Interplay of Coulomb and nonparabolicity effects in the intersubband absorption of electrons and holes in quantum wells

Quantum well intersubband absorption with contributions from both valence and conduction subbands is computed with a nonequilibrium Keldysh Green’s function formalism, assuming an optical pump and probe scheme in undoped samples. The coupling between conduction and valence bands leads to contributions to the TE mode from the electrons, which are enhanced due to Coulomb corrections and may be resolved even in the presence of the dominating hole contributions. A strong contrast in the evolution of absorption spectra with increasing carrier density is predicted between TM and TE polarizations. The influence of strongly k -dependent dipole moments in combination with many-body effects is analyzed for intersubband transitions, including the evolution of the spectra with increasing excitation power. For the TE case, extra features appear in the spectra, due to interplays between band structure and Coulomb effects which are not present in the TM mode. The spectral evolution on both polarizations, broadening, number, and relative strength of the resolved peaks are in strong contrast with free-carrier results. Numerical results are given for four different structures.