| Applied hydrostatic pressure modifies the Coulomb bound states of a quasi-two dimensional electron gas in the quantum wells by increasing the effective mass and by tuning the free electron density . Here, we explore the consequence of these effects on several transitions observed in the far-infrared and visible spectra of doped GaAs/AlGaAs multiple quantum wells.;In the far-infrared region we performed magneto-spectroscopy measurements on the cyclotron resonance, D0 1s → 2p+ and D- singlet/singlet-like transitions. Previous work showed that with excess electron density the negative donor ion (D -) singlet transition in the quantum wells is blue-shifted. At atmospheric pressure, this transition was also shown to exhibit discontinuities in the slope of the magnetic field dependence of the energy transition at integer and fractional filling factors. By applying hydrostatic pressure we were able to tune the electron density in the well, allowing us to study on a single sample the blue-shift of the D- singlet-like transition over a wide range of filling factors. Although our results are in good agreement with previous theoretical and experimental results, we also observe an anomalous branching at approximately 7.5T, which indicates the presence of a resonant level.;In the visible region, photoluminescence studies of neutral, bound and charged excitons in modulation doped GaAs/AlGaAs quantum wells were performed as functions of applied pressure, temperature, excitation power and photon energy. Varying both pressure and incident power allows sensitive selection of the different excitonic transitions. From these studies we conclude that the Gamma-X crossover within the barriers at approximately 7--9kbar accelerates photo-pumping of electrons to the barriers. A semi-empirical kinetic model is able to account for the power, temperature and pressure dependencies of this process. |
