Surface state engineering of metal/MoS 2 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.