UV Photodiodes Research Articles

Fast photodiode arrays for high frequency fluctuation measurements of reconnecting flux ropes.

An array of compact, high-bandwidth (>200MHz) and low-cost optical photodiodes has been developed and implemented on the PHASe MApping (PHASMA) experiment. Using purpose-built electronics, an array of 16 photodetectors was constructed and used to monitor broadband (1-5MHz) fluctuations in light intensity emitted by flux ropes undergoing electron-only magnetic reconnection. These measurements reveal a swath of oscillatory behavior, including wave propagation inward toward the diffusion region at approximately the local electron Alfvén speed. Custom 3D-printed collection optics and mounting hardware allow quick reconfiguration of the array for radial or axial measurements. The electronics design is flexible enough to be used with other current-sourcing transducers, such as avalanche photodiodes; silicon photomultipliers; and infrared, x-ray, and UV photodiodes. A noise-rejecting electrical layout allows for low-noise operation close to pulsed plasma discharges. A 16-channel, 64-pixel tomographic array was constructed and initial reconstructions are presented.

4H-SiC 64 pixels CMOS image sensors with 3T/4T-APS arrays

For radiation-hardened CMOS image sensors (CIS), 4H-SiC 64 pixel array CIS were developed, and real time imaging with an operation frequency of 30 Hz was demonstrated. Two types of pixel arrays with a 3-transistor active pixel sensor (3T-APS) and a 4-transistor active pixel sensor (4T-APS) were fabricated with SiC MOSFETs, UV photodiodes and 3-layered Al interconnections. The SiC pixel arrays were combined with peripheral circuits and an optical lens, and SiC 64 pixel CIS with 3T-/4T-APS arrays were developed.

Pressure effect on the structural, electronic, mechanical, optical and thermal properties of Ga2TiX6 (X = Cl, Br): A DFT simulation

The pressure effect on the physical properties of Ga2TiX6(X = Cl, Br) has been carried out through density function theory (DFT) accomplished via CASTEP guidelines. At ambient condition the structural aspects of Ga2TiX6(X = Cl, Br) show well accord with the previous theoretical data. A dramatically decrease of lattice constants, cell volumes and bond length with pressure is perceived. The negative enthalpy energy ensured the chemical formation of Ga2TiX6(X = Cl, Br). The positive stiffness constants (Cij) ensure the mechanical stability of Ga2TiX6(X = Cl, Br) at ambient and hydrostatic pressure. Moreover, the fundamental polycrystalline factors of phases Ga2TiX6(X = Cl, Br) such as bulk, shear and Young’s moduli, Poisson’s and Pugh’s fraction, machinability index as well as hardness of these materials have been calculated and discussed at ambient and hydrostatic pressure. Having very low values of bulk modulus (<100 GPa) they can be considered as soft materials. The increase of machinable index with pressure ensure the high lubricating properties, low friction, and high plastic strain of Ga2TiX6(X = Cl, Br) and also ensure their possible industrial applications. Band structure analysis ensure the semiconducting nature of Ga2TiX6(X = Cl, Br) at ambient condition but the semiconducting nature shift to metallic manner at 55 GPa and 65 Gpa respectively. The decrease of total density of states is observed at high pressure. The creation of new bond at high pressure is also observed in materials Ga2TiX6(X = Cl, Br). The investigated optical features ensured that the studied phases can be used in UV photodiodes, and UV light emitters since they revel intense peaks at UV region. Very low Debye temperature, melting temperature and thermal conductivity are observed at ambient condition which ensures that the compounds Ga2TiX6(X = Cl, Br) can be used as thermal barrier coating materials (TBC).

Fabrication and evaluation of figures of merit of ZnO polymer-based hybrid UV photodiodes

Fabrication and evaluation of figures of merit of ZnO polymer-based hybrid UV photodiodes

Perovskite Stannate Heterojunctions for Self‐Powered Ultraviolet Photodiodes Operated in Extreme Environments

AbstractHigh‐performance UV photodetectors call for sensitive and energy‐efficient signal detection in extreme environments. To satisfy the requirement of a UV detection without an external power consumption, self‐powered UV photodetectors must be realized by an optimal combination of heterostructure with maximum built‐in potential using novel wide‐bandgap materials. Here, self‐powered UV photodiodes are designed via the band engineering of a wide‐bandgap Sr(Sn,Ni)O3/BaSnO3 heterojunction for the first time. Based on the theoretical concept of acceptor doping by Ni substitution in SrSnO3, remarkably, this heterojunction with a conduction band offset of 0.94 eV shows strong nonlinear electrical characteristics with extremely low Idark (≈100 fA) owing to the spatial gradient of the potential barrier across the interfaces, outstanding photo‐to‐dark current ratio (&gt;107 at 25 °C and &gt; 104 at 300 °C), and high stability under various extreme conditions upon UV illumination even without external bias (V = 0 V). This study suggests a novel strategy that utilizes band engineering to maximize sensitivity and minimize energy consumption in harsh environments for UV imaging using the newly discovered wide‐bandgap semiconductors.

Piezo-phototronic effect modulated performances of guest-substrate integrated p–i–n GaN ultraviolet detectors

High quality freestanding p–i–n GaN UV photodiodes were successfully fabricated on flexible mica by using selective electrochemical (EC) etching and an In–Au (50 nm/50 nm) bonding layer, which is convenient and the thermal damage is low.

Highly efficient, self-powered UV photodiodes based on leadfree perovskite nanocrystals through interfacial engineering

Double perovskite crystals are promising alternatives for lead-based perovskites that has potential to address toxicity and instability issues. In this study, Cs2AgBiCl6 nanocrystals (NCs) with high absorption coefficients were synthesized by hot-injection method. The bandgap engineering was realized by tuning the halide composition in Cs2AgBiCl6 to Cs2AgBiBr6. Both NCs were used as light-absorbing layers in lead-free perovskite photodiodes that exhibit wavelength-selectivity for UV–visible light operatable even at a bias voltage of 0 V. Cs2AgBiBr6-based photodiode exhibits a characteristic detection peak at 340 nm with a responsivity of 3.21 mA W−1, a specific detectivity up to 8.91 × 1010 Jones and a fast response speed with a rise/fall time of 30/35 ms. The excellent performance of self-driven photodiodes lights up the prospect of lead-free perovskite NCs in highly efficient optoelectronic devices.

Enhancement of the performance of a ZnO-based nanostructured flexible UV photodiode grown on the carbon clothe by piezo-phototronic effect

The current study aims to evaluate the piezo-phototronic effect on the performance of the prepared ZnO-based UV Photodiodes (PDs). To this end, the electrochemical method was employed to facilitate the growth of ZnO Nanowires (NWs) on the Carbon Clothe (CC) substrate. The results obtained from Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyses demonstrated well-grown ZnO NWs arrays with high coverage density and crystal quality on the substrate. The current-voltage (I–V) measurement was employed in the UV illumination and dark conditions to determine the photo-responsivity and detectivity of the prepared device to the UV light. In addition, the photocurrent and overall device performances were modified under UV illumination and applying compressive strain, given its role in increasing the barrier height. As a result, more photo-generated charge carriers can migrate to the electrode without recombination in comparison with free strain conditions. This phenomenon is known as the piezo-phototronic effect. Further, the findings of this study revealed that CC could be an appropriate alternative to the fabricated flexible PDs instead of other expensive flexible substrates such as Indium Tin Oxide/Poly-Ethylene Terephthalate (ITO/PET).

Investigation of AlGaN-Delta–GaN-Based UV Photodiodes in a Metal–Semiconductor–Metal Configuration for Efficient and Fast Solar Blind UV Sensing

Metal–semiconductor–metal (MSM) configured UV photodiodes (PD’s) were designed and fabricated on an AlGaN/GaN–based substrate for efficient and ultrafast UV detection. The purpose was to investigate the feasibility of obtaining efficient and ultrafast temporal response from these devices in the UV given the challenges associated with the formation of Schottky contacts on laterally oriented AlGaN/GaN thin films. Two sets of devices were implemented using Pt and Au as metal contacts with 5-μm finger width, 5-μm finger spacing, and a 50-μm × 50-μm active area. Spectral and voltage bias studies were done to establish the spectral profile and the effect of bias voltage on the responsivity of the detectors at 265 nm. The best vertical MSM PD’s produced 0.6-A/W responsivity under 10-V bias voltage at 265 nm. Peak spectral responsivities were recorded as 1.35 A/W and 1.25 A/W at 240 nm for Pt and Au PD’s, respectively.

Analysis of structural defects with the chemical composition of rGO/GaN nanocomposites using Raman spectroscopy

In this work, Raman spectroscopy was employed to examine the interface properties of chemically synthesized Gallium Nitride decorated reduced graphene oxide (rGO/GaN) nanocomposites. From the Raman analyses, a redshift of 6.68 cm−1 was detected in the E2 (high) phonon mode of GaN which indicates that GaN has tensile stress in the rGO network. As calculated from intensity ratios of the D to G band, there was the detection of fewer structural defects in the rGO/GaN nanocomposites while increasing the amount of GaN from 1 to 20 wt%. Moreover, from the analysis of the width of the 2D peak, less stacking of graphene sheets was discovered with more association of GaN nanoparticles. Photoluminescence (PL) studies revealed the absolute intensity corresponding to both the near band edge (NBE) GaN and blue PL emission of rGO increases with more incorporation of GaN. This implies that the radiative charge carrier recombination on rGO/GaN surface was increased thus improving the optical quality of the rGO/GaN nanocomposites. rGO/GaN nanocomposites have been reported to be useful in energy storage applications and can further be extended to applications such as LEDs, solar cells, photodetectors, UV photodiodes, and gas sensors in the prospect.

Atomically Thin Delta-Doping of Self-Assembled Molecular Monolayers by Flash Lamp Annealing for Si-Based Deep UV Photodiodes.

Delta doping (δ-doping) can find a wide range of applications in advanced metal oxide semiconductor field effect transistors, deep UV photodetectors, quantum devices, and others. In this work, we formed a δ-doping layer in silicon by employing flash lamp annealing to treat the PCl3 monolayers grafted on silicon surfaces. The δ-doping layer is atomically thin (<1 nm). Low-temperature Hall measurements show that the δ-doping layer is in a metallic state and exhibits a weak localization phenomenon, implying that a two-dimensional electron gas is formed. When we form such an n-type δ-doping layer on a highly doped p-type Si substrate, a highly sensitive solar-blind UV photodetector is created, which traditionally was only possible by using wide band gap semiconductors such as gallium nitride (GaN) or silicon carbide (SiC).

SORCE and TSIS‐1 SIM Comparison: Absolute Irradiance Scale Reconciliation

AbstractThe Solar Radiation and Climate Experiment (SORCE) and Total and Spectral Irradiance Sensor (TSIS‐1) conducted an intercomparison for the two Spectral Irradiance Monitors (SIM) spanning 704 days from 23 March 2018 to 25 February 2020 and permitted 554 time‐matched pairs of observations. This comparison was conducted during the extremely quiescent Solar Cycle 24 minimum, so all observed differences and drifts between the two sensors are instrumental in nature. The TSIS‐1 SIM benefitted from advanced calibration capabilities based on SI standards that were not available during the preflight calibration time period of SORCE. For this reason, a revision of the SORCE SIM absolute scale is appropriate. As expected, wavelength dependent differences in absolute agreement are a function of detector sensitivity and local changes in spectral slope. At the time of the comparison SORCE SIM has been on‐orbit for 17 years while TSIS‐1 observations commenced immediately after a 100‐day outgassing and commissioning period. Peak‐to‐peak absolute scale differences are about 12% with a mean fractional difference of 0.7% ± 2.9%. The greatest scale differences occur at the change‐over between the UV and visible photodiodes in the 310 nm region, and a systematic disagreement is present in the 850–1,600 nm range. A multiplicative scale correction factor has been developed to reconcile the TSIS‐1 and SORCE difference with a wavelength dependent error on the mean typically less than 0.01% derived from every matched pair of observations.

A new approach to fabrication of UV photodiodes based on ZnO/PPy on carbon clothe substrate

The current study reports the fabrication of an ultraviolet photodetector composed of zinc oxide nanorods (ZnO NRs) and polypyrrole nanoparticles (PPy NPs) on a carbon clothes substrate. The use of high temperature tolerant and suitable conductive flexible carbon fibers results in an excellent mechanical and thermal stability of the detector. Samples were synthesized by an uncomplicated electrochemical technique. The morphology and crystal structure of the samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The optical properties of the samples were evaluated using UV–Vis absorption spectra, that is showed absorption edge at 250 nm. Photoluminescence (PL) spectra showed near band edge emission peaks. The photoresponse to UV light in the prepared device was characterized by the current-potential (I–V) curves. Nanocomposite formation on the entire surfaces of carbon fiber caused more current than other sensors with similar detection areas. The photoresponse of the UV photodetectors was tested with 360 and 250 nm illumination wavelengths. Furthermore, the UV photoelectric properties of the ZnO/PPy photodetector had an enhancement compared with the device based on ZnO NRs. This structure enabled to detect the short wavelength of 250 nm in UVC region which is much lower than optimum detection wavelength of normal ZnO based detectors. The results showed that the UV flexible photodetector based on ZnO/PPy nanocomposite had also shown higher sensitivity in comparison with the photodetectors based on pure ZnO NRs.

Classical and quantum regression analysis for the optoelectronic performance of NTCDA/p-Si UV photodiode

Due to the pivotal role of UV photodiodes in many technological applications in tandem with the high efficiency achieved by machine learning techniques in regression and classification problems, different artificial intelligence techniques are adopted to simulate and model the performance of organic/inorganic heterojunction UV photodiode. Herein, the performance of a fabricated Au/NTCDA/p-Si/Al photodiode is explained in a detailed manner and has shown an excellent responsivity and detectivity for UV light of intensities ranging from 20 to 80mW/cm2. A linear current–irradiance relationship is exhibited by the fabricated photodiode under illumination up to 65mW/cm2. It also shows good response times of trise=408ms and tfall=490ms. Furthermore, we have not only fitted the characteristic I-V curve but also evaluated three classical algorithms; K-Nearest Neighbour, Artificial Neural Network, and Genetic Programming besides using a Quantum Neural Network to predict the behavior of the device. The models have achieved outstanding results and managed to capture the trend of the target values. The Quantum Neural Network has been used for the first time to model the photodiode characteristics. The trained models are of great significance since they can be used to reduce the characterization and measurement times.

Effect of donor on the performance of self-powered UV photodiodes based on solution-processed TPD:Alq3 and NPD:Alq3 active layers

In this work, the impact of donor material on the optical and photodiode response is revealed by comparing the performance of self-powered photodiodes based on D:Alq3 (D=TPD or NPD) composite. The active layers were fabricated from solution-processed composites using the well-known spin coating technique, followed by their optical and electrical characterizations. The photodiodes were utilized for the UV light detection in a self-powered mode, in which no external power is required, but it is generated through the photovoltaic effect. Results showed that the NPD film has provided a broader and more intensive optical absorption towards the UV light compared to that of TPD. Also, photoluminescence quenching in the NPD:Alq3 composite was found to highly outperform that of the TPD:Alq3. These were ascribed to the effect of extra pi conjugated bonds present in the NPD, which are originated from the aromatic rings. Consequently, the NPD:Alq3 photodiodes presented a respective sensitivity, responsivity and detectivity of 1.3×105, 1.07 mA/W and 5.25×1011 Jones at 0 V. Moreover, the response (0.34 s) and recovery time (0.28 s) of these devices were found to be smaller compared to those reported in literature.

SnO2/ZnO/p-Si and SnO2/TiO2/p-Si heterojunction UV photodiodes prepared using a hydrothermal method

Low dimensional nanostructures (NSs) exhibit superior properties for the fabrication of electronic and optoelectronic devices. The integration of these structures into the semiconductor devices is a novel efficient way to achieve high performance heterojunction UV photodiodes due to the enhanced light harvesting and facilitated charge-transfer. Herein, we report the effect of the type of metal oxide seed layers on the formation of SnO2NSs and the performance of SnO2/p-Si heterojunction UV photodiodes. The seed layers were fabricated by depositing ZnO and TiO2 thin films (TFs) on p-Si substrate by spin-coating method. The synthesis of SnO2NSs on each seed layers was achieved by hydrothermal growth technique. It was found that the morphology of nanostructures and light sensing performance of the heterojunction UV photodiodes were significantly influenced by type of seed layers. The photoresponsivity of our fabricated devices were found to be 68 mA/W for SnO2-NSs/ZnOTF/p-Si (device-1) and 92 mA/W for SnO2-NSs/TiO2-TF/p-Si (device-2). Thus, the device-2 is considered to be a better choice over the device-1 for UV detection applications. This research might shed light on new approaches to boost the performance of the heterojunction UV photodiodes.

Fabrication of silicon carbide microchannels by thin diamond wheel grinding

Silicon carbide (SiC) microchannels are attractive for their wide applications in microsensors, MOS devices, UV photodiodes, microcatalytic reactors, and microchannel heat exchangers in harsh environments. However, the machining of SiC microchannels poses many challenges because of the difficulty and cost involved in the material removal process due to the high hardness and brittleness of SiC ceramic. In the present study, we developed a thin diamond wheel grinding process to fabricate SiC microchannels in a conventional vertical milling machine. Microchannels with trapezoidal shapes were successfully processed in SiC substrates by thin diamond wheels. The formation, geometric dimensions, and surface quality of SiC microchannels were studied together with the analysis of material removal mechanism. The effects of grinding processing parameters, i.e., wheel speed, feed speed, grinding depth, and grinding tool parameters including grit size and thickness of diamond grinding wheel, on the geometric dimension and surface morphology were comprehensively explored. The top width of microchannels first increased and then decreased with the increase in wheel speed, whereas a reverse tendency was observed with increasing grinding depth, feed speed, and grit size. The surface roughness decreased continuously with increasing wheel speed, but it tended to increase with the increase in feed speed generally. The variations in geometric dimensions and surface roughness of SiC microchannels can be related to the crack or fracture propagations and material removal mechanism during the thin diamond wheel grinding process. Besides, the influential significance of the above processing and grinding tool parameters were also evaluated by analysis of variance (ANOVA).

Experimental investigation on laser micromilling of SiC microchannels

Silicon carbide (SiC) microchannels show their promising merits in the applications of microchannel heat sink cooling systems, microsensor MOS devices, and UV photodiodes. The fabrication of SiC microchannels is critical for their wide applications. In this study, a laser micromilling method is utilized to process SiC microchannels. A series of SiC microchannels are fabricated using a pulsed fiber laser. Based on the SEM observations and 3D confocal microscope measurements, the formation of microchannels is analyzed. The effects of laser processing parameters, such as laser output power, scanning speed, and scanning times as well as the predetermined microchannel width, on the geometric dimension and surface morphology are systematically assessed. The common recast layer deposited around the laser-scanned areas in the laser micromilling of metallic structures was not found for the SiC microchannels. A transition between triangular and trapezoidal shapes occurred for the laser-micromilled microchannels depending on the processing parameters and predetermined width. The microchannel depth increased monotonically with the laser output power and laser scanning time but decreased with increasing scanning speed. On the contrary, the bottom width of microchannels presented an inverse trend. The surface roughness was dependent on the laser scanning speed, scanning time, as well as predetermined width.

Temperature dependence of commercial 4H-SiC UV Schottky photodiodes for X-ray detection and spectroscopy

Two commercial-off-the-shelf (COTS) 4H-SiC UV photodiodes have been investigated for their suitability as low-cost high temperature tolerant X-ray detectors. Electrical characterisation of the photodiodes which had different active areas (0.06mm2 and 0.5mm2) is reported over the temperature range 0°C to 140°C together with measurements of the X-ray photocurrents generated when the detectors were illuminated with an 55Fe radioisotope X-ray source. The 0.06mm2 photodiode was also investigated as a photon counting spectroscopic X-ray detector across the temperature range 0°C to 100°C. The depletion widths (at 120V reverse bias) of the two diodes were found to be 2.3µm and 4.5µm, for the 0.06mm2 and 0.5mm2 detectors respectively, at 140°C. Both devices had low leakage currents (<10 pA) at temperatures ≤40°C even at high electric field strengths (500kV/cm for 0.06mm2 diode; 267kV/cm for 0.5mm2 diode). At 140°C and similar field strengths (514kV/cm for 0.06mm2 diode; 269kV/cm for 0.5mm2 diode), the leakage currents of both diodes were <2nA (corresponding to leakage current densities of 2.4µA/cm2 and 0.3µA/cm2 for each diode respectively). The results demonstrated that both devices could function as current mode detectors of soft X-rays at the temperatures <80°C and that when coupled to a low noise charge sensitive preamplifier, the smaller diode functioned as a photon counting spectroscopic X-ray detector at temperatures ≤100°C with modest energy resolution (1.6keV FWHM at 5.9keV at 0°C; 2.6keV FWHM at 5.9keV at 100°C). Due to their temperature tolerance, wide commercial availability, and the radiation hardness of SiC, such detectors are expected to find utility in future low-cost nanosatellite (cubesat) missions and cost-sensitive industrial applications.

Role of Oxygen Interstitial Defects in Fabrication of UV Photodiodes Using Vertically Aligned (Al,Ga):ZnO Nanowires

Role of Oxygen Interstitial Defects in Fabrication of UV Photodiodes Using Vertically Aligned (Al,Ga):ZnO Nanowires