Direct formation of vertically coupled quantum dots in Stranski-Krastanow growth

Alternate short-period GaAs-InAs deposition following InAs pyramid formation on a GaAs (100) surface leads to the creation of vertically split pyramids. This splitting is driven by the energetics of the Stranski-Krastanow growth mode. The strain energy is reduced due to the successive transfer of InAs from the buried part of the pyramid to the uncovered part. The resulting arrangement represents a laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs parts. Results of optical studies demonstrate the expected electronic coupling in vertical direction. Coupling is found to decrease the radiative lifetime and to result in low-energy shifts of the corresponding peaks in luminescence and absorption spectra. Vertically coupled quantum dots exhibit injection lasing at very low current densities.