Electrical transport in two dimensional heterostructures

Emerging two dimensional materials including transition metal dichalcogenides (TMDs) are of interest due to their electronic and optoelectronic applications including tunnel field effect transistors (TFETs) and photodetectors.¹ TMDs are of interest due to their bandgap range between 1.5 and 2.1 eV² and vertical stacking of these various layered TMDs allow for the possibility of multi-layered heterostructures and bandgap tuning. These layers are often stacked using exfoliation, which allow for initial investigations but do not ultimately lead to pristine interfaces, that are key to unlocking the true electronic potential of these materials. Synthesis routes including powder vaporization and metal organic chemical vapor deposition can be used to achieve direct growth of TMDs that achieve high quality interfaces. The vertical transport of TMDs on epitaxial graphene and multiple stacking of various TMDs including molybdenum disulfide (MoS₂)/tungsten diselenide (WSe₂) and epitaxial graphene via direct synthesis techniques was studied and is shown to lead to unique transport properties. The ability to synthesize these pristine interfaces yields vertical transport properties that include negative differential resistance (NDR). RF measurements of these heterojunctions will also be discussed.