As semiconductor architectures advance into the nanoscale regime, spatially resolving local electrical properties presents a critical challenge. In this paper, we report a high-resolution method based on contact-mode conductive scanning probe microscopy to characterize quantum structures. By exploiting the barrier sensitivity of the localized tip-sample Schottky contact, this technique achieves a nanoscale resolution that surpasses the limitation of the tip radius. We validate this capability by successfully resolving low-dimensional semiconductor heterostructures, enabling the electrical imaging of 1-5 nm quantum wells. Additionally, the system is sensitive enough to detect photogenerated carriers under optical injection. Leveraging these superior characterization capabilities, we further investigated the superlattice (SL) structure within extended wavelength InAlAs/InGaAs p-i-n photodetectors. The measurements indicate the effectiveness of the SL layers at the interfaces in suppressing dislocation propagation. Simultaneously, it was observed that the SL layers have a blocking effect on Zn diffusion under different conditions, providing valuable insights for optimizing diffusion parameters. Both effects of SLs have a key impact on the performance improvement of extended-wavelength devices, which can significantly affect dark current and noise. These results demonstrate that this electrical characterization method is an indispensable tool for nanostructure analysis, providing crucial feedback for the interface engineering and practical optimization of next-generation optoelectronic devices.

Phase engineering of two-dimensional transition metal dichalcogenides enables precise modulation of their electronic properties and holds great promise for next-generation electronic devices. However, achieving spatially controlled and reversible phase transitions reliably remains a key challenge for practical applications. Here, we demonstrate a localized and controllable phase transition from the semiconducting 2H to the metallic 1T′ phase in MoTe2 via laser irradiation. This transition, confirmed by Raman spectroscopy and atomic force microscopy, leads to a remarkable increase in conductivity, with the current response enhanced by up to three orders of magnitude. Furthermore, we reveal that the laser-induced 1T′ phase exhibits spontaneous reversion to the original 2H phase over time when stored under vacuum, accompanied by a corresponding decay in electrical conductance. This reversible and tunable phase-switching behavior highlights the potential of laser-controlled phase patterning for applications in reconfigurable electronics, particularly in memristive devices. Our work not only establishes a method for spatially defined phase engineering but also provides critical insights into the dynamics of phase stability, offering a foundation for the design of future controllable phase-change systems.

Topological semimetals, due to their distinctive band structures and topological protection characteristics, show high mobility and peculiar transport properties, enabling significant nonlinear effects for efficient technical exploitation in the millimeter-wave/terahertz (THz) range. Here, a layered topological semimetal beta-PdBi2 was synthesized via the melt-growth technique and subsequently integrated with graphene to form an always-on rectenna in terms of van der Waals integration, leveraging the unique electronic and mechanical properties of topological semimetals, as well as the efficient thermionic emission enabled by weak Fermi-level pinning. The rectenna demonstrates exceptional performance metrics across a frequency range from 0.02 to 0.32 THz, with a responsivity as high as 805 V/W, a fast response time of 163 ns, and a Noise Equivalent Power (NEP) as low as 1.03 & times; 10-11 W/Hz1/2 even at zero bias, which underscores its outstanding performance in low-noise environments. Moreover, the rectenna also acts as a sub-THz mixer, realizing frequency conversion beyond 100 GHz, accompanied by a tunable intermediate frequency bandwidth that exceeds 53 GHz, rivaling state-of-the-art graphene microwave devices. Our strategy provides a universal energy-harvesting building block that becomes increasingly ubiquitous in applications across the millimeter-wave and terahertz regimes, representing an encouraging advance towards semimetal electronics.

In planar photodetectors, light absorption and charge carrier collection occur approximately 1-5 mu m beneath the surface. This makes it difficult to resolve the spatially resolved photoresponse of the detector under operating conditions. In this study, laser beam induced current combined with a precision cleavage technique is employed to investigate the photoresponse characteristics in both the lateral and vertical directions of planar InGaAs PIN detectors, allowing for detailed extraction of the PN junction profile, photocurrent distribution, and minority carrier diffusion length before and after rapid thermal annealing. This combined technique provides a path for exploring the spatial distribution and transport properties of photogenerated carriers in planar detectors under operating conditions. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0277382

The on-chip near-infrared (NIR) light source devices based on van der Waals (vdW) layered materials are increasingly sought after due to their broad applications, including optoelectronic communication, computing, and sensing. The accomplishment of the electrical injection of electrons and holes is highly attractive as a step toward the realization of electrically driven NIR lasers for communication systems. Here, we demonstrated a NIR light-emitting diode (LED) device based on γ-InSe microflakes. The device was constructed by stacking few-layer graphene (Gr) and layered γ-InSe to form Gr/γ-InSe/Gr heterostructure. Thanks to the high-quality Schottky junction, room temperature electrically driven NIR light emission from γ-InSe was successfully achieved. Our results exhibit a simple method to construct NIR LED device based on vdW layered material, indicating the promise of γ-InSe for on-chip integrated optoelectronic devices.

Doping plays a key role in functionalizing semiconductor devices, yet traditional chemical approaches relying on foreign-atom incorporation suffer from doping asymmetry, pronounced lattice disorder, and constrained spatial resolution. Here, we demonstrate a physical doping technique to directly write nanoscale doping patterns into layered semiconductors (MoS2). By applying localized tensile and compressive stress via an atomic force microscopy probe, p-type and n-type conductances are simultaneously written into the designed area with sub-100 nm resolution, as verified by spatially resolved capacitance and photocurrent experiments. Density functional theory calculations reveal strain-driven shifts of donor and acceptor levels as large as several hundreds of meV, linking mechanical stress to semiconductor doping. The fabricated strain-engineered junction efficiently rectifies the current flow and performs logic operations with a stable dynamic response. This strain-driven approach enables spatially precise doping in van der Waals materials without degrading crystallinity, offering a versatile platform for nanoscale semiconductor devices.

Space infrared dim target recognition is an important applications of space situational awareness (SSA). Due to the weak observability and lack of geometric texture of the target, it may be unreliable to rely only on grayscale features for recognition. In this paper, an intelligent information decision-level fusion method for target recognition which takes full advantage of the ensemble classifier and Dempster–Shafer (DS) theory is proposed. To deal with the problem that DS produces counterintuitive results when evidence conflicts, a contraction–expansion function is introduced to modify the body of evidence to mitigate conflicts between pieces of evidence. In this method, preprocessing and feature extraction are first performed on the multi-frame dual-band infrared images to obtain the features of the target, which include long-wave radiant intensity, medium–long-wave radiant intensity, temperature, emissivity–area product, micromotion period, and velocity. Then, the radiation intensities are fed to the random convolutional kernel transform (ROCKET) architecture for recognition. For the micromotion period feature, a support vector machine (SVM) classifier is used, and the remaining categories of the features are input into the long short-term memory network (LSTM) for recognition, respectively. The posterior probabilities corresponding to each category, which are the result outputs of each classifier, are constructed using the basic probability assignment (BPA) function of the DS. Finally, the discrimination of the space target category is implemented according to improved DS fusion rules and decision rules. Continuous multi-frame infrared images of six flight scenes are used to evaluate the effectiveness of the proposed method. The experimental results indicate that the recognition accuracy of the proposed method in this paper can reach 93% under the strong noise level (signal-to-noise ratio is 5). Its performance outperforms single-feature recognition and other benchmark algorithms based on DS theory, which demonstrates that the proposed method can effectively enhance the recognition accuracy of space infrared dim targets.

AbstractAvalanche or carrier-multiplication effect, based on impact ionization processes in semiconductors, has a great potential for enhancing the performance of photodetector and solar cells. However, in practical applications, it suffers from high threshold energy, reducing the advantages of carrier multiplication. Here, we report on a low-threshold avalanche effect in a stepwise WSe2 structure, in which the combination of weak electron-phonon scattering and high electric fields leads to a low-loss carrier acceleration and multiplication. Owing to this effect, the room-temperature threshold energy approaches the fundamental limit, Ethre ≈ Eg, where Eg is the bandgap of the semiconductor. Our findings offer an alternative perspective on the design and fabrication of future avalanche and hot-carrier photovoltaic devices.

Efficient coupling in broad wavelength range is desirable for wide-spectrum infrared light detection, yet this is a challenge for intersubband transition in semiconductor quantum wells (QWs). High-Q cavities mostly intensify the absorption at peak wavelengths but with shrinking bandwidth. Here, we propose a novel approach to expand the operating spectral range of the Quantum Well Infrared Photodetectors (QWIPs). By processing the QWs into asymmetric micro-pillar array structure, the device demonstrates a substantial enhancement in spectral response across the wavelength from 7.1 µm to 12.3 µm with guided mode resonance (GMR) effects. The blackbody responsivity is then increased by 3 times compared to that of the 45° polished edge-coupled counterpart. Meanwhile, the dark current density remains unchanged after the deep etching process, which will benefit the electrical performance of the detector with reduced volume duty ratio. In contrast to the symmetric micro-pillar array that contains simple resonance mode, the detectivity of QWIP in asymmetric pillar structure is found to be improved by 2-4 times within the range of 9.5 µm to 15 µm.

Improving the signal-to-noise ratio of infrared photodetectors is a primary goal especially for those operating in the long wavelength range. Optical design in the sub-wavelength scale provides a feasible routine toward this purpose, previous efforts mainly concentrated on integrating metallic antennas and plasmonic cavities with light absorption materials like semiconductor quantum wells (QWs). This study presents an all-dielectric way that can profit the electrical and photoelectric performance of detector concurrently. By fabricating the multiple QWs into linked micro-pillar arrays, the device yields 2.3 times enhanced responsivity at 12.55 mu m relative to that of the 45 degrees degrees mesa counterpart, meanwhile the dark current density is found to decrease by 5.7-fold at-2.5 V and 50 K. These help to elevate the background-limited infrared photodetection (BLIP) temperature of the micro-pillar array QW photodetector by 4.0 K.

In van der Waals materials, the electronic property, including the bandgap as well as the charge carrier mobility and lifetime, significantly changes as its thickness shrinks to the monolayer limit. While such characteristic brings additional freedom and convenience in regard to device design and fabrication, it also raises uncertainty in terms of the semiconductor device functionality due to the competing roles of those factors in tuning the charge carrier transport. In this work, we perform scanning photocurrent microscopy experiments on different sets of MoS2 homojunctions under zero bias voltage and show the reverse photocurrent distribution among them. Specifically, in the combination of 1L–3L MoS2, the band offset is large and thus dominates the photocarrier separation. In the combination of 3L–7L MoS2, by contrast, the effect of band offset is negligible, and the mismatch in minority carrier diffusion length takes charge of the photoresponse. The authors hope that the findings presented here offer a perspective on the current transport and thus functionality realization in layered materials.

The multifunctional integrated on-chip near-infrared (NIR) light source and detection devices based on vdW layered materials are increasingly sought after due to their broad applications, including optoelectronic communication, computing, and sensing. Most of luminescence or detection devices based on vdW layered materials are demonstrated to have only a single function due to the limitation of material properties. Here, we demonstrated a multifunctional integrated on-chip NIR electroluminescence (EL) and self-powered photodetector (SPPD) device constructed by stacking few-layer graphene (Gr) and layered γ-InSe to form asymmetric Gr/γ-InSe/Gr heterostructure. Room temperature electrically driven NIR from γ-InSe was successfully achieved by the high quality Schottky junction (rectification ratio up to "5×" 〖"10" 〗^"3" ), with a turn-on voltage of ~ 1.4 V. The γ-InSe EL maintained over 90 % initial EL intensity after two hours continuous operation in air. Meanwhile, the Gr/γ-InSe/Gr SPPD exhibits a broad spectrum photoresponse (405-940nm), low specific noise current (8.7"×" 10-26 A2/Hz), high specific detectivity (~ 108 Jones @ 405 nm) and high-quality reflective imaging. Our results establish a simple preparation and tunable vdW layered material multifunctional integrated NIR EL and SPPD device, indicating the promise of γ-InSe for on-chip integrated optoelectronic devices.

For quantum well (QW) photodetectors and lasers, doping to obtain desired electron density in QWs is a critical factor to realize the optimal device behavior. In this study, we employed scanning spreading resistance microscopy (SSRM) to resolve the carriers in individual QWs, and investigate the relevance between carrier concentration and the performance of three Quantum Well Infrared Photodetectors (QWIPs) with n-type density designed as 2.5 x 10(17) cm(-3), 5 x 10(17) cm(-3) and 2 x 10(18 )cm(-3) respectively. It's found that the actual dopant densities of silicon in QWs obtained by secondary ions mass spectroscopy (SIMS) can be considerably deviate from the nominal values. Meanwhile the electron concentrations in QWs estimated from the SSRM measurement are 2.4 x 10(17) cm(-3), 4.7 x 10(17) cm(-3) and 1.0 x 10(18) cm(-3) respectively, which accounts for the increment of the responsivity and the degradation in dark current among the three QWIPs. The SSRM study dicloses the insuffcient activation of Si dopant in nano-sized GaAs QWs, and in another aspect, it confirms the optimal carrier concentration for realizing ideal signal-to-noise ratio of the QWIPs.

Light detection through intersubband transition faces combined demands of retaining normal incidence coupling, enhancing absorption, and suppressing dark current which is usually fulfilled by separate parts in devices. In this paper, 50-period GaAs/AlGaAs quantum well (QW) layers are designed and fabricated into arrays of subwavelength columns, which induces resonant mode to confine the infrared light inside the columns with strengthened electric field component in the z-direction. The self-grating-coupled QWs exhibit broadened absorption in the long wavelength range with peak absorption increased by 4.5 times at 8.7 mu m relative to that of the 450 polished edge-coupled counterpart. Meanwhile, the dark current is reduced by 51% due to the reduction of the electrical area. With the joint benefits of guiding and compressing incident light in squeezed volumes, it's demonstrated that the dark current limited specific detectivity (D*dark) of quantum well infrared photodetectors (QWIPs) could be raised by 6.4 times when merged into photonic structures.

Space infrared (IR) target recognition has always been a key issue in the field of space technology. The imaging distance is long, the target is weak, and the feature discrimination is low, making it difficult to distinguish between high-threat targets and decoys. However, most existing methods ignore the fuzziness of multi-dimensional features, and their performance mainly depends on the accuracy of feature extraction, with certain limitations in handling uncertainty and noise. This article proposes a space IR dim target fusion recognition method, which is based on fuzzy comprehensive of spatio-temporal correlation. First, we obtained multi-dimensional IR features of the target through multi-time and multi-spectral detectors, then we established and calculated the adaptive fuzzy-membership function of the features. Next, we applied the entropy weight method to ascertain the objective fusion weights of each feature and computed the spatially fuzzified fusion judgments for the targets. Finally, the fuzzy comprehensive function was used to perform temporal recursive judgment, and the ultimate fusion recognition result was obtained by integrating the results of each temporal recursive judgment. The simulation and comparative experimental results indicate that the proposed method improved the accuracy and robustness of IR dim target recognition in complex environments. Under ideal conditions, it can achieve an accuracy of 88.0% and a recall of 97.5% for the real target. In addition, this article also analyzes the impact of fusion feature combinations, fusion frame counts, different feature extraction errors, and feature database size on recognition performance. The research in this article can enable space-based IR detection systems to make more accurate and stable decisions, promoting defense capabilities and ensuring space security.

Periodic pillars of semiconductor in sub-wavelength size can serve multiple roles as diffracting, trapping and absorbing light for effective photoelectric conversion which has been intensively studied in the visible range. Here, we design and fabricate the micro-pillar arrays of AlGaAs/GaAs multi quantum wells(QWs) for high performance detection of long wavelength infrared light. Compared to its planar counterpart, the array offers 5.1 times intensified absorption at peak wavelength of 8.7 µm with 4 times shrinked electrical area. It's illustrated by simulation that the normal incident light is guided in the pillars by HE11 resonant cavity mode to form strengthened Ez electrical field, which enables the inter-subband transition of n-type QWs. Moreover, the thick active region of dielectric cavity that contains 50 periods of QWs with fairly low doping concentration will be beneficial to the optical and electrical merits of the detectors. This study demonstrates an inclusive scheme to substantially raise the signal to ratio of infrared detection with all-semiconductor photonic structures.

In semiconductor manufacturing, PN junction is formed by introducing dopants to activate neighboring electron and hole conductance. To avoid structural distortion and failure, it generally requires the foreign dopants localize in the designated micro-areas. This, however, is challenging due to an inevitable interdiffusion process. Here we report a brand-new junction architecture, called “layer PN junction”, that might break through such limit and help redefine the semiconductor device architecture. Different from all existing semiconductors, we find that a variety of van der Waals materials are doping themselves from n- to p-type conductance with an increasing/decreasing layer-number. It means the capability of constructing homogeneous PN junctions in monolayers’ dimension/precision, with record high rectification-ratio (>10 5 ) and low cut-off current (<1 pA). More importantly, it spawns intriguing functionalities, like gate-switchable-rectification and noise-signal decoupled avalanching. Findings disclosed here might open up a path to develop novel nanodevice applications, where the geometrical size becomes the only critical factor in tuning charge-carrier distribution and thus functionality.

Titanium nitride (TiN), with its tunable work function, serves as an electrode metal in the scaling fin-type field-effect transistor and plays the key role for low threshold operation. Measuring the effective work function of thin TiN films is desirable for rapid evaluation before device fabrication. In this work, Kelvin probe force microscopy is applied to study the impact of various factors on the surface potential of TiN films with an uncertainty below 30 mV. By scraping and gauging the potential evolvement of TiN in different circumstances, it is revealed that the surface effect is the major obstacle to determine the work function of the as-deposited TiN. For thick films, the potential drops over 530 mV for a fresh TiN surface relative to that of an aged one. For TiN films thinner than 5 nm, the potential changes by 290 mV due to surface oxidation. This enables a quantitative assessment on the effective work function as well as the surface charge density of TiN films.

Space target feature extraction and space infrared target recognition are important components of space situational awareness (SSA). However, owing to far imaging distance between the space target and infrared detector, the infrared signal of the target received by the detector is dim and easily contaminated by noise. To effectively improve the accuracy of feature extraction and recognition, it is essential to suppress the noise of the infrared signal. Hence, a novel denoising and extracting feature method combinating optimal variational mode decomposition (VMD) and dual-band thermometry (DBT) is proposed. It takes the mean weighted fuzzy-distribution entropy (FuzzDistEn) of the band-limited intrinsic mode functions (BLIMFs) as the optimization index of dragonfly algorithm (DA) to obtain the optimal parameters (K, α) of VMD. Then the VMD is utilized to decompose the noisy signal to obtain a series of BLIMFs and the Pearson correlation coefficient (PCC) is proposed to determine the effective modes to reconstructe the denoising signal. Finally, based on the denoising signal, the feature of temperature and emissivity-area product are calculated using the DBT. The simulation and experiment results show that the proposed method has better noise reduction performance compared with the other denoising methods, and the accuracy of feature extraction is improved at different noise equivalent irradiance. This provides more accurate feature of temerpature and emissivity-area product for space infrared dim target recognition.

In neuromorphic hardware, peripheral circuits and memories based on heterogeneous devices are generally physically separated. Thus, exploration of homogeneous devices for these components is key for improving module integration and resistance matching. Inspired by the ferroelectric proximity effect on two-dimensional (2D) materials, we present a tungsten diselenide–on–lithium niobate cascaded architecture as a basic device that functions as a nonlinear transistor, assisting the design of operational amplifiers for analog signal processing (ASP). This device also functions as a nonvolatile memory cell, achieving memory operating (MO) functionality. On the basis of this homogeneous architecture, we also investigated an ASP-MO integrated system for binary classification and the design of ternary content-addressable memory for potential use in neuromorphic hardware.