GaAs Spectrometer for Planetary Electron Spectroscopy

Abstract

AbstractWork toward 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, multimission 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; 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 to 20 °C using a laboratory 63Ni radioisotope β− 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 β− 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).