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

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 4sp derived band near the Fermi level (E_F), and Fe 3d narrow bands located at -0.5 and -1.1 eV away from E_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_ 3 eV to the Fe 3d states. Present results indicate that, in spite of sizable U_ /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.