Investigation on the Formation Mechanism of In-N Codoped p-Type ZnCdO Thin Films: Experiment and Theory

Indium and nitrogen codoped ZnCdO films [ZCO:(In, N)] have been grown on quartz substrates by radio frequency magnetron sputtering deposition followed by ion-implantation technique. The room-temperature Hall measurements confirm that a stable p-type ZCO:(In, N) film is obtained by optimizing postimplantation annealing temperature (T-ann) and time (t(ann)). The Raman measurements reveal that the concentration of NO acceptors in stable p-type film is higher than unstable p-type films and much higher than n-type films, which indicates that choosing appropriate annealing window plays a key role in stabilizing the NO acceptors to obtain the stable p-type ZCO:(In, N). Both theory and experiment indicate that the stable p-type conductivity of ZCO:(In, N) is attributed to the formation of passive complexes (-Cd-O-In-N-), which can form an impurity band above the valence band maximum, resulting in a decrease in the ionization energy of the acceptor and an improvement in the stability of p-type ZCO:(In, N). The Hall measurements also confirm that the p-type films would convert to n-type conductivity under both higher T-ann and longer t(ann). Combined with the transition state calculations, the possible reasons of such phenomenon are discussed in detail at the end of the article.