Annealing of Electron Bombardment Damage in Lithium-Containing Silicon

The results of these measurements are applicable to the design of lithium-containing solar cells. Data concerning the speed and stability of recovery from irradiation damage is presented, including the dependence of these parameters on the lithium and oxygen concentration of the silicon. Floatzone-refined silicon doped with lithium to a concentration ¿ 5 x 1014cm-3 exhibits post-irradiation damage properties similar to those measured on quartz-crucible (Q.C.) silicon doped with lithium from 1015 to 1016cm-3. The speed of recovery from damage (e.g., the mobility) is several hundred times faster in oxygen-lean float-zone-refined silicon than in oxygen-rich quartz-crucible-grown silicon. Two mechanisms of annealing, namely by neutralization and by dissociation of carrier-removal centers were observed in these experiments. Both mechanisms of annealing take place in float-zone (F.Z.) silicon doped with lithium from 4 x 1015 to 1016cm-3, but only the mechanism of neutralization is observed in samples of float-zone silicon doped with lithium concentrations ¿ 5 x 1014cm-3. In contrast to this behavior, only the mechanism of neutralization is observed in quartz-crucible silicon doped with lithium from 1015 to 1016cm-3. A continuous decrease in carrier density is observed to occur for periods ranging from five months to 18 months in irradiated-float-zone silicon with lithium concentrations ¿ 5 x 1014cm-3, and in quartz-crucible silicon with lithium concentrations from 1015 to 1016cm-3, respectively. This mechanism produces uncharged complexes of lithium. A defect located at an energy of ¿ EC-0.12 eV was measured in irradiated-float-zone silicon doped with lithium concentration ¿ 5 x 1014cm-3.