(446e) Internal Ordering and Electronic Structure of Self-Assembled Core/Shell-Like Quantum Dots

Heterogeneous semiconductor quantum dots (QDs) are semiconductor nanocrystals with non-uniform compositional distribution that have attracted significant technological interest in optoelectronic and photovoltaic device fabrication. To investigate the possibility of rigorous single-step synthesis routes to minimally strained core/shell-like QDs, we have studied sytematically the distribution of atomic species in ternary compound semiconductor nanocrystal systems, emphasizing on surface/interface segregation as a potential means for self-assembly of core/shell-like semiconductor QDs.

In this presentation, we report results on the equilibrium concentration profiles in ZnSe_1-xTe_x, In_xGa_1-xAs, and In_xGa_1-xP QDs according to a computational analysis of full nanocrystal relaxation and on the corresponding electronic structure of the QDs. The full relaxation consists of coupled compositional, structural, and volume relaxation of the semiconductor nanocrystals. Our analysis is based on first-principles density functional theory (DFT) calculations and employs Monte Carlo (MC) and conjugate-gradient (CG) methods. Specifically, the MC and CG relaxation computations are based on a classical valence force field description of interatomic interactions, which has been parameterized according to DFT calculations of segregation energies using slab supercells. The computed equilibrium concentration profiles are explained based on a phenomenological species transport theory that we have developed for surface segregation of constituent and dopant atoms in the dilute limit. We have determined the electronic structure of the QDs corresponding to equilibrium concentration distributions over the entire compositional range (0 ≤ x ≤ 1) and to QD morphologies that include faceted equilibrium nanocrystal shapes. Our results identify the effects of internal order/disorder on the electronic properties of these QDs that self-assemble into such thermodynamically stable, minimally strained hetero-nanostructures.