Enhanced strain relaxation in a two-step process of Ge_xSi_1-x/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

Two-layer Ge_xSi_1-x heterostructures, with a finite fraction of germanium up to x=0.48 and a thickness of at most 0.65 μm, were grown by molecular-beam epitaxy. It is shown that plastic relaxation of the second step is significantly enhanced. It is assumed that threading dislocations with a density of 10⁵–10⁶ cm^-2, which appear in the first step in the process of its plastic relaxation, are sources of misfit dislocations positioned between the first and second steps. Cross-sectional transmission electron microscopy showed the superior quality of the dislocation network in the stepped regions. Threading dislocation densities in the second step were determined with the help of etching pits and were found to be close to 10⁵ cm^-2. © 2004 American Institute of Physics.