Physics and Engineering of Radiation Detection

5.2. Diamond Detectors 309

in diamond has an approximate temperature dependence of the form (32)

μe∝

1

T

. (5.2.3)

This profile is much softer than the ones we saw for semiconductor materials, which
is a good thing in terms of detector design and operation specially because in this
case the detector does not necessarily require temperature control and monitoring.
However before we jump to any conclusion in this regard let us see how the holes
behave at different temperatures in diamond. Fig.5.2.2 shows such a profile for
natural diamond and boron doped CVD diamond.

Figure 5.2.2: Variation of hole mobility in

diamond with respect to the absolute tem-

perature for natural diamond (•)andboron

doped CVD diamond ()(32).

According to Fig.5.2.2, the temperature dependence of hole mobility for CVD
diamond is somewhere between

μh∝

T−^1.^5 for T< 400 K and

T−^2.^8 for T≥ 400 K.

(5.2.4)

This certainly does not look as good as the mobility profile for electrons. However
the point to note here is that the temperature dependence near and below the room
temperature is still not so steep that one would argue for cooling the material.
A parameter that is routinely used to characterize the detectors made of CVD
diamond is the drift lengthdDdefined as

dD=(μeτe+μhτh)E, (5.2.5)

whereτeandτhare thedeep trapping lifetimesof electrons and holes respectively and
Eis the electric field intensity. Of course here we are using our earlier conclusion that