Growth kinetics on silicon facets during low-temperature crystallization from indium solution

摘要

Large-grained Si layers are attractive for cost-effective thin film solar cells. Our experiments using a low-temperature steady-state solution growth procedure for growing Si crystallites on glass show the dominance of Si{111} facets. Recesses observed in the centers of these facets suggest that growth starts at {100} vertices and/or {110} edges and continues rather by spreading of monatomic steps on the {111} facets than by nucleation on these planes. The aim of this paper is to explain the observed morphology by calculation and to find out if the growth can be improved by nucleation on {111} facets. Thermodynamic analysis shows that {100} facets are rough under our growth conditions. Therefore, the calculation of two-dimensional (2D) nucleation is focused on the flat {110}, and {111} facets. The dissolution enthalpy of silicon in indium is used to evaluate the ledge free energy of Wulff-shaped 2D nuclei on both planes. It results, that 2D nucleation takes place on {110} planes already at low degrees of supersaturation. In contrast, the saturated solution would have to be undercooled by 34.2 K to explain observed size of grown crystallites by 2D nucleation on {111} planes. Such high degree of supersaturation does not occur in the experiments. Hence, the calculations support the assumed growth model.