Intrinsic Sliding Ferroelectricity and High‐Quality Superlinear Emission in Van der Waals γ‐InSe Semiconductor

Abstract High‐quality single crystals are the fundamental foundation for advancing 2D van der Waals (vdW) layered semiconductors toward applications in low‐consumptive nanodevices. The easily formed stacking faults (SFs) in vdW layered materials hide the intrinsic optical/electrical properties, adverse to practical application. Here, a unique low‐temperature annealing strategy is adopted to eliminate the SFs in flexible γ‐InSe and optimize the crystal quality. The annihilation dynamics of the SFs are revealed by using the in situ heating observation on the state‐of‐the‐art spherical aberration‐corrected transmission electron microscopy. The annealed γ‐InSe not only exhibits intrinsic out‐of‐plane sliding ferroelectricity in a wide thickness range from a single unit cell (trilayer) to tens of nanometers, but also demonstrates efficient superlinear photoluminescence with higher beam quality and lower thresholds. This should expedite the applications of intrinsic γ‐InSe in near infrared emitter and lasing, in‐memory computing, and ferroelectric photovoltaics or detectors.