Highly luminescent and direct band gap black phosphorus (BP) nanocrystals (NCs) synthesized using a cost‐effective sonochemical exfoliation route are reported. Microscopic studies have confirmed the exfoliation of few‐layer nanoflakes and BP NCs with variable average size between ≈2 and ≈8 nm. Structural and vibrational characteristics reveal the superior crystalline quality by retaining the phase and crystalline symmetry in NCs. Size‐dependent absorption characteristics are observed by controlling the nanoparticle size and show a progressive blue shift near band edge absorption on reducing the size, useful for selective multicolor photodetection. Temperature‐dependent photoluminescence measurements from room temperature (300 K) down to 10 K are performed. Most interestingly, BP NCs with the lowest diameter exhibit a novel negative thermal quenching behavior as compared to positive thermal quenching observed usually in bulk semiconductors and BP NCs with larger diameter. Metal–semiconductor–metal type (Au/BP‐NCs/Au) photodetectors are fabricated to study their photoresponse properties, which reveal the potential application of BP NCs as optical modulators.

Flexible photodetectors were fabricated on a PET platform, exhibiting a two-colour band photoresponse, besides infrared tunability with high responsivity and detectivity.

Two-dimensional (2D) semiconductors with a direct band gap are attractive for the fabrication of 2D/Si heterostructures for complementary metal−oxide−semiconductor compatible nanophotonic devices. We report the characteristics of sonochemically exfoliated molybdenum diselenide (MoSe 2 ) nanocrystals (NCs) integrated on large-area Si platforms to demonstrate tunable and broadband heterojunction photodetectors. The exfoliation of bulk materials to the 2H-semiconducting phase of MoSe 2 NCs exhibiting excitonic absorption peaks with characteristic 2D nature is established. A gradual blue shift in the absorption peaks accompanied by the stiffening of A 1g Raman mode supports the size-dependent properties of NCs. Spectral response of MoSe 2 -NCs/ Si (2D/3D) heterojunction devices reveal size-tunable and broadband (400−1400 nm) photoresponse, with the optimum sample (size ∼12 nm) showing a peak responsivity and a detectivity of ∼960 mA/W and ∼1.8 × 10 12 Jones, respectively, at a low bias (−2 V).

We report the enhanced photodetection properties of MoSe2/Au–ZnO vertical heterostructures by probing the synergistic effect of Au nanoislands on the optical response of one-dimensional (1D) vertically standing ZnO nanorods (NRs) and few-layer two-dimensional (2D) MoSe2 nanoflakes, collectively. Plasmonic effects mediated strong light–matter interactions in Au–ZnO hybrids are established through spectroscopic studies. A notable red shift accompanied by a quenched intensity of visible photoluminescence of ZnO NRs supports the energy transfer process from ZnO NRs to Au nanoislands in the plasmonic hybrid. The coupling of defect-originated green emission of ZnO NRs with plasmonic absorption (∼560 nm) and the strategic position of Au nanoislands facilitate easy transfer of plasmonic charge carriers across the heterojunctions and enhance the signal throughout the total operational bandwidth (up to ∼900 nm) of the devices considerably. Such robust devices using 2D/1D mixed-dimensional heterostructures and their direct resonant coupling with strategically integrated 0D plasmonic nanoislands make highly responsive (∼0.43 A/W) broadband photodetectors for future nanophotonic applications.

We report the superior broadband photodetection characteristics of few-layer phosphorene known as black phosphorus (BP) nanosheets integrated with silver nanoparticles (Ag NPs) using vertical heterojunctions on a Si platform. The exfoliation of BP nanosheets and preparation of an Ag NP:BP (Ag-BP) hybrid have been accomplished through environment-friendly and cost-effective chemical routes. The hybrid sample exhibits broadband light absorption with a strong plasmonic peak around ∼425 nm due to the localized surface plasmon resonance (LSPR) of Ag NPs of average size ∼6.0 nm. Spectroscopic analysis of the Ag-BP hybrid ascertains strong light−matter interactions around the LSPR band of Ag NPs. The size-dependent optical response of BP nanostructure/Si state-of-the-art broadband (300−1600 nm) photodiodes has been studied extensively. The enhancement of broadband photoresponse characteristics is demonstrated using the plasmonic Ag-BP 0D-2D hybrid nanostructure compared to pristine BP, where the peak responsivity in the former is shifted to the visible region (∼440 nm) compared to UV response (∼340 nm) of the latter. The tunable spectral responsivity with a peak value of ∼3.2 A/W (@ ∼440 nm and −5 V) for the Ag-BP/Si heterojunction device demonstrates the potential of plasmonic BP hybrids for future nanophotonic devices.