Conduction type and defect levels of β-FeSi2 films grown by MBE with different Si/Fe ratios

[100]-oriented β-FeSi2 films were grown on Si(001) substrates by molecular beam epitaxy (MBE) with a deposited Si to Fe atomic ratio (Si/Fe ratio) varied from 1.6 to 2.8. It was found that the conduction type of the β-FeSi2 films changed from p- to n-type between the deposited Si/Fe=2.4 and 2.8. Rutherford Back Scattering (RBS) measurements revealed that the real Si/Fe ratio of β-FeSi2 is 2.0–2.1 for all the samples after 900°C annealing for 14h, showing that stoichiometry of the grown films is almost satisfied even though the deposited Si/Fe ratio was away from stoichiometry.