Enhanced Photocarrier Generation and Charge Transport in N-GQD/MoS₂ Heterostructure Phototransistor for Next-Generation Optoelectronics

Nitrogen-doped graphene quantum dots (N-GQDs) have attracted growing interest as photoactive materials for optoelectronic applications due to their high absorption coefficient, tunable bandgap, and strong photoluminescence. However, the low carrier mobility of GQD films often limits charge transport and device performance. To overcome this challenge, we developed N-GQD/MoS₂ heterostructure field-effect phototransistors (FEPTs) that integrate the superior charge transport of MoS₂ with the strong light-harvesting ability of N-GQDs. The N-GQDs were synthesized and interfaced with MoS₂ thin films to form a hybrid photoactive layer. Optical characterizations using UV–vis absorption and photoluminescence (PL) spectroscopy confirmed efficient photoexcitation and charge transfer between N-GQDs and MoS₂. Electrical measurements under illumination revealed that both pristine MoS₂ and N-GQD/MoS₂ FEPTs exhibit increased photocurrent and carrier mobility, with the N-GQD/MoS₂ device showing significantly enhanced photoresponsivity. This improvement is attributed to efficient photocarrier generation in N-GQDs and subsequent charge transfer to MoS₂. The slight reduction in mobility compared to pristine MoS₂ is explained by the n-type doping effect of N-GQDs, which modulates the channel conductivity and charge accumulation near the dielectric interface. These findings demonstrate that N-GQD/MoS₂ heterostructures offer a promising route toward high-performance, broadband phototransistors for next-generation optoelectronic and photonic devices.