Study of radiation damage in silicon detectors for high ... - F9

2Operation and Radiation Damage of Silicon Detectors2.1 Basics of Operation of Silicon DetectorsA silicon position-sensitive detector is an array of diodes on a silicon wafer. When reversebiased, it is operating like an ionization chamber. Ionising particles passing a silicon detectorgenerate electron-hole pairs along their paths. The number of pairs is proportionalto the particles' energy loss. The creation of an electron-hole pair requires a mean energyof 3.6 eV with average energy loss in silicon of about 390 eV/m foraminimum-ionisingparticle. For a typical detector thickness of about 300 m, one obtains on average 3 10 4electron-hole pairs, a signal detectable with low-noise electronics.pad (p + ) guard ring (p + )n bulk+backplane (n )Figure 2.1: Aschematic view of a pad detector. The highly doped p + pad and guard ring areshown on the p side of the diode.As the emphasis of this study was in the radiation damage of the silicon bulk,silicon pad detectors (diodes) proved to be the ideal device. Simple processing providesgood reproducibility and low cost. Simple structure of pad detectors (gure 2.1) stronglyreduces the eects of surface radiation damage. Detectors consist of high resistivity bulk,highly n doped (n + ) on one side (backplane). The other (p) side consists of a large highlydoped p + pad, often surrounded by one or more p + rings (guard rings). Due to simple11