Coupling Effects in Vertically Stacked Double Quantum Dots: Tight-Binding Approach

Published

October 16, 2008

Author(s)

W Jaskolski, M Zielinski, Garnett W. Bryant

Abstract

Atomic-scale effects on electronic coupling in coupled quantum dots are studied. The empirical tight-binding approach is used to obtain the electronic structure, charge densities and optical absorption spectra of coupled, InAs/GaAs, self-assembled, vertically stacked, double dots. Pyramidal and lens shaped dots are investigated. A model with unstrained dots is considered to isolate the atomistic effects. Electron levels in coupled dots follow closely the simple analogy of coupled dots as artificial molecules because the interdot coupling of electron states is determined by the symmetry of the electron envelope function. The calculations show significant coupling between the dots when the dots are separated by several monolayers of GaAs. Double-dot electron states having bonding and antibonding character are formed. The coupling of hole states is more complicated because the coupling depends both of the hole envelope function and the atomic character of the hole state. The hole ground state for widely spaced coupled dots is formed from an antisymmetric combination of the single-dot hole ground states. The hole ground state for closely spaced dots is formed from the symmetric combination of the single-dot hole ground states. The symmetry of the coupled-dot hole states is determined by which atomic component of the hole state is dominant in the region between dots. This anomalous reversal in hole-state symmetry reorders hole levels, changes state symmetries, and makes substantial changes in optical spectra. The lowest transition is dark for widely-spaced dots but bright for closely-spaced dots. The calculated red-shift of the lowest transition for closely-spaced dots agrees well with experimental data.

Citation

Physical Review B (Condensed Matter and Materials Physics)

Pub Type

Journals

Keywords

electronic structure, optical spectra, quantum dots, tight-binding

Citation

Jaskolski, W. , Zielinski, M. and Bryant, G. (2008), Coupling Effects in Vertically Stacked Double Quantum Dots: Tight-Binding Approach, Physical Review B (Condensed Matter and Materials Physics) (Accessed April 27, 2024)