Luminescence measurements of a Ga 1−x Al x As/ GaAs double quantum well in in-plane magnetic fields up to 22 T are reported. The properties of spatially direct and indirect excitons are studied. We show that the strong indirect exciton luminescence survives in samples with low nonradiative recombination up to high in-plane magnetic fields. This contrasts with previously published results, where its strong suppression, observed for magnetic fields as low as of 10 T, was explained by the exciton center-of-mass momentum conservation. We attribute the discrepancy to a relatively low nonradiative recombination in the studied sample in comparison with the radiative recombination of localized indirect excitons.

The effect of an external electric field F on the excitonic photoluminescence ͑PL͒ spectra of a symmetriccoupled double quantum well ͑DQW͒ is investigated both theoretically and experimentally. We show that the variational method in a two-particle electron-hole wave-function approximation gives a good agreement with measurements of PL on a narrow DQW in a wide interval of F including flat-band regime. The experimental data are presented for a molecular-beam-epitaxy-grown DQW consisting of two 5-nm-wide GaAs wells, separated by a 4-monolayers ͑ML's͒-wide pure AlAs central barrier, and sandwiched between Ga 0.7 Al 0.3 As layers. The bias voltage is applied along the growth direction. Spatially direct and indirect excitonic transitions are identified, and the radius of the exciton and squeezing of the exciton in the growth direction are evaluated variationally. The excitonic binding energies, recombination energies, oscillator strengths, and relative intensities of the transitions as functions of the applied field are calculated. Our analysis demonstrates that this simple model is applicable in the case of narrow DQW's, not just for a qualitative description of the PL peak positions but also for the estimation of their individual shapes and intensities. ͓S0163-1829͑99͒01532-5͔ PHYSICAL REVIEW B 15 SEPTEMBER 1999-I VOLUME 60, NUMBER 11 PRB 60 0163-1829/99/60͑11͒/7740͑4͒/$15.00 7740

No abstract