2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009;
Pittsburgh, Pennsylvania
Session J6: Computational Modeling of Crystallization and Nucleation Phenomena
11:15 AM–2:15 PM,
Tuesday, March 17, 2009
Room: 406
Sponsoring
Unit:
DCOMP
Chair: Jim Belak, Lawrence Livermore National Laboratory
Abstract ID: BAPS.2009.MAR.J6.5
Abstract: J6.00005 : Growth and optical properties of embedded silicon nanocrystals*
1:39 PM–2:15 PM
Preview Abstract
Abstract
Author:
Luciano Colombo
(Dept. Physics - Univ. Cagliari (Italy))
The optoelectronic properties of nanostructured silicon (nc-Si)
are governed by the interplay between the local chemical bonding
features and the complex overall atomic structure. Interesting
enough, a-Si has a larger optical absorption than the c-Si and,
therefore, biphasic a-c silicon systems (i.e. nanocrystallites
embedded into an amorphous matrix) are currently under
investigation for next-generation photovoltaics. Biphasic systems
undergo crystallization upon thermal annealing and, therefore, it
is quite difficult to predict theoretically their
finite-temperature optoelectronic properties.
In this talk I will present our ongoing research on the growth
and the optoelectronic properties of textured nanocrystalline
silicon, here modeled as a distribution of cylindrical grains
embedded into an amorphous matrix.
As for the growth, I argue that by large-scale atomistic
simulations it is possible to infer a continuum model for the
crystallinity evolution upon thermal annealing.[1] In particular,
at low crystallinity, it is proved that--consistently with the
standard Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory--the a-c
phase transformation is dominated by the isolated grain
evolution; conversely, at later stages deviations from the KJMA
theory are observed, mainly due to atomic-scale features. I also
prove that such effects can be included by using an improved
phenomenological version of the KJMA theory.[2]
As for the finite-temperature optoelectronic properties, I
present a divide-and-conquer computational procedure, based on a
combination of empirical tight-binding and model-potential
molecular dynamics. This procedure is applied to investigate
local and average optoelectronic properties of very large
nanostructured silicon systems and to predict the variation of
the optical absorption upon crystallinity.[3] I show that the
optical absorption of a nc-Si sample corresponds to a simple
linear combination between c-Si and a-Si phases and it is not
affected by electron confinement within grains. Strain effects on
combined absorption are discussed as well.
\\[3pt]
[1] A. Mattoni, L. Colombo, Phys. Rev. Lett. 99, 205501 (2007)\\[0pt]
[2] A. Mattoni, L. Colombo, Phys. Rev. B 78, 075408 (2008)\\[0pt]
[3] A. Mattoni, L. Colombo, submitted (2008)
*Financial support by EU-STREP NANOPHOTO project and by ``Fondazione Banco di Sardegna'' is acknowledged.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.MAR.J6.5