Visible-blind UV Photodetectors Research Articles

All solution-processed SnO2/1D-CsAg2I3 heterojunction for high-sensitivity self-powered visible-blind UV photodetector

All solution-processed SnO2/1D-CsAg2I3 heterojunction for high-sensitivity self-powered visible-blind UV photodetector

Highly stable and sensitive photon detection performance of ZnO thin film for ultraviolet light

The photo detection characteristics of spray pyrolysis deposited ZnO thin film on glass substrate at 250 OC was demonstrated for fabrication of highly stable visible-blind UV photodetector. This photodetector exhibits lower dark current < 0.04 μA, higher UV photosensitivity ∼4750, responsivity of 0.14 A/W and detectivity of 1.24 × 1012 Jones at an average intensity of 140 μW/cm2 of 340 nm. This Ag/ZnO/Ag device show excellent photo response (rise and decay) time of ∼4 and 6 ms with external quantum efficiency of 51%. The observed photocurrent in the device is associated with adsorption and light-induced desorption of oxygen from the defect sites on the film surfaces. The adsorbed oxygen removes the electron trap centers and increasing the free carrier density in ZnO.

Visible-blind UV photodetectors using a polymer/ZnO nanocomposite thin film

We report the fabrication and characterization of visible-blind UV photodetectors using thin films of polymer/zinc oxide (ZnO) nanocomposites. Polymer-ZnO nanocomposites based on three polymers, poly(methyl methacrylate)(PMMA), polystyrene(PS) and poly(vinylidene difluoride-trifluoroethylene(P(VDF-TrFE)) were studied. The electrical response of the detectors to 365 nm and 254 nm UV light illumination was probed. P(VDF-TrFE)/ZnO nanocomposite-based device exhibited the best performance compared to the other devices, possibly due to its ferroelectric property. Further, we prepared P(VDF-TrFE)/ZnO nanocomposite with different wt% of ZnO nanoparticles and characterized them by atomic force microscopy (AFM), X-ray diffraction (XRD), fourier transform- infrared spectroscopy (FTIR), UV-Visible absorption spectroscopy, and Photoluminescence (PL). XRD and FTIR studies confirmed the formation of the β phase of P(VDF-TrFE) in pristine polymer films and their nanocomposites. The influence of the top electrode material on the photodetector performance of nanocomposites was studied. P(VDF-TrFE)/5 wt% ZnO nanocomposite with Ag top electrode exhibited the best performance with on-off ratio, 1.4 × 104; responsivity, 14.43 A/W; linear dynamic range, 83.09 dB and detectivity, 2.27 × 1013 jones under 365 nm light illumination. The ferroelectric polarization mechanism of P(VDF-TrFE) and the choice of electrode play an important role in the performance of the devices.

Zero-biased and visible-blind UV photodetectors based on nitrogen-doped ultrananocrystalline diamond nanowires

Taking advantage of the superflat surface of ultrananocrystalline diamond (UNCD), highly precise UNCD nanowire (NW) arrays were fabricated to develop high-performance UV photodetectors. The large surface-to-volume ratio of a nanowire significantly increases the number of surface trap states, and the reduced dimensionality effectively confines the active area of the charge carrier and shortens the transit time, which results in an enhanced photoconductivity and response speed. In this paper, the zero-biased UV photodetectors based on nitrogen-incorporated ultrananocrystalline diamond nanowire arrays have been demonstrated and characterized. The estimated responsivity was 2.0 A/W for 350 nm incident light when the device operated at room temperature. The UVA and UVB photocurrent signals from this visible blind photodetector were well defined with a rise and decay time of less than 1 s.

Dynamics of charge carriers and photoresponse of TPD/n-Si hybrid structure for visible-blind UV self-biased photodetection applications

Herein, we represent the fabrication of self-biased visible-blind UV photodetector based on thermally deposited N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) film over n-type silicon substrate giving rise to the structure Au/TPD/n-Si/Al heterojunction. The microelectronic parameters of the fabricated heterojunction Au/TPD/n-Si/Al as well as the charge carriers' transport mechanisms in forward and reverse bias conditions are analyzed and interpreted in detail under the dark conditions and the influence of temperature. The manufactured photodetector showed a significant response to UV illumination with high photocurrents and noticeable values of open-circuit voltage. The fabricated UV photodetector under self-biasing and illumination intensity (100 mW/cm2) records values of responsivity, specific detectivity, linear dynamic range, signal to noise ratio, the response time, and ON/OFF ratio equals 147 mA/W, 6.4 × 1010 Jones, 58.69 dB, 945.5, 82/80 ms, and 861.98, respectively. This high, stable, and fast performance of the fabricated sensor suggest this architecture as an efficient integrated platform for self-biased UV photodetection.

Heteroepitaxial growth of high Mg-content single-phased W-MgZnO on ZnO matrixes in various nucleation states for solar-blind and visible-blind dual-band UV photodetectors

High Mg-content single-phase wurtzite Mg0.51Zn0.49O (W-Mg0.51Zn0.49O) films were realized by radio frequency (RF) magnetron sputtering technique on quartz (SiO2) substrates. The metal-semiconductor-metal (MSM) solar-blind (SB) and visible-blind (VB) dual-band ultraviolet (DB-UV) photodetectors (PDs) were also fabricated based on heteroepitaxial growth of W-Mg0.51Zn0.49O films on ZnO buffer layer (BL) at different nucleation states. Under 270 nm of irradiation, the Au/Mg0.51Zn0.49O/ZnO (30 min) PD exhibited an optimal external quantum efficiency (EQE, 304.4%) and specific detectivity (1012), which indicated that the ZnO BL obtained with a 30 min treatment time was most efficient to improve the detection of SB-UV wavelength. The origin of these results was attributed to the contact area and adhesion strength between MgZnO and ZnO matrices. The results showed a feasible way to obtain high Mg-content wurtzite MgZnO alloys and performance improvement through ZnO BL, which is favorable to the applicability in SB/VB DB-UV PDs.

Enhanced Performance of MgZnO/ZnO Dual-band UV Photodetectors Depend on depletion region with different electrode width

In this work, visible-blind dual-band UV photodetectors with different interdigital electrode width were fabricated on MgZnO/ZnO bilayer film by the radio frequency (RF) magnetron sputtering technique. The devices exhibit excellent photo-response at 320 nm and 360 nm, respectively. Meanwhile, the PD with larger electrode width possesses higher photo- response and lower dark current (Id), which proved that the wider electrode is more favourable to enhance the performance of PDs. The result is originate from the stronger electric filed on the depletion region related to the electrode width. This demonstrates a facile way to fabricate dual-band UV PDs with high properties for practice application.

Highly Visible-Blind ZnO Photodetector by Customizing Nanostructures With Controlled Defects

In this work, a highly visible-blind UV photodetector with a large photo-responsivity using ZnO nanostructures is demonstrated. A large photoconductive gain of 2050 and external quantum efficiency of $2.05\times 10 ^{5}$ % at 350 nm (illumination intensity of 1 mW/cm2) incident radiation has been successfully achieved by morphological transition engineering i.e. growth of nanoplates around the nanorods. Further, by suppression of intrinsic defect states during the growth of nanostructures, high UV to visible rejection ratio of $4.78\times 10 ^{5}$ and photoresponsivity of 578 A/W has been accomplished. The device has demonstrated high selectivity for UV-A radiations, with a sharp responsivity peak at 350 nm of 60 nm FWHM. Moreover, the specific photo-detectivity was calculated to be as high as $2.15\times 10 ^{\mathbf {15}}$ cmHz $^{1/2}\,\,\text{W}^{-1}$ . The proposed device has the capability to establish ZnO as a potential candidate for the variety of commercial applications, where high responsivity along with large UV to visible rejection ratio are the major requirements.

Dual-Phase CsPbCl3-Cs4PbCl6 Perovskite Films for Self-Powered, Visible-Blind UV Photodetectors with Fast Response.

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl3-Cs4PbCl6 films. It is achieved by spin-coating of a certain dose of CH3NH3Cl/CsCl solution onto a CsI-PbBr2-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl3-Cs4PbCl6 film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl3-Cs4PbCl6 film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W-1, an exceptional specific detectivity (D*) maximum of 1.35 × 1012 Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.

High-Responsivity MSM Solar-Blind UV Photodetector Based on Annealed ITO/Ag/ITO Structure Using RF Sputtering

In this paper, a novel ITO/Ag/ITO (IAI) multilayer UV photodetector was successfully prepared via RF magnetron sputtering technique to achieve the dual-benefit of improved photoresponse and outstanding visible blindness properties. The influence of the annealing process on the performance of the elaborated IAI UV photodetector was carried out. Moreover, the structural and photoelectrical properties of the sputtered tri-layered structures with and without annealing effects were also analyzed. It was found that the elaborated UV -photodetector provides near perfect UV absorbance of 96%. This achievement is attributed to the improved light trapping capability and tunable plasmonic resonance effects induced by the efficient optical coupling between free-space UV photons and Ag plasmons. It was also revealed that the heat treatment paves a new path toward preparing efficient visible-blind UV photodetectors, where the annealed sample demonstrated a superior rejection ratio of 225 as compared to that of the unannealed counterpart. Besides, electrical characterization underlined the ability of the annealed IAI UV photodetector at 500°C for offering exciting opportunities, where it exhibits a high responsivity of 3.8mA/W at self-powered condition. Therefore, by well optimizing both IAI multilayer geometry and annealing conditions, we were able to elaborate an ultrathin photodetector suitable for high-performance and flexible UV sensing applications.

Structural, DFT, optical dispersion characteristics of novel [DPPA-Zn-MR(Cl)(H2O)] nanostructured thin films

The spin coating technique has been utilized to deposit good adhesion successfully and highly uniform [DPP-Zn(Cl)2(H2O)2], [DPPA-Zn(Cl)2(H2O)2] and [DPPA-Zn-MR(Cl)(H2O)] thin films. The fabricated film thicknesses ranged from 100 to 150 nm. The molecular structure characteristics of compounds have been investigated by FT-IR, 1H NMR, and FAB-Mass spectroscopic. The structural and morphological properties of [DPP-Zn(Cl)2(H2O)2], [DPPA-Zn(Cl)2(H2O)2] and [DPPA-Zn-MR(Cl)(H2O)] thin films were examined by X-ray diffraction (XRD), and scanning electron microscope (SEM), respectively. According to the density functional calculations (DFT) results, the interaction of the zinc complexes conforms to lose associations, the interaction energies for all complexes in the matrix. The bonding mechanism of the zinc complexes includes both σ-dative and π-back bonding components. The measured optical properties of [DPP-Zn(Cl)2(H2O)2], [DPPA-Zn(Cl)2(H2O)2] and [DPPA-Zn-MR(Cl)(H2O)] thin films such as transmittance (T), absorbance (A) and reflectance (R) in UV-vis-NIR spectrum has been used to calculate optical features at room temperatures. The electrophilicity index (ω) of this zinc complexes are ≅ 10.86–13.84. These are significant interesting quantum chemical characteristics. The transparency of the complexes is within the range of ≅ 85–90% in the visible range. The optical band gap (Ego) of [DPP-Zn(Cl)2(H2O)2], [DPPA-Zn(Cl)2(H2O)2] and [DPPA-Zn-MR(Cl)(H2O)] thin films were estimated by DFT and they found to be 1.045, 0937 and 0.736 eV, respectively. The refractive index (n) and the single oscillator energy (Eo) were discussed by the single oscillator Wemple–Didomenico (WD) model. The high accuracy of the novel zinc complexes along with its appropriate optical band gap enabled us to build an efficient visible-blind UV-photodetector, indicating its potential in optoelectronic applications.

Self-powered visible-blind UV photodetectors based on p-NiO nanoflakes/n-ZnO nanorod arrays with an MgO interfacial layer

ZnO NRs and NiO nanoflakes were prepared by chemical bath deposition and the self-powered UV PDs based on NiO/ZnO NRs heterojunctions were fabricated. The suitable MgO insertion layer can effectively improve the performance of UV PDs.

P-GaN/n-ZnO nanorods: the use of graphene nanosheets composites to increase charge separation in self-powered visible-blind UV photodetectors

ZnO-based heterojunctions have found applications as self-powered ultraviolet photodetectors (PDs). However, high doping levels are not compatible with high mobility for metallic doped ZnO-based PDs so further development has been inhibited. This study demonstrates a method to increase the open-circuit voltage (Voc) that allows keeping a sufficiently high level of mobility of ZnO, using a ZnO nanorod/GaN heterojunction that incorporates graphene nanosheets as the active layer. These hybrid PDs have triple the value for Voc of PDs that have only pure ZnO and better exhibit photo-response characteristics. The results of surface Kelvin probe microscopy and x-ray photoelectron spectrometer show that the complex defects that occur because Zn interstitials form a shallow donor in ZnO are mainly responsible for the increase in the value of Voc. Using this functional nanostructure as an active layer represents a new method for the manufacture of high-performance self-powered PDs.

High-Performance Visible-Blind UV Phototransistors Based on n-Type Naphthalene Diimide Nanomaterials.

This study investigates the performance of single-crystalline nanomaterials of wide-band gap naphthalene diimide (NDI) derivatives with methylene-bridged aromatic side chains. Such materials are found to be easily used as high-performance, visible-blind near-UV light detectors. NDI single-crystalline nanoribbons are assembled using a simple solution-based process (without solvent-inclusion problems), which is then applied to organic phototransistors (OPTs). Such OPTs exhibit excellent n-channel transistor characteristics, including an average electron mobility of 1.7 cm2 V-1 s-1, sensitive UV detection properties with a detection limit of ∼1 μW cm-2, millisecond-level responses, and detectivity as high as 1015 Jones, demonstrating the highly sensitive organic visible-blind UV detectors. The high performance of our OPTs originates from the large face-to-face π-π stacking area between the NDI semiconducting cores, which is facilitated by methylene-bridged aromatic side chains. Interestingly, NDI-based nanoribbon OPTs exhibit a distinct visible-blind near-UV detection with an identical detection limit, even under intense visible light illumination (for example, 104 times higher intensity than UV light intensity). Our findings demonstrate that wide-band gap NDI-based nanomaterials are highly promising for developing high-performance visible-blind UV photodetectors. Such photodetectors could potentially be used for various applications including environmental and health-monitoring systems.

ZnO polymer composite based visible blind UV photo detector

Spherical ZnO nanoparticles with average diameter ∼50 nm are synthesized by hydrothermal method. Composites of the nanoparticles with different polymers have been prepared and UV detection properties are measured. The dielectric medium perturbs electron-phonon interaction as well as the optoelectronic properties. Moreover, the luminescence properties of the materials effected due to composite formation. In case of NP-polymer composite NPs are capped and there is negligible further adsorption and desorption of O2 molecules occurred on the surface. This increases the photocurrent as well as photosensitivity. For ZnO based photo detector, there is a small but not negligible photo response near 620 nm. The photo response in this particular wavelength is not observed in case of ZnO-PVP composite and it can be used as visible blind UV detector.

Surface conversion of ZnO nanorods to ZIF-8 to suppress surface defects for a visible-blind UV photodetector.

ZnO nanomaterials are promising building blocks for an efficient UV photodetector; however, their slow sensing behavior and undesired response to visible light, which are attributed to surface defects, such as oxygen or zinc vacancies, are challenges that remain to be addressed. Here, we transformed the ZnO nanorod surface into a zeolitic imidazolate framework-8 (ZIF-8) to eliminate ZnO surface defects. Vertical-type photodetectors were fabricated incorporating a Schottky junction at the ZIF-8/gold (Au) top electrode and could respond to UV light with a rapid response and recovery (1-2 s) and demonstrated a UV-to-visible rejection ratio in the order of 103, qualifying them as efficient visible-blind UV photodetectors. It is noteworthy that the ZIF-8 layer effectively separated the photogenerated electron-hole pairs, and thus reduced their recombination probability. The enhanced photodetector displayed excellent figures-of-merit: a responsivity of 291 A W-1 and a detectivity of 5.9 × 1013 cm Hz1/2 W-1 under illumination at 295 nm.

Hexagonal boron nitride pattern embedded in AlN template layer for visible-blind ultraviolet photodetectors

We introduced the use of solution-processed few-layer hexagonal boron nitride (h-BN) stripe patterns embedded in the lateral epitaxial overgrowth (LEO) of AlN grown on sapphire substrates using high temperature metal organic chemical vapor deposition (MOCVD). This straightforward usage of h-BN film contributes to reducing the lattice mismatch and almost entirely terminates the threading dislocations originating from the AlN/sapphire interface, which results in a low pit density and the absence of air-voids in the AlN template. Compared with AlN templates grown on conventional sapphire substrates, the full width at half maximum of the AlN template grown on the h-BN pattern in the (0002) and (10-12) planes decreased from 376 arcsec to 227 arcsec and from 495 arcsec to 398 arcsec, respectively. For device applications, AlGaN-based visible-blind UV photodetectors fabricated using the as-obtained high quality AlN templates show one order of magnitude reduction of the dark leakage current and 50% increase in the responsivity. Our results suggest that the h-BN pattern plays a promising role in the growth of a high quality AlN template, leading to the improvement of performance of AlGaN-based optoelectronic devices.

Three-dimensional nano-heterojunction networks: a highly performing structure for fast visible-blind UV photodetectors.

Visible-blind ultraviolet photodetectors are a promising emerging technology for the development of wide bandgap optoelectronic devices with greatly reduced power consumption and size requirements. A standing challenge is to improve the slow response time of these nanostructured devices. Here, we present a three-dimensional nanoscale heterojunction architecture for fast-responsive visible-blind UV photodetectors. The device layout consists of p-type NiO clusters densely packed on the surface of an ultraporous network of electron-depleted n-type ZnO nanoparticles. This 3D structure can detect very low UV light densities while operating with a near-zero power consumption of ca. 4 × 10-11 watts and a low bias of 0.2 mV. Most notably, heterojunction formation decreases the device rise and decay times by 26 and 20 times, respectively. These drastic enhancements in photoresponse dynamics are attributed to the stronger surface band bending and improved electron-hole separation of the nanoscale NiO/ZnO interface. These findings demonstrate a superior structural design and a simple, low-cost CMOS-compatible process for the engineering of high-performance wearable photodetectors.

Fast and Sensitive Solution-Processed Visible-Blind Perovskite UV Photodetectors.

The first visible-blind UV photodetector based on MAPbCl3 integrated on a substrate exhibits excellent performance, with responsivities reaching 18 A W(-1) below 400 nm and imaging-compatible response times of 1 ms. This is achieved by using substrate-integrated single crystals, thus overcoming the severe limitations affecting thin films and offering a new application of efficient, solution-processed, visible-transparent perovskite optoelectronics.

Integrated synthesis and surface passivation of ZnO nanoparticles to enhance UV spectrum selectivity

A novel, simple and effective surface passivation technique is introduced to enhance UV spectrum selectivity of ZnO nanoparticles (NPs). The technique which exploits an absorbed layer of dimethylformamide, enables the synthesis and surface passivation of ZnO NPs through a single-step process. Pure ZnO NPs and passivated ones were characterized to evaluate the integrity of passivating layer as well as quality of the final product. Morphological examinations were performed using field-emission scanning and transmission electron microscopies. X-ray diffractometry, energy dispersive X-ray and fourier-transform infrared spectroscopies were employed to analyze the phase and chemical composition of the samples. We also compared optical properties of the surface-passivated and pure ZnO NPs. Photoluminescence measurements revealed a peak value for UV emission at 394 nm and one for violet emission at 412 nm for the passivated and pure samples; respectively. A significant enhancement was observed in the spectrum selectivity and absorption efficiency of the passivated ZnO NPs in the UV range. The passivated NPs exhibited high UV-to-visible rejection ratio and UV-blocking capacity which provide a promising candidate for visible-blind UV photodetectors and UV shielding applications.