Effect of vacuum annealing on the structural, optical, and electrical properties of spray-deposited Ga-doped ZnO thin films

Gallium-doped zinc oxide (GZO) transparent conducting thin films were prepared by a cost-effective spray-pyrolysis method on glass substrates at 400?degrees C for various concentration of gallium (05?at.%) in the spray solution. Electrical, optical, and structural properties of as-deposited and annealed GZO films were investigated using Hall measurement, optical transmission, X-ray diffraction, and atomic force microscopy. As-prepared and vacuum annealed GZO films at 400?degrees C are preferentially orientated along the (002) crystallographic direction and annealing has enhanced the crystallinity of the films. A vacuum-annealed GZO film (3?at.%) acquired the lowest resistivity of 6.5?X?10-3?Omega?cm with Hall mobility and carrier concentration of 18?cm2/V?s and 5.4?X?1019?cm-3, respectively. The transmittance of GZO film for 1?at.% is similar to 84% in the visible region (400-800?nm) and it is markedly increased to similar to 92% with the transmission edge shift towards the shorter-wavelength side on annealing. However, neither doping nor vacuum annealing of ZnO films modify the near band edge (3.26?eV) of the film appreciably. Ga doping is found to compensate the radiative oxygen vacancy levels and thus quench the green luminescence at 2.8?eV.