Polarity Flipping in SnSe Empowering Wavelength Selective\nSelf-Powered Broadband Photodetection

The\ndemand for high-performance self-powered photodetectors with\nbroadband wavelength selectivity has intensified due to their applications\nin various fields such as imaging, sensing, communication, and environmental\nmonitoring. Among emerging materials, tin selenide (SnSe) has garnered\nsignificant attention for its promising optoelectronic properties.\nIn this study, we have investigated the phenomenon of polarity flipping\nin sputtering-grown pure SnSe film and its impact on broadband wavelength\nselective photodetection. The designed metal semiconductor metal device\nwith an active area of 9 μm<sup>2</sup> exhibits a maximum responsivity\nof 10.82 mAW<sup>–1</sup>, a high external quantum efficiency\nof 378.76%, and the lowest noise equivalent power of 5.3 × 10<sup>–13</sup> WHz<sup>–1/2</sup> for 1064 nm light illumination\nof optical power 16.2 nW in self-bias mode. The proposed pure SnSe-based\ndevice exhibits wavelength-dependent polarity switching in self-bias\nmode for the spectral range UV–NIR, enabling the device to\nfunction in bidirectional mode. The polarity flipping response in\nthe photodetector makes it possible to differentiate between different\nphotons, such as ultraviolet/visible and near-infrared. This capability\ncan improve the accuracy and efficiency of environmental monitoring\nsystems, enabling better detection and analysis of various environmental\nfactors, such as light pollution, radiation levels, and atmospheric\ncomposition. We elucidated the possible phenomenon underlying polarity\nflipping through a comprehensive characterization of the material’s\nstructural, optical, and electrical properties. Our findings reveal\nthat the controlled phase during sputter deposition can significantly\nalter the crystalline structure, resulting in tunable optical properties\nand enhanced photoresponse across a broad wavelength range. Additionally,\nthe polarity flipping phenomenon enables the photodetector to exhibit\nunprecedented broadband wavelength selectivity, thus opening avenues\nfor developing advanced optoelectronic devices. This research advances\nour fundamental understanding of phase-controlled SnSe thin film and\npaves the way for designing and fabricating highly efficient self-powered\nphotodetectors with tailored spectral response characteristics.