Aluminium and zinc co-doped CuInS₂ QDs for enhanced trion modulation in monolayer WS₂ toward improved electrical properties

Considering the significant influence of trions on the optical and electronic properties of two-dimensional transition metal dichalcogenides, the precise tuning of trions in a large range is important for optoelectronic or trion-related applications. Herein, a detailed comparison of eco-friendly CuInS₂ (CIS) quantum dots (QDs) and (Al, Zn) co-doped CIS QDs on tuning the trion ratio and electrical properties in a mechanically-exfoliated monolayer (ML) WS₂ is presented. With a similar QD thickness, the trion modulation ability of CIS QDs is largely enhanced after co-doping due to existing extra donor states. In particular, the trion ratio of ML WS₂ can be precisely tuned from 0.05 to 0.7 by varying the QD species and QD thickness, while only a small range (0.05-0.15) of the trion ratio in ML WS₂ is achieved under gate voltage. Moreover, the electron mobility and electron concentration of WS₂-based field-effect transistors (FETs) are significantly improved after QD modification, exhibiting potential applications in FETs and photodetectors.