  Although MoS2 field-effect transistors (FETs) with high-k dielectrics are
promising for electron device applications, the underlying physical origin of
interface degradation remains largely unexplored. Here, we present a systematic
analysis of the energy distribution of the interface state density (Dit) and
the quantum capacitance (CQ) in a dual-gate monolayer exfoliated MoS2 FET. The
CQ analysis enabled us to construct a Dit extraction method as a function of
EF. A band tail distribution of Dit with the lowest value of 8*1011 cm-2eV-1
suggests that Dit is not directly related to the sharp peak energy distribution
of the S vacancy. Therefore, the Mo-S bond bending related to the strain at the
interface or the surface roughness of the SiO2/Si substrate might be the
origin. It is also shown that ultra-thin 2D materials are more sensitive to
interface disorder due to the reduced density of states. Since all the
constituents for the measured capacitance are well understood, I-V
characteristics can be reproduced by utilizing the drift current model. As a
result, one of the physical origins of the metal/insulator transition is
suggested to be the external outcome of interface traps and quantum
capacitance.
