Magneto-optical studies of highly p-type modulation-doped $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells

We report on the optical properties of 150-Å-wide p-type modulation-doped quantum wells (QW’s) with hole concentrations in the range of $0.7\times {10}^{12}–3.1\times {10}^{12}\hspace{0.5em}{\mathrm{cm}}^{-2}$ under high applied magnetic fields up to 14 T. The magnetoexciton is clearly observed in undoped QW’s, but is affected by the band mixing effect and finally quenched in the highly doped samples. The survival of the exciton up to a carrier concentration of $0.7\times {10}^{12}\hspace{0.5em}{\mathrm{cm}}^{-2}$ is confirmed. The free carrier Landau level model including the valence-band mixing effect and the conduction-band nonparabolicity can nicely describe the electronic transitions in this doping regime. Moreover, the band-gap renormalization is found to be insensitive to the magnetic field variation. As a consequence, the values of interband transition energies together with the corresponding many-body shifts are accurately evaluated. Finally, an anomalous absorption feature near the Fermi edge is found to arise upon the application of high magnetic fields. This transition is proposed to be associated with a band-tail effect.