Abstract: FeS₂ thin films with different grain sizes were synthesized by the sulfuration reaction of Fe films with different thickness at 673K for 20h. The microstructure, microstress and optical absorption of the films were investigated. The average grain size of the FeS₂ films changes from 40nm to 80nm when the film thickness changes from 120nm to 550nm. The internal microstrain, lattice distortion, absorption coefficient and energy gap decrease with the grain size increasing. The mechanism responsible for the result can be attributed to the variation of
the degree of microstress, the distribution of energy level of crystal defect
states and the height of grain boundary barrier due to the change of the
crystal planar defects density with the grain size changing.

Key words: FeS2, grain size, microstrain, energy gap