Lattice vibrations and electrical transport in (Bi1-xInx)2Se3 films

We present Raman, terahertz transmission, and transport measurements on (Bi_1-xIn_x)₂Se₃ films to study the evolution of phonon modes and resistivity with an increasing indium content across the metal-insulator phase transition. The frequencies of two Raman-active modes _E^{g 2} and _A^{1 g 2} as well as an infrared-active mode E_u increase with an increasing indium content due to the smaller atomic weight of indium compared to bismuth. Terahertz data are fitted by a Drude-Lorentz model. Drude scattering rates increase from 47 to 75 cm^-1 with an increasing indium content from 0% to 16% due to stronger impurity scattering. The carrier concentration drops significantly for x = 24%. The temperature dependence of the resistivity switches from metallic at x = 16% to insulating at x = 24%, indicating a metal-insulator transition in between.