Crystal structure and elementary electronic properties of Bi-stabilized α-In2Se3

The introduction of Bi as a substitution for In at ~12% in In2Se3 stabilizes the α-polymorph and facilitates the crystal growth by the modified Bridgeman method. The crystal structure (R−3m, Z = 3, a = 3.9978(8) Å, c = 28.276(6) Å) and composition, (In0.88Bi0.12)2Se3, of the crystals were determined by single crystal X-ray diffraction. The structure, of the tetradymite type, displays positional disorder within the middle Se layer. Optical measurements indicate that (In0.88Bi0.12)2Se3 has an indirect band gap of about 1.19 eV, shown by electronic structure calculations to be from valence band states near the Γ point to conduction band states at the L point. Resistivity and Hall effect measurements on Sn-doped crystals of composition (In0.88Bi0.115Sn0.005)2Se3 show it to have a relatively high semiconducting resistivity, about 6 × 104 Ω cm at 300 K, with an n-type carrier concentration varying from 1012/cm3 at 300 K to 1015/cm3 at 400 K.