Search Results (101)

In this study, the influence of HfO₂ interlayer thickness on the performance of heteroepitaxial α-Ga₂O₃ layer-based metal–insulator–semiconductor–insulator–metal (MISIM) ultraviolet photodetectors is examined. A thin HfO₂ interlayer enhances the interface quality and reduces the density of interface traps, thereby improving the performance of UVC photodetectors. The fabricated device with a 1 nm HfO₂ interlayer exhibited a significantly reduced dark current and higher photocurrent than a conventional metal–semiconductor–metal (MSM). Specifically, the 1 nm HfO₂ MISIM device demonstrated a photocurrent of 2.3 μA and a dark current of 6.61 pA at 20 V, whereas the MSM device exhibited a photocurrent of 1.1 μA and a dark current of 73.3 pA. Furthermore, the photodetector performance was comprehensively evaluated in terms of responsivity, response speed, and high-temperature operation. These results suggest that the proposed ultra-thin HfO₂ interlayer is an effective strategy for enhancing the performance of α-Ga₂O₃-based UVC photodetectors by simultaneously suppressing dark currents and increasing photocurrents and ultimately demonstrate its potential for stable operation under extreme environmental conditions. Full article

Visible light communication (VLC) is an emerging communication technology that integrates lighting and communication, offering significant advantages in terms of data transmission rates and broad application prospects. With advancements in semiconductor technology, micro-light-emitting diodes (micro-LEDs) have emerged as one of the most promising light sources for high-speed VLC systems, owing to their high brightness, low power consumption, and high modulation bandwidth. Recent developments have also seen substantial progress in high-bandwidth GaN-based visible light detectors, which complement the transmission capabilities of micro-LEDs. This paper reviews the latest advancements in micro-LEDs as high-speed transmitters for VLC, detailing their capabilities in terms of bandwidth, data rates, modulation techniques, and diverse applications, including structured lighting systems that combine positioning, communication, and illumination. Additionally, the advantages of using micro-LEDs in GaN-based photodetectors (PDs) are discussed, highlighting their potential in enhancing bandwidth and data rates and facilitating high-speed communications across multifunctional applications. Therefore, this review will benefit the further development of micro-LEDs and their application in 6G communication and global interconnect. Full article

Topological insulators (TIs) hold considerable promise for the advancement of optoelectronic technologies, including spectroscopy, imaging, and communication, owing to their remarkable optical and electrical characteristics. This study proposes a novel combination of Bi${}_2$Se${}_3$ TIs and ReSe${}_2$ for self-powered broadband photodetectors with high sensitivity and fast response time. The Bi${}_2$Se${}_3$/ReSe${}_2$ heterojunction photodetector achieves broadband response spectra ranging for 375 nm to 1 $\mathsf{\mu }$m. It demonstrates a significant responsivity of 64 mA/W at a wavelength of 600 nm (1 mW/cm${}^2$), exhibits a rapid response speed of 345 $\mathsf{\mu }$s rise/336 $\mathsf{\mu }$s fall time, and has a 3 dB bandwidth of 1.4 kHz under zero-bias conditions. The high performance can be attributed to the suitable energy band structure of Bi${}_2$Se${}_3$/ReSe${}_2$ and high carrier mobility in surface states of Bi${}_2$Se${}_3$. Excitingly, self-powered TIs photodetectors allow for high-quality signal transmission. The TIs employed in photodetectors can stimulate the production of new optoelectronic features, but they could also be used for highly integrated photonic circuits in the future. Full article

Belle II is a particle physics experiment working at an high luminosity collider within a hard irradiation environment. The Time-Of-Propagation detector, aimed at the charged particle identification, surrounds the Belle II tracking detector on the barrel part. This detector is composed by 16 modules, each module contains a finely fused silica bar, coupled to microchannel plate photomultiplier tube (MCP-PMT) photo-detectors and readout by high-speed electronics. The MCP-PMT lifetime at the nominal collider luminosity is about one year, this is due to the high photon background degrading the quantum efficiency of the photocathode. An alternative to these MCP-PMTs is multi-pixel photon counters (MPPC), known as silicon photomultipliers (SiPM). The SiPMs, in comparison to MCP-PMTs, have a lower cost, higher photon detection efficiency and are unaffected by the presence of a magnetic field, but also have a higher dark count rate that rapidly increases with the integrated neutron flux. The dark count rate can be mitigated by annealing the damaged devices and/or operating them at low temperatures. We tested SiPMs, with different dimensions and pixel sizes from different producers, to study their time resolution (the main constraint that has to satisfy the photon detector) and to understand their behavior and tolerance to radiation. For these studies we irradiated the devices to radiation up to $5\times {10}^{11}1$ MeV neutrons equivalent (neq) per cm² fluences; we also started studying the effect of annealing on dark count rates. We performed several measurements on these devices, on top of the dark count rate, at different conditions in terms of overvoltage and temperatures. These measurements are: IV-curves, amplitude spectra, time resolution. For the last two measurements we illuminated the devices with a picosecond pulsed laser at very low intensities (with a number of detected photons up to about twenty). We present results mainly on two types of SiPMs. A new SiPM prototype developed in collaboration with FBK with the aim of improving radiation hardness, is expected to be delivered in September 2025. Full article

Heterojunctions are commonly used in optoelectronic devices to improve device performance. However, interface defects and lattice mismatch often hinder carrier transport and reduce efficiency, emphasizing the need for further exploration of diverse heterojunction structures. In this study, a heterojunction device constructed from Bi₂O₃ and Ga₂O₃ is demonstrated. The microstructures and photoelectrical properties of Bi₂O₃ and Ga₂O₃ thin films were investigated. Bi₂O₃ and Ga₂O₃ thin films show a bandgap of 3.19 and 5.10 eV. The Bi₂O₃/Ga₂O₃ heterojunction-based device demonstrates rectification characteristics, with a rectification ratio of 2.72 × 10³ at ±4.5 V and an ON/OFF ratio of 1.07 × 10⁵ (4.5/−3.9 V). Additionally, we fabricated a sandwich-structured photodetector based on the Bi₂O₃/Ga₂O₃ heterojunction and investigated its ultraviolet photoresponse performance. The photodetector exhibits low dark current (0.34 pA @ −3.9 V) and fast response rise/fall time (<40/920 ms). This work offers important perspectives on the advancement of large-area, low-cost, and high-speed Bi₂O₃ film-based heterojunction photodetectors. Full article

Photodetectors are critical components in modern optoelectronic systems due to their extensive applications in information conversion and image storage. Selenium (Se), an element with a low melting point, a broad spectral response, and rapid response speed, exhibits a disadvantage of high optical reflectivity, which leads to a reduction in response. Spiro-MeOTAD, featuring controllable energy bands and facile processing, has its practical application limited by inadequate thermal and environmental stability. In this study, Spiro-MeOTAD-1 with enhanced stability was prepared through the optimization of dopants (Zn(TFSI)₂ and CNT:TiO₂) within Spiro-MeOTAD, to create a Se-F/Spiro-MeOTAD-1 heterojunction photodetector by subsequently compositing with selenium foam (Se-F). The self-powered device demonstrates exceptional photovoltaic performance within the wavelength range of 350–800 nm at 0 V bias, exhibiting a maximum responsivity of 108 mA W⁻¹, a switching ratio of 5 × 10³, a specific detectivity of 2.96 × 10¹² Jones, and a response time of 20 ms/50 ms. The device also demonstrates elevated environmental stability pretreatment at 140 °C following a one-month period. The photodetection stability of the Se-F/Spiro-MeOTAD-1 flexible PD was demonstrated by its capacity to retain 76.3% of its initial light current when subjected to 70 bending cycles at 30°. This finding further substantiates the photodetection stability of the material under various bending conditions. Further verification of the applicability of Spiro-MeOTAD-1 in Se-based devices establishes a novel paradigm for designing photodetectors with enhanced performance and stability. Full article

One-dimensional (1D) nanomaterials have attracted considerable attention in the fabrication of nano-scale optoelectronic devices owing to their large specific surface areas, high surface-to-volume ratios, and directional electron transport channels. Compared to 1D metal oxide nanostructures, 1D metal sulfides have emerged as promising candidates for high-efficiency photodetectors due to their abundant surface vacancies and trap states, which facilitate oxygen adsorption and dissociation on their surfaces, thereby suppressing intrinsic carrier recombination while achieving enhanced optoelectronic performance. This review focuses on recent advancements in the performance of photodetectors fabricated using 1D binary metal sulfides as primary photosensitive layers, including nanowires, nanorods, nanotubes, and their heterostructures. Initially, the working principles of photodetectors are outlined, along with the key parameters and device types that influence their performance. Subsequently, the synthesis methods, device fabrication, and photoelectric properties of several extensively studied 1D metal sulfides and their composites, such as ZnS, CdS, SnS, Bi₂S₃, Sb₂S₃, WS₂, and SnS₂, are examined. Additionally, the current research status of 1D nanostructures of MoS₂, TiS₃, ReS₂, and In₂S₃, which are predominantly utilized as 2D materials, is explored and summarized. For systematic performance evaluation, standardized metrics encompassing responsivity, detectivity, external quantum efficiency, and response speed are comprehensively tabulated in dedicated sub-sections. The review culminates in proposing targeted research trajectories for advancing photodetection systems employing 1D binary metal sulfides. Full article

This work presents a high-speed hybrid communication system integrating Underwater Optical Wireless Communication (UOWC), Multimode Fiber (MMF), and Free-Space Optics (FSO) channels, leveraging Orbital Angular Momentum (OAM) beams for enhanced data transmission. A Photodetector, Remodulate, and Forward Relay (PRFR) is employed to enable wavelength conversion from 532 nm for UOWC to 1550 nm for MMF and FSO links. Four distinct OAM beams, each supporting a 5 Gbps data rate, are utilized to evaluate the system’s performance under two scenarios. The first scenario investigates the effects of absorption and scattering in five water types on underwater transmission range, while maintaining fixed MMF length and FSO link. The second scenario examines varying FSO propagation distances under different fog conditions, with a consistent underwater link length. Results demonstrate that water and atmospheric attenuation significantly impact transmission range and received optical power. The proposed hybrid system ensures reliable data transmission with a maximum overall transmission distance of 1125 m (comprising a 25 m UOWC link in Pure Sea (PS) water, a 100 m MMF span, and a 1000 m FSO range in clear weather) in the first scenario. In the second scenario, under Light Fog (LF) conditions, the system achieves a longer reach of up to 2020 m (20 m UOWC link + 100 m MMF span + 1900 m FSO range), maintaining a BER ≤ 10⁻⁴ and a Q-factor around 4. This hybrid design is well suited for applications such as oceanographic research, offshore monitoring, and the Internet of Underwater Things (IoUT), enabling efficient data transfer between underwater nodes and surface stations. Full article

Two-dimensional materials have emerged as core components for next-generation optoelectronic devices due to their quantum confinement effects and tunable electronic properties. Indium selenide (InSe) demonstrates breakthrough photoelectric performance, with its remarkable light-responsive characteristics spanning from visible to near-infrared regions, offering application potential in high-speed imaging, optical communication, and biosensing. This study investigates the doping characteristics of InSe using first-principles calculations, focusing on the doping and adsorption behaviors of Argentum (Ag) and Bismuth (Bi) atoms in InSe and their effects on its electronic structure. The research reveals that Ag atoms preferentially adsorb at interlayer vacancies with a binding energy of −2.19 eV, forming polar covalent bonds. This reduces the band gap from the intrinsic 1.51 eV to 0.29–1.16 eV and induces an indirect-to-direct band gap transition. Bi atoms doped at the center of three Se atoms exhibit a binding energy of −2.06 eV, narrowing the band gap to 0.19 eV through strong ionic bonding, while inducing metallic transition at inter-In sites. The introduced intermediate energy levels significantly reduce electron transition barriers (by up to 60%) and enhance carrier separation efficiency. This study links doping sites, electronic structures, and photoelectric properties through computational simulations, offering a theoretical framework for designing high-performance InSe-based photodetectors. It opens new avenues for narrow-bandgap near-infrared detection and carrier transport optimization. Full article

Recent advancements in ultraviolet (UV) photodetection technology have driven intensive research on zinc oxide (ZnO) nanomaterials due to their exceptional optoelectronic properties. This review systematically examines the fundamental detection mechanisms in ZnO-based UV photodetectors (UVPDs), including photoconductivity effects, the threshold dimension phenomenon and light-modulated interface barriers. Based on these mechanisms, a large surface barrier due to surface-adsorbed O₂ is generally constructed to achieve a high sensitivity. However, this improvement is obtained with a decrease in response speed due to the slow desorption and re-adsorption processes of surface O₂ during UV light detection. Various improvement strategies have been proposed to overcome this drawback and keep the high sensitivity, including ZnO–organic semiconductor interfacing, defect engineering and doping, surface modification, heterojunction and the Schottky barrier. The general idea is to modify the adsorption state of O₂ or replace the adsorbed O₂ with another material to build a light-regulated surface or an interface barrier, as surveyed in the third section. The critical trade-off between sensitivity and response speed is also addressed. Finally, after a summary of these mechanisms and the improvement methods, this review is concluded with an outlook on the future development of ZnO nanomaterial UVPDs. Full article

Two-dimensional (2D) Xenes, including graphene where X represents C, Si, Ge, and Te, represent a groundbreaking class of materials renowned for their extraordinary electrical transport properties, robust photoresponse, and Quantum Spin Hall effects. With the growing interest in 2D materials, research on germanene-based systems remains relatively underexplored despite their potential for tailored optoelectronic functionalities. Herein, we demonstrate a facile and rapid chemical synthesis of tellurium-doped germanene hydride (Te-GeH) nanostructures (NSs), achieving precise atomic-scale control. The 2D Te-GeH NSs exhibit a broadband optical absorption spanning ultraviolet (UV) to visible light (VIS), which is a critical feature for multifunctional photodetection. Leveraging this property, we engineer photoelectrochemical (PEC) photodetectors via a simple drop-casting technique. The devices deliver excellent performance, including a high responsivity of 708.5 µA/W, ultrafast response speeds (92 ms rise, 526 ms decay), and a wide operational bandwidth. Remarkably, the detectors operate efficiently at zero-bias voltage, outperforming most existing 2D-material-based PEC systems, and function as self-powered broadband photodetectors. This work not only advances the understanding of germanene derivatives but also unlocks their potential for next-generation optoelectronics, such as energy-efficient sensors and adaptive optical networks. Full article

Dual-mode photodetectors (DmPDs) have attracted considerable interest due to their ability to integrate multiple functionalities into a single device. However, 2D material/InP heterostructures, which exhibit built-in electric fields and rapid response characteristics, have not yet been utilized in DmPDs. In this work, we fabricate a high-performance DmPD based on a graphene/InP Van der Waals heterostructure in a facile way, achieving a broadband response from ultraviolet-visible to near-infrared wavelengths. The device incorporates two top electrodes contacting monolayer chemical vapor deposition (CVD) graphene and a bottom electrode on the backside of an InP substrate. By flexibly switching among these three electrodes, the as-fabricated DmPD can operate in a self-powered photovoltaic mode for energy-efficient high-speed imaging or in a biased photoconductive mode for detecting weak light signals, fully demonstrating its multifunctional detection capabilities. Specifically, in the self-powered photovoltaic mode, the DmPD leverages the vertically configured Schottky junction to achieve an on/off ratio of 8 × 10³, a responsivity of 49.2 mA/W, a detectivity of 4.09 × 10¹¹ Jones, and an ultrafast response, with a rising time (τ_r) and falling time (τ_f) of 2.8/6.2 μs. In the photoconductive mode at a 1 V bias, the photogating effect enhances the responsivity to 162.5 A/W. This work advances the development of InP-based multifunctional optoelectronic devices. Full article

With the rapid development of high-speed imaging, aerospace, and telecommunications, high-performance photodetectors across a broadband spectrum are urgently demanded. Due to abundant surface configurations and exceptional electronic properties, two-dimensional (2D) materials are considered as ideal candidates for broadband photodetection applications. However, broadband photodetectors with both high responsivity and fast response time remain a challenging issue for all the researchers. This review paper is organized as follows. Introduction introduces the fundamental properties and broadband photodetection performances of transition metal dichalcogenides (TMDCs), perovskites, topological insulators, graphene, and black phosphorus (BP). This section provides an in-depth analysis of their unique optoelectronic properties and probes the intrinsic physical mechanism of broadband detection. In Two-Dimensional Material-Based Broadband Photodetectors, some innovative strategies are given to expand the detection wavelength range of 2D material-based photodetectors and enhance their overall performances. Among them, chemical doping, defect engineering, constructing heterostructures, and strain engineering methods are found to be more effective for improving their photodetection performances. The last section addresses the challenges and future prospects of 2D material-based broadband photodetectors. Furthermore, to meet the practical requirements for very large-scale integration (VLSI) applications, their work reliability, production cost and compatibility with planar technology should be paid much attention. Full article

Gallium oxide (Ga₂O₃), an ultrawide bandgap semiconductor, is an ideal material for solar-blind photodetectors, but challenges such as low responsivity and response speed persist. In this paper, one-dimensional (1D) Ga₂O₃ nanorods were designed to achieve high photodetection performance due to their effective light absorption and light field confinement. Through modulating source concentration, pH value, temperature, and reaction time, 1D β-Ga₂O₃ nanorods were controllably fabricated using a cost-effective hydrothermal method, followed by post-annealing. The nanorods had a diameter of ~500 nm, length from 0.5 to 3 μm, and structure from nanorods to spindles, indicating that different β-Ga₂O₃ nanorods can be utilized controllably through tuning reaction parameters. The 1D β-Ga₂O₃ nanorods with a high length-to-diameter ratio were chosen to construct metal-semiconductor-metal type photodetectors. These devices exhibited a high responsivity of 8.0 × 10⁻⁴ A/W and detectivity of 4.58 × 10⁹ Jones under 254 nm light irradiation. The findings highlighted the potential of 1D Ga₂O₃ nanostructures for high-performance solar-blind ultraviolet photodetectors, paving the way for future integrable deep ultraviolet optoelectronic devices. Full article

Optoelectronic devices combining single-layer graphene (SLG) and colloidal semiconducting nanocrystal (NC) heterojunctions have recently gained significant attention as efficient hybrid photodetectors. While most research has concentrated on systems using heavy metal-based semiconductor NCs, there is a need for further exploration of environmentally friendly nanomaterials, such as Cu_2−xS. Chemical ligands play a crucial role in these hybrid photodetectors, as they enable charge transfer between the NCs and SLG. This study investigates the photoresponse of an SLG/Cu_2−xS NCs heterojunction, comparing the effect of two short molecules—tetrabutylammonium iodide (TBAI) and 3,4-dimethylbenzenethiol (DMBT)—as surface ligands on the resulting structures. We have analysed charge transfer at the heterojunctions between SLG and the Cu_2−xS NCs before and after modification with TBAI and DMBT using Raman spectroscopy and transconductance measurements under thermal equilibrium. The photoresponse of two hybrid devices based on three layers of Cu₂₋_xS NCs, deposited in one case on SLG/Cu_2−xS/TBAI (“TBAI-only” device) and in the other on SLG/Cu_2−xS/DMBT (“DMBT + TBAI” device), with a TBAI treatment applied, for both, after each layer deposition, has been evaluated under 450 nm laser diode illumination. The results indicate that the TBAI-only device exhibited a significant increase in photocurrent (4 μA), with high responsivity (40 mA/W) and fast response times (<1 s), while the DMBT + TBAI device had lower photocurrent (0.2 μA) and responsivity (2.4 μA), despite similar response speeds. The difference is attributed to DMBT’s π–π interactions with SLG, which enhances electronic coupling but reduces SLG’s mobility and responsivity. Full article