Solid-state Photomultiplier Research Articles

Non-Markovian Hole Excess Noise in Avalanche Amorphous Selenium Thin Films.

Enhancing the signal-to-noise ratio in avalanche photodiodes by utilizing impact ionization gain requires materials exhibiting low excess noise factors. Amorphous selenium (a-Se) as a wide bandgap at ∼2.1 eV, a solid-state avalanche layer, demonstrates single-carrier hole impact ionization gain and manifests ultralow thermal generation rates. A comprehensive study of the history dependent and non-Markovian nature of hot hole transport in a-Se was modeled using a Monte Carlo (MC) random walk of single hole free flights, interrupted by instantaneous phonon, disorder, hole-dipole, and impact-ionization scattering interactions. The hole excess noise factors were simulated for 0.1-15 μm a-Se thin-films as a function of mean avalanche gain. The hole excess noise factors in a-Se decreases with an increase in electric field, impact ionization gain, and device thickness. The history dependent nature of branching of holes is explained using a Gaussian avalanche threshold distance distribution and the dead space distance, which increases determinism in the stochastic impact ionization process. An ultralow non-Markovian excess noise factor of ∼1 was simulated for 100 nm a-Se thin films corresponding to avalanche gains of 1000. Future detector designs can utilize the nonlocal/non-Markovian nature of the hole avalanche in a-Se, to enable a true solid-state photomultiplier with noiseless gain.

INFIERI 2021: Hands-on Lab – LiDAR

LiDAR is an acronym of “Light Detection and Ranging”, which is to measure the distance to an object (“Ranging”) by detecting the light being reflected (“Light Detection”). The "hands-on" lab is made of two sections: (1) overviewing the technology, the application, and the key devices of LiDAR, and (2) a laboratory where we operate a LiDAR setup, do calibration, and look into signals in the electronics. In the section (1), we learn the “basics” of the LiDAR. In the section (2), we learn “real stuff” by using a LiDAR setup. We use a simple desktop LiDAR setup developed by Hamamatsu photonics K.K. (HPK), adapted for the hands-on lab in collaboration with the author. The LiDAR setup, which is using “cutting-edge” solid-state devices, is a direct time-of-flight LiDAR equipped with a 905 nm laser diode and a 16-ch MPPC photon counting image sensor. The light emitter is a pulsed solid-state laser (PLD) of 905 nm infra-red light. The light receiver (a photon counting image sensor (PCI)) is a linear-array of 16 channel MPPC (a solid-state photomultiplier) with a readout ASIC. The setup is also equipped with a visible-light camera, with which we correlate the visual image with the feature of the LiDAR setup. In the LiDAR laboratory, we do “aiming” (i.e., calibrate) by detecting the infra-red laser light, and correlating visual imaging and LiDAR “ranging”. We get insight into the LiDAR setup by monitoring time-of-flight (TOF) and energy (pulse height with time-over-threshold technology (TOT)) signals in the electronics with an oscilloscope. Through the process, we learn the real stuff of LiDAR and the issues associated.

Design and Simulation of an Advanced Solid-state Photomultiplier for Fiber-Optic Communication Systems

Detection of weak infrared light is essential for high data rate fiber-optic communication systems since itsperformance depends heavily on the sensitivity and bandwidth of photodetectors. Semiconductor diodes are themost common types of photodetectors that are widely considered. Indium Arsenide (InAs), being an AvalanchePhotodiode (APD), has become a solid-state photodetector of choice owing to its ability to detect infrared light ofup to about 3.5 μm. In this work, the depletion width and electric field profile of p-i-n InAs were simulated andused to obtain the multiplication gain. The effect of combining a series of p-i-n InAs in order to obtain longerdepletion width for the purpose of achieving high multiplication gain was investigated. To achieve this main target,the work was designed in two stages. The first stage involved designing a simple p-n junction of InAs to test themodel. Further improvement of the design to increase the depletion region was carried out by sand-witching anintrinsic piece of semiconductor material between the p and n-regions to form p-i-n InAs. The results obtainedshowed that the modification led to an interesting increase in the depletion width, electric field and themultiplication gain. In the second stage, the series of p-i-n InAs were combined to form an “Advanced solid-statephotomultiplier”. For the first time, a larger depletion width was achieved and thus increased multiplication gain.The results presented deduced that this novel design is promising since an appreciable gain much greater than 1000was achieved at about 6 V. Therefore, this could be used as an alternative to photomultiplier tube as well as otherexpensive photodetectors available.

Scintillation gamma radiation sensors based on solid-state photomultipliers in wireless industrial internet networks

The article examines the principles of developing wireless networks of autonomous gamma sensors in order to create systems for spatial environmental radiation monitoring. The main task of such systems is to control the level of gamma radiation in areas where potential sources of ionizing radiation are located. An autonomous gamma-ray spectrometer is used as a measuring sensor. The authors propose to apply measuring sensors based on a silicon photomultiplier to create autonomous wireless networks of the industrial Internet for radiation monitoring. To confirm the possibility of using this class of receivers as part of gamma spectrometers, the main structural elements of the system were modeled, and the experimental model of the gamma spectrometer was prototyped. The linearity and energy resolution of the experimental sample were also investigated. To test the model for constructing a gamma spectrometer, a CsI (Tl) scintillation crystal and a Sensl Array-60035-4P photomultiplier were used. The established range of recorded energies is in the range from 121 keV to 1332 keV, the relative energy resolution for the 137Cs peak is 11.07 %, the linearity of the transfer characteristic is 99.91 %. Based on this sensor, the architecture of an automated wireless system for monitoring the spatial distribution of gamma radiation has been developed. The results of the work allow the use of radiation monitoring systems in accordance with the requirements of Industry 4.0.

A Review of Semiconductor Based Ionising Radiation Sensors Used in Harsh Radiation Environments and Their Applications

This article provides a review of semiconductor based ionising radiation sensors to measure accumulated dose and detect individual strikes of ionising particles. The measurement of ionising radiation (γ-ray, X-ray, high energy UV-ray and heavy ions, etc.) is essential in several critical reliability applications such as medical, aviation, space missions and high energy physics experiments considering safety and quality assurance. In the last few decades, numerous techniques based on semiconductor devices such as diodes, metal-oxide-semiconductor field-effect transistors (MOSFETs) and solid-state photomultipliers (SSPMs), etc., have been reported to estimate the absorbed dose of radiation with sensitivity varying by several orders of magnitude from μGy to MGy. In addition, the mitigation of soft errors in integrated circuits essentially requires detection of charged particle induced transients and digital bit-flips in storage elements. Depending on the particle energies, flux and the application requirements, several sensing solutions such as diodes, static random access memory (SRAM) and NAND flash, etc., are reported in the literature. This article goes through the evolution of radiation dosimeters and particle detectors implemented using semiconductor technologies and summarises the features with emphasis on their underlying principles and applications. In addition, this article performs a comparison of the different methodologies while mentioning their advantages and limitations.

Silicon Photo-Multipliers

The measurement of single or few photons with a time resolution of 1 ns or below is an experimental technique with many applications in research, medicine and industry. Until recently, vacuum photo-multipliers (PMTs) dominated this field. In the 1990s avalanche photo-diodes came into use, and in the last decade solid-state photo-multipliers (SSPMs) have replaced PMTs in many applications. In most cases early samples, not yet optimised for the specific application, have been used. In the meantime industry and research institutes have significantly improved the performance of SSPMs.

Scintillation Light Detection with MAPD-3NK and MPPC-S12572-010P Readout

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Performance comparison of different readouts for position-sensitive solid-state photomultiplier arrays

A thorough comparison of five different readouts for reading out a 2 × 2 array of 5 mm × 5 mm position-sensitive solid-state photomultipliers (PS-SSPM) was undertaken. The five readouts include reading out the 20 signals (16 position and 4 timing) individually, two signal multiplexing readouts, and two position decoding readouts. Flood histogram quality, signal-to-noise ratio (SNR) and energy resolution were compared at different bias voltage (27.0– 32.0 V, at 0.5 V intervals) and at a fixed temperature of 0 °C by coupling a 6 × 6 array of 1.3 mm × 1.3 mm × 20 mm polished LSO crystals to the center of the PS-SSPM array. The timing resolution was measured at a bias voltage of 31.0 V (optimal bias voltage in terms of flood histogram quality). The best flood histogram quality value and signal-to-noise were 7.3 ± 1.6 and 33.5 ± 3.1, respectively, and were obtained by shaping and digitizing the 16 position signals individually. The capacitive charge-division readout is the simplest readout among the five evaluated but still resulted in good performance with a flood histogram quality value of 3.3 ± 0.4 and a SNR of 18.3 ± 1.3. The average energy resolution and the average timing resolution were 15.2 ± 1.2% and 8.4 ± 1.6 ns for individual signal readout and 15.9 ± 1.2% and 8.8 ± 1.3 ns by using the capacitive charge-division readout method. These studies show that for an ultra-high spatial resolution applications using the 2 × 2 PS-SSPM array, reading out the 20 signals individually is necessary, whilst the capacitive charge-division readout is a cost-effective readout for less demanding applications.

Domestic Development of Single-Photon Emission Computed Tomography (SPECT) Unit with Detector based on Silicon Photomultipliers

The idea of creating a single-photon emission computed tomography unit with solid-state photomultipliers is not new [1], as the problems of analog-to-digital conversion with a lot of noise and a wide range of values of intrinsic spatial resolution of the detector in a center and relevant fields of view could not be solved by means of gamma-camera detector architectures based on vacuum photomultipliers. This paper offers a new SPECT imaging solution that is free from these problems.

Coherent Bremsstrahlung on Colliding Beams and Possibility of its Detection

A new type of coherent electromagnetic process – coherent bremsstrahlung – on colliding beam setups with short bunches is examined. It is shown that solid-state photomultipliers can be used to detect, register, and investigate coherent bremsstrahlung.

Impact of an AlAs window layer upon the optical properties of AlxGa1−xAs photodiodes

Recently developed advanced scintillators, which have the ability to distinguish gamma-ray interaction events from those that accompany neutron impact, require improved quantum efficiency in the blue to near UV region of the spectrum. We utilize GaAs/Al0.8Ga0.2As photodiode elements as components in a wide band-gap solid-state photomultiplier as a lower-cost, lower logistical burden, and higher quantum efficiency replacement for the photomultiplier tube. An AlAs window layer is employed as a means to increase the diode’s optical performance. Relative to structures absent the window layer, simulations and measurements demonstrate that the AlAs layer produces a spatial coincidence between regions of large drift fields with regions of high photon absorption. In addition to the AlAs layer, secondary ion mass spectrometry measurements show that an unexpected high degree of inter-diffusion of GaAs and AlAs quenches the photon-detection efficiency, a decrease that can be avoided by its post-growth removal. With the AlAs layer, the peak external quantum efficiency of 49% is achieved at 450 nm with 10 V reverse bias, which does not fully deplete the device. Simulations show that full depletion can result in efficiencies exceeding 90%. In order to enhance the optical response, a simple anti-reflective coating layer is designed using the existing passivation layer components that successfully minimizes the reflection at the wavelength range of interest (300 nm–500 nm).

Effects of Proton Radiation on Noise Performance in Solid-State Photomultipliers

Solid-state photomultiplier (SSPM) devices are a viable alternative to photomultiplier tubes for nuclear and space radiation detection and science instruments. Noise terms such as dark noise, cross talk, after-pulsing, and their radiation sensitivity directly affect the photodetector performance for harsh environment applications. This paper presents the results from proton radiation-hardness tests conducted for two sets of SSPMs designed and fabricated in two different commercial complementary metal oxide silicon (CMOS) processes: $0.18\hbox{-}\mu\text{m}$ and $0.8 \mu\text{m}$ . Following proton exposures to the SSPMs at 100 krad, 500 krad and 1 Mrad, the measured proton induced dark noise at unity gain is higher in $0.18\hbox{-}\mu\text{m}$ SSPMs, but the dark current in Geiger mode is higher in $0.8 \mu\text{m}$ devices. The results and analysis suggest a higher proton-induced surface/sidewall dark current than bulk dark current in $0.18\hbox{-}\mu\text{m}$ samples. The proton induced bulk defect densities are similar between $0.18\hbox{-}\mu\text{m}$ and $0.8 \mu\text{m}$ SSPMs. Reasonable excess noise measurement results were obtained in $0.18\hbox{-}\mu\text{m}$ SSPM samples, and inter-pixel cross talk and after-pulsing remain statistically unchanged after proton exposure. The radiation insensitivity of after-pulsing noise suggests that shallow trap density responsible for after-pulsing is not significantly affected by proton irradiations in these CMOS high gain photodetectors.

A detector based on silica fibers for ion beam monitoring in a wide current range

A detector based on doped silica and optical fibers was developed to monitor the profile of particle accelerator beams of intensity ranging from 1 pA to tens of μA. Scintillation light produced in a fiber moving across the beam is measured, giving information on its position, shape and intensity. The detector was tested with a continuous proton beam at the 18 MeV Bern medical cyclotron used for radioisotope production and multi-disciplinary research. For currents from 1 pA to 20 μA, Ce3+ and Sb3+ doped silica fibers were used as sensors. Read-out systems based on photodiodes, photomultipliers and solid state photomultipliers were employed. Profiles down to the pA range were measured with this method for the first time. For currents ranging from 1 pA to 3 μA, the integral of the profile was found to be linear with respect to the beam current, which can be measured by this detector with an accuracy of ∼1%. The profile was determined with a spatial resolution of 0.25 mm. For currents ranging from 5 μA to 20 μA, thermal effects affect light yield and transmission, causing distortions of the profile and limitations in monitoring capabilities. For currents higher than ∼1 μA, non-doped optical fibers for both producing and transporting scintillation light were also successfully employed.

Scintillation neutron detectors based on solid-state photomultipliers and lightguides

Neutron detectors based on scintillation screens ZnS(Ag)/LiF and solid-state photomultipliers have been developed. Lightguides are used to collect light. The application of a coincidence scheme provides a low dark count and a neutron detection efficiency as high as 70%. A scheme of x-y neutron detector based on wavelength shifting fibers is also proposed. Tests of the proposed versions of detectors in a neutron beam have shown their efficiency.

A single-mode data acquisition architecture for PET/MRI.

The development of MRI compatible detectors based on compact solid state photomultipliers has recently led to simultaneous fully integrated PET/MRI systems for human imaging. The PET acquisition design for MRI integration is known to have several additional constraints, including smaller space, electromagnetic compatibility issues and thermal management. The current work presents the PET acquisition architecture that has been developed for the TRIMAGE project, whose aim is to provide a cost effective, commercial grade trimodality PET/MRI/EEG scanner. The TRIMAGE PET component consists of 216 modules of 2.5 cm x 2.5 cm, arranged in 18 rectangular detectors of 5 cm x 15 cm, the latter in the axial direction, to form a full ring of 31 cm diameter. Each module consists of a staggered dual layer LYSO matrix read out by two arrays of 4 x 8 SiPMs and an ASIC. The detector board hosts a low-power low-end FPGA that performs pixel identification, energy calibration and handles the communication between the ASICs and the motherboard, which is located in proximity of the scanner. Data is streamed using high-density shielded cables and high-speed LVDS transmission to 9 low-end SoC FPGAs and from there to a central mainboard where coincidences and events statistics are processed. Coincidence data is finally transmitted to a host PC for image reconstruction. The proposed architecture and technological solutions will be presented and discussed.

SiPM prototype for direct VUV registration

A number of proposed experiments aimed at dark matter studies are based on detection of luminescence in liquid argon at 128nm. Existing solid-state photomultipliers do not have the capability to detect emission at 128nm in the photon counting mode. Spectral properties of a new silicon photomultiplier prototype for vacuum ultraviolet registration are presented. The prototype demonstrates the photon detection efficiency about 1% in 112–182nm range.

Single-Photon Detectors: From Traditional PMT to Solid-State SPAD-Based Technology

Solid-state photomultipliers (SSPM) made by multielement SPAD (single-photon avalanche detector) are nowadays jousted to replace the traditional, vacuum-tube photomultipliers (PMT) based on the photocathode and dynode-chain technology. We revisit the milestones and the conceptual steps leading to single-photon detectors, from the PMT to the SSPM. Then, we discuss state-of-the-art performances of the two detectors and point out that SSPMs are equalling or even surpassing PMTs for response time and sensitivity, while are still lagging for acceptance area, linearity and dark current. We finally compare the detectors in applications to pulse spectrometry, fast waveform analysis, and photon counting.

Shortwave infrared negative feedback avalanche diodes and solid-state photomultipliers

In recent years, significant progress has been made in InP-based Geiger-mode single photon avalanche diodes (SPADs), and a variety of circuits for enabling Geiger-mode operation have been proposed and demonstrated. However, due to the inherent positive feedback of the impact ionization avalanche process, Geiger-mode SPADs are constrained by certain performance limitations, particularly with regard to counting rate and the inability to resolve photon number. To overcome some of the performance limitations of regular SPADs, we have developed negative feedback avalanche diodes (NFADs) that employ a negative feedback mechanism to regulate the avalanche process. The NFAD fabrication process is based on the design platform we use to achieve state-of-the-art performance SPADs and is very flexible. The operation of NFAD devices is also very simple, with only a direct current (DC) bias being required. Various discrete devices and matrices composed of different elements have been designed, fabricated, and characterized. For discrete devices, ∼10% photon detection efficiency has been realized consistent with acceptable afterpulsing probability. The negative feedback mechanism significantly improves the uniformity of the output pulse heights and avalanche charge per detection event, resulting in a low “charge excess noise” factor. When configured in a matrix format, the NFAD devices were demonstrated to have the ability to resolve photon number and work effectively as solid-state photomultipliers (SSPMs) in the shortwave infrared (SWIR) region. The InGaAs/InP NFAD SSPMs have the potential to replace photomultiplier tubes and provide a solid-state solution in applications where the requirement for single-photon sensitivity in the SWIR region beyond ∼0.9 μm cannot be met by silicon photomultipliers. The NFAD devices have been used in various quantum optics and quantum key distribution applications and demonstrated an excellent performance.

Wireless, low-cost, FPGA-based miniature gamma ray spectrometer

A compact, low-cost, wireless gamma-ray spectrometer is a tool sought by a number of different organizations in the field of radiation detection. Such a device has applications in emergency response, battlefield assessment, and personal dosimetry. A prototype device fitting this description has been constructed in the Advanced Radiation Instrumentation Laboratory at Oregon State University. The prototype uses a CsI(Tl) scintillator coupled to a solid-state photomultiplier and a 40MHz, 12-bit, FPGA-based digital pulse processor to measure gamma radiation, and is able to be accessed wirelessly by mobile phone. The prototype device consumes roughly 420mW, weighs about 28g (not including battery), and measures 2.54×3.81cm2. The prototype device is able to achieve 5.9% FWHM energy resolution at 662keV.

A Study of Position-Sensitive Solid-State Photomultiplier Signal Properties.

We present an analysis of the signal properties of a position-sensitive solid-state photomultiplier (PS-SSPM) that has an integrated resistive network for position sensing. Attractive features of PS-SSPMs are their large area and ability to resolve small scintillator crystals. However, the large area leads to a high detector capacitance, and in order to achieve high spatial resolution a large network resistor value is required. These inevitably create a low-pass filter that drastically slows what would be a fast micro-cell discharge pulse. Significant changes in the signal shape of the PS-SSPM cathode output as a function of position are observed, which result in a position-dependent time delay when using traditional time pick-off methods such as leading edge discrimination and constant fraction discrimination. The timing resolution and time delay, as a function of position, were characterized for two different PS-SSPM designs, a continuous 10 mm × 10 mm PS-SSPM and a tiled 2 × 2 array of 5 mm × 5 mm PS-SSPMs. After time delay correction, the block timing resolution, measured with a 6 × 6 array of 1.3 × 1.3 × 20 mm3 LSO crystals, was 8.6 ns and 8.5 ns, with the 10 mm PS-SSPM and 5 mm PS-SSPM respectively. The effect of crystal size on timing resolution was also studied, and contrary to expectation, a small improvement was measured when reducing the crystal size from 1.3 mm to 0.5 mm. Digital timing methods were studied and showed great promise for allowing accurate timing by implementation of a leading edge time pick-off. Position-dependent changes in signal shape on the anode side also are present, which complicates peak height data acquisition methods used for positioning. We studied the effect of trigger position on signal amplitude, flood histogram quality, and depth-of-interaction resolution in a dual-ended readout detector configuration. We conclude that detector timing and positioning can be significantly improved by implementation of digital timing methods and by accounting for changes in the shape of the signals from PS-SSPMs.