Effects of hydrogen plasma treatment on the electrical and optical properties of ZnO films: Identification of hydrogen donors in ZnO

Wurtzite ZnO has many potential applications in optoelectronic devices, and the hydrogenated ZnO exhibits excellent photoelectronic properties compared to undoped ZnO; however, the structure of H-related defects is still unclear. In this article, the effects of hydrogen-plasma treatment and subsequent annealing on the electrical and optical properties of ZnO films were investigated by a combination of Hall measurement, Raman scattering, and photoluminescence. It is found that two types of hydrogen-related defects, namely, the interstitial hydrogen located at the bond-centered (H_BC) and the hydrogen trapped at a O vacancy (H_O), are responsible for the n-type background conductivity of ZnO films. Besides introducing two hydrogen-related donor states, the incorporated hydrogen passivates defects at grain boundaries. With increasing annealing temperatures, the unstable H_BC atoms gradually diffuse out of the ZnO films and part of them are converted into H_O, which gives rise to two anomalous Raman peaks at 275 and 510 cm^-1. These results help to clarify the relationship between the hydrogen-related defects in ZnO described in various studies and the free carriers that are produced by the introduction of hydrogen. © 2010 American Chemical Society.