Photoemission (XPS and UPS) study of amorphous Bi₂Se₃ film

Photoemission (XPS and UPS) measurements were performed for elemental Se and Bi and, crystalline and amorphous Bi₂Se₃ films to terminate the long-standing controversy about the charge transfer in Bi-doped chalcogenide glasses. It was elucidated that the Bi atoms in amorphous Bi₂Se₃ are positively charged owing to an electronic charge transfer from the Bi atoms to the Se atoms. A comparison of the chemical shift of the core levels and the valence band between amorphous and crystalline Bi₂Se₃ indicates that the bonding is more covalent in amorphous phase than in crystalline phase, suggesting that although the Bi atoms in crystalline Bi₂Se₃ are six-fold coordinated by Se atoms, the Bi atoms in the amorphous phase are three-fold coordinated like the As and Sb atoms in amorphous chalcogenides.