Strain-Induced Two-Dimensional Electron Gas in Selectively DopedSi/SixGe1−xSuperlattices

We report the observation of two-dimensional electron systems and enhanced mobilities in Si/${\mathrm{Si}}_{0.5}$ ${\mathrm{Ge}}_{0.5}$ strained-layer multilayer structures. The built-in strain is measured by phonon Raman spectroscopy. The mobility enhancement depends strongly on the position of the doped region within the layers. The experimental results can be explained in a consistent way when carrier confinement in the Si layer is assumed. The importance of the built-in strain in lowering the conduction band in Si is emphasized.