The low temperature electrical properties of modulation-doped two-dimensional electron gases (2DEG) in the SiGe system were studied. The effect on the electrical properties of removing the substrate from the growth chamber after the growth of the virtual substrate, chemically cleaning the virtual substrate and then growing the 2DEG on a thin SiGe buffer were investigated. The results demonstrate that the carrier density and mobility decrease as the regrowth interface is moved closer to the 2DEG. Lower temperature desorption of the passivating chemical oxide improves the mobility and carrier density when a regrowth interface is close to the quantum well. The mismatch of Ge content in the virtual substrate and the heterolayers was also shown to produce a reduction in the carrier density and mobility. Crown