X-ray scattering study of interface structures in Si-Si1-xGex superlattices grown on vicinal Si(111) substrates

The interface structures of Si-Si1-xGex (x = 0.1, 0.3) superlattices grown on vicinal Si(111) substrates are determined from grazing-angle x-ray scatt ering data. Diffuse intensity distributions in reciprocal space are calcula ted using, new formulae developed to explicitly take account of the partial ly correlated periodic roughness due to the substrate miscut and the step b unching, in addition to random roughness. The calculated intensity maps wel l explain the experimental ones observed from the Si-Si0.9Ge0.1 and Si-Si0. 7Ge0.3. The bunched steps at the substrate Si(111) surface are widely dispe rsed at the Si/Si0.7Ge0.3 interfaces, while the bunched step structure is r eplicated onto the Si/Si0.9Ge0.1 interfaces. The different step configurati ons are ascribed to the three-times greater misfit strain in the Si-Si0.7Ge 0.3. The two interfaces have distinct in-plane terrace/stepped area ratios of similar to3 and 0.35-0.7. The periodic terrace-step structures are equal ly well correlated in the two supelattices in the out-of-plane direction, w hile the random roughness has smaller correlation lengths in the Si-Si0.9Ge 0.1 than in the Si-Si0.7Ge0.3.