Electronic structure of beta-FeSi2 modified by r.f.-plasma of semiconducting SiH4, GeH4 gas

Structural modification of iron-disilicides beta -FeSi2 has been investigat ed to improve the thermoelectric properties of the materials by r.f.-plasma processing in SiH4, GeH4 or their mixed gases. The plasma treatment of bet a -FeSi2 micrograins in SiH4 or GeH4 gas prior to sintering results in an a nomalous increase in the hole mobility in the temperature region lower than 400 K. X-Ray photoemission spectroscopy (XPS) measurements revealed that t he valence states at the interface between a coated Si or Ge layer and a be ta -FeSi2 core material are changed by the interdiffusion of Si into beta - FeSi2 for SiH4 plasma and by the out-of-diffusion of Ge from the base mater ial for GeH4 plasma. From electron paramagnetic resonance (EPR) measurement s, it is also found that the carrier mobility at temperatures lower than 40 0 K is limited by structural defects at the grain-boundary interface, and t hat the defects are greatly reduced by the r.f.-plasma treatment. (C) 2001 Elsevier Science B.V. All rights reserved.