Accurate Extraction of Schottky Barrier Height and Universality of Fermi Level De-pinning of van der Waals Contacts

TL;DR

This paper introduces a simple method to accurately measure Schottky barrier heights at van der Waals contacts, revealing their universal de-pinned nature and demonstrating improved ambipolar carrier injection for optoelectronic applications.

Contribution

It proposes a novel technique for precise SBH extraction at vdW interfaces and demonstrates the universal de-pinning behavior across various materials.

Findings

vdW contacts exhibit universal de-pinned Fermi levels

The new technique accurately estimates SBH, reducing ambiguities

vdW contacts enable superior ambipolar carrier injection in devices

Abstract

Due to Fermi level pinning (FLP), metal-semiconductor contact interfaces result in a Schottky barrier height (SBH), which is usually difficult to tune. This makes it challenging to efficiently inject both electrons and holes using the same metal - an essential requirement for several applications, including light-emitting devices and complementary logic. Interestingly, modulating the SBH in the Schottky-Mott limit of de-pinned van der Waals (vdW) contacts becomes possible. However, accurate extraction of the SBH is essential to exploit such contacts to their full potential. In this work, we propose a simple technique to accurately estimate the SBH at the vdW contact interfaces by circumventing several ambiguities associated with SBH extraction. Using this technique on several vdW contacts, including metallic 2H-TaSe$_2$, semi-metallic graphene, and degenerately doped semiconducting SnSe$_2$, we demonstrate that vdW contacts exhibit a universal de-pinned nature. Superior ambipolar carrier injection properties of vdW contacts are demonstrated (with Au contact as a reference) in two applications, namely, (a) pulsed electroluminescence from monolayer WS$_2$ using few-layer graphene (FLG) contact, and (b) efficient carrier injection to WS$_2$ and WSe$_2$ channels in both nFET and pFET modes using 2H-TaSe$_2$ contact.