Graphene Photodetectors Research Articles

Zero-bias mid-infrared graphene photodetectors with bulk photoresponse and calibration-free polarization detection

Bulk photovoltaic effect (BPVE), featuring polarization-dependent uniform photoresponse at zero external bias, holds potential for exceeding the Shockley-Queisser limit in the efficiency of existing opto-electronic devices. However, the implementation of BPVE has been limited to the naturally existing materials with broken inversion symmetry, such as ferroelectrics, which suffer low efficiencies. Here, we propose metasurface-mediated graphene photodetectors with cascaded polarization-sensitive photoresponse under uniform illumination, mimicking an artificial BPVE. With the assistance of non-centrosymmetric metallic nanoantennas, the hot photocarriers in graphene gain a momentum upon their excitation and form a shift current which is nonlocal and directional. Thereafter, we demonstrate zero-bias uncooled mid-infrared photodetectors with three orders higher responsivity than conventional BPVE and a noise equivalent power of 0.12 nW Hz−1/2. Besides, we observe a vectorial photoresponse which allows us to detect the polarization angle of incident light with a single device. Our strategy opens up alternative possibilities for scalable, low-cost, multifunctional infrared photodetectors.

An ultrafast multi-layer Graphene/InGaAs/InAlAs/InAs P-I-N photodetector with 100 GHz bandwidth

In recent years, the data traffic has grown exponentially and the forecasts indicate a huge market that could be addressed by optoelectronics. However, the processing capacity, space, and energy consumption of the available technology is a serious bottleneck for the exploitation of these markets. Graphene material is a new candidate using in optoelectronics’ devices such as photodetector. The responsivity of Graphene photodetectors depends critically on the elevated temperature of the electronic subsystem upon photoexcitation. We performed in this study a multi layer Graphene/InGaAs /InAlAs/InAs Photodetector PIN simulation with Atlas under Silvaco tcad Tools using Graphene and high electronmobility II I-V materials. Our devices exhibit 100 GHz bandwidth with 40 ps transient reponse, (2.7 × 10−7 A) of photocurrent, high responsivity with value of 1.26A/W and a suitable efficiency η of 95 % with reasonable rejection ration of Iilumination/Idark of 2 order of magnitude.

Effects of doping graphene on the performance of graphene–silicon hybrid photoconductive detectors

The photoconductive detector based on a graphene–silicon heterostructure retains excellent optoelectrical properties, in which the graphene plays an indispensable role, acting as the carrier transporting channel. Herein, we systematically investigate by simulation and experiment how doping graphene will affect the performance of graphene–silicon hybrid photoconductors. Compared with lightly p-doped graphene devices, the responsivity can be made nine times better through increasing the p-type doping level. In addition, the net photocurrent can also be enhanced by about four times through increasing the n-type doping level of graphene. We attribute this improvement to the barrier height change adjusted by doping graphene, which can optimize the lifetime and transport of photocarriers. Such a graphene–doping method, that manipulates the junction region, could offer useful guidance for achieving high-performance graphene photodetectors.

Ultrafast, Zero-Bias, Graphene Photodetectors with Polymeric Gate Dielectric on Passive Photonic Waveguides.

We report compact, scalable, high-performance, waveguide integrated graphene-based photodetectors (GPDs) for telecom and datacom applications, not affected by dark current. To exploit the photothermoelectric (PTE) effect, our devices rely on a graphene/polymer/graphene stack with static top split gates. The polymeric dielectric, poly(vinyl alcohol) (PVA), allows us to preserve graphene quality and to generate a controllable p–n junction. Both graphene layers are fabricated using aligned single-crystal graphene arrays grown by chemical vapor deposition. The use of PVA yields a low charge inhomogeneity ∼8 × 1010 cm–2 at the charge neutrality point, and a large Seebeck coefficient ∼140 μV K–1, enhancing the PTE effect. Our devices are the fastest GPDs operating with zero dark current, showing a flat frequency response up to 67 GHz without roll-off. This performance is achieved on a passive, low-cost, photonic platform, and does not rely on nanoscale plasmonic structures. This, combined with scalability and ease of integration, makes our GPDs a promising building block for next-generation optical communication devices.

Enhancing the graphene photocurrent using surface plasmons and a p-n junction

The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness, ultrabroadband detection, and an ultrafast response speed. However, owing to the low optical absorption of pristine monolayer graphene, the intrinsically low responsivity of graphene photodetectors significantly hinders the development of practical devices. To address this issue, numerous efforts have thus far been made to enhance the light–graphene interaction using plasmonic structures. These approaches, however, can be significantly advanced by leveraging the other critical aspect of graphene photoresponsivity enhancement—electrical junction control. It has been reported that the dominant photocarrier generation mechanism in graphene is the photothermoelectric (PTE) effect. Thus, the two energy conversion mechanisms involved in the graphene photodetection process are light-to-heat and heat-to-electricity conversions. In this work, we propose a meticulously designed device architecture to simultaneously enhance the two conversion efficiencies. Specifically, a gap plasmon structure is used to absorb a major portion of the incident light to induce localized heating, and a pair of split gates is used to produce a p-n junction in graphene to augment the PTE current generation. The gap plasmon structure and the split gates are designed to share common key components so that the proposed device architecture concurrently realizes both optical and electrical enhancements. We experimentally demonstrate the dominance of the PTE effect in graphene photocurrent generation and observe a 25-fold increase in the generated photocurrent compared to the un-enhanced cases. While further photocurrent enhancement can be achieved by applying a DC bias, the proposed device concept shows vast potential for practical applications.

Photodetection Using Atomically Precise Graphene Nanoribbons

In the search for high-sensitivity, low-noise, and high-bandwidth photodetectors, materials are a key ingredient. One- and two-dimensional materials are of particular interest in this area due to their extraordinary properties such as ballistic transport. Here, we demonstrate nanoscale photoconductive photodetectors using aligned atomically precise seven-atom wide armchair-edge graphene nanoribbons. The detector responsivity is 0.035 mAW–1 at a bias voltage of 2 V. The dark current is below 30 pA for a bias voltage of 1.5 V, which is orders of magnitude lower than that of typical graphene photodetectors. The possibility to align the nanoribbons and to tune their optical and electronic properties by choice of ribbon width and edge structure enables nanoscale polarization-resolving photodetectors optimized for specific spectral ranges. Graphene nanoribbons with identical electronic and optical properties can be prepared on a large scale using bottom-up synthesis, making them a highly interesting material for electronics and optoelectronics.

Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies

AbstractUltrafast and sensitive (noise equivalent power <1 nW Hz−1/2) light-detection in the terahertz (THz) frequency range (0.1–10 THz) and at room-temperature is key for applications such as time-resolved THz spectroscopy of gases, complex molecules and cold samples, imaging, metrology, ultra-high-speed data communications, coherent control of quantum systems, quantum optics and for capturing snapshots of ultrafast dynamics, in materials and devices, at the nanoscale. Here, we report room-temperature THz nano-receivers exploiting antenna-coupled graphene field effect transistors integrated with lithographically-patterned high-bandwidth (∼100 GHz) chips, operating with a combination of high speed (hundreds ps response time) and high sensitivity (noise equivalent power ≤120 pW Hz−1/2) at 3.4 THz. Remarkably, this is achieved with various antenna and transistor architectures (single-gate, dual-gate), whose operation frequency can be extended over the whole 0.1–10 THz range, thus paving the way for the design of ultrafast graphene arrays in the far infrared, opening concrete perspective for targeting the aforementioned applications.

On-Chip Ultrafast Plasmonic Graphene Hot Electron Bolometric Photodetector.

We investigate a waveguide-integrated plasmonic graphene photodetector operating based on the hot carrier photo-bolometric effect, which is characterized simultaneously by high responsivity on the scale of hundreds of A/W and high speed on the scale of 100’s of GHz that is limited only by the product of the electronic heat capacitance and thermal resistance. We develop a theory of the bolometric effect originating from the band nonparabolicity of graphene and estimate responsivity due to the bolometric effect, which is shown to significantly surpass the responsivity of the coexisting photoconductive effect, thus convincingly demonstrating the dominance of the bolometric effect. Based on the theory, we propose a novel detector configuration based on a hybrid waveguide that allows for efficient absorption in graphene over a short distance and subsequently a large change of conductivity. The results demonstrate the potential of graphene for high-speed communication systems.

Room Temperature Graphene Mid-Infrared Bolometer with a Broad Operational Wavelength Range

The last decade has witnessed the realization of numerous different types of graphene photodetectors with a strong focus on the visible and near-infrared spectral range, in which various high-perfo...

Photogating for small high-responsivity graphene middle-wavelength infrared photodetectors

We demonstrated a middle-wavelength infrared (MWIR) graphene photodetector using the photogating effect. This effect was induced by photosensitizers situated around a graphene channel that coupled incident light and generated a large electrical charge. The graphene-based MWIR photodetector consisted of a top graphene channel, source–drain electrodes, an insulator layer, and a photosensitizer, and its photoresponse characteristics were determined by current measurements. Irradiation of the graphene channel of the vacuum cooled device by an MWIR laser generated a clear photoresponse, as evidenced by modulation of the output current during irradiation. The MWIR photoresponse with the photogating effect was 100 times greater than that obtained from conventional graphene photodetectors without the photogating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The effect of the graphene channel size on the responsivity was evaluated to assess the feasibility of reducing the photodetector area, and decreasing the channel area from 100 to 25 μm2 improved the responsivity from 61.7 to 321.0 AW − 1. The results obtained in our study will contribute to the development of high-performance graphene-based IR imaging sensors.

High-performance silicon\u2212graphene hybrid plasmonic waveguide photodetectors beyond 1.55\u2009\u03bcm

Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range. However, the reported fast graphene photodetectors mainly operate in the 1.55 μm wavelength band. In this work, we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductive effects by introducing an ultrathin wide silicon−graphene hybrid plasmonic waveguide, which enables efficient light absorption in graphene at 1.55 μm and beyond. When operating at 2 μm, the present photodetector has a responsivity of ~70 mA/W and a setup-limited 3 dB bandwidth of >20 GHz. When operating at 1.55 μm, the present photodetector also works very well with a broad 3 dB bandwidth of >40 GHz (setup-limited) and a high responsivity of ~0.4 A/W even with a low bias voltage of −0.3 V. This work paves the way for achieving high-responsivity and high-speed silicon–graphene waveguide photodetection in the near/mid-infrared ranges, which has applications in optical communications, nonlinear photonics, and on-chip sensing.

Graphene light-field camera

A new light-field imaging scheme, employing stacks of transparent graphene photodetectors, has been demonstrated, providing a path to greatly simplify the otherwise complex three-dimensional imaging.

Compact Graphene Plasmonic Slot Photodetector on Silicon-on-Insulator with High Responsivity

Graphene has extraordinary electro-optic properties and is therefore a promising candidate for monolithic photonic devices such as photodetectors. However, the integration of this atom-thin layer material with bulky photonic components usually results in a weak light-graphene interaction leading to large device lengths limiting electro-optic performance. In contrast, here we demonstrate a plasmonic slot graphene photodetector on silicon-on-insulator platform with high-responsivity given the 5 um-short device length. We observe that the maximum photocurrent, and hence the highest responsivity, scales inversely with the slot gap width. Using a dual-lithography step, we realize 15 nm narrow slots that show a 15-times higher responsivity per unit device-length compared to photonic graphene photodetectors. Furthermore, we reveal that the back-gated electrostatics is overshadowed by channel-doping contributions induced by the contacts of this ultra-short channel graphene photodetector. This leads to quasi charge neutrality, which explains both the previously-unseen offset between the maximum photovoltaic-based photocurrent relative to graphenes Dirac point and the observed non-ambipolar transport. Such micrometer compact and absorption-efficient photodetectors allow for short-carrier pathways in next-generation photonic components, while being an ideal testbed to study short-channel carrier physics in graphene optoelectronics.

Investigating photoresponsivity of graphene-silver hybrid nanomaterials in the ultraviolet.

There have been several reports of plasmonically enhanced graphene photodetectors in the visible and the near infrared regime but rarely in the ultraviolet. In a previous work, we have reported that a graphene-silver hybrid structure shows a high photoresponsivity of 13 A/W at 270 nm. Here, we consider the likely mechanisms that underlie this strong photoresponse. We investigate the role of the plasmonic layer and examine the response using silver and gold nanoparticles of similar dimensions and spatial arrangement. The effect on local doping, strain, and absorption properties of the hybrid is also probed by photocurrent measurements and Raman and UV-visible spectroscopy. We find that the local doping from the silver nanoparticles is stronger than that from gold and correlates with a measured photosensitivity that is larger in devices with a higher contact area between the plasmonic nanomaterials and the graphene layer.

Ranging and light field imaging with transparent photodetectors

The core of any optical imaging system is a photodetector. Whether it is film or a semiconductor chip in a camera, or indeed the retina in an eye, conventional photodetectors are designed to absorb most of the incident light and record a projected two-dimensional (2D) distribution of light from a scene. The intensity distribution of light from 3D objects, however, can be described by a 4D light field, so optical imaging systems that can acquire higher dimensions of optical information are highly desirable1–3. Here, we report a proof-of-concept light field imaging scheme using transparent graphene photodetector stacks. On a transparent substrate we fabricate a photodetector using graphene as the light-sensing layer, the conducting channel layer, the gate layer and interconnects, enabling sensitive light detection and high transparency at the same time. This technology opens up the possibility of developing sensor arrays that can be stacked along the light path, enabling entirely new configurations of optical imaging devices. We experimentally demonstrate depth ranging using a double stack of transparent detectors and develop a method for computational reconstruction of a 4D light field from a single exposure that can be applied following the successful fabrication of dense 2D transparent sensor arrays. A highly transparent photodetector using graphene as the light-sensing layer, conducting channel layer, gate layer and interconnects enables new approaches for light field photodetection and imaging involving simultaneous detection across multiple focal planes.

Sc3N@C80 and La@C82 doped graphene for a new class of optoelectronic devices

Hybrid graphene photodetectors (PDs) with endohedral Sc3N@C80 and La@C82 were used by the Kaul Research Group at the University of North Texas to dope graphene p-type and n-type, respectively, that resulted in significant optoelectronic property enhancement of the PDs.

A broadband all-fiber integrated graphene photodetector with CNT-enhanced responsivity.

Carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene have great potential for high-performance all-carbon photodetectors due to their unique optical and electronic properties. Here, we assemble a hybrid CNT/graphene film prepared by depositing CNTs on a single layer graphene with a side-polished optical fiber to achieve a novel all-fiber integrated photodetector. Because CNTs strongly enhanced the interaction between graphene and the fiber mode, the photodetector shows an extra-high photoresponsivity over the visible and infrared region. Especially at 1550 nm, the photoresponsivity is found to be ∼1.48 × 105 A W-1, which is 6.5 times larger than those of photodetectors without CNTs. These findings provide a highly versatile, reproducible, and low-cost platform to integrate novel zero-, one-, and two-dimensional materials into optical fibers and deliver more sophisticated functionalities.

Interface phonon polariton coupling to enhance graphene absorption.

Here we present a graphene photodetector of which the graphene and structural system infrared absorptions are enhanced by interface phonon polariton (IPhP) coupling. IPhPs are supported at the SiC/AlN interface of device structure and used to excite interband transitions of the intrinsic graphene under gated-field tuning. The simulation results show that at normal incidence the absorbance of graphene or system reaches up to 43% or closes to unity in a mid-infrared frequency range. In addition, we found the peak-absorption frequency is mainly decided by the AlN thickness, and it has a red-shift as the thickness decreases. This structure has great application potential in graphene infrared detection technology.

High-responsivity turbostratic stacked graphene photodetectors using enhanced photogating

High-responsivity graphene photodetectors were fabricated using turbostratic stacked graphene, which provided enhanced photogating. Photogating is a promising means of increasing the responsivity of graphene photodetectors, and this effect is proportional to carrier mobility. Turbostratic stacked graphene exhibits higher carrier mobility than conventional monolayer graphene because it has the same band structure as monolayer graphene while preventing scattering by the underlying SiO2 layer. The photoresponse of these devices at a wavelength of 642 nm was approximately twice that obtained for a conventional monolayer graphene photodetector. The results reported show the feasibility of producing high-responsivity graphene-based photodetectors using a simple fabrication technique.

Multi-channels electrode parallel structure graphene photodetector with high performance

Graphene has attracted great attention in the field of optoelectronic application owing to its excellent electrical and optical properties. This paper reports a multi-channels electrode parallel structure monolayer pure graphene photodetector and it is verified that the device with this structure can obtain higher performance, larger photocurrent amplitude and smaller device resistance without adding additional manufacturing processes. During the measurement, the laser covers the whole surface of the device to simulate the actual operating conditions, which reveals the feasibility of using graphene photodetector with multi-channels parallel structure for the actual application. By adjusting the bias voltage, the photo responsivity of the photodetector can reach A/W level, which is much higher than the pure graphene photodetectors reported in previous research (a few mA/W). The reported novel electrode structure for graphene field transistor can be provide great opportunities for future graphene detectors.