p-Type conductivity and stability of Ag-N codoped ZnO thin films

Silver and nitrogen codoped ZnO films [ZnO:(Ag, N)] were grown on quartz substrates by radio frequency magnetron sputtering deposition followed by ion-implantation technique. Room-temperature (RT) Hall-effect measurements confirm that Ag-N codoped ZnO film is converted to p-type ZnO under optimum post-annealing conditions. The p-type conductivity of ZnO:(Ag, N) is attributed to the formation of the AgZn-NO pairs and/or NO-AgZn-NO triangles, which can create impurity bands above the VBM of ZnO due to the p-d interaction between accepters and hence offer improved incorporation and activation of acceptors. The sample exhibited a stable conductivity-type over four month period after post-annealing, but apparent degradation of p-type characteristic was observed. It is demonstrated that the Ag aggregation (metallic Ag and/or Ag2O) can be stable in the film and metastable interstitial nitrogen is easy to diffuse and be trapped by acceptor NO to form double-donor (N2)O at RT, resulting in a decrease in the conductivity and stability of p-type ZnO:(Ag, N) film.