  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 ($\lt65\,$mV/dec), a high carrier
mobility ($68\,$cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$), and a negligible scanning
hysteresis ($\lt15\,$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.
