Reactively sputtered TiO 2 layers on SnO 2:F substrates: A Raman and surface photovoltage study

Abstract

DC reactively sputtered TiO 2 layers on SnO 2:F substrates were investigated by Raman and surface photovoltage spectroscopy. The stoichiometry and layer thicknesses were investigated by elastic recoil detection analysis. The deposition temperature, the O 2/(O 2 + Ar) ratio and the deposition time were varied systematically. With increasing temperature, the layers become crystalline with the rutile modification dominating. Rutile phase preferentially forms on vertical facets of SnO 2 crystallites. Anatase phase starts to form during prolonged deposition and at lower O 2/(O 2 + Ar) ratios. The energy of the exponential absorption tails below the band gap, a measure of the defect density of the films, is determined by the deposition temperature and not by other parameters if the deposition temperature is relatively high, irrespective of the content of crystalline phases or the value of the band gap. Charge separation takes place at length scales significantly shorter than the layer thicknesses (diffusion length less than 6 nm). TiO 2 films sputtered at 380 °C show rectifying behaviour with a carbon contact.