Strain-induced quantum dots: Fabrication and optical properties

High quality quantum dots have been fabricated by using self-organized InP islands as stressors. The tensile strain due the islands creates local potential minima in an InGaAs/GaAs quantum well under the islands, and confines both electrons and holes into these minima. The ground state emission from the dots is redshifted by up to 105 meV from the quantum well emission due to this lateral confinement potential, and clearly resolved emission peaks are observed from the excited states. From the time-resolved photoluminescence measurements an interlevel relaxation time of 0.6 ns between the first excited state and the ground state and a radiative lifetime of 0.9 ns for the quantum dot ground state are obtained. Photoluminescence up-conversion measurements show subpicosecond onset of the dot luminescence at high excitation densities, suggesting that Coulomb scattering is responsible for the fast capture process. A large Zeeman splitting of the higher angular momentum states is observed in a magnetic field perpendicular to the sample surface.