O+O2 resulted in the formation of a needle microstructure; a spaghetti-like network microstructure formed when using NO2+O2 at the same temperature. Lateral growth at 800 °C from sites within the needle and network microstructures resulted in dense films containing shallow hexagonal pits that increased in number and depth with an increase in film thickness. Triple-axis XRD measurements indicated that the crystal structure of the films mimic the underlying substrates. Growth on [112¯0]-oriented ZnO substrates at the single temperature of 600 °C resulted in a dense film composed of needles oriented in-plane along [0 0 0 1]. Atomic force microscopy and secondary ion mass spectroscopy revealed an rms value of 5.4 nm and hydrogen of concentration of 6.5×1018 with the carbon concentration below the detection limit of 1.3×1019 atoms/cm3.