Electronic structure of a narrow-gap semiconductor FeGa3investigated by photoemission and inverse photoemission spectroscopies

Abstract

We have performed a photoemission and inverse photoemission spectroscopic study of a narrow-gap semiconductor FeGa${}_{3}$, in order to characterize the occupied and unoccupied electronic states. The energy-gap size was found to be $~0.4$ eV, and the valence-band maximum (VBM) was located around the A point of the Brillouin zone. We observed a dispersive Ga $4\mathit{sp}$ derived band near the Fermi level (${E}_{\mathrm{F}}$), and Fe $3d$ narrow bands located at $\ensuremath{-}0.5$ and $\ensuremath{-}1.1$ eV away from ${E}_{\mathrm{F}}$. In contrast to the case of FeSi, there was no temperature-dependent peak enhancement at the VBM on cooling. The observed density of states and band dispersions were reasonably reproduced by the LDA$+$$U$ calculation with the on-site effective Coulomb interaction ${U}_{\mathrm{eff}}~3$ eV to the Fe $3d$ states. Present results indicate that, in spite of sizable ${U}_{\mathrm{eff}}/W~0.6$ ($W$: band width), electron correlation effects are not significant in FeGa${}_{3}$ compared with FeSi since the VBM consists of the dispersive band with the reduced Fe $3d$ contribution, and the energy gap is large.