The Characterization of Germanium and Silicon for Nuclear Radiation Detectors.

Abstract

ABSTRACTSemiconductor nuclear radiation detectors require deep depletion depths (0.03–3.0 cm) and effective charge collection distances which are several times longer than these depletion depths. These requirements place stringent limitations on the net electrically active impurity concentration, and on the concentration of deep centers which can trap carriers generated by the incident nuclear radiation. This need for extremely pure material distinguishes the interests and efforts of the semiconductor detector community from the rest of the semiconductor community. This paper reviews the characterization of shallow-level, deep-level, neutral, and extended defects in germanium and silicon for nuclear radiation detectors. Photothermal ionization spectroscopy has been used extensively to identify the residual hydrogenic impurities in high-purity (∣NA–ND∣ ≈ 1010–1011 cm−3 ) germanium and silicon. Deep level transient spectroscopy has been effectively used to detect and identify deeper levels in high-purity germanium. Residual neutral defects are not necessarily passive: they may complex to form deep or shallow levels, they may precipitate, or they may act as nucleation sites for precipitation. The properties of extended defects (dislocations, lineage, inclusions, precipitates) and their effects on device performance are fundamentally less well understood, as the origin of the electrical activity of these defects is uncertain. It has been found in numerous instances that chemical interactions among defects are important even in these high-purity semiconductors.