MULTI-VALENCE-SUBBAND MAGNETOTRANSPORT IN A MODULATION-DOPED p-TYPE Ge_(1-x)Si_x/Ge/Ge_(1-x)Si_x QUANTUM WELL

摘要

We show, from self-consistent calculations, that the effective mass for motion of holes along a two-dimensional (111) Ge layer is almost an order of magnitude smaller than the bulk heavy hole mass, which determines the intersubband distances. This creates a unique situation of multiple populated electric subbands at moderate hole densities p_s and layer widths. Depopulation of two or more upper subbands in a 38 nm wide p-Ge layer with p_s = 5 x 10~(15) m~(-2) has been revealed from the magnetoresistance in high parallel magnetic fields, while a collapse of the quantum Hall state for rilling factor ν = 1 indicates that two ground subbands merge in a self-formed double-quantum-well potential profile. The latter effect in the valence band is shown to be sensitive to the layer deformation.