From: hackbard Date: Wed, 3 Feb 2010 14:28:03 +0000 (+0100) Subject: starting with migration experiments now X-Git-Url: https://hackdaworld.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dce12b752a5ab03cff99d115795bcf7defdb62a8;p=lectures%2Flatex.git starting with migration experiments now --- diff --git a/posic/thesis/defects.tex b/posic/thesis/defects.tex index afaaf80..3d41711 100644 --- a/posic/thesis/defects.tex +++ b/posic/thesis/defects.tex @@ -452,19 +452,30 @@ This is in agreement with results of the Erhard/Albe potential simulations which However, this fact could not be reproduced by spin polarized VASP calculations performed in this work. Present results suggest this configuration to be a real local minimum. In fact, an additional barrier has to be passed to reach this configuration starting from the \hkl<1 0 0> interstitital configuration, which is investigated in section \ref{subsection:100mig}. -The carbon atom has been displaced along the axes ... relaxation back ... indicating a real local minimum. +After slightly displacing the carbon atom along the \hkl<1 0 0> (equivalent to a displacement along \hkl<0 1 0>), \hkl<0 0 1> and \hkl<1 -1 0> direction the resulting structures relax back into the bond-centered configuration. +As we will see in later migration simulations the same would happen to structures where the carbon atom is displaced along the migration direction, which approximately is the \hkl<1 1 0> direction. +These relaxations indicate that the bond-cenetered configuration is a real local minimum instead of an assumed saddle point configuration. Figure \ref{img:defects:bc_conf} shows the structure, the charge density isosurface and the Kohn-Sham levels of the bond-centered configuration. The linear bonds of the carbon atom to the two silicon atoms indicate the $sp$ hybridization of the carbon atom. Two electrons participate to the linear $\sigma$ bonds with the silicon neighbours. The other two electrons constitute the $2p^2$ orbitals resulting in a net magnetization. This is supported by the charge density isosurface and the Kohn-Sham levels in figure \ref{img:defects:bc_conf}. -The blue torus, reinforcing the assumption of the p orbital, illsutrates the resulting spin up electron density. +The blue torus, reinforcing the assumption of the p orbital, illustrates the resulting spin up electron density. In addition, the energy level diagram shows a net amount of two spin up electrons. \section[Migration of the carbon \hkl<1 0 0> interstitial]{\boldmath Migration of the carbon \hkl<1 0 0> interstitial} \label{subsection:100mig} In the following the problem of interstitial carbon migration in silicon is considered. +Since the carbon \hkl<1 0 0> dumbbell interstitial is the most probable hence most important configuration the migration simulations focus on this defect. + +There are different methods of computing migration paths and energies. +Methods and shortcomings. + +Three different migration paths are accounted in this work. +In the first path the carbon atom + +Results and comparison with diffusion experiments. \section{Combination of point defects}