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@@ -64,34 +64,25 @@ Three types of models were established: defect-free models, point defect models,
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此结构除了 h 位与 k 位的区别以外,还需要考虑发生替换的两个原子位于面内还是面外(将会导致对称性的不同)。
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The defect-free and point defect models were established
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with a size of $12.4 #sym.angstrom times 10.7 #sym.angstrom times 10.1 #sym.angstrom$,
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with dimensions of $12.4 #sym.angstrom times 10.7 #sym.angstrom times 10.1 #sym.angstrom$,
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containing approximately 128 atoms.
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This size should be large enough to calculate phonon properties for defect-free and point defect 4H-SiC,
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since the defect-free results obtained with these models were within 5% errors of the experimental data,
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and further increasing the model size did not improve the accuracy.
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Twelve point defect models were considered, including Si vacancies (V#sub[Si]),
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C vacancies (V#sub[C]), nitrogen substitutions (N#sub[Si]), and aluminum substitutions (Al#sub[C]).
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Considering the symmetry of 4H-SiC, which is p63mc (cite),
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there are two different sites, k and h,
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which can be approximated as cubic (k) or hexagonal (h) based on the local environment.
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For point defect models, we considered five different structures,
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including Si vacancies (V#sub[Si]), C vacancies (V#sub[C]),
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nitrogen substitutions (N#sub[Si]), aluminum substitutions (Al#sub[C]),
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and the structure of a nitrogen substitute carbon and carbon substitute silicon (N#sub[C]C#sub[Si])
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which is proposed by xxx (ref) to be a possible structure of nitrogen doping.
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Besides,
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For surface defect models, larger models where used to ensure the accuracy of the phonon properties.
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This supercell size was found sufficient for accurately capturing the phonon properties
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of both defect-free and point-defect-containing 4H-SiC,
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as the calculated phonon frequencies for the defect-free model deviated by less than 5% from experimental values,
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and further increasing the cell size yielded negligible improvements.
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Twelve point defect configurations were investigated,
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including Si vacancies (V#sub[Si]-h and V#sub[Si]-k), C vacancies (V#sub[C]-h and V#sub[C]-k),
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nitrogen substitions on C cites (N#sub[C]-h and N#sub[C]-k),
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aluminum substitutions on Si cites (Al#sub[Si]-h and Al#sub[Si]-k),
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and nitrogen substitutions on C sites followed by C substitutions on Si site
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(N#sub[C]C#sub[Si]-i-h, N#sub[C]C#sub[Si]-i-k, N#sub[C]C#sub[Si]-o-h and N#sub[C]C#sub[Si]-o-k),
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where -h and -k denote the quasi-hexagonal and quasi-cubic sites,
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and -i and -o denote the in-plane and out-of-plane configurations, respectively.
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(图:a k 位与 h 位对比 b 面内与面外对比)
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For surface defect models, larger models where used to ensure the accuracy of the phonon properties.
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因此对于无缺陷和点缺陷的模型,我们使用 xxA x xxA x xxA 的模型大小。
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