Low temperature nanoscopic kinetics of hydrogen plasma-enhanced crystallization of a-Si:H films

Abstract

A nanoscopic kinetic model of controlled plasma-assisted microcrystallite formation (PAμCF) of Si in pre deposited a-Si:H films at low temperatures is proposed. The model suggests mechanisms for enhancement of the Si crystallization in a-Si:H films at low temperatures by treatment of the films in plasma. The model reveals certain kinetic advantages of hydrogen plasmas for the formation of Si crystalline nuclei in a-Si:H compared to other plasmas (Ar plasma, etc.). These advantages make the hydrogen plasma substantially more efficient in the PAμCF of Si in a-Si:H films. The proposed mechanism for PAμCF of Si is associated with the formation on the surface of the a-Si:H film and in the adjacent nanometer material layer of nanoscale (picosecond) short-lived hot spots of high energy density (or effective temperature). The hot spots are generated in the material by energetic plasma ions of energy εis=20–100 eV accelerated by the electrical field in the thin plasma layer near the solid surface. The hot spots promote Si crystallization in a-Si:H. It is shown how the plasma composition, energy, mass, and fluxes of the plasma ions impinging on the surface of the a-Si:H film determine the Si nucleation rate and density of Si microcrystallization.