Electrical Contact to MoS2 for Sensitive Capacitance Measurements

When electrons confined to two dimensions are subjected to a low temperature and high magnetic field environment, exact quantization of macroscopic material properties can occur, known as the integer (IQHE) and fractional (FQHE) quantum Hall effects. Important experimental platforms utilized to investigate the IQHE and FQHE are graphene-based van der Waals (vdW) heterostructures due to their high carrier mobility and easy access to low carrier density regimes. These heterostructures are limited in their scope however as graphene does not possess an energy band gap or strong spin-orbit coupling, two properties that lead to unique effects on the IQHE and FQHE. This is in stark contrast with other 2D materials such as the semiconducting transition metal dichalcogenides (TMDs) which contain both necessary ingredients. In this thesis, baseline measurements of penetration field capacitance (Cp) are confirmed on a monolayer graphene (MLG) vdW heterostructure at T = 3 K and B = 2 T, showing the ability to resolve features of electronic incompressibility. Cp and transport measurements are also presented on a few-layer MoS2 heterostructure, allowing a direct comparison between the two measurement techniques to resolve the conduction band edge of MoS2. Due to Schottky barrier formation between few-layer graphene contacts and MoS2, the resulting contact is non-ohmic, limiting measurements of Cp and transport to above 200 K. Concluding, a semimetallic bismuth contact method is investigated on a few-layer MoS2 sample, achieving multiple ohmic contacts with extracted Schottky barrier heights of 30 meV and -15 meV. The ohmic contact results in linear IV characteristics and large on-off ratios of 107 down to T = 3 K at low carrier densities n < 3 10−12 cm−2. This work sets a foundation for sensitive capacitance measurements of the interesting class of TMDs in the low carrier density regime.