Enhanced Photocurrent of the Ag Interfaced Topological Insulator Bi₂Se₃ under UV- and Visible-Light Radiations

Bi₂Se₃ is a topological quantum material that is used in photodetectors, owing to its narrow bandgap, conductive surface, and insulating bulk. In this work, Ag@Bi₂Se₃ nanoplatelets were synthesized on Al₂O₃(100) substrates in a two-step process of thermal evaporation and magnetron sputtering. X-ray diffractometer (XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS) revealed that all samples had the typical rhombohedral Bi₂Se₃. Field-emission scanning electron microscopy (FESEM)-energy dispersive x-ray spectroscopy (EDS), XPS, and HRTEM confirmed the presence of the precipitated Ag. The optical absorptance of Bi₂Se₃ nanoplatelets in UV-visible range decreased with the Ag contents. Results of photocurrent measurements under zero-bias conditions revealed that the deposited Ag affected photosensitivity. A total of 7.1 at.% Ag was associated with approximately 4.25 and 4.57 times higher photocurrents under UV and visible light, respectively, than 0 at.% Ag. The photocurrent in Bi₂Se₃ at 7.1 at.% Ag under visible light was 1.72-folds of that under UV light. This enhanced photocurrent is attributable to the narrow bandgap (~0.35 eV) of Bi₂Se₃ nanoplatelets, the Schottky field at the interface between Ag and Bi₂Se₃, the surface plasmon resonance that is caused by Ag, and the highly conductive surface that is formed from Ag and Bi₂Se₃. This work suggests that the appropriate Ag deposition enhances the photocurrent in, and increases the photosensitivity of, Bi₂Se₃ nanoplatelets under UV and visible light.