Sputter-deposited polycrystalline tantalum-doped SnO₂ layers

In this study, tin oxide (SnO₂) thin films doped with 1 cation percent tantalum were deposited on amorphous fused silica substrates by RF-magnetron sputter deposition. Electrical and optical properties were subsequently measured and analyzed as a function of deposition temperature (300 to 700 °C) and oxygen ratio in the process gas (0 to 50%). In situ photoelectron spectroscopy was used to determine tantalum incorporation, sample stoichiometry, valence band electronic structure and Fermi level position. Samples were analyzed with respect to their optical and electrical characteristics by spectral transmittance and Hall measurement. Electrical resistivity reached values as low as 1.7 × 10⁻³ Ω cm with a charge carrier density of 3.3 × 10²⁰ cm⁻³ and a mobility of 12 cm² V⁻¹ s⁻¹. Electrical transport properties were related to structural properties as determined by atomic force microscopy, scanning electron microscopy and X-ray diffraction. It was found that electrical properties are a strong function of substrate temperature, mainly due to a reduced charge carrier density for deposition temperatures below 700 °C. This is thought to be caused by an intrinsic compensation mechanism which has not yet been identified. - Highlights: • SnO₂:Ta films were deposited at varying temperatures and oxygen partial pressures. • In situ X-ray and ultraviolet photoelectron spectra of sputtered SnO₂:Ta are presented. • Electrical properties decrease rapidly for substrate temperatures lower than 700 °C. • Authors suggest deposition temperature dependent compensation mechanism. • Nature of compensation mechanism unclear, possibly point defect