Silicon Nanowire Arrays with Nitrogen-Doped Graphene Quantum Dots for Photodetectors

A significantly improved silicon nanowire (SiNW)-based broadband photodetector is obtained in this work using the core–shell structure of SiNWs with hydrothermally processed nitrogen doped graphene quantum dots (N-GQDs). The performance of the photodetector device is enhanced significantly by enlarging the effective surface area of the SiNW/N-GQD heterostructure by controlled KOH etching of SiNWs. In combination with SiNWs, low-cost hydrothermal processed N-GQDs are used as a light absorber in the UV region and also as an emitter in the visible region which is reabsorbed by the SiNWs to enhance the device performance. The SiNW/N-GQD heterostructure photodetector exhibits a large photocurrent to dark-current ratio (∼0.8 × 10 2 under zero bias and as high as ∼0.5 × 10 4 under −2 V bias for 2 min KOH etching), remarkably low dark current (∼55 nA under −2 V bias for 2 min KOH etching and is six orders lower compared to control SiNWs device), and significantly improved external quantum efficiency (EQE) exceeding 150% in the near IR and ∼500% at 460 nm wavelength in the visible region. Such higher EQE may arise due to the (i) enhanced optical absorption, (ii) suppressed dark current, (iii) photomultiplication of charge carriers because of the presence of trap states, and (iv) improved carrier transport and collection efficiency due to core–shell structure and nanoscale morphology control. It is expected that the reported SiNWs/N-GQDs core–shell heterostructure device might be useful for high-performance optoelectronic applications in the near future.