Strain-induced material intermixing of InAs quantum dots in GaAs

A systematic investigation of the stacking behavior of InAs quantum dots (QDs) with varying GaAs interlayer thickness d is presented. We compare two-fold stacks of large QDs (≈25 nm base width), which emit at 1.30 μm, to small QDs (≈20 nm base width) emitting at 1.14 μm. For large islands photoluminescence yields an energetic blueshift of the second layer islands with decreasing d, although transmission electron microscopy clearly reveals a ≈70% larger dot size in the second layer, whereas for small islands a similar size increase of the dots in the upper layer and an energetic redshift are observed. A detailed analysis of confinement and material intermixing effects suggests that for large QDs strain driven material intermixing is dominant. For small QDs the confinement effect plays the major role and causes the observed photoluminescence energy redshifts.