Ge channels with extremely high compressive strain were fabricated. SiGe buffer layers with Ge concentration from 40% to 65% were grown on Si substrates by gas source molecular beam epitaxy (MBE), and subsequently modulation-doped Ge channel structures were grown on the buffers by solid source MBE. High crystal quality Ge channel layers with the compressive strain as high as 2.4% were realized due to low-temperature growth. Magnetotransport properties were investigated for the structures. Well-resolved Shubnikov-de Haas oscillations were observed and Dingle ratios beyond 10 were obtained. This indicated that remote impurity scattering is dominant rather than interface roughness scattering, reflecting high-quality channel layers in spite of the large strain. Moreover, reduced effective masses due to the large strain were demonstrated. (c) 2006 Elsevier B.V. All rights reserved.