High-Performance Fully Nanostructured Photodetector with Single-Crystalline CdS Nanotubes as Active Layer and Very Long Ag Nanowires as Transparent Electrodes

Engineering of Cd x Zn1-x S Nanomaterials for Fabrication of Hybrid Cd x Zn1-x S/Si Heterojunction Broadband Photo Detectors

Effective engineering of nanostructured materials provides a scope to explore the underlying photoelectric phenomenon completely. A simple cost-effective chemical reduction route is taken to grow nanoparticles of Cd x Zn1-x S with varying x = 1, 0.7, 0.5, 0.3, and 0. X-ray diffraction confirms the formation of different phases of targeted Cd x Zn1-x S, while field emission scanning electron microscopy shows change of nanostructures. Energy-dispersive X-ray spectroscopy determines the composition of the grown nanostructures as CdS, Cd0.7Zn0.3S, Cd0.5Zn0.5S, Cd0.3Zn0.7S, and ZnS. The optical absorption study determines the band gap shift with change of composition as well as with quantum confinement. The fluorescence lifetime for each nanomaterial is determined by time-correlated single photon counting, and Raman analysis revealed that ZnS exhibits the highest blue shift. Thus, there is a possibility to apply such grown nanomaterials for fabrication of heterojunction-based photodetectors (PDs) in a broad wavelength region. Cd x Zn1-x S nanostructures on n-type bulk silicon (Si) were successfully fabricated by a simple cost-effective spin coating method and present hybrid heterojunction PDs. The fabricated p-n heterojunction exhibits good rectifying behavior at room temperature under a reverse bias condition. Also, it was observed that the heterojunction is extremely sensitive to the irradiation of visible light because of the significant optoelectric effect with a good I light/I dark ratio (here, I light is the current in the presence of light and I dark is the dark current), quick response time (40 to 1005 ms), and good reproducibility (three cycles of I light/I dark for each sample are observed). It was observed that the responsivity value gradually decreases for x = 1 to x = 0 in the Cd x Zn1-x S/n-Si heterojunction, i.e., it is maximum for CdS NRs (6.74 × 10-3 mA/W), intermediate for Cd0.5Zn0.5S NPs (4.49 × 10-3 mA/W), and minimum for ZnS NPs (2.72161 × 10-4 mA/W). A similar nature has been observed in the case of detectivity, and hence it is a maximum (1.45 × 106 Jones) for CdS NRs. The photocurrent generation at the heterojunction showed excellent "on" and "off" switching behavior in the presence and absence of light illumination. Response time and gain change significantly with change of composition. The responsivity and detectivity with good photoresponse originated from the realization of special microstructures, enhancing the photoelectric behavior of Cd x Zn1-x S materials for applications in low-dimensional PDs covering a large wavelength region.

Enhanced luminescence/photodetecting bifunctional devices based on ZnO:Ga microwire/p-Si heterojunction by incorporating Ag nanowires

With the disadvantages of indirect band gap, low carrier mobility, and large lattice mismatch with other semiconductor materials, one of the current challenges in Si-based materials and structures is to prepare low-dimensional high-performance optoelectronic devices. In this work, an individual ZnO microwire via Ga-incorproration (ZnO:Ga MW) was employed to prepare a light-emitting/detecting bifunctional heterojunction structure, combined with p-type Si crystal wafer as a hole transporting layer. In a forward-bias regime, red luminescence peaking at around 680 nm was captured. While, the fabricated heterojunction device also exhibited an obvious photoresponse in the ultraviolet wavelengths. Interestingly, the introduction of Ag nanowires (AgNWs) are utilized to increase light output with amplitude 4 times higher than with that of naked wire-based LEDs. Similarly, the performance parameters of the fabricated n-AgNWs@ZnO:Ga MW/p-Si heterojunction photodetector are significantly enhanced, containing a responsivity of 5.52 A W^-1, detectivity of 2.34 × 10¹² Jones, external quantum efficiency of 1.9 × 10³% illuminated under 370 nm at -1 V. We compare this work with previous reported photodetectors based on various ZnO/Si-based materials and structures, some performance parameters are not superior, but our constructed n-AgNWs@ZnO:Ga MW/p-Si heterojunction photodetector has comparable overall characteristics, and our findings stand out especially for providing an inexpensive and suitable pathway for developing low-cost, miniaturized and integrated ultraviolet photodetectors. The demonstration of AgNWs enhanced low-dimensional light-emitting/detecting bifunctional photodiodes can offer a promising scheme to construct high-performance Si-based optoelectronic devices.

Self-template Synthesis of Metal Halide Perovskite Nanotubes as Functional Cavities for Tailored Optoelectronic Devices

Intriguing optoelectronic features of low-dimensional perovskites drive researchers to develop novel nanostructures for exploring new photophysical properties and meeting the requirements of future practical applications. Here, we report the facile and universal synthesis of metal halide perovskite nanotubes (NTs) in a micro alkylammonium emulsion system for the first time. The [PbBr₆]^4--based NTs with a diameter of 300 nm and length of 100 μm were synthesized through the reaction of PbBr₂ and long-chain bromide in advance, which can be controllably converted into general metal halide perovskite APbBr₃ (A = Cs, FA, MA) with preserved tubular morphology by introducing the Cs⁺, MA⁺, and FA⁺ cations. Importantly, the NTs can readily couple with other nanofillers exhibiting tunable and novel optoelectronic properties demonstrated by the photodetectors. The device performance can be significantly improved and broadened to infrared photoresponse through the introduction of Au nanocrystal (NC) plasma and PbS NCs, respectively. These results demonstrate that the metal halide perovskite NTs are expected to enrich the diversity of nanostructures and have a huge potential in the fabrication of integrated, light-manipulated, and miniaturized electronic and photonic devices.

Erasable memory properties of spectral selectivity modulated by temperature and bias in an individual CdS nanobelt-based photodetector

Single CdS nanobelt-based photodetectors are strongly dependent on bias and temperature. They not only show a strong photoresponse to close bandgap energy light with ultrahigh responsivity of approximately 10⁷ A W^-1, large photo-to-dark current ratio of 10⁴, photoconductive gain of 10⁷, and fast response and recovery speed at a large bias of 20 V, but can also show a weak photoresponse to above- and below-bandgap energy light. Moreover, their spectral response range can show tunable selectivity to above- and below-bandgap light, which can be accurately controlled by temperature and bias. More importantly, the modulated spectral response characteristics show excellent memory behaviour after reversible writing and erasing by using temperature and bias. In nanostructures, abundant surface states and stacking fault-related traps play a vital role in the ultrahigh photoresponse to bandgap light and the erasable memory effect on spectral response range selectivity. Given the erasable memory of the spectral response selectivity with excellent photoconduction performance, the CdS NBs possess important applications in new-generation photodetection and photomemory devices.

Chemical vapor deposition growth of ReS2 nanowires for high-performance nanostructured photodetector

Rhenium disulfide (ReS2) is a recently discovered next-generation transition metal dichalcogenides (TMDs) material that exhibits unique properties, which have resulted in its wide use in the fabrication of electronic and optoelectronic devices. Studies on ReS2 have mainly focused on the synthesis and applications of two-dimensional (2D) materials, while studies on one-dimensional (1D) ReS2 have yet to be reported. Herein, 1D single-crystal ReS2 nanowires have been synthesized successfully for the first time via chemical vapor deposition (CVD) and utilized as the active layer in a nanostructured photodetector. The crystal structure, phonon vibration modes, and chemical states of the single-crystal ReS2 nanowires have been investigated. Furthermore, the nanostructured photodetector using single-crystal ReS2 nanowires as the active layer and Ag nanowire networks as the transparent electrodes exhibited excellent performance, including a higher photoresponsivity (5.08 × 105), the highest external quantum efficiency (1.07 × 106), and the largest specific detectivity (6.1 × 1015) among ReS2 nanostructure-based photodetectors reported to date. Furthermore, the photodetector performance under vacuum conditions was investigated, which provides some information on the work mechanism of the ReS2 photodetector.

Tape-Based Photodetector: Transfer Process and Persistent Photoconductivity

We report a facile transfer method to fabricate flexible photodetectors directly on tape, wherein the films formed by different processes were integrated together. The tape-based photodetectors with CdS nanowire (NW) active layers exhibited good performances as those fabricated by conventional processes. The obvious persistent photocurrent in our device was eliminated by introducing a conductive polymer poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) onto the CdS NW layer. By adjusting the concentration of the PEDOT:PSS aqueous solution, a device with a fast response, ultrashort decay time, and relatively large photocurrent was obtained. The decay times were 11.59 and 6.64 ms for devices using electrodes of silver NWs and gold, respectively. These values are much shorter than the shortest decay times (on the order of hundreds of milliseconds) reported previously.

A facile and green template-engaged synthesis of PbSe nanotubes with the assistance of Vc

PbSe nanotubes (NTs) were synthesized through a low cost, facile and green hydrothermal route in combination with the assistance of ascorbic acid.

Self-powered ZnS Nanotubes/Ag Nanowires MSM UV Photodetector with High On/Off Ratio and Fast Response Speed

In this study, we design and demonstrate a novel type of self-powered UV photodetectors (PDs) using single-crystalline ZnS nanotubes (NTs) as the photodetecting layer and Ag nanowires (NWs) network as transparent electrodes. The self-powered UV PDs with asymmetric metal-semiconductor-metal (MSM) structure exhibit attractive photovoltaic characteristic at 0 V bias. Device performance analysis reveals that the as-assembled PDs have a high on/off ratio of 19173 and a fast response speed (τ_r = 0.09 s, τ_f = 0.07 s) without any external bias. These values are even higher than that of ZnS nanostructures- and ZnS heterostructure-based PDs at a large bias voltage. Besides, its UV sensivity, responsivity and detectivity at self-powered mode can reach as high as 19172, 2.56 A/W and 1.67 × 10¹⁰ cm Hz^1/2 W^-1, respectively. In addition, the photosensing performance of the self-powered UV PDs is studied in different ambient conditions (e.g., in air and vacuum). Moreover, a physical model based on band energy theory is proposed to explain the origin of the self-driven photoresponse characteristic in our device. The totality of the above study signifies that the present self-powered ZnS NTs-based UV nano-photodetector may have promising application in future self-powered optoelectronic devices and integrated systems.

One-step fabrication of single-crystalline ZnS nanotubes with a novel hollow structure and large surface area for photodetector devices

ZnS nanotubes (NTs) were successfully prepared via a one-step thermal evaporation process without using any templates. The resulting NTs were single crystalline and structurally uniform. Based on experimental analysis, a tube-growth vapor-liquid-solid process was proposed as the growth mechanism of ZnS NTs. A metal-semiconductor-metal full-nanostructured ultraviolet (UV) photodetector with ZnS NTs as the active layer, and Ag nanowires of low resistivity and high transmissivity as electrodes, was fabricated and characterized. The ZnS NT-based device displayed a high I _on/I _off ratio of up to ∼1.56 × 10⁵ with a high response to UV incident light at low operation voltage. This work is a meaningful exploration for preparing other one-dimensional semiconductor NTs, and developing a high-performance and power-saving UV sensor.

Ultraviolet/visible photodetectors with ultrafast, high photosensitivity based on 1D ZnS/CdS heterostructures

One-dimensional (1D) semiconducting heterostructures have been widely studied for optoelectronics applications because of their unique geometry and attractive physical properties. In this study, we successfully synthesized 1D ZnS/CdS heterostructures, which can be used to fabricate high performance ultraviolet/visible photodetectors. Due to the separation of photo-generated electron-hole pairs, the resultant photodetector showed excellent photoresponse properties, including ultrahigh Ion/Ioff ratios (up to 10(5)) and specific detectivity (2.23 × 10(14) Jones), relatively fast response speed (5 ms), good stability and reproducibility. Moreover, the as-fabricated flexible photodetectors showed great mechanical stability under different bending conditions. Our results revealed the possibility of 1D ZnS/CdS heterostructures for application in the detection of UV and visible light. The main advantages of the heterostructures have great potential application for future optoelectronic devices.