  Semiconducting two-dimensional transition metal chalcogenide crystals have
been regarded as the promising candidate for the future generation of
transistor in modern electronics. However, how to fabricate those crystals into
practical devices with acceptable performance still remains as a challenge.
Employing tungsten disulfide multilayer thin crystals, we demonstrate that
using gold as the only contact metal and choosing appropriate thickness of the
crystal, high performance transistor with on/off ratio of $10^{8}$ and mobility
up to $234\:cm^{2}V^{-1}s^{-1}$ at room temperature can be realized in a simple
device structure. Further low temperature study revealed that the high
performance of our device is caused by the minimized Schottky barrier at the
contact and the existence of a shallow impurity level around 80 meV right below
the conduction band edge. From the analysis on temperature dependence of
field-effect mobility, we conclude that strongly suppressed phonon scattering
and relatively low charge impurity density are the key factors leading to the
high mobility of our tungsten disulfide devices.
