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% there should be a short motivation for the material system!\r
Silicon carbide (SiC) has a number of remarkable physical and chemical properties.\r
-The wide band gap semiconductor (2.3 eV - 3.3 eV) exhibiting a high breakdown field, saturated electron drift velocity and thermal conductivity in conjunction with its unique thermal and mechanical stability as well as radiation hardness is a suitable material for high-temperature, high-frequency and high-power devices\cite{wesch96}, which are moreover deployable in harsh environments\cite{capano97}.\r
+The wide band gap semiconductor (2.3 eV - 3.3 eV) exhibiting a high breakdown field, saturated electron drift velocity and thermal conductivity in conjunction with its unique thermal and mechanical stability as well as radiation hardness is a suitable material for high-temperature, high-frequency and high-power devices\cite{wesch96,morkoc94}, which are moreover deployable in harsh and radiation-hard environments\cite{capano97}.\r
% there are different polytpes with different properties and 3c-sic in special\r
SiC, which forms fourfold coordinated covalent bonds, tends to crystallize into many different modifications, which solely differ in the one-dimensional stacking sequence of identical, close-packed SiC bilayers\cite{fischer90}.\r
-Different polytypes exhibit different properties, where the only cubic phase (3C-SiC) shows increased values for the thermal conductivity and breakdown field compared to other polytypes\cite{wesch96}, which is of special interest for highly efficient and high-power electronic device applications.\r
+Different polytypes exhibit different properties, in which the cubic phase (3C-SiC) shows increased values for the thermal conductivity and breakdown field compared to other polytypes\cite{wesch96}, which is thus most effective for high-performance electronic devices.\r
\r
% (thin films of) 3c-sic can be produced by ibs\r
-Next to epitaxial layer growth by chemical vapor deposition\cite{powell90} and molecular beam epitaxy\cite{mbe}, ion beam synthesis (IBS) constitutes a promising method to produce 3C-SiC epitaxial layers of high quality in silicon\cite{ibs}.\r
-\r
-\r
- \r
-\r
-The relevant structures are with $\approx$ 20000 atoms/nanocrystal way too large to be completely be described with high accuracy \r
-quantum mechanical methods. Modelling the processes described above require the use of less accurate methods, like e.g. classical \r
-potentials (Erhard/Albe\cite{albe},Stillinger-Weber\cite{stillinger},...). Whether such potentials are appropriate for the description of the \r
-physical problem has, however, to be verified first by applying both methods to relevant processes that can be treated by both methods. \r
-In this work, we have implemented and compared the applicability of several (?) classical potentials to ab initio results for one \r
-of the most important processes of our original question. \r
-\r
-In the following we will present a comparative investigation of density functional theory (DFT) studies and \r
-classical potential calculations of the structure, energetics and mobility of carbon defects in silicon. \r
+Next to the fabrication of 3C-SiC layers by chemical vapor deposition (CVD) and molecular beam epitaxy (MBE) on hexagonal SiC\cite{powell90,fissel95,fissel95_apl} and Si\cite{nishino83,nishino87,kitabatake93,fissel95_apl} substrates, high-dose carbon implantation into crystalline silicon (c-Si) with subsequent or in situ annealing was found to result in SiC microcrystallites in Si\cite{borders71}.\r
+% maybe split CVD and MBE from IBS and explain remaining problems:\r
+% - on 6H-SiC: twin boundaries\r
+% - on Si: structural defects due to thermal conductivity and lattice mismatch\r
+Utilized and enhanced, ion beam synthesis (IBS) has become a promising method to form thin SiC layers of high quality exclusively of the 3C polytype embedded in and epitactically aligned to the Si host featuring a sharp interface\cite{lindner99,lindner01,lindner02}.\r
+% precipitation model\r
+However, only little is known on the SiC conversion in C implanted Si.\r
+High resolution transmission electron microscopy (HREM) studies\cite{werner96,werner97,lindner99_2} suggest the formation of C-Si dimers (dumbbells) on regular Si lattice sites, which agglomerate into large clusters indicated by dark contrasts and otherwise undisturbed Si lattice fringes in HREM.\r
+Once a critical radius of 2 nm to 4 nm is reached a topotactic transformation into a 3C-SiC precipitate occurs.\r
+The transformation is manifested by the disappearance of dark contrasts in favor of Moir\'e patterns due to the lattice mismatch of 20 \% of the 3C-SiC precipitate and c-Si.\r
+The insignificantly lower Si density of SiC ($\approx 4$ \%) compared to c-Si results in the emission of only a few excess Si atoms.\r
+% motivation to understand the precipitation and link to atomistic simulations\r
+A detailed understanding of the underlying processes will enable significant technological progress in 3C-SiC thin film formation and likewise offer perspectives for processes which rely upon prevention of precipitation events, e.g. the fabrication of strained pseudomorphic Si$_{1-y}$C$_y$ heterostructures\cite{strane96,laveant2002}.\r
+\r
+Atomistic simulations offer a powerful tool to study materials on a microscopic level providing detailed insight not accessible by experiment.\r
+Relevant structures consisting of $\approx 10^4$ atoms for the nanocrystal and even more atoms for a reasonably sized Si host matrix are too large to be completely described by high accuracy quantum mechanical methods.\r
+Directly modelling the dynamics of the processes mentioned above almost inevitably requires the atomic interaction to be described by less accurate though computationally more efficient classical potentials.\r
+The most common empirical potentials for covalent systems are the Stillinger-Weber\cite{stillinger85}, Brenner\cite{brenner90}, Tersoff\cite{tersoff_si3} and environment-dependent interatomic (EDIP)\cite{bazant96,bazant97,justo98} potential.\r
+Until recently\cite{lucas10}, a parametrization to describe the C-Si multicomponent system within the mentioned interaction models did only exist for the Tersoff\cite{tersoff_m} and related potentials.\r
+Whether such potentials are appropriate for the description of the physical problem has, however, to be verified first by applying classical and quantum-mechanical methods to relevant processes that can be treated by both methods.\r
+An extensive comparison\cite{balamane92} concludes that each potential has its strengths and limitations and none of them is clearly superior to others.\r
+Despite their shortcomings these potentials are assumed to be reliable for large-scale simulations\cite{balamane92,huang95,godet03} on specific problems under investigation providing insight into phenomena that are otherwise not accessible by experimental or first principles methods.\r
+Bsp wo es nicht funktioniert -> gao und denevanth aus neuem edip + modified potentials aus meiner liste ...\r
+\r
+\cite{balamane92,huang95,godet03}\r
+\r
+In this work, the applicability of a Tersoff-like bond order potential\cite{albe_sic_pot} (claiming good ... nachschauen bei paper, dass dann doch edip nimmt) to some basic processes involved in the initially mentioned SiC precipitation mechanism is investigated by comparing results gained by classical and ab inito calculations.\r
+\r
+In the following a comparative investigation of density functional theory (DFT) studies and classical potential calculations of the structure, energetics and mobility of carbon defects in silicon is presented.\r
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\section{Methodology}\r
projects / lectures / latex.git / blobdiff