Zn-vacancy related defects in Zn-polar and O-polar ZnO films fabricated by pulsed laser deposition

Abstract

O-polar and Zn-polar ZnO films were fabricated by pulsed laser deposition. The Zn-polar sample has a lower electron concentration and higher electron mobility compared with the O-polar sample. This is due to the lower abundance of hydrogen which acts as shallow donor in the Zn-polar film. A Coincidence Doppler broadening study showed that V_Zn-2V_O is the single dominant V_Zn-related type defect in the as-grown O-polar ZnO film, while in the as-grown Zn-polar film, a mixture of V_Zn-related defects were identified. The intensity ratio of near band edge emission to defect emission for the Zn-polar ZnO sample was much larger than that of the O-polar sample. A magnetic study using a superconducting quantum interface device (SQUID) showed that both polarities were ferromagnetic at room temperature. Correlations found between the saturation magnetization, the V_Zn-2V_O defect concentration and the grain surface to volume ratio suggested that the room temperature ferromagnetism originates from V_Zn-2V_O defects residing in the vicinity of the grain boundary.