High Hole Mobility in Modulation-Doped and Strain-Controlled p-Si0.5Ge0.5/Ge/Si1-Xs GeXs Heterostructures Fabricated Using Molecular Beam Epitaxy

New heterostructures of modulation-doped p-Si0.5Ge0.5/Ge/Si1-X s Ge X s are fabricated using molecular beam epitaxy. The strain in the Ge channel layer can be precisely controlled by changing the composition of the Si1-X s Ge X s buffer layer. As a result, a large energy discontinuity (0.22 eV) in the valence band is realized. This leads to the realization of a high hole mobility (4500 cm2/V ·s) at 77 K.