Increasing Polycrystalline Zinc Oxide Grain Size by Control of Film Preferential Orientation

We investigate the structural evolution of polycrystalline zinc oxide films grown by low pressure metal–organic chemical vapor deposition. The goal is to achieve larger grains—leading to higher charge carrier mobility from lower grain boundary density—by controlling the grain orientation during growth. The results are 2-fold. First we describe how the combination of deposition temperature and gas flow influences the nucleation and film thickening stages: low temperature and high gas flow favor a high nucleation density and the development of c-textured films, whereas high temperature and low gas flow lead to a lower nucleation density and a-textured films. Second we demonstrate how a fine control of the film preferential orientation at the different growth stages allows the fabrication of films with grains that are 25% larger, hence improving the carrier mobility with respect to the reference film.