Controllable Inverse Photoconductance in Semiconducting Nanowire Films

Tunable Drift-Diffusion Synergy in Suspended Te Nanowires for Multistate Photodetection

Tuning the interplay between photoconductive (drift-driven) transport and photothermoelectric (diffusion-driven) transport in a single device remains crucial for next-generation optoelectronics and in-sensor computing. Here, we present a suspended tellurium nanowire (Te NW) photodetector that concurrently harnesses and actively balances these two transports using asymmetric (local) or symmetric (flood) illumination in tandem with a bias voltage. This enables on-demand transitions from diffusion-dominated to drift-dominated photoresponses at room temperature, a feat not realized in prior Te-based detectors. Under zero bias with local illumination, robust photothermoelectric diffusion yields positive or negative photocurrents, with a responsivity Ri of 124.28 A/W and specific detectivity (D*) of 7.80 × 1011 Jones. Conversely, flood illumination under finite bias triggers photoconductive drift, with a peak responsivity Ri of 65.03-68.79 A/W and D* of 7.99 × 1010-8.47 × 1010 Jones. By programming the illumination and bias conditions, we realize positive, negative, or zero photocurrent states, forming a three-mode response platform. Remarkably, the device exhibits a sub-100 μs response time and retains stable detection under ambient conditions, illustrating its viability for real-world applications. This work establishes a versatile blueprint for broadband, multistate photodetection toward in-sensor computing tasks.

High Hole Mobility van der Waals Junction Field-Effect Transistors Based on Te/GaAs for Multimode Photodetection and Logic Applications

Recently, interface scattering and low mobility have significantly impeded the performance of two-dimensional (2D) P-type transistors. 2D semiconductor tellurium (Te) has garnered significant interest owing to its unique atomic chain crystal structure, which confers ultrahigh hole mobility. van der Waals heterojunction enhances transistor performance by reducing scattering at the gate-channel interface, attributed to its high-quality interface. In this study, we present Te/gallium arsenide (GaAs) hybrid dimensional JFETs exhibiting sizable on-state currents, elevated transconductance, and mobility as high as 328.4 cm2V-1s-1. Achieving a low-power device, we lowered the threshold voltage from 1.9 to 1 V by modifying the carrier concentration of the gate. Furthermore, enhancing negative photoconductivity on the Te surface is achieved by tuning the depth of the channel depletion region, thereby achieving an enhanced negative photoconductivity mechanism with universal applicability. Based on this, a photodetector featuring both positive and negative photoconductivity and a photovoltaic effect was developed. The negative photoresponsivity and detectivity at 635 nm of the device are -64 AW-1 and 1.41 × 1010 Jones, respectively. Utilizing these properties, we develop Te/GaAs JFET-based logic gate circuits and single-point negative photoconductive imaging applications. This provides a potential research avenue for future logic circuits and optoelectronic devices.

Incompatible Geometry Regulation of Nanowire Assemblies Enabled Light-Driven Shape Morphing and Motions

Photoresponsive shape-changing materials have significant applications in miniaturized smart robotics and biomedicine powered in a remote and wireless manner. Existing light-fuelled soft materials suffer from limited continuous shape manipulation and constrained mobility and locomotive modes. One promising solution is developing a hierarchical structure design approach to integrate rapid, reversible photoactive molecular alignment and mechanically incompatible geometry in a macroscopic system. Here, a nanowire assemblies-induced geometry engineering method is reported for the fabrication of silver nanowire-incorporated nematic liquid crystalline elastomers with prominent anisotropic structures at multi-length scales and incompatible elasticity that show sharp morphological transitions among the rings, helicoids, and spirals with diverse helical configurations. The engineered composite films can realize complex light-driven motions including rotating, rolling, and jumping with the controlled directionality and magnitude that are pre-encoded in their both molecular and macroscopic configurations. Owing to the great controllability of multimodal locomotion, a spiral robot can undertake task-specific configuration to climb up complex terrains. The complete regulatory relationship among molecular orientation, shape geometry, and light-driven motions is also established. This study may open an avenue for elaborate design and precise fabrication of novel shape-morphing materials for future applications in intelligent robotic systems.

Mechanically Stable and Damage Resistant Freestanding Ultrathin Silver Nanowire Films with Closely Packed Crossed-Lamellar Structure

One-dimensional (1D) functional nanowires are widely used as nanoscale building blocks for assembling advanced nanodevices due to their unique functionalities. However, previous research has mainly focused on nanowire functionality, while neglecting the structural stability and damage resistance of nanowire assemblies, which are critical for the long-term operation of nanodevices. Biomaterials achieve excellent mechanical stability and damage resistance through sophisticated structural design. Here, we successfully prepared a mechanically stabilized monolamella silver nanowire (Ag NW) film, based on a facile bubble-mediated assembly and nondestructive transfer strategy with the assistance of a porous mixed cellulose ester substrate, inspired by the hierarchical structure of biomaterial. Owing to the closely packed arrangement of Ag NWs combined with their weak interfaces, the monolamellar Ag NW film can be transferred to arbitrary substrates without damage. Furthermore, freestanding multilamellar Ag NW films with impressive damage resistance can be obtained from the monolamellar Ag NW film, through the introduction of bioinspired closely packed crossed-lamellar (CPCL) structure. This CPCL structure maximizes intra- and interlamellar interactions among Ag NWs ensuring efficient stress transfer and uniform electron transport, resulting in excellent mechanical durability and stable electrical properties of the multilamellar Ag NW films.

Insight into interfacial dynamics of photogenerated carriers in Cs3Bi2I9/Au heterostructure nanocomposites for high-sensitivity broadband photodetection with negative photoconductivity

The negative photoconductivity (NPC) effect is becoming an increasingly significant factor in the development of next-generation optoelectronics. However, research in the field of NPC-dominated optoelectronics remains in its infancy and frequently encounters challenges related to fabrication complexity, slow photoresponse speed, instability, and a limited spectral response range. Herein, a Cs3Bi2I9/Au heterostructure nanocomposite was prepared via a simple self-assembly process utilizing electrostatic interactions with Au nanoparticles (NPs) and lead-free Cs3Bi2I9 nanoplates. The Cs3Bi2I9/Au nanocomposite-based photodetectors (PDs) demonstrate a broadband photoresponse (405-1550 nm), enhanced rise/fall times (27.2/40.0 µs), and reduced noise density (4.7 × 10-13 A/Hz1/2 at 1 Hz). In contrast to the positive photoconductivity (PPC) effect observed in colloidally synthesized Cs3Bi2I9 nanoplate-based PDs, the NPC can be attributed to the decrease in photocurrent under light illumination during the processes of recombination and trapping of photogenerated carriers induced by the incorporation of Au NPs. These findings are expected to provide valuable insights into achieving high-performance NPC-dominated PDs by regulating the dynamics of photogenerated carriers in perovskite heterostructures.

Interfacial-Assembly-Induced In Situ Transformation from Aligned 1D Nanowires to Quasi-2D Nanofilms

As the dimensionality of materials generally affects their characteristics, thin films composed of low-dimensional nanomaterials, such as nanowires (NWs) or nanoplates, are of great importance in modern engineering. Among various bottom-up film fabrication strategies, interfacial assembly of nanoscale building blocks holds great promise in constructing large-scale aligned thin films, leading to emergent or enhanced collective properties compared to individual building blocks. As for 1D nanostructures, the interfacial self-assembly causes the morphology orientation, effectively achieving anisotropic electrical, thermal, and optical conduction. However, issues such as defects between each nanoscale building block, crystal orientation, and homogeneity constrain the application of ordered films. The precise control of transdimensional synthesis and the formation mechanism from 1D to 2D are rarely reported. To meet this gap, we introduce an interfacial-assembly-induced interfacial synthesis strategy and successfully synthesize quasi-2D nanofilms via the oriented attachment of 1D NWs on the liquid interface. Theoretical sampling and simulation show that NWs on the liquid interface maintain their lowest interaction energy for the ordered crystal plane (110) orientation and then rearrange and attach to the quasi-2D nanofilm. This quasi-2D nanofilm shows enhanced electric conductivity and unique optical properties compared with its corresponding 1D geometry materials. Uncovering these growth pathways of the 1D-to-2D transition provides opportunities for future material design and synthesis at the interface.

Spectrum-Dependent Image Convolutional Processing via a Two-Dimensional Polarization-Sensitive Photodetector

Currently, the improvement in the processing capacity of traditional processors considerably lags behind the demands of real-time image processing caused by the advancement of photodetectors and the widespread deployment of high-definition image sensors. Therefore, achieving real-time image processing at the sensor level has become a prominent research domain in the field of photodetector technology. This goal underscores the need for photodetectors with enhanced multifunctional integration capabilities than can perform real-time computations using optical or electrical signals. In this study, we employ an innovative p-type semiconductor GaTe0.5Se0.5 to construct a polarization-sensitive wide-spectral photodetector. Leveraging the wide-spectral photoresponse, we realize three-band imaging within a wavelength range of 390-810 nm. Furthermore, real-time image convolutional processing is enabled by configuring appropriate convolution kernels based on the polarization-sensitive photocurrents. The innovative design of the polarization-sensitive wide-spectral GaTe0.5Se0.5-based photodetector represents a notable contribution to the domain of real-time image perception and processing.

Biomimetic wafer-scale alignment of tellurium nanowires for high-mobility flexible and stretchable electronics

Flexible and stretchable thin-film transistors (TFTs) are crucial in skin-like electronics for wearable and implantable applications. Such electronics are usually constrained in performance owing to a lack of high-mobility and stretchable semiconducting channels. Tellurium, a rising semiconductor with superior charge carrier mobilities, has been limited by its intrinsic brittleness and anisotropy. Here, we achieve highly oriented arrays of tellurium nanowires (TeNWs) on various substrates with wafer-scale scalability by a facile lock-and-shear strategy. Such an assembly approach mimics the alignment process of the trailing tentacles of a swimming jellyfish. We further apply these TeNW arrays in high-mobility TFTs and logic gates with improved flexibility and stretchability. More specifically, mobilities over 100 square centimeters per volt per second and on/off ratios of ~104 are achieved in TeNW-TFTs. The TeNW-TFTs on polyethylene terephthalate can sustain an omnidirectional bending strain of 1.3% for more than 1000 cycles. Furthermore, TeNW-TFTs on an elastomeric substrate can withstand a unidirectional strain of 40% with no performance degradation.

A polar-switchable and controllable negative phototransistor for information encryption

Anomalous negative phototransistors have emerged as a distinct research area, characterized by a decrease in channel current under light illumination. Recently, their potential applications have been expanded beyond photodetection. Despite the considerable attention given to negative phototransistors, negative photoconductance (NPC) in particular remains relatively unexplored, with limited research advancements as compared to well-established positive phototransistors. In this study, we designed ferroelectric field-effect transistors (FeFETs) based on the WSe2/CIPS van der Waals (vdW) vertical heterostructures with a buried-gated architecture. The transistor exhibits NPC and positive photoconductance (PPC), demonstrating the significant role of ferroelectric polarization in the distinctive photoresponse. The observed inverse photoconductance can be attributed to the dynamic switching of ferroelectric polarization and interfacial charge transfer processes, which have been investigated experimentally and theoretically using Density Functional Theory (DFT). The unique phenomena enable the coexistence of controllable and polarity-switchable PPC and NPC. The novel feature holds tremendous potential for applications in optical encryption, where the specific gate voltages and light can serve as universal keys to achieve modulation of conductivity. The ability to manipulate conductivity in response to optical stimuli opens up new avenues for developing secure communication systems and data storage technologies. Harnessing this feature enables the design of advanced encryption schemes that rely on the unique properties of our material system. The study not only advances the development of NPC but also paves the way for more robust and efficient methods of optical encryption, ensuring the confidentiality and integrity of critical information in various domains, including data transmission, and information security.