Lasers, Optics & Photonics

Biography

Biography: Weida Hu

Abstract

Bonded tightly in the plane and stacked with weak van der Waals force, two-dimensional (2D) materials have attracted increasing attention over the past decade owing to their unique structures and physical properties. To date, 2D materials comprise graphene, black phosphorus (BP), transition metal dichalcogenides (TMDs), boron nitride (BN) and so forth. Among them, graphene was fi rst discovered and studied as early as 2004. Because of the reduced feature dimensions, quantum confi nement eff ects in 2D systems are particularly signifi cant. With weaker dielectric screening in a several-nanometer or even atomic thickness, stronger Coulomb interactions occur. 2D systems provide an open platform for exploring novel physical phenomena and mechanisms. For instance, the breaking of inversion symmetry and strong valley-spin coupling in TMDs cause them to exhibit valley-dependent circular dichroism and scaling the material from multilayer to monolayer can realize an indirect-to-direct bandgap transition. Th erefore much eff ort has been devoted to seeking various applications based on 2D materials and the study of photodetectors based on 2D materials is a hot research fi eld. In this report, we introduce localized field enhanced 2D material photodetectors (2DPDs) from ultraviolet, visible to infrared in the sight of the infl uence of device structure on photodetector performance instead of directly illustrating the detection mechanisms. Six kinds of the localized field are summarized. Th ey are a ferroelectric fi eld, photogating electric fi eld, floating gate induced electrostatic fi eld, interlayer built-in fi eld, localized optical fi eld and photo-induced temperature gradient fi eld, respectively. By suppressing the background noise, enhancing the optical absorption, improving the electron-hole separation effi ciency, amplifying the photogain or extending the detection range, these localized fi elds are demonstrated to eff ectively promote the detection ability of 2DPDs. Particularly, among them, the photogating has been demonstrated to play a very important role especially in photodetectors based on hybrid structures. We consider photogating as a way of conductance modulation through photo-induced gate voltage instead of simply and totally attributing it to trap states. A high gain-bandwidth product as high as 109Hz has been achieved for photodetectors enhanced by the trap- and hybrid-induced photogating, though a trade-off has to be made between gain and bandwidth. We also put forward the general photogating according to another three reported studies very recently. General photogating may enable simultaneous high gain and high bandwidth, paving the way to explore novel high-performance photodetectors.