Probing electron transport across a LSMO/Nb:STO heterointerface at the nanoscale

TL;DR

This study combines conventional I-V measurements and BEEM to analyze electron transport at the LSMO/Nb:STO heterointerface, revealing temperature-dependent Schottky barrier behavior and nanoscale homogeneity, providing new insights into interface properties.

Contribution

It demonstrates that BEEM can effectively characterize nanoscale homogeneity and temperature effects on Schottky barriers at complex oxide interfaces, distinguishing intrinsic properties from bias-induced modifications.

Findings

Schottky barrier height decreases at low temperatures in I-V measurements

BEEM shows no intrinsic SBH change at low temperatures

Nanoscale SBH is spatially homogeneous across the interface

Abstract

We investigate electron transport across a complex oxide heterointerface of La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) on Nb:SrTiO$_3$ (Nb:STO) at different temperatures. For this, we employ the conventional current-voltage method as well as the technique of Ballistic Electron Emission Microscopy (BEEM), which can probe lateral inhomogeneities in transport at the nanometer scale. From current-voltage measurements, we find that the Schottky Barrier height (SBH) at the LSMO/Nb:STO interface decreases at low temperatures accompanied by a larger than unity ideality factor. This is ascribed to the tunneling dominated transport caused by the narrowing of the depletion width at the interface. However, BEEM studies of such unbiased interfaces, do not exhibit SBH lowering at low temperatures, implying that this is triggered by the modification of the interface due to an applied bias and is not an intrinsic property of the interface. Interestingly, the SBH at the nanoscale, as extracted from BEEM studies, at different locations in the device is found to be spatially homogeneous and similar both at room temperature and at low temperatures. Our results highlight the application of BEEM in characterizing electron transport and their homogeneity at such unbiased complex oxide interfaces and yields new insights into the origin of the temperature dependence of the SBH at biased interfaces.