Efficient Ultraviolet Photodetectors Research Articles

Highly efficient ultraviolet photodetector based on molybdenum-doped nanostructured NiO/ITO thin film

Nanostructured pure and molybdenum (Mo)-doped nickel oxide (NiO) thin films with various concentrations of Mo dopants were successfully sputtered on indium-doped tin oxide (ITO) substrates to apply in the ultraviolet (UV) photodetector sensors. The influence of Mo concentration on the thin films' structural, morphological, and optical properties was studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive X-ray, and UV–Vis spectrophotometer. The XRD studies confirm that all the prepared films are polycrystalline and possess a cubic phase structure. The FE-SEM images suggest that the distribution of the prepared samples on the substrate is homogeneous and free from any cracks. Spectrophotometry studies reveal the decrement of the optical band gap with the increase of Mo concentration in NiO thin films. All thin-film current–voltage curves measured under dark conditions and UV illumination of 390 nm showed Ohmic contacts. A noticeable improvement in the responsivity and external quantum efficiency (EQE) with the increased Mo concentration was detected. The metal–semiconductor–metal (MSM) employed in NiO thin films showed maximum responsivity and EQE of 539 mA/W and 171.4% at 390 nm, respectively, for the sample with 1.73 at% Mo doping.

High-performance and ultra-sensitive ultraviolet photodetector based on surface passivated α-Fe2O3 thin film

Nanostructured α-Fe2O3 is a versatile material and has attracted extensive attention due to its promising electrochemical and photoelectrochemical properties, which are widely investigated in water splitting, photoelectrochemical devices, gas sensors, and catalysis. Moreover, its band gap (Eg = 2.0 eV) allows it to absorb visible light, but due to poor charge carrier mobility, ultrafast recombination of the photo-generated carriers, and surface oxygen vacancy defects its application as a photodetector got restricted. Herein with a surface passivated α-Fe2O3 film deposited on the glass substrate, the ultraviolet photodetector is demonstrated. The surface passivated photodetector is sensitive to ultraviolet light, showing a substantial enhancement in the photo-responsivity of 1.41 A/W, the external quantum efficiency of 515%, the photo-sensitivity of 1650%, and a reduction in response time of 0.06 ms (for 340 nm at a bias of +30 V) as compared with the device before surface passivation (0.228 A/W, 83%, 34%, and 1.6 ms), respectively. These improved properties are observed due to the suppression of surface defects via surface passivation, which increases free carrier concentration transport across the film. The surface passivated α-Fe2O3 thin film-based photodetector with high photo-responsivity, photo-sensitivity, high speed, and ultraviolet photoresponse is promising for practical applications, and this platform opens up new avenues for the development of low-cost, and highly efficient ultraviolet photodetectors.

Electric and optoelectronic balances of silicon photodetectors coupled with colloid carbon nanodots

We present the efficient ultraviolet photodetectors made with the incorporation of colloid carbon nanodot (CCND) layers with silicon substrates. By investigating the morphologies, microstructure, light absorption and carrier dynamics, the control over CCND thickness is envisioned for the improvement of photosensing characteristics. We find that 35-nm thick CCNDs coupled with Si can reach remarkable sensing responsivity of 15.9 A/W and detectivity of 2.94 × 1014 Jones under detecting lights with wavelength of 352 nm. The underlying mechanism is interpreted by the synergetic contributions from reduced dynamic dark currents and efficient charge separation from CCND/Si heterojunction.

Fabrication of GaN nano-towers based self-powered UV photodetector

The fabrication of unique taper-ended GaN-Nanotowers structure based highly efficient ultraviolet photodetector is demonstrated. Hexagonally stacked, single crystalline GaN nanocolumnar structure (nanotowers) grown on AlN buffer layer exhibits higher photocurrent generation due to high quality nanotowers morphology and increased surface/volume ratio which significantly enhances its responsivity upon ultraviolet exposure leading to outstanding performance from the developed detection device. The fabricated detector display low dark current (~ 12 nA), high ILight/IDark ratio (> 104), fast time-correlated transient response (~ 433 µs) upon ultraviolet (325 nm) illumination. A high photoresponsivity of 2.47 A/W is achieved in self-powered mode of operation. The reason behind such high performance could be attributed to built-in electric field developed from a difference in Schottky barrier heights will be discussed in detail. While in photoconductive mode, the responsivity is observed to be 35.4 A/W @ − 3 V along with very high external quantum efficiency (~ 104%), lower noise equivalent power (~ 10–13 WHz−1/2) and excellent UV–Vis selectivity. Nanotower structure with lower strain and dislocations as well as reduced trap states cumulatively contributed to augmented performance from the device. The utilization of these GaN-Nanotower structures can potentially be useful towards the fabrication of energy-efficient ultraviolet photodetectors.

High performance UV photodetector based on MoS2 layers grown by pulsed laser deposition technique

Highly efficient ultraviolet (UV) photodetector based on Molybdenum Disulfide (MoS 2 ) layers has been fabricated using pulsed laser deposition (PLD) technique. Systematic layer dependent photoresponse studies have been performed from single layer to 10 layers of MoS 2 by varying the laser pulses to see the effect of the number of layers on the photoelectrical measurements. Raman and Photoluminescence studies have been carried out to ensure the growth of high-quality MoS 2 layers. Layers of MoS 2 grown at 100 pulses were found to exhibit the characteristic Raman phonon modes i.e. E 1 2g and A 1g at 383.8 cm −1 and 405.1 cm −1 respectively and Photoluminescence (PL) spectra show B exciton peak for MoS 2 at around 625 nm suggesting the growth of high-quality MoS 2 layers. Atomic force microscopy (AFM) thickness profiling and cross sectional-high resolution transmission electron microscopy (HRTEM) analysis gives the thickness of grown MoS 2 to be 2.074 nm and 1.94 nm, respectively, confirming the growth of trilayers of MoS 2 . X-ray photoelectron spectroscopy (XPS) spectra of the grown trilayer sample show characteristic peaks corresponding to Molybdenum and Sulphur doublet (Mo 4+ 3d 5/2,3/2 and S 2p 3/2 , 1/2 ) confirming the chemical state of pure MoS 2 phase without the presence of any Molybdenum oxide state. Dynamic photoelectrical studies with Indium Tin Oxide (ITO) as contact electrode upon UV laser illumination show superior responsivity of 3 × 10 4 A/W at 24 μW optical power of the incident laser (λ = 365 nm) and very high detectivity of 1.81 × 10 14 Jones at a low applied bias of 2 V. The obtained results are highly encouraging for the realization of low power consumption and highly efficient UV photodetectors based on MoS 2 layers. • Optimization of high-quality large area MoS2 layers utilizing the PLD technique. • Demonstration of low power operated UV photodetector on optimized MoS2 layers. • Explained the Physics of the UV photodetector using energy band diagrams. • Work justifies the development of efficient photodetectors using PLD technique.

High speed efficient ultraviolet photodetector based on 500 nm width multiple WO3 nanowires

This work presents the fabrication of a photodetector based on multiple WO3 nanowires for ultra-violet detection. This photodetector exhibits a photo-to-dark current ratio of the order of 4 with a high relative change in conductance around 8100 upon 340 nm illumination at 0.87 mW/cm2. The photodetector exhibits a high responsivity of 47.3 A/W and a high 340 nm–450 nm rejection ratio of ∼8800 with excellent stability. A low noise equivalent power of 0.37 fW/√Hz and a high detectivity of ∼1012 Jones are observed. We obtained a fast response with a rise time (tr) of 112 μs and a fall time (tf) of 84 μs. These promising results demonstrate the applicability of the photodetector for high speed ultra-violet detection.

Efficient ultraviolet photodetector device based on modulated wide band gap Type-II CuO/CdSe core-shell nanowires

A high-performance ultraviolet photodetector has been successfully fabricated based on new CuO/CdSe core-shell nanowires (NWs). The obtained modulated optical band gap due to quantum confinement effect has the capability to detect photons with energies (3.96 eV) significantly larger than the band gap of CuO (1.2 eV) and CdSe (1.7 eV), which is mainly attributed to the abrupt interface between the CuO core and CdSe shell. The fabricated CuO/CdSe core-shell heterostructure NWs as photodetector device showed responsivity 0.63A/W with external quantum efficiency approximately 3.14 × 102% under illumination of wavelength 254 nm. The strong response of CuO/CdSe NWs photodetector is explained by the Type-II band alignment which cause the separation of photo generated electron–hole pairs and their charge transfer at the junction.

Laser molecular beam epitaxy growth of porous GaN nanocolumn and nanowall network on sapphire (0001) for high responsivity ultraviolet photodetectors

We report on high-responsivity metal-semiconductor-metal (MSM) structure based ultraviolet (UV) GaN photodetectors fabricated on various GaN nanostructures such as porous nanocolumn network (PNCN), nanowall networks (NWNs), and granular and compact thin films. Different GaN nanostructures were hetero-epitaxially grown on c-sapphire using laser molecular beam epitaxy by tuning the AlN buffer layer growth parameters. High resolution x-ray rocking curve measurements indicate that the crystalline quality of GaN critically depends on the selection of AlN buffer layer growth conditions such as type of ablation target and growth temperature. The porous GaN nanostructures revealed a nearly stress-free wurtzite structure as deduced by Raman spectroscopy measurements. Room temperature photoluminescence spectroscopy showed that the GaN films possess a near band emission (NBE) peak at ∼ 3.39 eV along with a broad yellow luminescence (YL) with maxima at 2.25 eV. For GaN PNCN and NWN structures, the NBE-to-YL emission ratio is more than an order higher compared to the GaN films. The fabricated MSM based UV-detector on GaN PNCN and NWN exhibited a high photo-responsivity of ∼27.72 and 24.8 A/W, respectively, under 2 V applied bias at room temperature. The GaN PNCN and NWN nanostructures with excellent photo-responsivity and optical quality prove to be promising candidates for the fabrication of efficient UV photodetectors due to their continuity in lateral direction, high surface area-to-volume ratio and tailored surfaces.

Efficient UV photodetector based on heterojunction of n-ZnO nanorods/p-diamond film

ZnO nanorods (NRs) have been successfully fabricated on p-type boron-doped diamond (BDD) substrate by hydrothermal method. The current–voltage characteristics of the ZnO NRs/BDD heterojunction show a typical rectifying behavior with extremely low reverse leakage current and high rectification ratio of around 370 at bias of 3 V. Exposed to ultraviolet (UV) illumination with a wavelength of 365 nm, the time dependent photoresponse manifests high sensitivity and consistent transients with a rise time of 4.9 s and decay time of 6.4 s. Circulating on/off measurement under UV detection demonstrates the excellent stability and repeatability for as-fabricated ZnO NRs/BDD heterojunction. Furthermore, the mechanism for UV detection on the ZnO NRs/BDD heterojunction has also been discussed.

Strain induced piezoelectric effect in black phosphorus and MoS2 van der Waals heterostructure

The structural, electronic, transport and optical properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdw) heterostructure are investigated by using first principles calculations. The band gap of BP/MoS2 bilayer decreases with the applied normal compressive strain and a semiconductor-to-metal transition is observed when the applied strain is more than 0.85 Å. BP/MoS2 bilayer also exhibits modulation of its carrier effective mass and carrier concentration by the applied compressive strain, suggesting that mobility engineering and good piezoelectric effect can be realized in BP/MoS2 heterostructure. Because the type-II band alignment can facilitate the separation of photo-excited electrons and holes, and it can benefit from the great absorption coefficient in ultra-violet region, the BP/MoS2 shows great potential to be a very efficient ultra-violet photodetector.

Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection.

We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance, and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction, and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials.

Few-layer graphene/ZnO nanowires based high performance UV photodetector

A graphene and zinc oxide nanowires (G/ZnO NWs) based ultraviolet (UV) photodetector presents excellent responsivity and photocurrent gain with detectivity. Graphene due to higher charge carrier transport mobility induces faster response to UV illumination at the interface between ZnO and graphene with improved response and decay times as compared to a ZnO NWs device alone. A linear increase is revealed for both the responsivity and photocurrent gain of the G/ZnO NWs device with the applied bias. These results suggest that the G/ZnO NWs device exhibits great promise for highly efficient UV photodetectors.

Tailored Electrospinning of WO₃ Nanobelts as Efficient Ultraviolet Photodetectors with Photo-Dark Current Ratios up to 1000.

In this work, polycrystalline WO3 nanobelts were fabricated via an electrospinning process combined with subsequent air calcination. The resultant products were characterized by X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy in regard to the structures. It has been found that the applied voltage during the electrospinning process played the determined role in the formation of the WO3 nanobelts, allowing the controlled growth of the nanobelts. The ultraviolet (UV) photodetector assembled by an individual WO3 nanobelt exhibits a high sensitivity and a precise selectivity to the different wavelength lights, with a very low dark current and typical photo-dark current ratio up to 1000, which was the highest for any WO3 photodectectors ever reported. This work could not only push forward the facile preparation of WO3 nanobelts but also represent, for the first time, the possibility that the polycrystalline WO3 nanobelts could be a promising building block for the highly efficient UV photodetectors.

Efficient ultraviolet photodetectors based on TiO2nanotube arrays with tailored structures

We report the front-illuminated ultraviolet photodetectors based on TiO2nanotube arrays with efficient photodetecting activities.

Ultraviolet Radiation Detection by Barium Titanate Thin Films Grown by Sol-gel Hydrothermal Method

Ferroelectric Barium titanate, BaTiO 3 (BTO) thin film has been prepared successfully by sol-gel hydrothermal method (SG-HT) which combines the basic sol-gel process with hydrothermal treatment. High resolution X-ray diffraction (HR-XRD) study reveals single phase polycrystalline tetragonal structure of the prepared BTO thin film. Optical properties were studied using UV- Visible spectroscopy and band gap was found to be 3.51 eV. The I–V characteristics revealed a low dark current (I off ) of 6.07 × 10 -9 A for the prepared BTO thin film which increases to 4.06 × 10 -6 A (I on ) by almost three orders of magnitude when illuminated with UV radiation (λ = 365 nm, Intensity = 24 μW/cm 2 ). The photoconductive gain (K = I on /I off ), was found to be 6.7 × 10 2 . It can be clearly seen that the prepared BTO film can be utilized as an efficient Ultraviolet photodetector.

A highly efficient UV photodetector based on a ZnO microwire p–n homojunction

A highly efficient ultraviolet photodetector was successfully obtained based on a Sb-doped p-type ZnO microwire p–n homojunction which consisted of a single Sb-doped p-type ZnO microwire and a single undoped ZnO microwire. The ultralong Sb-doped ZnO single crystalline microwires were synthesized via a chemical vapor deposition method. The ZnO microwire homojunction showed well-defined rectification characteristics, which indicated the p-type conductivity of the Sb-doped ZnO microwire. An ultraviolet photodetector with an external quantum efficiency of 64.5% was obtained based on the ZnO microwire p–n homojunction. The photodetector showed high wavelength selectivity with a full width at half maximum of 6 nm for the photoresponse peak located at 386 nm.

Deposition of ZnO nanostructured film at room temperature on glass substrates by activated reactive evaporation

ZnO nanostructured films were deposited on glass substrates at room temperature by activated reactive evaporation technique. Thermal evaporation of zinc at high deposition rate in presence of oxygen plasma resulted in deposition of ZnO nanostructured film with different flower-like morphologies on glass substrates. The structural and morphological properties of these nanostructured films were studied by XRD, SEM and TEM. A gas phase growth mechanism has been proposed for the formation of nanostructures. The room temperature photoluminescence spectra of these films exhibited weak ultraviolet (UV) and strong broad visible emission peaks. Further, the position of visible emission peak is found to vary with morphology of the grown nanostructured films. Photocurrent measurements indicated that these ZnO nanostructured films show high sensitivity to UV light, and hence can be used as efficient UV photodetectors.

Highly efficient ultraviolet photodetectors based onTiO2 nanocrystal–polymer composites via wet processing

Solution-processed inorganic/organic hybrid films based on anataseTiO2 nanocrystals and poly (9,9-dihexylfluorene) (PFH) are fabricated via a simple spin-coatingmethod and characterized by atomic force microscopy, UV–vis absorption andphotoluminescence spectra. The photodetector devices are made from hybridTiO2/PFH bulkheterojunction films sandwiched between poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate)pre-coated ITO and Al electrodes. The device characteristics, including current–voltage (I–V)curves under UV illumination, spectral response, response time and bias dependence, are studied.The photovoltaic effect is observed and the photocurrent shows an increase with increasingTiO2 content from 2.5 to 11 wt%. The high UV photo-to-dark current ratio of103, fast response time less than 200 ms and a responsivity of54.6 mA W − 1 are obtained for the hybrid photodetector. The fast photoresponse is attributed to theenhanced interfacial dissociation of excitons. The overlap of the spectral response with theUV–A range (320–400 nm) and the low-cost wet fabrication method show their potential forenvironmental and biological uses.

Wide-bandgap Zn2GeO4 nanowire networks as efficient ultraviolet photodetectors with fast response and recovery time

Ultraviolet (UV) photodetectors based on ternary Zn2GeO4 nanowire (NW) networks are demonstrated. The devices show fast response and recovery time, which is attributed to the unique NW-NW junction barrier dominated conductance for network devices. The UV-light induced barrier height modulation is much faster than the oxygen adsorption/desorption processes. The wide-band gap Zn2GeO4 NWs also exhibit high wavelength selectivity for deep UV detection. We demonstrate that ternary oxide NW-networks are ideal building blocks for nanoscale photodetectors with superior performance and facile fabrication processes.