(262a) Effects of Composition and Compositional Distribution On the Optoelectronic Properties and Function of Semiconductor Ternary Quantum Dots

The function of nanometer-size quantum dots (QDs) of ternary compound semiconductors, such as In_xGa_1-xAs, ZnSe_1-xS_x, and ZnSe_1-xTe_x, used in the fabrication of optoelectronic and photovoltaic devices can be optimized by precise tuning of their electronic band gap through control of the QD composition (x) and diameter.  In this presentation, we report results on compositional distributions in ternary QDs and how they affect the QDs’ electronic band gap.  We follow a hierarchical modeling approach that combines first-principles density functional theory (DFT) calculations and classical Monte Carlo simulations with a continuum model of species transport in spherical nanocrystals.  In certain cases, the model predicts the formation of a concentration boundary layer near the nanocrystal surface, i.e., the formation of core/shell-like structures with shell regions rich in the surface segregating species.  A systematic parametric analysis generates a database of transport properties, which can be used to design post-growth thermal annealing processes that enable the development of thermodynamically stable QDs.

Based on the continuum transport model, we have analyzed species interdiffusion kinetics in ternary semiconductor nanocrystals during their thermal annealing and used the modeling results to interpret the evolution of near-surface species concentration according to X-ray photoelectron spectroscopy (XPS) measurements. We have also explored the impact of composition and compositional distribution on the ternary QDs’ electronic band gaps based on first-principles DFT calculations and found that ternary QDs with thermodynamically stable compositional distributions allow for precise band-gap tuning.  Our findings lead to a proposal for an efficient one-step ternary QD synthesis method followed by annealing to promote self assembly of the thermodynamically stable configuration for optimal optoelectronic function in devices.