Electronic structure of a narrow-gap semiconductor KAg₃Te₂

KAg₃Te₂ with a layered crystal structure has been predicted to be a possible topological insulator. Through electrical transport measurements, we revealed its semiconducting behavior with a narrow band gap of ∼0.4 eV and p-type character. The infrared transmission spectra of single crystals yielded an optical band gap of ∼0.3 eV. Angle-resolved photoemission spectroscopy reveals a bulk energy gap at the Brillouin zone center, with no observable surface state, suggesting that KAg₃Te₂ is a topological trivial narrow-gap semiconductor. The experimentally determined effective mass of the holes in KAg₃Te₂ is very small (∼0.12 m_e). The valence band maximum is quasi-two-dimensional, while the conduction band minimum is fully three-dimensional. Such intriguing dimensional anisotropy can be attributed to the distinct orbital contributions from K, Ag, and Te atoms to the respective bands.