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4H-SiC Schottky photodiodes, with 25 μ m epitaxial layers, employing thin (20 nm) Ni 2 Si Schottky contacts, were investigated for high temperature photon counting X-ray spectroscopy. Important X-ray photodiode detector parameters were extracted from electrical characterization within the temperature range 160 °C to 0 °C. The devices were found to be fully depleted at an applied electric field of 20 kV/cm; a leakage current density of 33 nA cm -2 ± 1 nA cm−2 at 160 °C, was measured for one of the devices. The detectors were subsequently connected to low-noise photon counting readout electronics and investigated for their spectral performance at temperatures up to 100 °C. With the charge-sensitive preamplifier operated at the same temperature as the detector the best energy resolution (Full Width at Half Maximum at 5.9 keV) obtained decreased from 2.20 keV ± 0.04 keV (120 e − rms ± 2 e − rms) at 100 ∘ C to 1.20 keV ± 0.03 keV (65 e - rms ± 2 e − rms) at 0 ∘ C. The dominant source of noise broadening the 55Fe X-ray photopeak was found to be the dielectric noise, except for the spectra accumulated at 100 °C and long shaping times (> 6 μ s), in those case the main source of photopeak broadening was the white parallel noise. [ABSTRACT FROM AUTHOR]

A GaAs 63 Ni radioisotope betavoltaic cell is reported over the temperature range 70 °C to −20 °C. The temperature effects on the key cell parameters were investigated. The saturation current decreased with decreased temperature; whilst the open circuit voltage, the short circuit current, the maximum power and the internal conversion efficiency values decreased with increased temperature. A maximum output power and an internal conversion efficiency of 1.8 pW (corresponding to 0.3 μW/Ci) and 7% were observed at −20 °C, respectively. [ABSTRACT FROM AUTHOR]

Five mesa p+-i-n+ photodiodes (each of 0.126 mm2 area) were investigated as conversion devices for X-ray-voltaics, in order to understand the comparative effects between different semiconductor materials, device structures, and X-ray incident power, and to explore them for use in future radioisotope microbatteries. Three semiconductor materials (AlInP, InGaP, and GaAs) and three i layer thicknesses of one material, AlInP (2 μm, 6 μm, and 10 μm), were investigated under the illumination of various controlled X-ray incident powers. The highest short circuit current was achieved with the GaAs device due to its thickest active layer and highest linear absorption coefficients at the most numerous incident X-ray photon energies (Mo Kα at 17.48 keV; Mo Kβ at 19.6 keV). The highest open circuit voltage was achieved with the 10 μm AlInP device due to its widest bandgap (cf. InGaP and GaAs) and its highest short circuit current (cf. the 2 μm and the 6 μm AlInP devices). The greatest output X-ray power was recorded with the InGaP device due to its highest fill factor (i.e. relatively low series and high shunt resistance) compared to the rest of the devices, although the GaAs device had the highest theoretical output X-ray power. A method for selecting the most suitable semiconductor material and device structure of conversion devices for radioisotope microbatteries (for exhibiting the highest power output) is presented considering the incident X-ray spectrum, while highlighting the importance of non-ideal device effects (reduced charge collection efficiency, increased series resistance, and reduced shunt resistance). [ABSTRACT FROM AUTHOR]

The ultimate conversion efficiency of semiconductor radioisotope microbatteries is set by the average energy consumed in the creation of an electron-hole pair, ω. Although the Klein relationship between ω and semiconductor bandgap, E g , is widely cited, not only for radioisotope microbatteries, but indeed for a multitude of fields requiring accurate values of ω , its validity has been recently questioned; new experimental measurements have resulted in the refined Bertuccio-Maiocchi-Barnett (BMB) relationship. Here, it is shown that the new relationship indicates the ultimately achievable conversion efficiencies of radioisotope microbatteries are much greater than had ever been expected. For example, it appears possible to produce planar 63Ni-Diamond radioisotope microbatteries with output powers 130× greater than has currently been achieved. The ultimate limit for batteries employing pore channels rather than planar designs is likely to be even greater still. These new findings open the possibility of using radioisotope microbatteries in a far greater variety of applications than has been traditionally assumed. As well as being of direct applicability to radioisotope microbatteries, the results highlight the need to reconsider the use of the Klein relationship in all fields that currently employ it. • The conversion efficiency of radioisotope microbatteries has been reconsidered. • Ultimate conversion efficiencies are much higher than traditionally expected. • All materials with bandgaps >1.1 eV are affected. • 63Ni-diamond batteries may have 130 × higher output power than so far achieved. [ABSTRACT FROM AUTHOR]

An electronic grade single crystal chemical vapour deposition diamond was investigated as a prototype high temperature spectroscopic electron (β- particle) detector for future space science instruments. The diamond detector was coupled to a custom-built charge-sensitive preamplifier of low noise. A 63Ni radioisotope source (endpoint energy 66 keV) was used to provide a spectrum of β- particles incident on the detector. The operating temperature of the detector/preamplifier assembly was controlled to allow its performance to be investigated between +100 °C and −20 °C, in 20 °C steps. Monte Carlo modelling was used to: a) calculate the β- particle spectrum incident on the detector; b) calculate the fraction of β- particle energy deposited into the detector; and c) predict the β- particle spectrum accumulated by the instrument. Comparison between the model and experimental data suggested that there was a 4.5 μm thick recombination region at the front of the detector. The spectrometer was demonstrated to be fully operable at temperatures, T , −20 °C ≤ T ≤ 80 °C; the results suggested that some form of polarisation phenomenon occurred in the detector at > 80 °C. This article presents the first report of an energy calibrated (≲ 50 keV) spectroscopic β- particle diamond detector. • A proof-of-principle high temperature tolerant electron spectrometer is reported. • The spectrometer utilised a prototype chemical vapour deposition diamond detector. • Electrons from a63Ni radioisotope β− particle source detected spectroscopically. • The instrument operated successfully at temperatures ≤80 °C. [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]