Photochromism and anomalous crystallite orientation of ZnO films prepared by a sputtering-type electron cyclotron resonance microwave plasma

This letter describes the crystal structure and the photochromism of ZnO films, which are prepared by a sputtering-type electron cyclotron resonance microwave plasma. c-axis preferential orientation and (101) preferential orientation are realized in the Zn oxide films, which are deposited on a glass substrate at a low temperature below 200 °C. Both films have an excellent crystallite orientation that is the best reported to date. The films with anomalous crystallite orientation exhibit typical photochromic characteristics, which are induced by x-ray irradiation. The photochromism is caused by a color center, that is, the O2− vacancy in ZnO films. The absorption center exists in an energy range of 1.5–4 eV.