Strained InGaAs/GaAs multiquantum well (MQW) structures grown on (111)B GaAs sub- strates incorporate strong internal piezoelectric fields. In contrast to (100)-oriented MQW p-i-n structures, the room temperature photoluminescence (PL) peak position and lineshape depend on the barrier width, which controls the ‘‘envelope field’’ across the MQW. The complex behavior of the PL peak position with excitation power results from a competition between screening of the well and envelope fields, and the photovoltaic effect.
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
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