Hard x-ray photoelectron spectroscopy study on valence band structure of semiconducting BaSi₂

The valence band structures of a 35-nm-thick BaSi₂ epitaxial film on Si(111) have been explored at room temperature by hard x-ray photoelectron spectroscopy (HAXPES). The experimentally obtained photoelectron spectrum is well reproduced by first-principles calculations based on the pseudopotential method. The top of the valence band consists mainly of Si 3s and 3p states in BaSi₂, suggesting that the effective mass of holes is small in BaSi₂. This is favorable from the viewpoint of solar cell applications. The observed spectrum shifted slightly to the lower energy side due to n-type conductivity of BaSi₂. The valence band top was observed at about 0.8 eV below the Fermi level in the HAXPES spectrum.