Zone model for zinc oxide deposited by combustion chemical vapor deposition

A zone model describing the microstructures of zinc oxide films deposited by combustion chemical vapor deposition as a function of temperature and precursor concentration was developed experimentally. Homologous temperatures from 0.2 to 0.5, and precursor concentrations from 0.0025 to 0.04 M were investigated. Zinc 2-ethylhexanoate was used as precursor. Low deposition temperatures and/or high precursor concentrations favor the growth of amorphous ZnO (zone A). At moderate deposition temperatures and/or lower precursor concentrations, relatively smooth crystalline, small grained films form (zone T microstructure). The largest deposition temperatures and/or lowest precursor concentrations result in films with columnar grains (zone II microstructure). ZnO could not be deposited at homologous temperatures greater than approximately 0.5 because of its high vapor pressure. Kinetic measurements of the zone A to zone T transition resulted in an activation energy of 64 +/- 9 W/mol for the responsible mechanism. Similarly, measurements of grain size as a function of deposition temperature yielded an activation energy of 60 +/- 21 kJ/mol. These activation energies are consistent with surface diffusion being responsible for both the amorphous to crystalline transition and grain growth in the crystalline films. (C) 2001 Elsevier Science B.V. All rights reserved.