Contact engineering for temperature stability improvement of Bi-contacted MoS₂ field effect transistors

Semimetallic bismuth (Bi) is one of the most effective strategies for reducing the contact resistance of two-dimensional transition metal dichalcogenide field effect transistors (FETs). However, the low melting point of Bi contact (271.5° C) limits its reliable applications. In this study, we demonstrated that the temperature stability of Bi-contacted electrodes could be improved by inserting a high-melting point semimetallic antimony (Sb) between the Bi contacting layer and the gold (Au) capping layer. The proposed Bi/Sb/Au contact electrodes tended to form a metal mixture with a continuous surface during the heating process (Voids appeared on the surface of the Bi/Au contact electrodes after heating at 120° C). Because of the improved contacting layer formed by the semimetal Bi/Sb alloy, the fabricated Bi/Sb/Au-contacted molybdenum sulfide (MoS₂) FETs with different gate lengths demonstrated higher on-state current stability after heating treatment than the Bi/Au contact. Because of the Bi/Sb/Au contact and poly (methyl methacrylate) package, the MoS₂ FETs demonstrated time stability of at least two months from the almost unchanged transfer characteristics. The electrical stability indicates that the insertion of semimetallic Sb is a promising technology for reliable Bi-based contact.