Influence of Growth Temperature on the Characteristics of Ga-Doped ZnO Thin Films Deposited by Magnetron Sputtering

Ga-dope ZnO (ZnO:Ga) thin films with n-type semiconducting behavior were grown on c-sapphire substrates by radio frequency magnetron sputtering at various growth temperatures. The room temperature grown ZnO:Ga film showed a slight preferred orientation along the c-axis with small domain size and high density of stacking faults. The increase in growth temperature from 300 to 550 degrees C resulted in the growth of granular shaped epitaxial ZnO:Ga films due to insufficient thermal energy and large lattice mismatch. The films grown at above 550 degrees C showed a flat surface with the simultaneous improvement of the electrical carrier concentration and carrier mobility (6.3 x 10(18)/cm(-3) and 27cm(2)V(-1)s(-1), respectively). In addition, there was an increase in the grain size and a decrease in the dislocation density in the high temperature grown films. The low-temperature photoluminescence of the ZnO:Ga films grown at <450 degrees C showed the redshift in deep-level emission, which was attributed to a transition from Zn-i to O-i level. (C) 2009 The Japan Society of Applied Physics