Investigation of photoconductive effect on Bi2Te3 epitaxial film

Abstract

In this work, we present the results of photoconductivity measurements performed in the temperature range of 12 K-300 K on a 150 nm-thick Bi 2 Te 3 film grown by molecular beam epitaxy on a (111) BaF 2 substrate. A transition from negative to positive photoconductivity is found to occur around 125 K. Resistivity and Hall data measured under light and dark conditions qualitatively elucidate the observed phenomena. The Arrhenius plot of recombination times obtained from photoconductivity decay curves measured at different temperatures gives the activation energy associated with the bulk trap level. Using this activation energy as the effective trap potential, we calculated the generation and recombination rates as a function of temperature. The analysis provides a quantitative explanation that predicts the transition effect observed in the experiment. No evidence of contribution from surface states is found from the magnetoresistance curves measured at low temperatures.

Boosting the surface conduction in a topological insulator

“…How can we understand the salient features observed in all these experiments in a consistent way? From the similarities between the light-induced and electrical current-driven reduction of the resistivity, a common mechanism is expected and therefore both purely optical 4,6 and purely electric-field-induced effects 10,33,34 are excluded. In addition, we observe essentially the same behaviour in samples with different off-stoichiometry/doping level, in microfabricated samples (see below), and in a bulk metallic sample (when the Fermi level is in the bulk conduction band), see Extended Data 6.…”

“…The mechanism proposed here-space-charge separation between the surface and bulk carriers-is relevant for any topological insulator. It is surprising that these effects have remained largely unnoticed and not understood [4][5][6][7][8][9][10][11] . Possibly, the anomaly in transport observed in Cd-doped Bi 2 Se 3 42 and Sn-doped Bi 1.1 Sb 0.9 Te 2 S 43 are…”

Photosensitive Elements Based on Two-Dimensional Bismuth Telluride: Obtaining and Current–Voltage Characteristics

“…In the last few years, several original studies that demonstrated the possibility of obtaining bismuth telluride-based photosensors that are sensitive in a wide wavelength range from the UV to terahertz range were published. In most of the presented studies, Bi 2 Te 3 was used as a photosensitive layer in the form of epitaxial layers [16] or separate individual nanoparticles: nanowires [17,18] or plates [19,20].…”

Switching on surface conduction in a topological insulator

“…We understand this effect in terms of the well-known concept of surface charge accumulation 6,7 via a Schottky barrier formation 8,9 , and propose that the same mechanism underlies also the slow relaxations seen with spectroscopic probes in our and other 10-16 materials, which might thus also be persistent. We expect our technique to be readily transferable to other materials and probes, thereby shedding light on unexplained slow relaxations in transport [17][18][19] and beyond.…”

“…How can we understand the salient features observed in all these experiments in a consistent way? From the similarities between the light-induced and electrical current-driven reduction of the resistivity, a common mechanism is expected and therefore both purely optical 19,24 and purely electric-field-induced effects 17,33,34 are excluded.…”