Electron Transport at the TiO2 Surfaces of Rutile, Anatase, and Strontium Titanate: The Influence of Orbital Corrugation

The two-dimensional electron gas in SrTiO3 created by an overlayer of amorphous LaAlO3 is compared with those at the TiO2-terminated surfaces of rutile and anatase. Differences in conductivity are explained in terms of the limiting Ti-O-Ti bond angles (orbital corrugation), band dispersion, and polaron formation. At 300 K, the sheet conductivity and mobility of anatase exceed those for SrTiO3 or rutile by one or two orders of magnitude, respectively. The electrons in rutile become localized below 25 K.