Deep Ultraviolet Light Research Articles

Colloidal Self-Assembly of Highly-Ordered Silica Inverse Opals for Deep Ultraviolet Diffraction

The fabrication of highly-ordered ~2 µm thick silica inverse opal (IO) photonic crystal (PhC) films is reported. These IO films diffract deep ultraviolet light (UV, < 250 nm) and are prepared using...

Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer

We have envisaged and designed a novel III-V nitride based deep ultraviolet light emitting diode (LED) with reasonably high efficiency at higher current density using a double-side grading in electron blocking layer (EBL). Double-side step- and linear-grading in EBL yield better performance attributable to improved hole injection, stifled electron overflow and diminished electrostatic field in the active region. The performance curves indicate that double sided linear grading in EBL has 5.63 times enhancement in power compared to the conventional LED and the efficiency droop is as low as 15% at the current density of 200 A cm−2 for the emission wavelength of ∼273 nm.

Solar cell based on vertical graphene nano hills directly grown on silicon

We demonstrate a solar cell application based on vertical graphene nano hills (VGNH) directly grown without using a catalyst. The photovoltaic device based on VGNH grown on top of interfacial layer Al2O3 is compared with that on top of bare silicon by critically analyzing its electrical properties. The role of the interfacial layer is to minimize surface recombination and enhance its built-in potential. Our key process is simple to fabricate large-area devices, avoiding an unreliable transfer process. In addition, the thickness of VGNH is optimized and the surface texturing of silicon is performed to overcome the crucial problem of the high reflectivity of silicon. A low reflectivity of thick layers of VGNH is achieved with low series resistance despite of the vertical structure, which is beneficial for high photocurrent. A higher work function of VGNH ∼4.7 eV is measured by KPFM. The conversion efficiency of 10.97% is achieved with an active area of 0.9 cm2 by co-doping with PEDOT: PSS and inorganic acid HNO3. Moreover, the photo-responsivity of the VGNH-based device is estimated as 1.196 AW-1 under deep ultraviolet light.

High-gravity-assisted green synthesis of rare-earth doped calcium molybdate colloidal nanophosphors

Abstract In this work, we report an innovative route for the synthesis of rare-earth doped calcium molybdate (CaMoO4) nanophosphors by using high gravity rotating packed bed (RPB) technology and paraffin liquid as the solvent. The significant intensified mass transfer and micromixing of reactants in the RPB reactor are benefiting for homogeneous doping of rare-earth ions in the host materials, leading to nanophosphors with high quantum efficiency. The use of liquid paraffin as the solvent eliminates the safety risks associated with volatile organic compounds, increasing the potential for clean production of nanophosphors. Under excitation of deep ultraviolet (DUV) light, the CaMoO4:Na+, Eu3+ nanophosphors exhibit red emission at peak wavelength of 615 nm and quantum yield of up to 35.01%. The CaMoO4:Na+,Tb3+ nanophosphors exhibit green emission at peak wavelength of 543 nm with quantum yield of up to 30.66%. The morphologies of the nanophosphors are tunable from nanofibers through nanorods to nanodots and the possible mechanism of controlling the formation of different nanostructures is proposed on the basis of experimental results and theoretical analysis of mesoscience. These nanophosphors are highly dispersible in organic solvents and utilized for fabricating fabrication of flexible, freestanding luminescent films based on silicone resin. We also demonstrate the red LEDs consisting of the hybrid films of CaMoO4:Na+,Eu3+ nanoparticles as color-converting phosphors and DUV LEDs as illuminators, offering strong potential for future nanophosphors-basedsolid-state lighting systems.

CdS core-Au/MXene-based photodetectors: Positive deep-UV photoresponse and negative UV–Vis-NIR photoresponse

Exploring photodetectors with higher responsitivity and broader spectral response is crucial for optoelectronic applications. Inverse photoresponse is discovered from photodetectors based on cadmium sulfide modified by Au (CdS core-Au). The devices are capable of detecting photons with a broader spectrum from deep-ultraviolet to near-infrared. Under the illumination of visible light at 405 nm, negative photoresponse with higher responsivity (86 mA/W) and larger specific detectivity (1.34 × 1011 Jones) are observed owing to the thermal mechanism. Upon deep-ultraviolet light illumination, the photodetectors exhibit positive photoresponse. These findings provide a new approach to broad spectral photodetectors and other inventive optoelectronic devices.

Titania:Graphdiyne nanocomposites for high-performance deep ultraviolet photodetectors based on mixed-phase MgZnO

Approachable graphdiyne (GDY), characterized by discrepancy hybridized carbon atoms of inhomogeneous π-bonding and carbon 2pz overlapping of orbitals, reveals versatility applications. Previously, interfaces high density between different structure materials induce the high response of photodetector, but the ratio of photocurrent to dark current is restricted for either limited materials properties or lattice mismatch when junctions formed. In this work, titania (TiO2) nanocrystals with a rational phase of anatase are encapsulated on GDY particles, further, the TiO2:GDY nanocomposites are synthesized. High specific surface area GDY, as a proper sustaining material optimizes the characters of TiO2 nanocrystals. Then TiO2:GDY nanocomposites cooperate with Mg0.3Zn0.7O (MZO) are mean to fabricate lateral bilayer ultraviolet photodetector. Because of the formed heterojunction between TiO2:GDY nanocomposites and MZO, the ultraviolet photodetector is highly sensitive to deep ultraviolet light, when optical band gap of MZO is as high as 3.8 eV. The responsivity of TiO2:GDY/MZO bilayer photodetector is also increased by more than one order of magnitude to 76 mA W−1 compares to the MZO device without TiO2:GDY nanocomposites while the photocurrent rejection is about three orders of magnitude from 254 nm to 365 nm. Meanwhile, signal-to-noise ratio is calculated as high as 1.5 × 105 in this work.

Polarization detection in deep-ultraviolet light with monoclinic gallium oxide nanobelts

Detection of polarization in deep-ultraviolet (DUV) wavelength is of great importance, especially in secure UV communication. In this paper, we report DUV polarization detectors based on ultra-wide bandgap β-Ga2O3 nanobelts, which belong to a monoclinic system with a strong anisotropic lattice structure. Single-crystalline β-Ga2O3 nanobelts are synthesized at high-temperature via chemical vapor deposition (CVD). Crystallographic investigation is performed to determine the crystal orientation of the nanobelts, by the combination of selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), crystal modeling and diffraction simulation. The photoresponse to unpolarized DUV light shows a high responsivity of 335 A W−1 and high sensitivity even to a low illumination power of pW. Strong anisotropy in responsivity and response speed, depending on incident light polarization, is observed. The underlying mechanism is attributed to the combination of internal dichroism and 1D morphology, as indicated by the DFT calculation and FDTD simulation. This work shows a way of DUV polarization detection using CVD grown Ga2O3 nanobelts, which could broaden the investigation of the Ga2O3 material and DUV photodetection.

深紫外光栅反常偏振器件的设计与分析

深紫外光栅反常偏振器件的设计与分析

Surface Plasmon Coupling with Radiating Dipole for Enhancing the Emission Efficiency and Light Extraction of a Deep Ultraviolet Light Emitting Diode

In this paper, we numerically investigated the emission characteristics of surface plasmon (SP)-enhanced deep ultraviolet light emitting diode (DUV-LED) by employing Al/Al2O3 core-shell nanoparticle(NP) structure on the p-GaN contact layer by utilizing finite-difference time-domain (FDTD) method. The results suggest that normalized dipole power of TE (TM) polarization is enhanced (inhibited) in the DUV range by coupling with in-plane substrate localized surface plasmon (LSP) mode from Al/Al2O3 core-shell nanoparticle (NP). It is found that normalized upward extraction power for both polarizations can also be significantly increased by scattering effect when photons and excitons coupling with in-plane air LSP mode induced on the NP; thus, the light extraction efficiency (LEE) can be substantially enhanced. The depth d between quantum well (QW) and NP and NP size have a remarkable influence on LSP resonance wavelength. Through careful regulation of NP size and depth d, the emission characteristics in DUV range (240–280 nm) exhibit a considerable amelioration.

Photonic crystal tunnel junction deep ultraviolet light emitting diodes with enhanced light extraction efficiency.

We report on the demonstration of top emitting AlGaN tunnel junction deep ultraviolet (UV) light emitting didoes (LEDs) operating at ∼267 nm. We show, both theoretically and experimentally, that the light extraction efficiency can be enhanced by nearly a factor of two with the incorporation of AlGaN nanowire photonic crystal structures. A peak wall-plug efficiency (WPE) ∼3.5% and external quantum efficiency (EQE) ∼5.4% were measured for AlGaN LEDs directly on-wafer without any packaging. This work demonstrates a viable path for achieving high efficiency deep UV LEDs through the integration of AlGaN planar and nanoscale structures.

Highly Deep Ultraviolet-Transparent h-BN Film Deposited on an Al0.7Ga0.3N Template by Low-Temperature Radio-Frequency Sputtering.

Hexagonal boron nitride (h-BN) is an attractive wide-bandgap material for application to emitters and detectors operating in the deep ultraviolet (DUV) spectral region. The optical transmittance of h-BN in the DUV region is particularly important for these devices. We report on the deposition of thick h-BN films (>200 nm) on Al0.7Ga0.3N templates via radio-frequency sputtering, along with the realization of ultrahigh transmittance in the DUV region. The fraction of the gas mixture (Ar/N2) was varied to investigate its effects on the optical transmittance of BN. DUV light transmittance of as high as 94% was achieved at 265 nm. This value could be further enhanced to exceed 98% by a post-annealing treatment at 800 °C in a N2 ambient for 20 min. The phase of the highly DUV–transparent BN film was determined to be a purely hexagonal structure via Raman spectra measurements. More importantly, these deposition processes were performed at a low temperature (300 °C), which can provide protection from device performance degradation when applied to actual devices.

Carbon pair defects in aluminum nitride

AlN bulk single crystals grown by the physical vapor transport method may be beneficially applied as substrates for deep ultraviolet light emitting devices or as a basic material for piezoelectric resonators operating at high temperatures. Identification of point defects which deteriorate the optical, electrical, and electromechanical properties of AlN crystals for such applications is the subject of the present work. Using Raman spectroscopy, two local vibrational modes (LVMs) were discovered at wave numbers of 1189 cm−1 and 1148 cm−1. By analyzing an AlN crystal intentionally enriched with the carbon isotope 13C, it is unambiguously shown that the two LVMs originate from two different, but in each case carbon-related defects. Furthermore, it is evidenced that the defect underlying the LVM at 1189 cm−1 contains exactly two carbon atoms. The tricarbon defect-related LVM reported earlier in an infrared absorption study is found to be Raman active at 1772 cm−1. The Raman scattering intensity of all three LVMs strongly depends on the photon energy of the exciting light what is interpreted as a resonance Raman effect. This allows linking the identified defects with their contribution to the strong, carbon-related ultraviolet absorption around 4.7 eV and proves that these defects introduce optically and electrically active deep levels in the bandgap of AlN.

Gigahertz-repetition-rate, narrowband-deep-ultraviolet light source for minimization of acquisition time in high-resolution angle-resolved photoemission spectroscopy.

Ultrahigh-repetition-rate (1.1 GHz), deep-ultraviolet coherent light at 208.8 nm is generated by applying an external Fabry-Pérot cavity for repetition-rate multiplication to the fourth harmonics of a 10-ps, mode-locked Ti:sapphire laser. Its small pulse energy minimizes the unwanted space charge effect, while its high repetition rate drastically reduces the acquisition time in high-energy resolution angle-resolved photoemission spectroscopy using hemispherical electron analyzers. The absence of the space charge effect in the photoemission spectrum near the Fermi edge of polycrystalline Au at 8 K demonstrates this idea.

Visible light-induced thymine dimerisation based on large localised field gradient by non-uniform optical near-field

The localised excitations of several molecular reactions utilising optical irradiation have been studied in the field of molecular physics. In particular, deoxyribonucleic acid (DNA) strands organise the genetic information of all living matter. Therefore, artificial methods for freely controlling reactions using only light irradiation are highly desirable for reactions of these strands; this in regard with artificial protein synthesis, regional genetic curing, and stochastic analysis of several genetic expressions. Generally, DNA strands have strong absorption features in the deep ultra-violet (DUV) region, which are related to the degradation and reconstruction of the strand bonding structures. However, irradiation by DUV light unavoidably induces unintended molecular reactions which can damage and break the DNA strands. In this paper, we report a photo-induced molecular reaction initiated by the irradiation of DNA strands with visible light. We utilised photo-dissociation from the vibrational levels induced by non-uniform optical near-fields surrounding nanometric Au particles to which DNA strands were attached. The results were experimentally observed by a reduction in the DUV absorbance of the DNA strands during irradiation. There was a much higher yield of molecular reactions than expected due to the absorbance of visible light, and no defects were caused in the DNA strands.

Deep-ultraviolet integrated photonic and optoelectronic devices: A prospect of the hybridization of group III–nitrides, III–oxides, and two-dimensional materials

Progress in the design and fabrication of ultraviolet and deep-ultraviolet group III–nitride optoelectronic devices, based on aluminum gallium nitride and boron nitride and their alloys, and the heterogeneous integration with two-dimensional and oxide-based materials is reviewed. We emphasize wide-bandgap nitride compound semiconductors (i.e., (B, Al, Ga)N) as the deep-ultraviolet materials of interest, and two-dimensional materials, namely graphene, two-dimensional boron nitride, and two-dimensional transition metal dichalcogenides, along with gallium oxide, as the hybrid integrated materials. We examine their crystallographic properties and elaborate on the challenges that hinder the realization of efficient and reliable ultraviolet and deep-ultraviolet devices. In this article we provide an overview of aluminum nitride, sapphire, and gallium oxide as platforms for deep-ultraviolet optoelectronic devices, in which we criticize the status of sapphire as a platform for efficient deep-ultraviolet devices and detail advancements in device growth and fabrication on aluminum nitride and gallium oxide substrates. A critical review of the current status of deep-ultraviolet light emission and detection materials and devices is provided.

Dielectrophoretic Assembly of Aluminum Nitride (AlN) Single Nanowire Deep Ultraviolet Photodetector

High UV-light sensitivity, fast response, and low power consumption are the most important features of nanowire-based devices for new applications in photodetectors, optical switches, and image sensors. Single AlN nanowire deep ultraviolet (UV) photodetector has been fabricated utilizing very high-quality AlN nanowires through a very practical dielectrophoretic assembly scheme. The low-voltage (≤ 3 V) operating UV photodetector has selectively shown a high photocurrent response to the 254 nm UV light. Furthermore, the photocurrent transients have been modelled to determine the rise and decay time constants as 7.7 s and 11.5 s, respectively. In consequence, combination of deep UV light selectivity and low voltage operation make AlN nanowires great candidates for the development of compact deep UV photodetectors.

Highly efficient deep UV generation by four-wave mixing in gas-filled hollow-core photonic crystal fiber.

We report on a highly efficient experimental scheme for the generation of deep-ultraviolet (UV) ultrashort light pulses using four-wave mixing in gas-filled kagomé-style photonic crystal fiber. By pumping with ultrashort, few microjoule pulses centered at 400nm, we generate an idler pulse at 266nm and amplify a seeded signal at 800nm. We achieve remarkably high pump-to-idler energy conversion efficiencies of up to 38%. Although the pump and seed pulse durations are ∼100 fs, the generated UV spectral bandwidths support sub-15fs pulses. These can be further extended to support few-cycle pulses. Four-wave mixing in gas-filled hollow-core fibers can be scaled to high average powers and different spectral regions such as the vacuum UV (100-200nm).

Three-wavelength optoelectronic system for hemodialysis monitoring

Novel spectrophotometric method and optoelectronic spectral equipment for automatic on-line monitoring of hemodialysis treatment are introduced. The method allows determination of the concentrations of uric acid and creatinine in effluent dialysate by measuring ultraviolet (UV) absorption at three wavelengths. An optoelectronic spectral sensor with three deep ultraviolet light emitting diodes (LED), a flow-through quartz cuvette connected to the outlet of a dialysis machine, and a solar-blind UV photodetector was designed. Dedicated software for sensor control, spectral data acquisition, and spectral analysis was developed. The results of preliminary clinical trials of the developed system are presented.

Gamma irradiation-induced phase transitions of boron nitride nanoparticles

Recently different methods are explored to synthesize suparhard orthorhombic boron nitride (o-BN) nanomaterials which have a wide range of industrial applications in the sensors, fiters, battery, biological applications and deep ultraviolet light emitting diodes. In this research work, a simple method is reported to synthesis of cubic boron nitride nanoparticles (c-BNNPs) via gamma irradiation induced phase transition of hexagonal boron nitride nanoparticles (h-BNNPs). X Ray Diffraction (XRD) and Raman Spectroscopy results confirmed the phase transition of h-BNNPs to o-BNNPs at the dose of 21 kGy. At the dose of 24 kGy, high resolution transmission electron microscopy (HRTEM) results showed that phase of hexagonal boron nitride nanoparticles (h-BNNPs) are transformed to B2O3 whereas at lower dose (18 kGy), coalescence of hexagonal boron nitride nanoparticles (h-BNNPs) is observed through high resolution transmission electron microscopy (HRTEM) results. X-rays diffractions (XRD) results showed that grain size of hexagonal boron nitride nanoparticles (h- BNNPs) is increased. Mechanism of phase transition and coalescence of hexagonal boron nitride nanoparticles (h-BNNPs) are explained via high energy and short wavelength gamma radiations act on B-N covalent bond isotopically.

Catalyst‐Free Vapor–Solid Deposition Growth of β‐Ga2O3 Nanowires for DUV Photodetector and Image Sensor Application

AbstractPhotodetection in the solar‐blind deep‐ultraviolet (DUV) regime (200–280 nm) has received significant attention for its many critical applications in military and civil areas. In this study, a vapor–solid synthesis technique for catalyst‐free growth of single‐crystalline β‐Ga2O3 nanowires is developed. A photodetector made of the nanowires is highly sensitive to 265 nm DUV illumination with excellent photoresponse performance. The performance parameters including Ilight/Idark ratio, responsivity, specific detectivity and response speed can attain ≈103, ≈233 A W−1, ≈8.16 × 1012 Jones, and 0.48/0.04 s, respectively. Additionally, the detector has an abrupt response cutoff wavelength at ≈290 nm with a reasonable DUV/visible (250–405 nm) rejection ratio exceeding 102. It is also found that the device can operate properly at a large applied bias of 200 V with the responsivity being enhanced to as high as ≈1680 A W−1. Moreover, such a nanowires‐based photodetector can function as a DUV light image sensor with a reasonable spatial resolution. Holding the above advantages, the present DUV photodetector based on catalyst‐free grown β‐Ga2O3 nanowires possesses huge possibility for application in future DUV optoelectronics.