Physics and Engineering of Radiation Detection

5.1. Semiconductor Detectors 277

T (K)

250 260 270 280 290 300 310

-3)

(cmi

n

1012

1013

Figure 5.1.17: Dependence of

intrinsic charge concentration in

germanium on absolute temper-

ature.

Fortunately, germanium can be obtained in extremely pure form^2 .Thelower
resistivity is therefore mainly due to low band gap energy. There are a number of
elements that can be used to dope germanium to make it suitable for use as detection
medium. The most common of such doping agents are listed in Table.5.1.6.

Table 5.1.6: Common donor and acceptor elements used to dope silicon. Also given
are their ionization energies (47).

Doping Agent Symbol Type Ionization Energy (eV)

Arsenic As Donor 0.014

Phosphorus P Donor 0.013

Antimony Sb Donor 0.010

Bismuth Bi Donor 0.013

Lithium Li Donor 0.093

Aluminum Al Acceptor 0.011

Boron B Acceptor 0.011

Gallium Ga Acceptor 0.011

Indium In Acceptor 0.012

Thallium Tl Acceptor 0.013

(^2) High Purity Germaniumor HPGe detectors are widely used forγ-ray spectroscopy.