Engineering Graphene Quantum Dots for Enhanced Ultraviolet and Visible Light p-Si Nanowire-Based Photodetector

In this work, a significant improvement of the classical silicon nanowire (SiNW)-based photodetector was achieved through the realization of core-shell structures using newly designed GQD^PEIs via simple solution processing. The poly(ethyleneimine) (PEI)-assisted synthesis successfully tuned both optical and electrical properties of graphene quantum dots (GQDs) to fulfill the requirements for strong yellow photoluminescence emission along with large band gap formation and the introduction of electronic states inside the band gap. The fabrication of a GQD^PEI-based device was followed by systematic structural and photoelectronic investigation. Thus, the GQD^PEI/SiNW photodetector exhibited a large photocurrent to dark current ratio (I_ph/I_dark up to ∼0.9 × 10² under 4 V bias) and a remarkable improvement of the external quantum efficiency values that far exceed 100%. In this frame, GQD^PEIs demonstrate the ability to arbitrate both charge-carrier photogeneration and transport inside a heterojunction, leading to simultaneous attendance of various mechanisms: (i) efficient suppression of the dark current governed by the type I alignment in energy levels, (ii) charge photomultiplication determined by the presence of the PEI-induced electron trap levels, and (iii) broadband ultraviolet-to-visible downconversion effects.