INTERFACE PHASE-TRANSITION AS OBSERVED IN ULTRA-THIN FESI2 EPILAYERS

Because its optical gap is dose to 0.85 eV, the semiconducting orthorh ombic disilicide beta-FeSi2 has been extensively studied since it migh t find applications in integrated optoelectronic devices. During the c ourse of these investigations several unexpected pseudomorphic phases of ultra thin FeSi2 layers have been observed on top of the Si substra tes. The growth of these phases and their physicochemical properties h ave been investigated for a large variety of preparation methods and s urface techniques. In this paper, particular attention will be paid to the mechanisms of stabilization of such metastable phases due to thei r epitaxy on Si substrates, and to their transition, both electronic a nd structural, towards the beta-FeSi2 phase. Recent findings concernin g the growth at low temperature of the metallic alpha-FeSi2 phase will also be discussed since they might shed light on the hierarchy of the se phase transitions and offer a useful way to achieve, by a subsequen t post-annealing, high quality semiconducting beta-FeSi2 grains.