Surface-induced thickness limit of conducting La-doped SrTiO3 thin films

We report on a surface-induced, insulating, electrically dead layer in ultrathin conducting La-doped SrTiO3 thin films. Systematic studies on electrical properties as a function of film thickness and La-doping levels reveal that the insulating layer has a constant thickness and traps a constant amount of electron density regardless of La-doping levels. Growing an additional capping layer on top of the La-doped SrTiO3 surface counteracts the reduced conductivity, indicating a strong relationship between the insulating layer and the surface structure. Our results emphasize the importance of surface state studies for functional oxides in the thin film limit and provide a guiding principle for the fabrication of La-doped SrTiO3-based oxide nanoscale devices. Published under license by AIP Publishing.