A Synchrotron Radiation Photoemission Study of SiGe(001)-2×1 Grown on Ge and Si Substrates: The Surface Electronic Structure for Various Ge Concentrations.

Beyond the macroscopic perspective, this study microscopically investigates SiGe(001)-2×1 samples that were grown on the Ge(001) and Si(001) substrates via molecular-beam epitaxy, using the high-resolution synchrotron radiation photoelectron spectroscopy (SRPES) as a probe. The low-energy electron diffraction equipped in the SRPES chamber showed 2×1 double-domain reconstruction. Analyses of the Ge 3d core-level spectra acquired using different photon energies and emission angles consistently reveal the ordered spots to be in a Ge-Ge tilted configuration, which is similar to that in Ge(001)-2×1. It was further found that the subsurface layer was actually dominated by Ge, which supported the buckled configuration. The Si atoms were first found in the third surface layer. These Si atoms were further divided into two parts, one underneath the Ge-Ge dimer and one between the dimer row. The distinct energy positions of the Si 2p core-level spectrum were caused by stresses, not by charge alternations.