Effects of annealing on structure, resistivity and transmittance of Ga doped ZnO films

Effects of annealing on the electrical resistivity and transmittance properties of Ga doped ZnO (GZO) thin films deposited on glass by radio frequency (RF) magnetron sputtering were investigated. The electrical resistivity of a GZO thin film is effectively decreased by annealing in a reducing atmosphere such as N2 + 5%H2. This is attributed to passivation of grain boundaries and zinc ions by hydrogen atoms resulting in increases in carrier concentration and mobility. However, annealing at a temperature >400deg;C is less effective. The lowest resistivity of 2·3 × 10−4 Ω cm is obtained by annealing at 400°C in an N2 + 5%H2 atmosphere. The optical transmittance of the GZO film is improved by annealing regardless of the annealing atmosphere. Annealing in an N2 + 5%H2 atmosphere widens the optical band gap, while annealing in an O2 atmosphere makes the band gap narrower, which can be explained as a blue shift phenomenon.