Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 4. SOLID STATE DETECTOR THEORY 18
Landau distribution
L(x)
0.18
0.16
Exact ≅ CERN Library
0.14
Moyal’s Function
0.12
0.1
0.08
0.06
0.04
0.02
0
-5 -2.5 0 2.5 5 7.5 10 12.5 15 17.5 20
x
Figure 4.2: The exact Landau distribution, which iscovered by the CERN Library approximation
in this plot, and Moyal's approximation.
4.3 Principal Detector Layout
Most solid state detectors are made for particle tracking. Thus, the absolute signal value
is irrelevant in most cases. However, as the signal coming from a MIP traversing the
detectors is only in the order of several thousand electrons, one aims to maximize the
signal-to-noise ratio (SNR). While the signal size depends on the detector material and
geometry, the amplier usually dominates the noise gure.
In order to minimize particle scattering and absorption, tracking detectors are made of
thin layers of material, usually in the order of a few hundred micrometers, with electrodes
on opposite sides to apply the \bias" voltage and drain the particle induced signal. One
electrode can be formed as strips or pixels to obtain position information, as discussed in
chapter 8. Nevertheless, for a simple model we will assume pad contacts.
Fig. 4.3 shows the detector function, which is in principal a charge movement inside a
capacitor.
In the band model, the number of charges in the conduction band per unit volume at
equilibrium, called intrinsic carrier density n i , is given by
n 2 i
= N C N V e , Eg
kT ; (4.4)
N C;V
= 2 3
2m
h 3 e;h kT 2
: