Title: Description of radiation damage in diamond sensors using an effective defect model,
Abstract: The BCML system is a beam monitoring device in the CMS experiment at the LHC.
As detectors poly-crystalline diamond sensors are used. Here high particle
rates occur from the colliding beams scattering particles outside the beam
pipe. These particles cause defects, which act as traps for the ionization,
thus reducing the CCE. However, the loss in CCE was much more severe than
expected. The reason why in real experiments the CCE is so much worse than in
laboratory experiments is related to the rate of incident particles. At high
particle rates the trapping rate of the ionization is so high compared with the
detrapping rate, that space charge builds up. This space charge reduces locally
the internal electric field, which in turn increases the trapping rate and
hence reduces the CCE even further. In order to connect these macroscopic
measurements with the microscopic defects acting as traps for the ionization
charge the TCAD simulation program SILVACO was used. Two effective acceptor and
donor levels were needed to fit the data. Using this effective defect model the
highly non- linear rate dependent diamond polarization as function of the
particle rate environment and the resulting signal loss could be simulated.