The low temperature electrical properties of modulation-doped two dimensional electron gases (2DEGs) in the SiGe system were studied. The effects 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 modulation-doped structure 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. The uniformity of the regrown wafers was also investigated. A monotonic increase in carrier density and a decrease in mobility were observed towards the edge of the wafers. Appropriate mechanisms will be discussed.