Spin-Enhanced\nSelf-Powered Light Helicity Detecting\nBased on Vertical WSe<sub>2</sub>–CrI<sub>3</sub> <i>p–n</i> Heterojunction

Two-dimensional (2D) magnetic semiconductors\noffer an intriguing\nplatform for investigating magneto-optoelectronic properties and hold\nimmense potential in developing prospective devices when they are\ncombined with valley electronic materials like 2D transition-metal\ndichalcogenides. Herein, we report various magneto-optoelectronic\nresponse features of the vertical hBN–FLG–CrI<sub>3</sub>–WSe<sub>2</sub>–FLG–hBN van der Waals heterostructure.\nThrough a sensible layout and exquisite manipulation, an hBN–FLG–CrI<sub>3</sub>–FLG–hBN heterostructure was also fabricated\non identical CrI<sub>3</sub> and FLGs for better comparison. Our results\nshow that the WSe<sub>2</sub>–CrI<sub>3</sub> heterostructure,\nacting as a <i>p</i>–<i>n</i> heterojunction,\nhas advantageous capability in light detection, especially in self-powered\nlight helicity detecting. In the WSe<sub>2</sub>–CrI<sub>3</sub> heterojunction, the absolute value of photocurrent <i>I</i><sub>PH</sub> exhibits obvious asymmetry with respect to the bias <i>V</i>, with the <i>I</i><sub>PH</sub> of reversely\nbiased WSe<sub>2</sub>–CrI<sub>3</sub> <i>p–n</i> heterojunction being larger. When the CrI<sub>3</sub> is fully spin-polarized\nunder a 3 T magnetic field, the reversely biased WSe<sub>2</sub>–CrI<sub>3</sub> heterojunction exhibits advantageous capability in light\nhelicity detecting. Both the short-circuit currents <i>I</i><sub>SC</sub> and <i>I</i><sub>PH</sub> show one-cycle\nfluctuation behaviors when the quarter-wave plate rotates 180°,\nand the corresponding photoresponsivity helicities can be as high\nas 18.0% and 20.1%, respectively. We attribute the spin-enhanced photovoltaic\neffect in the WSe<sub>2</sub>–CrI<sub>3</sub> heterojunction\nand its contribution to circularly polarized light detection to the\ncoordination function of the spin-filter CrI<sub>3</sub>, the valley\nelectronic monolayer WSe<sub>2</sub>, and the spin-dependent charge\ntransfer between them. Our work helps us understand the interplay\nbetween the magnetic and optoelectronic properties of WSe<sub>2</sub>–CrI<sub>3</sub> heterojunctions and promotes the developing\nprogress of prospective 2D spin optoelectronic devices.