Evidence of weak strain field in InAs/GaAs submonolayer quantum dots

We used rapid thermal annealing and low-temperature photoluminescence to compare the optoelectronic properties of InAs/GaAs Stranski-Krastanov and submonolayer quantum dots. After annealing, the former showed large changes in their optical spectra, whereas the latter remained almost insensitive and had optical properties similar to those of an InGaAs quantum well. This contrast was attributed to the presence of In segregation during the submonolayer deposition that led to strong In–Ga intermixing and hindered the formation of the submonolayer quantum dots. The optical results point out that, in such conditions, the strain field in the InAs/GaAs system is too weak to effectively provide vertical alignment of the small two-dimensional islands nucleated in consecutive InAs submonolayers. To further improve the properties of submonolayer quantum dots, segregation should be reduced and an initial (2 × 4) surface reconstruction should be preferred, as it is the only one able to provide true two-dimensional InAs islands.