Study of Transparent Conducting Ga-doped ZnO Films Grown by Reactive Co-sputtering of Zn and GaAs

Ga-doped ZnO films were deposited by rf reactive co-sputtering of Zn and GaAs at 375 degrees C with 3 % GaAs/Zn target coverage at different percentages of O-2 (4 - 10 %) in the Ar-O-2 sputtering atmosphere. Heavily doped films were obtained with 4 - 5.5 % O-2 in sputtering atmosphere, exhibiting resistivity of (7 - 13) x 10(-4) Omega-cm, carrier concentration of (7.1 - 11.5) x 10(20) cm(-3) and Hall mobility of (5.5 - 8.7) cm(2)V(-1)s(-1) These films exhibited high transparency (80 - 85 %) in the visible, plasma resonance similar to 1300 nm followed by high reflectance in infrared, along with increase in band gap by about 0.5 eV, which are characteristic heavy doping effects. With increase in O-2 percentage to 6 % or higher, the films exhibit a sharp decrease in resistivity by over three orders, due to lower and possibly non- substitutional incorporation of Ga, which appears to be controlled critically by the oxygen percentage in the sputtering atmosphere.