Nanoscale current transport in epitaxial $SrTiO3$ on $n+-Si$ investigated with conductive atomic force microscopy

We have used conductive atomic force microscopy to image the nanoscale current distribution in $SrTiO3$ grown epitaxially on $n+-Si$ by molecular beam epitaxy. Topographic and current images were obtained simultaneously in contact mode with a bias voltage applied to the sample. Topographic images show a flat surface with a roughness of about 0.5 nm. Current images show small areas with local current flow on the order of pA for voltages larger than ∼2 V in forward bias and larger than ∼4 V in reverse bias. Histograms of the magnitude of the electrical current show a relatively narrow log-normal distribution, suggesting a common current mechanism with a Gaussian distribution in a parameter on which the current depends exponentially. Analysis of current images and histograms over a range of bias voltages suggests thermionic emission as the dominant current mechanism, rather than conduction associated with localized defects such as pin-holes, threading dislocations or grain boundaries. The analysis yields a barrier height of ∼0.5–0.6 eV with and a relative dielectric constant of 5–15, which is in reasonable agreement with previous reports using a dead layer model.