Edge-Epitaxial Growth of InSe Nanowires toward High-Performance Photodetectors

Carrier Recirculation Induced High-Gain Photodetector Based on van der Waals Heterojunction

Two-dimensional (2D) materials have attracted great attention in the field of photodetection due to their excellent electronic and optoelectronic properties. However, the weak optical absorption caused by atomically thin layers and the short lifetime of photocarriers limit their optoelectronic performance, especially for weak light detection. In this work, we design a high-gain photodetector induced by carrier recirculation based on a vertical InSe/GaSe heterojunction. In this architecture, the photogenerated holes are trapped in GaSe due to the built-in electric field, suppressing the recombination rate of photocarriers, so the electrons can recirculate for multiple times in the InSe channel following the generation of a single electron-hole pair, resulting a high photoconductive gain (10⁷). The responsivity and detectivity of the InSe/GaSe heterojunction can reach 1037 A/W and 8.6 × 10¹³ Jones, which are 1 order of magnitude higher than those of individual InSe. More importantly, the InSe/GaSe heterojunction can respond to weaker light (1 μW/cm²) compared to individual InSe (10 μW/cm²). Utilizing GaSe as the channel and InSe as the electrons trapped layer, the same experimental phenomenon is achieved. This work can provide an approach for designing a highly sensitive device utilizing a 2D van der Waals heterojunction, and it also possesses wide applicability for other materials.

Activating Silent Synapses in Sulfurized Indium Selenide for Neuromorphic Computing

The transformation from silent to functional synapses is accompanied by the evolutionary process of human brain development and is essential to hardware implementation of the evolutionary artificial neural network but remains a challenge for mimicking silent to functional synapse activation. Here, we developed a simple approach to successfully realize activation of silent to functional synapses by controlled sulfurization of chemical vapor deposition-grown indium selenide crystals. The underlying mechanism is attributed to the migration of sulfur anions introduced by sulfurization. One of our most important findings is that the functional synaptic behaviors can be modulated by the degree of sulfurization and temperature. In addition, the essential synaptic behaviors including potentiation/depression, paired-pulse facilitation, and spike-rate-dependent plasticity are successfully implemented in the partially sulfurized functional synaptic device. The developed simple approach of introducing sulfur anions in layered selenide opens an effective new avenue to realize activation of silent synapses for application in evolutionary artificial neural networks.

Sensitive, High-Speed, and Broadband Perovskite Photodetectors with Built-In TiO2 Metalenses

Monolithic integration of nanostructured metalenses with broadband light transmission and good charge transport can simultaneously enhance the sensitivity, speed, and efficiency of photodetectors. The realization of built-in broadband metalenses in perovskite photodetectors, however, has been largely challenged by the limited choice of materials and the difficulty in nanofabrication. Here a new type of broadband-transmitting built-in TiO₂ metalens (meta-TiO₂ ) is devised, which is readily fabricated by one-step and lithograph-free glancing angle deposition. The meta-TiO₂ , which comprises of sub-100 nm TiO₂ nanopillars randomly spaced with a wide range of sub-wavelength distances in 5-200 nm, shows high transmittance of light in the wavelength range of 400-800 nm. The meta-TiO₂ also serves as an efficient electron transporting layer to prevent the exciton recombination and facilitate the photoinduced electron extraction and transport. Replacing the conventional mesoporous TiO₂ with the meta-TiO₂ comprehensively leads to enhancing the detection speed by three orders of magnitude to a few hundred nanoseconds, improving the responsivity and detectivity by one order of magnitude to 0.5 A W^-1 and 10¹³ Jones, respectively, and extending the linear dynamic range by 50% to 120 dB.

Phase-Selective Synthesis of Ultrathin FeTe Nanoplates by Controllable Fe/Te Atom Ratio in the Growth Atmosphere

Phase controllable synthesis of 2D materials is of significance for tuning related electrical, optical, and magnetic properties. Herein, the phase-controllable synthesis of tetragonal and hexagonal FeTe nanoplates has been realized by a rational control of the Fe/Te ratio in a chemical vapor deposition system. Using density functional theory calculations, it has been revealed that with the change of the Fe/Te ratio, the formation energy of active clusters changes, causing the phase-controllable synthesis of FeTe nanoplates. The thickness of the obtained FeTe nanoplates can be tuned down to the 2D limit (2.8 nm for tetragonal and 1.4 nm for hexagonal FeTe). X-ray diffraction pattern, transmission electron microscopy, and high resolution scanning transmission electron microscope analyses exhibit the high crystallinity of the as-grown FeTe nanoplates. The two kinds of FeTe nanoflakes show metallic behavior and good electrical conductivity, featuring 8.44 × 10⁴ S m^-1 for 9.8 nm-thick tetragonal FeTe and 5.45 × 10⁴ S m^-1 for 7.6 nm-thick hexagonal FeTe. The study provides an efficient and convenient route for tailoring the phases of FeTe nanoplates, which benefits to study phase-sensitive properties, and may pave the way for the synthesis of other multiphase 2D nanosheets with controllable phases.

In Situ Growth of GeS Nanowires with Sulfur-Rich Shell for Featured Negative Photoconductivity

The negative photoconductivity (NPC) effect originating from the surface shell layer has been considered as an efficient approach to improve the performance of optoelectronic nanodevices. However, a scientific design and precise growth of NPC-effect-caused shell during nanowire (NW) growth process for achieving high-performance photodetectors are still lacking. In this work, GeS NWs with a controlled sulfur-rich shell, diameter, and length are successfully prepared by a simple chemical vapor deposition method. As checked by transmission electron microscopy, the thickness of the sulfur-rich shell ranges from 10.5 ± 1.5 to 13.4 ± 2.5 nm by controlling the NW growth time. The composition of the sulfur-rich shell is studied by X-ray photoelectron spectroscopy, showing the decrease of S in the GeS_x shell from the surface to core. When configured into the well-known phototransistor, a featured NPC effect is observed, benefiting the high-performance photodetector with high responsivity of 10⁵ A·W^-1 and detectivity of 10¹² Jones for λ = 405 nm with ultralow intensity of 0.04 mW·cm^-2. However, the thicker-shell NW phototransistor shows an unstable photodetector behavior with smaller negative photocurrent because of more hole-trapping states in the thicker shell. All results suggest a careful design and controlled growth of an NPC-effect-caused shell for future optoelectronic applications.