Intrinsic Electronic Properties of BN Encapsulated, van der Waals Contacted MoSe${}_2$ FETs

Two-dimensional (2D) semiconductors have attracted considerable interest for their unique physical properties. Here, we report the intrinsic cryogenic electronic transport properties in few-layer MoSe${}_2$ field-effect transistors (FETs) that are simultaneously van der Waals contacted with gold electrodes and are fully encapsulated in ultraclean hexagonal boron nitride dielectrics. The FETs exhibit electronically favorable channel/dielectric interfaces with low densities of interfacial traps (${10}^{10}$cm${}^{-2}$), which lead to outstanding device characteristics at room temperature, including a near-Boltzmann-limit subthreshold swings ($<65$mV/dec), a high carrier mobility ($68$cm${}^2\cdot$V${}^{-1}\cdot$s${}^{-1}$), and a negligible scanning hysteresis ($<15$mV). The dependence of various contact-related quantities on temperature and carrier density are also systematically characterized to understand the van der Waals contacts between gold and MoSe${}_2$. The results provide insightful information on the device physics in van der Waals contacted and encapsulated 2D FETs.