Title: Oxidation-mediated van der Waals interface engineering for high performance p-type 2D FETs

Abstract:

In two-dimensional (2D) materials-based field-effect transistors (FETs), p-type 2D FETs have still exhibited inferior device performance compared to n-type 2D FETs, due to high contact resistance and absence of effective doping strategy. Even though previous attempts to improve p-type contacts employed WO_x layers formed by oxidizing WSe₂, uncontrollable excessive p-doping increases the off-current, thereby leading to small on/off current ratio. Here, we introduce highly precise oxidation process of WSe₂ to achieve p-type doping and small contact resistance. Mild oxygen plasma treatment and subsequent low-pressure (LP) annealing yields a WO_x/WSe₂ heterointerface. Charge transfer doping of WSe₂ by WO_x can be precisely tuned by the WO_x thickness. Furthermore, mild oxidation process enables the formation of ultraclean van der Waals (vdW) gap at the WO_x/WSe₂ interface, minimizing the damage of WSe2. The subsequent LP annealing at low temperature preserves vdW gap, suppressing oxide-induced scattering and preventing an increase of hysteresis. The WO_x-covered WSe₂ FETs show high on-current (I_on) of ~230.6 μA/μm, small subthreshold swing (SS) of ~100.6 mV/dec, and small contact resistance (R_c) of ~1.49 kΩ∙μm for L_ch = 300 nm. Our oxidation-based vdW interface engineering strategy is BEOL-friendly and applicable to monolithic CMOS integration, enabling tunable p-type doping and improved contact resistance in p-type 2D FETs, thereby advancing industrial 2D CMOS.