High-energy transitions of shallow magnetodonors in a GaAs/Al_0.3Ga_0.7As multiple quantum well

The high-energy states of a shallow donor in a GaAs/Ga_0.7Al_0.3As multiple-quantum-well structure subjected to a magnetic field in the growth direction are studied both theoretically and experimentally. Effects due to higher confinement subbands as well as due to the electron-phonon interaction are investigated. We show that most of the peaks in the infrared photoconductivity spectrum are due to direct transitions from the ground state to the m = ±1 magnetodonor states associated with the first subband, but transitions to the m = ±1 states of the third subband are also apparent. The remaining photoconductivity peaks are explained by phonon-assisted impurity transitions.