Consequences of subband nonparabolicity on intersubband excitations inp-doped GaAs/AlxGa1−xAs quantum wells

By means of resonance Raman spectroscopy we have observed a characteristic shift of hole-intersubband transitions with excitation energy in p-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum-well structures. As possible reasons for the shift, the nonparabolicity of the valence subbands as well as fluctuations of the well width are discussed. Both contributions can be separated experimentally by application of an external magnetic field, which quantizes the in-plane motion of the carriers. For our samples, we can show that the shifts observed for B=0 T are mainly caused by subband nonparabolicity. This interpretation is confirmed by a comparison with results of a simulation of single-particle Raman spectra based on a subband calculation with Luttinger’s 4×4 Hamiltonian. Corresponding shifts are observed both in depolarized and polarized spectra.