Investigation on a source of dominant donor in vanadium-doped ZnO films grown by reactive RF magnetron sputtering

The influences of 02 gas addition in argon plasma on reactive RF magnetron sputtering deposition of vanadium doped ZnO (VZO) films were examined. ZnO or VZO films with vanadium concentration of 2 at% were deposited on a quartz substrate. Vanadium doping caused oxygen deficiency in ZnO and formed a large number of zinc interstitials (Zn-i;), oxygen vacancies (V-O), and zinc vacancies (V-zn). Carrier density of VZO decreased from 9 x 10(2) to 9x10(18) cm(-3) between O-2 partial pressure ratio (alpha(O2)) of 0.6% and 1.0% in spite of the increase in valence number of vanadium. This result suggests that Zn-i is the dominant donor in VZO since Zn-i is a shallow level defect. Average optical transmittance (T-v) at wavelength between 450 and 800 nm of VZO was 61% while that of ZnO was 82% without oxygen addition. Although the optical transmittance of VZO was largely deteriorated by optical absorption of V-O, T-v of VZO improved by oxygen addition and reached 85% at alpha(O2) of 1.0% via suppression of Vo formation.