Band structure and polarization effects in photothermoelectric spectroscopy of a Bi2Se3 device

• Published in: Applied physics letters 2022-03, Vol.120 (12)
• Main Authors: Pournia, Seyyedesadaf, Jnawali, Giriraj, Need, Ryan F., Jackson, Howard E., Wilson, Stephen D., Smith, Leigh M.
• Format: Article
• Language: English
• Subjects: Applied physics; Conduction bands; Linear polarization; Optical transition; Spectral signatures; Thermoelectric materials; Topological insulators
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0075924

Bi2Se3 is a prototypical topological insulator, which has a small bandgap (∼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.