Effect of doping behaviors of Ag and S on the formation of p-type Ag–S co-doped ZnO film by a modified hydrothermal method

•A modified hydrothermal method is used to fabricate p-type Ag–S codoped ZnO films with high hole density.•A hole density of ~ 1018 cm− 3 is obtained in the p-type Ag–S codoped ZnO films.•AgZn+–nSO2 − complex acceptor in Ag–S codoped ZnO films play a key role in realizing high hole density.

Reproducible p-type Ag–S co-doped ZnO (ASZO) films were grown on glass substrate by a modified hydrothermal method, where reaction solution is separated from alkali solution and O2 is removed from autoclave to avoid deoxidation of Ag+ and oxidation of S2 − in the solution. It is found that the Ag substitutes for the Zn in monovalent state (AgZn+) and the S for the O in bivalent state (SO2 −) in the ASZO. Both AgZn+ and SO2 − have two doping states, each AgZn+ is surrounded by 4O2 − to form AgZn+ acceptor and each SO2 − is surrounded by 4Zn2 +, while AgZn+ bounds with nSO2 − to form AgZn+–nSO2 −(n ≤ 4) complex acceptor. It is demonstrated that Ag doping can suppress the formation of interstitial Zn and O vacancies in the ASZO and S doping can enhance solubility of Ag in the ASZO. Hall measurement indicates that the p-type ASZO film has a hole density as high as 1018 cm− 3, which is much higher than that of ASZO prepared by magnetron sputtering. The mechanism of the formation of the p-type ASZO with high hole density is suggested in the present paper.