High-performance Photodetectors Research Articles

Van Hove Singularity-Enhanced Raman Scattering and Photocurrent Generation in Twisted Monolayer-Bilayer Graphene.

Twisted monolayer-bilayer graphene (TMBG) has recently emerged as an exciting platform for exploring correlated physics and topological states with rich tunability. Strong light-matter interaction was realized in twisted bilayer graphene, boosting the development of broadband graphene photodetectors from the visible to infrared spectrum with high responsivity. Extending this approach to the case of TMBG will help design advanced quantum nano-optoelectronic devices because of the reduced symmetry of the system. Here, we observe the formation of van Hove singularities (VHSs) in TMBG by monitoring the significant enhancement of the Raman intensity of the G peak and the intensity ratio of G and 2D peaks. The strong interlayer coupling also leads to the appearance of twist-angle-dependent Raman R and R' peaks in TMBG. Furthermore, the constructed graphene photodetectors from 13.5°-TMBG show significantly enhanced photoresponsivity (∼31 folds of monolayer graphene and ∼15 folds of trilayer graphene) when the energy of incident photons matches the interval energy between the two VHSs in the conduction and valence bands. Our findings establish TMBG as a tunable platform for investigating the light-matter interaction and designing high-performance graphene photodetectors with combined high responsivity and high selectivity.

Enhanced Performance of a Self-Powered Au/WSe2/Ta2NiS5/Au Heterojunction by the Interfacial Pyro-phototronic Effect.

The growing need for wearable electronics and self-powered electronic devices has driven the successful development of self-powered two-dimensional (2D) photodetectors using the photovoltaic effect of Schottky and p-n junctions. However, there is an urgent need to develop multifunctional photodetectors capable of harvesting energy from different sources to overcome their limitations in efficiency and cost. While the pyro-phototronic effect has been shown to effectively influence optoelectronic processes in heterojunctions, the number of reported two-dimensional heterojunctions exhibiting interfacial pyroelectricity is still limited, and the responsivity and detectivity based on such heterojunctions tend to be low. In this study, a photodetector based on an Au/WSe2/Ta2NiS5/Au heterojunction was designed and fabricated. By harnessing the interfacial pyro-phototronic effect arising from the built-in electric fields at the Au/WSe2 Schottky junction and WSe2/Ta2NiS5 heterojunction, the photodetector exhibits a broadband response range of 405-1064 nm, with approximately 12 times enhancement in output current compared to solely relying on the photovoltaic effect. Under 660 nm light irradiation, the self-powered photodetector exhibits a responsivity of 121 mA/W, an external quantum efficiency of 22.64%, and a specific detectivity of 2 × 1012 Jones. Notably, its pyroelectric coefficient exceeds 8 × 103 μC·m-2·K-1. These findings pave the way for effectively detecting weak light and temperature variation while presenting a new strategy for developing high-performance photodetectors utilizing the interfacial pyro-phototronic effect.

(Invited) In Situ and Operando Scattering Studies on Quantum Dot-Based Devices

Colloidal quantum dots (QDs) made e.g. of PbS are attractive for various optoelectronic applications due to their tunable band gap with a large absorption wavelength range from the visible to the near-infrared region. Moreover, due to the high intrinsic permittivity, the exciton binding energy of PbS is smaller than in cadmium chalcogenide QDs and polymer materials, which is beneficial for devices driven by charge carrier generation and transport, e.g. photovoltaics and photodetectors.In this work, we introduce wet chemical deposition methods beyond spin coating such as printing and spray deposition of QDs as a facile and potentially large-scale deposition method for high-performance photodetectors. The inner structures including the inter-dot distance of neighboring QDs and the structure, in the deposited QD solids, are studied by grazing-incidence small-angle X-ray scattering (GISAXS). In addition, the facet orientation of the QDs in the QD solids is characterized by grazing-incidence wide-angle X-ray scattering (GIWAXS). In particular, in situ GISAXS/GIWAXS studies during film formation are able to provide detailed information about the complex kinetic processes [1,2]. Operando GISAXS/GIWAXS studies on QD-based devices such as solar cells bring an in-depth understanding of the degradation mechanisms, which is key for improving the device stability and thereby bringing these novel materials into real-world applications [3]. Superlattice deformation in QD films on flexible substrates via uniaxial strain is followed in situ with GISAXS, providing a fundamental understanding of the impact of strain on the performance of flexible devices based on QD films, such as wearable electronics and next-generation solar cells on flexible substrates [4]. Nanoscale Horiz. 5, 880-885 (2020)Nano Energy 78, 105254 (2020)Energy Environ. Sci. 14, 3420-3429 (2021)Mater. Horizon 8, 383-395 (2023)

Infrared photodetectors based on wide bandgap two-dimensional transition metal dichalcogenides via efficient two-photon absorption

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention due to their outstanding optoelectronic properties and ease of integration, making them ideal candidates for high-performance photodetectors. However, the excessive width of the bandgap in some 2D TMDs presents a challenge for achieving infrared photodetection. One approach to broaden the photoresponse wavelength range of TMDs is through the utilization of two-photon absorption (TPA) process. Unfortunately, the inefficiency of TPA hinders its application in infrared photodetection. In this study, we propose the design of two photodetectors utilizing high TPA coefficient materials, specifically ReSe2 and MoS2, to exploit their TPA capability and extend the photoresponse to the near-infrared region at 1550 nm. The ReSe2 photodetector demonstrates an unprecedented responsivity of 43 μA W−1, surpassing that of current single-material TPA photodetectors. Similarly, the MoS2 photodetector achieves a responsivity of 18 μA W−1, comparable to state-of-the-art TPA photodetectors. This research establishes the potential of high TPA coefficient 2D TMDs for infrared photodetection.

Space-confined synthesis of two-dimensional InP crystals for high-performance self-powered Schottky photodiode

Atomic-thin III-V semiconductors with nanometer thickness have emerge as promising candidate for diverse applications in optoelectronics. In this work, by using a space-confine approach, ultra-thin indium phosphide (InP) crystals were obtained with thickness scaled down 10 nm, which demonstrate an extremely giant second harmonic generation (SHG) susceptivity up to 2.05 × 10−9 m/V under 1064 nm excitation, among the best of reported two-dimensional semiconductors. In addition, a high-performance Schottky photodiode with asymmetric electrical contact was implemented. The self-powered device exhibits a high responsivity of 15.3 mA W−1 and a detectivity of 1.94 × 1010 Jones under 532 nm light illumination, revealing a high on/off ratio of photocurrent exceeding 103 under zero bias, accompanied by rapid response times of only milliseconds. The results offer a streamlined avenue to develop ultrathin III-V semiconductor for high-performance photodetectors in future applications.

High-performance GaN ultraviolet polarization-sensitive photodetector based on ferroelectric polarization LiNbO3

High responsivity ultraviolet (UV) photodetectors (PDs) are essential for abundant civilian and military applications. Gallium nitride (GaN) has emerged as an ideal material for UV PD fabrication due to its favorable properties. However, the quality of GaN epitaxial layers significantly impacts device performance and reliability. Sapphire-based GaN epitaxial growth technology enables the realization of high-quality GaN epitaxial layers, making it the preferred choice for GaN substrates. Nonetheless, the thermal expansion coefficient mismatch between sapphire and GaN can lead to crystal mismatch and stress accumulation at high temperatures, affecting device performance and reliability. In contrast, lithium niobate (LiNbO3) exhibits similar coefficients of thermal expansion to GaN, mitigating crystal mismatch and stress accumulation issues. Here, we report the realization of a GaN UV PD by laminating GaN membrane onto ferroelectric LiNbO3 through selective electrochemical etching of the sapphire-based GaN epitaxial film. The LiNbO3-based GaN PD achieves a specific high on/off ratio of 107. At a 5 V bias voltage, the device exhibits a high peak responsivity of 1.712 × 103 A/W under 325 nm laser illumination. Furthermore, the device demonstrates excellent performance for polarization light detection, with a polarization ratio of approximately 54.95. Exploiting the local ferroelectric polarization of x-cut LiNbO3, the photogenerated electron–hole pairs in GaN are efficiently separated by the electrostatic field from the polarization of ferroelectric LiNbO3, resulting in enhanced light-to-electric conversion efficiency. Our work presents a method for fabricating high responsivity GaN-based UV PD, showcasing the potential of integrating ferroelectric LiNbO3 to enhance device performance.

Ultraviolet photodetector improvement based on microspheres

Owing to the ideal optical cavity structure, the microsphere has always played a significant role in micro/nano optoelectronic devices for its high light-confined ability and large surface-volume ratio, which have been applied in lots of areas including intracellular lasers, tunable lasers, and so on. Furthermore, the microsphere cavity will be a useful and efficient means to improve the photodetector (PD) performance by enhancing the light absorption efficiency and light energy in the arrays. Herein, the wide-bandgap semiconductor microspheres are introduced in the PD, which are synthesized by a simple and universal hydrothermal method. The sensitive ultraviolet PD is constructed and obtained with a metal-semiconductor-metal type device structure. The oxide defect concentration in the ZnO microspheres is modulated through thermal treatment to improve the performance, including higher photo-to-dark current ratio near 600, responsivity of 7.6✕10−5 A/W, detectivity of 4.6✕107 Jones, and response speed. Moreover, the microspheres fabricated flexible device presents great detecting performance with different bending degrees. The results display the excellent prospect of semiconductor microspheres to flexible ultraviolet high-performance PDs, which possess the broad and potential development prospect in flexible even on-chip optoelectronic devices.

Emulating Ebbinghaus forgetting behavior in a neuromorphic device based on low dimensional h-BN

Artificial synaptic devices that can mimic the biological synaptic functions of learning and forgetting are essential for the realization of neuromorphic computation, which could replace the von Neumann architecture. In this Letter, we have described a high-performing ultraviolet photodetector (wavelength 375 nm) using thin films of single-layer hexagonal boron nitride (h-BN) for potential use in fabricating a neuromorphic device. Furthermore, the classical Ebbinghaus forgetting curve can be optimized using various parameters such as the optical pulse width, number of pulses, and frequency of pulses. Our results show that the characteristic time constant (τ) has much more variability, indicating better performance control than the Ebbinghaus exponent (β). Furthermore, the performance of the optical synapse is very stable for low energy consumption, as low as 2–3 pJ.

High-performance self-powered electrochemical photodetectors based on co-precipitation and hydrothermally synthesized HgS nanoparticles

High-performance self-powered electrochemical photodetectors based on co-precipitation and hydrothermally synthesized HgS nanoparticles

High-performance broadband photodetector with imaging application based on tantalum nickel selenium at room temperature

High-performance broadband photodetector with imaging application based on tantalum nickel selenium at room temperature

Solution-processed quantum dot short-wavelength infrared photodetectors via integrating 2D MXenes into electron transport layer

Solution-processed quantum dots (QDs) have attracted intensive attention in short-wavelength infrared (SWIR) photodetectors due to their excellent optical properties and tunable size-dependent bandgap. However, the intrinsic defects of the widely used ZnO electron-transport layer (ETL) and the inappropriate band alignment at the interface between the ETL and photoactive QDs inevitably impact the optoelectronic performance of the photodetector. Herein, a high-performance self-powered SWIR photodetector is developed by using 2D Ti3C2 MXenes to passivate the defects of ZnO ETL and to tailor the band alignment at the interface of the ETL/photoactive layer through interface engineering. As a result, the SWIR photodetectors demonstrate the ultra-high light-to-dark current (Ilight/Idark) ratio of ∼ 105 and the low dark current density of 8.33 × 10-4 mA/cm2, and the high specific detectivity (D*) of 1.99 × 1011 Jones at 0 V. By the systematic characterizations, it is proofed that 2D MXene can efficiently passivate defects in ZnO and optimize the alignment of energy levels between the ETL and photoactive layer, which will suppress the recombination of electrons and holes and eventually promote photogenerated carrier transfer at the interface and thus improve device performance. This work revealed that the high-performance solution-processed QD based SWIR photodetector enabled by interface engineering will promote the development of optoelectronic devices in the future.

Hf2CO2-based heterojunctions for efficient photocatalytic hydrogen production and highly responsive self-powered flexible photodetector

The heterojunctions based transition metal carbide (MXenes) provides new possibilities for achieving high-performance photodetector. The electronic, mechanical, optical, and photocatalytic properties of the Hf2CO2-based heterojunctions are calculated based on first-principles calculations, and the photocurrent (Iph) and extinction ratio (ER) are calculated based on quantum transport simulations. The Hf2CO2/Sc2CF2, Hf2CO2/Zr2CO2, and Hf2CO2/Sc2CCl2 heterojunctions are ionic semiconductors with indirect bandgap. The Hf2CO2/Sc2CF2 heterojunction exhibits high solar to hydrogen efficiency (ηSTH) of 40.14 % and applying biaxial strain can effectively modulate the ηSTH of the Hf2CO2/Zr2CO2 heterojunction. The Hf2CO2/Zr2CO2 heterojunction has low overpotentials (ηHER) of 0.19 V and exhibits high electron mobility. The photodetector based on the Hf2CO2/Zr2CO2 heterojunction exhibits high Iph, and the photodetector based on the Hf2CO2/Sc2CF2 heterojunction has large ER and sensitivity to infrared and ultraviolet polarized light. The Iph and ER are significant increase by bending the photodetector. Our research indicates the potential applications of the Hf2CO2-based heterojunctions in photocatalytic water splitting and photodetector.

Cu2O/TiO2 core–shell nanowire heterojunction for high-performance self-powered photodetector

High-performance self-powered photodetectors (PDs) have great commercial value in optical communication, intelligent sensing and medical diagnosis. However, the limited active area of traditional thin film heterojunction seriously restricts the photoelectric performance of the detector. In this paper, the Cu2O/TiO2 core-shell nanowire (NW) heterojunction PD was synthesized for the first time by simple hydrothermal and electrochemical deposition methods, which effectively improved the response performance and response speed of the device based on its broad photoactive area and ordered carrier transport path. The PD exhibits significant diode behavior, with rectification ratios of 543 at ±2 V. The responsivity is as high as 6.8 mA W−1 at zero bias under 490 nm illumination. The short rise and decay times measured are 0.09 and 0.18 s at zero bias, respectively. Obviously, this low-cost, high-performance self-powered Cu2O/TiO2 core-shell NW heterojunction PD shows great promise in future optoelectronic device applications.

Tuning of optoelectronic performance of SrTiO3 by surface termination and thickness

The outstanding optical and electrical properties make ternary oxides highly suitable for advanced optoelectronic applications comparing to the traditional silicon-based materials and heterostructures. SrTiO3 (STO), a pivotal perovskite oxide with a direct energy band gap of 3.2 eV, exhibits significant promise in ultraviolet (UV) photodetection. However, the photovoltaic performance of homoepitaxial STO has long been neglected. In this study, we investigated the optoelectronic characteristics of STO by manipulating the crucial factors of surface termination and thickness using oxide molecular beam epitaxy (oxide MBE). We achieved an exceptional charge carrier mobility of 56.5975 cm2 V-1s−1, along with an impressive ON/OFF ratio of 6000 % and a specific detectivity (D*) of 2.95 × 109 Jones (cm Hz1/2 W−1) under near-UV irradiation at room temperature. We observed a thickness-dependent semiconductor-to-metal transition with a critical thickness of 3.5 u.c. STO. The metallic STO displayed an extremely high mobility exceeding 105 cm2 V−1 s−1, accompanied by a substantial MR value exceeding 1000 % at 3 K. Furthermore, the thickness-dependent Hall effect and photoluminescence (PL) indicated that oxygen defects may govern the semiconducting/metallic behavior of STO. This study illustrates the optoelectrical capabilities of homoepitaxial STO, paving the way for advanced and high-performance photodetection in intricate optical materials and devices through homoepitaxy.

Toward High-Performance Self-Powered Near-Ultraviolet Photodetection by Constructing a Unipolar Heterojunction.

Constructing a unipolar heterojunction is an effective energy band engineering strategy to improve the performance of photoelectric devices, which could suppress dark current and enhance detectivity by modulating the transfer of carriers. In this work, unipolar heterojunctions of Si/PbI2 and GaSb/PbI2 are constructed successfully for high-performance self-powered near-ultraviolet photodetection. Owing to the unique band offset of unipolar heterojunctions, the transport of holes is blocked, and only photogenerated electrons in PbI2 can flow unimpeded under the driving force of the built-in electric field. Thus, the recombination of photogenerated electron-hole pairs is suppressed, contributing to high-performance near-ultraviolet photodetection. The as-fabricated Si/PbI2 self-powered near-ultraviolet photodetector exhibits a low dark current of 10-13 A, a high Ilight/Idark ratio of 104, and fast response times of 26/24 ms, which are much better than those of the PbI2 metal-semiconductor-metal photodetector. Furthermore, the as-fabricated GaSb/PbI2 unipolar heterojunction photodetector also exhibits impressive self-powered near-ultraviolet photodetection behaviors. Evidently, this work shows the potential of unipolar heterojunctions for next-generation Si-based and GaSb-based high-performance photodetection.

Isotope Synergetic Effect on Hybrid Organic–Inorganic Perovskite Single Crystal Carrier Transport and High-Performance Photodetectors

Isotope Synergetic Effect on Hybrid Organic–Inorganic Perovskite Single Crystal Carrier Transport and High-Performance Photodetectors

Electrostatic Force-Assisted Transfer of Flexible Silicon Photodetector Focal Plane Arrays for Image Sensors.

Flexible photodetectors are pivotal in contemporary optoelectronic technology applications, such as data reception and image sensing, yet their performance and yield are often hindered by the challenge of heterogeneous integration between photoactive materials and flexible substrates. Here, we showcase the potential of an electrostatic force-assisted transfer printing technique for integrating Si PIN photodiodes onto flexible substrates. This clean and dry process eliminates the need for chemical etchants, making it a highly desirable method for manufacturing high-performance flexible photodetector arrays, expanding their widespread applications in electronic eyes, robotics, and human-machine interaction. As a demonstration, a 5 × 5 flexible Si photodetector focal plane array is constructed for imaging sensors and shaped into a convex semicylindrical form to achieve a π field of view with long-term mechanical and thermal stability. Such an approach provides a high yield rate and consistent performance, with the single photodetector demonstrating exceptional characteristics, including a responsivity of 0.61 A/W, a response speed of 39.77 MHz, a linear dynamic range of 108.53 dB, and a specific detectivity of 2.75 × 1012 Jones at an applied voltage of -3 V at 940 nm.

High-performance solar-blind photodetector based on Si-doped α-Ga2O3 thin films grown by mist chemical vapor deposition

α-Ga2O3 has gained increasing attention in the field of photodetectors because of its wide bandgap and exceptional chemical and physical properties. Si-doped α-Ga2O3 single-crystal epitaxial films were successfully deposited on sapphire substrates using an affordable and non-vacuum-based mist chemical vapor deposition (Mist-CVD) technique. An interdigital metal-semiconductor-metal (MSM) photodetector with excellent performance was prepared by using the thin film. At 254 nm illumination and a bias voltage of 20 V, the photodetector has a high light-to-dark current ratio of 3.24×106, a responsivity of 3.23×102 A/W, a detectivity of 8.80×1015 Jones, and an external quantum efficiency of 1.58×105%. The results show that Si-doped α-Ga2O3 thin films have great potential for application in high-performance photodetectors.

Growth of Monolayer MoS2 Flakes via Close Proximity Re-Evaporation.

We report a two-step growth process of MoS2 nanoflakes using a low-pressure chemical vapor deposition technique. In the first step, a MoS2 layer was synthesized on a c-plane sapphire substrate. This layer was subsequently re-evaporated at a higher temperature to form mono- or few-layer MoS2 flakes. As a result, the close proximity re-evaporation enabled the growth of pristine MoS2 nanoflakes. Atomic force microscopy analysis confirmed the synthesis of nanoclusters/nanoflakes with lateral dimensions of over 10 μm and a flake height of approximately 1.3 nm, demonstrating bi-layer MoS2, whereas transmission electron microscopy analysis revealed triangular MoS2 nanoflakes, with a diffraction pattern proving the presence of single crystalline hexagonal MoS2. Raman data revealed the typical modes of high-quality MoS2 nanoflakes. Finally, we presented the photocurrent dependence of a MoS2-based photoresist under illumination with light-emitting diode of 405 nm wavelength. The measured current-voltage dependence across various luminous flux outlined the sensitivity of MoS2 to polarized light and thus opens further opportunities for applications in high-performance photodetectors with polarization sensitivity.

Organic-Inorganic Rubrene/WS2 Heterostructure for Broadband Detection and Polarization Imaging.

Organic single crystals exhibit improved carrier mobility, longer exciton diffusion length, anisotropic charge transport, and unique linear dichroism, while its high exciton binding energy seriously limits the free-carrier generation and photoelectric conversion efficiency. Layered van der Waals heterostructures, which integrate organic crystals with high mobility two-dimensional (2D) inorganic semiconductors, are promising for promoting exciton dissociation and boosting sensitivity by utilizing the interfacial potential and photogating effect. In this work, organic single-crystal rubrene is integrated with a few-layer WS2 to design the high-performance photodetector. The device exhibits an excellent responsivity of 1000 A W-1, and a fast speed of 180 μs, which is far superior to the individual WS2 device. Equally importantly, this device provides excellent polarization detection performance by virtue of the anisotropic properties of rubrene, and the dichroic ratios are 1.56, 1.5, and 1.7 for 375, 405, and 658 nm irradiation, respectively. Finally, several high-resolution single-pixel broadband polarization imaging was demonstrated. Our work shows that organic-inorganic heterostructure is an essential candidate for improving optoelectronics performance and has potential for polarization imaging.