Measuring the Barrier Height at Transition Metal Dichalcogenide Heterojunctions

Transition metal dichalcogenides (TMDs) have attracted much interest in recent years as channel materials for high performance Field Effect Transistors (FETs). However, a large Schottky barrier tends to form at the interface of TMD channels and most conventionally used metal contacts. Chuang et al. demonstrated low-resistance Ohmic contacts to WSe₂, MoS₂, and MoSe₂ channels by inserting a degenerately doped TMD at the contact areas.¹ While the low contact resistance suggests a substantially reduced barrier, a systematic study is necessary to probe the reduction of the Schottky Barrier Height (SBH) and better understand the mechanism of carrier injection at TMD heterojunctions that enables the success of the 2D-2D contact strategy. In this work, we investigate how the band alignment affects the Schottky barrier Height.
While ohmic contacts are achieved between degenerately -doped MoS₂ drain/source and WSe₂ channel, a SBH in the range of tens to hundreds of meV is observed for individual 2D/2D junctions consisting of -doped WSe₂ contact and MoSe₂ channel. For comparison, we also study isolated Schottky barriers at TMD/metal junctions by fabricating asymmetrically contacted WSe₂ FETs consisting of a 2D/2D ohmic contact and a TMD/metal Schottky contact.