Self-powered, ultrafast, visible-blind UV detection and optical logical operation based on ZnO/GaN nanoscale p-n junctions

Fast and enhanced broadband photoresponse of a ZnO nanowire array/reduced graphene oxide film hybrid photodetector from the visible to the near-infrared range

In the present work, a ZnO nanowire array/reduced graphene oxide film hybrid nanostructure was realized, and the photovoltaic responses from the visible to the near-infrared range were investigated. Compared with the pure ZnO nanowire array and rGO thin film, the hybrid composite exhibited a fast and greatly enhanced broadband photovoltaic response that resulted from the formation of interfacial Schottky junctions between ZnO and rGO.

High performance organic-inorganic perovskite-optocoupler based on low-voltage and fast response perovskite compound photodetector

Organic-inorganic hybrid photodetectors attract considerable attention because they can combine the advantages of both organic and inorganic systems. Here, a perovskite compound with a broad absorption spectrum and high power conversion efficiency is used as a photosensitive layer in an organic/inorganic hybrid heterojunction photodetector with a high and fast response. The high sensitivity exceeding 10⁴ is obtained at bias of 0–4 V. Using a tandem organic light-emitting diode (OLED) as the light source, we fabricated an optocoupler device. The optocoupler achieved a maximum photoresponsivity of 1.0 A W⁻¹ at 341.3 μWcm⁻² at an input voltage of 6 V. The device also exhibits rapid response times of τ_rise ~ 20 μs and τ_fall ~ 17 μs; as well as a high current transfer ratio (CTR) of 28.2%. After applying an amplification circuit, the CTR of the optocoupler increases to 263.3%, which is comparable with that of commercial inorganic optocouplers. The developed hybrid optocoupler thus shows great promise for use in photonics.

Enhancing photoresponsivity of self-powered UV photodetectors based on electrochemically reduced TiO2 nanorods

Enhanced photoresponsivity of the R-NRA device is due to the enhancement of charge separation and transfer at the electrode/electrolyte interface.

A self-powered ultraviolet photodetector based on solution-processed p-NiO/n-ZnO nanorod array heterojunction

A self-powered and rapid-response UV photodetector with p-NiO/ZnO-nanorod array heterojunction was developed. Under a small forward bias of 0.1 mV, the UV photosensitivity exceeded the value of ~10⁵ previously reported.

Self-powered ultrafast broadband photodetector based on p-n heterojunctions of CuO/Si nanowire array

A new self-powered broadband photodetector was fabricated by coating an n-silicon nanowire (n-Si NW) array with a layer of p-cupric oxide (CuO) nanoflakes through a new simple solution synthesis method. The p-n heterojunction shows excellent rectification characteristics in the dark and distinctive photovoltaic behavior under broadband light illumination. The photoresponse of the detector at zero bias voltage shows that this self-powered photodetector is highly sensitive to visible and near-infrared light illuminations, with excellent stability and reproducibility. Ultrafast response rise and recovery times of 60 and 80 μs, respectively, are shown by the CuO based nanophotodetector. In addition, the broadband photodetector can also provide a rapid binary response, with current changing from positive to negative upon illumination under a small bias. The binary response arises from the photovoltaic behavior and the low turn-on voltage of the CuO/Si NW device. These properties make the CuO/Si NW broadband photodetector suitable for applications that require high response speeds and self-sufficient functionality.

Piezotronic interface engineering on ZnO/Au-based Schottky junction for enhanced photoresponse of a flexible self-powered UV detector

Exploiting piezoelectric effect to engineer material interface has been confirmed as a promising way to optimize the performance of optoelectronic devices. Here, by using this effect, we have greatly improved the photoresponse of the fabricated ZnO/Au Schottky junction based self-powered UV detector. A 440% augment of photocurrent, together with 5× increased sensitivity, was obtained when the device was subjected to a 0.580% tensile strain. The enhancement can be attributed to the facility separation and extraction of photoexcites due to the formation of the stronger and expanding built-in field, which is a result of charge redistribution induced by piezoelectric polarization at the ZnO/Au interface. This study not only can strengthen the understanding of piezoelectric effects on energy devices but also can be extended to boost performances of optoelectronic devices made of piezoelectric semiconductor materials.

A high performance quasi-solid-state self-powered UV photodetector based on TiO2 nanorod arrays

Self-powered UV photodetectors based on TiO2 and ZnO nanorod arrays have attracted lots of attention in recent years due to their various advantages. Impressive performances were observed in photochemical cell based UV detectors. However, liquid electrolytes are not ideal for long-term operation and are inconvenient for practical applications. Hence there is an urgent demand for replacing liquid electrolytes with solid-state hole transfer materials. Herein we report a nanostructured quasi-solid-state UV photodetector fabricated using a liquid crystal (LC)-embedded electrolyte with a light-trapping scheme. Vertical rutile TiO2 nanorod arrays grown on fluorine-doped tin oxide conductive glass were used as the active photoanode. A high incident photon-to-current conversion efficiency of 29% at 383 nm and a quick response time of less than 0.03 s were observed. In addition, it was revealed that the quasi-solid-state UV photodetector showed visible-blind, high responsivity, fast time response and good photosensitivity linearity in a wide light intensity range. The LC-embedded electrolyte with a light-trapping scheme enhanced the light absorption and thus improved the photodetecting performance. This self-powered device is a promising candidate for application in high-sensitivity and high-speed UV light photodetectors.

A self-powered ultraviolet detector based on a single ZnO microwire/p-Si film with double heterojunctions

Recently, self-powered devices based on a p-n heterojunction have been widely reported, but there are few reports about self-powered UV detectors based on a single ZnO microwire/p-Si film with double heterojunctions. Compared with the common p-n heterojunction type devices, the fabricated devices with double heterojunctions based on a single n-type ZnO microwire and a p-type Si film exhibited excellent electrical performance such as an ideal rectification behaviour and a low turn-on voltage. At zero bias, the fabricated device can deliver a photocurrent of 71 nA, a high photosensitivity of about 3.17 × 10(3) under UV light (0.58 mW cm(-2)) illumination and a fast rising and falling time of both less than 0.3 s. Furthermore, the photocurrent increased with the rising of the optical intensity at low power intensities. The physical mechanism has been explained by energy band diagrams.

CdS nanoscale photodetectors

CdS nanostructures have received much attention in recent years as building blocks for optoelectronic devices due to their unique physical and chemical properties. This progress report provides an overview of recent research about rational design of CdS nanoscale photodetectors. Three kinds of photodetectors according to the metal-semiconductor contact types are discussed in detail: Ohmic contact, Schottky contact, and field enhanced transistor configuration. The focus is on the tuning of optical and electrical properties CdS nanostructures by element doping, composition and bandgap engineering, and heterojunction integration, along with thus modified device performances generated during these tuning processes. Latest concepts of photodetector design such as flexible, self-powered, plasmonic, and piezophototronic photodetectors with novel properties are introduced to demonstrate the future directions of such an exciting research field.

A back-to-back MOS-Schottky (Pt-SiO2-Si-C-Pt) nano-heterojunction device as an efficient self-powered photodetector: one step fabrication by pulsed laser deposition

An efficient self-powered photodetector design involving a C-Si hetero-interface with back-to-back MOS-Schottky (Pt-SiO2-Si-C-Pt) device action is presented. Pulsed laser deposition of a carbon thin film is used which dynamically removes the native surface oxide to form the desired Schottky interface. The combined device action yields two orders of magnitude photoresponse at zero bias.

Rapid fabrication technique for interpenetrated ZnO nanotetrapod networks for fast UV sensors

Two flame-based synthesis methods are presented for fabricating ZnO-nanostructure-based UV photodetectors: burner flame transport synthesis (B-FTS)and crucible flame transport synthesis (C-FTS). B-FTS allows rapid growth of ZnO nanotetrapods and in situ bridging of them into electrical contacts. The photo detector made from interconnected ZnO nanotetrapod networks exhibits fast response/recovery times and a high current ratio under UV illumination.

ZnO(N)-Spiro-MeOTAD hybrid photodiode: an efficient self-powered fast-response UV (visible) photosensor

Organic-inorganic hybrid photo-detectors with a self-sufficient mode of operation represent a research area of great current interest. In most efficient photodetectors and optoelectronic devices compound semiconductors containing toxic elements such as Cd, As, Te, S, Se etc. are used and these are also expensive. Hence there is also a rapidly growing interest in replacing these with environmentally friendly and earth-abundant materials. Herein, we report a facile solution-processed fabrication of a self-powered organic-inorganic hybrid photodetector using n-type oriented ZnO nanorods and p-type Spiro-MeOTAD semiconductor. ZnO is eco-friendly and earth-abundant, and Spiro-MeOTAD is non-hazardous. We show that the latter has far less toxicity than the toxic elements stated above. This visible blind UV photodetector shows high sensitivity (10(2)) and a UV/visible rejection ratio of 300. It also exhibits fast response times of τ(rise) ~ 200 μs and τ(fall) ~ 950 μs. Importantly, with a small modification of nitrogen incorporation in ZnO one can also realize a highly-sensitive self-powered visible light photodetector with at least 1000% (or higher) improvements in quality factors (photocurrent/sensitivity/response time) as compared to previously reported organic-inorganic hybrid photo-detectors based on metal-chalcogenides (CdS-PANI or CuInSe2-P3HT). Interestingly, the broadband sensitivity of such N:ZnO-Spiro-MeOTAD photodiode enables sensing of low intensity (~28 μW cm(-2)) ambient white light with a high photocurrent density of 120 nA cm(-2) making it an efficient ambient white light detector.

A highly responsive UV photodetector based on hierarchical TiO2 nanorod/nanoparticle composite

The large surface area provided by TiO₂ nanoparticles, the well-defined electron transport pathway offered by TiO₂ nanorods and the homojunction formed at the interface between them contribute to the fast and high photoresponse of a hierarchical composite.

A ZnO nanowire-based photo-inverter with pulse-induced fast recovery

We demonstrate a fast response photo-inverter comprised of one transparent gated ZnO nanowire field-effect transistor (FET) and one opaque FET respectively as the driver and load. Under ultraviolet (UV) light the transfer curve of the transparent gate FET shifts to the negative side and so does the voltage transfer curve (VTC) of the inverter. After termination of UV exposure the recovery of photo-induced current takes a long time in general. This persistent photoconductivity (PPC) is due to hole trapping on the surface of ZnO NWs. Here, we used a positive voltage short pulse after UV exposure, for the first time resolving the PPC issue in nanowire-based photo-detectors by accumulating electrons at the ZnO/dielectric interface. We found that a pulse duration as small as 200 ns was sufficient to reach a full recovery to the dark state from the UV induced state, realizing a fast UV detector with a voltage output.

ZnO nanoneedle/H2O solid-liquid heterojunction-based self-powered ultraviolet detector

ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode.

Low-dimensional nanostructure ultraviolet photodetectors

Low-dimensional (LD) nanostructures are ideal systems for constructing high-performance photodetectors due to their tailored geometries, high surface-area-to-volume ratios and rationally designed surfaces. This article provides a brief summary about recent progress on LD nanostructures based visible-light-blind ultraviolet photodetectors. The current challenges and an outlook on the future developments of this research field are summarized and highlighted.

Self-powered UV-vis photodetector based on ZnIn2S4/hydrogel interface

The photosensing properties of vertically aligned ZnIn2S4 nanopetal films grown hydrothermally on FTO coated glass are examined without and with surface dispensed agarose gel. For the ZnIn2S4 nanopetals photodetector (without gel) there is no photoresponse for zero bias. Most interestingly, with surface dispensation of agarose gel, the hybrid electronic-iontronic interface system shows a strong photoresponse even under zero bias, a highly efficient self-powered UV-visible light photodetector. Indeed, the zero bias ZnIn2S4/gel hybrid photoresponse is a factor of 100 stronger as compared to the response of the only ZnIn2S4 device (at -1.5 V bias) and that too without any significant degradation in response time. The possible operating mechanisms are proposed.

High performance stretchable UV sensor arrays of SnO2 nanowires

A high performance, stretchable UV sensor array was fabricated based on an active matrix (AM) device that combined field effect transistors of SWCNTs and SnO2 nanowires. The AM devices provided spatial UV sensing via the individual sensors in the array. SnO2 NW UV sensors showed an average photosensitivity of ∼10(5) and a photoconductive gain of ∼10(6) under very low UV (λ = 254 nm) power intensities of 0.02-0.04 mW cm(-2). The UV sensing performance was not deteriorated by a prestrain of up to 23% induced by radial deformation, consistent with the mechanical analysis.

Graphene plasmon enhanced photoluminescence in ZnO microwires

We report the temperature dependent photoluminescence (PL) properties of monolayer graphene-Au-nanoparticle-ZnO (GAZ) microwire hybrid structures. By comparing with the bare ZnO wire without coverage of graphene, a three times enhancement of PL was found in the GAZ hybrid structures. The enhancement is attributed to the coupling between the PL photons from ZnO and the graphene surface plasmons with ~1-2 nm Au as a corrugated surface. Our results may be valuable for designing graphene-ZnO hybrid based optical and photoelectrical devices.

High-performance photoelectrochemical-type self-powered UV photodetector using epitaxial TiO₂/SnO₂ branched heterojunction nanostructure

TiO₂/SnO₂ branched heterojunction nanostructure with TiO₂ branches on electrospun SnO2 nanofiber (B-SnO₂ NF) networks serves as a model architecture for efficient self-powered UV photodetector based on a photoelectrochemical cell (PECC). The nanostructure simultaneously offers a low degree of charge recombination and a direct pathway for electron transport. Without correcting 64.5% loss of incident photons through light absorption and scattering by the F-doped tin oxide (FTO) glass, the incident power conversion efficiency reaches 14.7% at 330 nm, more than twice as large as the nanocrystalline TiO₂ (TiO₂ NC, 6.4%)-film based PECC. By connecting a PECC to an ammeter, the intensity of UV light is quantified using the output short-circuit photocurrent density (J(sc)) without a power source. Under UV irradiation, the self-powered UV photodetector exhibits a high responsivity of 0.6 A/W, a high on/off ratio of 4550, a rise time of 0.03 s and a decay time of 0.01 s for J(sc) signal. The excellent performance of the B-SnO₂ NF-based PECC type self-powered photodetector will enable significant advancements for next-generation photodetection and photosensing applications.

High responsivity, fast ultraviolet photodetector fabricated from ZnO nanoparticle-graphene core-shell structures

We report a simple, efficient and versatile method for assembling metal oxide nanomaterial-graphene core-shell structures. An ultraviolet photodetector fabricated from the ZnO nanoparticle-graphene core-shell structures showed high responsivity and fast transient response, which are attributed to the improved carrier transport efficiency arising from graphene encapsulation.

Self-powered UV photosensor based on PEDOT:PSS/ZnO micro/nanowire with strain-modulated photoresponse

Developing tailored micro/nanostructure interfaces is an effective way to make novel optoelectronic devices or enhance their performances. Here we report the fabrication of a PEDOT:PSS/ZnO micro/nanowire-based self-powered UV photosensor. The generation of photocurrent at zero bias is attributed to the separation of photogenerated electron-hole pairs within the built-in electric field at the PEDOT:PSS/ZnO interface upon UV light illumination. Furthermore, the piezotronic effect on the UV photoresponsivity under different strains is investigated, which is due to the modification of energy band diagram at the p-n heterojunction by strain-induced piezoelectric polarization. This study demonstrates a prospective approach to engineering the performance of a photodetector through straining and may offer theoretical supporting in future optoelectronic device fabrication and modification.

Photovoltaic device on a single ZnO nanowire p-n homojunction

A photovoltaic device was successfully grown solely based on the single ZnO p-n homojunction nanowire. The ZnO nanowire p-n diode consists of an as-grown n-type segment and an in situ arsenic-doped p-type segment. This p-n homojunction acts as a good photovoltaic cell, producing a photocurrent almost 45 times larger than the dark current under reverse-biased conditions. Our results demonstrate that the present ZnO p-n homojunction nanowire can be used as a self-powered ultraviolet photodetector as well as a photovoltaic cell, which can also be used as an ultralow electrical power source for nanoscale electronic, optoelectronic and medical devices.