Mobility Enhancement in Modulation‐Doped Si ‐ Si1 − x Ge x Superlattice Grown by Molecular Beam Epitaxy

We report the first observation of enhanced electron mobility in strained layer superlattices grown on Si substrates by molecular beam epitaxy. A alloy layer between substrate and superlattice provides for a strain distribution on both the Si and the layers in the superlattice. The superlattice layers are modulation doped by Sb. At an average doping level of , a mobility enhancement at room temperature of more than a factor 5 is obtained compared to equivalently doped bulk Si. Maximum mobility is achieved with modulation doping of just the lower gap . Temperature dependent Hall measurements show a clearly reduced impurity scattering of the electrons, indicating the existence of a two‐dimensional electron gas.