Formation of Radiation-induced Defects in Si Crystals Irradiated with Electrons at Elevated Temperatures

摘要

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_iO_i) complexes. The introduction rates of the VO and C_iO_i 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 (V_2) and trivacancies (V_3) to V_2-oxygen and V_3-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.