Khranovskyy V. Regularities of the deposition parameters, doping and thermal annealing influence on the structural, optical and electrical properties of zinc oxide films

The thesis is devoted to the investigation of the properties of the polycrystalline ZnO films, deposited by PEMOCVD at temperature range 200 - 500 °C. The improvement of the films structural properties via increase of the films texture along c-axis and grain size enlargement were observed with the increase of the deposition temperature; however, the films possessed the polychromatic luminescence spectra. At application of the homoepitaxial ZnO buffer layer the structural quality improves via texture increase, grain size enlargement and decrease of the biaxial strain in the ZnO film. The thermal diffusion of the hydrogen from the substrate into growing ZnO films is demonstrated. It is revealed, that films, deposited at 350 °C on SiNx:H/Si, demonstrate the most intense monochromatic near band edge emission in the ultraviolet range of spectra (380 nm). The hydrogen effect on the luminescence properties of ZnO is explained by hydrogen passivation of the deep level defects, responsible for the defect luminescence. Gallium doping of the ZnO films results in the gradual decrease of the electrical resistivity of the ZnO films (10^-2 10^-4 Оhm сm) at their high optical transmittance within visible range 400 - 800 nm (Т > 90%). Gallium doping (1 wt. % at substrate temperature 250 °C) causes the increase of carriers concentration to 5,2x1019 сm-3 at their mobility 3,4 сm^2/V·s and is assisted by c-axis texture increase. The further gallium concentration increase (3 - 10 wt.%) results in the change of the films preferential orientation from (002) to (101), decrease of the grain size and films surface smoothing. The Burshtain - Moss effect is demonstrated with the increase of the Ga concentration. It is revealed that the annealing temperature as high as 800 °C is favorable for activation of the electrically neutral Ga atoms in ZnO films. The possibility to decrease the resistivity of ZnO:Ga films from 3,5x10^-2 to 2x10^-4 Ohm cm is demonstrated by application the rapid thermal annealing