The zinc oxide films were deposited in an RF
(13.56 MHz) diode sputtering unit (Alcatel, France).
The pumping system consists of a standard rotary
pump, diffusion pump and a liquid nitrogen trap. A
3-inch diameter stoichoimetric target of ZnO was
used. Sputtering was carried out in pure argon
atmosphere in ‘sputtered-up’ configuration. The Si
wafers of 2-inch diameter were clamped on to the
substrate holder. The sputtering process was performed
in the pressure range of 5–20 mTorr and the
RF power ranging from 100 to 300 W. Films were
deposited at various sputtering pressures and RF
power. The target to substrate distance was kept
constant at 45 mm for all the depositions. No
external substrate heating was done during the
deposition. However, during sputtering process the
temperature due to self-heating is expected to rise to
approximately 150 "C.