ABSTRACT
This chapter presents a modified Volterra approach in equilibrium theory for strain relaxation in metastable heteroepitaxial semiconductor structures, which includes the surface effects on mismatch accommodation by tetragonal distortion of the cubic lattice cells and the elastic interaction between straight misfit dislocations. It discusses the effect of the Airy stress function that removes the fictitious shear and normal stresses at the crystal surface and thus make the crystal stress-free. The chapter shows that the image-force method provides an equilibrium theory that correctly predicts experimentally observed values of critical layer thickness. It explores the case of silicon (Si)-capped silicon–germanium epilayer on Si substrate in some detail to expand the basic equilibrium theory for strained layer relaxation to such a Si/SiGe/Si geometry with two adjacent interfaces and a free surface at the top of the heteroepitaxial stack. The chapter shows that Volterra dislocation model is also appropriate when the film thickness is smaller than the misfit dislocation spacing.
