Electronic Raman scattering in p-doped GaAs/Ga1-xAlxAs quantum-well structures: Scattering mechanisms and many-particle interactions

By means of resonance Raman spectroscopy we have investigated intersubband transitions of quasi-two-dimensional (2D) hole gases in p-type modulation-doped GaAs/Ga1-xAlxAs quantum-well structures. The observed excitations have an essentially single-particle character due to Landau damping of collective excitations and due to single-particle scattering by energy-density fluctuations under conditions of extreme resonance. In samples with well widths of typically 100–200 Å and 2D hole densities ρ∼1011 cm-2, we observe a characteristic variation of intersubband-transition energies with laser frequency in depolarized and in polarized scattering configurations. This variation is caused by the nonparabolic subband dispersion of the 2D single-particle hole subbands. Experiments under variation of p, by illuminating the sample with photons that have energies above the band gap of the Ga1-xAlxAs barriers, allow an estimate of the relative strengths of direct and exchange Coulomb interactions. From these experiments a greater relative strength of the exchange interaction, in comparison to that found for 2D electron gases, can be deduced.