Anneal induced transforms of radiation defects in heavily electron irradiated Si diodes

Abstract

In this work, the spectra of deep traps attributed to radiation defects in n-type Czochralski (CZ) grown Si with dopant concentrations of 1015 cm−3 have been studied. Samples were irradiated with 6.6 MeV electrons with fluences in the range of (1–5) × 1016 e/cm2. Irradiated samples were annealed using isochronal 24 hour heat treatments in nitrogen (N2) gas at ambient temperature and by discretely varying the temperature from 80 °C to 280 °C. The as-irradiated and annealed samples were studied by combining capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and temperature dependent carrier trapping lifetime (TDTL) measurements. Schottky barrier contacts and ohmic contacts were deposited on the samples by Au magnetron sputtering and metal sintering, respectively, for C-V and DLTS measurements after each heat treatment procedure. In order to reduce the uncertainties due to contact quality, TDTL contact-less measurements were performed using microwave probed photoconductivity transient (MW-PC) technique. Using these techniques, we observe suppression of the rather deep carrier emission centres after heat treatment at elevated temperatures. However, the reduction of deep acceptor concentrations after anneals at elevated temperatures was observed to be accompanied by considerable increase of shallow acceptor concentrations which effectively compensate the dopants. The activation energies of the predominant peaks within the spectrum, displayed as temperature dependent carrier trapping lifetime variations, were measured and are shown to be in good agreement with those obtained from the DLTS spectra.