Semiconductor detector materials...

An ideal semiconductor detector material will:

  • have as large an absorption coefficient as possible (i.e. high atomic number);
  • provide as many electron-hole pairs as possible per unit of gamma energy (low , where is the average energy needed to create an electron-hole pair);
  • provide good electron and hole mobility;
  • be available in high purity as near perfect single crystals; and
  • be available in reasonable amounts at reasonable costs.

The table below details possible candidates:

Material Atomic number Operating


Band gap





Mobilty (cm2V-1s-1)
Electrons Holes
Si 14

Room temp.

1.106 3.62 2.33 1350 480
Ge 32 Liquid N2 0.67 0.67 5.32 3.5104 4.2104
CdTe 48, 52 Room temp. 1.47 1.47 6.06 1000 80
HgI2 80, 53 Room temp. 2.13 2.13 6.30 100 4

Silicon is an obvious choice because of the efforts of the electronics industry in producing high purity material at reasonable cost. The disadvantage is its low atomic number. For this reason germanium is the most common detector material. Other semiconductor materials have a larger band gap than Germanium making them suitable for room temperature operation.

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