SEMICONDUCTING IRON SILICIDE THIN-FILMS ON SILICON-(111) WITH LARGE HALL-MOBILITY AND LOW RESIDUAL ELECTRON-CONCENTRATION

Unprecedented Hall mobility, electron concentration and photoconductiv ity are demonstrated in semiconducting beta-FeSi2 thin films prepared on Si(111) surfaces by co-sputtering of iron and silicon followed by p ost-anneal. Characterization of the silicide as a function of the init ial temperature and post-treatment shows that annealing temperatures a bove 800 degrees C are needed to obtain single phase beta-FeSi2. React ive deposition on substrates heated at 850 degrees C leads to textured films. Majority carriers are electrons in all these unintentionally d oped films. Hall concentrations between 1.8 x 10(17) and 5 x 10(15) el ectrons cm(-3) and respective Hall mobilities from 290 to 900 cm(2) V- 1 s(-1) are measured at room temperature, involving two different cond uction band minima in these two extreme cases. Only deep centres exist in the samples having the lower carrier concentration. In such a situ ation, raw data must be corrected for the substrate contribution to ex tract values which are relevant for the beta-FeSi2 film alone. Photoco nductivity also takes place in these samples: at 80 K, it shows a maxi mum value at the direct band gap of beta-FeSi2 while at 296 K a step s till appears at the same energy. Such results are a consequence of the important decrease of the residual impurity concentration in comparis on to values previously published.