a Study of Defects Produced in Silicon by Electron Irradiation at Cryogenic Temperatures.

This dissertation describes studies of defects produced in silicon by electron irradiation (1.5 - 3.0 MeV) in situ at cryogenic temperatures (4.2 K, 20.4 K). The experimental techniques used in these studies were Electron Paramagnetic Resonance (EPR) and Deep Level capacitance Transient Spectroscopy (DLTS). Although many defects were observed in these studies, there are three areas of emphasis that can be singled out. During this study, interstitial boron was shown to have negative-U properties. DLTS studies, employing novel optical techniques, succeeded in detecting the single donor (0/+) level at E(,c) - .13 eV. Correlation of the properties of this new level and the previously detected acceptor (-/0) level at E(,c) - .45 eV, demonstrates the negative-U ordering. The donor level exhibits a large Poole-Frenkel effect which, when properly accounted for, provides a direct connection to the EPR identified interstitial boron atom. This represents the first unambiguous identification of a negative-U defect in any solid. Studies aimed at understanding the properties of the silicon self-interstitial were undertaken using EPR and DLTS as complementary techniques. Although the self-interstitial has still eluded direct detection, it was possible to explore the trapping, release, and migration of this defect. This was accomplished by monitoring the presence of interstitial-related defects; these include the non-reorientable divacancy, two unidentified EPR centers labeled Si-G25 and Si-L1, and a DLTS level that has been identified as arising from interstitial carbon. Oxygen was also concluded to be an important interstitial trap. The ionization-enhanced migration of the isolated lattice vacancy was explored in n-type silicon using both EPR and DLTS. These studies were undertaken to complement the more extensive studies in p-type silicon performed by A. P. Chatterjee. These studies demonstrate that the same ionization-enhanced process takes place in both n-type and p-type silicon, with the vacancy migrating in a positively charged state. The driving force for this migration appears to be electron capture at the vacancy site. In addition, several DLTS experiments were performed that strengthen the experimental evidence that the vacancy also has negative-U properties.