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.

Nanoparticle-nanowire heterostructures provide a new platform for photodetection applications owing to their higher light absorption, large responsivity, and excellent separation efficiency of photogenerated electron-hole pairs. Herein, we report a SnS 2 /Si nanowire heterostructure photodetector with excellent optoelectronic properties. A high-quality SnS 2 /Si nanowire heterostructure was prepared by simply spin coating a wet chemically synthesized SnS 2 on a vertically standing Si nanowire made by metal assisted chemical etching. The as-prepared SnS 2 /Si nanowire heterostructure exhibits a robust p-n junction with excellent photodetector characteristics. The photodetector based on the heterostructure shows a photo-responsivity of ∼3.8 A W −1 , a specific detectivity up to ∼ 2 × 10 14 Jones, and an on/off ratio up to ∼ 10 2 at 340 nm illumination wavelength with a significantly low optical power density of 53.75 nW/mm 2 at zero bias (0 V). The photoresponsivity reached its maximum value of ∼10 2 A/W and detectivity of ∼1 × 10 14 Jones at the same wavelength with an applied bias of −2 V. In addition, the heterostructure photodetector provides significantly good photodetector key parameters (responsivity ∼5.3 A/W, detectivity ∼ 7.5 × 10 12 Jones, rise/decay time ∼0.4/0.4 s) at −2 V bias over a wide spectral range from 400 to 1100 nm. The Si nanowire and SnS 2 nanoparticle heterostructure devices with an enhanced junction area open up an exciting field for novel non-toxic and environmental friendly broadband optical detection applications and optoelectronic memory devices with high responsivity, ultrahigh sensitivity, and self-sufficient functionality at low power consumption and low cost with ease of processing.

As one kind of ecofriendly organic semiconductor materials, chlorophyll has attracted great attention with useful optical properties. Although pigments such as chlorophyll-a (Chl-a) are explored widely, chlorophyll-b (Chl-b) is rarely studied even though it possesses outstanding optical properties with impressive stability. Here, Chl-b is extracted from spinach leaves using a very simple and cost-effective method to study its potential use on Si nanowire (NW) heterostructures having volume concentration varying from 0 to 6%. In comparison to the control Si NW device, the Chl-b/SiNW heterostructure exhibits superior optoelectronic performances including high on/off ratio (∼10 3 ), good external quantum efficiency (∼208%), high responsivity (∼0.73 A/W), improved detectivity (∼2.2 × 10 12 Jones), and relatively faster response time (<1 s) under 435 nm illumination. In addition, it offers quite promising values of the abovementioned figure of merits of a photodetector over the wide spectral range from 350−1100 nm. This low-cost and high-sensitivity Chl-b/SiNW heterostructure device thus opens up challenging research possibilities for green energy conversion and biophotonic applications on Si-compatible complementary metal−oxide−semiconductor platforms.

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