Growth and processing of crystalline materials is in general accompanied by the creation of strain and stress, be it due to thermal gradients during cooling and heating, be it induced by intended structural processing in growth and device production. The latter is especially important to take into account because of the recent rise of large band gap semiconductor materials. For example, SiC as a material for high temperature and power devices, is not yet available as single crystals without lattice defects, although established growth procedures exist. Even worse, the group-III-nitrides cannot be grown as bulk single crystals presently, instead they have to be grown on foreign substrates that cause misfit and differential thermal stress.
This presentation gives an overview over various processes that are available to crystals to relax stress. We consider elastic, plastic and diffusive relaxation using examples from the rather well investigated epitaxial systems of the Si-Ge semiconductors group. We will then discuss current problems in III-nitride- and SiC-growth.