FAST NEUTRON-INDUCED CHANGES IN NET IMPURITY CONCENTRATION OF HIGH-RESISTIVITY SILICON

Resistivity changes produced by 1 Mev neutron irradiation at room temperature have been measured in float-zone grown n and p-type silicon with initial resistivities ranging from 1.8 to 100 kOMEGAcm. Observed changes are discussed in terms of net electrically active impurity concentration. A model is presented which postulates escape of Si self-interstitials and vacancies from damage clusters and their subsequent interaction with impurities and other preexisting defects in the lattice. These interactions lead to transfer of B and P from electrically active substitutional configurations into electrically inactive positions (B(i) , P(i), and E-center), resulting in changes of net electrically active impurity concentration. The changes in spatial distribution of resistivity are discussed, and the experimental data are fit by theoretical curves. Differences in the behavior of n-type and p-type material are explained on the basis of a faster removal of substitutional P and a more nonuniform spatial distribution of the original P concentration.