FORMATION OF TERNARY (FE1-XCOX)SI-2 STRUCTURES BY ION-BEAM-ASSISTED DEPOSITION AND ION-IMPLANTATION

beta-FeSi2 layers produced by Ion Beam Assisted Deposition (IBAD) of i ron on (100) silicon substrates were implanted with cobalt ions. The p hase formation in the ternary system Fe-Co-Si is studied in the as-imp lanted state as well as after different annealing treatments. Optimum conditions are investigated for the formation of the ternary silicide beta-(Fe1-xCox)Si-2 in order to tune the band gap by changing the Co c oncentration, using RBS, AES combined with sputter depth profiling, XR D, IR absorption and reflection, and resistivity measurements. Increas ing the cobalt dose results in an increasing amount of CoSi and FeSi i n the as-implanted state for implantation temperatures less than or eq ual to 250 degrees C. The partial amorphization observed for RT implan tation enhances the probability of incorporation of cobalt into the te rnary silicide. Implantation at 400 degrees C causes an almost complet e formation of beta-(CoxFe1-x)Si-2. The monosilicide in the low temper ature samples is dissolved by post-implantation annealing at 800 degre es C. For implantation at 250 degrees C, annealing at 800 degrees C re sults in a sizeable fraction of CoSi2. A homogeneous depth distributio n of cobalt is only obtained after annealing at 900 degrees C. Because of the decrease of the beta --> alpha transition temperature with inc reasing cobalt content, at 900 degrees C the alpha phase is formed for the highest cobalt concentration. After a final retransformation anne aling (800 degrees C/48 h + 750 degrees C/48 h) a shift of the band ga p energy from 0.89 eV to 0.73eV is measured for beta-(Fe0.85Co0.15)Si- 2.