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

The influences of O2 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 (Zni), oxygen vacancies (VO), and zinc vacancies (VZn). Carrier density of VZO decreased from 9×1020 to 9×1018 cm−3 between O2 partial pressure ratio (αO2) of 0.6% and 1.0% in spite of the increase in valence number of vanadium. This result suggests that Zni is the dominant donor in VZO since Zni is a shallow-level defect. Average optical transmittance (Tv) 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 VO, Tv of VZO improved by oxygen addition and reached 85% at αO2 of 1.0% via suppression of VO formation.