Development of Te/Bi₂Se₃ heterostructures for photodetectors sensitive to VIS and NIR wavelengths

In recent years, two-dimensional materials (2DMs) have attracted considerable interest for their remarkable properties, which allow for them to be employed in many fields. In particular, 2DMs are increasingly finding application in the field of optoelectronics, with the aim of reducing manufacturing costs and device dimensions to enhance their efficiency. Furthermore, the van der Waals lattice structure of 2DMs enables them to be easily integrated with silicon technology. Unfortunately, the thin nature of these materials might result in weak light absorption. To address this issue, heterostructures of 2DMs are fabricated: combining them allows the tuning of electronic bandgaps, obtaining low-cost devices in a given range of wavelengths. Topological insulators (TIs) are 2DMs characterized by an insulating bulk gap and Dirac helical electronic surface states. Among these, Bi₂Se₃ demonstrates considerable potential in high-speed detection, due to the high mobility of surface electronic states and its 0.3 eV bandgap, which enable it to operate at telecommunications wavelengths (λ=1550 nm). On the other hand, Te is a material with a thickness-dependent bandgap which extends from 0.3 eV (bulk) to 1.2 eV (monolayer). The absorbance of Te films in the infrared range is higher than Bi₂Se₃ of the same thickness. Considering these properties, we fabricated, through a low-cost vapor–solid deposition technique, a photodetector based on a Te/Bi₂Se₃ heterostructure, deposited onto a prepatterned n-Si substrate, in order to increase performance in both the VIS and IR spectral range. Single layers of Te and Bi₂Se₃ and Te/Bi₂Se₃ heterostructures were separately characterized by XRD and SEM to investigate their structural and morphological properties. The obtained Te/Bi₂Se₃ photodetectors are sensitive to both VIS (λ=633 nm) and IR (λ=1550 nm) light, exhibiting a responsivity of 2.6 A/W and a detectivity of 2.6 x 10¹¹ Jones at λ=633 nm, and showing a linear and ultrafast response (108 ns).