Resonances between the cavity mode and five excitonic transitions in an InxGa1-xAs/GaAs/AlAs/AlGaAs vertical-cavity surface-emitting laser structure using photomodulated reflectance

An InxGa1-xAs/GaAs/AlAs/AlGaAs vertical-cavity surface-emitting laser structure has been studied by conventional reflectance and photomodulated reflectance (PR) spectroscopies. Slight fluctuations in molecular beam epitaxy growth conditions led to thickness variations of < similar to 12% along the wafer radius. While this did not appreciably affect the energy of the quantum well (QW) transitions, it did give rise to a significant but smooth variation in the cavity mode energy. PR spectroscopy was used to study the interaction between the cavity mode and QW excitons, as the overlap between them was varied by probing different wafer regions. The PR signal was strongly enhanced when the cavity mode and a QW transition were in good alignment. We were able to investigate five distinct such resonances between the cavity mode and the ground-state and four other, higher-order, QW transitions. A theory has already been developed for the PR modulation of the coupled cavity and exciton modes, based on energy-dependent Seraphin coefficients. A similar but simplified model was used to fit all the PR spectra, and the resulting QW transition energies then compared with those predicted by a theoretical model which includes excitonic binding energy effects. (C) 2000 American Institute of Physics. [S0021-8979(00)02623-2].