Transcription of Chapter 8 Hyper-Pure Germanium Detector
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Chapter 8 Hyper-Pure Germanium Detector
Med Phys 4RA3, 4RB3/6R03 Radioisotopes and Radiation Methodology 8-1 Chapter 8 Hyper-Pure Germanium Detector Introduction Silicon semiconductor detectors described in the previous Chapter have depletion depths less than 1 mm, which are sufficient for charged particle spectroscopy or soft X-ray detection. For photon spectroscopy in the energy region of hundred keV or several MeV, much thicker semiconductor detectors are required. Fig. shows the mean free path of a photon in silicon and Germanium . It is obvious that a depletion depth of at least several cm is required. Due to its higher atomic number, Ge has a much lager linear attenuation coefficient, which leads to a shorter mean free path. Thus, Ge is preferred for hard X-ray or gamma-ray detection to achieve higher detection efficiency.
In both Si and Ge, the material with highest available purity tends to be p-type, which requires addition of donor atoms for compensation. The alkali metals like Li, Na tend to form interstitial donors in Si and Ge. When one of these donor materials (practically Li) is introduced into Si or Ge, the donor atoms are easily ionized
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