Real-time diagnostics are an essential tool in the development and improvement of growth processes for new materials. Here we use real-time spectroscopic polarimetric observations of zinc oxide deposition, 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. With the transition between deposition and etching being 13% in the diethylzinc flow rate, it is unlikely that we would have discovered this process without the use of real-time spectroscopic ellipsometry. New photoluminescence data support our conclusion that using this cyclical growth process yields improved material. (C) 2010 Elsevier By. All rights reserved.