Observation of conductivity type conversion in undoped ZnO films grown by pulsed laser deposition on silicon (100) substrates

We report a conductivity type conversion of ZnO films from n to p-type for films grown on silicon (100) substrates by pulsed laser deposition under low constant oxygen overpressure. Conductivity conversion is attributed to a competition between donor and acceptor-like native defects correlating with growth conditions and surface differences between phosphorus doped n-type and boron doped p-Si substrates. Effects of growth temperature on intrinsic defects including oxygen vacancies, zinc vacancies and hydrogen impurity contamination are discussed. Our results show that the interplay of defect-related centers is critical to the electrical behavior and conductivity type of ZnO grown on Si substrates.