Tailoring Work Functions of Heterostructures by Varying the Depth of a Buried Monolayer

Abstract

The work function is a critical parameter for device design and understanding of materials properties, but contemporary experimental literature on tailored work functions is rather scarce. This paper presents a promising new approach to work function design that uses pulsed laser deposition (PLD) growth with unit cell precision. It is shown that a monolayer buried within a material can influence the work function as a function of the layer depth. This method can preserve properties of the original material's surface, and furthermore, a sensitive material can be used as the monolayer, both of which are beneficial for device design. Proof of concept is demonstrated by inserting a nominal monolayer of barium oxide (BaO) into strontium titanate (SrTiO3) (001) at different depths, revealing a previously unknown work function trend. Density functional theory (DFT) calculations, surface characterization, and scanning transmission electron microscopy (STEM) studies verify the quality of the heterostructures and help to understand how charge transfer, slight barium diffusion, and termination effects account for the observed work function trends. This work function tunability is a promising approach for future devices that require a tailored work function, which can easily be extended to a wider variety of materials.