Large Area Avalanche Photodiodes Research Articles

Absolute light yield of the EJ-204 plastic scintillator

The absolute light yield of a scintillator, defined as the number of scintillation photons produced per unit energy deposited, is a useful quantity for scintillator development, research, and applications. Yet, literature data on the absolute light yield of organic scintillators are limited. The goal of this work is to assess the suitability of the EJ-204 plastic scintillator from Eljen Technology to serve as a reference standard for measurements of the absolute light yield of organic scintillators. Four EJ-204 samples were examined: two manufactured approximately four months prior and stored in high-purity nitrogen, and two aged approximately eleven years and stored in ambient air. The scintillator response was measured using a large-area avalanche photodiode calibrated using low energy γ-ray and X-ray sources. The product of the quantum efficiency of the photodetector and light collection efficiency of the housing was characterized using an experimentally-benchmarked optical photon simulation. The average absolute light yield of the fresh samples, 9100 ± 400 photons per MeV, is lower than the manufacturer-reported value of 10400 photons per MeV. Moreover, the aged samples demonstrated significantly lower light yields, deviating from the manufacturer specification by as much as 26%. These results are consistent with recent work showcasing environmental aging in plastic scintillators and suggest that experimenters should use caution when deploying plastic scintillators in photon counting applications.

Secondary scintillation yield in pure krypton

The absolute secondary scintillation yield is of paramount importance for modelling dual-phase or high-pressure gas detectors, to be used in contemporary and in future rare event detection experiments. In addition, the search for neutrinoless double electron capture complements the search for neutrinoless double beta decay and has been measured for 124Xe in several Dark Matter and Double Beta decay detectors, operating at present. Krypton presents itself as an interesting candidate for double electron capture detection experiments. We have studied the krypton secondary scintillation yield, at room temperature, as a function of electric field in the gas scintillation gap. A large area avalanche photodiode has been used to allow the simultaneous detection of the scintillation pulses as well as the direct interaction of x-rays, the latter being used as a reference for the calculation of the number of charge carriers produced by the scintillation pulses and, thus, the determination of the number of photons impinging the photodiode. An amplification parameter of 113 photons per kV per drifting electron and a scintillation threshold of 2.7 Td (0.7 kVcm−1bar−1 at 293 K) was obtained, in good agreement with the simulation data reported in the literature. On the other hand, the ionisation threshold in krypton was found to be around 13.5 Td (3.4 kVcm−1bar−1), less than what had been obtained by the most recent simulation work-package. The krypton amplification parameter is about 80% and 140% of those measured for xenon and argon, respectively.

Reflectivity of VUV-sensitive silicon photomultipliers in liquid Xenon

Silicon photomultipliers are regarded as a very promising technology for next-generation, cutting-edge detectors for low-background experiments in particle physics. This work presents systematic reflectivity studies of Silicon Photomultipliers (SiPM) and other samples in liquid xenon at vacuum ultraviolet (VUV) wavelengths. A dedicated setup at the University of Münster has been used that allows to acquire angle-resolved reflection measurements of various samples immersed in liquid xenon with 0.45° angular resolution. Four samples are investigated in this work: one Hamamatsu VUV4 SiPM, one FBK VUV-HD SiPM, one FBK wafer sample and one Large-Area Avalanche Photodiode (LA-APD) from EXO-200. The reflectivity is determined to be 25–36 % at an angle of incidence of 20° for the four samples and increases to up to 65 % at 70° for the LA-APD and the FBK samples. The Hamamatsu VUV4 SiPM shows a decline with increasing angle of incidence. The reflectivity results will be incorporated in upcoming light response simulations of the nEXO detector.

Highly sensitive monolithic optoelectronic receiver with large-area avalanche photodiode for optical wireless communication at low data rates

A highly sensitive monolithic optical receiver, applicable in optical fiber and wireless communication is presented. The proposed chip is capable of processing data rates of up to 10 Mb / s and offers compatibility to standard CMOS logic by creating full 3.3-V output swing. The photodetector of the system is carried out as a large-area fully integrated avalanche photodiode with a diameter of 800 μm and a high responsivity to red light with a wavelength of 675 nm. The receiver features pseudo differential signal processing with offset cancellation feedback to achieve desensitization to background light irradiation usually appearing with optical wireless communication. Additionally, common-mode feedback was implemented to prevent pulse width distorted output signals. Measurements at 2.5, 5, and 10 Mb / s reveal high sensitivities of −50.4, −47.65, and −42.7 dBm, respectively, for BER < 10 − 9 in dark conditions. For the design, a 0.35-μm CMOS process was chosen.

Research and design of underwater wireless optical communication system with dual light sources

With the deepening exploration of ocean, underwater wireless communication technology has become the key to restrict its development. Aiming at the requirement of high speed and long distance underwater wireless communication, an underwater bidirectional link communication system for marine commercial was designed. The laser LD and LED dual emission light sources were adopted at the transmitting end, the system design scheme of dual emission light sources was proposed, and the feasibility of the scheme by designing the corresponding drive circuits was verified. At the receiving end, 5 mm large-area APD and high-sensitivity PMT dual receiving detector were used to receive optical signals, which were suitable for long-distance and high-speed communication. The information processing part of the system was completed by FPGA, and information interaction was carried out with PC through network communication. Finally, the whole system was designed and commercialized. The underwater simulation experiment shows that the communication rate of the system can reach 60 Mbps when the communication distance is 5 m and the bit error rate is 10−7. The communication rate of the system can reach 10 Mbps when the communication distance is 60 m and the bit error rate is 10−7.

High gain, large area, and solar blind avalanche photodiodes based on Al-rich AlGaN grown on AlN substrates

We demonstrate large area (25 000 μm2) Al-rich AlGaN-based avalanche photodiodes (APDs) grown on single crystal AlN substrates operating with differential (the difference in photocurrent and dark current) signal gain of 100 000 at 90 pW (&amp;lt;1 μW cm−2) illumination with very low dark currents &amp;lt;0.1 pA at room temperature under ambient light. The high gain in large area AlGaN APDs is attributed to a high breakdown voltage at 340 V, corresponding to very high breakdown fields ∼9 MV cm−1 as a consequence of low threading and screw dislocation densities &amp;lt; 103 cm−2. The maximum charge collection efficiency of 30% was determined at 255 nm, corresponding to the bandgap of Al0.65Ga0.35N, with a response of 0.06 A/W. No response was detected for λ &amp;gt; 280 nm, establishing solar blindness of the device.

The Electromagnetic Calorimeter for the PANDA Target Spectrometer

The future experiment with a next generation detector will focus on hadron spectroscopy. It will use cooled anti-proton beams with a momentum between 1.5 GeV/c and 15 GeV/c interacting with various targets. This allows to directly form all states of all quantum numbers and measure their widths with an accuracy of a few tens of keV. The experiment will be located at the exceptional Facility for Anti-proton and Ion Research in Germany (FAIR), which is currently under construction. The electromagnetic target calorimeter of the experiment has the challenging aim to detect high energy photons with excellent energy resolution over the full dynamic range from 15 GeV down to a few tens of MeV within a 2 T solenoid. The target calorimeter itself is divided into a barrel and two endcaps. The individual crystals will be read out with two precisely matched large area avalanche photo diodes. In the very inner part of the forward endcap vacuum phototetrodes will be used instead. To reach the demands of the experiment, improved PbWO4 (PWO) scintillator crystals, cooled down to −25°C have been chosen. They provide a fast decay time for highest count rates, short radiation length for compactness, improved light yield for lowest thresholds and excellent radiation hardness [1]. The main part of the 15,740 crystals needed have been produced by the Bogoroditsk Plant of Technochemical Products (BTCP) in Russia. After stopping their business, a new potential producer for the missing 41% of crystals have been found. The company Crytur in Czech Republic provided 150 promising preproduction crystals so far. Except some of the very first produced crystals, all samples exceed the required high quality parameters. Most of them have already been used for the first major assembly stage of assembling one of the 16 barrel slice segments, which will be presented as well.

Development of Multichannel Readout Electronics for a CsI(TI) Gamma Detection Array at ETF of Cooler Storage Ring

We present a multichannel readout electronics developed for a CsI(TI) gamma detection array with 1024 large area avalanche photodiodes at the external target facility of cooler storage ring in the institute of modern physics. The full read-out electronics consist of 32 identical analog boards, eight acquisition and control boards (ACBs), and a PXI chassis. An analog board can handle energy and time measurements for 32 channels. The ACB implements analog output signal conversion, slow control, fast timing control signals generation, and data acquisition. The energy linearity of the readout electronics is better than 0.2% in the dynamic range of 0.06–0.60 V. The relative resolution of intrinsic electronics is about 0.24% at output voltage of 0.57 V.

VUV-Sensitive Silicon Photomultipliers for Xenon Scintillation Light Detection in nEXO

Future tonne-scale liquefied noble gas detectors depend on efficient light detection in the VUV range. In the past years Silicon Photomultipliers (SiPMs) have emerged as a valid alternative to standard photomultiplier tubes or large area avalanche photodiodes. The next generation double beta decay experiment, nEXO, with a 5 tonne liquid xenon time projection chamber, will use SiPMs for detecting the $178\,\text{nm}$ xenon scintillation light, in order to achieve an energy resolution of $\sigma / Q_{\beta\beta} = 1\, \%$. This paper presents recent measurements of the VUV-HD generation SiPMs from Fondazione Bruno Kessler in two complementary setups. It includes measurements of the photon detection efficiency with gaseous xenon scintillation light in a vacuum setup and dark measurements in a dry nitrogen gas setup. We report improved photon detection efficiency at $175\,\text{nm}$ compared to previous generation devices, that would meet the criteria of nEXO. Furthermore, we present the projected nEXO detector light collection and energy resolution that could be achieved by using these SiPMs.

On the double peak structure of avalanche photodiode response to monoenergetic x-rays at various temperatures and bias voltages

The double response of a large area avalanche photodiode, a planar RMD model S1315, to 6-keV x-rays was investigated as a function of APD biasing voltage and for different operating temperatures. Our data are consistent with the interpretation that the dissimilar APD response is due to x-ray interactions in the different APD-layer structures; interactions in the APD entrance layer just below the front electrode, where the electric field intensity is very low lead to pulses with higher risetime and lower amplitudes, when compared with interactions in the deeper layers where the electric field is more intense. Average pulse risetime values of 14 and 7 ns have been measured in our setup, the slower pulses presenting average amplitudes which are around 20% lower than those of the faster pulses. While the fast risetime does not depend significantly on APD biasing voltage and on temperature, the slow risetime presents a slight decrease with increasing bias voltage and decreasing temperature, a behaviour that is consistent with the increase of the electric field as a result of the increase in the APD biasing voltage. The fraction of the slow pulses reduces from 60% to 40% as the APD biasing increases from about 1.58 to 1.64 kV, indicating a reduction in the thickness, from 25 to 15 μm, in the weak-electric-field entrance layer.

(Invited) ALD Metal Fluorides for Ultraviolet Filter and Reflective Coating Applications

We report on the development of atomic layer deposition (ALD) processes for integrating optical filter coatings directly onto back-illuminated silicon sensors for ultraviolet applications. These devices, including CCD imaging arrays and large-area avalanche photodiodes, are modified with a two-dimensional doping method utilizing molecular beam epitaxy to provide high internal quantum efficiency in the UV. Detector integrated coatings are then required to recover additional external losses due to natural silicon reflectance at these short wavelengths. This includes the development of broadband AR coatings, multilayer narrowband coatings, and metal-dielectric filters for solar-blind devices. The use of ALD is attractive for this purpose because the low deposition temperature and thermal surface reactions do not degrade the 2D doping layers, and therefore do not result in reduced detector quantum efficiency. Applications implementing these coated detectors related to terrestrial and space astronomy, astrophysics missions, and particle physics experiments will be discussed. Cosmology is experiencing a very exciting time in exploration. Communities of scientists and technology innovators are studying four concepts for flagship future missions selected and supported by NASA. Two of these four missions are Earth-orbiting large aperture telescope observatories that will include UV capabilities. Currently, these ongoing studies have identified high efficiency detectors and high reflectivity mirror coatings as high priority technologies, particularly those that can extend and enhance system performance for UV wavelengths shorter than those previously explored by missions like the Hubble Space Telescope. At wavelengths below 200 nm, typical ALD dielectric oxide materials like TiO2, HfO2, SiO2, and Al2O3 exhibit large optical losses; we have pursued the development of new processes for ALD metal fluorides to extend coating performance into this far UV wavelength range. Thin films of MgF2, AlF3, and LiF are demonstrated using anhydrous hydrogen fluoride (HF) as the fluorine-containing precursor. This is in contrast to alternate ALD methods for fluoride materials which often utilize reactive metal fluorides as the fluorine precursors, and can result in thin films with components of residual metal oxide contamination. The use of HF has allowed for films with good UV optical properties at deposition temperatures as low 100 °C. This enables compatibility with a variety of 2D-doped silicon sensor formats as well as optical components like polymeric diffraction gratings. The deposition rate of these fluoride materials has a more significant substrate temperature dependence than other common ALD chemistries that often display a ‘window’ of uniform film growth per ALD cycle. Characterization of these coatings is performed with measurements of far UV reflectance and transmittance, x-ray photoelectron spectroscopy, x-ray diffraction, ellipsometry, and atomic force microscopy. These ALD fluoride materials are also effective protective coatings for reflective aluminum optics. Protected UV Al mirrors with ALD AlF3 overcoats are shown to be competitive with state-of-the-art commercial mirrors made with conventional physical vapor deposition (PVD) methods. The use of ALD in these components holds promise in reducing the thickness of the overcoat relative to PVD approaches. This has significant performance implications for far UV mirrors and the ultimate short wavelength cutoff of Al mirrors for potential future NASA astrophysics missions. The large scale coating uniformity, and corresponding reflectance uniformity of ALD overcoats is also attractive for the same applications. Additionally, the use of HF-based ALD chemistries can also allow for the thermal atomic layer etching (ALE) of a variety of materials including aluminum oxide. By combining these ALE methods with ALD encapsulation, it is possible to chemically strip the oxidation that occurs on metallic aluminum and effectively replace it with thin fluoride layers. Stable Al mirrors with protective fluoride coatings approximately 3 nm thick are demonstrated with this combined ALE/ALD approach. The environmental stability of these coatings will be described in the context of resistance to high-humidity conditions. Figure 1

The BELLE Electromagnetic Calorimeter and its Upgrade to BelleII

The new SuperKEKB collider will be an upgrade of the existing KEKB electron-positron asymmetric machine, with a target luminosity of 8×1035 cm−2s−1, about 40 times greater than the previous one. The accelerator upgrade is based on the novel low-emittance "nanobeams" scheme. The detector will also be upgraded to cope with the higher luminosity, pile-up and occupancy. We report on the development of the new pure CsI calorimeter for the forward region. An intensive R&D has been carried out to study the performance of pure CsI crystals with Large Area Avalanche Photodiodes readout (LAAPD). Results on the signal to noise ratio for different sensors and front end electronics configurations will be presented as well as the use of filters and wavelength shifters. Measurements with a source, simulating the background machine, have been performed and will also be presented.

Optical Characterization of Tissue Phantoms Using a Silicon Integrated fdNIRS System on Chip.

An interface circuit with signal processing and digitizing circuits for a high frequency, large area avalanche photodiode (APD) has been integrated in a 130 nm BiCMOS chip. The system enables the absolute oximetry of tissue using frequency domain Near Infrared Spectroscopy (fdNIRS). The system measures the light absorbed and scattered by the tissue by measuring the reduction in the amplitude of signal and phase shift introduced between the light source and detector which are placed a finite distance away from each other. The received 80 MHz RF signal is downconverted to a low frequency and amplified using a heterodyning scheme. The front-end transimpedance amplifier has a 3-level programmable gain that increases the dynamic range to 60 dB. The phase difference between an identical reference channel and the optical channel is measured with a 0.5° accuracy. The detectable current range is [Formula: see text] and with a 40 A/W reponsivity using the APD, power levels as low as 500 pW can be detected. Measurements of the absorption and reduced scattering coefficients of solid tissue phantoms using this system are compared with those using a commercial instrument with differences within 30%. Measurement of a milk based liquid tissue phantom show an increase in absorption coefficient with addition of black ink. The miniaturized circuit serves as an efficiently scalable system for multi-site detection for applications in neonatal cerebral oximetry and optical mammography.

Optical Wireless APD Receiver With High Background-Light Immunity for Increased Communication Distances

The design and measurement of a monolithically integrated optoelectronic chip consisting of two different receivers are presented. A high-speed receiver for communication including a highly sensitive, large-area avalanche photodiode builds one receiver. A data rate of 1 Gbit/s with a BER $0.35~\mu \text{m}$ CMOS technology. The performance in a wireless communication scenario with strong background irradiance is explored, and a comparison with published optoelectronic integrated receivers is given.

Precision Measurement of the Radiative β Decay of the Free Neutron.

The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the β decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335±0.00005[stat]±0.00015[syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582±0.00023[stat]±0.00062[syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies.

Performance evaluation of newly developed SrI2(Eu) scintillator

The development of europium-doped strontium iodide (SrI2(Eu)) has attracted considerable attention, because of its excellent material properties as regards gamma-ray scintillator applications. These include its excellent energy resolution, high light output (>80,000ph/MeV), and high effective atomic number (Z=49). Here we report on the performance of ϕ 1in×1in SrI2(Eu) cylindrical crystals newly fabricated by Union Materials Inc. In this study, we measured the energy resolution and light output at 10 °C temperature intervals between −40 and 40°C, using an optically coupled 2-in photomultiplier tube (PMT) (Super Bialkali, Hamamatsu). The SrI2(Eu) light output increased by 0.12%/°C as the temperature decreased. At −40°C, we obtained the optimal energy resolution recording 2.91±0.02% full width at half maximum (FWHM) for 662keV gamma rays measured with 137Cs. For comparison, we also measured the same crystal using both a large-area (19×19mm2) avalanche photodiode detector (APD) and 8×8 multi-pixel photon counter (MPPC) arrays of 3×3mm2 pixels. The energy resolutions of 2.94±0.02%, 3.14±0.06% and 3.99±0.01% were obtained using PMT, APD, and MPPC, respectively, as measured at −20°C. We also measured the inherent background of SrI2(Eu) in a cave composed of Cu–Pb blocks with their thickness of 5–10cm confirming that SrI2(Eu) has an extremely low inherent background radiation. In this study, we have shown that SrI2(Eu) is a promising scintillator that can be utilized for radiation measurements incorporating low-energy X-rays to high-energy gamma rays, and can thus be applied in various medical, industrial, and environmental treatment fields in the near future.

The Forward Endcap of the Electromagnetic Calorimeter for the PANDA Detector at FAIR

The versatile 4π-detector PANDA will be built at the Facility for Antiproton and Ion Research (FAIR), an accelerator complex, currently under construction near Darmstadt, Germany. A cooled antiproton beam in a momentum range of 1.5 – 15GeV/c will be provided by the High Energy Storage Ring (HESR). All measurements at PANDA rely on an excellent performance of the detector with respect to tracking, particle identification and energy measurement. The electromagnetic calorimeter (EMC) of the PANDA detector will be equipped with 15744 PbWO4 crystals (PWO-II), which will be operated at a temperature of – 25° C in order to increase the light output. The design of the forward endcap of the EMC has been finalized. The crystals will be read out with Large Area Avalanche Photo Diodes (LAAPDs) in the outer regions and with Vacuum Photo Tetrodes (VPTTs) in the innermost part. Production of photosensor units utilizing charge integrating preamplifiers has begun. A prototype comprised of 216 PbWO4 crystals has been built and tested at various accelerators (CERN SPS, ELSA/Bonn, MAMI/Mainz), where the crystals have been exposed to electron and photon beams of 25MeV up to 15GeV. The results of these test measurements regarding the energy and position resolution are presented.

The backward end-cap for the PANDA electromagnetic calorimeter

The PANDA experiment at the new FAIR facility will cover a broad experimental programme in hadron structure and spectroscopy. As a multipurpose detector, the PANDA spectrometer needs to ensure almost 4π coverage of the scattering solid angle, full and accurate multiple-particle event reconstruction and very good particle identification capabilities. The electromagnetic calorimeter (EMC) will be a key item for many of these aspects. Particle energies ranging from some MeVs to several GeVs have to be measured with a relative resolution of 1% ⊕ 2%/√E/GeV . It will be a homogeneous calorimeter made of PbWO4 crystals and will be operated at -25°C, in order to improve the scintillation light yield. With the exception of the very forward section, the light will be detected by large area avalanche photodiodes (APDs). The current pulses from the APDs will be integrated, amplified and shaped by ASIC chips which were developed for this purpose. The whole calorimeter has been designed in three sections: a forward end-cap, a central barrel and a backward end-cap (BWEC). In this contribution, a status report on the development of the BWEC is presented.

Progress status for the Mu2e calorimeter system

The Mu2e experiment at FNAL aims to measure the charged-lepton flavor violating neutrinoless conversion of a negative muon into an electron. The conversion results in a monochromatic electron with an energy slightly below the muon rest mass (104.97 MeV). The calorimeter should confirm that the candidates reconstructed by the extremely precise tracker system are indeed conversion electrons while performing a powerful μ/e particle identification. Moreover, it should also provide a high level trigger for the experiment independently from the tracker system. The calorimeter should also be able to keep functionality in an environment where the background delivers a dose of ~ 10 krad/year in the hottest area and to work in the presence of 1 T axial magnetic field. These requirements translate in the design of a calorimeter with large acceptance, good energy resolution O(5%) and a reasonable position (time) resolution of ~ < 1 cm (<0.5ns). The baseline version of the calorimeter is composed by two disks of inner (outer) radius of 351 (660) mm filled by 1860 hexagonal BaF2 crystals of 20 cm length. Each crystal is readout by two large area APD's. In this paper, we summarize the experimental tests done so far as well as the simulation studies in the Mu2e environment.

Performance analysis for the CALIFA Barrel calorimeter of the R3B experiment

The CALIFA calorimeter is an advanced detector for gamma rays and light charged particles, accordingly optimized for the demanding requirements of the physics programme proposed for the R3B facility at FAIR. The multipurpose character of CALIFA is required to fulfil challenging demands in energy resolution (5–6% at 1MeV for gamma rays) and efficiency. Charged particles, e.g. protons of energies up to 320MeV in the Barrel section, should also be identified with an energy resolution better to 1%.CALIFA is divided into two well-separated sections: a “Forward EndCap” and a cylindrical “Barrel” covering an angular range from 43.2° to 140.3°. The Barrel section, based on long CsI(Tl) pyramidal frustum crystals coupled to large area avalanche photodiodes (LAAPDs), attains the requested high efficiency for calorimetric purposes. The construction of the CALIFA Demonstrator, comprising 20% of the total detector, has already been initiated, and commissioning experiments are expected for 2014.The assessment of the capabilities and expected performance of the detector elements is a crucial step in their design, along with the prototypes evaluation. For this purpose, the Barrel geometry has been carefully implemented in the simulation package R3BRoot, including easily variable thicknesses of crystal wrapping and carbon fibre supports. A complete characterization of the calorimeter response (including efficiency, resolution, evaluation of energy and reconstruction losses) under different working conditions, with several physics cases selected to probe the detector performance over a wide range of applications, has been undertaken. Prototypes of different sections of the CALIFA Barrel have been modeled and their responses have been evaluated and compared with the experimental results. The present paper summarizes the outcome of the simulation campaign for the entire Barrel section and for the corresponding prototypes tested at different European installations.