Excitons, biexcitons, and trions in self-assembled (In,Ga)AsGaAs quantum dots: Recombination energies, polarization, and radiative lifetimes versus dot height

Gustavo A. Narvaez, Gabriel Bester, and Alex Zunger
Phys. Rev. B 72, 245318 – Published 13 December 2005

Abstract

We calculate the height dependence of recombination energies, polarization, and radiative lifetimes of the optical transitions of various excitonic complexes: neutral excitons (X0), negatively (X) and positively charged (X+) trions, and biexcitons (XX0) in lens-shaped, self-assembled In0.6Ga0.4AsGaAs quantum dots. By using an atomistic pseudopotential method combined with the configuration-interaction method, we predict the following. (i) The recombination energy of the lowest transition of X blueshifts as height increases, whereas that of X+ redshifts. Remarkably, the recombination of XX0 shows a redshift at small heights, reaches a maximum shift, and then blueshifts for taller dots. This feature results from the height dependence and relative magnitude of the interelectronic direct Coulomb interaction. (ii) Changes in dot height lead to a bound-to-unbound crossover for X, X+, and XX0. (iii) When considering the [110] and [11¯0] directions, the lowest transitions of X0 and XX0 manifest [110] vs [11¯0] in-plane polarization anisotropy that switches sign as a function of height as well as alloy randomness. X and X+ show transitions with negligible polarization anisotropy regardless of height. (iv) The ground state of X0 is split in a low-energy pair that is forbidden (dark) and a high-energy pair that is allowed; thus, at T=0K, the radiative lifetime τ(X0) is long (ms) due to the dark exciton. On the other hand, at T=10K, τ(X0) decreases moderately as height increases and its magnitude ranges from 23ns. The ground state of X and X+, and that of XX0 is allowed (bright); so, τ(X), τ(X+), and τ(XX0) are fast (ns) even at T=0K. These radiative lifetimes depend weakly on height. In addition, τ(X)τ(X+)1.1ns, while τ(XX0)0.5ns. We compare our predictions with available spectroscopic data.

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  • Received 1 September 2005

DOI:https://doi.org/10.1103/PhysRevB.72.245318

©2005 American Physical Society

Authors & Affiliations

Gustavo A. Narvaez, Gabriel Bester, and Alex Zunger

  • National Renewable Energy Laboratory, Golden, Colorado 80401, USA

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Vol. 72, Iss. 24 — 15 December 2005

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