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Ionising radiation on PIN diode

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					Ionising radiation on PIN diode
There are two major effects on silicon due to ionising radiation: the first is the creation of electrons/holes pairs and the second is the defects creation in the lattice of the silicon crystalline structure. In a full-depleted PIN diode, the first effect leads to a current proportional to the instantaneous particles flux. The second leads to an increase of the leakage current that depends not only on the total dose adsorbed by the diode, but also, due to annealing effects that occur on the crystalline lattice, on its rate. Assuming that the dose rate is low enough or/and that the measurements are done a long time after the irradiation, so that the annealing is exhausted, the increase of the leakage current is proportional only to the total dose adsorbed by the diode. This note intends to summarize some numbers of the radiation effects over a 1cm2 PIN diode, 330 m thick, fully depleted.

Dose and MIPs
The energy deposited in silicon by MIPs creating electron/holes pairs can be measured in standard dosimetry units (Gray). The dose due to a MIP is the energy deposited by the MIP divided by the PIN diode mass:
Dose E MIP  MIPs M

whith

E MIP 

dE   d dx

and

M   d S

where  is the silicon density, d and S are PIN diode thickness and surface, dE/dx is the normalized energy loss of MIPs in silicon, and its value is:
dE MeV Gy  1.664  2.66  10 6 2 dx g / cm Kg / m 2

So:
1MIP  2.66  10 10 Gy 1Gy  3.76  10 9 MIPs

Current and Dose Rate
The charge collected by the PIN diode due to a MIP is given by the ratio between the energy deposited by the MIP and the ionisation energy of an electron/hole pair (3.6 eV), times the electron charge:

dE MeV Gy  1.664  2.66  10 6 2 dx g / cm Kg / m 2


				
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