Local-field effect on the linear optical intersubband absorption in multiple quantum wells

Using a microscopic local-field formulation, the linear optical absorption of a multiple-quantum-well (MQW) structure associated with intersubband transitions is investigated. Taking as a starting point a fundamental self-consistent integral equation for the local field, the p-polarized electric-field distribution inside each quantum well in the MQW structure is studied. It is demonstrated that the local field is essentially determined from a set of linear algebraic equations. Within the infinite-barrier approximation with an effective well width, numerical calculations of the optical absorption spectra are presented for a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum well for different parameters such as the two-dimensional (sheet) electron concentration, the angle of incidence, and the number of wells. The numerical results show that the local-field effect leads to a notable blueshift of the peak-position energy in the absorption spectra as the sheet density of the electrons is increased, and that for larger angles of incidence the electromagnetic interaction among quantum wells gives rise to a significant broadening of the absorption peak when the number of wells is sufficiently large.