Comparative concentration analysis of Cr and Co in FeSi 2 films performed by ERDA and RBS

Abstract

Thin films of β-FeSi 2 doped by Co or Cr were grown on Si substrates by molecular beam epitaxy (MBE) using three separately controlled evaporation sources. The dopant concentration was measured concurrently by heavy-ion ERDA with 129Xe ions of 140–250 MeV, by heavy-ion RBS with 15 MeV 14N and by standard RBS with 1.4 MeV 4He ions. Among these techniques, the TOF–ERDA was most powerful in providing a high mass resolution and a low detection limit for Co and Cr (≈0.1 at.%) . Because of the complete overlap of the dopant signals with the Fe signal the standard RBS spectra were evaluated by relying on the differences between the scattering cross-sections from the dopant atoms and Fe. This approach proved to be applicable as far as the dopants had a constant depth profile with sufficiently high concentration. For Cr concentrations exceeding the miscibility limit the RBS results deviate significantly from those of ERDA due to increasing dopant depth inhomogeneities.