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 struc ture has been studied by conventional reflectance and photomodulated reflec tance (PR) spectroscopies. Slight fluctuations in molecular beam epitaxy gr owth conditions led to thickness variations of < similar to 12% along the w afer radius. While this did not appreciably affect the energy of the quantu m well (QW) transitions, it did give rise to a significant but smooth varia tion in the cavity mode energy. PR spectroscopy was used to study the inter action 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. W e 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 cavi ty and exciton modes, based on energy-dependent Seraphin coefficients. A si milar but simplified model was used to fit all the PR spectra, and the resu lting QW transition energies then compared with those predicted by a theore tical model which includes excitonic binding energy effects. (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)02623-2].