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Two InGaAs/GaAs/AlAs vertical-cavity surface emitting laser ͑VCSEL͒ structures have been studied by conventional reflectance ͑R͒ and photomodulated reflectance ͑PR͒ spectroscopies at ϳ300 K and ϳ80 K. Growth variations across the samples ͑Ͻ2%͒ give rise to smooth changes in the cavity mode energy so that it can be tuned through the position of resonance with the quantum well ͑QW͒ ground-state exciton, by varying the position of measurement. The R spectra show the cavity mode but at best only a weak excitonic feature. In contrast, the PR shows two prominent and distinct signals, and there is a strong enhancement ͑up to 40 times͒ at resonance. A theory has been developed for the PR modulation of the coupled cavity and exciton modes, based on energy dependent Seraphin coefficients. This was used to fit all the PR spectra simultaneously in each complete set of position dependent measurements, using seven parameters, only one of which, the cavity mode energy, varied significantly. The resulting cavity mode and excitonic energies do not clearly show an anticrossing behavior near resonance, implying only a weak exciton-cavity coupling. The ability of PR to detect, in a nondestructive manner, both the cavity and exciton modes, and the extent to which they are in resonance, suggests it could be extremely useful in the characterization of VCSEL structures near their operating temperature. ͓S0163-1829͑99͒01904-9͔

In the previous paper, a line shape model was developed to describe photomodulated reflectance ͑PR͒ spectra of vertical-cavity surface emitting laser ͑VCSEL͒ structures in the vicinity of the resonance between the cavity mode and ground-state quantum well ͑QW͒ exciton, in the weak cavity exciton coupling regime. Here, this model is extended to cavity mode resonances with higher-order QW transitions, both allowed and forbidden. In addition, the model's validity is further confirmed by demonstrating a way of obtaining ''pseudo-PR'' spectra of the QW ground-state and higher-order transitions. These spectra are derived by monitoring changes in PR line shape, as the cavity mode energy is tuned through the QW transitions. These spectra are virtually free of VCSEL cavity effects, and represent plots of the energy dependence of the imaginary part of the modulated QW dielectric function, ⌬ 2 . The ⌬ 2 spectra can be fitted using conventional excitonic PR line shapes to extract the energies and linewidths of the ground-state and higher-order QW transitions. Examples are given for two InGaAs/GaAs/AlAs VCSEL structures. The results of this technique are confirmed by comparing with those obtained in two other experimental approaches: ͑i͒ measuring sets of complete PR spectra, at different positions on the sample, of the resonances between the cavity mode and various QW excitons, and fitting these with the new line shape model; ͑ii͒ measuring the PR spectrum of the exposed QW after removal of the top Bragg stack by etching, and fitting in the conventional way. All the results are found to be in good agreement both with each other and with the ground-state and higher-order QW transition energies calculated using a three-band k•p model. ͓S0163-1829͑99͒02004-4͔

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