Topological Insulator Based Dual State Photo‐Switch Originating Through Bulk and Surface Conduction Channels.

Topological insulators are novel electronic materials, where time reversal symmetry protects the spin‐polarized surface states from backscattering. Although, the bulk offers a trivial semiconducting response to incident light, but the metallic surface states exhibit interesting electrical response towards the incident radiation, such as polarization dependent surface photocurrent and topological phase transitions. Here, we study the temperature dependent near‐infrared photoresponse in bismuth selenide (Bi2Se3) nano‐flakes. A very good photo‐sensitivity to near‐infrared 800 nm wavelength is observed for the temperature range 300–2 K. Voltage responsivity at 2 K (1.481 × 1010 VW−1) is estimated to be four‐order greater than at 300 K (2.095 × 106 VW−1) and is comparatively much higher than the previously reported values of voltage responsivity in other materials. Interestingly, we also find the temperature dependent existence of both positive and negative photoresponse in our device. An anomalous photoresponse reversal is observed at 2 K, where resistance of the nano‐flake increases under light illumination. We propose that this phenomenon is due to the topological surface states, which have dominant transport contribution at very low temperatures. These observations establish the fact that topological insulators can be further engineered to develop a dual state photo‐switch, by manipulating the bulk and surface state conduction contribution. [ABSTRACT FROM AUTHOR]