Study on anomalous high p -type conductivity in ZnO films on silicon substrate prepared by ultrasonic spray pyrolysis

N-In codoped ZnO films were prepared by ultrasonic spray pyrolysis. Hall-effect measurements indicate that the films on silicon exhibit anomalous high p -type conductivity, while films on insulating substrates show n -type conductivity. Scanning capacitance microscopy was employed to analyze the microconductivity type of ZnO films. The grains of ZnO film on silicon show n -type conductivity and no significant p -type grains were found. The authors further investigated the microstructure of ZnO film and the band structure of the ZnOSi interface and propose a model of an interface state induced two-dimensional hole gas as the origin of the anomalous high p -type behavior.