High Purity N-Type Gallium Arsenide for Nuclear Particle Detection

Room temperature operating X and alpha ray spectrometers have been made with gallium arsenide. Surface barrier diodes, using gold or palladium have been fabricated on high purity material grown by liquid phase epitaxy. The epitaxial layers have a thickness varying from 30 to 120 μM and an electrically active impurity concentration varying from 5.1012 to 1.1014 per cc. These layers deplete with only 8 volts reverse bias. Diodes of 4 to 8 mm2 area have given a resolution 15.5 kev FWHM on 5.48 MeV alpha particles at room temperature and 40 keV at 120°C. Similar devices have given a resolution of better than 5 keV FWHM on 60 keV X-rays at 25°C. The bulk generated currents are as low as 2.5 nanoamperes per cubic millimeter.