Molecular Dynamics Simulations On The Growth Of A-Si:H/c-Si Thin Film

a-Si:H/c-Si heterojunction solar cell takes not only the advantage of thin-filmmanufacturing technology, but also the advantages of both crystalline silicon andamorphous silicon. It has the potential prospect to be a high-efficiency and low-costsilicon solar cell. This paper attempts to apply molecular dynamics method tosimulate the growth of a-Si:H/c-Si thin film. The effects of substrate temperature,incident kinetic energy, incident frequency and growth plane of substrate on the thea-Si:H film structural characteristics were investiaged. The Voronoi polyhedralstructure analysis method was applied to analyze the arrangement of atoms. Theresults are as follows:(1) The studies of a-Si:H/c-Si(001) and a-Si:H/c-Si(111) thin film growth underdifferent substrate temperature shows that: as the substrate temperature increased, thesurface roughness decreased and the inherent density increased, the contents of H,SiH and dangling bonds decreased for the a-Si:H thin films growth on both Si (001)and Si (111) substrate. The difference was that the relationship between the surfaceroughness and temperature of Si (111) substrate was closer linearity than that of Si(001) substrate. And the inherent density of the film growth on Si (111) substrateshowed more porous than that of Si (001) substrate. And further the reaons of theseresults were analyzed and discussed.(2) The studies of a-Si:H/c-Si(001) and a-Si:H/c-Si(111) thin film growth underdifferent incident kinetic energy shows that: as the incident kinetic energy increased,the change trends are similar for the films both growth on Si (001) substrate and Si(111) substrate, i.e. the surface roughness decreased, the inherent density increased,the contents of H and dangling bonds decreased, and their rate of change was fast firstand then slow. The difference between the two substrates was the critical energy forthe variety of SiH content,0.64eV for Si(001) and0.16eV for Si (111). And furtherthe reaons of these results were analyzed and discussed.(3) The studies of a-Si:H/c-Si(001) and a-Si:H/c-Si(111) thin film growth underdifferent incident frequency shows that: the surface morphology and inherent density of a-Si:H films were not associated with incident frequency, the contents of SiH, Hand dangling bond density. The reasons of them were that the incident frequency hadlittle effect on the SiH3radical adsorption rate, the radical surface diffusion and thecrystallization rate of the film.(4) The neighbor Voronoi polyhedra topology structure of hydrogenatedamorphous silicon thin films were too complicated to count the polyhedron indexeffectively. But the metric properties of Voronoi polyhedra shows that: the structureof thin films which growth at low temperature were more complicated than at hightemperature; As the substrate temperature increased, the probability of hole structurein the films would decrease, and the Voronoi polyhedral would be less distorted, beclose to spherical structure.(5) By using the nearest neighbor Voronoi polyhedron analysis method, we foundthat: As the substrate temperature increased, the content of <4,0,0,0> polyhedral,which represented local tetrahedron structure, increased in a-Si:H films growth bothon Si(001) substrate and on Si(111) substrate; When the energy was less than0.04eVof Si(001) or0.16eV of Si(111) substrate, the increase of incident kinetic energywould result in the increase of the local tetrahedron structure. After those criticalenergy, the increase of incident kinetic energy was not associated with the localtetrahedral arrangement.(6) By using the second-nearest neighbor Voronoi polyhedron analysis method,we found that: As the substrate temperature and incident kinetic energy increased, thecontents of low coordination polyhedra, such as <0,4,4,0>,<1,3,3,1>,<0,4,4,1>,<0,3,6,0> and <0,4,4,2>, decreased. While the contents of high coordinationpolyhedra, such as <0,3,6,3>,<0,2,8,2>,<0,4,4,4> and <0,3,6,4>, increased. Thecontents of the four types of second-nearest neighbor Voronoi polyhedra increasedindicated that the atomic paracrystalline structure arrangement of second-nearestneighbor silicon atoms in a-Si:H films gradually enhanced.