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A prototype In0.53Ga0.47As p+-i-n+ x-ray photodiode, fabricated from material grown by metalorganic vapour phase epitaxy, was investigated as a novel detector of x-rays. The detector was connected to a custom low-noise charge sensitive preamplifier and standard readout electronics to produce an x-ray spectrometer. The detector and preamplifier were operated at a temperature of 233 K (−40 °C). An energy resolution of 1.18 keV ± 0.06 keV Full Width at Half Maximum at 5.9 keV was achieved. This is the first time InGaAs (GaInAs) has been shown to be capable of spectroscopic photon counting x-ray detection.

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.

Work towards producing a radiation-hard and high temperature tolerant direct detection electron spectrometer is reported. The motivation is to develop a low-mass, low-volume, low-power, multi-mission capable instrument for future space science missions. The resultant prototype electron spectrometer employed a GaAs p+-i-n+ mesa photodiode (10 µm i layer thickness; β00 μm diameter) and a custom-made charge-sensitive preamplifier. The GaAs detector was initially electrically characterized as a function of temperature. The detector-preamplifier assembly was then investigated for its utility in electron spectroscopy across the temperature range 100 °C to 20 °C using a laboratory 63Ni radioisotope - particle source (end point energy = 66 keV). Monte Carlo simulations using the computer program CASINO were conducted and showed that the spectrometer had a quantum detection efficiency which increased with increasing electron energy up to 70 keV; a quantum detection efficiency of 73 % was calculated. The accumulated 63Ni - particle spectra together with CASINO simulations of the detected spectra showed that the GaAs based spectrometer could be used for counting electrons and measuring the energy deposited per electron in the detector’s active region (i layer). The development of a GaAs electron spectrometer of this type may find use in future space missions to environments of intense radiation (such as at the surface of Europa for investigation of electron-driven radiolysis of ice) and high temperature (such as at Mercury, and comets passing close to the Sun).

A commercial-off-the-shelf (COTS) Si p + -i-n + photodiode (Hamamatsu S5973), designed for visible and infrared detection, was repurposed for use as a low-cost and readily available detector for photon counting X-ray and γ -ray spectroscopy. The detector was investigated for its spectroscopic performance, while being coupled to a custom-made charge sensitive preamplifier, under the illumination of photons with energies up to 59.54 keV. The detector-preamplifier system was subjected to temperatures from 80 °C to 20 °C. Energy resolutions (Full Width at Half Maximum, FWHM) of 0.66 keV ± 0.05 keV at 5.9 keV, 0.70 keV ± 0.04 keV at 22.16 keV, and 0.74 keV ± 0.06 keV at 59.54 keV, were achieved at 20 °C. The energy resolution deteriorated at 80 °C, reaching a value of 1.8 keV ± 0.1 keV FWHM at 59.54 keV. The results suggested that the performance, in terms of energy resolution, of the currently reported COTS Si detector was better than that achieved with certain purpose-grown wide bandgap detectors at 20 °C and 40 °C and better than that achieved with other repurposed Si detectors at 20 °C, opening new possibilities for applications for the Hamamatsu S5973 detectors and increasing the availability of low cost X-ray and γ -ray spectroscopy instrumentation.

The roles of bulk surface states and interfacial defects are probed experimentally using a combination of current–voltage, capacitance–voltage, and impedance measurements. The critical importance of the quality of both the film and interfaces is evident in current–voltage measurements where shunting and interface states result in large dark currents and the subsequent loss of Jsc. These properties are shown to be critically related to the nature and role of the PbS QD interface with the (nominally) ohmic gold contact. Specifically, the nonideality of this interface results in the formation of an electric field and therefore a Schottky barrier that opposes the transport of carriers across the conventional ZnO–PbS CQD system. Nonidealities in the structure and absorber layer are also reflected in nonmonotonic behavior and dispersion in C–V measurements with trapping processes on the CQD surfaces, and the ZnO/PbS and PbS/Au interfaces also affecting the carrier dynamics, which is reflected in the response ti...

In this work, a 200 μm diameter InGaP (GaInP) p+-i-n+ mesa photodiode was studied across the temperature range 100 °C to 20 °C for the development of a temperature-tolerant electron spectrometer. The depletion layer thickness of the InGaP device was 5 μm. The performance of the InGaP detector was analysed under dark conditions and then under the illumination of a 183 MBq 63Ni radioisotope beta particle source. The InGaP photodiode was connected to a custom-made low-noise charge-sensitive preamplifier to realise a particle counting electron spectrometer. Beta spectra were collected at temperatures up to 100 °C with the InGaP device reverse biased at 5 V. The spectrum accumulated at 20 °C was compared with the spectrum predicted using Monte Carlo simulations; good agreement was found between the predicted and experimental spectra. The work is of importance for the development of electron spectrometers that can be used for planetary and space science missions to environments of high temperature or extreme radiation (e.g. Mercury, Jupiter’s moon Europa, near-Sun comets), as well as terrestrial applications.

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.

A GaAs/Al0.8Ga0.2As separate absorption and multiplication (SAM) x-ray avalanche photodiode (APD) structure was grown by metalorganic vapor phase epitaxy. Mesa photodiodes of different diameters (200 μm and 400 μm) were fabricated from the structure. Two of the photodiodes (one of each diameter) were characterized at 20 °C for their electrical properties and response to x rays using an 55Fe radioisotope x-ray (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV) source. An energy resolution of 508 eV ± 5 eV full width at half maximum (FWHM) at 5.9 keV was achieved at an apparent avalanche gain, M, of 1.1. This is the best energy resolution so far reported for GaAs/AlxGa1−xAs x-ray SAM APDs. The noise components associated with the achievable spectroscopic energy resolutions are reported. Comparisons between the 200 μm and 400 μm diameter GaAs/AlxGa1−xAs SAM x-ray APDs and recently studied GaAs p+-i-n+ detectors were made, showing that the inclusion of the avalanche layer improves the achievable energy resolution; energy resolutions of 508 eV FWHM at 5.9 keV at M = 1.1 and 603 eV FWHM at 5.9 keV at M = 1.2 were achieved with the 200 μm and 400 μm diameter GaAs/AlxGa1−xAs SAM x-ray APDs, respectively; this is better than was previously reported for similar devices without avalanche layers: 690 eV FWHM at 5.9 keV and 730 eV FWHM at 5.9 keV for 200 μm and 400 μm diameter GaAs p+-i-n+ detectors, respectively [Lioliou et al., J. Appl. Phys. 122, 244506 (2017)].

Two 400 μm diameter Al0.52In0.48P p+-i-n+ mesa photodiodes (6 μm i layer) were fabricated from a wafer grown by metalorganic vapour phase epitaxy (MOVPE) and then studied at temperatures from 140 °C to -20 °C for the development of temperature tolerant 55Fe X-ray photovoltaic and 63Ni betavoltaic microbatteries. The Al0.52In0.48P epitaxial layers are the thickest so far reported for this emerging application. At each temperature, the performances of the Al0.52In0.48P detectors were analysed in dark conditions, as well as under the illumination of a 182 MBq 55Fe radioisotope X-ray source and a 185 MBq 63Ni radioisotope source. An open circuit voltage as high as 1.13 V was found for both the Al0.52In0.48P X-ray photovoltaic cells at -20 °C; whilst an open circuit voltage of 0.47 V was found for the best 63Ni betavoltaic cell, at the same temperature. Maximum output powers of 1.44 pW and 1.36 pW were obtained from the two X-ray photovoltaic cells at -20 °C; combining the output powers of these two Al0.52In0.48P X-ray photovoltaic cells, a total maximum output power as high as 2.8 pW could be obtained at 20 °C. Maximum output powers of 0.18 pW and 0.13 pW were instead extracted from the two betavoltaic cells at -20 °C, these could lead to a total maximum output power as high as 0.3 pW at 20 °C. Conversion efficiencies of 2.2% and 0.06% were found, respectively, for the best Al0.52In0.48P X-ray photovoltaic and betavoltaic cells at -20 °C. With respect to previously reported Al0.52In0.48P X-ray photovoltaic cells with thinner i layers, the 6 μm Al0.52In0.48P X-ray photovoltaic cells had higher short circuit current, open circuit voltage, maximum output power, and conversion efficiency. The 6 μm Al0.52In0.48P betavoltaic cells instead presented similar performances to previously analysed Al0.52In0.48P betavoltaic cells.

Two GaAs p+-i-n+ mesa X-ray photodiodes were characterized for their electrical and photon counting X-ray spectroscopic performance over the temperature range of 100 °C to –20 °C. The devices had 10 μm thick i layers with different diameters: 200 μm (D1) and 400 μm (D2). The electrical characterization included dark current and capacitance measurements at internal electric field strengths of up to 50 kV/cm. The determined properties of the two devices were compared with previously reported results that were made with a view to informing the future development of photon counting X-ray spectrometers for harsh environments, e.g., X-ray fluorescence spectroscopy of planetary surfaces in high temperature environments. The best energy resolution obtained (Full Width at Half Maximum at 5.9 keV) decreased from 2.00 keV at 100 °C to 0.66 keV at –20 °C for the spectrometer with D1, and from 2.71 keV at 100 °C to 0.71 keV at –20 °C for the spectrometer with D2. Dielectric noise was found to be the dominant source of noise in the spectra, apart from at high temperatures and long shaping times, where the main source of photopeak broadening was found to be the white parallel noise.