— Novel Instrumentation for Nuclear Fuel Cycle Monitoring
Forthcoming: 3:00 ~ 4:00 pm (ET),
- January 26, 2023, Prof. Steven Ringel (OSU): Ga2O3 defects.
October 27, 2022
- Prof. Anant Agarwal (OSU), “SiC Diodes for Radiation Sensors”
Abstract: SiC diodes offer a possibility of extremely low dark current to enable highly sensitive radiation detectors at room temperature. SiC diodes can be fabricated in 3 different types: 1. Schottky Barrier diodes, 2. Implanted PiN diodes, and 3. Epitaxial PiN diodes. Epitaxial PiN diodes offer the prospects of lowest dark current of the three diode types whereas Schottky diodes tend to have the largest dark current. The implanted diodes show intermediate level of dark current. Given the present status of materials and fabrication technology, there is significant variation in dark current among a batch of diodes made at the same time, batch to batch and substrate material from different vendors. This points to defects in the SiC material as being the primary cause for leakage currents.
In this presentation, we will show dark current data from different types of SiC diodes and discuss the techniques for future improvements in the materials and fabrication technology. Once low dark current can be uniformly obtained over many diodes, bigger diode assemblies can be produced to improve the sensitivity of the detectors. The Readout circuit is equally important to use the detectors in an effective manner. For best performance, it is important to integrate the readout circuits in SiC CMOS technology in future. Some initial progress in this direction will be discussed.
August 25, 2022
- Dr. Yuguo Tao (Prof. Anna Erickson’s group, GT), “An Overview of SiPM Fundamentals and Our Recent Research Progress”
Abstract: Silicon photomultiplier (SiPM) has been attractive in many areas due to its low operation voltage, insensitivity to magnetic field, robustness and compactness. In this talk, we will give an overview of the fundamentals of SiPM, including its theory of operation, the device design physics, and the description of the main parameters, such as internal gain, photon detection efficiency, quantum efficiency, the primary and correlated noise sources. In addition, we will share a flashback of our development of SiPM design, including the selective emitter to reduce metal-induced carrier recombination, the atomic-layer deposited Al2O3 to reduce surface recombination, and the back-illuminated SiPM structure with multi-layer antireflection coatings on upright nano-micro pyramids to reduce photon losses due to reflection and to minimize or eliminate the dead areas (such as quenching resistor, contact metal, guard ring, and isolation trench) on the detector side where the photons are incident.
July 28, 2022
- Sushovan Dhara (Prof. Siddharth Rajan’s group, OSU), “Development of 𝛽-Ga2O3 Trench Schottky Diodes by Novel Low-Damage Ga-Flux Etching for radiation sensing applications”
Abstract: Wide bandgap (WBG) electronic materials such as 𝛽-Gallium oxide (𝛽-Ga2O3) have recently attracted interest for their increased performance in high-frequency, high-power applications when compared to existing Silicon microelectronics. Another advantage of such WBG semiconductors is that it is less susceptible to displacement-induced degradation and can operate under high-temperature. For radiation sensing applications, vertical device architectures like Schottky barrier diodes (SBDs) can be useful as particle detectors. In this work, we demonstrate the development of 𝛽-Ga2O3 trench Schottky barrier diode for extreme environment operation and radiation sensing applications. The trench structures were formed using a novel damage-free Ga-etching technique. A high-quality aluminum oxide dielectric layer deposited by molecular beam epitaxy was integrated into the device structure. Metal-oxide-semiconductor (MOS) capacitors fabricated with this Al2O3 dielectric layer exhibited a low hysteresis and confirm the presence of negative Al2O3 fixed charges. Further, DC electrical measurement of the diodes showed a very low reverse leakage current along with a high parallel plate electric field of >4 MV/cm, making it a promising device for extreme-environment operation and radiation sensing applications.
June 30, 2022
- Prof. Raymond Cao (OSU), “Development of WBG sensors for radiation detection in a harsh environment”
Abstract: The research update from Dr. Cao’s group will be focused on the development of wide band-gap (WBG) semiconductors, namely 4H-SiC, GaN and b-Ga2O3, for their applications in the fuel cycle monitoring of actinides. One case study will be firstly presented for a packaged SiC Schottky diode with uranium isotope electrodeposited onto its metal contacts while being immersed in melting salt at 550 C. The alpha particles spectrum was then directly acquired from the preconcentrated uranium to determine the ratio of U-234 and U-238 concentrations. With this application in mind, we continued our study by electroplating Am-241 onto the Schottky metal of in-house fabricated SiC sensors with a dual purpose as an alpha voltaic battery. The long-term radiation damage is studied by continually monitoring the spectroscopic performance of the fabricated sensor. Interestingly, the constant charge generation by alpha particles inside the SiC under bias will distort the spectrum, which is attributed to the polarization due to charge trapping. The spectrum can be controllably returned to its normal shape after photoexcitation by a blue laser. On GaN, we are trying to demonstrate its intrinsic neutron sensitivity by N-14(n,p)C-14 reaction through fabrication, test, and irradiation of GaN Schottky devices. Finally, I will also present our latest radiation sensor fabrication and testing based on b-Ga2O3, which is considered the replacement for Si but still suffer intrinsically from its low electron mobilities at <200 cm^2/V-s at 300 K for donor doping densities lower than 10^18 cm^3.
May 26, 2022
- Caleb Chandler (Prof. Alan Sellinger’s group, CSM), “Advancing Plastic Scintillator Performance and Fabrication”
Abstract: Plastic scintillators are used to detect ionizing radiation by producing an optical light response. Traditionally these detector materials have consisted of a radically polymerized matrix, such as poly(vinyltoluene), that is responsible for solubilizing fluorophores, establishing transparency, and maintaining structural integrity. Our research aims to improve the plastic scintillator space by exploring different matrix materials and new methods of fabrication. This talk will provide updates on our use of elastomeric polysiloxane matrix materials, and our work towards additively manufacturing poly(vinyltoluene) via a photoinitated cationic polymerization. Several polysiloxane matrices have been screened and modified for use as scintillators. Small molecules containing covalently linked boron-10 have been incorporated into the polysiloxanes for thermal neutron detection capabilities. In other work, thermoplastic poly(vinyltoluene) has been cured with kinetics similar to those of commercial acrylate-based 3D printing resins. Current successes and challenges associated with vat-style printing of this photoinitiated formulation will be presented.
April 28, 2022
- Prof. Andreas Velten (UW), “Single Photon Cameras for Radiation Detection”
Abstract: We present our design and simulation for a gamma source imaging system based on a scintillator and a single photon camera. Single Photon Avalanche Diode cameras are an emerging camera sensor that is able to detect individual photons in each pixel and record their arrival times with up to picosecond precision. SPAD sensors can be manufactured using the same CMOS foundries and processes that are applied to regular CMOS cameras resulting in similar sensor cost and readily available sophisticated manufacturing infrastructure. This has resulted in a rapid increase in the resolution of SPAD cameras at decreasing cost. Utilizing these sensors for radiation detection enables compact and inexpensive instruments with capabilities that currently are only available in much larger and complex detectors. In this presentation I will go over our ongoing work to implement the first SPAD camera based gamma imaging system.
March 24, 2022
- Oliver Moreno (Prof. Bernard Kippelen’s group, GT), “Enabling Low-Cost Radiation Detectors Through Organic Electronic Device Design, Fabrication, and Integration”
Abstract: The first part of our presentation focuses on device innovations performed by our group at Georgia Tech. Our group has developed stretchable organic photodiodes with performance adequate for low-light level detection. The stretchability matches the mechanical properties of human skin, appropriate for wearable electronics and detectors with deformable form factors. The devices show low electronic noise currents in the range of tens of femtoamperes, noise equivalent power (NEP) in tens of picowatts at 60% strain, response time of 142 μs, and a high strain at break of 189% . This was achieved using a blend of an elastomeric material SEBS, with P3HT and ICBA donor/acceptor materials. We also show progress in 3D-printable plastic scintillators utilizing Bi-containing compounds and organic dyes exhibiting delayed fluorescence for enhanced capture cross-section and light yield.
The second part of our presentation discusses our collaborative work with the Electronic Detector Group at Brookhaven National Laboratory. Our collaboration has entered the prototype phase to study large volume kton water-based liquid scintillators (WbLS), useful for high-energy particle physics experiments, and potentially remote-monitoring and sensing of nuclear fuel cycles for nonproliferation. There is an operational 1 ton prototype detector, consisting of a tank capable of testing variants of WbLS. Work is ongoing in DAQ system, data analysis, and simulations, with a focus on separating Cherenkov and scintillation light from charged particles and high energy gamma rays. Future work will focus on quantifying probability of detection, and spectral discrimination of gamma rays and neutrons by incorporation of low-cost metal photocathodes, organic electronic surface modifiers, and optical filters.
February 24, 2022
- Kate Thompson (Prof. Philip Townsend’s group, UW) “Bioindicators for early detection of environmental contamination”.
Abstract: High metal concentrations in soils are associated with agricultural inputs, mining, munitions activities, and other industrial processes. Metal contamination can jeopardize human health, compromise food safety, and lower crop productivity. Furthermore, high metal concentrations can profoundly alter ecosystems by inhibiting biomass production, plant recolonization, and community assembly. These risks are functionally under-quantified because conventional methods are not feasible for monitoring contaminants through time or at relevant scales for management decisions.
Hyperspectral remote sensing is widely used to monitor plant stress, agricultural productivity, and plant functional traits because it quantifies changes in plant chemistry and physiology without labor-intensive or destructive sampling. By identifying diagnostic spectral features of environmental stressors, spectral profiles of vegetated landscapes could be operationalized as passive, non-destructive, and low-cost bioindicators to monitor the environment for contaminants.
In 2021, I conducted a field experiment to explore whether hyperspectral imaging could identify unique, pre-visual stress indicators in vegetation exposed to chromium (VI), copper, and a combination of copper and drought. Data processing and analysis are still underway, so preliminary results are not yet available. However, I will present the experimental setup and qualitative data exploration that I expect to be valuable milestones in developing bioindicators for early detection of environmental stressors.
January 27, 2022
- Prof. Jinsong Huang (UNC), “Metal Halide Perovskites for Radiation Detection”.
Abstract: Metal halide perovskites are increasingly explored for radiation detection after their booming in solar cells applications. Their unique defect properties, which are found to be critical in contributing to the very high efficiency solar cells from the very defective films, can also be utilized for light or charge conversion and collection processes in radiation detectors. In this talk, I will brief the understanding and advance in metal halide perovskites as room temperature semiconductor detectors, scintillators, as well as photodetectors that convert radiation quanta into electric signal in direct or indirect modes. Perovskite materials of single crystals, polycrystalline films, and nanoparticles will be covered which address different challenges of radiation detection.
October 28, 2021
- Evan Cornuelle, Joe McGlone, Aaron R. Arehart and Prof. Steven A. Ringel (OSU), “Radiation-induced defects in gallium oxide materials and devices”.
Abstract: gallium oxide devices are of significant interest for applications in radiation environments and detection systems due to several unique materials properties such as its very wide bandgap (4.8 eV) that leads to potential very sensitive, low dark current detectors, and its very high chemical bond strength that leads to projections of superior resistance to radiation so that devices and circuits can be used for applications in radiation environments that greatly exceed the capabilities of conventional Si technologies. However, compared with conventional electronics, gallium oxide is at a very early stage of development and only in the past few years have high performance devices been demonstrated. This presentation covers the status of knowledge regarding how high energy particle irradiation influences properties of the component layers that comprise gallium oxide FETs, with a particular focus on the creation of traps due to neutrons and protons, and how these affect transistor performance parameters.
September 23, 2021
- Muhammad Ismail Khan (OSU), “Progress Towards an Integrated Silicon-Carbide Neutron-Detector Module”.
Abstract: Silicon carbide (SiC) is a semiconductor with wide bandgap energy, which makes it attractive for high-temperature applications, most notably power electronics. Historically, there has also been an interest in using SiC for neutron detection, due to the semiconductor’s temperature tolerance and radiation hardness. Researchers have demonstrated the effectiveness of Schottky and p-i-n SiC diodes as radiation detectors. This project aims to continue this research endeavor with the development of an integrated SiC neutron-detector module consisting of a diode detector and readout circuitry integrated on a common substrate. Both ion implantation and epitaxial growth will be used for fabrication detector diodes at a local facility. For the readout circuitry, there is interest in the conventional scheme of pulse-height spectroscopy as well as in the scheme demonstrated for single photon detection. Challenges in the project include obtaining good charge collection efficiency, handling high bias voltage, reducing leakage current, determining optimum fabrication procedures, and gaining access to foundries and testing facilities.
August 26, 2021
- Haley Schramm (WSU), “Probing Molecular Mechanisms of Radioresistance: Toward Tunable Pigmentation for Passive Fungal Sensor Arrays of Radiation Exposure”
Abstract: Enhanced growth is often observed for irradiated, melanized fungi. While well documented, the chemical and physical mechanisms of radioresistance have not been decoupled from cellular growth. A suitable model organism, Exophiala dermatitidis, is a highly studied fungus with its genome fully sequenced. Both a melanized, wild type strain and a genetically modified albino mutant have been obtained and cultured. Initial experiments suggested that melanin was directly connected to radioresistance. However, transcriptomic studies proved inconclusive in identifying gene products that are causal in radioresistance between the wild type culture and an albino mutant. By quantitatively measuring protein differences in the wild type, melanized culture and the albino mutant, existing distinctions with respect to the origins of radioprotection in melanized fungi will be addressed. Applicable strains of E. dermatitidis that are suitable for both broad-scale fundamental studies of radioprotection and their potential for use in variable pigmentation arrays as biosensors for radiation will be developed.
June 24, 2021
- Dr. Yuguo Tao (GT), “Optimization of SiPM Photosensing at Ultraviolet Wavelength”
Abstract: In conjunction with scintillators, SiPM have become very active in the investigation area of nuclear instruments and methods as an alternative to photomultiplier tube (PMT) to detect light with very low intensity. However, the peak value of photo-detection efficiency (PDE) of conventional SiPM is still limited to around 50%. Among the efficiency limiting factors are avalanche triggering probability, geometrical fill factor, and quantum efficiency (QE), which is limited to 80% at the peak. Furthermore, QE is rapidly reduced from the peak value as the wavelength enters ultraviolet range, due to three main factors: (1) photon losses due to the reflection at Si surface capped with SiNx layer as conventional antireflection coatings (ARC); (2) surface recombination of the photo-generated primary carriers at the Si surface where defect centers (ie. dangling bonds) are passivated with conventional SiO2; (3) Auger recombination of the photo-generated primary carriers within the heavily doped p+ layer prior to transverse to the high field region to trigger an avalanche event. In this talk, we will cover three technical strategies for increasing quantum efficiency at ultraviolet wavelength range: multi-layer antireflection coatings, Si surface passivation, and selective emitter. Our objective is to reveal the materials and device physics that currently limit overcoming the fundamental bottlenecks (photon reflection and carrier recombination), and to demonstrate high device performance for ultraviolet sensitive SiPM.
May 27, 2021
- Prof. Siddharth Rajan (OSU), “Fundamentals and Current Status of III-Nitride based High-Performance Transistors”
Abstract: Transistors based on the III-Nitride semiconductor system (GaN, AlGaN, and AlN) are being used increasingly across a range of applications for communication, radar, and efficient power electronics. In this presentation, I will discuss the fundamentals of III-Nitride transistors for RF, power, and logic applications. I will outline some unique aspects of device design for III-Nitride transistors, including band engineering, polarization, and device characteristics. I will then discuss some novel approaches for transistors with improved performance for RF applications that we have been pursuing in the last years. Finally, I will discuss our recent work under the ETI program on realizing III-Nitride logic circuits for radiation-tolerant applications.
March 25, 2021
- Neil Taylor (OSU), “Evaluation of Metal Printing and Cleanroom Fabricated SiC and Ga2O3 Radiation Sensors”
Abstract: Aerosol inkjet deposition is a type of 3D printing that enables the deposition of functional material onto a substrate. Fabrication of radiation and temperature sensors can be achieved rapidly and easily through the deposition of metal nanoparticle inks onto a semiconductor wafer. These devices offer a simple, yet effective device configuration capable of high energy resolution alpha spectroscopy. They represent a well-suited candidate for the implementation of AM into the nuclear field. Silicon carbide, a wide band gap semiconductor, has been explored as an alternative to silicon that can operate at elevated temperatures and harsh environments. Silicon carbide Schottky diode radiation detectors were fabricated using aerosol inkjet deposition and compared current best cleanroom fabricated silicon carbide devices. A variety of metal inks including gold, silver, nickel, and platinum were all tested. The temperature sensing capability of the silicon carbide devices were explored as a possible dual use of the devices. The temperature sensing of the devices was further explored using a wireless passive printed device. Simulation of printed layer’s effect on resolution and the detection capability of the printed devices were simulated using MCNP and SRIM. Hexagonal boron nitride ink was printed on top of previously printed devices to investigate the ability to print a neutron conversion layer. Gallium oxide stands as another wide bandgap material for possible usage as next generation power electronic devices and radiation detectors. This material has similar properties to silicon carbide such as a high band gap, high breakdown electric field, and good thermal and chemical stability. Devices fabricated from gallium oxide were characterized electrically and tested for their radiation detection capabilities through alpha and X-ray irradiation.
February 25, 2021
- Caleb Chandler (CSM), Jonathan Arrue (GT), “Tailoring Polysiloxane Matrices in Plastic Scintillators for Pulse Shape Discrimination”
Abstract: Plastics have found use as scintillators due to their relative ease of fabrication, stability, light-weight, and ability to distinguish gamma and neutron response through pulse shape discrimination (PSD). A renewed interest in polysiloxanes as a matrix material in scintillators has recently shown that competitive PSD and light yield can be achieved using lower dopant loadings (<5 wt% versus > 20wt% in polyvinyltoluene). Current efforts have been directed towards synthesizing siloxanes tailored specifically for radiation detection. Through a collaborative cycle of synthesis and measurement, advancements have been made towards identifying and optimizing high phenyl content polysiloxane scintillators for PSD. Measurements and analysis have also been performed on PSD dependence on temperature. Current measurements are above ambient room temperature but future experiments will be completed below ambient temperature. Future approaches to improving detection capabilities of these polymer-based scintillators will be discussed.
January 28, 2021
- Prof. Andreas Velten (UW), “Capturing dynamic scenes with single photon avalanche diode array cameras”
Abstract: Single Photon Avalanche Diode Arrays are cameras where each pixel can timetag the arrival of individual photons with picosecond time resolution. CMOS SPAD cameras with growing spatial resolutions are becoming available and are part of a growing number of consumer devices from simple LiDAR proximity sensors, to the 3D imaging system on the latest iPhone. While the primary current commercial application for SPAD arrays is Light Detection and Ranging (LiDAR) for 3D imaging, applications in passive imaging and imaging of ultra-fast events, such as fluorescence lifetime, are also being explored. The basic task of a SPAD pixel is the same as that of a regular camera pixel: Estimate the light flux as a function of time. The way this task is achieved, however, is so different that many of the concepts and methods that we use to describe cameras and to process their data, do not apply. SPAD array cameras don’t have a frame exposure time and therefore don’t exhibit the motion blur that occurs in conventional cameras. SPAD pixels don’t saturate like regular camera pixels. Their noise is dominated by Poisson noise while many computational imaging methods work only with additive Gaussian noise. In this talk I will introduce our algorithms for motion deblurring and high dynamic range imaging of SPAD videos.
November 24, 2020
- Prof. Philip Townsend, Kate Thompson (UW), “Hyperspectral remote sensing for nonproliferation”
Abstract: We use hyperspectral remote sensing (from the leaf level to satellites) to characterize plant physiology and chemistry. We ask weather vegetation signals in spectral data can be used as an indicator of plant exposure to radiation or bi-products. Our research as part of ETI involves collaboration with National Labs on existing studies. Specifically, we outline the three studies that we are pursuing to test the capabilities of hyperspectral imaging.
- Prof. Bernard Kippelen (GT), “An introduction to organic semiconductors and their use in optoelectronic devices”
Abstract: In this presentation we will review the basics of organic semiconductors and their use in solid-state optoelectronic devices. The discussion is intended for the non-expert in organic electronics but with a solid understanding of traditional semiconductor material and device physics. The photophysics and electrical properties of organic molecules and polymers will be reviewed and the key enabling technologies necessary to fabricate high performance devices will be presented. Finally, the modeling and key metrics of organic photodiodes and their relevance for radiation detection will be discussed.
October 22, 2020
- Prof. Steven Ringel (OSU), “High Energy Particle Radiation Studies of Gallium Oxide and Aluminum Gallium Oxide”
Abstract: Beta-phase gallium oxide (β-Ga2O3) has material properties that have generated a large and growing interest for applications in opto-electronics, power devices, and RF devices. The wide bandgap of ~4.6-4.8 eV leads to a large breakdown field that increases the Baliga and Johnson figures of merit, indicating potentially superior performance in high power and high frequency devices. The large bandgap also indicates a propensity for better radiation hardness due to higher required displacement energies making gallium oxide of great interest for electronic devices used in systems for radiation sensing and harsh radiation environments. The complimentary material aluminum gallium oxide enables heterostructures which can be realized to expand the range of potential devices. This work will focus on understanding the changes caused by proton radiation for each defect level and also getting a baseline of the β-(AlxGa1-x)2O3 material quality and defect spectrum. With the knowledge of which defects are intrinsic and respond to radiation, theoretical studies for the displacement energies and possible intrinsic defects associated with each level will be discussed.
- Prof. Milton Garces (UH), “Assessment of ML-Capable Cyber-Physical SWAP-C COTS Data Collection and Computing Platforms”
Abstract: New smartphone data collection and computing apps under development will acquire additional metrics to permit quantitative cost-benefit analyses of small size, weight, power and cost (SWAP-C) platforms. The initial testing platforms are newer, commercial off-the-shelf (COTS) Android and iOS smartphones and tablets (presently targeting Android OS 10 and iOS 11 and greater) with on-board machine learning (ML) capabilities. We are expanding development to single-board computing environments. A cross-platform application programming interface (API M) is presently in the implementation, testing, and evaluation stage. API M will facilitate collection of finer-grained metrics on temperature, power, and communications to accompany enhanced data collection and edge computing capabilities. New data acquisition platforms have been purchased for testing and evaluation under API M in FY21. The Nvidia Jetson developer kits are designed for edge ML applications have substantial computing power given their relatively small size, and low weight, power consumption, and cost. Three Nvidia developer kits were chosen for evaluation: the Jetson Nano, the Jetson Xavier NX, and the Jetson AGX Xavier; the least powerful being the Nano and the most powerful being the AGX Xavier. The Nano has a 128 core, Maxwell based GPU with a quad core ARM processor and 4 GB of LPDDR4 ram. The theoretical performance is 472 GFLOPs (FLOPS = single-precision floating point operations per second). The Xavier NX has a 384 core GPU with 48 Tensor cores coupled with a 6 core ARM processor and 8 GB of LPDDR4 ram. Its theoretical performance is 21 Tera operations per second (TOPS). TOPS can be integer or float operations. The AGX Xavier has a 512 core, Volta GPU with 64 tensor cores. It has an 8 core ARM processor and 32 GB of LPDDR4 ram and its theoretical performance is 32 TOPS. A Linux-based app client is being tested on a Jetson Nano with a USB microphone. For comparative testing, Raspberry Shake & Booms were purchased. These are plug and play Raspberry Pi 3 single board computers coupled with a single vertical geophone velocity sensor with an infrasound sensor, a 24-bit digitizer, and a hyper-damper. The Raspberry Shake & Booms are capable of recording at 100 samples per second and can stream miniseed data either to the public shake server or to private, conventional data acquisition servers such as Seiscomp3 or Earthworm instances. Tests are also continuing of Raspberry Pi 3 platforms running both Linux and Android. In addition, Seeed Studio ReSpeaker USB and expansion board microphone arrays have been procured for integration and evaluation. Data acquisition, processing, streaming, command, control, communication, and computing (C4) capabilities of these SWAPC platforms will be compared to those of Android and iOS smartphones and tablets.
September 24, 2020
- Peter Rudd (UNC), “Observing charge trapping in metal halide perovskites using time-resolved photoluminescence to assess material quality for photodetector application”
Abstract: Metal halide perovskite (MHP) materials have arisen in the past decade as a highly promising high-efficiency, low-cost technology for many semiconductor applications such as ionization radiation detection, photodetectors, and photovoltaics. Particularly, MHP photodetectors have demonstrated high detectivity with fast response times. The performance of MHP devices is highly dependent on the material quality. Time-resolved photoluminescence (TRPL) is frequently used to quickly assess the quality of metal halide perovskite (MHP). Often these photoluminescent transients can be misinterpreted in that decay lifetimes are directly assigned to be the charge carrier lifetime. Here using excitation intensity and temperature dependent TRPL measurements of both MAPbI3 and perovskites with mixed cations (MA+, FA+, Cs+) and anions (I–, Br–), we observe the strong influence of charge carrier trapping on the TRPL curves, which is strongly dependent on both film quality and experimental conditions. Films with higher trap densities measured by thermal admittance spectroscopy can actually demonstrate longer TRPL lifetimes, suggesting that longer PL decay lifetimes do not necessarily equate to perovskite films with improved optoelectronic properties. We adapt a model of a charge trapping, detrapping, and recombination processes in semiconductors to demonstrate the strong influence on the TRPL transients made by trap state distributions and capture mechanisms, which in the presence of very strong trapping manifest as strict biexponential decay transients. To more effectively utilize TRPL as an assessment of perovskite film quality, we suggest the decay measurements be presented with the full context of experimental conditions and other techniques such as steady-state PL intensity and trap density measurements, to ensure the proper conclusions are reached regarding charge carrier recombination and trapping within the perovskite thin films. Better understanding of how to properly interpret the TRPL transients of MHP materials provides the ability to quickly assess material quality and thus their potential application as a photodetector.
- Prof. Anant Agarwal (OSU), “Development of SiC Diodes and CMOS Circuits for Neutron Detector Array”
Abstract: The radiation detectors based on silicon carbide (SiC) with wide energy gap are the most promising ionizing radiation detectors in high temperature and harsh radiation environments. Neutron measurement in nuclear fuel cycle or in other high radiation field are among the applications of these detectors. Today, SiC technology has matured to a point where SiC CMOS technology is being developed for many applications. The ongoing work in SiC CMOS IC technology will be described and how this leads to a neutron sensor array to be fabricated under this project. The array of PiN diodes along with readout circuits with each diode is a way to build a large neutron detector. The technical issues with building a monolithic readout circuit will be described.
July 23, 2020
- Yuguo Tao, Arith Rajapakse, Luke Maloney, Jonathan Arrue, and Anna Erickson (GT), “Study of Excellent Surface Passivation Provided by Atomic Layer Deposited Al2O3 for SiPM”
Abstract: Carrier recombination on the active area surface is one of critical factors limiting quantum efficiency and thus photo-detection efficiency of silicon photomultipliers (SiPM). In this talk, we will share our study on an excellent passivation of boron-doped p-type (p+) silicon surfaces by Al2O3 thin film that is synthesized by plasma-assisted atomic layer deposition (ALD), including a comparison study with thermal SiO2 and SiNx. In addition, Al2O3 thin film can also yield very low values of effective surface recombination velocity on low resistivity n-type and p-type silicon, which should maintain well-passivated surfaces on guard ring and trench isolation regions of SiPM. These demonstrate the potential of Al2O3 passivation on p+ surfaces to improve quantum efficiency thus photo-detection efficiency of SiPM device with p+/ n–/n/n+ structure. Further investigation is in process by employing Al2O3 passivation into SiPM prototype device.
- Haley Schramm (WSU), “Probing Molecular Mechanisms of Radioresistance in Melanized Fungus”
June 25, 2020
- Prof. Alan Sellinger (MINES), “Polysiloxane matrices in plastic scintillators for efficient pulse shape discrimination”
Abstract: Plastics have found use as scintillators due to their relative ease of fabrication and ability to distinguish gamma and neutron response through pulse shape discrimination. In the last decade, a renewed interest in applying polysiloxanes as a matrix in these scintillators has resulted in materials with better radiation hardness and faster fabrication time. Recent efforts have shown that competitive pulse shape discrimination and light yield can be achieved using lower dopant loadings (5 wt% or less) in polysiloxanes versus traditional PVT-based (> 20 wt%). These advances have also brought forth fundamental questions concerning why polysiloxanes outperforms traditional plastic scintillators. Current studies of dopant solubility and future work involving synthetic control of matrix composition and excimer formation will be discussed.
- Wyatt Moore, Adithya Balaji, and Siddharth Rajan (OSU), “Recent progress on Ga2O3 sensors and GaN electronics”
Abstract: In this presentation we will discuss our recent work on Ga2O3-based sensors and GaN radiation-tolerant circuits. In the first part of the presentation, we will discuss the design, demonstration, and characteristics of vertical Ga2O3-based Schottky and heterojunction diodes, and designs for future Ga2O3 sensors that could enable lower dark current and higher sensitivity. In the second part of the presentation we will discuss our efforts to develop a broadly accessible platform for GaN-based logic circuits based on enhancement-depletion mode transistor circuit designs.
May 28, 2020
- Prof. Raymond Cao, and Neil Taylor (OSU), “Microelectronic devices: inkjet writing metal contacts on SiC for making alpha detectors”
Abstract: 4H-SiC Schottky diodes with printed gold (Au), silver (Ag), and platinum (Pt) contacts were evaluated for the detection of alpha particles and also compared with cleanroom fabricated devices. TEM of the device cross-sections was performed to investigate the printed metal and semiconductor epitaxial layer interface, which revealed the imperfections in the metal-semiconductor contact. These printed devices have demonstrated the best energy resolution of 1.89% at 5.486 MeV, compared to 0.29% achieved by the best cleanroom fabricated SiC devices.
- Prof. Andreas Velten (UW), “Ultra-Fast Imaging with Single Photon Detectors”
Abstract: Single photon detectors have superior sensitivity and signal to noise ratio to analog detectors. Photon counting techniques, however, are not frequently used in imaging because of difficulties in handling high light levels and complexity of the required electronics. We analyze different strategies for imaging with simple photon counting detectors to improve dynamic range, sensitivity, and spatial resolution.
April 23, 2020
- Prof. Philip Townsend (UW)
- Prof. Bernard Kippelen (GT), “Progress in organic photodetectors: beyond silicon”
March 26, 2020
- Kristen Booth (OSU), “Neutron sensor: SiC PiN diode leakage current experiment”
- Prof. Jinsong Huang (UNC), “Halide perovskites for sensitive, fast weak light detection”
- Prof. Steve Rangel (OSU), “Radiation-induced defects and device effects in wide and ultra-wide bandgap semiconductors”
February 27, 2020
- Prof. Siddharth Rajan (OSU)
- Prof. Brian Clovers (WSU)
- Arith Rajapakse (GT)
January 23, 2020
- Prof. Raymond Cao (OSU)
- Prof. Andreas Velten (UW)
- Prof. Alan Sellinger (CSM)