Detector Structure Research Articles

Pulsed beam monitoring for electron FLASH.

Safe implementation and translation of FLASH radiotherapy to the clinic requirehs development of beam monitoring devices capable of high temporal resolution with wide dynamic ranges. Ideal detectors should be able to monitor LINAC pulses, withstand high doses and dose rates, and provide information about the beam output, energy/range, and profile. Two novel detectors have been designed and tested for ultra-high dose-rate (UHDR) monitoring: a multilayer nano-structured 3-layer high-energy-current (HEC3) detector, and a segmented large area, 4-section flat (S4) detector with the goal of exploring their properties for a future combined design. A Novalis-TX LINAC was converted to produce a 10 MeV electron-FLASH beam. Pulses were monitored using both HEC3 and S4 detectors. The HEC3 detector structure consisted of three electrode layers separated by a nanoporous aerogel (Aero): Al(50µm)-Aero(100µm)-Ta(10µm)-Aero(100µm)-Al(50µm). The S4 structure was comprised of three layers: Cu(100nm)-air(1mm)-Al(100nm) with contact potential for charge collection. Both detectors are self-powered as they do not require an external voltage bias for charge collection. The beam was also characterized using a photodiode, Gafchromic EBT-XD Film, OSLDs, and an Advanced Markus Chamber. The electron-FLASH beam displayed a Gaussian-like profile with 15cm FWHM at isocenter. Electron-FLASH dose rates up to an average of 260Gy/s were measured on the surface of a solid water phantom at isocenter with an instantaneous dose rate of 1.8×105Gy/s and a dose per pulse of up to 1Gy/pulse. Both HEC3 and S4 detectors could record individual pulses for repetition rates of 360Hz with a 4 µs pulse-width. The HEC3 detector signal increased linearly with dose, MU, number of pulses, and dose rate up to 850Gy/s with no loss of functionality at high doses or dose rates. The S4 detector showed linearity with MU and number of pulses at each of the four channels independently showing potential for spatial information and steering but lacked dose rate independence. Two novel detectors, HEC3 and S4, successfully measured electron-FLASH pulses and hence can be considered capable of electron-FLASH beam monitoring in different capacities. HEC3 detector technology is suitable for monitoring high-dose and UHDR beams with high temporal resolution required for pulse counting. We envision the combination of the HEC3 internal structure with the S4 piece-wise design for real-time monitoring of the temporal structure, spatial profiles, energy, and dosimetric properties of UHDR beams.

Electroabsorption in InGaAs and GaAsSb p-i-n photodiodes

The application of an electric field to a semiconductor can alter its absorption properties. This electroabsorption effect can have a significant impact on the quantum efficiency of detector structures. The photocurrents in bulk InGaAs and GaAsSb p-i-n photodiodes with intrinsic absorber layer thicknesses ranging from 1 to 4.8 μm have been investigated. By using phase-sensitive photocurrent measurements as a function of wavelength, the absorption coefficients as low as 1 cm−1 were extracted for electric fields up to 200 kV/cm. Our findings show that while the absorption coefficients reduce between 1500 and 1650 nm for both materials when subject to an increasing electric field, an absorption coefficient of 100 cm−1 can be obtained at a wavelength of 2 μm, well beyond the bandgap energy when they are subject to a high electric field. The results are shown to be in good agreement with theoretical models that use Airy functions to solve the absorption coefficients in a uniform electric field.

Optimization of CMOS Detector Structures coupled with 2.58 THz Miniaturized Differential Antenna and High-Speed Imaging

Optimization of CMOS Detector Structures coupled with 2.58 THz Miniaturized Differential Antenna and High-Speed Imaging

Theoretical Study of Quaternary nBp InGaAsSb SWIR Detectors for Room Temperature Condition.

This paper presents a theoretical analysis of an nBp infrared barrier detector's performance intended to operate at a room temperature (300 K) based on AIIIBV materials-In1-xGaxAsySb1-y quaternary compound-lattice-matched to the GaSb substrate with a p-n heterojunction ternary Al1-xGaxSb barrier. Numerical simulations were performed using a commercial Crosslight Software-package APSYS. The band structure of the nBp detector and the electric field distribution for the p-n heterojunction with and without a potential barrier were determined. The influence of the barrier-doping level on the detector parameters was analyzed. It was shown that Shockley-Read-Hall (SRH) recombination plays a decisive role in carrier transport for lifetimes shorter than 100 ns. The influence of the absorber/barrier thickness on the detector's dark current density and photocurrent was investigated. It was shown that valence band offset does not influence the device's performance. The quantum efficiency reaches its maximum value for an absorber's thickness of ~3 μm. The performed simulations confirmed the possibility of the detector's fabrication exhibiting high performance at room temperature based on quaternary compounds of AIIIBV materials for the short wavelength infrared range.

Room temperature mid-wave infrared guided mode resonance InAsSb photodetectors

We demonstrate room temperature operation of mid-wave infrared photodetectors leveraging a guided mode resonance architecture and bulk alloy InAsSb absorbers. Room temperature operation with low dark current is achieved by using detector structures with ultra-thin (150, 250 nm) absorbers leveraging the strong confinement enabled by the guided mode architecture. Devices with 1D and 2D grating arrays are fabricated and characterized, and compared to unpatterned detector devices. We see enhancement in the detectors’ optical response associated with coupling to both TE- and TM-polarized guided modes and good agreement between experimental and theoretically-predicted behavior. We show strong enhancement for unpolarized light incident on 2D grating arrays, with a broader spectral response than observed for polarized light incident upon 1D grating GMR detectors. The bulk InAsSb detectors presented in this work offer enhanced performance at room temperature for a range of imaging and sensing applications.

A double-sided 3D trench electrode detector using an 8-inch CMOS process: 3D simulation and experimental investigation

A double-sided 3D trench electrode detector (DS-3DTED) structure is proposed in this work to investigate the manufacturing process implementation of 3D detectors for high-energy physics, x-ray spectroscopy and x-ray cosmology applications. The device's electrical characterization, including electrostatic potential and electric field distributions, I–V, C–V, full depletion voltage and transient current with x-ray incidence, was performed with Synopsys® Sentaurus TCAD tools. In addition, a manufacturing method to realize the DS-3DTED device is presented. A 311 μm deep trench has been achieved through the Bosch process on the IMECAS 8-inch CMOS platform to verify the feasibility of the device structure. The maximum depth-to-width ratio is close to 105:1 when the trench width is 2 μm, which is an excellent foundation for manufacturing future 3D detector with a large fill factor and small dead region.

Broadband self-powered MoS2/PdSe2/WSe2 PSN heterojunction photodetector for high-performance optical imaging and communication.

Two-dimensional (2D) semi-metal transition metal dichalcogenides (TMDs) have drawn significant attention for their distinctive physical properties. However, the inherent high dark current of these materials and the single structure of detectors hinder the further development of photodetectors with high performance. Here, we construct a PSN (p-type semiconductor/semi-metal/n-type semiconductor) architecture by sandwiching 2D semi-metal between two semiconductor layers. In this architecture, the top and bottom layers generate an internal built-in electric field, while the middle layer serves as an absorption layer for low-energy photons and facilitates the dissociation of photo-generated carriers. As a result, the heterojunction device demonstrates a wide spectrum optical response from visible to infrared light (405 nm to 1550 nm) without requiring an external voltage. Working in self-powered mode at room temperature, the device achieves a responsivity of 0.56 A/W, a detectivity of 5.63 × 1011 Jones, and a rapid response speed of 190/74 µs. Additionally, the device shows potential for applications in fast optical communication and multi-wavelength optical imaging. This work presents a novel approach for developing a new type of broadband, self-powered, high-performance miniaturized semi-metal-based photodetector.

Novel approach of thionyl chloride detection and disposal using a benzimidazole-based derivative: perspectives and proposals

AbstractBenzimidazoles are important heterocyclic compounds that exhibit a wide range of pharmacological and biological properties. Among all, sensitivity to Lewis acids provide a possibility to act as a fluorescent detectors for senzing the cathions, radicals, highly reactive low-molecular species with hazardous effects to environment and human health. Herein, we present the design and synthesis of N-((1H-benzo[d]imidazol-2-yl)methyl)cinnamamide (I) for the detection of readily reactive thionyl chloride (SOCl2). Treatment of SOCl2 with a novel benzimidazole-based compound I is accompanied by immediate color change. Although the process is irreversible the change noticeable by eye is profitable for a simple and rapid protection against the SOCl2 exposure at amounts harmful for surroundings and body. In the context of environmental issue, the chemical reaction between the detector I and thionyl chloride is beneficial for the safe waste disposal. Thionyl chloride is recaptured in the structure of I throughout the reaction leading to a formation of stable compound II. Incorporation of residual traces of SOCl2 into the structure of organic-type detector I represents effective route to achieve non-reactive and non-damaging derivatives. Accordingly, the organic non-liquid waste is subsequently stored and disposed in a safe manner.

Detection of human finger joints in ultrasound images: structure and optimization

Synovitis is the inflammation of a synovial membrane surrounding a joint. Its assessment is an important step in the diagnosis and treatment of rheumatoid arthritis. Joint detection is the first stage of an automated method of assessment of a degree of synovitis, from an Ultrasound (USG) image of a finger joint and its surrounding area. A joint detector consists of three parts: image preprocessing, feature extraction, and classification. Each part contains adjustable parameters that must be set experimentally to ensure the proper operation of the detector. Both the structure of a joint detector and a procedure for finding a near-optimal configuration of the adjustable parameters are described. The optimization process is based on two evaluation measures: Area Under the Receiver Operating Characteristic Curve (AUC) and False Positive Count (FPC). The optimization process decreases the number of pictures with multiple detections, which was the main point of works presented in this paper. This was achieved by increasing the number of components of the homogeneous mixed-SURF descriptor which has the greatest influence on the final result. Non-SURF descriptors achieve poorer classification results. Our research led to the creation of a better joint detector which could positively influence the final results of inflammation level classification.

Long-Time Coherent Integration for the Spatial-Based Bistatic Radar Based on Dual-Scale Decomposition and Conditioned CPF

This paper addresses the problem of weak maneuvering target detection in the space-based bistatic radar system through long-time coherent integration (LTCI). The space-based bistatic radar is vulnerable to the high-order range migration (RM) and Doppler frequency migration (DFM), since the target, the receiver and the transmitter all can play fast movement independently. To correct high- order RM and DFM, this usually involves joint high-dimensional parameter searching, incurring a large computational burden. In our previous work, a dual-scale (DS) decomposition of motion parameters was proposed, in which the optimal GRFT is conditionally decoupled into two cascade procedures called the modified generalized inverse Fourier transform (GIFT) and generalized Fourier transform (GFT), resulting in the DS-GRFT detector. However, even if the DS-GRFT detector preserves the superior performance and dramatically decreases the complexity, high-dimensional searching is still required. In this paper, by analyzing the structure of the DS-GRFT detector, we further designed a conditioned cubic phase function (CCPF) tailored to the range–slow-time signal after GIFT, breaking the joint high-dimensional searching into independent one-dimensional searching. Then, by connecting the proposed CCPF with the GIFT, we achieved a new LTCI detector called the DS-GIFT-CCPF detector, which obtained a significant computational cost reduction with acceptable performance loss, as demonstrated in numerical experiments.

Hardware method for zero optical path difference position detection of FTIR spectrometer

This paper presents a method for accurately controlling the position of the zero optical path difference in the transformation process from interferogram of Fourier transform infrared (FTIR) spectrometer to spectrogram. This position has a significant impact on the position, consistency, and repeatability of spectral lines in restored spectrograms. The proposed method, known as the double-slit photoelectric aiming and triggering method (DS-PATM), can be used to precisely control the zero optical path difference position, as well as the starting and ending positions of sampling, thereby ensuring identical optical path difference in the spectrometer system. The working principle of DS-PATM is elaborated in detail, followed by a description of the optical structure of the photoelectric aiming detector and the photoelectric aiming trigger circuit. Subsequently, a displacement detection system of the spectrometer moving mirror is developed. The system is experimentally validated through displacement aiming and triggering experiments of the moving mirror of the FTIR spectrometer, conducted under standard measurement environment. The results demonstrate that using the proposed method, the standard deviation of zero optical path difference position can be measured with a confidence probability (math.) of 99.7% and a resolution of 0.1 cm−1 for Fourier transform spectrometer, yielding a value of 0.08 μm. This confirms the effectiveness of the detection system and its ability to meet the requirements of sampling interferogram with high resolution.

Design and characterization of type-II superlattice-based InAs/AlSb/GaSb detector structure

In this study, N-Structured based InAs/AlSb/GaSb Type-II Superlattice pbin type detector structures are investigated. These systems make absorption in the infrared region in the electromagnetic spectrum as detectors. Structural characterization of these systems is aimed. n-type GaSb is used as the substrate. InAs/AlSb/GaSb-based repetitive SL layers are formed as n-layer, i-layer, p-layer, and p-contact layer from the bottom InAsSb layer to the top GaSb cap layer for 120, 300, 15, and 80 periods, respectively. Structural characterization of all layers is made by using SIMS and XRD systems analyses. The structural depth profile of the SL layers has been presented comparatively through SIMS analysis. The interfacial transitions observed in the depth profile are consistent with the designed T2SL layers. By using XRD characterization, crystal quality parameters, lattice constants, periodicity, and deviation of superlattice peak from the substrate are determined. Such dislocation density and strain are measured AS 7.85x107cm−2 and 6.4x10-3 nm, respectively. AFM analysis technic is used to examine the surface morphology of the structure. Also, SEM analysis is used to examine the cross-section of the structure. The cross-sectional measurements allowed the observation of interfacial transitions within the SL structure. In this study, super lattice with high crystal quality is achieved and results show that T2SL detector structures have succeeded.

Electronics design for a muon imaging system using triangular plastic scintillators with WLS fiber readouts

Muon imaging technology has developed rapidly over the past decades with extensive applications. In many cases, plastic scintillator detectors are preferred because of their high cost performance, ease of processing and robustness in harsh environments. To reduce imaging time and improve imaging quality, detectors tend to have large areas and high position resolutions. The challenge to the electronics for such detectors is to maintain the scale of electronics acceptable while improving the high position resolution of the detector. In this paper, the basic detector unit is a triangular strip of plastic scintillator, each embedded with two wavelength-shifting (WLS) fibers read out by the silicon photomultipliers (SiPMs). Since the hit position of muon on the detector is determined by the splitting ratio of the scintillation light on two adjacent scintillator strips, it is necessary the readout electronics has high linearity and low noise. The possibility of the electronics channel multiplexing on the same detector plane is fully explored so that four WLS fibers can be read out by one SiPM realizing 2:1 readout channel compression. Furthermore, since multiple electronics modules are connected by a daisy chain structure, the electronics system is very scalable with its data acquisition system (DAQ) independent of detector size. In addition to detailing the position encoding readout scheme, the design of electronics module and the DAQ system, the electronics system has been implemented and applied to a prototype detector for performance evaluation. Using scintillator strips with 11 mm pitch size, the position resolution of the detector reaches 1.49 mm, which demonstrates that the designed electronics is suitable for the new detector structure, and the combination of the two has a good application prospect in muon imaging.

Effect of “M” and “B” superlattice barrier layers on dark current of long-wavelength infrared detectors

This paper studies superlattice materials with M barrier (InAs/GaSb/AlSb/GaSb superlattice) and B barrier (InAs/AlSb superlattice) structures. Firstly, it introduces the diffusion current, generation-recombination current, tunneling current and surface leakage current in devices, and analyzes the factors affecting different dark current mechanisms. Secondly, it theoretically analyzes the influence of the two barrier structures on device performance. Finally, devices were fabricated using these two structures, and the device performance was characterized. At a bias voltage of −50 mV and operating temperature of 77K. The PπMN type long-wave infrared (LWIR) detector has an RA of 91.4 Ω cm2 and a LW dark current density of 3.51 × 10−4 A cm−2. The PπBN type LWIR detector has an RA of 439 Ω cm2 and a LW dark current density of 2.81 × 10−4 A cm−2. Meanwhile, by fitting the data at different temperatures, the activation energy Ea of the PπMN type LWIR detector is 119.8 meV, with dark current mainly determined by diffusion current and generation-recombination current. The activation energy Ea of the PπBN type LWIR detector is 126.2 meV, with dark current mainly determined by diffusion current. This experimentally verifies the dominant dark current mechanisms for the two barrier structures of LWIR detectors, providing strong support for the design of superlattice detector structures.

Optical, Mechanical and Electrical Characteristics of Thermal Uncooled Bolometric Type Detector Based on Vanadium Oxide

Determination of optical, mechanical and electrical characteristics is one of the decisive factors in the design of instrumentation structures of thermal uncooled bolometer-type detectors (microbolometers). The paper presents the results of optimization calculations by means of computer simulation of absorption, transmittance and reflection spectra of device structures of microbolometers based on thermosensitive vanadium oxide film by finite-difference time-domain method (FDTD). The characteristics of the investigated microbolometer structure were checked for compliance with mechanical and electrical requirements for this class of devices.

Novel pyroelectric single crystals PIN-PMN-PT and their applications for NDIR gas detectors

Ternary manganese-doped (1−x−y)Pb(In1/2Nb1/2)O3-xPb(Mg1/3Nb2/3)O3-yPbTiO3 (Mn-doped PIN-PMN-PT) single crystals have demonstrated remarkable pyroelectric properties alongside enhanced temperature stability. These attributes hold substantial promise for the advancement of high precision nondispersive IR (NDIR) applications. In this study, Mn-doped 0.21Pb(In1/2Nb1/2)O3-0.49Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystals were introduced and carefully investigated. A compensated structure of pyroelectric IR detector based on Mn-doped PIN-PMN-PT single crystal was designed and fabricated, and a CO2 gas concentration monitoring module was built. Results showed that Mn-doped PIN-PMN-PT single crystals exhibit high pyroelectric coefficient, and better thermal stability than binary (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 system. The compensated pyroelectric IR detectors using Mn-doped PIN-PMN-PT single crystals as element chips showcase a performance that is approximately fourfold higher than that of commercial LiTaO3 pyroelectric detectors. The NDIR CO2 gas sensor module was assembled and exhibited remarkable accuracy along with an impressively low minimum detection concentration. These outcomes underscores its substantial potential for practical utilization in gas monitoring applications.

Experimental validation and mathematical simulation for laser protection performance of light field imaging

Photoelectric imaging systems typically employ a focal plane detector structure, rendering them vulnerable to laser damage. Laser damage can severely impair or even completely deprive the information acquisition capability of photoelectric imaging systems. A laser damage protection method based on a microlens array light field imaging system is proposed to prevent photoelectric imaging systems from laser damage. The technique utilizes the light field modulation effect of the microlens array to homogenize the spot energy, thereby reducing the maximum single-pixel receiving power at the image sensor. The method’s effectiveness has been verified through numerical simulations and experimental validation. First, the laser transmission theoretical model of light field imaging is proposed. Then an experimental setup is established, and measurements are conducted to capture the spot profiles and intensity distributions on the imaging plane across various defocus distances. Finally, the impact of the propagation distance on the maximum single-pixel receiving power and suppression ratio of the light field imaging system is experimentally measured. The simulation and experimental results indicate that, with the proposed method, the energy suppression ratio can easily reach two orders of magnitude, significantly reducing the probability of laser damage in photoelectric imaging systems.

Design and optimization of a conical electrostatic objective lens of a low-voltage scanning electron microscope for surface imaging and analysis in ultra-high-vacuum environment

Low-voltage scanning electron microscopy (LV-SEM) with landing energies below 5 keV has been widely used due to its advantages in mitigating the damage and charging effects to a specimen and enhancing surface information due to small interaction volume of electrons inside a specimen. Additionally, for elemental analysis of the surfaces of bulk specimens with Auger electron spectroscopy (AES) or electron energy loss spectroscopy (EELS), ultra-high-vacuum (UHV) environment is essential to maintain clean surfaces without the absorption of gas molecules during the electron beam irradiation for the acquisition of spectral data. In this study, we propose the optimal design and condition of a conical Electrostatic Objective Lens (EOL) for a UHV LV-SEM to achieve the high spatial resolution and secondary electron (SE) detection efficiency. The EOL is composed of only the three electrodes (retarding, focusing and booster electrodes) and the insulators, which is suitable for maintaining a UHV environment with less out-gassing. The cone angle of the EOL is determined as 60° to integrate a spectrometer in the UHV LV-SEM and in a large size and a higher tilt angle of the sample. Through the optimization with the simulations, the EOL achieves the minimized spherical and chromatic aberration coefficients of 0.05 and 0.03 mm at the sample side, respectively, at the landing energy of 50 eV and the shortest working distance (WD) of 1 mm for high-resolution imaging. In addition, the probe diameter of the optimized EOL is 2.3 nm at 1 keV and 5.7 nm at 50 eV with a WD of 1 mm and a probe current of 10 pA, which are comparable to previously studied compound objective lenses with magnetic and electrostatic lenses. Using a longer WD of 4 mm for analysis, the probe diameter was 5.4 nm at 1 keV and the SE detection efficiency was 83.3 % owing to the separated scintillator detector structure from the booster electrode.These results imply that the optimized EOL has the potential to be applied to a high-performance UHV LV-SEM for the surface imaging and analysis with a simple system configuration.

Water-assisted mass preparation of CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafers for high-performance X-ray detection

Lead halide perovskite wafers with large lateral size, controllable thickness, and desirable optoelectronic characteristics are promising for X-ray detectors. Herein, CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafers are prepared via water-assisted coprecipitation and spray coating. The preparation involved pressure-induced aggregation of the CsPbBr3-CsPb2Br5 powder produced through coprecipitation using of H2O/MeOH mixed solvent into CsPbBr3-CsPb2Br5 wafers, followed by spraying a CsI/H2O solution onto the wafer surface to transform it into a CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafer. Multiple favorable properties, including compact surface, high crystallinity, excellent carrier transportation, large/adjustable size, low cost, and mass producibility, can be identified for the CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafer. An X-ray detector with high performance and excellent stability is realized with this wafer. It yields high resistivity (ρ; 1.3 × 109 Ω cm−2, exceptional carrier mobility (μ)/lifetime (τ) (μτ) product (1.01 × 10−3 cm2 V−1), high sensitivity (20555.1 μC Gyair−1 cm−2), and low detection limit (127.7 nGy s−1). Hence, our research provides a reliable strategy for optimizing the structure and performance of perovskite wafer-based X-ray detectors and enabling mass preparation.

Timing estimation of the exponentiated energy-weighted average for crosshair light sharing TOF-DOI PET detector

In TOF-PET, the method of timestamp calculation is an important factor that affects coincidence resolving time (CRT). In independent readout detectors, for one-to-one coupled detectors, the first hit (FH) timestamp is the optimal one, while in light-sharing detectors, the optimal timestamp must be calculated from multiple timestamps. The method for the latter performs energy-weighted averaging (EWA) using several photosensors with earlier timestamps, but the light distribution varies depending on the detector structure. Here, we developed an exponentiated energy-weighted averaging (EEWA) method for our previously developed light-sharing detector that limits light spreading. The crosshair light-sharing (CLS) PET detector was developed as a TOF-DOI PET detector. It uses fast LGSO crystals with dimensions of 1.45 × 1.45 × 15 mm3 arranged in a 2D crystal array with three layers of enhanced specular reflectors (ESRs) forming a loop structure within a pair of crystals. The 2D crystal array is optically connected to an 8 × 8 MPPC array. The signals of the MPPC array are individually read out and processed by using TOFPET2 ASICs. To effectively utilize multiple timestamps, the EEWA method introduces a power term to the energy, giving priority to timestamps with higher energy. Additionally, we use Lumirror to increase the light collection efficiency and we compared its performance with the ESRs. In the FH method, the CRTs of the ESR and Lumirror arrays were 250 and 232 ps, respectively. In the EWA method, the CRT deteriorated as the number of MPPCs used was increased compared to the FH method. In the EEWA method, by optimizing the number of MPPCs used and the power factor, the CRT was improved to 226 and 221 ps, respectively. In summary, we developed the EEWA method for timestamp estimation and achieved an improvement of up to 24 ps in CRT.