Work Function Modulation of Bi/Au Bilayer System toward p-Type WSe<sub>2</sub> FET
Ryuichi Nakajima, Tomonori Nishimura, Keiji Ueno, Kosuke Nagashio
Abstract
In order to attain high-performance p-type field-effect transistors (FETs) based on two-dimensional materials, it becomes imperative to mitigate Fermi level pinning. Employing Bi with a low work function of ∼4.2 eV, characterized by its low melting point, significant vapor pressure, and smaller density of states, has been instrumental in establishing pinning-free n-type contacts. In this context, we present a new approach for establishing p-type contacts. This approach involves the modulation of the effective work function through a bilayer electrode structure comprising ultrathin Bi and a thick Au with a high work function of ∼5.1 eV. The modulation of the effective work function has been clearly confirmed through capacitance─voltage measurements, conducted as a function of the thickness of the Bi layer. Consequent to these findings, a p-type WSe 2 Schottky FET was demonstrated employing 2-nm-thick Bi/Au electrodes.