Band tail interface states and quantum capacitance in a monolayer molybdenum disulfide field-effect-transistor

Abstract

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.