Zone model development for combustion chemical vapor deposition of zinc oxide thin films

Zinc oxide was deposited on amorphous silica via combustion CVD over a range of substrate temperatures and solution reagent concentrations. The substrate temperature was varied between 190°C and 850°C and solution reagent concentration was varied between 0.0025M and 0.04M. All other variables were held constant. The resulting microstructures were characterized and categorized to form a zone model as a function of temperature and concentration.; The zone model is divided into three general microstructures; Zone A, Zone T, and Zone II. Zone A is formed at low substrate temperatures and is characterized by cauliflower-like, amorphous material. Zone II is produced at high substrate temperatures and is characterized by well-defined columnar grains. Zone T is an intermediate zone between Zone A and Zone II that is crystalline and characterized by small grains. Substrate temperature is the primary determinant for the resulting zone, but solution reagent concentrations contribute. Higher concentrations promote amorphous growth, while lower concentrations promote crystalline growth.; The transition temperature between Zone A (amorphous) and Zone T (crystalline) has been modeled. The activation energy for diffusion derived from this transition (E_tr 64 9 J/mol) supports the hypothesis that surface diffusion within the crystalline region is responsible for the transition. Within the crystalline region, grain sizes increase with temperature. The activation energy for diffusion derived from grain size (E_GS = 60 ± 21 J/mol) supports the hypothesis that surface diffusion is responsible for increased grain size.; Deposition rates were also measured. Growth rates up to seven microns per hour were produced. The deposition rate increased with temperature except for a decrease at the transition between Zone A and Zone T and a sharp decline at high temperatures. The high vapor pressure of zinc oxide at high temperatures prevents the deposition of films. Deposition rates increased with solution reagent concentration, but relative deposition efficiencies decreased slightly.; Small amounts (two percent or less) of sulfur, an impurity in the solvent, were found in some of the films. Several depositions were repeated with the sulfur impurity removed with similar results. Thus, the impurities were not the determining factor for the coating microstructures.