Fano-limited Energy Resolution Research Articles

Fast electron initiated electron–hole pair creation in semiconductors

Through Monte Carlo modeling, it is shown that the statistics of electron–hole pair creation in semiconductors (and by extension, presumably, ion-pair creation in gas proportional counters) are substantially different for fast electrons (and by extension, presumably, alpha particles, ions, etc.) cf. x-ray/γ-ray photons. New variables are introduced to quantify the differences in the statistics: the loss parameter, ζ(E′), which acts on the average e−–h+ pair creation energy; and the broadening factor, B(E′), which acts on the Fano factor. E′ is the initial energy of the fast electron. ζ(E′) and B(E′) are computed for a variety of semiconductor materials. A new equation for the statistically limited energy resolution of a particle counting fast electron spectrometer is established. This new equation supersedes and replaces that for the Fano-limited energy resolution of a particle counting fast electron spectrometer. The implications impact a wide variety of fields wherever fast electrons (or alpha particles, ions, etc.) and/or Fano statistics are used; this includes, inter alia, quantum computing, x-ray excitonics, space science, optoelectronics, nuclear engineering, particle physics, photovoltaics, and even neural response variability in the brain.

DePFET—Recent Developments and Future Prospects

The DePFET is a sensor amplifier structure first proposed in 1987. In recent years, DeFPET based sensors have been deployed for particle tracking at Belle II experiment and been launched into space aboard the planetary science mission BepiColombo in its MIXS instrument. In the future DePFETs are proposed for the Wide Field Imager aboard the ATHENA satellite and developed for use as real-time imager for transmission electron microscopes These sensors have all been tailored to the needs of the respective application, providing high frame rates and accurate position resolution for tracking, Fano-limited energy resolution and position resolution matched to telescopes for X-ray spectroscopy or high frame rates and maximized dynamic range for applications on TEMs. In addition to this, several DePFET based concepts, implementing additional functionality on pixel level have been tested in recent years. Among these are the tailoring of the internal gates shape to implement a non-linear signal response and provide a larger dynamic range or a drastic increase of the DePFETs amplification. Furthermore, super pixels providing capabilities to reach sub electron noise and single electron resolution through repetitive readout, a fast electronic shutter at pixel level and the realization of multiple storage regions within one pixel have been tested. It was further demonstrated, that combinations of these features can also be realized. Over all, it is noted that advances in DePFET technology will provide sensors that are optimally tailored to the need of a specific application.

A New Spectroscopic Imager for X-rays from 0.5 keV to 150 keV Combining a Fully Depleted pnCCD Coupled to a Columnar CsI(Tl) Scintillator with Fano Limited Energy Resolution and Deep Subpixel Spatial Resolution

A New Spectroscopic Imager for X-rays from 0.5 keV to 150 keV Combining a Fully Depleted pnCCD Coupled to a Columnar CsI(Tl) Scintillator with Fano Limited Energy Resolution and Deep Subpixel Spatial Resolution - Volume 27 Issue S1

Energy response characterization of InGaP X-ray detectors

Two custom-made In0.5Ga0.5P p+-i-n+ circular mesa spectroscopic X-ray photodiodes with different diameters (200 μm and 400 μm) and a 5 μm i layer have been characterized for their response to X-ray photons within the energy range 4.95 keV to 21.17 keV. The photodiodes, operating uncooled at 30 °C, were coupled, in turn, to the same custom-made charge-sensitive preamplifier. X-ray fluorescence spectra of high-purity calibration foils excited by a Mo target X-ray tube were accumulated. The energy resolution (Full Width at Half Maximum) increased from 0.79 ± 0.02 keV at 4.95 keV to 0.83 ± 0.02 keV at 21.17 keV, and from 1.12 ± 0.02 keV at 4.95 keV to 1.15 ± 0.02 keV at 21.17 keV, when using the 200 μm and 400 μm diameter devices, respectively. Energy resolution broadening with increasing energy was attributed to increasing Fano noise (negligible incomplete charge collection noise was suggested); for the first time, the Fano factor for In0.5Ga0.5P was experimentally determined to be 0.13, suggesting a Fano limited energy resolution of 145 eV at 5.9 keV. The charge output of each system had a linear relationship with photon energy, across the investigated energy range. The count rate of both spectroscopic systems increased linearly with varying X-ray tube current up to ∼105 photons s−1 cm−2 incident photon fluences. The development of In0.5Ga0.5P based spectrometers is particularly important for hard X/γ-ray astronomy, due to the material’s large linear X-ray and γ-ray absorption coefficients and the ability to operate uncooled at high temperatures.

Characterization of a novel pixelated Silicon Drift Detector (PixDD) for high-throughput X-ray astrophysics

Multi-pixel fast silicon detectors represent the enabling technology for the next generation of space-borne experiments devoted to high-resolution spectral-timing studies of low-flux compact cosmic sources. Several imaging detectors based on frame-integration have been developed as focal plane devices for X-ray space-borne missions but, when coupled to large-area concentrator X-ray optics, these detectors are affected by strong pile-up and dead-time effects, thus limiting the time and energy resolution as well as the overall system sensitivity. The current technological gap in the capability to realize pixelated silicon detectors for soft X-rays with fast, photon-by-photon response and nearly Fano-limited energy resolution therefore translates into the unavailability of sparse read-out sensors suitable for high throughput X-ray astronomy applications. In the framework of the ReDSoX Italian collaboration, we developed a new, sparse read-out, pixelated silicon drift detector which operates in the energy range 0.5–15 keV with nearly Fano-limited energy resolution (⩽150 eV FWHM @ 6 keV) at room temperature or with moderate cooling (∼0°C to +20°C). In this paper, we present the design and the laboratory characterization of the first 16-pixel (4 × 4) drift detector prototype (PixDD), read-out by individual ultra low-noise charge sensitive preamplifiers (SIRIO) and we discuss the future PixDD prototype developments.

MIXS on BepiColombo and its DEPFET based focal plane instrumentation

Focal plane instrumentation based on DEPFET Macropixel devices, being a combination of the Detector–Amplifier structure DEPFET with a silicon drift chamber (SDD), has been proposed for the MIXS (Mercury Imaging X-ray Spectrometer) instrument on ESA's Mercury exploration mission BepiColombo. MIXS images X-ray fluorescent radiation from the Mercury surface with a lightweight X-ray mirror system on the focal plane detector to measure the spatially resolved element abundance in Mercury's crust. The sensor needs to have an energy resolution better than 200 eV FWHM at 1 keV and is required to cover an energy range from 0.5 to 10 keV, for a pixel size of 300 × 300 μ m 2 . Main challenges for the instrument are radiation damage and the difficult thermal environment in the mercury orbit. The production of the first batch of flight devices has been finished at the MPI semiconductor laboratory. Prototype modules have been assembled to verify the electrical properties of the devices; selected results are presented here. The prototype devices, Macropixel prototypes for the SIMBOL-X focal plane, are electrically fully compatible, but have a pixel size of 0.5×0.5 mm 2. Excellent homogeneity and near Fano-limited energy resolution at high readout speeds have been observed on these devices.

Evaluation of a CdZnTe pixel array for X- and γ-ray spectroscopic imaging

X-ray imaging is an essential tool for a wide range of disciplines. Whilst the majority of applications rely on analog integrating or on photon counting formats, the future development of this field lies in the exploitation of spatially resolved spectroscopy and in particular, using materials which can operate with near Fano limited energy resolution at room temperature. This communication focuses on a new prototype 16×16 cadmium zinc telluride (CdZnTe) pixel array fabricated by eV Products [ http://www.evproducts.com/ [1]], which, assembled with an ASIC made by Ideas ASA [ http://www.ideas.no/products/ASICs/pdf/XA1.6.pdf [2]], provides both imaging and spectroscopic capabilities at the individual pixel level. We report detailed results of hard X-ray measurements carried out at the X1 beam line of the HASYLAB synchrotron radiation facility in Hamburg, Germany [ http://www-hasylab.desy.de/facility/ [3]].

High resolution imaging silicon-x-ray spectrometers

X-rays in the energy bandwidth of 100eV up to 30keV can be nicely detected with modern silicon detectors with integrated readout electronics. Matrix-type silicon detectors exhibit a position resolution of the order of microns, a time resolution in the microsecond range and a Fano limited energy resolution. All properties can be measured simultaneously with one single device. The properties of silicon drift detectors (SDD) will be derived from basic physical principles and compared with measurements. Fully depleted charge coupled devices (pnCCDs) have been used in space observatories and on ground. Monolythic systems with sensitive areas of 1-36 cm 2 are currently operated with pixel sizes from 30 to 150 μm. Controlled drift detectors, a combination of a SDD and a CCD was operated with up to 100 000 pictures per second. X-ray active pixel sensors (APS) on the basis of the detector-amplifier structure DEPFET have been fabricated and tested recently with great success. The achieved energy resolution at room temperature was better than 150 eV (FWHM). They are foreseen for ESA's future X-ray mission XEUS. At the same time thinned and faster DEPFET arrays are being developed for linear collider applications. The fabrication of the detectors and the electronics is made in research labs for optimum flexibility during research and with the possibility of commercial transfers to institutions and companies.