Optical properties of (Bi_1-xIn_x)₂Se₃ thin films

Bi₂Se₃ is a topological insulator with unique optical properties, including linearlydispersing surface states. Many of the proposed device applications for Bi₂Se₃ require a lattice-matched trivially-insulating component. It is known that (Bi_1-xIn_x)₂Se₃ is a trivial band insulator for moderate indium concentrations. In this paper, we grow and characterize the optical properties of (Bi_1-xIn_x)₂Se₃ films with varying indium concentrations. We find that the lattice constant and optical bandgap for (Bi_1-xIn_x)₂Se₃ varies linearly with concentration. We perform infrared reflection measurements as a function of polarization and angle, enabling us to model the permittivity for these materials. Again, we find that most parameters vary linearly with concentration. Our results for the pure end members are consistent with the literature values. This is the first report of optical values for the intermediate compounds, which are likely to be integral components of future topological insulator optical devices.