Improvements of dot-size uniformity of the columnar InGaAs quantum dot structures with GaAs(Sb)/AlGaAsSb composite layers

This study grew high quality vertically-aligned InGaAs quantum dots (QDs) on a GaAs (001) substrate by using the molecular beam epitaxy system. The GaAsSb/AlGaAsSb composite overgrown layer was adopted to cap on InGaAs QDs for improving the dot size uniformity. From the experimental results, the Sb-contained overgrown layer was observed to reduce the In-Ga intermixing and contribute to the enhancement of the dot-size uniformity. Through the measurements of transmission emission microscopy, energy-dispersive X-ray spectroscopy (EDX) and electron-energy-loss spectrometry, vertically-aligned QDs with GaAsSb/AlGaAsSb composite structure show high dot density and dot-size uniformity. In addition, the Sb composition was observed accumulate on the top region of QDs because of the strain field distribution.