Eur. Phys. J. B 72, 193-201 (2009)
https://doi.org/10.1140/epjb/e2009-00359-0

Mixed Si-Ge nanoparticle quantum dots: a density functional theory study

¹ Industrial Research Limited, 69 Gracefield Road, P.O. Box 31-310, 5040 Lower Hutt, New Zealand
² MacDiarmid Institute of Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, 6140 Wellington, New Zealand

Corresponding author: ^a brentgwalker@gmail.com

Received: 28 February 2009
Revised: 9 August 2009
Published online: 27 October 2009

Abstract

We present a systematic study of small mixed composition Si and Ge nanoparticle quantum dots performed using density functional theory (DFT) and time-dependent density functional theory (TDDFT) with real space grids and norm-conserving pseudopotentials. Quantum dot models are obtained by distributing Si and Ge atoms within basic models containing a specified number of atomic sites, tetrahedrally-coordinated about a central site, with H atoms added to terminate the surfaces. We consider models containing up to 35 semiconductor atoms, and a number of subsets of the total number of possible configurations (e.g. alternating elements in successive shells). Following calculation of structural and energetic properties, the optical absorption spectra are determined using time-dependent DFT within Casida's linear-response approach. With respect to Si, the inclusion of Ge moves spectral weight to lower energies. We observe that the relative fractions of Si and Ge have stronger effects on the absorption spectra than the structural distribution of those atoms within the nanoparticle, which tends to have quite small effects.