Effect of oxygen pressure on the p-type conductivity of Ga, P co-doped ZnO thin film grown by pulsed laser deposition

The effect of the oxygen partial pressure on the conductivity of (Ga, P) co-doped ZnO thin films (ZnO:Ga_0.01P_0.02, ZnO:Ga_0.01P_0.04) was investigated. The thin films were grown by using the pulsed laser deposition (PLD) method. As the oxygen partial pressure increased from 1 mTorr to 200 mTorr, the electron carrier concentration of the ZnO:Ga_0.01P_0.04 thin films decreased. Above 200 mTorr, however, the electron carrier concentration increased and a transition from n-type to p-type conductivity was observed. On the other hand, in the case of the ZnO:Ga_0.01P_0.02 thin films, their electron carrier concentration continuously decreased as the oxygen partial pressure increased from 1 to 500 mTorr, showing the typical n-type semi-conductive characteristics. The X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) analyses were used to characterize the n-type to p-type conductivity transitions with increasing oxygen partial pressure.