Ultrafast Photodetectors Research Articles

"Exploring the complementary Potential of DVT-Grown InxMo1-xS2 (x = 0.05 & 0.1) for Enhanced Photoelectrochemical Photodetectors and Dye Degradation"

The platform used in this work, InxMo1-xS2 (x = 0.05 & 0.1) nanosheets, allows for exploration of two crucial areas: remediation of the environment and optoelectronic applications. The sonochemical exfoliation approach generated the MoS2 nanosheets. The exfoliated MoS2 has a 2H-hexagonal lattice structure and a P63/mmc space group. The MoS2 nanosheets' lateral shape was observed using transmission electron microscopy (TEM), and their extremely crystalline nature was verified by selected area electron diffraction (SAED). The absorption spectra of MoS₂ nanosheets show unique A and B excitonic resonances. It investigates pulse photo-response characteristics associated with dye degradation methods, emphasizing InxMo1-xS2 (x = 0.05 & 0.1) efficiency in destroying dyes and enabling photocatalytic degradation, particularly with methylene blue (MB) solutions. After 120 min of exposure to light, these nanosheets are effective, breaking down organic pigments. The work also indicates a distinct pulse photoresponse in InxMo1-xS2 (x = 0.05 & 0.1) Nanosheets, increasing their potential as ultrafast photodetectors for optoelectronics. Built-in electrodes produce noticeable photocurrents under 8 mV bias and polychromatic light, demonstrating a strong photovoltaic effect. The In0.05Mo0.95S2 nanosheet-based working electrodes are significantly photovoltaic, with a photocurrent of 3.427 mA under an 8 mV bias and 100 mW/cm2 of polychromatic light. These electrodes have a remarkable peak photoresponsivity of 2.715 A/W under optimum conditions. In the end, this work demonstrates the potential of InxMo1-xS2 (x = 0.05 & 0.1) nanosheets in improving optoelectronic devices and environmentally friendly solutions by revealing when dye degradation and pulse photo-response interact with one another.

Sliding Ferroelectricity Induced Ultrafast Switchable Photovoltaic Response in ε-InSe Layers.

2D sliding ferroelectric semiconductors have greatly expanded the ferroelectrics family with the flexibility of bandgap and material properties, which hold great promise for ultrathin device applications that combine ferroelectrics with optoelectronics. Besides the induced different resistance states for non-volatile memories, the switchable ferroelectric polarizations can also modulate the photogenerated carriers for potentially ultrafast optoelectronic devices. Here, it is demonstrated that the room temperature sliding ferroelectricity can be used for ultrafast switchable photovoltaic response in ε-InSe layers. By first-principles calculations and experimental characterizations, it is revealed that the ferroelectricity with out-of-plane (OOP) polarization only exists in even layer ε-InSe. The ferroelectricity is also demonstrated in ε-InSe-based vertical devices, which exhibit high on-off ratios (≈104) and non-volatile storage capabilities. Moreover, the OOP ferroelectricity enables an ultrafast (≈3ps) bulk photovoltaic response in the near-infrared band, rendering it a promising material for self-powered reconfigurable and ultrafast photodetector. This work reveals the essential role of ferroelectric polarization on the photogenerated carrier dynamics and paves the way for hybrid multifunctional ferroelectric and optoelectronic devices.

Photodetectors Based on ZrS3/MoS2 Heterostructures.

High-performance photodetectors with the detection capability of linearly polarized light have broad applications in both military and civilian fields. Quasi-one-dimensional ZrS3 as an emerging anisotropic two-dimensional material has come under the spotlight owing to its intriguing properties. However, the performance of the ZrS3 photodetector is seriously restricted by its low responsivity. Herein, a novel high-performance photodetector based on the van der Waals ZrS3/MoS2 heterostructure is proposed. Attributed to the charge trapping-assisted photogating effect, interlayer carrier transitions, and fast spatial separation of the photogenerated electron-hole pairs, the device displays superior photoresponse characteristics ranging from the ultraviolet to the visible spectrum in terms of high responsivity up to 212 A/W, an extraordinary external quantum efficiency of 8.5 × 104%, and a prompt rise/decay time of 0.19/0.38 ms. In addition, owing to the profound birefringence and dichroism effects in ZrS3 together with strong light-matter interactions in the heterostructure, profound linear-polarization sensitivity is demonstrated with a dichroic ratio of about 2.8. Overall, this photodetector not only is integrated with the excellent properties of ZrS3 and monolayer MoS2 but also further enhances the advantages through interlayer couplings, which demonstrate the strong potential of the ZrS3-based devices for high-performance, ultrafast, and polarization-sensitive photodetection.

Nanopatterning Induced Si Doping in Amorphous Ga2O3 for Enhanced Electrical Properties and Ultra-Fast Photodetection.

Ga2O3 has emerged as a promising material for the wide-bandgap industry aiming at devices beyond the limits of conventional silicon. Amorphous Ga2O3 is widely being used for flexible electronics, but suffers from very high resistivity. Conventional methods of doping like ion implantation require high temperatures post-processing, thereby limiting their use. Herein, an unconventional method of doping Ga2O3 films with Si, thereby enhancing its electrical properties, is reported. Ion-beam sputtering (500eV Ar+) is utilized to nanopattern SiO2-coated Si substrate leaving the topmost part rich in elemental Si. This helps in enhancing the carrier conduction by increasing n-type doping of the subsequently coated 5nm amorphous Ga2O3 films, corroborated by room-temperature resistivity measurement and valence band spectra, respectively, while the nanopatterns formed help in better light management. Finally, as proof of concept, metal-semiconductor-metal (MSM) photoconductor devices fabricated on doped, rippled films show superior properties with responsivity increasing from 6 to 433mAW-1 while having fast detection speeds of 861µs/710µs (rise/fall time) as opposed to non-rippled devices (377ms/392ms). The results demonstrate a facile, cost-effective, and large-area method to dope amorphous Ga2O3 films in a bottom-up approach which may be employed for increasing the electrical conductivity of other amorphous oxide semiconductors as well.

Controlled growth of Sb2Te3 nanoplates and their applications in ultrafast near-infrared photodetection

This work presents a study on controlled growth of Sb2Te3 nanoplates via chemical vapor deposition and their potential applications in near-infrared photodetectors. The lateral size of the nanoplates is investigated by studying two main growth parameters: argon carrier gas flow rate and growth temperature. As the argon gas flow rate increases from 20 sccm to 60 sccm, the average lateral size of Sb2Te3 nanoplates gradually increases from 3.68 μm to 10.31 μm as the growth of Sb2Te3 nanoplate under lower argon gas flow rate is limited by the Sb2Te3 molecules delivered onto the substrate surface. In contrast, at a higher argon gas flow rate of 80 sccm, the average lateral size decreases to 8.77 μm due to the combined effect of a saturated substrate surface reaction rate and increased heat loss by convection. Similarly, the average lateral size of Sb2Te3 nanoplates progressively increases from 4.21 μm at a growth temperature of 400 °C to 10.31 μm at 410 °C, which could be ascribed to the limited reaction rate of active Sb2Te3 molecules/atoms on the substrate surface at lower growth temperature. The average size then saturates at 10.06 μm at 415 °C upon further increasing the growth temperature as the growth of Sb2Te3 nanoplates is limited by the amount of vaporized Sb2Te3 molecules delivered onto the substrate surface. The fabricated photodetector based on Sb2Te3 nanoplates presents a wide spectral response from 400 to 980 nm, with a maximum photo-response observed at 850 nm. Notably, the photo-response time of the Sb2Te3 nanoplate photodetector is measured as small as 64 μs, indicating its ultrafast photo-response characteristics. The photodetector also exhibits good performance with a responsivity of 155.6 mA W−1 and a specific detectivity of 1.68 × 109 Jones at 850 nm with a light power intensity of 130.0 mW cm−2.

Resonant Tunneling-Enhanced Photoresponsivity in a Twisted Graphene van der Waals Heterostructure.

Leveraging its ultrahigh carrier mobility, zero-bandgap linear dispersion, and extremely short response time, graphene exhibits remarkable potential in ultrafast broad-band photodetection. Nonetheless, the inherently low responsivity of graphene photodetectors, due to the low photogenerated carrier density, significantly impedes the development of practical devices. In this study, we present an improved photoresponse within a graphene-hexagonal boron nitride-graphene vertical tunnel junction device, where the crystallographic orientation of the two graphene electrodes is aligned. Through meticulous device structure design and the adjustment of bias and gate voltages, we observe a 2 orders of magnitude increase in tunneling photocurrent, which is attributed to the momentum-conserving resonant electron tunneling. The enhanced external photoresponsivity is evident across a wide temperature and spectral range and achieves 0.7 A/W for visible light excitation. This characteristic, coupled with the device's negative differential conductance, suggests a novel avenue for highly efficient photodetection and high-frequency, logic-based optoelectronics using van der Waals heterostructures.

Ultrafast and self-driven flexible photodetector based on vertical MoS2/Si heterojunction through enhanced light-trapping structures and Al2O3 interface passivation

The self-driven flexible photodetector is vitally important for next-generation optoelectronics. Two-dimensional (2D) molybdenum sulfide (MoS2) as a typical family member of transition-metal dichalcogenides (TMDs) has shown larger potential applications in the high-sensitivity photodetection due to its self-physical properties. Herein, the ultrafast MoS2/Si flexible photodetector with ultrathin Al2O3 passivation interface and high light-trapping structures was fabricated. The MoS2/Al2O3/Si flexible photodetector exhibits excellent performance with a high responsivity of 0.047 A/W, detectivity up to 5.67 × 1011 Jones and rise/fall time of 25.6/3.2 μs. Furthermore, this optoelectronic device can withstand bending angles of 120° and work well after 500 bending times. This unique performance can be attributed to the flexible Si substrate with good mechanical properties, high-light trapping structures and an Al2O3 passivation interface. This device can find potential applications in e-skins, flexible displays and smart health care.

Synergistic exploration of dye degradation and pulse photoresponse using MoS2 nanosheets: Towards sustainable remediation and optoelectronic advancements

Two essential areas of research with important implications for environmental cleanup and optoelectronic device applications are dye degradation and the comprehension of the pulse photo-response of transition metal dichalcogenide (TMDC) materials. Using MoS2 Nanosheets, this study evaluates the pulse photo-response characteristics of dyes and their degradation mechanisms. The article focuses into the effectiveness of MoS2 materials in dye removal as well as their function in photocatalytic degradation processes. Additionally, the MoS2 nanosheets are easy to utilise in solutions containing methylene blue (MB) and can be used as a high-performance recyclable photocatalyst to photodegrade organic dyes like methylene blue (MB) in around 120 min when exposed to light. The pulse photoresponse behaviour of MoS2 Nanosheets (NSs) is also investigated, with an emphasis on their distinct charge carrier dynamics and potential uses in ultrafast photodetectors. The working electrodes constructed from MoS2 nanosheets demonstrate an obvious photovoltaic effect with a photocurrent of 6.920 A/cm2 at zero bias and 100 mW/cm2 of polychromatic light. Due to optimal conditions, the maximum photoresponsivity of 5.669 mA/W and Detectivity of 7.708 × 108 Jones is achieved. The intention is to provide details on the way dye degradation and pulse photo-response interact synergistically in MoS2 nanosheets and highlight their potential for improved optoelectronic devices and environmentally friendly remediation.

A simple 230 MHz photodetector based on exfoliated WSe2 multilayers.

We demonstrate 230 MHz photodetection and a switching energy of merely 27 fJ using WSe2 multilayers and a very simple device architecture. This improvement over previous, slower WSe2 devices is enabled by systematically reducing the RC constant of devices through decreasing the photoresistance and capacitance. In contrast to MoS2, reducing the WSe2 thickness toward a monolayer only weakly decreases the response time, highlighting that ultrafast photodetection is also possible with atomically thin WSe2. Our work provides new insights into the temporal limits of pure transition metal dichalcogenide photodetectors and suggests that gigahertz photodetection with these materials should be feasible.

Tri-layered Si/Co3O4/ZnO heterojunction for high-performance visible photodetection

Tri-layered heterojunction devices based on oxide thin films are attracting significant attention for ultra-fast visible photodetection.

Ultrafast and broadband photodetection based on selenized AgSbS2 thin films prepared by spray pyrolysis deposition and modified with indium nitrate

Broadband AgSbS2(Se) photodetectors are fabricated using spray pyrolysis with a post-selenization process. Indium nitrate is introduced to break the surface blockade to selenidation, largely enhancing the light response range and photocurrent.

MOFs-derived hierarchical NiO-Co3O4 for versatile pulses generation

Polyhedral NiO-Co3O4 materials, as a novel type of metal organic frameworks (MOFs), are considered to be attractive emerging materials in the fields of optoelectronics, energy storage systems, sensing and catalysis because of their high specific surface area, rich variable metal sites and unique morphology. Ultrafast pulse has become an important research tool in basic research and industrial application fields, including supercontinuum generation, laser material processing, laser surgery, lidar and terahertz generation. The saturable absorber (SA) is a key component that affects the laser parameters and generates ultrafast pulses, so it has caused an upsurge in the research of SA. Although MOFs and their derivatives have attracted the attention of researchers in many fields, few works have been carried out in ultrafast photonics. Here, we use the cobalt-based zeolite imidazole framework (ZIF-67-Co) as a precursor to synthesize NiO-Co3O4 polyhedron by calcination, and utilize it as an effective SA in a compact erbium-doped fiber laser (EDFL). The NiO-Co3O4 SA was measured based on home-made double-arm measurement system, which showed that its modulation depth was 5.6%. It shows that high-quality Q-switched mode-locking (QML) with a repetition rate of 5.2 MHz and a pulse width of 1.41 ps can be obtained when the pump power reaches 251.1 mW. After further improvement of the EDFL, we obtained a stable continuous wave mode-locked (CWML) pulse with a pulse duration of 1.35 ps. This is the first demonstration of a versatile pulse fiber laser based on a NiO-Co3O4 polyhedral SA. This work shows that the novel NiO-Co3O4 polyhedron is expected to serve as a highly potential nonlinear optical element in the fields of ultrafast photonics, light modulators and photodetectors.

Role of oxygen functional groups and attachment of Au nanoparticles on graphene oxide sheets for improved photodetection performance.

Integrating low-dimensional graphene oxide (GO) with conventional Si technology offers innovative strategies for developing ultrafast wideband photodetectors. In this study, we synthesized GO and explored its potential application in broadband photodetection alongside silicon heterostructures. The as-synthesized GO contains various oxygen functional groups, as evidenced by X-ray photoelectron and Fourier transform infrared spectroscopy. These functional groups contribute to increased photo absorption, enhancing photodetection performance. The systematic reduction of these functional groups from the GO surface via thermal annealing decreases photo absorption and consequently lowers the photocurrent. This reduction diminishes photo absorption and amplifies the dark current by approximately 25 times, from 20 nA to 496 nA. This dark current increase is attributed to the electron mobility following the reduction of functional groups. However, attaching plasmonic gold nanoparticles (Au NPs) to the GO surface enhances UV-Vis absorption in the visible region, enabling broadband detection. The even distribution of attached Au NPs on the GO surface is confirmed through field emission transmission electron microscopy. While thermal annealing of GO diminishes the responsivity from 4.6 A W-1 to 3.0 A W-1, the attachment of Au NPs augments the responsivity by more than two-fold, reaching 10.0 A W-1. Thus, it highlights the importance of rich oxygen functional groups in GO and the attachment of Au NPs to achieve more efficient photo-sensing properties.

Ultrafast and Broad-Band Graphene Heterojunction Photodetectors with High Gain.

Graphene possesses an exotic band structure that spans a wide range of important technological wavelength regimes for photodetection, all within a single material. Conventional methods aimed at enhancing detection efficiency often suffer from an extended response time when the light is switched off. The task of achieving ultrafast broad-band photodetection with a high gain remains challenging. Here, we propose a devised architecture that combines graphene with a photosensitizer composed of an alternating strip superstructure of WS2-WSe2. Upon illumination, n+-WS2 and p+-WSe2 strips create alternating electron- and hole-conduction channels in graphene, effectively overcoming the tradeoff between the responsivity and switch time. This configuration allows for achieving a responsivity of 1.7 × 107 mA/W, with an extrinsic response time of 3-4 μs. The inclusion of the superstructure booster enables photodetection across a wide range from the near-ultraviolet to mid-infrared regime and offers a distinctive photogating route for high responsivity and fast temporal response in the pursuit of broad-band detection.

103 GHz germanium-on-silicon photodiode enabled by an optimized U-shaped electrode

High-performance germanium photodiodes are crucial components in silicon photonic integrated circuits for large-capacity data communication. However, the bandwidths of most germanium photodiodes are limited by the intractable resistance–capacitance parasitic effect. Here, we introduce a unique U-shaped electrode to alleviate this issue, reducing the parasitic effect by 36% without compromising any other performance. Experimentally, a large bandwidth of 103 GHz, an optical responsivity of 0.95 A/W at 1550 nm, and a dark current as low as 1.3 nA are achieved, leading to a record high specific detectivity. This is the first breakthrough to 100 GHz bandwidth among all vertical germanium photodiodes, to the best of our knowledge. Open eye diagrams of 120 Gb/s on-off keying and 200 Gb/s four-level pulse amplitude signals are well received. This work provides a promising solution for chip-based ultra-fast photodetection.

Controlled Synthesis of a High‐Mobility Bi3O2.5Se2 Semiconductor by Oxidation of Bi2Se3 for Fast and Highly Sensitive Photodetectors

AbstractThe search of new high‐mobility two‐dimensional (2D) semiconductors is crucial for the development of next‐generation photodetectors, since current photodetectors based on single 2D semiconductors usually cannot simultaneously own ultrafast response rate and ultrahigh sensitivity. Here, using a facial method of sequentially oxidizing Bi2Se3 at optimal O content, a series of bismuth oxyselenide semiconductors (Bi3O2.5Se2, Bi2O2Se, Bi2SeO5) with appealing electronic applications are successfully synthesized. The crystal and band structures of a superlattice‐free Bi3O2.5Se2 phase are resolved by 3D electron diffraction and density functional theory calculations, showing a unique non‐neutral layered structure, moderate band gap, and small effective mass. More importantly, the concept of Bi2Se3 + O2 can be extended to synthesize the superlattice‐free Bi3O2.5Se2 ultrathin films by chemical vapor deposition, whose room‐temperature mobility can be as high as ≈150 cm2 V−1 s−1 based on Hall measurements. The ultrathin Bi3O2.5Se2 photodetectors with a simple device configuration simultaneously own ultrafast response time (≈31 µs), ultrahigh responsivity (≈8 × 104 A/W), and large detectivity (≈8 × 1013 Jones). This work not only introduces a facile way to regulate the phase in the bismuth oxyselenide family, but also provides an alternative candidate for ultrafast and ultrasensitive photodetectors.

Graphene‐Based Silicon Photonic Devices for Optical Interconnects

AbstractThe exponential growth of global data traffic is driven by the unprecedented digitalization of the world. To meet the demands of next‐generation high‐capacity data communication systems, innovative solutions are required. Silicon photonics has gained significant attention due to its ability to integrate multiple core functions of optical interconnects into small‐scale chips, offering cost‐effective and scalable manufacturing capabilities. By leveraging silicon photonics, it becomes possible to address the challenge of scaling system complexity while reducing size, cost, and energy consumption. Despite its advantages, silicon has inherent limitations that restrict its application range, such as the weak plasma dispersion effect and relatively large bandgap. Recently, graphene has emerged as a promising solution for traditional silicon photonics because of its exceptional electrical and optical properties. For instance, graphene on a silicon chip enables nearly pure phase modulation and ultrafast photodetection beyond 500 GHz. Moreover, the demonstrated compatibility of graphene with wafer‐level integration paves the way for mass production of graphene‐based silicon photonic devices, offering improved yield, scalability, and cost‐effectiveness. In this work, a comprehensive review is provided, focusing on graphene‐based silicon photonic devices and their applications in optical interconnects, aiming to explore the potential of graphene in advancing silicon photonic technology.

Ag nanoparticle assisted vertically aligned β-Ga2O3 nanowire deposited by GLAD technique for ultrafast photodetection

In this study, we report the fabrication of Silver (Ag) nanoparticle (NP) assisted vertically oriented β-Ga2O3 nanowires on Silicon (Si) - substrate by the Glancing angle deposition (GLAD) technique. The fabricated samples were annealed at 900 °C. The optoelectronic properties of both As-deposited and annealed devices are studied thoroughly. The sample shows an increase in average crystallite size upon annealing with a decrease in lattice strain and dislocation density. FEG-SEM image confirms the growth of well-aligned vertically oriented nanowires with Ag NP in the midway of each nanowire. The UV–Vis absorption spectra show that Ag NP's presence results in the appearance of a significant absorption hump in the visible range, thereby broadening the light absorption capability of β-Ga2O3. The improvement in crystalline quality and reduction in defects after annealing resulted in a better response for the annealed device. These results indicate that annealing the Ag NP-assisted β-Ga2O3 NW device could become a feasible option for high-speed photodetectors, as it demonstrates a faster photoresponse time and a lower turn-on voltage.

An adaptive laser processing method of multilayer heterogeneous materials by monitoring dynamic spectrum at kHz-MHz level

Laser micro/nano processing exhibits significant advantages in manufacturing capability and performance. However, the properties of ablated materials cannot be sensed and identified during processing is an intractable challenge. In particular, multilayer heterogeneous materials often evolve into excessive residues and damages during laser selective removal. In this study, we developed an adaptive laser processing method that includes material interface adaptive and laser power adaptive for selective removal of multilayer heterogeneous materials by monitoring dynamic spectrum at kHz-MHz level. The mechanism of interface sensing and the threshold of laser selective removal of multilayer materials were investigated. Dual-channel parallel detection mode of the blazed grating with the ultrafast photodetector at the kHz-MHz pulse level has been designed and verified for monitoring adjacent layers synchronously. High-speed signals with a pulse width of 30 ns and a repetition frequency of 0–15 MHz were identified by the Field Programmable Logic Gate Array (FPGA), and pulse-level closed-loop feedback was finished. Patterned selective removal on an FR-4 copper clad laminate (CCL) and flexible printed circuit (FPC) was completed. The method exhibited sensitive signal characteristics, accurately sensed the material interface, and provided a clear criterion for identifying the removal process of multilayer materials by quantitative analysis of signal variation, which provides an innovative scheme for laser intelligent manufacturing of multilayer heterogeneous materials.

Broadband and ultrafast photodetector based on PtSe2 synthesized on hBN using molecular beam epitaxy

Two-dimensional (2D) van der Waals materials are potential candidates for high-performance optoelectrical devices owing to the bandgap modulation, high on/off ratio, and ultra-stability. However, the challenge of synthesizing large-area, uniform, and high-quality 2D van der Waals materials should be addressed to manufacture large-scale and uniform optoelectrical devices using these materials. Although several previous studies investigated synthesis methods using chemical vapor deposition and molecular beam epitaxy (MBE), there are certain limitations such as the non-uniformity, lots of grain boundaries, and low carrier mobility. Here, by studying a method for synthesizing PtSe2 on hBN buffer layer using MBE, we fabricated a PtSe2-based broadband photodetector. The high-quality PtSe2 synthesized on hBN was evaluated using Raman spectroscopy and scanning transmission electron spectroscopy. These revealed that the synthesized PtSe2 had a high quality and small grain boundary compared with PtSe2 synthesized on SiO2. Owing to the reduction in the carrier scattering and carrier recombination because of the high-quality and small grain boundaries, the photodetector using PtSe2 synthesized on hBN displayed optoelectrical properties that were significantly better than those of PtSe2 synthesized on SiO2. Therefore, using hBN as a buffer layer for PtSe2 growth, a remarkable performance of complex optoelectrical devices could be achieved.