Surface State Engineering of Metal/MoS2 Contacts Using Sulfur Treatment for Reduced Contact Resistance and Variability

Variability and difficulty in achieving good ohmic contacts are major bottlenecks toward the realization of high-performance molybdenum disulphide (MoS2)-based devices. The role of surface state engineering through a simple sulfur-based technique is explored to enable reliable and superior contacts with high work function (WF) metals. Sulfur-treated multilayered MoS2 FETs exhibit significant improvements in ohmic nature, nearly complete alleviation in contact variability,  2x gain in extracted field-effect mobility, 6x and 10x drop in contact resistance, and high drain currents with Ni and Pd contacts, respectively. Raman and X-ray photoelectron spectroscopy measurements confirm lack of additional channel doping and structural changes, after sulfur treatment. From temperature-dependent measurements, the reduction of Schottky barrier height at Ni/MoS2 and Pd/MoS2 is estimated to be 81 and 135 meV, respectively, indicating the alteration of surface states at the metal/MoS2 interface with sulfur treatment. The key interface parameters, such as Fermi pinning factor, charge neutrality level, and the density of surface states, are estimated using the classical metal/semiconductor junction theory. This first report of surface state engineering in MoS2 demonstrates the ability to create excellent contacts using high WF metals, without additional channel doping, and sheds light on a relatively unexplored area of metal/transition metal dichalcogenides interfaces.