InAs Quantum Dots: Predicted Electronic Structure of Free-Standing versus GaAs-Embedded Structures

Using an atomistic pseudopential approach, we have contrasted the (i) strain profiles, (ii) strain-modified band offsets, (iii) energies of confined electrons and holes, and (iv) wave functions and Coulomb interactions between electrons and holes for three types of InAs quantum dots: (a) a free-standing spherical dot, (b) a GaAs-embedded spherical dot, and (c) a GaAs-embedded pyramidal dot. Acomparison of (a) and (b) reveals the effects of strain, while a compound of (b) and (c) reveals the effects of shape. We find that the larger band offsets in the 'free-standing' dots (i) produce greater quantum confinement of electrons and holes and (ii) act to confine the wave functions more strongly within the dot, resulting in larger electron-hole Coulomb energies. The lower symmetry of thepyramidal dot produces a richer strain profile than the spherical dots, which splits the degeneracy of the hole states and polarizes the emitted light.