Optical reflectance in GaAs/AlGaAs quantum wells

Molecular-beam epitaxial GaAs/AlGaAs bulk layers and quantum well heterostructures have been grown and characterized at 3 K using broadband optical reflectance and photoluminescence spectroscopy. Reflectance spectra display sharp, well-defined features due to strong near-band gap excitonic effects that cause the reflectance to deviate by over 50% from the bulk value in some cases. Features due to impurity-bound excitons, free-to-bound transitions, and free excitons have all been identified in quantum well heterostructures. Interband transitions involving the n=1 light hole and higher-lying subbands are much more readily observed in reflectance spectra than in photoluminescence, including ‘‘forbidden’’ Δn≠0 transitions. Additionally, reflectance has been used to probe the interfaces, revealing fine structure due to monolayer and submonolayer deviations in well thickness.