Abstract
Electron irradiation of silicon transistors in the Cambridge high-voltage microscope indicates that the formation of interstitial clusters in irradiated silicon depends on the charge state of the interstitial. It appears that:
(1) (a) Heavy p-doping is capable of pinning the Fermi level sufficiently to prevent it from crossing the interstitial level corresponding to a neutral state, so interstitials have a positive charge except at high temperatures.
(b) In n-type material, the interstitial appears to be neutral.
(c) For irradiation at high temperatures, i.e. near intrinsic temperatures, clustering is independent of the type and nature of the dopant, so the interstitial appears to be neutral in both n- and p-type material.
(2) The electric field ionization at the p–n junction depletion region inhibits clustering of interstitials in this region at moderate temperatures; at high temperatures clustering is observed due to break-down of the junction.
(3) All these effects can be explained by an interstitial level which is perhaps 0·40 ± 0·05 eV above the top of the valence band.