P-Type Doping of WS₂ Quantum Dots via Pulsed Laser Ablation

Doping provides an advantage to engineering the optical and electrical characteristics of transition-metal dichalcogenides (TMDs). Here, we report the doping of WS₂ quantum dots (QDs) with diethylenetriamine (DETA) using pulsed laser ablation. The synthesized DETA-doped 2H-WS₂ QDs with an average size of ∼6 nm have been demonstrated by transmission electron microscopy. With the introduction of DETA during pulsed laser ablation, current modulation, carrier concentration, and field-effect mobility are greatly enhanced, demonstrating a successful doping in WS₂ QDs. The positive shift of the threshold voltage in gate-dependent conductance measurements reveals p-type doping for DETA-doped WS₂ QDs. A remarkable improvement in photoluminescence in WS₂ QDs by 74-fold has been achieved after DETA doping. An anomalous dopant-dependent negative photoconductivity was observed for WS₂ QDs, originating from light-induced desorbing of water (oxygen) molecules on the surface. The proposed doping approach can provide a vehicle to modulate the optical and electrical properties in WS₂ QDs and could be important in the performance improvement of WS₂-QD-based devices.