  We use real-time spectroscopic polarimetric observations of growth and a
chemical model derived therefrom, to develop a method of growing dense,
two-dimensional zinc oxide epitaxially on sapphire by metalorganic chemical
vapor deposition. Particulate zinc oxide formed in the gas phase is used to
advantage as the deposition source. Our real-time data provide unequivocal
evidence that: a seed layer is required; unwanted fractions of ZnO are
deposited; but these fractions can be removed by cycling between brief periods
of net deposition and etching. The transition between deposition and etching
occurs with zinc precursor concentrations that only differ by 13%. These
processes are understood by considering the chemistry involved.

Materials Science