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 ps and layer widths. Depopulation of two or more upper subbands in a 38 nm wide p- Ge layer with ps=5×1015 m -2 has been revealed from the magnetoresistance in high parallel magnetic fields, while a collapse of the quantum Hall state for filling 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.
