Low-energy Photon Detector Research Articles

GaN-Based Low-Energy X-Ray Single Photon Detector With Photon Energy Resolution and Fast Response

GaN-Based Low-Energy X-Ray Single Photon Detector With Photon Energy Resolution and Fast Response

A perovskite-graphene device for X-ray detection

This study examines a perovskite-based graphene field effect transistor (P-GFET) device for X-ray detection. The device architecture consisted of a commercially available GFET-S20 chip, produced by Graphenea, with a layer of methylammonium lead iodide (MAPbI3) perovskite spin coated onto the top of it. This device was exposed to the field of a molybdenum target X-ray tube with beam settings between 20 and 60 kVp (X-ray tube voltage) and 30–300 μA (X-ray tube current). Dose measurements were taken with an ion-chamber and thermo-luminescent dosimeters and used to determine the sensitivity of the device as a function of the X-ray tube voltage and current, as well as source-drain voltage. The X-ray tube was also simulated in this work with GEANT4 and MCNP to determine the dose rate and power incident on the device during irradiation. These simulations were then used to determine the responsivity as a function of the X-ray tube voltage and current, as well as the source-drain voltage. Overall, a strong positive correlation between sensitivity and source-drain voltage was found. Conversely, the sensitivity was found to decrease – roughly exponentially – as a function of both the X-ray tube current and energy. Similar trends were seen with responsivity. We report the models used for the study as well as address the feasibility of the device as a low-energy (<70 keV) X-ray photon detector.

A-Si EPID Modeling in GATE for Monte Carlo Investigation on the Optical Properties of Gd&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;S:Tb and Lu&lt;sub&gt;2&lt;/sub&gt;SiO&lt;sub&gt;5&lt;/sub&gt;:Ce Scintillators

A detailed a-Si Electronic Portal Imaging Device (EPID) was implemented in GATE (Geant4 application for tomographic emission) toolkit for Monte Carlo simulations, employing the standard electromagnetic processes and optical photon processes. The composition of the scintillating material is varied using the conventional terbium-doped gadolinium oxysulfide phosphor (Gd2O2S:Tb) and cerium-doped lutetium oxyorthosilicate (Lu2SiO5:Ce) which is widely used in Positron Emission Tomography (PET) detectors due to its supremacy in aiding the detection of low-energy photons. It was found that the number of optical photons produced is higher when using the Lu2SiO5:Ce scintillator resulting in a slightly better signal-to-noise ratio (SNR). The scattering within the EPID components was also investigated where the majority of the detected secondary particles were created in the scintillator. The results also show that the copper plate layer of the EPID contributes to additional Compton electrons and bremsstrahlung and annihilation photons to the measurements in the scintillator and photodiode layer. The glass substrate, graphite plates, electronic components, and aluminum bottom cover are also found to contribute a huge fraction of backscattered particles to the measurements at the photodiode layer.

Monolayer Graphene Terahertz Detector Integrated with Artificial Microstructure

Graphene, known for its high carrier mobility and broad spectral response range, has proven to be a promising material in photodetection applications. However, its high dark current has limited its application as a high-sensitivity photodetector at room temperature, particularly for the detection of low-energy photons. Our research proposes a new approach for overcoming this challenge by designing lattice antennas with an asymmetric structure for use in combination with high-quality monolayers of graphene. This configuration is capable of sensitive detection of low-energy photons. The results show that the graphene terahertz detector-based microstructure antenna has a responsivity of 29 V·W-1 at 0.12 THz, a fast response time of 7 μs, and a noise equivalent power of less than 8.5 pW/Hz1/2. These results provide a new strategy for the development of graphene array-based room-temperature terahertz photodetectors.

Broadband photodetection using metal excess silver sulfide nanocrystals

In the quest for photosensitive materials in the infrared spectral range that do not contain heavy metals, we investigated silver sulfide nanocrystals and found broadband detection from the visible to the infrared (IR) up to 2500 nm wavelength. The silver sulfide nanocrystals were synthesized by a facile method at room temperature, and integrated into a planar photodetector architecture. The device performance was studied in visible and near-infrared (NIR) regions. The photodetection studies showed that the Ag2S photodetector with high sulfur atom vacancy concentration detected 1550 nm and 2500 nm wavelength with relatively high responsivity and specific detectivity at room temperature and 78 K, respectively. The photophysical, structural, and DFT studies indicate that the origin of high-performance near-IR detection ability of the proposed photodetector up to 2500 nm wavelength was related to the formation of S vacancies. In particular, DFT studies demonstrated that bandgap narrowing occurs in silver sulfide crystals by the presence of S vacancies. Although many research works highlighted highly crystalline materials with low defects, the results in this study demonstrated the promising effects of sulfur vacancies in silver sulfide nanocrystals for low-energy photon detection.

A Weyl semimetal WTe2/GaAs 2D/3D Schottky diode with high rectification ratio and unique photocurrent behavior

Since the discovery of Dirac semimetal graphene, two-dimensional (2D) Weyl semimetals (WSMs) have been widely used in low-energy photon detection, polarization imaging, and other systems due to their rich physical characteristics, such as unique nonlinear optical structure, topological nontrivial electronic structure, thickness-tunable bandgap, high electric conductivity, and so on. However, it is difficult to detect the photocurrent signal at room temperature because of its large intrinsic background current. Fortunately, the fabrication of a van der Waals (vdW) heterojunction based on WSM can effectively suppress the background current, greatly extend the detection range, improve the light absorption efficiency, and increase the response speed. Herein, the 2D type-II WSM 1T′-WTe2/bulk GaAs vdW vertical Schottky diode is investigated. Benefiting from the lateral built-in electric field of 260 meV and zero-bandgap structure of 52 nm 1T′-WTe2, it delivers a rectifying ratio over 103 and can respond to the wavelength range of 400–1100 nm. Particularly, when the light power density is 0.02 mW/cm2, the maximum photoresponsivity (R) and specific detectivity (D*) under 808 nm are 298 mA/W and 1.70 × 1012 Jones, respectively. Meanwhile, the Ilight/Idark ratio and response time are 103 and 520/540 μs, respectively. Moreover, an abnormal negative response behavior can be observed with thin WTe2 (11 nm) under 1064 nm illumination because of the open surface bandgap. It is suggested that such 2D WTe2/GaAs mixed-dimensional vdW structure can be extended to other WSM/3D semiconductor junctions and used in fast response and wide broadband spectrum photodetectors' arrays.

Centimeter-Sized Stable Zero-Dimensional Cs3Bi2I9 Single Crystal for Mid-Infrared Lead-Free Perovskite Photodetector

The detection of broadband spectroscopy is a huge challenge for modern optoelectronics, especially for extremely high- or low-energy photons. For metal halide perovskites significant progress has been made in high-energy photons such as X-rays, but there is little exploration of the perovskites in the high-performance detection of low-energy photons, especially mid- or far-infrared photons. Most infrared photodetectors suffer large dark currents, and perovskite photodetectors’ performances are significantly limited by ion migration. Here, a facile solution evaporation method is developed to grow a centimeter-scale zero-dimensional (0D), lead-free perovskite Cs3Bi2I9 single crystal for high-performance mid-infrared photodetectors with ultralow dark current drifts. The 0D Cs3Bi2I9 perovskite single crystal (PSC) photodetector shows an ultralow dark current drift (1.67 × 10–17 A cm–2 V–1 s–1, 9 orders of magnitude smaller than that of MAPbI3) and ultralow power consumption (smaller than 1 pA at 1 V bias) for greatly inhibited ion migration. The photodetector achieves effective photodetection from the ultraviolet to the mid-infrared (from 343 to 4000 nm) at room temperature based on the photoelectric and photobolometric effects with the best responsivity of 3.15 mA/W and detectivity of 8.7 × 108 jones at the wavelength of 343 nm at 0.033 mW/cm2. This work opens a door for low-dimensional perovskite-based mid-infrared detectors and provides a new path for the development of infrared perovskite photonics.

Ti/Au Ultrathin Films For TES Application

Transition-Edge Sensors (TESs) are versatile superconducting microcalorimeters used as single photon detectors in a large range of electromagnetic wavelength, from X-rays to near-infrared. Among the many materials investigated in literature, Ti/Au is one of the most widely used bilayer to fabricate TES thanks to simple deposition process, long term stability material and protection against oxidation of Ti film by Au over layer. Moreover, the critical temperature of Ti/Au can be tuned by trimming the thickness of Ti and Au films. For low energy photon detection, the Ti/Au superconducting layer performs simultaneously as absorber and thermometer. This implies that a TES thickness reduction helps to significantly reduce the thermal capacitance, which has a direct impact on the detector energy resolution. In this paper we present a study of the superconducting properties of Ti/Au films, grown in UHV by thermal evaporation as a function of Ti thickness. The chemical state of Ti and Ti/Au were analyzed by X-ray photoelectron spectroscopy, to evaluate the protective effect of Au film. The film morphology, structure and optical properties were investigated by ellipsometry. The critical temperature showed a marked trend on film thickness and was strongly affected by Au cover layer. Ti film of only 12 nm thick covered with 10 nm Au film showed a remarkable critical temperature of about 300 mK.

Indirect Photon-counting Detector (PCD) for Transmission Imaging

Photon-counting detectors (PCDs) are replacing energy integrating detectors in electromagnetic wave transmission imaging to achieve high performance. The purpose of this study was to develop an indirect PCD system for transmission imaging. The detector module is a combination of scintillator and SiPM, the SiPM is insensitive to magnetic field and operating at low voltage. A 2D array of a GAGG coupled with SiPM, positioning logic circuit, and preamplifier were enclosed in housing that sealed from light. A channel reduction circuit was used to identify the channel from the positioning logic circuit, and then output an analog pulse signal corresponding to the valid channel. The pulse signal measurements were performed using a oscilloscope. The profile analysis of the flood map confirmed that each point was distinct in both the center and peripheral regions. Additionally, the letters engraved on the phantom in the images were confirmed. Therefore, the indirect PCD system has potential for transmission imaging. Our future work will design an indirect PCD for low-energy photon detection and multi-energy imaging.

Precision efficiency calibration of a high-purity co-axial germanium detector at low energies

Following work done in the energy region above 100 keV, the high-precision calibration of a co-axial high-purity germanium detector has been continued in the energy region below 100 keV. Some of the previous measurements and Monte-Carlo simulations have been repeated with higher statistics and a new source measurement with 169Yb has been added. For the energy range from 40 keV to 100 keV, an absolute precision for the detection efficiency of ±0.2% has been reached, as previously obtained for energies above 100 keV. The low-energy behaviour of the germanium detector was further scrutinised by studying the germanium X-ray escape probability for the detection of low-energy photons. In addition, one experimental point, a γ ray at 2168 keV from the decay of 38K, has been included for the total-to-peak ratios agreeing well with simulations. The same γ ray was also added for the single- and double-escape probabilities. Finally, the long term stability of the efficiency of the germanium detector was investigated by regularly measuring the full-energy peak efficiency with a precisely calibrated 60Co source and found to be perfectly stable over a period of 10 years.

Simple coincidence technique for cosmic-ray intensity exploration via low-energy photon detection

Changes in cosmic-ray intensity can significantly influence the search for rare events or processes in nuclear and astroparticle physics through corresponding variations in detector background count rate. In this work, we present an approach to explore cosmic-ray intensity and corresponding cascade production of secondary particles in the detector vicinity using low-energy photon background spectra induced by cosmic rays at the earth’s surface. The coincidence system based on a plastic scintillator and an extended range HPGe detector, including a multiparameter device, was used for the acquisition of low-energy photon spectra. This system was also simulated by the GEANT4 toolkit, and the simulated and experimental spectra were compared. Single aperiodic events, as well as possible periodic behavior of low-energy photon emission were searched for.

Indirect Photon-Counting Detector with a GAGG Scintillator for Low-Energy Photon Detection

Indirect Photon-Counting Detector with a GAGG Scintillator for Low-Energy Photon Detection

Multi-spectral frequency selective mid-infrared microbolometers.

Frequency selective detection of low energy photons is a scientific challenge using natural materials. A hypothetical surface which functions like a light funnel with very low thermal mass in order to enhance photon collection and suppress background thermal noise is the ideal solution to address both low temperature and frequency selective detection limitations of present detection systems. Here, we present a cavity-coupled quasi-three dimensional plasmonic crystal which induces impedance matching to the free space giving rise to extraordinary transmission through the sub-wavelength aperture array like a "light funnel" in coupling low energy incident photons resulting in frequency selective perfect (~100%) absorption of the incident radiation and zero back reflection. The peak wavelength of absorption of the incident light is almost independent of the angle of incidence and remains within 20% of its maximum (100%) up to θi≤45˚. This perfect absorption results from the incident light-driven localized edge "micro-plasma" currents on the lossy metallic surfaces. The wide-angle light funneling is validated with experimental measurements. Further, a super-lattice based electronic biasing circuit converts the absorbed narrow linewidth (Δλ/λ0< 0.075) photon energy inside the sub-wavelength thick film (< λ/100) to voltage output with high signal to noise ratio close to the theoretical limit. Such artificial plasmonic surfaces enable flexible scaling of light funneling response to any wavelength range by simple dimensional changes paving the path towards room temperature frequency selective low energy photon detection.

The TITAN in-trap decay spectroscopy facility at TRIUMF

This paper presents an upgraded in-trap decay spectroscopy apparatus which has been developed and constructed for use with TRIUMF׳s Ion Trap for Atomic and Nuclear science (TITAN). This device consists of an open-access electron-beam ion-trap (EBIT), which is surrounded radially by seven low-energy planar Si(Li) detectors. The environment of the EBIT allows for the detection of low-energy photons by providing backing-free storage of the radioactive ions, while guiding charged decay particles away from the trap centre via the strong (up to 6T) magnetic field. In addition to excellent ion confinement and storage, the EBIT also provides a venue for performing decay spectroscopy on highly charged radioactive ions. Recent technical advancements have been able to provide a significant increase in sensitivity for low-energy photon detection, towards the goal of measuring weak electron-capture branching ratios of the intermediate nuclei in the two-neutrino double beta (2νββ) decay process. The design, development, and commissioning of this apparatus are presented together with the main physics objectives. The future of the device and experimental technique are discussed.

A novel multi-cell silicon drift detector for Low Energy X-Ray Fluorescence (LEXRF) spectroscopy

The TwinMic spectromicroscope at Elettra is a multipurpose experimental station for full-field and scanning imaging modes and simultaneous acquisition of X-ray fluorescence. The actual LEXRF detection setup consists of eight single-cell Silicon Drift Detectors (SDD) in an annular configuration. Although they provide good performances in terms of both energy resolution and low-energy photon detection efficiency, they cover just about 4% of the whole photoemission solid angle. This is the main limitation of the present detection system, since large part of the emitted photons is lost and consequently a high acquisition time is required. In order to increase the solid angle, a new LEXRF detection system is being developed within a large collaboration of several institutes. The system, composed of 4 trapezoidal multi-cell silicon drift detectors, covers up to 40% of the photoemission hemisphere, so that this geometry provides a 10 times improvement over the present configuration. First measurements in the laboratory and on the TwinMic beamline have been performed in order to characterize a single trapezoidal detector, configured and controlled by means of two multichannel ASICs, which provide preamplification, shaping and peak-stretching, connected to acquisition electronics based on fast ADCs and FPGA and working under vacuum.

Detection Efficiency for Measuring 241Am in Axillary Lymph Nodes Using Different Types and Sizes of Detectors

The detection efficiency and interference susceptibility of four different types of low energy photon detectors, each with a unique geometric arrangement, were compared for direct measurement of Am deposited in the axillary lymph nodes. Although the most efficient detector was a single large 23,226 mm square phoswich detector, it was also the most susceptible to confounding depositions from activity deposited in adjacent organs. The array of two 2,800 mm high purity germanium detectors exhibited the highest efficiency per unit detector area with some resistance to confounding from activity deposited in the lungs. The array of two 4,560 mm NaI(Tl) detectors was the least susceptible to confounding and nearly as efficient per square millimeter as the high purity germanium detector array. Thus, selection of a detector system for in vivo measurement of activity deposited in the axillary lymph nodes should consider whether there is a likelihood for activity deposited in other organs, such as the lungs, skeleton, or liver, to create an interference that will confound the measurement result.

THE LIVERMORE PHANTOM HISTORY AND SUPPLEMENTATION

In vivo monitoring facilities determine the absence or presence of internally entrained radionuclides. To be of greatest utility, the detection systems must detect and quantify the nuclides of interest at levels of interest. Phantoms have been developed to improve measurements at in vivo monitoring facilities. Since the 1970's, the torso phantom originally developed at Lawrence Livermore National Laboratory (LLNL, or simply "Livermore") continues to be a well-used tool at lung monitoring facilities, especially for the detection of low-energy photons from transuranics. The history of its development from need through design development and current availability is summarized. The authors have taken the LLNL phantom one step further by scanning the phantom surface and announce the availability of the scan files on the Internet.

Electrical and optical properties of bismuth telluride/gallium nitride heterojunction diodes

Semiconducting bismuth telluride has a band gap energy of about 0.15eV at room temperature and is a good material for middle wavelength IR (MWIR) detection [S.K. Mishra, S. Satpathy, O. Jepsen, J. Phys. Condens. Matter, p. 461]. We have grown bismuth telluride thin films on gallium nitride (on sapphire) by pulsed laser deposition at a substrate temperature of 300°C. The structural characteristics and surface morphology of the films were studied by X-ray diffraction and scanning electron microscopy, respectively. The chemical composition of the as-deposited bismuth telluride thin films was determined by X-ray photoelectron spectroscopy and was found to be different from that of the bulk target, changing from stoichiometric Bi2Te3 to bismuth rich. A bismuth rich p-Bi2Te3/n-GaN/Al2O3 heterojunction was fabricated for photovoltaic detection of low energy photons. The wide band gap semiconducting n-GaN layer and the Al2O3 substrate act as a window for IR transmission. A sensitive IR photoresponse of the heterojunction is obtained by back-side illumination. The photocurrent measured is 0.18μA according to the irradiation change in the current–voltage characteristics. The current–voltage characteristics allow us to evaluate the series resistance (Rs), zero-bias resistance (R0) and ideality factors (n) of the junctions. Our results have suggested that bismuth telluride is a potential candidate for photovoltaic mid-infrared detection.

Modelling a silicon photomultiplier (SiPM) as a signal source for optimum front-end design

Silicon photomultipliers (SiPM) have proven to be very attractive devices for low-energy photon detection. Thanks to their high gain and excellent timing resolution, they compare favourably to photomultiplier tubes (PMT) in many applications. Their electrical characteristics have to be taken into account to properly design the front-end electronics. Here, an electrical model of the SiPM is defined and an extraction procedure for the parameters involved in this model is proposed, based on suitable measurements performed on the real detector.

Study of fission fragments produced by 14N + 235U reaction

This work was performed to understand the structure of neutron-rich fission fragments around the 130 mass region. A thin 235U target was bombarded by a 14N beam with 10 MeV/A from the Separated Sector Cyclotron at the iThemba Laboratory for Accelerator Based Sciences, Cape Town, South Africa. The main goal was to detect and identify fission fragments and to obtain their mass distribution by using solar cell detectors in the AFRODITE (African Omnipurpose Detector for Innovative Techniques and Experiments) spectrometer. The X-rays emitted from fission fragments were detected by LEP (Low Energy Photon) detectors and γ-rays emitted from excited states of the fission fragments were detected by CLOVER detectors in the spectrometer.