Highly Enhanced Photoresponsivity of a Monolayer WSe₂ Photodetector with Nitrogen-Doped Graphene Quantum Dots

TLDR

Hybrid 2D material–quantum dot structures are attractive for nanoscale optoelectronics because QDs efficiently absorb light and inject carriers into high‑mobility 2D transition‑metal dichalcogenides. The study introduces a heterostructure comprising a monolayer of tungsten diselenide coated with nitrogen‑doped graphene quantum dots. The device’s performance is enhanced by photogating and back‑gate voltage modulation, yielding a responsivity of 2578 A W⁻¹. The N‑GQD‑covered WSe₂ photodetector achieves a 480 % higher photoresponsivity, retains 46 % of its performance after 30 days, and benefits from enhanced neutral exciton emission due to n‑doping.

Abstract

Hybrid structures of two-dimensional (2D) materials and quantum dots (QDs) are particularly interesting in the field of nanoscale optoelectronic devices because QDs are efficient light absorbers and can inject photocarriers into thin layers of 2D transition-metal dichalcogenides, which have high carrier mobility. In this study, we present a heterostructure that consists of a monolayer of tungsten diselenide (ML WSe2) covered by nitrogen-doped graphene QDs (N-GQDs). The improved photoluminescence of ML WSe2 is attributed to the dominant neutral exciton emission caused by the n-doping effect. Owing to strong light absorption and charge transfer from N-GQDs to ML WSe2, N-GQD-covered ML WSe2 showed up to 480% higher photoresponsivity than that of a pristine ML WSe2 photodetector. The hybrid photodetector exhibits good environmental stability, with 46% performance retention after 30 days under ambient conditions. The photogating effect also plays a key role in the improvement of hybrid photodetector performance. On applying the back-gate voltage modulation, the hybrid photodetector shows a responsivity of 2578 A W-1, which is much higher than that of the ML WSe2-based device.