Discharge power dependence of structural, optical and electrical properties of DC sputtered antimony doped tin oxide (ATO) films

Antimony doped tin oxide (ATO) is a transparent conducting oxide (TCO), which has been the focus of intensified study due to its wide range of technological applications and low cost. In the present work ATO films have been prepared by reactive DC magnetron sputtering from a metallic target at different discharge power densities without direct substrate heating. Then a post-deposition annealing at 350 °C in N2 during 20 min was performed. There is a process window for the optimal sputter deposition of ATO with a minimum resistivity of about 3.3×10−3 Ω cm observed in samples deposited at a power density of 1.13 W/cm2. These samples, which present a (2 1 1) preferential orientation, have good electrical conductivity and good transparency in the visible range. Higher values of sputtering discharge power density (1.24 W/cm2) change the preferential orientation to (1 0 1) because of the formation of oxygen vacancy planes. These samples are less conductive and transparent because their layered structure reduces the free charge mobility and allows the formation of Sb in its unusual oxidation state 4+ (between Sb3+ and Sb5+), which produces a sample blue darkening. Higher discharge power densities, above 1.41 W/cm2, produce amorphous samples and an abrupt resistivity increase. The aim of the present work is to go into more depth in the knowledge of ATO in order to develop thin films with optimal electrical and optical properties.