Li-defect interactions in electron-irradiated n-type silicon

Single-crystal silicon, both with and without oxygen, has been diffused with lithium to concentrations similar to 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 1/2. 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 degrees K followed by annealing at higher temperatures show that both EPR defects described above begin to form at about 200 degrees K and begin to decrease at about 275 degrees K - just as does the 250 degrees K 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.