Effects of oxygen partial pressure during sputtering growth on physical properties of Zn0.93Mn0.07O thin films

We have studied structural, optical, electrical, and magnetic properties of Zn0.93Mn0.07O thin films grown by RF magnetron sputtering under ambient gas mixtures of O2 and Ar. As the oxygen partial pressure increases, the electron concentration systematically decreases and photoluminescence peaks related to oxygen vacancies gradually diminish. These results suggest that oxygen vacancies are majority donors. Smooth surface morphology and electron concentration as low as ∼1015 cm−3 are obtained simultaneously for the film grown in an optimal oxygen partial pressure. This film exhibits ferromagnetism with the Curie temperature of 78 K, while other films grown in higher or lower oxygen partial pressure show paramagnetic behavior down to low temperature. The disappearance of the ferromagnetism can be explained in terms of crystalline quality and surface smoothness rather than electron concentration.