Carbon Interstitial-Related Metastable Defects in Electron-Irradiated Silicon.

The experimental techniques used in the studies were Electron Paramagnetic Resonance (EPR), Deep Level capacitance Transient Spectroscopy (DLTS), Thermally Stimulated CAPacitance (TSCAP), and Photoluminescence (PL). The defects have a common constituent, interstitial carbon, and they form when interstitial carbon migrates at room temperature and is trapped by substitutional carbon to form one or phorphorus to form the other. We identify an acceptor state for the isolated interstitial carbon atom by detecting a new EPR center, Si-L6, for C_{rm i}^{-} and correlating it with an electrical level at E_{rm c}-0.10eV. The C_{rm i}C _{rm s} pair, we believe, is the first bistable system in any solid for which detailed microscopic structural information has been obtained. Two EPR centers, Si-G17 and Si-L7, arise from two configurations (A and B) of the defect in its filled (negative) single acceptor state (-/o). The donor state (o/+) of the defect displays the same bistability. Both the positive and negative charge states of the defect share the common stable configuration A. The stable configuration when the defect is in the neutral charge state is the B configuration. This configuration is responsible for the 0.97eV (G-line) luminescence which displays the identical bistability. The microscopic model for the A configuration involves a carbon-silicon interstitialcy (each atom 3-fold coordinated) next to a 4-fold coordinated C_ {rm s} atom. In the B configuration, the defect rearranges its bonds so that both carbon atoms are substitutional (4-fold coordinated) with a 2-fold coordinated Si atom nestled between. Configurational coordinate energy surfaces are determined for each of the three charge states. A new dominant trap for mobile C_ {rm i} in n-type FZ sample has also been discovered. The defect shows a remarkable four-level multistability with a DLTS emission peak from its stable configuration superimposed on that of the normal phosphorus -vacancy pair which has been a DLTS level at E_ {rm c}-0.44eV. Three other metastable configurations show up after 240K minority carrier injection, which can be individually frozen in and studied by DLTS and TSCAP. We conclude the defect arises from the C _{rm i}P_ {rm s} pair. A tentative charge state structure model for the metastable defect has been proposed. (Abstract shortened with permission of author.).