Ultrabroadband Absorption and High-Performance Photodetection in Europium-Doped 2D Topological Insulator Bi₂Se₃ Nanosheets

Abstract

In the pursuit of materials with exceptional optoelectronic functionalities in the visible to mid-IR region, the topological insulators are very promising because they have unique Dirac-like surface states and high light-absorption properties. Herein, we report on a low-temperature, facile, solution-processable method for the synthesis of undoped and Eu-doped 2D layered Bi 2 Se 3 nanosheets (NSs) with exceptional optical functionalities. 2D geometry provides highly effective light absorption and efficient charge transportation via topologically protected surface states of Bi 2 Se 3 NSs. Our study reveals that as-grown Bi 2 Se 3 NSs possess major native defects, particularly the Se vacancies that are responsible for ultrabroadband absorption and bulk conduction. Interestingly, Eu doping in Bi 2 Se 3 partially compensates the intrinsic defects, and the Eu-doped Bi 2 Se 3 NSs show reduced band gap and very high absorption coefficient (2.87 × 10 5 cm −1 ) over the broad range of 400−2500 nm. We achieve a lower dark current and a higher photocurrent with increasing doping concentration. Interestingly, the undoped Bi 2 Se 3 NSs exhibited negative photoconductivity, which is completely suppressed in the Eu-doped Bi 2 Se 3 NSs due to the reduction in trapping sites. The role of defects in the ultrabroadband absorption and high photoconductivity was elucidated through the rapid thermal annealing studies. To demonstrate its application, we fabricate a planar photodetector using the Eu-doped 2D Bi 2 Se 3 NSs and investigate device characteristics at specific wavelengths 405, 657, and 808 nm. The device with undoped Bi 2 Se 3 NSs shows the highest photoresponsivity at 405 nm, while the Eu-doped NSs show superior performance at 657 and 808 nm. Additionally, the doped photodetectors possess broadband and high responsivity/ detectivity with a peak responsivity of 130 A/W and a peak detectivity of 1.482 × 10 13 Jones, which are the highest among the reported values. The present report demonstrates an effective strategy to develop ultrabroadband and high-performance optoelectronic applications of doped 2D topological insulators.

Two-dimensional bismuth oxyselenide quantum dots as nanosensors for selective metal ion detection over a wide dynamic range: sensing mechanism and selectivity

“…As compared to the NS, the absorption edge for the QDs is blue-shifted due to the confinement effect. The bandgap of the as-synthesized samples were calculated using the following equation: 52 αhν 2 = A ( hν − E g )where α is the optical absorption coefficient, hν is the incident photon energy, and A is a constant. The Tauc plot of the samples is shown in Fig.…”

Interfacial Charge Transfer Induced Enhanced Near-Infrared Photoluminescence and Enhanced Visible Photodetection in Two-Dimensional/Zero-Dimensional Bi2Se3/CsPbBr2I Heterojunctions with Type-I Band Alignment

“…Both the devices show a fast photoresponse because of the superior carrier mobility of the 2D Bi 2 Se 3 NS. An increase in the growth time with the heterojunction formation might be due to the low carrier mobility caused by the high carrier concentration, as the electrons are transferred from the perovskite NCs to the Bi 2 Se 3 layers . Carrier trapping into deep subgap states is dominant in lead-based perovskite systems.…”

“…The narrow energy bandgap and the layered structure of Bi 2 Se 3 make it suitable for high-performance photodetectors and thermoelectric applications. Our recent work on Eu-doped 2D Bi 2 Se 3 showed high-performance photodetection over the visible to infrared region . However, there has been no study involving the 0D perovskite NCs and topological insulator.…”

Defect-induced photogating effect and its modulation in ultrathin free-standing Bi2O2Se nanosheets with a visible-to-near-infrared photoresponse

“…So far, many semiconductor nanostructures have exhibited negative PC, e.g. , as in p-type single-walled carbon nanotubes, 32 Bi-doped p-type ZnSe nanowires, 33 n-type InAs nanowires, 34 n-type InN thin films, 35 Bi 2 Se 3 nanosheets, 36 etc. Many theoretical predictions and experimental studies have been reported and debated to determine the origin of negative PC in such semiconductors.…”