Optical, electrical and structural properties of polycrystalline /spl beta/-FeSi2 thin films fabricated by electron beam evaporation of ferrosilicon

Ferrosilicon (FeSi/sub 2/) grains (99.9%) were evaporated at room temperature onto a (100)-oriented n-type FZ Si substrate using electron beam deposition technique. Optical, electrical and structural properties were systematically investigated as a function of subsequent isochronal (2 hrs) annealing temperature (T/sub a/) in the range of 400/spl sim/950/spl deg/C. X-ray diffraction and Raman scattering analysis suggested the formation of polycrystalline /spl beta/-FeSi/sub 2/ above T/sub a/=500/spl deg/C, whereas above T/sub a/=800/spl deg/C, Si agglomeration was observed to form. The electrical resistivity of these samples reached a maximum (0.542 /spl Omega//spl middot/cm) at T/sub a/=700/spl deg/C, and then it decreased with increasing T/sub a/. Its decrease process was explained by considering the creation of Si vacancies, which could presumably be acting as holes. It is of great interest that in T/sub a/=600/spl sim/800/spl deg/C, the majority carrier converts from n- to p-type. Typical carrier concentrations and mobilities were determined to be /spl mu//sub n/=39.4 cm/sup 2//V/spl middot/sec, n/sub e/=6.59/spl times/10/sup 17/ cm/sup -3/ for n-type /spl beta/-FeSi/sub 2/ with T/sub a/=600/spl deg/C and /spl mu//sub h/=20.3 cm/sup 2//V/spl middot/sec, n/sub h/=2.22/spl times/10/sup 18/ cm/sup -3/ for p-type /spl beta/-FeSi/sub 2/ with T/sub a/=850/spl deg/C. Optical absorption measurements revealed that the nature of the bandgap varies from an indirect to direct one with increasing Ta.