Carrier Removal in Neviron Irradiated Silicon

It is demonstrated that a spherical defect cluster is not adequate to explain the doping dependence of carrier removal in neutron damaged silicon. To resolve this problem, a cylindrical cluster of the type calculated by Van Lint et al is examined. This type of cluster can be described as a "supercluster" composed of several subclusters of extremely high defect concentration (1021 cm-3) of lower concentration (1018cm-3). The subclusters arise from the final stopping of the recoil atoms. Subclusters are less than 60 Ã… in diameter and contain up to 100 individual defects. The tree of defects arises from displacements occurring along the tracks of the recoiling lattice atoms. From a consideration of the distribution of space charge and electric potential associated with this type of structure quantitative predictions are made of the doping dependence of carrier removal. These predictions depend un the cluster dimensions and the Fermi energy within the cluster. Since the cluster dimensions can be obtained from the work of Van Lint et al, the predictions depend on only one undetermined parameter. Excellent fit has been obtained between this theory and published data on carrier removal. The indicated values of the Fermi energy within the cluster were 0.48, 0.38, 0.51 eV for N-type float zone, N-type Czochralski, and P-type silicon respectively. These values are not inconsistent with an assignment based on known energy levels of the divacancy and the A-center.