Origin of highly stable conductivity of H plasma exposed ZnO films.

H was intentionally incorporated into as-deposited ZnO films by plasma exposure treatment. The resistivity of ZnO films was reduced to the order of 10(-3) Ω cm after H plasma treatment, and high conductive stability was identified using a post-annealing process. To find an explanation for the stable conductivity, first-principle calculation was performed. Results predicted that H atoms trapped in oxygen vacancies (V(O)) have the lowest formation energy. By reducing oxygen vacancies in as-deposited films by adding O2 into the working atmosphere, we further testified that H in V(O) is the origin of highly stable conductivity of ZnO films. Our study provided a solution to the problem of how to incorporate H into the V(O) position to produce highly stable H doped ZnO films.