Achieving Low Resistance Ohmic Contacts to Transition Metal Dichalcogenides (TMDCs)

Abstract

Transition metal dichalcogenides (TMDCs) harbor great potential for use in high performance electronic devices. However, their practical usage has been hindered by a lack of suitable low resistance ohmic contacts, resulting in high contact resistances and low electron mobilities. Our study aims to investigate the performances of alternative contacts strategies such as exfoliated graphite contacts, bottom-up gold (Au) contacts and evaporated gold-capped indium (In-Au) contacts to exfoliated tungsten disulfide (WS₂) by first fabricating field-effect transistors (FET) and later, conducting transfer line measurements (TLM). Our results show that evaporated gold-capped indium/WS₂ contacts achieved the best ohmic performance out of the three contact strategies with a significantly higher field effect electron mobility of 114 cm²V⁻¹ s⁻¹ and a lower contact resistance of 462 k Ω µm to few layer WS₂ and a mobility of 5.45 cm²V⁻¹ s⁻¹ and contact resistance of 169 M Ω µm to monolayer WS₂ at room temperature, while graphite/WS₂ contacts and bottom up Au/WS₂ contacts yielded poor non-ohmic characteristics with a field effect electron mobility of 0.0409 and 0.00542 cm²V⁻¹ s⁻¹ respectively. Our results also show that low resistance ohmic contacts for WS₂ can be achieved through the direct evaporation of gold-capped indium (In–Au) contacts. This is of current relevance and importance as WS₂ has been found to have a plethora of applications from high mobility field-effect transistors to quantum information processing and the formation of the low resistance ohmic contact is a fundamental step towards achieving these goals.