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

Abstract

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.

2D Materials for Photothermoelectric Detectors: Mechanisms, Materials, and Devices

“…The appealing factor of Bi 2 Se 3 is the small thermal conductivity with a value of ≈0.55 W m −1 K −1 as presented in Figure 14f, which means that a larger temperature gradient can be formed more easily in the two terminals of this material. [119] The mobility of Bi 2 Se 3 is studied to have a value of 550 cm 2 V −1 s −1 at 300 K, [123] and considering the parameters mentioned above, a large ZT value of 0.6 was reported. [124] Recently, the topological surface states were applied to optimize the PTE effect in a Bi 2 Se 3 nanoribbons device, as presented in Figure 15a.…”

“…However, comparing with the large Seebeck coefficient of Bi 2 Te 3 , the Seebeck coefficient of Bi 2 Se 3 is rather smaller, with a limited value of 51–82 µV K −1 as reported. [ 123 ] Figure 14d illustrated a comparison between the Seebeck coefficient of Bi 2 Te 3 and Bi 2 Se 3 , indicating that Bi 2 Se 3 exhibits a smaller value, which constrained its applications in thermoelectric photodetectors. The appealing factor of Bi 2 Se 3 is the small thermal conductivity with a value of ≈0.55 W m −1 K −1 as presented in Figure 14f, which means that a larger temperature gradient can be formed more easily in the two terminals of this material.…”