Non-Newtonian strain relaxation in highly strained SiGe heterostructures

Abstract
Semiconductor strained-layer structures routinely incorporate layer stresses in the GPa regime. At these stresses, models for strain relaxation cannot be based on material parameters determined at small stresses. A new analysis of experimental data on strain relaxation in metastable SiGe/Ge(001) strained-layer structures allows the effects of high stresses on relaxation kinetics to be determined. The activation energy for plastic flow is found to decrease roughly linearly with increasing stress, in a manner analogous to non-Newtonian viscous flow in fluids. As a result, macroscopic relaxation occurs more easily and becomes dramatically more abrupt as the growth temperature is reduced than would be extrapolated from the small-stress behavior. Implications for design and fabrication of metastable strained-layer devices are discussed.