Physical properties of erbium implanted tungsten oxide films deposited by reactive dual magnetron sputtering

Amorphous and partially crystalline WO₃ thin films were prepared by reactive dual magnetron sputtering and successively implanted by erbium ions with a fluence in the range from 7.7 x 10¹⁴ to 5 x 10¹⁵ ions/cm². The electrical and optical properties were studied as a function of the film deposition parameters and the ion fluence. Ion implantation caused a strong decrease of the resistivity, a moderate decrease of the index of refraction and a moderate increase of the extinction coefficient in the visible and near infrared, while the optical band gap remained almost unchanged. These effects could be largely ascribed to ion-induced oxygen deficiency. When annealed in air, the already low resistivities of the implanted samples decreased further up to 70°C, whereas oxidation, and hence a strong increase of the resistivity, was observed at higher annealing temperatures