Structural and optical properties of GaAs–AlxGa1−xAs quantum wells

Abstract

We report structural and optical data on single and multiple GaAs–AlxGa1−x As quantum well structures. The layers were grown in a fully automated system incorporating a high speed rotation stage of our own design. All layers were grown in the substrate temperature range 680–700 °C using an As2 source. Growth rates were normally about 1 μm/h for GaAs. The substrate rotation stage is capable of operation at up to 200 rpm compared to commercial equipment operating limits of about 10 rpm. This enables rotation of the substrate once during the deposition of each monolayer, thus avoiding the modulation of alloy composition found at lower rotation speeds. We present data showing the excellent layer uniformity obtained with this device. We have carried out TEM and photoluminescence studies on single quantum well structures grown with and without a prelayer of AlAs. The well with the prelayer shows a peak assigned to the n=1(e−hh) free exciton and a considerable decrease in impurity related luminescence at 6 K. We relate these results to improvements in structural properties seen in TEM. Multiple quantum well structures have been grown showing strong photoluminescence up to 300 K. Peaks assigned to the n=1(e−hh) and n=1(e−lh) transitions have been observed at room temperature and the possible excitonic nature of these peaks is discussed.