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 Î, where Î
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
temperature
|
Band gap
(eV)
|
Î
(eV) |
Density
(gcm-3) |
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 |
3.5×104 |
4.2×104 |
| 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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