Quantitative compositional profiles of enhanced intermixing in GaAs/AlGaAs quantum well heterostructures annealed with and without a SiO2 cap layer

Cross-sectional scanning transmission electron microscopy together with energy-dispersive x-ray spectroscopy (EDX) was used to quantitatively analyze quantum well intermixing (QWI) of a GaAs quantum well (QW) structure with AlGaAs barriers for samples capped with SiO2 or uncapped. Energy-dispersive x-ray analysis shows inter-diffusion of Ga and As into the SiO2 layer and Si into top GaAs layer. The enhanced QWI due to rapid thermal annealing (RTA) with the cap layer produces a square-like broadening of the QWs, while the QW broadening remains mostly Gaussian like for uncapped samples. A photoluminescence blueshift is seen for both capped and uncapped samples after RTA. Void-like defects have been observed to form and coalesce at higher anneal temperatures in the top GaAs layer at the interface with the SiO2. This is consistent with the Kirkendall process occurring at the interface producing the voids and also resulting in the production of interstitial atoms which diffuse employing the 'kick-out' mechanism to produce the flat-bottomed QW broadening.