Degeneracy and effective mass in the valence band of two-dimensional (100)-GaAs quantum well systems

Quantum Hall measurement of two-dimensional high-mobility [μ∼2×106 cm2/(V·s)] hole systems confined in a 20 nm wide (100)-GaAs quantum well have been performed for charge densities between 4 and 5 × 1010 cm−2 in a temperature range of 10–160 mK. The Fourier analysis of the Shubnikov-de Haas (SdH) oscillations of the magnetoresistance vs. the inverse of the magnetic field 1/B reveals a single peak, indicating a degenerate heavy hole (HH) band. The hole density p=(e/h)·f agrees with the Hall measurement result within 3%. The HH band degeneracy is understood through the diminishing spin-orbit interaction due to the low charge density and the nearly symmetric confinement. SdH oscillations fitted for 0.08 T ≤ B ≤ 0.24 T to the Dingle parameters yield an effective mass between 0.30 and 0.50 me in good agreement with previous cyclotron resonance results.