272 Chapter 5. Solid State Detectors
and the second is a range of donor density where the effects are most profound. It is
apparent that increasing the donor density by three orders of magnitude decreases
the electron and hole mobilities by approximately a factor of 10. Any change in
donor density with time can therefore have serious effect on detector performance.
Figure 5.1.11: Dependence of
electron mobility on the donor
density in silicon at 300 K
(19).We will see later in the chapter that the physical damage to silicon caused by
radiation has the potential to change the intrinsic charge density. This is one of
the reasons why prolonged deployment of silicon detectors in high radiation envi-
ronments is associated with slow non-linearities in detector response. The practice,
therefore, is to closely monitor the detector for changes and to use temperature
lowering and bias increase to compensate for the deterioration.
Figure 5.1.12: Dependence
of hole mobility on the donor
density in silicon at 300 K
(19).Let us now examine how the mobilities of electrons and holes depend on tem-
perature. It has been found that in silicon both types of charge carriers respond
approximately in the same manner to temperature changes. The temperature de-