PROPERTIES OF ZnO THIN FILMS DEPOSITED BY RF SPUTTERING UNDER SUBSTRATE BIAS
Crystalline polarity in wurtzite-type oxide semiconductors is of crucial importance in terms of physical and chemical properties for future optoelectronic applications. Indeed, many of the optical and electronic properties of zinc oxide(ZnO) vary with the crystalline polarity. Thus, it is important to establish how to fabricate and to characterize the polarity-controlled ZnO materials. In this study, it is revealed that external electric bias (V_sub ) applied to substrates is effective to the control of the polarity during RF sputtering. This method enables polarity-selective depositions of non-doped ZnO films without any crystalline templates and impurity doping. Further investigations made it clear that the growth conditions, such as RF output power and target-substrate distance, are also importance to control of the polarity. It is significant that the polarity of ZnO films determines at the V_ sub of initial nucleation stage, and is not inversed on the overlayer deposited at different V_sub. Finally, electronic properties of ZnO thin films are determined only by the crystalline polarity. The conducting properties of Zn-polar ZnO films are higher than those of O-polar films. This method can potentially be used to tailor the properties of ZnO thin films. I expect that this study will open an approach to improve material’s functionalities for creating future optoelectronic and micromechanical devices.