Electrical Contact between an Ultrathin Topological Dirac Semimetal and a Two-Dimensional Material
Liemao Cao, Guanghui Zhou, Qingyun Wu, Shengyuan A. Yang, Hui Ying Yang, Yee Sin Ang, L. K. Ang
Abstract
Ultrathin films of the topological Dirac semimetal ${\mathrm{Na}}_{3}\mathrm{Bi}$ have recently been revealed as unusual electronic materials with field-tunable topological phases. Here we investigate the electronic and transport properties of ultrathin ${\mathrm{Na}}_{3}\mathrm{Bi}$ as an electrical contact to a two-dimensional (2D) metal (i.e., graphene) and 2D semiconductors (i.e., ${\mathrm{Mo}\mathrm{S}}_{2}$ and ${\mathrm{WS}}_{2}$ monolayers). Using combined first-principles density-functional theory and nonequilibrium Green's function simulation, we show that the electrical coupling between bilayer-${\mathrm{Na}}_{3}\mathrm{Bi}$ thin film and graphene results in a notable interlayer charge transfer, thus inducing sizable $n$-type doping in the ${\mathrm{Na}}_{3}\mathrm{Bi}/$graphene heterostructures. In the case of ${\mathrm{Mo}\mathrm{S}}_{2}$ and ${\mathrm{WS}}_{2}$ monolayers, the lateral Schottky transport barrier is significantly lower than for many commonly studied bulk metals, thus revealing bilayer ${\mathrm{Na}}_{3}\mathrm{Bi}$ to be a high-efficiency electrical contact material for 2D semiconductors. These findings open up an avenue for utilizing topological semimetal thin film as an electrical contact to 2D materials, and further expand the family of 2D heterostructure devices into the realm of topological materials.