On the Dodson–Tsao excess stress for glide of a threading dislocation in a strained epitaxial layer

The concept of excess stress was originally introduced in a study of elastic strain relaxation in an epitaxial layer grown beyond its critical thickness, where it was proposed as the relevant stress in a kinetic law for dislocation motion. The concept has subsequently been applied in a variety of studies of strain relaxation, but without a standard definition as a basis for quantitative comparisons. The purpose here is to propose a fundamental definition of excess stress as the particular stress measure which is work-conjugate to the Burgers displacement during glide of a threading dislocation in a strained layer. This definition also has the feature of being consistent with definitions of effective stress in kinetic laws of glide in bulk materials.