Study of bulk grown silicon–germanium radiation detectors

Results of p+−i−n+-like (PIN) devices fabricated with a single crystal, Czochralski grown silicon germanium are reported. It is shown that the material has a high potential for x-ray detector applications. The devices were characterized under dark conditions as well as under infrared laser illumination and gamma-ray photons. The Si1−xGex semiconductor contains ∼5% (atomic concentration) of germanium and has a measured resistivity of ∼100 Ω cm. The devices show diode behavior with frequency and temperature independent capacitance–voltage characteristics. The deep level transient spectroscopy results reveal a substantial concentration of trapping centers, some possibly related to the boron-vacancy complex. The devices were operated with x- and gamma-ray photons in spectroscopy mode at low temperatures and the results clearly show the beneficial effect of the added germanium on the absorption coefficient, which increased by a factor 2–3 compared to silicon. The results of the transient current characterization technique with a 1060 nm laser indicate a fast photoresponse with no afterglow effects. The main challenges seem to be the relatively low resistivity of the currently available material, limiting the active volume, and the high generation rate at room temperature. It should be emphasized that the SiGe used in this study was not particularly tailored for detector application during the growth.

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