DOI: 10.25377/sussex.6899954
title: Dataset for research paper: GaAs Spectrometer for Planetary Electron Spectroscopy

description: Data for 9 figures in research paper appearing in the Journal of Geophysical Research – Space Physics.<br><br><b>Figure 2.</b> Measured capacitance of the GaAs p<sup>+</sup>-i-n<sup>+</sup> mesa photodiode within the temperature range 100 °C to 20 °C.<br><br><b>Figure 3.</b> Calculated depletion width of the GaAs p<sup>+</sup>-i-n<sup>+</sup> mesa photodiode at 100 °C (filled triangles) and 20 °C (filled circles).<br><br><b>Figure 4.</b> Leakage current as a function of applied reverse bias of the GaAs p<sup>+</sup>-i-n<sup>+</sup> mesa photodiode in the temperature range 100 °C down to 20 °C.<br><br><b>Figure 5.</b> Quantum detection efficiency, QE, of the detector for electrons of each energy, in detector regions covered by top contacts (diamonds) and not covered by top contacts (circles) as a function of incident electron energy. The weighted quantum efficiency is also shown (open squares).<br><br><b>Figure 6.</b> Simulated <sup>63</sup>Ni β<sup>‑</sup> particle spectrum as emitted from the source (solid line), and incident on the top face of the detector (square dots).<br><br><b>Figure 8.</b> Experimentally measured <sup>63</sup>Ni β<sup>-</sup> particle spectra (counts per 1 keV as a function of energy) within the investigated temperature range (between 100 °C and 20 °C, with 20 °C decrements).<br><br><b>Figure 9.</b> Comparison between the accumulated <sup>63</sup>Ni β<sup>-</sup> particle spectrum at 20 °C (grey solid line) and the predicted to be detected spectrum (black dashes). The spectrum incident on the detector as calculated with CASINO simulations is also shown.<br><br><b>Figure 10.</b> Omnidirectional electron flux expected at Europa (9.5 R<sub>J</sub>) as a function of energy, after Paranicas et al. (2009).<br><br><b>Figure 11.</b> Comparison between the predicted to be incident on detector (solid line) and to be detected (black dashes) electron spectra (10 keV to 100 keV) of the radiation environment near Europa’s orbit. Electron energy losses within the top contact, the p<sup>+</sup> layer, and the n<sup>+</sup> layer/substrate explained the difference between the spectra predicted to be incident and predicted to be detected.<b><br></b><b>Abstract from research paper</b> 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<sup>+</sup>-i-n<sup>+</sup> mesa photodiode (10 µm i layer thickness; 200 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 <sup>63</sup>Ni radioisotope β<sup>-</sup> 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 <sup>63</sup>Ni β<sup>-</sup> 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).<br>