Morphological and photoelectrochemical properties of ALD TiO2 films

TiO2 films were grown by atomic layer deposition (ALD) at 200-500 degrees C with TiCl4 and H2O as gas sources. The relationships among deposition temperature, microstructure, and photoelectrochemical properties were investigated. The results showed that the crystalline form is anatase at deposition temperatures of 200-400 degrees C and is a mixture of anatase and rutile at 500 degrees C. The grain size changed with the deposition temperature and had a minimum at around 400 degrees C. The potential sweep voltammograms demonstrated that the photoelectrochemical properties of these TiO2 films were deteriorated by either the high defect density or the small grain size, or the existence of rutile phase. In order to modify the morphological properties of ALD TiO2 films, a two-stage ALD with first stage for a nucleation layer and second stage for stress release and grain growth was proposed. Expectedly, the photoelectrochemical properties were significantly improved by this approach. (C) 2008 The Electrochemical Society.