Oxygen partial pressure dependence of the structural properties of CdO thin films deposited by a modified reactive vacuum evaporation process

摘要

Thin films of cadmium oxide were thermally deposited on glass substrates at partial pressures of oxygen, pO(2) in the range 1.33 x 10(-2) to 0.133 Pa at a substrate temperature of 160 degreesC. Energy dispersive analysis of X-ray fluorescence (EDAX) revealed that the CdO films deposited at pO(2) value of 4.00 x 10(-2) Pa. were nearly stoichiometric. X-ray diffractometry (XRD) confirmed the polycrystalline nature of the film structure. All the films showed an fee structure of the NaCl-type, as the dominant phase. The films exhibited preferred orientation along the (111) diffraction plane. The texture coefficients calculated for the various planes at different oxygen partial pressures (pO(2)) indicated that the maximum prefer-red orientation of the films occurred along the (111) plane at an oxygen partial pressure of 4.00 x 10(-2) Pa. This was interpreted in terms of oxygen chemisorption and desorption processes. The lattice parameters determined from the diffraction peaks were in the range 4.655-4.686 Angstrom. The average lattice parameter a(0) found by extrapolation using the Nelson-Riley function was 4.696 Angstrom. Both the lattice parameter and the crystallite size were found to increase with increased partial pressure of oxygen. On the other hand, the strain and dislocation density were found to decrease as the partial pressure of oxygen was raised. A maximum (80%) in the optical transmittance lambda = 600 nm and minimum in the electrical resistivity (9.1 X 10(-4) Omega CM) of the films occurred at an optimum partial pressure of oxygen of 4.00 x 10(-2) Pa. The results are discussed. (C) 2004 Published by Elsevier B.V.