Quasi-Zero-Dimensional\nSource/Drain Contact for Fermi-Level\nUnpinning in a Tungsten Diselenide (WSe<sub>2</sub>) Transistor: Approaching\nSchottky–Mott Limit

Two-dimensional (2D) transition metal dichalcogenides\n(TMDCs) known\nfor their exceptional electrical and optical properties have emerged\nas promising channel materials for next-generation electronics. However,\nas strong Fermi-level pinning (FLP) between the metal and the 2D TMDC\nmaterial at the source/drain (S/D) contact decides the Schottky barrier\nheight (SBH), the transistor polarity is fixed to a certain type,\nwhich remains a challenge for the 2D TMDC field-effect transistors\n(FETs). Here, a S/D contact structure with a quasi-zero-dimensional\n(quasi-0D) contact interface, in which the dimensionality reduction\neffect alleviates FLP, was developed to gain controllability over\nthe polarity of the 2D TMDC FET. As a result, conventional metal contacts\non the WSe<sub>2</sub> FET showed n-type characteristics due to strong\nFLP (pinning factor of 0.06) near the conduction band, and the proposed\nquasi-0D contact enabled by the Ag conductive filament on the WSe<sub>2</sub> FET exhibited p-type characteristics with a SBH very close\nto the Schottky–Mott rule (pinning factor of 0.95). Furthermore,\nmodeling of Schottky barriers of conventional contacts, one-dimensional\n(1D) contacts, and quasi-0D contacts revealed that the SBH of the\nquasi-0D contact is relatively less subject to interface dipoles that\ninduce FLP, owing to more rapid decaying of dipole energy. The proposed\ncontact in this study provided a method that progressed beyond the\nalleviation of FLP to achieve controllable polarity. Moreover, reducing\nthe contact dimensionality to quasi-0D will enable high compatibility\nwith the further scaled-down nanoscale device contact structure.