Magnetotransport properties and subband structure of the two-dimensional hole gas in GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As heterostructures

Systematic magnetotransport measurements of two-dimensional holes in various GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$ As heterostructures are reported. The behavior of a heterojunction and a 200-Å quantum well can be explained on the basis of zero-field spin-split subbands, whereas that of a 100-Å quantum well is consistent with a spin-degenerate ground subband in the absence of a magnetic field. However, in a 50-Å quantum well we found an unusual relation between the filling factor and the spin splitting.