Silicon Microstrip Detectors, A New Tool for Charm Physics

The characteristic property of a monocrystalline semiconducting material is the small separation between the electronic conduction band and the valence band. A small amount of energy, Eg = 1.12 eV in the case of silicon, is therefore sufficient to excite an electron into the conduction band. The hole left in the valence band behaves like an independently moving positive charge carrier and has a mobility which is comparable to that of the free electron (1500 cm2 V-1 s-1 for e- and 600 cm2 V-1 s-1 for the hole1. At a given temperature there is equilibrium between the generation and recombination of free electrons and holes. Impurities and crystal defects act as generation or recombination centers and reduce therefore the mean free carrier lifetime. The introduction of electrically active donor or acceptor impurity atoms (“doping”) results in a n-type or p-type conductivity semiconductor with an excess of electrons respectively holes.