Atmospheric pressure chemical vapor deposition of doped zinc oxide thin films and their electrical and optical properties

Zinc oxide thin films have been deposited on various substrates in an atmospheric pressure chemical vapor deposition system. The film thicknesses and refractive indices were determined with an ellipsometer or a prism coupler. The structural properties of the films were examined by X-ray diffraction and scanning electron microscopy. The film compositions were determined by electron microprobe analysis and Rutherford backscattering and forward recoil spectrometry. Highly transparent and conductive zinc oxide films were produced by doping with foreign atoms such as the Group VII element fluorine and the Group III elements boron, aluminum and gallium. The electrical properties of the doped films were characterized by resistance and Hall coefficient measurements. The optical properties were obtained from UV-Visible-IR reflectance and transmittance measurements.; The crystallite size and orientation were found to depend on the deposition temperature and the oxidant and dopant used. The fluorine and aluminum concentrations in the films were generally below 1.5 at.%. The gallium concentration in the film increases almost linearly with the triethyl gallium concentration in the gas phase, up to a gallium concentration of 10 at.%.; All of the doped films have similar high conductivities. Fluorine doped films have lower electron densities and higher mobilities than do the films doped with the Group III elements. All of the dopants are n-type and increase the free electron density. Zinc oxide films doped with fluorine are more transparent to visible and near infrared light than films doped with the Group III elements.; A resistor network model was used to model the electrical and optical properties of zinc oxide films. The most important scattering mechanisms are ionized impurity and grain boundary scattering. The dispersion of the high frequency dielectric constant in the ultraviolet is modelled by a damped Lorentz oscillator. The absorption edge is modelled by an Urbach tail which predicts that the absorption coefficient near the band gap will increase exponentially. The film nonuniformity is taken into account by a thickness gradient and the reflectance and transmittance are averaged over different thicknesses. The film roughness acts as a refractive index gradient over the rough surface region and leads to diffuse reflectance and transmittance. (Abstract shortened with permission of author.)...