Infrared absorption due to electron–lattice-vibration scattering in AlAs/GaAs quantum wells

The infrared-absorption coefficient due to interaction of electrons with optical phonons is calculated as a function of frequency for an electron gas in AlAs/GaAs quantum wells. The absorption coefficient is given by the real part of the dynamical conductivity. A finite-temperature force-force correlation-function method is used to represent the Kubo expression for the conductivity. Calculations are made with use of a bulk description for the optical phonons and also by inclusion of the confinement of the phonons for several well widths and several carrier densities. It is found that the effects of the confinement on the phonon spectrum reduce the absorption. The absorption also is found to increase with increasing well width and increasing carrier concentration.