Pressure Tuning of Many-Electron Impurity Interactions in Confined Semiconductor Structures

We report studies of the free carrier and donor-bound FIR excitations of a confined electron gas in modulation doped GaAs/AlGaAs quantum wells (QW) as a function of the QW electron density. Applied pressure is used to tune the electron density via the Γ–X well–barrier crossover. As electrons are removed from the QWs, we observe successively the quenching of cyclotron resonance, the evolution of the D— singlet-like magnetoplasmon resonance into the D— singlet transition of isolated donors, and the emergence of the neutral donor D0 1s–2p+ line. Calculations predict a sharp drop in the QW electron density for 2.3 to 3.1 GPa, in accordance with experiment. A rapid decrease with B-field in the blue shift of the magnetoplasmon resonance at 2.2 GPa in one sample shows that pressure has shifted the ν < 1 filling-factor regime to a factor-of-two lower field.