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Abstract A Commercial-Off-The-Shelf (COTS) 4H-SiC p-n photodiode (sold as a UV detector) was investigated as detector of electrons (β − particles) over the temperature range 100 °C to 20 °C. The photodiode had an active area of 0.06 mm2. The currents of the photodiode were measured in dark condition and under the illumination of a 63Ni radioisotope β − particle source (endpoint energy = 66 keV). The photodiode was then coupled to a custom-made low-noise charge-sensitive preamplifier to make a direct detection particle counting electron spectrometer. 63Ni β − particle spectra were accumulated with the spectrometer operating at temperatures up to 100 °C. The quantum efficiency of the photodiode as well as the spectrum expected to be detected were calculated via Monte Carlo simulations produced using the CASINO computer program. Comparisons between the simulated and detected 63Ni β − particle spectra are presented. The work was motivated by efforts to apply COTS technologies to develop low-cost space science instrumentation; a low-cost electron spectrometer of this type could be included on a university-led CubeSat mission for space plasma physics and magnetosphere experiments. [ABSTRACT FROM AUTHOR]

A monolithic 2 × 2 square pixel Al 0.2 Ga 0.8 As p + –i–n + mesa X-ray photodiode array (each photodiode area 200 μ m by 200 μ m, 3 μ m i layer) has been fabricated from material grown by MOVPE. The array was electrically characterised across the temperature range 100 °C to -20 °C. Each pixel’s response to illumination with soft X-rays from an 55 Fe radioisotope X-ray source (Mn K α = 5 . 9 keV; Mn K β = 6 . 49 keV) was investigated across the temperature range 30 °C to -20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 0.76 keV ± 0.06 keV (with 30 V reverse bias applied to the detector). The measured energy resolution is the best so far reported for AlGaAs X-ray photodiodes at 20 °C. It is also the first time a small AlGaAs X-ray photodiode array has been demonstrated. Due to the temperature tolerance and the radiation hardness of AlGaAs, such detectors are expected to find utility in future space science missions exposed to intense radiation environments, for example missions to study the Jovian or Saturnian aurorae and high temperature planetary surfaces. [ABSTRACT FROM AUTHOR]

A low-cost Commercial-Off-The-Shelf (COTS) 4H-SiC 0.06 mm 2 UV p-n photodiode was coupled to a low-noise charge-sensitive preamplifier and used as photon counting X-ray spectrometer. The photodiode/spectrometer was investigated at X-ray energies from 4.95 keV to 21.17 keV: a Mo cathode X-ray tube was used to fluoresce eight high-purity metal foils to produce characteristic X-ray emission lines which were used to characterise the instrument. The energy resolution (full width at half maximum, FWHM ) of the spectrometer was found to be 1.6 keV to 1.8 keV, across the energy range. The energy linearity of the detector/spectrometer (i.e. the detector’s charge output per photon as a function of incident photon energy across the 4.95 keV to 21.17 keV energy range), as well as the count rate linearity of the detector/spectrometer (i.e. number of detected photons as a function of photon fluence at a specific energy) were investigated. The energy linearity of the detector/spectrometer was linear with an error < ± 0.7 %; the count rate linearity of the detector/spectrometer was linear with an error < ± 2 %. The use of COTS SiC photodiodes as detectors for X-ray spectrometers is attractive for nanosatellite/CubeSat applications (including solar flare monitoring), and for cost sensitive industrial uses. [ABSTRACT FROM AUTHOR]

Two commercial-off-the-shelf (COTS) 4H-SiC UV photodiodes have been investigated for their suitability as low-cost high temperature tolerant X-ray detectors. Electrical characterisation of the photodiodes which had different active areas (0.06 mm 2 and 0.5 mm 2 ) is reported over the temperature range 0 °C to 140 °C together with measurements of the X-ray photocurrents generated when the detectors were illuminated with an 55 Fe radioisotope X-ray source. The 0.06 mm 2 photodiode was also investigated as a photon counting spectroscopic X-ray detector across the temperature range 0 °C to 100 °C. The depletion widths (at 120 V reverse bias) of the two diodes were found to be 2.3 µm and 4.5 µm, for the 0.06 mm 2 and 0.5 mm 2 detectors respectively, at 140 °C. Both devices had low leakage currents (<10 pA) at temperatures ≤40 °C even at high electric field strengths (500 kV/cm for 0.06 mm 2 diode; 267 kV/cm for 0.5 mm 2 diode). At 140 °C and similar field strengths (514 kV/cm for 0.06 mm 2 diode; 269 kV/cm for 0.5 mm 2 diode), the leakage currents of both diodes were <2 nA (corresponding to leakage current densities of 2.4 µA/cm 2 and 0.3 µA/cm 2 for each diode respectively). The results demonstrated that both devices could function as current mode detectors of soft X-rays at the temperatures <80 °C and that when coupled to a low noise charge sensitive preamplifier, the smaller diode functioned as a photon counting spectroscopic X-ray detector at temperatures ≤100 °C with modest energy resolution (1.6 keV FWHM at 5.9 keV at 0 °C; 2.6 keV FWHM at 5.9 keV at 100 °C). Due to their temperature tolerance, wide commercial availability, and the radiation hardness of SiC, such detectors are expected to find utility in future low-cost nanosatellite (cubesat) missions and cost-sensitive industrial applications. [ABSTRACT FROM AUTHOR]

Three custom-made Al 0.2 Ga 0.8 As p-i-n mesa X-ray photodiodes (200 µm diameter, 3 µm i layer) were electrically characterised and investigated for their response to illumination with soft X-rays from an 55 Fe radioisotope X-ray source (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV). The AlGaAs photodiodes were shown to be suitable for photon counting X-ray spectroscopy at room temperature. When coupled to a custom-made low-noise charge-sensitive preamplifier, a mean energy resolution (as quantified by the full width at half maximum of the 5.9 keV photopeak) of 1.24 keV was measured at room temperature. Parameters such as the depletion width (1.92 µm at 10 V), charge trapping noise (61.7 e − rms ENC at 5 V, negligible at 10 V) and the electronic noise components (known dielectric noise (63.4 e − rms), series white noise (27.7 e − rms), parallel white noise (9.5 e − rms) and 1/ f series noise (2.2 e − rms) at 10 V reverse bias) affecting the achieved energy resolution were computed. The estimated charge trapping noise and mean energy resolution were compared to similar materials (e.g. Al 0.8 Ga 0.2 As) previously reported, and discussed. These results are the first demonstration of photon counting X-ray spectroscopy with Al 0.2 Ga 0.8 As reported to date. [ABSTRACT FROM AUTHOR]

A commercial-off-the-shelf (COTS) silicon carbide (4H-SiC) UV photodiode was electrically characterized and investigated as a low-cost spectroscopic photon counting detector of X-rays and γ -rays. The detector was coupled to a custom-built low-noise charge-sensitive preamplifier, and illuminated by 55Fe and 109Cd radioisotope X-ray sources and an 241Am radioisotope γ -ray source, thus providing photon energies from 5.9 keV to 59.5 keV. The detector and preamplifier were operated uncooled at temperatures between 20 °C and 100 °C. The energy resolution (full width at half maximum, FWHM) of the spectrometer was found to be 1.66 keV ± 0.15 keV at 5.9 keV and 22.16 keV, and 1.83 keV ± 0.15 keV at 59.5 keV when operated at 20 °C. At a temperature of 100 °C, the FWHM were 2.69 ± 0.25 keV, 2.65 keV ± 0.25 keV, and 3.30 keV ± 0.30 keV, at the same energies. Shaping time noise analysis found dielectric noise to be the dominant noise source, except when long amplifier shaping times were used at high temperatures when white parallel noise dominated. Noise associated with incomplete charge collection was found to be negligible at energies up to 22.16 keV and at temperatures ≤ 60 °C; but incomplete charge collection noise could not be discounted when the spectrometer was operated at higher temperature (80 °C) and at higher energy (59.5 keV). Although the detector was thin (and thus inefficient at high photon energies) the low cost and commercial availability of the SiC device make it an attractive prospect for use in cost-sensitive applications such as university-led CubeSat missions. [ABSTRACT FROM AUTHOR]

Previously, an Al 0.52 In 0.48 P p + -i-n + spectroscopic photon counting X-ray photodiode with 2 μ m thick i layer (200 μ m diameter) was shown to suffer from energy-dependent incomplete charge collection noise (Lioliou et al., 2019). Subsequent measurements on a larger (400 μ m diameter) Al 0.52 In 0.48 P p + -i-n + photodiode (reported here) revealed the presence of even greater incomplete charge collection noise. Given these findings, an expectation would have been that thicker Al 0.52 In 0.48 P structures (which would be required for efficient absorption of all but the softest X-rays) would have a greater incomplete charge collection noise contribution, thus suggesting that thick Al 0.52 In 0.48 P photodiodes may be of limited practicality as high performance detectors for photon counting X-ray spectroscopy. However, two new Al 0.52 In 0.48 P p + -i-n + photodiodes (with 6 μ m i layers) were fabricated from material grown by the same technique (metalorganic vapour phase epitaxy) in the same reactor, and are now shown here to exhibit no signs of detectable incomplete charge collection noise under the illumination of X-ray photons of energy 4.95 keV to 21.17 keV. As such, now that greater experience has been built with Al 0.52 In 0.48 P, concerns about incomplete charge collection noise in X-ray detectors made from the material appear to have been unwarranted; the path towards thick Al 0.52 In 0.48 P X-ray detectors is now clear. [ABSTRACT FROM AUTHOR]

A custom-made Al 0.52 In 0.48 P p + -i-n + circular mesa X-ray photodiode (200 μ m diameter; 2 μ m i layer thickness) has been investigated for its use in photon counting X-ray spectroscopy within the energy range 4.95 keV to 21.17 keV. This is the widest energy range so far used to characterize an AlInP X-ray detector. High-purity X-ray fluorescence calibration samples were excited by a Mo target X-ray tube to give characteristic energy photons with which to illuminate the detector. X-ray fluorescence spectra were accumulated with the Al 0.52 In 0.48 P X-ray detector coupled to a custom-made charge-sensitive preamplifier (both operated at a temperature of 30 °C ± 2 °C). The charge output linearly increased with X-ray photon energy. The energy resolution (Full Width at Half Maximum , FWHM) degraded from 0.99 keV ± 0.02 keV (80 e − rms) at 4.95 keV to 1.12 keV ± 0.02 keV (89 e − rms) at 21.17 keV. The increase of the FWHM with increased energy exceeded the increase expected as a consequence of Fano noise. Hence, the presence of energy dependent incomplete charge collection noise was suggested. The count rate linearly increased with increasing incident X-ray flux across the investigated flux range, up to ∼ 3. 8 × 105 photons s−1 cm−2. [ABSTRACT FROM AUTHOR]

The results of electrical characterisation and X-ray detection measurements of two different active area (0.06 mm 2 and 0.5 mm 2 ) commercial 4H-SiC Schottky photodiodes at room temperature are reported. The devices exhibited low dark currents (less than 10 pA) even at a high electric field strengths (403 kV/cm for 0.06 mm 2 diodes; 227 kV/cm for 0.5 mm 2 diodes). The results of the X-ray measurements indicate that the diodes can be used as photon counting spectroscopic X-ray detectors with modest energy resolutions: FWHM at 5.9 keV of 1.8 keV and 3.3 keV, for the 0.06 mm 2 and 0.5 mm 2 devices, respectively. Noise analysis of the photodiodes coupled to a custom low noise charge sensitive preamplifier is also presented. [ABSTRACT FROM AUTHOR]

The development and characterization of a prototype temperature tolerant (capable of operation up to at least 100 ​°C) particle counting electron spectrometer with an AlInP detector is reported. This is the first time that the response of an AlInP detector to electrons (β− particles) has been reported. The detector was a custom made circular mesa (200 ​μm diameter) Al 0.52 In 0.48 P p+-i-n+ (2 ​μm i layer) photodiode; this was coupled to a custom made low-noise charge-sensitive preamplifier and otherwise standard readout electronics. The detector was electrically characterized and the spectrometer was investigated for its response to illumination from a63Ni radioisotope β− particle source over the temperature range 100 ​°C–20 ​°C. The absorbed electron energy within the active region (i layer) of the AlInP detector and the expected to be detected spectra were calculated using Monte Carlo simulations. Comparisons between the simulated and measured spectra indicated that the response of the spectrometer was in agreement with the Monte Carlo model. Future generations of electron spectrometers of this type are expected to be useful for space science missions where the instrumentation would be subject to high temperatures and intense radiation (e.g. to study the radiolytic processes in comets close to perihelion). In order to inform development of future generations of AlInP electron detectors for such applications, the response of the prototype instrument to illumination with solar wind electrons was modelled within the experimentally verified energy range of the detector; avenues of future development to improve AlInP detector performance, identified from the presently reported results, was investigated and discussed. • An AlInP detector was demonstrated as capable of spectroscopic electron detection. • The spectrometer operated at ≤ 100 ​°C, under illumination of β− particles ≤66 ​keV. • Monte Carlo simulations informed β− particle spectra predicted to be detected. • Experimentally measured and predicted spectra were in agreement. • Avenues of future development to improve AlInP detector performance are discussed. [ABSTRACT FROM AUTHOR]

A prototype monolithic 2 × 2 square pixel Al 0.2 Ga 0.8 As p + -i-n + mesa photodiode array (each photodiode of area 200 μ m by 200 μ m , with a 3 μ m i layer) has been investigated for its utility as a detector for direct detection electron (β - particle) spectroscopy. Each photodiode was electrically characterised and its response to illumination from a 63Ni radioisotope β - particle source was investigated at 20 °C. The percentage of electron energy absorbed in the active layer (i layer), E a b s , of the photodiode and the spectrum expected to be detected, were calculated via Monte Carlo simulations. Comparisons between the simulated and detected 63Ni β - particle spectra are presented and demonstrate uniformity in response across the two by two pixel array. The percentage of electron energy absorbed in the active layer of the detector was at a maximum of 0.53 ± 0.04 for electrons with an energy of 38 keV; the percentage of electron energy absorbed in the active layer of the detector reduced to 0.29 ± 0.02 at 66 keV. To increase the percentage of electron energy absorbed in the active layer of the detector at high energies, inactive Al absorption layers placed atop the detecting structure were investigated as part of the modelling work. These additional Al layers partially attenuated the β - particles' energy, thus reducing the incident particles' energy to values more readily detected by the relatively thin photodiode. Al layers of 20 μ m , 100 μ m , and 500 μ m thickness were investigated and found, by modelling, to increase the percentage of electron energy absorbed in the active layer of such a spectrometer by 22 % at 100 keV; 46 % at 200 keV; and 20 % at 500 keV, respectively. [ABSTRACT FROM AUTHOR]