Tunable\nAmbipolar Polarization-Sensitive Photodetectors\nBased on High-Anisotropy ReSe₂ Nanosheets

Abstract

Atomically\nthin 2D-layered transition-metal dichalcogenides have\nbeen studied extensively in recent years because of their intriguing\nphysical properties and promising applications in nanoelectronic devices.\nAmong them, ReSe₂ is an emerging material that exhibits\na stable distorted 1<i>T</i> phase and strong in-plane anisotropy\ndue to its reduced crystal symmetry. Here, the anisotropic nature\nof ReSe₂ is revealed by Raman spectroscopy under linearly\npolarized excitations in which different vibration modes exhibit pronounced\nperiodic variations in intensity. Utilizing high-quality ReSe₂ nanosheets, top-gate ReSe₂ field-effect transistors\nwere built that show an excellent on/off current ratio exceeding 10⁷ and a well-developed current saturation in the current–voltage\ncharacteristics at room temperature. Importantly, the successful synthesis\nof ReSe₂ directly onto hexagonal boron nitride substrates\nhas effectively improved the electron motility over 500 times and\nthe hole mobility over 100 times at low temperatures. Strikingly,\ncorroborating with our density-functional calculations, the ReSe₂-based photodetectors exhibit a polarization-sensitive photoresponsivity\ndue to the intrinsic linear dichroism originated from high in-plane\noptical anisotropy. With a back-gate voltage, the linear dichroism\nphotodetection can be unambiguously tuned both in the electron and\nhole regime. The appealing physical properties demonstrated in this\nstudy clearly identify ReSe₂ as a highly anisotropic 2D\nmaterial for exotic electronic and optoelectronic applications.