Quantitative compositional profiles of enhanced intermixing in GaAs/AlGaAs quantum well heterostructures annealed with and without a SiO_2 cap layer

摘要

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 SiO_2 or uncapped. Energy-dispersive x-ray analysis shows inter-diffusion of Ga and As into the SiO_2 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 SiO_2. 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.