Formation of radiation-induced defects in Si crystals irradiated with electrons at elevated temperatures

Defects induced in silicon crystals by irradiations with 6 MeV electrons in the temperature range 60 to 500 °C have been studied by means of deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. Diodes for the study were fabricated on n-type epitaxially grown Si wafers. The DLTS spectra for the samples irradiated at elevated temperatures were compared with those for samples, which were subjected to irradiation at 60 °C and subsequent isochronal anneals in a furnace. The dominant radiation-induced defects in the samples irradiated at temperatures lower than 400 °C were found to be vacancy-oxygen (VO) and interstitial carbon - interstitial oxygen (C iOi) complexes. The introduction rates of the VO and CiOi centers increased about twice upon raising the irradiation temperature from 50 to 400 °C. It is argued that this effect is associated with either a) the suppression of the annihilation rate of Frenkel pairs or b) a decrease in the threshold energy for displacement of a host Si atom upon increase in the irradiation temperature. Transformations of deep level traps due to divacancies (V2) and trivacancies (V3) to V2-oxygen and V3-oxygen complexes were found to occur upon irradiation or annealing at temperatures exceeding 250 °C. A clear anti-correlation between changes in the minority carrier life time induced in the p+-n diodes by irradiation at different temperatures and changes in the concentrations of radiation-induced vacancy- and vacancy-oxygen-related complexes was found. © (2010) Trans Tech Publications.