Wafer-scale synthesis of wide bandgap 2D GeSe2 layers for self-powered ultrasensitive UV photodetection and imaging

Emerging wide-bandgap 2D GeSe2 has been considered as a promising candidate for next-generation ultraviolet (UV) imaging systems, which typically require miniaturization, high stability, and self-powered sensing capa-bility. Nevertheless, the lack of reliable wafer-scale synthesis strategies remains a major obstacle to unleashing its full device potential. Herein, we report the synthesis of inch-level 2D GeSe2 layers with precise layer control and customized patterns via a facile post-annealing approach, which reveals a layer-independent direct bandgap of-3.0 eV. Moreover, high-quality GeSe2/GaN mixed-dimensional van der Waals heterojunctions fabricated via in -situ growth mode display an ultrasensitive self-powered UV photoresponse with a UV-to-visible rejection ratio of 1.8 x 105, a large responsivity of 261.7 mA/W, a high specific detectivity of 1.24 x 1014 Jones, as well as an ultrafast response speed to track nanosecond pulsed UV signals. In particular, the photodetector could sense ultraweak UV signals with a minimum detection limit of 180 pW/cm2 at 360 nm. Besides, the large-area growth of GeSe2 enables the implementation of integrated photodiode arrays for the self-powered image sensor, demonstrating the great promise of 2D GeSe2 for high-sensitivity UV detection and imaging.