Interaction between surface morphology and misfit dislocations as strain relaxation modes in lattice-mismatched heteroepitaxy

We show how strained layer heteroepitaxial systems can serve as model systems for the study of dislocation energetics and kinetics in semiconductors through the introduction of strain-relieving misfit dislocation arrays. Such structures allow fundamental dislocation properties to be studied at carefully controlled stresses in the range 10 7 –10 9 Pa. A parallel strain relaxation mode in strained heterostructures is via coherent islanding or surface roughening of the epitaxial layer. This mechanism acts both in competition and in cooperation with injection of misfit dislocations, and provides a further degree of control for study of the fundamental energetic and kinetic properties of dislocations. Using ultra-sensitive in situ wafer curvature measurements of stress during molecular beam epitaxy growth of Ge x Si 1−x /Si heterostructures, the relative contributions of surface roughening and dislocation injection to strain relaxation may be qualitatively and quantitatively assessed. In addition, a new strain-stabilized morphology, ‘quantum fortresses’, comprising cooperative island nucleation around shallow strain-relieving pits, is identified during Ge 0.3 Si 0.7 /Si(100) heteroepitaxy. This configuration has potential application to nanoelectronic device architectures.