The role of fluorine in implanted amorphous silicon

High dose F⁺ and BF₂⁺ implantations into crystalline silicon have been performed to produce fluorinated amorphous silicon layers, and the properties of these layers have been studied by ESR, differential resistivity, and Hall-effect measurements as well as scanning electron microscopic observations. It is found that the amorphous layer is not recrystallized even after annealing at a temperature of 700°C. The spin density as determined by ESR measurements decreases with annealing temperature showing the effectiveness of fluorine atoms as dangling bond terminators. The conductivity of the amorphous layer is found to be of the order of 10 Ω^-1cm^-1, and the Hall mobility for holes is of the order of 10–10² cm²/V-s, both of which are relatively high for amorphous silicon. However, the percentage of boron activation is low and is found to decrease exponentially with the fluorine concentration.