Anomalous field dependence of deep level emission in proton irradiated silicon

In this study n-type silicon with doping ranging from 10(13) up to 10(16) cm(-3) have been irradiated with protons of energies from 1.3 to 9.5 MeV protons. The proton doses have been restricted to levels that result in point defect concentrations below 10% of the doping at the investigated depths in the samples. This makes quantitative analyses with deep level transient spectroscopy (DLTS) possible. The depth of interest is in the tail of the defect distribution where only a slight increase in concentration should be measured when moving deeper into the sample. However, the DLTS measures a dramatic drop in the defect concentration close to the surface, which is attributed to an experimental artifact when an electric field above 25 kV/cm is present. This anomalous held effect is especially prominent for the well known vacancy-oxygen center and the singly negative charge state of the divacancy, both acceptor levels that are not anticipated to display a Poole-Frenkel effect. (C) 1999 Published by Elsevier Science B.V. All rights reserved.