Reversible and controllable threshold voltage modulation for n-channel MoS₂ and p-channel MoTe₂ field-effect transistors via multiple counter doping with ODTS/poly-L-lysine charge enhancers

Confronted by the inherent physical limitations in scaling down Si technology, transition metal dichalcogenides (TMDCs) as alternatives are being tremendously researched and paid attention to. However, mature counter doping technology for TMDCs is still elusive, and thus, a controllable and reversible charge enhancer is adopted for acceptor (or donor)-like doping via octadecyltrichlorosilane (ODTS) (or poly-L-lysine (PLL)) treatment. Furthermore, multiple counter doping for TMDC field-effect transistors (FETs), combined with a threshold voltage (V_th) freezing scheme, renders the V_th modulation controllable, with negligible degradation and decent sustainability of FETs even after each treatment of a representative charge enhancer. In parallel, the counter doping mechanism is systematically investigated via photoluminescence spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy (AFM), surface energy characterization, and measurement of optoelectronic properties under illumination with light of various wavelengths. More impressively, complementary inverters, composed of type-converted molybdenum ditelluride (MoTe₂) FETs and hetero-TMDC FETs in enhancement mode, are demonstrated via respective ODTS/PLL treatments. Herein, driving backplane application for micro-light-emitting diode (µ-LED) displays and physical validation of a corresponding counter doping scheme even for flexible polyethylene terephthalate (PET) substrates could be leveraged to relieve daunting challenges in the application of nanoscale Si-based three-dimensional (3D) stacked systems, with potential adoption of ultralow power and monolithic optical interconnection technology.