This article presents a comprehensive analytical theory for the avalanche breakdown process in p-n junction diodes to address the critical reliance on empirical models in the design of avalanche photodiodes (APDs) and single-photon avalanche diodes (SPADs). The proposed model is derived from fundamental carrier continuity equations and impact excitation probability. Eventually, it yields closed-form expressions for the avalanche current density and the breakdown voltage. It demonstrates excellent agreement with experimental current-voltage characteristics across various semiconductors (Si, GaN, 4H-SiC, and InP) and a wide temperature range. TCAD simulations are also adopted to validate this model. The theory establishes a unified, physics-based criterion for defining the avalanche breakdown voltage, revealing its functional dependence on material parameters (bandgap, dielectric constant, and mean-free path) and doping concentrations. Significantly, it explicitly predicts the theoretical minimum and maximum limits for the breakdown voltage in a given material, which were well known but only implicitly reflected in previous empirical models. This work provides a rigorous theoretical framework for the steady-state dark avalanche current for the targeted design of diverse avalanche-based devices, ranging from low-breakdown-voltage SPADs for integrated quantum photonics to high-breakdown-voltage power devices, moving beyond trial-and-error approaches.

Photon-counting computed tomography (PCCT) has emerged as a transformative imaging technology, offering superior spatial resolution and energy discrimination. However, conventional tellurium-based detectors face significant challenges under high-flux conditions due to polarization effects and charge losses. This study presents an investigation of chromium-compensated gallium arsenide (GaAs:Cr) photoconductive devices as a viable alternative. Through detailed analysis of spectra responses, temperature-dependent dark current behavior, and detection performance across a flux range of 20-900 Mcps/mm2 under 40 keV X-ray irradiation, we demonstrate the major defect levels, high resistivity and carrier transport mechanisms of the detector.

The development of silicon-compatible, high-performance infrared photodetectors is crucial for advancing thermal imaging, security, and communication systems. While germanium is a promising near-infrared material, its behavior in nanostructured forms with silicon heterojunctions reveals complex photophysics. This work demonstrates a germanium nanowire photodetector grown on a silicon-on-insulator (SOI) platform that exhibits a striking, tunable coexistence of both positive photoconductivity (PPC) and negative photoconductivity (NPC). We show that the dominant photoresponse can be switched by the wavelength of incident light: NPC dominates at visible wavelengths (e.g., 532 nm), while PPC prevails in the near-infrared (e.g., 1310 nm). Through systematic experiments and FDTD and TCAD simulations, we elucidate that this phenomenon arises from the interplay of light absorption in the different layers of the heterostructure. At short wavelengths, strong absorption in the underlying Si layer forward-biases the heterojunction, injecting carriers that quench the Ge channel conductance (NPC). At long wavelengths, absorption is confined to the Ge layer, resulting in conventional PPC. Negative photoconductivity was consistently observed over the temperature range from 78 to 298 K. Notably, the maximum responsivity of the nanowire increased from -56.7 A/W at room temperature to -1421.5 A/W at 78 K. This is attributed to the suppression of surface recombination velocity, increasing the minority carrier lifetime by 2 orders of magnitude. The -3 dB bandwidth is 2.9 kHz under 532 nm light and 3.9 kHz under 1310 nm light. The minimum noise equivalent power is determined to be 5.3 x 10-14 W/Hz0.5, corresponding to a specific detectivity of 4.0 x 109 Jones at room temperature. Furthermore, we demonstrate that the crossover wavelength is intensity-dependent and that the photocurrent follows an established logarithmic model for nanowire photoconductors. This work provides a controllable model system for studying NPC and presents a novel device architecture with tunable, multifunctional photoresponse for advanced optoelectronic applications.

We report the feasibility, development, and experimental validation of fiber-optic physical unclonable functions (PUFs) using a semi-distributed interferometer (SDI) device. The SDI is a semi-stochastic optical fiber structure in which a short high-scattering fiber span is sandwiched within two mirrors to form a random reflection spectrum. With a suitable functionalization, the SDI can target biomarkers of biological samples such as urine, saliva, or tears, obtaining a response that is uniquely dependent on the concentrations of molecules in the analyte. In this paper, we validate this concept introducing opto-biological PUFs, in which the challenge-response pair can also detect access using the same physical token but a different biological sample (bio-challenge). We validate this concept using artificial samples of urine, saliva, and tears, exploiting multiplexing to increase redundancy and improve correct bio-identification. Using a standard telecom-grade interrogator, we achieve 18,502 net-bit codewords, with Hamming distance of 91-238 bits for intra-challenge, with an increment up to 128% in the bio-challenge case, and 8082-8710 bits for inter-challenge. Due to low device cost for both device and functionalization, and the opto-biological PUF potential, the SDI device stands as a promising device for high-end security.

Two-dimensional materials show promise in post-Moore electronics but face challenges in damage-free conformal transfer onto nanostructures. Here, we propose a conformal transfer strategy based on a poly (propylene carbonate) support layer with a low glass transition temperature. Through the synergistic regulation of temperature and stress, large-area monolayer MoS2 achieves damage-free conformal coverage of silicon nanowire (SiNW). The coverage height can reach up to 300 times the thickness of the nanowires themselves, far exceeding the geometric adaptation limits of conventional methods. By adjusting the aspect ratio of the SiNW, a spontaneous air gap is formed between the MoS2 gate electrode and the side wall of nanowire. This air gap acts as a layer with an ultra-low dielectric constant, thereby restructuring the gate-channel electrostatic boundary conditions. This MoS2/Si nanowire dual-mechanism transistor exhibits excellent electrical performance, featuring a subthreshold swing as low as 63.95 mV dec-1. These results unveil the application potential of hybrid-dimensional optoelectronic devices in compact transistor preamplifiers and logic device technology.

Phosphorus quantum dots (QDs) in silicon are a prominent candidate for semiconductor quantum computing based on donor spins. In this work, we report the formation of degenerate phosphorus QDs with a radius of 3 nm confined in a two-dimensional plane in silicon. A multilayer of SiO2/POx/SiO2 on Si substrate is first deposited by atomic layer deposition, which serves as the capping layer, doping source, and doping mask. Defective channels in the SiO2 doping mask layer are then created by random argon (Ar) ion implantation. Finally, phosphorus dopants from the doping source layer, driven by pulsed laser annealing, diffuse through the defective channels in SiO2 into Si substrate, forming phosphorus QDs confined in a two-dimensional (2D) plane near the Si surface. By reducing the Ar dose, we observe a sharp metal-to-insulator transition (MIT) in the resulting 2D electron system. Based on the MIT model for quantum dots, we find that each Ar ion implantation has a chance of only 6.4%–8.1% to create a phosphorus quantum dot.

Sorting particles based on intrinsic properties remains a central challenge in Lab-on-a-Chip technologies. Here, we present a magnetophoretic microfluidic platform for the controlled transport of magnetic microparticles and magnetically labeled cells along predefined magnetic tracks, as well as size- and magnetization-based sorting. The system integrates patterned magnetic thin films within a chip and operates in an in-plane rotating magnetic field that synchronizes particle motion, enabling precise positioning and transport. Introducing a small gap in the magnetic pattern allows selective particle transmission only under specific combinations of particle properties and field parameters, resembling semiconducting-like transport behavior. By tuning the magnetic field parameters, selective sorting is achieved based on two parameters: (1) particle size and (2) effective magnetic moment. The system is studied using simulations and experiments to identify critical frequencies governing particle transport across the gap. Machine learning models are further employed to classify particle transport states, achieving up to 95% prediction accuracy. Experimentally, the platform achieves approximately 96 ± 1.4% efficiency for size-based sorting of particles and approximately 98 ± 1.4% efficiency for sorting of HEK-293T cells with different magnetic loading conditions. For mixed populations of T cells and HEK-293T cells, approximately 98.33 ± 1.44% sorting efficiency is achieved through combined size and magnetization differences. This robust platform provides an efficient solution for particle and cell sorting, with applications in biomedical diagnostics and single-cell analysis.

Er-implanted Si (Er:Si) is a promising candidate for scalable planar quantum memory (QM) applications. In Er:Si, Er has a preference to coordinate with O impurities, and multiple types of Er center are typically formed after a post-implant anneal. Intrinsic Si was implanted with 1018 cm-3 Er, then annealed using a rapid quench annealing technique at 950 degrees C for 10 min with quench rates of 5 degrees C, 23 degrees C, 46 degrees C, 93 degrees C, 185 degrees C, and 400 degrees C/s. The evolution of photoluminescence (PL) peaks and their associated Er centers was tracked as a function of quench rate. Across all samples, five distinct Er centers were identified. Two centers, one with mixed Si/O coordination and one with Si-only coordination, exhibited fully resolved crystal-field splitting of the 4I15/2 ground state together with 2-3 hot lines from the 4I13/2 excited state; fitting crystal-field parameters for both was consistent with C2v symmetry. The mixed Si/O coordinated center was suppressed at quench rates above 185 degrees C/s, while the Si-only coordinated center was progressively enhanced with increasing quench rate up to the maximum of 400 degrees C/s. These results indicate that rapid quench annealing can favor the formation of Si-coordinated Er centers in Er:Si, which is required for QM applications. (c) 2026 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Self-assembled molecular monolayer doping remains as a research focus for its nature of being conformal, nondestructive, and self-limiting. However, the carrying molecules may contaminate the substrate and electrically deactivate the dopants. In this work, we investigate the electrical activities of sulfur dopants in GaAs introduced by the self-assembled molecular monolayer doping technique. The results from secondary ion mass spectrometry and low-temperature Hall measurements show that the activation energy of sulfur dopants is 68 meV, and that 91% of these dopants introduced into GaAs by the self-assembled molecular monolayer doping technique are electrically active. The impact of the carrying molecular contamination is minimal. We employ this monolayer doping technique to create a PN junction diode on a p-type GaAs substrate. The PN junction diode exhibits an outstanding performance with an ideality factor of 1.26 and a rectification ratio up to 104 within the bias of ±0.6 V.

Atomically thin MoS2 is a promising material for field-effect transistors (FETs) and electronic devices. However, traditional photolithographic processes introduce polymeric photoresist contamination to 2-D materials, leading to a large uncertainty in their electrical property. In this work, we demonstrate a novel fabrication method using gold as a mask for patterning and etching, which protects 2-D materials from contamination of polymeric photoresists. This technique enables the fabrication of clean monolayer MoS2 transistors with Ohmic contacts. MoS2 devices was mass-produced using both traditional photo-lithography (TPL) and gold mask lithography (GML). Statistics (similar to 200 devices) shows that MoS2 devices produced by TPL vary in electrical properties by three orders of magnitude, while those fabricated by GML are highly reproducible with the conductivity variance within one order of magnitude.

Lab-on-a-chip devices have been essential in driving the recent advancements in biological research. A major challenge is to precisely manipulate single particles within a group while maintaining the capability to work on a large number of particles. Inspired by the electrical circuits, we introduce capacitors based on drop-shaped magnetic thin films integrated into a microfluidic chip for the first time, enabling the manipulation of particles in a tri-axial rotating magnetic field. The drop-shaped magnetic films in a vertical bias magnetic field lower the attraction force between particles, preventing them from forming undesired clusters. We use both simulations and experiments to investigate the effect of particle size, capacitor geometry, applied magnetic field, and driving frequency on device operation. We combine the proposed magnetophoretic capacitor with magnetophoretic transistors to form an array of single cells paired with barcode-carrying magnetic beads, achieving loading efficiencies higher than 96%. This system allows us to study protein secretion profiles at the single-cell level. We demonstrated the capability of the chip to distinguish cells based on their protein expressions. The proposed design is expandable and potentially plays an important role in single-cell biology and medicine.

Delta doping (delta-doping) has extensive applications in advanced metal oxide semiconductor field effect transistors, quantum devices, and deep ultraviolet (DUV) photodetectors. In this work, we demonstrate a novel method for high-concentration phosphorus delta-doping in silicon using pulsed laser annealing assisted with argon preimplantation. The delta-doping layer has a peak phosphorus concentration of 1.44 x 1020 cm-3. Low-temperature Hall measurements reveal that the delta-doping layer is in a metallic state and exhibits a weak localization phenomenon, which implies the formation of a two-dimensional electron gas. As a demonstration, a highly sensitive deep UV photodetector is fabricated by forming an n-type delta-doping layer on a p-type Si substrate. The photoresponsivity of our delta doping PN junction photodiodes is 0.124 A/W, more than 2 times higher than that of the commercial photodiode. This finding offers a promising route for the realization of a highly doped delta-doping layer in silicon, with potential applications in a variety of electronic and optoelectronic devices.

2D materials like molybdenum disulfide (MoS2) have shown a significant potential in photodetection due to their tunable bandgap and strong light-matter interactions. In this study, we have developed a silicon-based PN junction phototransistor integrated with few-layer MoS2 to achieve tunable positive and negative photoconductivity. The device modulates photocurrent through a photo-induced voltage from the PN junction, and photocurrent measurements reveal a logarithmic dependence on light intensity.

In modern imaging systems, the application of multispectral imaging technologies is pervasive, furnishing an enhanced spectrum of information. Multispectral methods typically employ arrays of filters to selectively exclude light from undesired spectral bands, thus facilitating the capture of discrete narrowband data. However, the inherent multi-channel filtering process limits their energy utilization efficiency, a constraint that is magnified by the current trend of miniaturization in imaging devices. In this work, we have developed a pixel-level, metal-based, mid-infrared router by employing an inverse design method. This design achieved peak spectral efficiencies of 58.61% and 67.35% within the operational bands of 3.5–4.2 and 4.4–5 μm, respectively, and an average energy utilization efficiency across the entire operational range of 3.5–5 μm was elevated to 72%, which is 1.44 times higher than that of conventional filter-based systems. The designed routers were realized by standard nanofabrication processes that transfer the designed patterns into a gold film on a ZnS substrate. The spectral measurements show that the fabricated routers have a routing performance close to the simulation results.

Two-dimensional (2D) semiconductors have been of great interest for phototransistors and neuromorphic devices in recent years because of their unique optical and electronic properties. However, the detectable spectral range and light absorption efficiency are limited for 2D-semiconductor-based phototransistors. Herein, we report a high-performance deep-ultraviolet (DUV) sensitive phototransistor by integrating molybdenum disulfide (MoS2) with silicon carbide nanoparticles (SiC NPs) to form a van der Waals heterostructure (vdWH), which shows ultrahigh responsivity and detectivity, especially in the DUV spectral range. The SiC NPs/few-layer MoS2 vdWH phototransistor shows a 20-fold enhancement in responsivity (from 9.4 × 102 to 1.9 × 104 A/W) and 11-fold enhancement in detectivity (from 7.9 × 1012 to 8.4 × 1013 cm × Hz1/2/W) at 254 nm wavelength, compared to the phototransistor based on few-layer MoS2 alone. Moreover, the SiC NPs/few-layer MoS2 vdWH phototransistor also shows higher excitation postsynaptic current (EPSC) and longer retention time of postsynaptic current (PSC) compared to the phototransistor based on few-layer MoS2 alone. This enables vdWH devices to successfully mimic various biological synaptic functions, including paired-pulse facilitation (PPF), spike-duration-dependent plasticity, spike-number-dependent plasticity, spike-frequency-dependent plasticity, the transition from short-term plasticity (STP) to long-term plasticity (LTP), and long-term depression (LTD) capabilities. The simulation of a deep neural network (DNN) shows that the image inference accuracy based on these SiC NPs/few-layer MoS2 vdWH neuromorphic phototransistors reaches up to 98.99% even after considering the photoresponsivity variations. The high-performance dual-function neuromorphic optoelectronics based on SiC NPs/MoS2 vdWH hold great promise for ultrasensitive DUV photodetection, neuromorphic DUV visual sensing, and in-sensor computing applications in a single device.

Negative photoresponses in photodetectors can find important applications like image AI and image edge detection. In this Letter, we develop a few-layer MoS2 phototransistor photogated by a silicon-based N+P junction. Negative photovoltage will be generated on the open-circuit N+P junction by grounding the p-type substrate. The negative photovoltage modulates the conductance of the n-type MoS2 flake, creating negative photoconductance in the MoS2 channel. The light-intensity dependent photoresponses are characterized at cryogenic temperatures. The experimental results can be well fitted with the established device theory.

Defect engineering in two-dimensional (2D) materials offers new opportunities for applications such as gas sensing, single-atom catalysis, and guided nanoparticle self-assembly. However, achieving precise control over atomic-scale defects on the surfaces of 2D materials remains a significant challenge. Highly ordered pyrolytic bulk graphite (HOPG) is a typical 2D materials, in this work, we employed scanning tunneling microscopy (STM), Raman spectroscopy, and density functional theory (DFT) to examine defects formed on the surfaces of HOPG by ion irradiation with different parameters. Interestingly, three distinct types of defects including nanoscale surface defects (NSD), atomic surface defects (ASD) and sub-surface defects (SSD) are identified, depending on the ion energy and mass of irradiated ions. Adjusting ion mass and voltage allows for 97 % of irradiated As+ ions to induce defects. We employed a low-flux focused ion beam (FIB) to create circular rings of defects on the HOPG surface, which facilitates the self-assembly of gold nanoparticles into corresponding circular rings.

Silicon-based avalanche photodetectors (Si-APDs) are promising candidates for complementary metal oxide semiconductor (CMOS)-compatible optoelectronic systems, leveraging their inherent multiplication mechanism to compensate for silicon's weak absorption at the near-infrared (NIR) range through advanced structural engineering. However, conventional free-space Si-APDs suffer from inevitable limitations, most notably spatially nonuniform avalanche triggering arising from stochastic carrier injection, excessive multiplication noise caused by unregulated avalanche paths, and surface recombination losses at heterojunction interfaces, which collectively constrain their development in emerging NIR detection. Herein, we construct and demonstrate a novel SiO2-passivated Si nanowire (SiO2-SiNW)/graphene confinement-enhanced photodetector, where vertical SiO2-SiNWs function as a core-shell nanoresonator system. The proposed design structure leverages photon confinement to enhance light absorption at 1550 nm, while the localized field enhancement at the SiNW/graphene vertical van der Waals (vdW) interface facilitates avalanche photodetection. Through advanced structural engineering, the device exhibits a responsivity of 56.58 A/W and a high avalanche gain of 2.64 × 104, attributed to the synergistic interplay of nanoresonator-enhanced light-matter interaction and efficient carrier multiplication within the confined avalanche regime. The strategic integration of dielectric-engineered nanostructures with vdW heterostructures establishes a versatile platform for developing optoelectronic systems operating at NIR telecommunications, while enabling precise control over carrier transport and photon management at the nanoscale.

Luminescent encrypted labels can effectively solve the problem of counterfeiting. However, they suffer from complex design and fabrication, low space utilization, and limited capacity of encrypted information. Herein, we create multilayer infrared luminescent encryption labels using femtosecond-laser-activated Er-doped silicon. In comparison with other annealing techniques that treat the whole sample at once, femtosecond lasers have a high spatial precision and flexibility, which can locally anneal the Er-doped Si, generating stable and controllable multilayered photoluminescent patterns. It therefore can significantly enhance security and increase the information storage capacity. This work demonstrates a low-cost, high-capacity, and high-security encrypted label with great application value. Fs-laser-annealed Er-doped silicon is also a promising material to realize quantum light sources or gain materials for lasers at the communication band.