Two-dimensional (2D) van-der-Waals (vdW) layered ferroelectric semiconductors are highly desired for in-memory computing and ferroelectric photovoltaics or detectors. Beneficial from the weak interlayer vdW-force, controlling the structure by interlayer twist/translation or doping is an effective strategy to manipulate the fundamental properties of 2D-vdW semiconductors, which has contributed to the newly-emerging sliding ferroelectricity. Here, we report unconventional room-temperature ferroelectricity, both out-of-plane and in-plane, in vdW-layered γ-InSe semiconductor triggered by yttrium-doping (InSe:Y). We determine an effective piezoelectric constant of ∼7.5 pm/V for InSe:Y flakes with thickness of ∼50 nm, about one order of magnitude larger than earlier reports. We directly visualize the enhanced sliding switchable polarization originating from the fantastic microstructure modifications including the stacking-faults elimination and a subtle rhombohedral distortion due to the intralayer compression and continuous interlayer pre-sliding. Our investigations provide new freedom degrees of structure manipulation for intrinsic properties in 2D-vdW-layered semiconductors to expand ferroelectric candidates for next-generation nanoelectronics.

Fourier transform infrared (FTIR) spectrometer is a powerful tool for studying the photoluminescence (PL) properties of semiconductors, due to its well-known multiplexing and throughput advantages. However, it suffers from internal He–Ne laser disturbance in near-infrared and∕or environmental background thermal emission in mid- and far-infrared spectral regions. In this work, a modulated PL technique is developed based on step-scan (SS)-FTIR spectrometer. Theoretical analysis is conducted, and applications of the technique are given as examples in the PL study of mid-infrared HgCdTe thin films and near-infrared $\mathrm{Ga}\mathrm{In}\mathrm{P}∕\mathrm{Al}\mathrm{Ga}\mathrm{In}\mathrm{P}$ multiple quantum wells, respectively. The results indicate that the He–Ne laser and∕or thermal emission disturbance can be reduced at least $1∕1000$ and∕or even $1∕10000$ , respectively, by the modulated SS-FTIR PL technique, and hence a rather smooth PL spectrum can be obtained even under room temperature for HgCdTe thin films. A brief comparison is given of this technique with previously reported phase-sensitive modulation methods based on conventional rapid-scan (RS)-FTIR spectrometer, and the advantages of this technique over the former RS- FTIR-based ones are emphasized.

Intriguing “slidetronics” has been reported in van der Waals (vdW) layered non-centrosymmetric materials and newly-emerging artificially-tuned twisted moiré superlattices, but correlative experiments that spatially track the interlayer sliding dynamics at atomic-level remain elusive. Here, we address the decisive challenge to in-situ trace the atomic-level interlayer sliding and the induced polarization reversal in vdW-layered yttrium-doped γ-InSe, step by step and atom by atom. We directly observe the real-time interlayer sliding by a 1/3-unit cell along the armchair direction, corresponding to vertical polarization reversal. The sliding driven only by low energetic electron-beam illumination suggests rather low switching barriers. Additionally, we propose a new sliding mechanism that supports the observed reversal pathway, i.e., two bilayer units slide towards each other simultaneously. Our insights into the polarization reversal via the atomic-scale interlayer sliding provide a momentous initial progress for the ongoing and future research on sliding ferroelectrics towards non-volatile storages or ferroelectric field-effect transistors.

Among today’s nonvolatile memories, ferroelectric-based capacitors, tunnel junctions and field-effect transistors (FET) are already industrially integrated and/or intensively investigated to improve their performances. Concurrently, because of the tremendous development of artificial intelligence and big-data issues, there is an urgent need to realize high-density crossbar arrays, a prerequisite for the future of memories and emerging computing algorithms. Here, a two-terminal ferroelectric fin diode (FFD) in which a ferroelectric capacitor and a fin-like semiconductor channel are combined to share both top and bottom electrodes is designed. Such a device not only shows both digital and analog memory functionalities but is also robust and universal as it works using two very different ferroelectric materials. When compared to all current nonvolatile memories, it cumulatively demonstrates an endurance up to 10¹⁰ cycles, an ON/OFF ratio of ~10², a feature size of 30 nm, an operating energy of ~20 fJ and an operation speed of 100 ns. Beyond these superior performances, the simple two-terminal structure and their self-rectifying ratio of ~ 10⁴ permit to consider them as new electronic building blocks for designing passive crossbar arrays which are crucial for the future in-memory computing.

Although a lot of promising two-dimensional (2D) semiconductors with various bandgaps, represented by black phosphorus (0.3 eV), transition metal dichalcogenides (< 2 eV), and boron nitride (5 − 6 eV), have been extensively researched in photoelectronic and electronic devices, the spectrum of large bandgap materials is still very narrow, which limits the potential device applications in ultraviolet photodetection. The broad family of layered thio- and seleno-phosphates with wide and tunable bandgaps (1.3 − 3.5 eV) can complement the intermediate bandgaps from 1.6 to 4 eV, which can fill the gap between transition metal dichalcogenides and boron nitride. In this work, a high-performance ultraviolet photodetector based on multilayered CuInP₂S₆ was fabricated. It exhibits fast response times shorter than 0.5 ms, i.e., rise time ∼ 0.36 ms and fall time ∼ 0.44 ms for ultraviolet illumination (280 nm, 50 nW), which is superior than previously reported 2D layered-based UV detectors. Significantly, this photodetector also shows ultralow dark current (∼ 100 fA), a high on/off ratio (∼10³), and a specific detectivity of 7.38 × 10¹⁰ Jones. Our results provide an excellent candidate for low power consumption and high-speed photodetection.