Effect of surface structure on workfunction and Schottky-barrier height in SrRuO3/SrTiO3 (001) heterojunctions

We present an ab-initio theoretical study of work functions and surface energies of SrRuO3 (001) surfaces and Schottky-barrier heights (SBHs) at various interfaces in SrRuO3/SrTiO3 (001) heterostructure within the framework of the density-functional theory. The SrRuO3 workfunctions are found to exhibit strong dependence on surface terminations. The workfunction of two defect-free SrRuO3 (001) surface terminations, viz., SrO and RuO2, differ by as much as 2.37 eV. The p-type SBH at the RuO2/SrO/TiO2 interface is calculated to be 1.27 eV. The substitution of interfacial SrO layer by isoelectronic BaO layer induces small change in the p-SBH (similar to 0.06 eV). However, the p-SBH is reduced significantly (similar to 0.5 eV) as the RuO2 layer is substituted by MnO2 layer due to large change in the interfacial dipole. The p-SBH at different interfaces in SrRuO3/SrTiO3 structures are also estimated using semi-empirical metal-induced-gap-states (MIGS) model. The estimated values are found to be larger by similar to 2 eV than those obtained using ab-initio method, rendering the validity of MIGS model questionable in the prediction of SBH in all-oxide metal/dielectric heterojunctions. The modification of SBH by interfacial doping offers the possibility of contact resistance control in SrRuO3/SrTiO3 heterostructures and related devices. (C) 2014 AIP Publishing LLC.