High efficiency silicon X-ray detectors

Thick silicon multicathode detectors (SMCDs) for high efficiency X-ray detection have been designed, fabricated, and tested. These thick detectors (up to 1.5 mm thick) extend the practical X-ray detection range from the current level of ∼20 keV, up to ∼40 keV, while still maintaining the low noise and high count rate performance of the thinner (∼0.3 mm) SMCD technology. The increase in X-ray detection efficiency at higher energies will have a significant impact on practical uses of these detectors in a wide variety of X-ray fluorescence (XRF) applications. In addition to increasing the detection efficiency for X-rays, the thick silicon detectors will offer improved efficiency for high energy electrons, alphas, and other light particles in nuclear physics and astrophysics applications. Very high resistivity float zone material was used for the substrates to minimize the operating voltages required. Multiguard ring structures were designed to prevent the premature breakdown of the devices at the voltages required to fully deplete the thick detectors. We have measured 172 and 158 eV full-width at half-maximum energy resolution at 5.9 keV (at 4 μs and 12 μs peaking time, respectively, -55°C) on 1 mm thick prototype detectors. Spectral performance, energy resolution, efficiency, and count rate performance are presented.