Enhancing the barrier height in oxide Schottky junctions using interface dipoles

Abstract

We demonstrate a 0.37 eV increase in the n-type Schottky barrier height at the Pt/TiO2-terminated SrTiO3 (001) interface by insertion of an ultrathin insulator AgTaO3. While a conventional metal-insulator-semiconductor model predicts a reduction in the barrier height with insulator thickness, the observed increase originates from the two polar surface layers, (AgO)– and (TaO2)+ in AgTaO3 (001), forming an electrostatic dipole directed towards the metal, increasing the barrier height. Based on directly measured optical and dielectric properties of high quality AgTaO3 thin films, we determine the interface energy band diagram including the interface dipole. The capability to exploit the strong ionic charges of oxide surfaces to manipulate interface band alignments beyond bulk values greatly expands the design strategies for tailoring functional oxide interfaces. Up to now, the use of an ultrathin LaAlO3 layer could only decrease the barrier height, but now bidirectional control is possible.