Activating Phase-Transition Toughening in van der Waals Semiconductor GaTe.

Inorganic semiconductors are essential for modern electronics, but their inherent brittleness restricts their applications in flexible and wearable devices. This issue is particularly acute in low-symmetry structures, where the lack of slip systems further suppresses plastic deformation. Here, we reveal an intrinsic toughening mechanism in monoclinic GaTe using in situ SEM microfracture experiments. In contrast to the catastrophic brittle cleavage along the interlayer direction, cross-layer crack propagation undergoes continuous deflection, generating a highly tortuous crack path that enhances the mean fracture toughness by ∼60%. Combining high-resolution imaging with atomic simulations, we identify stress-triggered monoclinic-to-trigonal phase transitions at deflection points, which effectively impede and redirect crack propagation. The toughening mechanism is further validated in a flexible GaTe photodetector, which retains an excellent photoresponse and mechanical durability over tens of thousands of bending cycles. These findings lay a solid foundation for nanodevice applications in which both mechanical robustness and functional stability are required.