Structural, morphological, optical and electrical properties of Ga-doped ZnO transparent conducting thin films

The effects of Ga doping on microstructural, optical, and electrical properties of Ga-doped ZnO (GZO) thin films deposited on silicon substrate by sol-gel technique have been investigated. XRD results showed that all the as-prepared GZO films holds a wurtzite phase and a preferred orientation along the [002] direction. A change in grain size as well as surface roughness of the films was observed with further increasing Ga concentration. Optical transmittance spectra of the GZO thin films exhibited transmittance higher than 80% within the visible region, and a blue shifting of the optical band gap was observed with an increase of Ga doping, which can be explained on the basis of the Burstein-Moss effect. Spectroscopic ellipsometry (SE) measurement in the UV-vis-near infrared region are employed to deduce the refractive index and extinction coefficient of GZO thin films. The simulation is carried out using a double oscillator model, which includes the modified Psemi-M0 equation and the rho-tau Drude oscillator. The lowest resistivity of 3.4 × 10−3 Ω cm was obtained for the ZnO film doped with 5 at% of Ga after post-annealing at 450 °C for 1 h in a H2 atmosphere.