Effects of Ga concentration on the structural, electrical and optical properties of Ga-doped ZnO thin films grown by sol-gel method

Undoped ZnO and Ga-doped ZnO (GZO) thin films with different Ga concentrations were prepared by using the sol-gel spin-coating method. The surface morphologies and the growth orientations of the films were measured by using scanning electron microscopy and X-ray diffraction, respectively. The electrical properties were measured by using the Hall effect. The optical transmittances and reflectances of the films were measured as functions of the wavelength by UV-vis spectroscopy. The undoped ZnO thin films exhibited rough surfaces with particle-like structures. When Ga was incorporated, the particle sizes dramatically decreased without changes in the surface morphologies, and the c-axis growth orientations of the GZO thin films were significantly decreased. The optical transmittances clearly exhibited shifts in the band edge, and those in the visible range gradually increased with increasing Ga concentration. The absorption coefficients, refractive indices, extinction constants, dielectric constants, and optical conductivities of the films gradually decreased with increasing Ga concentration.