Competition between confinement potential fluctuations and band-gap renormalization effects inIn0.53Ga0.47As/In

Abstract

We present the results of our studies on the emission properties of In 0.53 Ga 0.47 As/ In 0.525 Ga 0.235 Al 0.25 As single and coupled double quantum wells ͑CDQWs͒ with different degrees of potential fluctuation. We have verified that the curve of the temperature ͑T͒ dependence of the emission peak energy ͑E PL ͒ is significantly influenced by the potential fluctuations ͑which are magnified by the presence of the internal barrier in the CDQW͒ as well as by the excitation density used in the photoluminescence ͑PL͒ measurements. As the excitation power increases, two effects occur simultaneously: the filling of the band-tail states related to potential fluctuations and the band-gap renormalization ͑BGR͒ caused by the increase in the density of photogenerated carriers. As the optical density increases, the E PL can shift to either higher ͑blueshift͒ or lower ͑redshift͒ energies, depending on the temperature at which the measurements are carried out. The temperature at which the displacement changes from a blueshift to a redshift is governed by the magnitude of the potential fluctuations and by the variation of BGR with excitation density.

Substrate orientation effect on potential fluctuations in multiquantum wells of GaAs∕AlGaAs

“…Below T X , the potential fluctuations dominate the excitonic transitions, and for temperature values superior than T X , the effect of band-gap energy renormalization starts to predominate. 18,19 Taking this into account, it can be observed that on ͑311͒ surfaces, the values of T X are higher than those on ͑100͒, showing that the potential fluctuations are higher in those surfaces.…”

“…[17][18][19][20] As far as we know, studies about the influence of substrate orientation on potential fluctuations in QWs are lacking. This article aims to analyze the influence of the substrate orientation on the potential fluctuations of GaAs/ Al x Ga 1−x As MQWs grown on ͓100͔ ͓311͔A, and ͓311͔B oriented GaAs substrates.…”

Exciton behavior in GaAs/AlGaAs coupled double quantum wells with interface disorder

“…This should be the band edge displacement to lower energies; however, the band filling is also occurring, displacing the PL peak to higher energies, relative to the band edge. In a previous work, about the BGR effect in InGaAs/InGaAlAs CDQWs [34], we have found that for the same laser intensity range, the PL peak energy displacement to lower energies is about half of the band edge displacement, due to the combination of BGR and band filling effects. In order to make a back-of the envelope calculation, the same proportionality was considered in the present case and we found a displacement of the PL peak of about 3.4 meV, in a very good agreement with the experimental results of $3 meV for the CDQW5 and $ 4 meV for the CDQW30.…”

“…This is due to the fact that, as the fluctuations are deeper, it is necessary a higher excitation power to fill up all the localized states and, therefore, above a certain excitation power, the effects of band-tail (related to the potential fluctuations) filling and BGR cancel each other out, and the value of the PL energy peak remains practically constant [34].…”

“…For excitation powers higher than 10 mW, practically all those states are populated and, therefore, the emission process occurs predominantly through free excitons and free carriers, and the band gap renormalization (BGR) effect begins to occur and affect the PL energy peak, displacing it to smaller energies (redshift) [34]. We have estimated the photogenerated carrier density in each CDQW, at 100 mW, finding $ 6.9 Â 10 10 cm À 2 .…”