Lateral and Vertical Electronic Transport in 2D Layered Materials

Electronic devices from two-dimensional (2D) systems have become the focus of research activities worldwide over the last couple of years. Since the discovery of graphene, many other 2D structures have been identified and studied with a particular focus on transition metal dichalcogenides (TMDs) like MoS₂, WSe₂, MoTe₂, and black phosphorus (BP). Different from graphene, these materials exhibit a finite bandgap, which makes them highly relevant for electronic device applications. While most of the previous studies have focused on the lateral transport in these structures, most recently attention has been drawn to the transport between van der Waals layers for tunneling device applications and to create “atomically abrupt” p-n junctions. Here we will discuss experimental results on the topic of lateral and vertical electronic transport in a number of 2D materials and heterostructures from the same. The results can be summarized as follows: 1) Schottky barriers and their response to drain and gate voltages give rise to unique ambipolar device characteristics that can be evaluated in terms of bandgaps and Schottky barrier heights; 2) Large current rectification ratios observed in lateral/vertical 2D heterostructures are a result of the Schottky barrier response; 3) Vertical transport masses can be determined from a quantitative analysis of vertical transport through TMDs; and 4) An electric field induced reversible phase transition from a metallic to a semiconducting phase can be achieved in certain binary and ternary TMDs.