The density-of-state effective masses of impurity doped polycrystalline ZnO thin films were measured by the method of four coefficients technique. By applying the first-order non-parabolicity approximation, the polaron effective mass and the bare band mass at the conduction band minimum, together with the corresponding non-parabolicity parameters, were analysed successfully. The determined perpendicular polaron mass of 0.29 me and the bare band mass of 0.247 me at the conduction band minimum corresponded very well to the previous results obtained for ZnO single crystals. The non-parabolicity parameter of 0.457 eV−1 derived for the polaron effective mass was larger than 0.33 eV−1 which was obtained for the bare band mass due to the increasing function of the Fröhlich coupling constant with respect to the bare band mass in polycrystalline ZnO films.
To improve the stability of sputter-deposited ZnO:Al (AZO) films at high temperature above 300 • C, an amorphous Zn-Sn-O (ZTO) film was deposited on the top of AZO films as an protective layer by co-sputtering of pure ZnO and SnO 2 targets. Amorphous ZTO films had resistivity in the range from 10 −2 to 10 −3 cm and were stable up to temperature of 400 • C. Heat treatments of bare AZO films in the atmosphere at 400 • C resulted in a dramatic increase in the resistivity accompanied by substantial decrease in carrier concentration and Hall mobility. The AZO films covered with the ZTO film showed remarkable improvement in thermal stability for subsequent heat treatments in the temperature range from 200 to 400 • C in the atmosphere as well as chemical stability in weak acidic solution. X-ray photoelectron spectroscopy analysis showed that the improvement was attained by ZTO layer acting as diffusion barrier of oxygens and/or water vapors.
Four Au : SiO 2 composite films with varying Au particle size at fixed volume fraction were fabricated by alternate sputtering, and their 3rd order nonlinear optical properties were investigated by the z-scan technique using picosecond pulse laser. TEM analysis was used to estimate the particle size for samples with varying Au nominal thickness, and size dependent linear absorption spectra were examined. Particle size dependence on the imaginary part of 3rd order susceptibility at surface plasmon wavelength together with the dispersion of the real and the imaginary components around surface plasmon wavelength were resolved and compared with the theoretical values.
ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing Al 2 O 3 dcontent of 1 (HA 1 ZO series) and 2 wt.% (HA 2 ZO series) on Corning glass (Eagle 2000) at substrate temperature of 150°C with Ar and H 2 /Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with different Al contents on the electrical, optical and structural properties of the as-grown films as well as the vacuum-and air-annealed films were examined. For the as-deposited films, the free carrier number in both series of HAZO films increased with increasing H 2 content in sputter gas. HA 2 ZO film series prepared from target containing 2 wt.% Al 2 O 3 showed better crystallinity and higher carrier concentration than HA 1 ZO film series deposited using target containing 1 wt.% Al 2 O 3 . The crystallinity and the Hall mobility of HA 2 ZO film series decreased with increasing H 2 content in sputter gas, while those of HA 1 ZO film series showed a reversed behavior. Although HA 2 ZO film series yielded lower resistivity than HA 1 ZO film series due to higher carrier concentrations, the higher figure of merit (expressed as 1/ρα, where ρ and α represents the resistivity and absorption coefficient, respectively) was observed for HA 1 ZO film series because of substantially low absorption loss in these films. When annealed in air ambient, HA 1 ZO film series showed much stronger stability than HA 2 ZO film series. Vacuum-annealing resulted in drop of the carrier concentrations as well as large shrinkage in lattice constant, which indicated that the hydrogen dopants are in relatively volatile state and can be removed easily from the films upon annealing.
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