Investigation of two-dimensional hole gases in Si/SiGe heterostructures

Two-dimensional (2D) hole gases are investigated experimentally and theoretically in modulation-doped Si/SiGe/Si double heterostructures with both symmetric and asymmetric doping grown by the rapid thermal chemical-vapor deposition technique. Shubnikov–de Haas and quantum Hall effect measurements show unambiguously that the charge transfer is equivalent at the two interfaces in this system. The 2D hole gas effective mass parallel to the interfaces is determined by microwave photoresistivity experiments. A simple theoretical analysis of these data leads to the determination of the valence-band profile and quantitatively explains the charge transfer. The hole mobility limitation is discussed and it is shown that the alloy scattering in SiGe could be the dominant process at low temperature.