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

Abstract

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 (Tann) and time (tann). 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 Tann and longer tann. Combined with the transition state calculations, the possible reasons of such phenomenon are discussed in detail at the end of the article.