Cyclotron resonance in ultra-low-hole-density narrow p-type GaAs/(Al,Ga)As quantum wells

Abstract

The cyclotron-resonance behavior of a series of p-type, low ${\mathrm{p}}_{\mathrm{s}}$ , asymmetrically doped (311)A quantum wells has been measured over two orders of magnitude in energy. Landau levels for the structures studied have been calculated for comparison with experiment. The calculations use a rotated Luttinger Hamiltonian and invoke the axial approximation. In the quantum limit and at certain far-infrared energies we observe two resonances widely separated in field. We find at the lowest fields that the samples exhibit a light effective mass. For the narrowest quantum well the cyclotron resonance (CR) broadens and shifts to a slightly lighter mass into the quantum limit, above about 2 T. The CR energy is modeled by inter-Landau-level transitions from the highest level, and a discontinuous evolution to a higher effective mass, observed as the second resonance above 8 T, is explained by crossing of the highest two Landau levels, as modeled in the calculation. The discontinuous evolution to a higher mass is found to shift to lower fields as the well width increases, as suggested from the modeling. For the wider quantum wells the influence of additional anticrossings at intermediate fields, due to the proximity of the second subband, is observed. CR energy for these samples is adequately modeled at energies above and below the region of subband anticrossing. The limitations of the modeling procedure have been discussed and a number of features of the experimental data are explained qualitatively in terms of the expected modifications to the hole Landau-level structure when full Landau-level mixing is incorporated into the modeling. The influence of hole-hole interactions and factors influencing the CR scattering time are also discussed briefly.