Growth dynamics of hydrogenated silicon nanoparticles under realistic conditions of a plasma reactor
Résumé
We present results of an extensive numerical study that was motivated by the experimental problem to understand under which conditions SinHm nanoparticles deposited by plasma enhanced chemical vapor deposition (PECVD) take an amorphous or a crystalline structure. A crystalline structure of those particles is crucial, for example, for the electrical properties and lifetime of polymorphous solar cells. First, we use a fluid dynamics model to characterize the experimentally employed silane plasma. The resulting relative densities for all plasma radicals, their temperatures, and their collision interval times are then used as input data for detailed semiempirical quantum molecular dynamics simulations. As a result the growth dynamics of nanometric hydrogenated silicon SinHm clusters is simulated starting out from the collision of individual SiHx radicals under the plasma conditions derived above. We demonstrate how the details of the plasma determine the amorphous or crystalline character of the forming nanoparticles. Finally, we show a preliminary absorption spectrum based on ab initio time-dependent DFT calculations for a crystalline Si10H16 cluster to demonstrate the possibility to monitor the cluster growth in situ.