Growth of dense ZnO films via MOVPE on GaN(0Â 0Â 0Â 1) epilayers using a low/high-temperature sequence

Dense zinc oxide thin films have been achieved on GaN(0 0 0 1) epilayers via the repetition of an iterative sequence involving the growth at 480 °C of needles having a decreasing diameter as a function of height followed by the lateral growth from the sidewalls of these needles and coalescence of the growth fronts at 800 °C. Each sequence resulted in a contiguous layer having a thickness of approximately 200 nm. Diethylzinc and UHP oxygen were used as sources of zinc and atomic oxygen, respectively; UHP argon served as both the carrier and the diluent gas. The final growth surface of each densified film contained hexagonal depressions caused by growth among needles of different heights and growth pits that increased in number with an increase in film thickness. These microstructural features were manifest upon and affected the densities and magnitudes of similar features produced in subsequent layers. Triple-axis X-ray diffraction measurements revealed that the orientations of the crystallographic planes and directions within the films mimicked those of the underlying GaN substrate. Concentrations of carbon and hydrogen oscillated throughout the films due to their incorporation primarily within the lower and larger volumes of the needles during each low-temperature deposition of this microstructure.