XAFS study on ZnO films grown by molecular beam epitaxy

Effects of growth conditions including lattice mismatch and growth temperature on the local structures of ZnO films prepared by MBE have been investigated using fluorescence EXAFS at Zn K edge. The ZnO films were deposited on the Si substrate at 200 degree C and on sapphire substrate at 200 degree C or 300 degree C respectively. The coordination number N in the first shell (number of O atoms immediately surrounding a central Zn atom) remains constant 4 or so for all samples. However, the degree of disorder σ2 (mean squared displacement) of the local structure is varied with the growth conditions. At the same growth temperature 200 degree C, the degree of disorder is reduced from 0.0080 (Angstrom)2 to 0.0054 (Angstrom)2 as the substrate is changed from Si to sapphire; on the same sapphire substrate, the degree of disorder decreases from 0.0054 (Angstrom)2 to 0.0039 (Angstrom)2 when the growth temperature is increased from 200 degree C to 300 degree C. Therefore, the higher growth temperature and smaller lattice mismatch can improve the disorder of local structures; the crystal quality of ZnO film will be improved as well . (authors)