STUDY OF SURFACE ATOMIC DIFFUSION ON PRE-PATTERNED SI SUBSTRATES BY MOLECULAR DYNAMICS SIMULATION: MODELING WITH THE USE OF HIGHLY EFFICIENT ALGORITHMS
Abstract
There is a growing interest of researchers to the creation of space-arranged arrays of quan-tum dots (QDs). These structures are promising as an element basis for thermally stable solid state lasers, field effect transistors with enhanced electron mobility, photosensitive matrices etc. Such structures can be obtained by heteroepitaxial growth on a pre-patterned template. Under the proper conditions of heteroepitaxy nanoislands may nucleate in the pits or grooves, forming the space-arranged array of QDs. In the area of basic research the microscopic mechanism of atom diffusion on a non-planar crystal surface is not studied enough. The target of this paper is the elucidation of atomic diffusion mechanism on pre-patterned Si substrates. In order to achieve the purpose virtual Si(001)-1×2 structure with a system of parallel grooves has been formed. The groove width and inter-distance were chosen the same, which corresponds to geometry of experi-mental pre-patterned substrates, prepared by nanoimprint lithography. An algorithm of calcula-tion of the pre-patterned substrate energy surface has been developed on the basis of molecular dynamics method. The energy surface was mapped out for Si (001) substrate in the region of groove. The positions of minima and saddle points at the energy surface have been found, surface diffusion activation energy was calculated for Ge atoms, and the typical Ge atoms migration paths on the groove walls have been determined. The analysis of microscopic mechanism of atomic dif-fusion on a pre-patterned substrate has been carried out. Possible reasons, preventing atom mi-gration inside grooves and nucleation of 3D nanoislands there, are discussed. MD simulations are related to big volume data processing and require significant machine time spent. In order to ac-celerate the calculations a parallel algorithm for neighbors seeking in a large system of atoms has been developed. The time of calculations has been obtained as depending upon the number of nuclei within a single node. The effect of acceleration is shown to be linear against the number of cores at least from 1 to 8.
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