Graphene-based Photodetectors Research Articles

Unbiased Plasmonic-Assisted Integrated Graphene Photodetectors.

Photonic integrated circuits (PICs) for next-generation optical communication interconnects and all-optical signal processing require efficient (∼A/W) and fast (≥25 Gbs–1) light detection at low (<pJbit–1) power consumption, in devices compatible with Si processing, so that the monolithic integration of electro-optical materials and electronics can be achieved consistently at the wafer scale. Graphene-based photodetectors can meet these criteria, thanks to their broadband absorption, ultra-high mobility, ultra-fast electron interactions, and strong photothermoelectric effect. High responsivities (∼ 1 A/W), however, have only been demonstrated in biased configurations, which introduce dark current, noise, and power consumption, while unbiased schemes, with low noise and zero consumption, have remained in the ∼ 0.1 A/W regime. Here, we consider the unbiased asymmetric configuration and show that optimized plasmonic enhanced devices can reach for both transverse-electric and transverse-magnetic modes (at λ = 1550 nm), ∼A/W responsivity, and ∼ 100 GHz operation speed at zero power consumption. We validate the model and material parameters by simulating experimental devices and derive analytical expressions for the responsivity. Our comprehensive modeling paves the way for efficient, fast, and versatile optical detection in PICs with zero power consumption.

Dual-Enhanced Photodetectors Combining Graphene Plasmonic Nanoresonators With Germanium-on-Insulator Optical Cavities

Two-dimensional graphene (2-D graphene) has limited application potential in optoelectronics because of its low light absorptivity and gapless property. This work presents photodetectors with increased light absorption efficiency, which couple 3-D graphene with the optical cavity structure of germanium-on-insulator (GeOI). Multiple reflections are generated at the 3-D graphene/GeOI heterojunction due to the unique plasmonic nanoresonator and optical cavity structures. The photodetectors exhibit excellent responsivity (R=0.9x10⁴ mAW⁻¹) and specific detectivity (D*= 3.96x10¹⁰ cmHz <formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex>$^{1/2}$</tex> </formula> W⁻¹) under 1550-nm illumination with fast response rates, excellent reproducibility, and long-term stability. The technique paves the way for creating novel high-performance graphene-based photodetectors with hybrid architectures.

Graphene-based deep-ultraviolet photodetectors with ultrahigh responsivity using chemical vapor deposition of hexagonal boron nitride to achieve photogating

This study presents high-responsivity graphene-based deep-ultraviolet (DUV) photodetectors using chemical vapor deposition (CVD)-hexagonal boron nitride (h-BN) photogating. To improve the DUV photoresponse, h-BN was used as a photosensitizer in graphene field-effect transistors (GFETs). The h-BN photosensitizers were synthesized using CVD and then transferred onto a SiO2/Si substrate. The behavior of h-BN irradiated with DUV light was investigated using cathodoluminescence and UV–VIS reflectance. Under 260 nm light, it exhibited a clear photoresponse with an ultrahigh responsivity of 19600 AW-1, which was 460% higher than a GFET device without h-BN photosensitizers. A noise equivalent power of 3.09×10−13 W/Hz1/2 was achieved.

Advances in Printable, Flexible and Transparent Graphene Photodetectors for Optoelectronics Applications

Photodetectors, often known as photosensors, are light or electromagnetic radiation sensors. Graphene is a carbon allotrope made up of a single layer of carbon atoms that are linked together in a hexagonal configuration. Carbon nanotubes, another emerging material, are made from rolled graphene. The high carrier mobility, linear dispersion, and 0 bandgap of graphene contribute to the ultra-fast, wide-spectrum response of graphene photodetectors from visible to infrared. The high responsivity of graphene photodetectors is 500 A/W for light of 450 nm and 4 A/W for light of 1064 nm. The strong compatibility of graphene with silicon technology has been explored, and recent discoveries open the way for chip integrated photodetectors with high-performance. This article will be covering different types of photodetectors which differ in type of materials used, along with graphene and type of methods of manufacture. It gives each device construction and working along with results on its responsivity and sensitivity. We then cover the innumerable applications of graphene-based photodetectors in communication sector, medical sector, and in flexible electronics which are discussed briefly. We also go through the advancements in materials and manufacturing processes, emphasizing that graphene photodetector devices are gaining popularity due to their capacity to provide long-term real-time precise monitoring. Lastly, we discuss advantages and hurdles that are to be overcome.

Towards integrated mode-division demultiplexing spectrometer by deep learning

Miniaturized spectrometers have been widely researched in recent years, but few studies are conducted with on-chip multimode schemes for mode-division multiplexing (MDM) systems. Here we propose an ultracompact mode-division demultiplexing spectrometer that includes branched waveguide structures and graphene-based photodetectors, which realizes simultaneously spectral dispersing and light fields detecting. In the bandwidth of 1500–1600 nm, the designed spectrometer achieves the single-mode spectral resolution of 7 nm for each mode of TE₁–TE₄ by Tikhonov regularization optimization. Empowered by deep learning algorithms, the 15-nm resolution of parallel reconstruction for TE₁–TE₄ is achieved by a single-shot measurement. Moreover, by stacking the multimode response in TE₁–TE₄ to the single spectra, the 3-nm spectral resolution is realized. This design reveals an effective solution for on-chip MDM spectroscopy, and may find applications in multimode sensing, interconnecting and processing.

Gold Enhanced Graphene-Based Photodetector on Optical Fiber with Ultrasensitivity over Near-Infrared Bands

Graphene has been widely used in photodetectors; however its photoresponsivity is limited due to the intrinsic low absorption of graphene. To enhance the graphene absorption, a waveguide structure with an extended interaction length and plasmonic resonance with light field enhancement are often employed. However, the operation bandwidth is narrowed when this happens. Here, a novel graphene-based all-fiber photodetector (AFPD) was demonstrated with ultrahigh responsivity over a full near-infrared band. The AFPD benefits from the gold-enhanced absorption when an interdigitated Au electrode is fabricated onto a Graphene-PMMA film covered over a side-polished fiber (SFP). Interestingly, the AFPD shows a photoresponsivity of >1 × 104 A/W and an external quantum efficiency of >4.6 × 106% over a broadband region of 980–1620 nm. The proposed device provides a simple, low-cost, efficient, and robust way to detect optical fiber signals with intriguing capabilities in terms of distributed photodetection and on-line power monitoring, which is highly desirable for a fiber-optic communication system.

Fermi-Surface Modulation of Graphene Synergistically Enhances the Open-Circuit Voltage and Quantum Efficiency of Photovoltaic Solar-Blind Ultraviolet Detectors.

Increasing the open-circuit voltage (VOC) is of a great significance to achieve high photoelectric conversion efficiency in photovoltaic applications. Here, we present a simple NO2 doping strategy that can significantly modulate the VOC of graphene-based solar-blind ultraviolet photodetectors from 0.96 to 1.84 V. The intriguing result can be demonstrated by the fact that NO2 doping lowers the Fermi surface of graphene and thus enhances quasi-Fermi level splitting of the whole device under illumination. The >103% increase of both external quantum efficiency and photoresponsivity compared to before doping is the result of a 0.88 V increase in the VOC. Our work sheds light on the forming mechanism of VOC in graphene-based photovoltaic detectors and further suggests alternative pathways to enhance the VOC of photovoltaic devices with high efficiency.

High performance plasmonically enhanced graphene photodetector for near-infrared wavelengths

Graphene is a very attractive material for applications in optoelectronic devices such as photodetectors because of fast response and broadband absorption. However, the weak absorption of the graphene layer limits the performance of graphene-based photodetectors. To this end, a high responsivity graphene-based plasmonic photodetector, operating over a wide optical wavelength range, is presented. In order to enhance the light absorption efficiency and, consequently, to improve the responsivity of the photodetector, a graphene layer and a specific plasmonic nanostructure are combined. The numerical simulation results reveal that nearly perfect light absorption is achieved at the wavelength of 1550 nm for the proposed structure and also, this structure is polarization insensitive and enables perfect absorption for TE and TM polarizations at the wavelength of 1550 nm. The circuit model of the structure is presented based on transmission line theory whose results are in very good agreement with the numerical simulation results. Also, the high responsivity of 513 mA/W and the bandwidth of 47 GHz are achieved for this scheme.

Solution-Processed Graphene-Nanographene van der Waals Heterostructures for Photodetectors with Efficient and Ultralong Charge Separation.

Sensitization of graphene with inorganic semiconducting nanostructures has been demonstrated as a powerful strategy to boost its optoelectronic performance. However, the limited tunability of optical properties and toxicity of metal cations in the inorganic sensitizers prohibits their widespread applications, and the in-depth understanding of the essential interfacial charge-transfer process within such hybrid systems remains elusive. Here, we design and develop high-quality nanographene (NG) dispersions with a large-scale production using high-shear mixing exfoliation. The physisorption of these NG molecules onto graphene gives rise to the formation of graphene-NG van der Waals heterostructures (VDWHs), characterized by strong interlayer coupling through π-π interactions. As a proof of concept, photodetectors fabricated on the basis of such VDWHs show ultrahigh responsivity up to 4.5 × 107 A/W and a specific detectivity reaching 4.6 × 1013 Jones, being competitive with the highest values obtained for graphene-based photodetectors. The outstanding device characteristics are attributed to the efficient transfer of photogenerated holes from NGs to graphene and the long-lived charge separation at graphene-NG interfaces (beyond 1 ns), as elucidated by ultrafast terahertz (THz) spectroscopy. These results demonstrate the great potential of such graphene-NG VDWHs as prototypical building blocks for high-performance, low-toxicity optoelectronics.

High performance dual band graphene-based plasmonic photodetector

One of the most important issues in the design of photodetectors is absorption efficiency. An innovative structure of a graphene-based photodetector consisting of an array of plasmonic nanostructures is proposed. Surface plasmons resonance occurs near the plasmonic nanostructures, enhancing the interaction between light and graphene; this gives rise to a strong light absorption. The numerical analysis results show that the proposed photodetector has a total absorption efficiency of 87.7% and a photocurrent of 1000 μA. Also, this structure exhibits the responsivity of 2053 mA / W and the bandwidth of 25.17 GHz at the wavelength of 1.55 μm. The other outstanding features of this design are low power consumption and being CMOS compatible. The results reveal the superiority of the proposed photodetector performance in terms of responsivity and optical bandwidth in comparison with the other existing designs.

Graphene photodetectors with asymmetric device structures on silicon chips

Graphene is a promising material for developing high-speed and wide-wavelength-range photodetectors. However, since the polarities of the photovoltages at each graphene/electrode interface of two electrodes on both ends of the graphene are opposite, they are canceled out under macroscopic light irradiation to the photodetectors. In this study, we propose two graphene-based photodetectors with different asymmetric device structures that can suppress the cancelation of photovoltage at the interfaces of two electrodes. One of the photodetectors has a local shadow mask, where only one side of the graphene/electrode interface is shadowed by a metal mask. The other has electrodes of different shapes, where the contact area of graphene/electrode interface is different by using a comb-shaped electrode. We measured the position dependence of light detection by scanning the focused light around the graphene photodetectors, and asymmetric photovoltage mapping can be obtained owing to the asymmetric structure of the two photodetectors. Furthermore, we also demonstrated macroscopic light detection by the photodetectors in the visible, near-infrared, and mid-infrared regions by suppressing the photovoltage cancelation. These graphene-based photodetectors with asymmetric structures are suitable for use as macroscopic photodetectors in the wide band of visible, near-infrared and mid-infrared regions.

Ultrahigh-speed graphene-based optical coherent receiver

Graphene-based photodetectors have attracted significant attention for high-speed optical communication due to their large bandwidth, compact footprint, and compatibility with silicon-based photonics platform. Large-bandwidth silicon-based optical coherent receivers are crucial elements for large-capacity optical communication networks with advanced modulation formats. Here, we propose and experimentally demonstrate an integrated optical coherent receiver based on a 90-degree optical hybrid and graphene-on-plasmonic slot waveguide photodetectors, featuring a compact footprint and a large bandwidth far exceeding 67 GHz. Combined with the balanced detection, 90 Gbit/s binary phase-shift keying signal is received with a promoted signal-to-noise ratio. Moreover, receptions of 200 Gbit/s quadrature phase-shift keying and 240 Gbit/s 16 quadrature amplitude modulation signals on a single-polarization carrier are realized with a low additional power consumption below 14 fJ/bit. This graphene-based optical coherent receiver will promise potential applications in 400-Gigabit Ethernet and 800-Gigabit Ethernet technology, paving another route for future high-speed coherent optical communication networks.

Interfacial Photogating Effect for Hybrid Graphene-Based Photodetectors

Ultrafast and high-sensitive photodetectors operating from the deep-ultraviolet to near-infrared region at room temperature are essential for many applications such as analytical chemistry, optical positioning, biomedical imaging, and remote sensing. Toward high-performance photodetectors, hybrid colloid quantum dots/graphene photodetectors based on the photogating mechanism have been intensively studied. An ultrahigh sensitivity has been obtained in the range from 105 to 109 A/W but the major challenge of these configurations is the slow operating speed on the millisecond to second time scale. Manipulating the transferring of carriers at the interface of semiconductor nanostructures and graphene is an essential key to optimize the interfacial photogating effect. Here, we grow an absorber layer directly on graphene by e-beam evaporation to obtain a fast photoresponse time of the detectors. Thus, the gap between the high responsivity and fast response time can be bridged. The photodetectors indicate a high photoresponsivity of ∼2.5 × 106 A/W at low incident intensity on the order of femto-watts, a specific detectivity of ∼8.5 × 1011 Jones, and a fast response process of ∼20 ns together with a slow component of ∼850 ns (response time of <1 μs) under a drain-to-source bias of 100 mV. The study has provided a method to obtain high-performance photodetectors based on graphene with high responsivity and fast response time.

Highly sensitive broadband binary photoresponse in gateless epitaxial graphene on 4H–SiC

Due to weak light-matter interaction, standard chemical vapor deposition (CVD)/exfoliated single-layer graphene-based photodetectors show low photoresponsivity (on the order of mA/W). However, epitaxial graphene (EG) offers a more viable approach for obtaining devices with good photoresponsivity. EG on 4H–SiC also hosts an interfacial buffer layer (IBL), which is the source of electron carriers applicable to quantum optoelectronic devices. We utilize these properties to demonstrate a gate-free, planar EG/4H–SiC-based device that enables us to observe the positive photoresponse for (405–532) nm and negative photoresponse for (632–980) nm laser excitation. The broadband binary photoresponse mainly originates from the energy band alignment of the IBL/EG interface and the highly sensitive work function of the EG. We find that the photoresponsivity of the device is > 10 A/W under 405 nm of power density 7.96 mW/cm2 at 1 V applied bias, which is three orders of magnitude greater than the obtained values of CVD/exfoliated graphene and higher than the required value for practical applications. These results path the way for selective light-triggered logic devices based on EG and can open a new window for broadband photodetection.

Graphene-based mid-infrared photodetectors using metamaterials and related concepts

Graphene, a semi-metal with a gapless band structure, has been used in mid-infrared (MIR) photodetectors (PDs) for some time. However, these detectors often suffer from low responsivity due to the intrinsically low absorption and ultra-short carrier lifetime in graphene, large dark current, and low detectivity due to the semi-metallic nature of graphene. Over the past decade, much effort has been devoted to addressing these issues. A variety of metamaterials and related concepts has been employed to improve the detector responsivity by enhancing the graphene absorption and/or the carrier collection efficiency. Here, we provide an overview of the graphene MIR PDs with and without the use of approaches for responsivity enhancement. We focus our attention on the state-of-the-art graphene MIR PDs whose performance is improved by employing metamaterials and related concepts, including band structure engineering, the photogating effect, integration with plasmonic nanostructures and waveguides, the use of asymmetric plasmons, coupled plasmon–phonon polaritons, and small-twist-angle bilayer graphene. We conclude by providing possible directions for further performance improvement of graphene MIR PDs and a discussion on future applications of these detectors.

Critical Strain-Induced Photoresponse in Folded Graphene Superlattices.

Strain engineering is the most effective method to break the symmetry of the graphene lattice and achieve graphene band gap tunability. However, a critical strain (>20%) is required to open the graphene band gap, and it is very difficult to achieve such a large strain. This limits the development of experimental research and optoelectronic devices based on graphene strain. In this work, we report a method for preparing large-strain graphene superlattices via surface energy engineering. The maximum strain of the curved lattice could reach 50%. In particular, our pioneering work reports the behavior of an ultrafast (as short as 6 ps) photoresponse in a strained folded graphene superlattice. The photocurrent map shows a large increase (up to 102) of the photoresponsivity in the tensile graphene lattice, which is generated by the interaction between the strained and pristine graphene. Through Raman spectroscopy, Kelvin probe force microscopy, and high-resolution transmission electron microscopy, we demonstrate that the ultrathreshold strain in the graphene bends triggers the opening of the graphene band gap and results in a unique photovoltaic effect. This work deepens the understanding of the strain-induced change of the photoelectrical properties of graphene and proves the potential of strained graphene as a platform for the generation of novel high-speed, miniaturized graphene-based photodetectors.

Semi-transparent reduced graphene oxide photodetectors for ultra-low power operation.

The emerged demand for high-performance systems promotes the development of two-dimensional (2D) graphene-based photodetectors. However, these graphene-based photodetectors are usually fabricated by an expensive photolithography and complicated transferred process. Here, a semi-transparent reduced graphene oxide (rGO) photodetector on a polyethylene terephthalate (PET) substrate with ultra-low power operation by simple processes is developed. The photodetector has achieved a transmittance about 60%, a superior responsivity of 375 mA/W and a high detectivity of 1012 Jones at a bias of -1.5 V. Even the photodetector is worked at zero bias, the photodetector exhibits a superior on/off ratio of 12. Moreover, the photoresponse of such photodetector displays little reduction after hundred times bending, revealing that the photodetector is reliable and robust. The proposed fabrication strategy of the photodetector will be beneficial to the integration of semi-transparent and low-power wearable devices in the future.

Highly polarization-sensitive, broadband, low dark current, high responsivity graphene-based photodetector utilizing a metal nano-grating at telecommunication wavelengths

Recent advances in graphene-based photodetectors have demonstrated the feasibility of utilizing graphene as a fantastic material for the development of future high-performance photodetectors. In this paper, a high-performance graphene-based photodetector is proposed with plasmonic structure by employing a single graphene layer, periodic metal nano-grating, and S i / S i O 2 substrate. The plasmonic coupling phenomena between graphene and the metal nano-grating can cause absorption enhancement in this structure. The proposed structure has almost perfect absorption at the telecommunication wavelength (1.55 µm), and its optical response shows a polarization-sensitive characteristic in the spectral range from 1 µm to 2.1 µm. Moreover, the electrical characterization and the dynamic response of this structure are obtained. Based on simulation results, the proposed structure under 0.5 mW incident optical power and at a wavelength of 1.55 µm exhibits a low dark current on the order of about 0.001 mA, maximum photocurrent of 0.81 mA, and responsivity of 1650 mA/W at a bias voltage of 3 V. Also, the rise time of the dynamic response is determined to be about 87 ps, and the 3 dB bandwidth of the frequency response is obtained to be about 4 GHz.

Efficient graphene in-plane homogeneous p-n-p junction based infrared photodetectors with low dark current

Graphene-based photodetectors have drawn a large amount of interests owing toits wide spectral response, however, the high dark current greatly limitstheir applications. In this study, we develop an efficient graphenein-plane homogeneous p-n-p junction based infrared (IR) photodetector withgreatly reduced dark current. The devices with p-n-p junctions exhibitexcellent photoresponse to 1.0$\\sim~$4.0 $\\mu~$m IR light illumination withultra-low dark current at the order of $\\sim~$10$^{~-~9}$ A in double p-n-pjunctions and 10$^{~-~13}$ A in three p-n-p junctions based photodetector,which is three and seven orders of magnitude lower than pristine graphenephototransistors, respectively. The excellent IR photodetection capabilitiescould be attributed to the synergistic effects of in-plane photovoltaiceffects as well as the photogating effects induced carrier injection fromthe silicon substrate. Our results suggest intriguing potential of graphenein-plane p-n-p junctions for applications in high-performance IRphotodetectors.

High-Responsivity Solar-Blind Ultraviolet Photodetectors Based on Carbon Nanodots/Graphene Hybrids

The intrinsically poor optical absorption and short carrier lifetime of graphene have restricted its practical application in photodetectors. Carbon nanodots (CNDs) have received much attention due to their fascinating optical properties, environmentally friendly nature, small size, and superiority of a large optical absorptivity. Thus, in this article, a hybrid photodetector based on CNDs and graphene has been proposed for the solar-blind ultraviolet (UV) photodetection, in which CNDs were integrated with graphene to form a hybrid structure which was capable of detecting UV light with 254 nm. Here, this article also demonstrated that a high photoresponsivity of ~433.33 A/W and a detectivity of ~1.08 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Jones can be obtained in the hybrid photodetector. UV illumination causes photogenerated electrons and holes in CNDs. Holes transfer to graphene and then recirculate many times, which originates from the high carrier mobility of graphene and the prolonged lifetime of excited electrons that remain trapped in CNDs. Our result demonstrates that the integration of graphene and CNDs shows better optical absorption and wavelength selectivity. Together with the mechanism, it paves a step for practical applications of quantum dots sensitized graphene-based photodetectors.