Li-Defect Interactions in Electron-Irradiated n -Type Silicon

Single-crystal silicon, both with and without oxygen, has been diffused with lithium to concentrations 10^17/cm^3, irradiated with 1-1. 5-MeV electrons, and the ensuing defects studied by EPR and electrical measurements. The presence of oxygen strongly affects the properties of these defects. In O-containing material, the room-temperature carrier-removal rate is 0. 25 cm^-1, and the carrier concentration continues to decrease after the cessation of the irradiation; in O-free material, the carrier-removal rate is 0. 39 cm^-1, but here the carrier concentration can either increase or decrease after cessation of the irradiation. EPR measurements have indicated the presence of two new defects which involve Li --- one in O-containing material and one in O-free material. Their introduction rates are much smaller than the carrier-removal rates. The defect in O-containing Si exhibits a strong hyperfine interaction with the Li^7 nucleus, while that in O-free Si exhibits no hyperfine structure. Their g values are 2. 0046 and 2. 0090, respectively, and are isotropic. The defects are observed in their electron-filled state, and indicate a net electron spin of. The defect spectra disappear (with time) at room temperature, and this, together with the carrier-concentration changes, can be explained by the formation of other Li-involved defects which lie deeper in the energy band gap and are not visible by EPR. Electron irradiation at 40 ^ followed by annealing at higher temperatures show that both EPR defects described above begin to form at about 200 ^ and begin to decrease at about 275 ^ --- just as does the 250 ^ reverse annealing observed generally for n-type Si. Based on these data, and the work of others, it is suggested that both defects form as a result of the motion of Si interstitials which produce a (Li-O-interstitial) complex in O-containing Si, and a (Li-interstitial) complex in O-free Si.