Abstract
A state of the art commercial detector, a PCO Edge 4.2 bi based on a back illuminated sCMOS sensor developed for applications in the visible light/ultra violet regime has been adapted for ...ultra-high vacuum operations and has been characterized using soft X-ray in the energy range from 30 eV to 1000 eV. The imager features 2048 × 2048 pixel with a pixel size of 6.5 μm × 6.5 μm and allows full frame acquisitions at 48 Hz with a dynamic range of 88 dB at a noise level of 1.9
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. Spatial resolution and quantum efficiency have been elucidated in the aforementioned energy range at a soft X-ray beam line at Elettra Sincrotrone Trieste. The handiness of the camera as well as its Python library package allows easy and fast integration into the beam line environments of synchrotron sources and free electron lasers.
Abstract
III-V-compound semiconductors offer many advantages over silicon-based technologies traditionally used in solid-state photodetectors, especially in hard X-ray applications that require high ...detection efficiency and short response times. Amongst them, gallium arsenide (GaAs) has very promising characteristics in terms of X-ray absorption and high carrier velocity. Furthermore, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics. This work reports on the experimental characterization by means of lasers and synchrotron radiation of gain, noise, and charge collection efficiencies of GaAs avalanche photodiodes (APDs), realized by molecular beam epitaxy (MBE), featuring separate absorption and multiplication regions (SAM) and different absorption region thicknesses. These devices have been fabricated to investigate the role of the thickness of the absorption region and of possible traps or defects at the metal-semiconductor interfaces in the collection efficiency in order to lay the groundwork for the future development of thicker GaAs devices for detection of hard X-rays.
Synchrotron radiation time structure is becoming a common tool for studying dynamic properties of materials. The main limitation is often the wide time domain the user would like to access with ...pump–probe experiments. In order to perform photoelectron spectroscopy experiments over time scales from milliseconds to picoseconds it is mandatory to measure the time at which each measured photoelectron was created. For this reason the usual CCD camera‐based two‐dimensional detection of electron energy analyzers has been replaced by a new delay‐line detector adapted to the time structure of the SOLEIL synchrotron radiation source. The new two‐dimensional delay‐line detector has a time resolution of 5 ns and was installed on a Scienta SES 2002 electron energy analyzer. The first application has been to characterize the time of flight of the photoemitted electrons as a function of their kinetic energy and the selected pass energy. By repeating the experiment as a function of the available pass energy and of the kinetic energy, a complete characterization of the analyzer behaviour in the time domain has been obtained. Even for kinetic energies as low as 10 eV at 2 eV pass energy, the time spread of the detected electrons is lower than 140 ns. These results and the time structure of the SOLEIL filling modes assure the possibility of performing pump–probe photoelectron spectroscopy experiments with the time resolution given by the SOLEIL pulse width, the best performance of the beamline and of the experimental station.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We report on a suite of modeling approaches for the optimization of Avalanche Photodiodes for X-rays detection. Gain and excess noise are computed efficiently using a non-local/history dependent ...model that has been validated against full-band Monte Carlo simulations. The (stochastic) response of the detector to photon pulses is computed using an improved Random-Path-Length algorithm. As case studies, we consider diodes consisting of AlGaAs/GaAs multi-layers with separated absorption and multiplication regions. A superlattice creating a staircase conduction band structure is employed in the multiplication region to keep the multiplication noise low. Gain and excess noise have been measured in devices fabricated with such structure and successfully compared with the developed models.
We propose a simple expression to relate the total excess noise factor of a single-carrier multiplication staircase avalanche photodiode (APD) to the excess noise factor and gain given by the ...individual conduction band discontinuities. The formula is valid when electron impact ionization dominates hole impact ionization; hence, it is especially suited for staircase APDs with In-rich multiplication regions, as opposed, for example, to GaAs/AlGaAs systems where hole ionization plays an important role. The formula has been verified by accurate means of numerical simulations based on a newly developed nonlocal history dependent impact ionization model.
Abstract
The results of a collaborative development activity aimed to the realization of multi-cell detectors based on monolithic SDD pixel technology will be described. Two kind of detection ...systems, skilled for the light lines at synchrotrons, have been brought to high levels of finalization and integration; a 64 cells detection system dedicated to absorption spectroscopy (XAFS) and a 32 cells detector for the X-ray microscopy (TwinMic). The main targets of this effort, led in a tight collaboration with the beam lines scientists, were large sensitive area, high rate capabilities, state of the art efficiency and energy resolution. The aim is to reduce the beam time demand for each single measurement while delivering a cutting edge analytical power.
All basic elements of those detection systems, from the detector’s design and production to the front-end and read-out electronics including the final engineering of the integrated system were customized to the specific use addressed.
Due to the high atomic number, low band gap and high electron mobility of III-IV semiconductors, the use of metamorphic InGaAs/InAlAs quantum well-based devices was proposed for fast pixelated photon ...detectors. In this work, we are presenting a double side-segmented quantum well (QW) device, discussing its spatial resolution and analysing the crosstalk between pixels. The fabricated devices were tested with needle-shaped beams of synchrotron radiation with different energies and spot sizes. The position of the synchrotron radiation was estimated with a 1.3-μm precision. The charge spread in the material and related crosstalk function between pixels were extracted from the position estimation measurements of the photon beams. The results show that the cross-talk between pixels is actually responsible for the different resolutions obtained, regardless of the experimental conditions, pointing out the importance of the geometry of the fabricated devices. Furthermore, it has been observed that the QW pixelation is mandatory for hybrid detector technology.
Beam monitoring in synchrotron radiation or free electron laser facilities is extremely important for calibration and diagnostic issues. Here we propose an in-situ detector showing fast response and ...homogeneity for both diagnostics and calibration purposes. The devices are based on In0.75Ga0.25As/In0.75Al0.25As QWs, which offer several advantages due to their direct, low-energy band gap and high electron mobility at room temperature. A pixelation structure with 4 quadrants was developed on the back surface of the device, in order to fit commercially available readout chips.
The QW devices have been tested with collimated monochromatic X-ray beams from synchrotron radiation. A rise in the current noise with positive bias was observed, which could be due to deep traps for hole carriers. Therefore, an optimized negative bias was chosen to minimize dark currents and noise. A decrease in charge collection efficiency was experienced as the beam penetrates into deeper layers, where a dislocation network is present. The prototype samples showed that individual currents obtained from each quadrant allow the position of the beam to be monitored for all the utilized energies. These detectors have a potential to estimate the position of the beam with a precision of about 10µm.
•Metamorphic InGaAs/InAlAs QW devices were grown by MBE.•Segmented detectors were fabricated as beam position monitors.•The QW detectors were tested with photon beams at energies of 2.14, 5 and 10keV.•The precision in position estimation was10µm for a 200-µm beam spot size.•Charge collection efficiency was roughly estimated to be 27%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Avalanche photodiodes based on GaAs/AlGaAs with separated absorption and multiplication regions (SAM-APDs) will be discussed in terms of capacitance, response to light (gain and noise) and time ...response. The structures have been fabricated by molecular beam epitaxy introducing a δ p layer doped with carbon to separate the multiplication and the absorption regions. The thickness of the latter layer defines the detection efficiency and the time resolution of the structure, which in turn allows tailoring the device for specific scientific applications. Within the multiplication region a periodic modulation of the bandgap is obtained by growing alternating nanometric layers of AlGaAs and GaAs with increasing Al content; this staircase structure enables the tuning of the bandgap and subsequently provides a well-defined charge multiplication. The use of such staircase hetero-junctions enhances electron multiplication and conversely reduces—at least in principle—the impact of the noise associated to hole multiplication, which should result in a decreased overall noise, when compared to p-i-n diodes composed by a single material. The first part of this paper focuses on the electrical characteristics of the grown structure and on the comparison with the simulated behaviour of such devices. In addition, gain and noise measurements, which have been carried out on these devices by utilizing photons from visible light to hard X-rays, will be discussed and will be compared to the results of a nonlocal history-dependent model specifically developed for staircase APDs.
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