Thermal Misfit Strain Relaxation in Ge/(001)Si Heterostructures

We used x-ray diffraction and transmission electron microscopy to study the mechanism of thermal misfit strain relaxation in epitaxial Ge films grown on Si(001) substrates by the two-step growth technique. Lattice misfit strain associated with Ge/Si(001)Si mismatched epitaxy is largely relieved by a network of Lomer edge misfit dislocations during the first step of growth. However, thermal misfit strain during growth is relieved primarily by interdiffusion at the Si/Ge heterointerface. Two SiGe compositions containing 0.5 at.% and 6.0 at.% Si detected at the interface relieve thermal mismatch strain associated with the two growth steps. A thermodynamic model has been proposed to explain the state of strain in the films.