Microtech2010 2010

Atomistic Simulations of Electronic Structure in Realistically-Sized Wurtzite InN/GaN Quantum Dots

K. Yalavarthi, V. Gaddipati, S. Ahmed
Southern Illinois University at Carbondale, US

Keywords: quantum dots, LED, solid-state lighting, strain, piezoelectricity, pyroelectricity, tight-binding, NEMO 3-D

Abstract:

In this work, within a fully atomistic framework, we investigate the electronic structure of wurtzite InN quantum dots self-assembled on GaN substrates. The main objectives are two-fold: (1) to explore the origin, nature and the role of crystal atomicity, strain-field, piezoelectric and pyroelectric potentials in determining the energy spectrum and the wavefunctions, and (2) to address the shift in the ground state, the symmetry-lowering and the non-degeneracy in the first excited state, the strong band-mixing in the overall conduction band electronic states, and their size and geometry dependence—a group of inter-related phenomena that has been revealed in recent spectroscopic analyses. We also demonstrate the importance of 3D atomistic material representation, and the need for using realistically-extended substrate and cap layers (multimillion atom modeling) in studying the built-in fields in these reduced-dimensional QDs. Models used in this study are as follow: (1) VFF Keating model for atomistic strain relaxation; (2) 20-band nearest-neighbor sp3d5s* tight-binding model for the calculation of single-particle energy states; and (3) microscopically determined polarization constants in conjunction with an atomistic 3-D Poisson solver for the calculation of piezo- and pyro- electric contributions.
 
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