High-pressure magneto-optical studies of two-dimensional-electron and exciton transitions in GaAs-AlxGa1-xAs quantum-well heterostructures.

Abstract

High-pressure photoluminescence measurements on modulation-doped and undoped GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum-well structures have been performed for the first time in magnetic fields up to 15 T. We have observed Landau fans from interband transitions of the two-dimensional free-electron gas in the modulation-doped sample between 0 and 9 kbar. In this pressure regime the slope of the Landau fan changes at the rate of 2.6%/kbar; this value is surprisingly larger than the predicted rate of increase for the reduced effective mass. Above 9 kbar, the free Landau transitions disappear and magnetoexciton behavior dominates the spectrum. The influence of pressure on the band gaps causes a controlled trapping of the free electrons from the GaAs well to DX centers (Si deep donors) in the ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As layers. Many-body effects are reduced and excitonic effects are enhanced. This is observed as a larger than predicted change in slope of the Landau transitions with pressure. The measurements were repeated on an undoped quantum-well sample. From the measured diamagnetic shift, an increase in the electron effective mass of 0.9%/kbar was determined. This value is comparable to that predicted by k\ensuremath{\cdot}p theory.