Large area, low capacitance Si(Li) detectors for high rate X-ray applications

Large area, single-element Si(Li) detectors were fabricated using a novel geometry which yields detectors with reduced capacitance and hence reduced noise at short amplifier pulse-processing times. A typical device employing the new geometry with a thickness of 6 mm and an active area of 175 mm² has a capacitance of only 0.5 pF, compared to 2.9 pF for a conventional planar device with equivalent dimensions. These low capacitance detectors, used in conjunction with low capacitance field effect transistors, will result in X-ray spectrometers capable of operating at very high count rates while still maintaining excellent energy resolution. The spectral response of the low capacitance detectors to a wide range of X-ray energies at 80 K is comparable to typical state-of-the-art conventional Si(Li) devices. In addition to their low capacitance, the new devices offer other advantages over conventional detectors. Detector fabrication procedures, I-V and C-V characteristics, noise performance, and spectral response to 2-60 keV X-rays are described