Misfit dislocation and threading dislocation distributions in InGaAs and GeSi/Si partially relaxed heterostructures

Single and compositionally graded InGaAs/GaAs and SiGe/Ge partially relaxed heterostructures of equivalent lattice mismatch and thickness have been characterized by high resolution X-ray diffraction and by X-ray double crystal topography. X-ray topography evidences a rapid decrease of the average length of misfit dislocation segments with the increase of the density of misfit dislocations both in InGaAs and GeSi/Si structures. For an equivalent amount of strain release, SiGe/Si heterostructures exhibit shorter misfit dislocation lengths with respect to InGaAs/GaAs heterostructures. Compositionally graded InGaAs/GaAs heterostructures show much longer misfit dislocation segments with respect to equivalent single heterostructures, thus confirming the effectiveness of composition grading to reduce the dislocation interaction. The threading dislocation density evaluated from the lattice mismatch and the average length of the misfit dislocations on the basis of a simple formula increases more rapidly as a function of strain release in GeSi/Si heterostructures with respect to InGaAs/GaAs ones.