Band Structure and Polarization Effects in Photothermoelectric Spectroscopy of a Bi2Se3 Device

Abstract

Bi2Se3 is a prototypical topological insulator which has a small band gap (~0.3 eV) and topologically protected conducting surface states. This material exhibits quite strong thermoelectric effects. Here we show in a mechanically exfoliated thick (~100 nm) nanoflake device that we can measure the energy dependent optical absorption through the photothermoelectric effect. Spectral signatures are seen for a number of optical transitions between the valence and conduction bands, including a broad peak at 1.5 eV which is likely dominated by bulk band-to-band optical transitions but is at the same energy as the well known optical transition between the two topologically protected conducting surface states. We also observe a surprising linear polarization dependence in the response of the device that reflects the influence of the metal contacts.

17 pages, 4 figures

References in corpus (5)

• Photocurrent generation with two-dimensional van der Waals semiconductors
• Strong surface scattering in ultrahigh mobility Bi2Se3 topological insulator crystals
• Topology and geometry under the nonlinear electromagnetic spotlight
• Ultrafast helicity control of surface currents in topological insulators with near-unity fidelity
• Helicity dependent photovoltaic effect in Bi2Se3 under normal incident light