Resonant electron-optical-phonon interactions for impurities in GaAs and GaAs/AlxGa1-xAs quantum wells and superlattices.

A systematic experimental study of confinement effects on the strength of electron-optical-phonon interactions is presented. The hydrogenic 1s-2p +1 transition of shallow donors in bulk GaAs and GaAs/Al x Ga 1-x As multiple quantum wells (MQW) and superlattices has been tuned through resonances with the GaAs optical phonons by magnetic fields up to 23.5 T and followed with far-infrared photoconductivity spectroscopy. Extremely large and asymmetric interaction gaps have been observed in both two-level and three-level resonance regions for small-well-width (125 A) MQW samples. These gaps decrease systematically as the well width increases, approaching the bulk limit for the largest-well-width (450 A) sample