Evolution of radiation induced defects and the type inversion in high resistivity silicon under neutron irradiation.

A model which describes the type conductivity inversion and the Fermi level stabilisation in high purity n-silicon under fast neutron irradiation has been considered. This model takes into account shallow impurities, oxygen, A- and E-centres and deep amphoteric centres (the vacancy complexes). The role of divacancies is dominant in the Fermi level stabilisation effect. The neutron fluence when the type inversion is observed has been calculated for various initial n-silicon. The results obtained describe peculiarities of the behaviour of neutron integral dosemeters. Characteristics of p-i-n diodes used as fast neutron sensors over a wide dose range and the influence of both the carrier life time and the silicon resistivity changes on the sensor sensitivity are discussed. Using long base diodes fabricated from high resistivity silicon (>10 kΩ.cm) allows the sensitivity to reach 5 V.Gy -1 (tissue).