Magneto-Raman scattering in GaAs/AlAs multiple quantum wells

Symmetric GaAs/AlAs multiple quantum wells of 44 and 99 Å well and barrier widths were studied by means of resonant LO-phonon Raman scattering in high magnetic fields. Experiments were performed in Faraday geometry with the field along the growth direction. LO-phonon Raman intensity profiles versus magnetic field were recorded in the four backscattering configurations (${\mathrm{\sigma }}^{+}$,${\mathrm{\sigma }}^{+}$), (${\mathrm{\sigma }}^{\mathrm{-}}$,${\mathrm{\sigma }}^{\mathrm{-}}$), ${\mathrm{\sigma }}^{+}$,${\mathrm{\sigma }}^{\mathrm{-}}$), and (${\mathrm{\sigma }}^{\mathrm{-}}$,${\mathrm{\sigma }}^{+}$). Raman resonances in the specimen with narrower well width are mainly related to electron–heavy-hole interband magneto-optical transitions conserving the Landau quantum number n. A more complex structure is found in the magneto-Raman profiles of the sample with wider wells due to the proximity of light and heavy mass valence subbands. Due to the mixing of these hole subbands and the resulting anticrossing of levels, some resonances related to allowed transitions vanish with increasing magnetic field and other features appear. In both samples we observe magneto-Raman oscillations in incoming and outgoing resonance. From fits of a theoretical model to the data, we determine values for electron effective masses ${\mathit{m}}_{\mathit{e}\mathrm{\perp }}^{\mathrm{*}}$ along the growth direction and ${\mathit{m}}_{\mathit{e}\mathrm{\parallel }}^{\mathrm{*}}$ in the planes of the quantum wells. We also deduce heavy- and light-hole masses and discuss their variation with magnetic field. Experimentally determined magneto-optical transition energies are related to wave vectors ${\mathbf{k}}_{\mathrm{\parallel }}$ of the zero-field in-plane quantum-well dispersion. A comparsion to band structure results confirms the anticrossing of heavy- and light-hole valence bands. We analyze magneto-Raman intensity profiles using a previously developed model, which allows a classification of the resonances.