Experimental Investigations of Electron-Optical - Interaction in Quasi-Two Systems.

Three different experimental techniques have been used to study the effects of confinement on the electron -LO phonon interaction in GaAs-Al_{ rm x}Ga_{rm i-x}As multiple quantum well structures; far infrared free carrier cyclotron resonance, the resonant impurity magnetopolaron effect of hydrogenic donors doped in the centers of the wells, and interband magnetoreflectivity. In each case the electron-LO phonon interaction is probed under "resonant" conditons in which a particular optical transition is studied through the magnetic field region that tunes the final state of this transition into resonance with a lower lying electronic state via the emission of an optical phonon. An enhanced polaron effect in the quasi -two-dimensional systems as compared with a three dimensional system has been observed. It is suggested that the apparent large interaction can be explained through the participation of phonons other than conventional zone-center LO phonons in the electron-phonon interaction in the multiple quantum well structures.