Interfacial microstructures of ultrathin Ge layers on Si probed by x-ray scattering and fluorescence yield

Angular dependence of grazing-incidence x-ray scattering and Ge Kα fluorescence yield were measured for buried ultrathin Ge layers grown on bulk Si by molecular beam epitaxy. Results obtained for samples with different Ge layer thickness are compared. The data reveal information on microstructures in these layered materials in terms of the average interfacial roughness, correlation lengths of height fluctuations, and Ge density profile. Structural parameters are obtained by comparison of experimental data with theoretical models.The results also indicate that the interfacial roughness at neighboring interfaces is highly correlated. Significant changes of microstructures in the Ge epilayer are found as the layer thickness approaches the critical thickness. The x-ray scattering techniques are demonstrated to be capable of detecting a precursor of lattice relaxation in multilayers of lattice-mismatched compound semiconductors.