Stress and efficiency studies in EFG

Modeling of the effect of transverse isotherm variation on residual stress has established that significant reductions in stress can be produced when the sheet edge is cooled with respect to the center. The potential to achieve large stress reductions exists but the quantitative details of the stress reductions depend on the creep relaxation. This is not known accurately in the region between 800 C and 1200 C where the residual stress is very sensitive to the transverse isotherm curvature. An apparatus for measurement of stress relaxation in silicon at these temperatures has been built and tested and will be used to examine creep behavior in more detail under a continuation contract. EBIC characterization of dislocated FZ silicon stressed at high temperatures has established correlations between the bulk minority carrier diffusion length and the dislocation density. Other results suggest that stress applied during annealing will influence diffusion length degradation arising from thermal effects. Studies of dislocation electrical activity as a function of dopant concentration indicate that increased dopant concentrations lead to a wider region of low current collection around the dislocation.