Collective excitations in InAs quantum well intersubband transitions

Intersubband transitions in semiconductor quantum well are studied using a density matrix theory that goes beyond the Hartree–Fock approximation by including the full second order electron–electron scattering terms in the polarization equation for the first time. Even though the spectral features remain qualitatively similar to the results obtained with dephasing rate approximation, significant quantitative changes result from such a more detailed treatment of dephasing. More specifically, we show how the interplay of the two fundamental collective excitations, the Fermi-edge singularity and the intersubband plasmon, leads to significant changes in lineshape as the electron density varies.