Surface Chemistry and Long-Term Stability of Amorphous Zn-Sn-O Thin Films

摘要： Amorphous (a-) oxides form an important category of transparent conducting/semiconducting thin films used as electrodes and channel layers in thin film transistors. The compositional flexibility of amorphous states, through doping, makes it possible to fine tune the electrical properties of films from conducting to semiconducting. However, surface chemistry and stability of these films are rarely addressed. Surface studies of amorphous materials, in general, are scarce due to disorder. Here, long-term surface stability of a-Zn-Sn-O films is investigated using grazing incidence X-ray absorption spectroscopy techniques. We present a detailed description of film surface structures and their evolution over time. It is found that the surface structure is, locally, a close analogue of the crystalline counterpart and that surface chemistry is governed by vacancies, strain, composition, and film density. It will be shown that the long-term stability of a film is questionable when the film has a high Zn content and a low density.