BURIED (FE1-XCOX)SI-2 LAYERS WITH VARIABLE BAND-GAP FORMED BY ION BEAM SYNTHESIS

Buried layers of (Fe1-xCox)Si-2 were prepared by sequent implantation of iron and cobalt into (100) silicon. The depth distributions of iron and cobalt and the atomic concentration ratio silicon/metal were dete rmined by Auger Electron Spectroscopy (AES) and Rutherford Backscatter ing Spectrometry (RES). The phase composition and the microstructure o f the silicide layer were studied by X-ray diffraction and electron mi croscopy. The band gap energy was evaluated from Infrared (IR) reflect ion and transmission experiments. The semiconducting beta-FeSi2 struct ure remains stable up to a cobalt fraction of x = 0.2 if the iron sili cide is stabilized by an intermediate annealing between iron and cobal t implantation. With increasing cobalt content, the electrical resisti vity as well as the energy of the direct band gap of the beta-(Fe1-xCo x)Si-2 layer decrease. In this way, a band gap tuning between 0.84 and 0.70 eV is possible. The gap energy is found to vary quadratically wi th the Co content in the composition range 0 < x < 0.15.