Donor and acceptor levels in undoped β-FeSi2 films grown on Si (001) substrates

Donor and acceptor levels of undoped n- and p-type beta -FeSi2 films were investigated in terms of temperature dependence of carrier density. beta -FeSi2 films were formed from Si/Fe multilayers on Si (001) substrates, Two kinds of donor (E-D = 0.075 eV and 0.21 eV) and acceptor levels (E-A = 0.10 eV and 0.19 eV) were observed, The density of these levels was found to be about 10(20) cm(-3), suggesting that they originate from defects rather than impurities included in the 4N-Fe source. The energy gap of the beta -FeSi2 film was determined to be about 0.80 eV. This value corresponded to the reported value of electroluminescence peak wavelength (1.6 mum) of the p-Si/beta -FeSi2 balls/n-Si(001) diode we reported recently, and is slightly smaller than the reported energy gap estimated from the absorption edge.