INFRARED SPECTROSCOPIC AND ELECTRONIC TRANSPORT-PROPERTIES OF POLYCRYSTALLINE SEMICONDUCTING FESI2 THIN-FILMS

Polycrystalline semiconducting FeSi2 thin films were grown on (100) Si substrates of high resistivity by electron beam evaporation of amorph ous Si/Fe ultrathin multilayers in an ultrahigh vacuum system, followe d by conventional vacuum furnace (CF) or rapid thermal annealing (RTA) . Infrared reflectance and transmittance measurements were employed fo r optical characterization of the samples at room temperature. The res ults indicate a direct transition at about 0.85 eV, an indirect transi tion at about 0.78 eV, and exponential band tail states within the ban d gap. The quality of the silicide is improved by increasing the annea ling temperature from 600 to 800 degrees C in the RTA process, while t he opposite is observed in the CF annealed samples. Transport measurem ents were performed on a typical beta-FeSi2 layer of high quality frow n by CF at low temperature. The measured mobility is about 97 cm(2)/V s and the hole concentration is about 1 X 10(17) cm(-3); The mobility is a factor of 10 higher and the hole concentration a factor of 100 lo wer than the corresponding published data, indicating a significantly improved quality of beta-FeSi2 layers. Temperature-dependent measureme nts Indicate that carrier transport is dominated by impurity conductio n. (C) 1996 American Institute of Physics.