Carbon Nanotube Photodetector Research Articles

High-speed carbon nanotube photodetector based on a planarized silicon waveguide

The integration of silicon waveguides with low-dimensional materials with excellent optoelectronic properties can enable compact and highly integrated optical devices with multiple advantages for multiple fields. A carbon nanotube (CNT) photodetector integrated on the silicon waveguide has the potential to meet on-chip high-speed optical interconnection systems, based on the outstanding properties of CNTs such as picosecond-level intrinsic photoresponse time, high charge carrier mobility, broad spectral response, high absorption coefficient, and so on. However, the thermal stability of the device may be compromised due to the local suspension in the channel for the height difference between the WG and the substrate. Here, we report a low-cost and low-optical-loss method to achieve the planarized silicon waveguide. After that, the CNT photodetectors integrated on the original and planarized waveguide with asymmetric palladium (Pd)-hafnium (Hf) metal contacts are fabricated. The influence of this planarization method on the performance of devices is analyzed via comparing the dark leakage current, the leakage current rectification ratio (CRR), the series resistances (R S ), and the photoelectric response. Finally, a CNT photodetector based on the planarized waveguide with a photocurrent (Iph) ∼510.84nA, a photoresponsivity (R I ) ∼51.04mA/W, the dark current ∼0.389µA, as well as a 3 dB bandwidth ∼34GHz at the large reverse voltage −3V is shown.

Optimizing fabrication and performance of liquid‐processed carbon nanotube photodetectors on various substrates

AbstractCarbon nanotubes (CNTs) have attracted interest for optoelectronic applications due to their unique electronic and optoelectronic properties. In particular, multiwall (MW) CNTs film acts as perfect photo‐collector surface with the possibility to tune the absorbance by controlling the film thickness. In this work, we demonstrate two types of hybrid Si‐MWCNTs photodetectors. The MWCNTs are solution‐processed and deposited on n‐silicon substrate covered by two different dielectrics (Si3N4 or SiO2). The MWCNTs/SiO2/n‐Si device is used here as reference, since the SiO2/Si system is the most widely investigated structure in microelectronics. The electrical and optical characteristics of the reference device are compared with the corresponding of our basic MWCNTs/Si3N4/n‐Si device. The MWCNTs are deposited on the substrate with the drop casting technique. Optical performance of the SiO2 device is comparable to the Si3N4 device thus revealing a quite interesting response under UV illumination. The Si3N4 device exhibited a peak equivalent quantum efficiency (EQE) of 57% at 3 μW of source illumination power, thus demonstrating a superior performance as compared to the SiO2 device (EQE of up to 55%, which is also promising for future applications). This performance can be attributed to the great absorption in UV region of CNTs layer. Apart from this technological goal, we also investigated how MWCNTs/Si3N4 or MWCNTs/SiO2 heterojunctions perform using standard electrical characterization techniques and how the presence of the CNTs change the dielectric characteristics of both substrates.

Shortwave Infrared Polarization Imaging and Monolithic Integrated Polarization Amplification Systems Based on Aligned Carbon Nanotube Arrays

AbstractNext‐generation shortwave infrared (SWIR) imaging systems generally require a multidimensional information sensing capability (including intensity, wavelength, polarization, phase, etc.), a highly integrated photodetector unit, and information processing, allowing for miniaturization and low‐cost production. However, traditional polarized SWIR imaging systems with integrated polarizer arrays as supplementary filters and silicon‐based amplifying circuits are complicated and very expensive. Here, a SWIR polarization‐sensitive photodetector and a monolithic integrated polarization amplification system (MIPAS) based on well‐aligned carbon nanotube (CNT) arrays are demonstrated. The polarization‐sensitive CNT photodetector exhibits anisotropic ratios of ≈5.18 and ≈7.56 at 1800 and 2000 nm wavelengths, respectively, and high‐resolution characteristics that can be utilized to image SWIR laser spots with a radius of less than 10 µm. Furthermore, MIPAS including a CNT field‐effect transistor, a CNT loading resistor, and a polarization‐sensitive CNT photodetector is used to increase the anisotropic ratio of the CNT photodetector. The amplified anisotropic ratio is improved up to 173 and 243 at 1800 and 2000 nm wavelengths, respectively, which is the maximum reported in the SWIR band. Our work demonstrates that the CNT polarization‐sensitive photodetector has the potential for SWIR polarization imaging with a monolithic integrated polarization amplification system.

High-Speed Carbon Nanotube Photodetectors for 2 μm Communications.

In the era of big data, the growing demand for data transmission capacity requires the communication band to expand from the traditional optical communication windows (∼1.3-1.6 μm) to the 2 μm band (1.8-2.1 μm). However, the largest bandwidth (∼30 GHz) of the current high-speed photodetectors for the 2 μm window is considerably less than the developed 1.55 μm band photodetectors based on III-V materials or germanium (>100 GHz). Here, we demonstrate a high-performance carbon nanotube (CNT) photodetector that can operate in both the 2 and 1.55 μm wavelength bands based on high-density CNT arrays on a quartz substrate. The CNT photodetector exhibits a high responsivity of 0.62 A/W and a large 3 dB bandwidth of 40 GHz (setup-limited) at 2 μm. The bandwidth is larger than that of existing photodetectors working in this wavelength range. Moreover, the CNT photodetector operating at 1.55 μm exhibits a setup-limited 3 dB bandwidth over 67 GHz at zero bias. Our work indicates that CNT photodetectors with high performance and low cost have great potential for future high-speed optical communication at both the 2 and 1.55 μm bands.

Silicon Waveguide-Integrated Carbon Nanotube Photodetector with Low Dark Current and 48 GHz Bandwidth.

Low-dimensional materials with excellent optoelectronic properties and complementary metal-oxide-semiconductor (CMOS) process compatibility have the potential to construct high-performance photodetectors used in a cost-efficient monolithic or hybrid integrated optical communication system. Carbon nanotubes (CNTs) have attracted a lot of attention due to special geometric structure and broad band response, high optical absorption coefficient, ps-level intrinsic light response, high carrier mobility and wafer-scaled production process. Here, we demonstrated a high-performance waveguide-integrated CNT photodetector with asymmetric palladium (Pd) and hafnium (Hf) contact electrodes. The ideal photodetector structure was realized via comparing with simulation and experimental results, where the optimized device achieved a high 3 dB bandwidth ∼48 GHz at 0 V, as well as a responsivity ∼73.62 mA/W and dark current ∼0.157 μA at -2 V bias voltage. This waveguide-integrated CNT photodetector with low dark current and high bandwidth is helpful for next-generation optical communication and high-speed optical interconnects.

High-Performance Visible-Near-Infrared Single-Walled Carbon Nanotube Photodetectors via Interfacial Charge-Transfer-Induced Improvement by Surface Doping.

Single-walled carbon nanotubes (SWCNTs) are considered to be promising candidates for next-generation near-infrared (NIR) photodetectors due to their extraordinary electrical and optical properties. However, the low separation efficiency of photogenerated carriers limits the full utilization of the potential of pristine SWCNTs as photoactive materials. Herein, we report a novel high-performance visible-NIR SWCNT-based photodetector via interfacial charge-transfer-induced improvement by Au nanoparticle (AuNP) surface doping. Under 1064 nm light illumination, the as-fabricated AuNP/SWCNT photodetector exhibits an excellent photoelectrical performance with a responsivity of 2.16 × 105 A/W and a high detectivity of 1.82 × 1014 Jones, which is three orders of magnitude higher than that of the SWCNT photodetector under the same conditions. Importantly, the interfacial charge transfer between AuNPs and SWCNTs has been first investigated using Raman shift statistics at room temperature. Experimental results indicate that the interfacial charge transfer induced by AuNP doping can reduce the Fermi level of SWCNTs and effectively improve the generation and transport of photogenerated carriers, thereby enhancing the photoelectric performance of SWCNT-based photodetectors. We believe that our results not only demonstrate a facile route to improve the performance of SWCNT-based photodetectors but also provide a novel methodology to characterize the interfacial charge transfer between dopants and SWCNTs.

(Invited, Digital Presentation) Macroscopically Aligned Carbon Nanotubes for Photonics, Electronics, and Thermoelectrics

The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting [1]. However, the long-standing goal in the preparation of CNT ensembles is how to maintain the extraordinary properties of individual CNTs on a macroscopic scale. The polydispersity and randomness remain two main challenges.Here, we will discuss different methods for creating macroscopically aligned CNTs, including spontaneous formation of wafer-scale aligned CNT films via controlled vacuum filtration [2-4] and production of ultrahigh-conductivity CNT fibers and films through solution spinning and coating [5,6]. We will then describe the optical [2,7-11], dc and ac electrical [2,12-17], thermal [18], and thermoelectric [19-21] properties of these materials. These results are promising for device applications in various fields such as flexible CNT broadband detectors [22-26], spectrally selective thermal emitters [11], and thermoelectric devices [20,21]. W. Gao et al., “Macroscopically Aligned Carbon Nanotubes for Flexible and High-Temperature Electronics, Optoelectronics, and Thermoelectrics,” Journal of Physics D: Applied Physics 53, 063001 (2020).X. He et al., “Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes,” Nature Nanotechnology 11, 633 (2016).W. Gao and J. Kono, “Science and Applications of Wafer-Scale Crystalline Carbon Nanotube Films Prepared through Controlled Vacuum Filtration,” Royal Society Open Science 6, 181605 (2019).N. Komatsu et al., “Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration,” Nano Letters 20, 2332 (2020).N. Behabtu et al., “Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity,” Science 339, 182 (2013).L. W. Taylor et al., “Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers,” Carbon 171, 689 (2021).K. Yanagi et al., “Intersubband Plasmons in the Quantum Limit in Gated and Aligned Carbon Nanotubes,” Nature Communications 9, 1121 (2018).W. Gao et al., “Continuous Transition between Weak and Ultrastrong Coupling through Exceptional Points in Carbon Nanotube Microcavity Exciton–Polaritons,” Nature Photonics 12, 362 (2018).M. E. Green et al., “Bright and Ultrafast Photoelectron Emission from Aligned Single-Wall Carbon Nanotubes through Multiphoton Exciton Resonance,” Nano Letters 19, 158 (2019).F. Katsutani et al., “Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon Nanotubes,” Physical Review B 99, 035426 (2019).W. Gao et al., “Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters,” ACS Photonics 6, 1602 (2019).X. Wang et al., “High-Ampacity Power Cables of Tightly-Packed and Aligned Carbon Nanotubes,” Advanced Functional Materials 24, 3241 (2014).A. Zubair et al., “Carbon Nanotube Fiber Terahertz Polarizer,” Applied Physics Letters 108, 141107 (2016).D. Tristant et al., “Enlightening the Ultrahigh Electrical Conductivities of Doped Double-Wall Carbon Nanotube Fibers by Raman Spectroscopy and First-Principles Calculations,” Nanoscale 18, 19668 (2016).N. Komatsu et al., “Modulation-Doped Multiple Quantum Wells of Aligned Single-Wall Carbon Nanotubes,” Advanced Functional Materials 27, 1606022 (2017).F. R. G. Bagsican et al., “Terahertz Excitonics in Carbon Nanotubes: Exciton Autoionization and Multiplication,” Nano Letters 20, 3098 (2020).A. Baydin et al., “Giant Terahertz Polarization Rotation in Ultrathin Films of Aligned Carbon Nanotubes,” Optica 8, 760 (2021).S. Yamaguchi et al., “One-Directional Thermal Transport in Densely Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 115, 223104 (2019).K. Fukuhara et al., “Isotropic Seebeck Coefficient of Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 113, 243105 (2018).Y. Ichinose et al., “Solving the Thermoelectric Trade-Off Problem with Metallic Carbon Nanotubes,” Nano Letters 19, 7370 (2019).N. Komatsu et al., “Macroscopic Weavable Fibers of Carbon Nanotubes with Giant Thermoelectric Power Factor,” Nature Communications 12, 4931 (2021).S. Nanot et al., “Broadband, Polarization-Sensitive Photodetector Based on Optically-Thick Films of Macroscopically Long, Dense, and Aligned Carbon Nanotubes,” Scientific Reports 3, 1335 (2013).X. He et al., “Photothermoelectric p-n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films,” ACS Nano 7, 7271 (2013).X. He et al., “Carbon Nanotube Terahertz Detector,” Nano Letters 14, 3953 (2014).X. He, F. Léonard, and J. Kono, “Uncooled Carbon Nanotube Photodetectors,” Advanced Optical Materials 3, 989 (2015).A. Zubair et al., “Carbon Nanotube Woven Textile Photodetector,” Physical Review Materials 2, 015201 (2018).

All-Carbon Photodetectors: Highly Sensitive Broadband Single-Walled Carbon Nanotube Photodetectors Enhanced by Separated Graphene Nanosheets (Advanced Optical Materials 23/2018)

All-Carbon Photodetectors: Highly Sensitive Broadband Single-Walled Carbon Nanotube Photodetectors Enhanced by Separated Graphene Nanosheets (Advanced Optical Materials 23/2018)

Room-Temperature Phototransistor with Negative Photoresponsivity of 108 A W-1 Using Fullerene-Sensitized Aligned Carbon Nanotubes.

Detection of low intensity light down to a few photons requires photodetectors with high gain. A new photodetector is reported based on C60 -sensitized aligned carbon nanotube (CNT) transistors with an extremely high responsivity of 108 A W-1 (gain > 108 ) in the ultraviolet and visible range, and 720 A W-1 (gain = 940) in the infrared range. In contrast to most sensitized phototransistors that operate on the photogating effect, the new photodetector operates on the modulation of the electrons scattering in the CNTs, leading to negative photoconductivity. Comparison with similar photodetectors using random CNT networks shows the benefit of using aligned CNTs. At room temperature, the aligned CNT photodetectors are demonstrated to detect a few tens of photons per CNT.

Highly Sensitive Broadband Single‐Walled Carbon Nanotube Photodetectors Enhanced by Separated Graphene Nanosheets

AbstractSingle‐walled carbon nanotube (SWCNT)/graphene Schottky junctions have great potential for high‐performance all‐carbon photodetector due to their excellent optical and electronic properties and efficient charge transfer. However, the further improvement of device performance is limited by the low absorption of ultrathin SWCNTs and large dark current of continuous graphene nanosheets. Here a proof‐of‐concept photodetector is reported using SWCNT/separated graphene (SGR) hybrid networks. The device is sensitive to a broadband wavelength from visible light to near‐infrared light (405–1064 nm), showing an extremely high photoresponsivity of >3000 A W−1, a fast response speed of 44 µs, and high photoconductive gain of ≈4 × 106. Furthermore, the results demonstrate first the charge transfer dynamics at the planar SWCNT/SGR Schottky junctions by combining Raman spectra with current–voltage curves. The architecture strategy opens a new general route to fabricate ultrahigh‐performance photodetectors based on SWCNT/SGR hybrids or other semiconductor/graphene hybrids.

Electrostatics and quantum efficiency simulations of asymmetrically contacted carbon nanotube photodetector

Electrostatic properties of asymmetrically contacted carbon nanotube barrier-free bipolar diode photodetector are studied by solving the Poisson equation self-consistently with equilibrium carrier statistics. For electric field parallel to tube’s axis, the maximum electric field occurs near contact but decays rapidly in a few nanometers, followed by a slowly increasing trend when it extends to the center of channel. By considering the field ionization and the diffusion effect of exciton, a model of estimation on quantum efficiency for the device is made. We find that the quantum efficiency increases with increasing exciton lifetime, decreasing diffusion constant and channel length. For devices with a channel length shorter than 50 nm, the contribution of field ionization to the quantum efficiency can reach 60%.

Comparison of the quantum efficiency and the responsivity of the single-walled carbon nanotube photodetector with different electrode metals

In this paper, experimental measurements of the photoconductivity in single-walled carbon nanotube (SWCNT) thin films were taken using four different electrodes (Pt, Pd, Au and Ti). Our work shows the impact of the light power intensities and wavelengths on the photoresponse signal. In this context, we have performed the electrical transport characteristics of the device at room temperature under visible continuous wavelength illumination. The photoconductivity measurements, achieved without gating, have shown a strong photoresponse enhancement at the nanotubes/electrode junctions. The obtained response has been generally attributed to the dissociation and subsequent diffusion of photoexcited carriers. We have also proven that a good choice of the metal electrode evidently enhances the photoconductivity of SWCNT-thin film. Due to its high work function and its excellent adhesivity on the thin film of SWCNTs, Au electrodes have shown the most important results than the others metals. The highest quantum efficiency ( $$ \eta $$ ) calculated in our case is about 12%, and the responsivity reaches 121.48 mA/W for Au–SWCNT contact.

Fully printed flexible carbon nanotube photodetectors

Here, we report fully printed flexible photodetectors based on single-wall carbon nanotubes and the study of their electrical characteristics under laser illumination. Due to the photothermal effect and the use of high purity semiconducting carbon nanotubes, the devices exhibit gate-voltage-dependent photoresponse with the positive photocurrent or semiconductor-like behavior (conductivity increases at elevated temperatures) under positive gate biases and the negative photocurrent or metal-like behavior (conductivity decreases at elevated temperatures) under negative gate biases. Mechanism for such photoresponse is attributed to the different temperature dependencies of carrier concentration and carrier mobility, which are two competing factors that ultimately determine the photothermal effect-based photoresponse. The photodetectors built on the polyimide substrate also exhibit superior mechanical compliance and stable photoresponse after thousands of bending cycles down to a curvature radius as small as 3 mm. Furthermore, due to the low thermal conductivity of the plastic substrate, the devices show up to 6.5 fold improvement in responsivity compared to the devices built on the silicon substrate. The results presented here provide a viable path to low cost and high performance flexible photodetectors fabricated entirely by the printing process.

Photodetectors: Room Temperature Broadband Infrared Carbon Nanotube Photodetector with High Detectivity and Stability (Advanced Optical Materials 2/2016)

On page 238, S. Wang, L.-M. Peng, and co-workers demonstrate the potential for constructing IR imaging systems based on solution-processed carbon nanotubes (CNTs). The inside cover depicts a part of the 150×150 detector array, showing a typical cascading photodetector with two virtual contacts, which can greatly increase the signal-to-noise ratio and therefore improve light detection. Compared with traditional IR systems, detectors based on solution-processed CNTs are simpler to fabricate, lower cost, and much more stable.

Advanced Optical Materials is Making its Way Up

It has been an eventful year for the optics research community and the optical industry sector, not least because 2015 was the UNESCO International Year of Light. Light technologies are the basis of a multi-billion dollar industry as well as an integral part of our everyday lives. Optical research is a motor for innovation and its application areas are numerous. This variety is reflected by the broad spectrum of high quality work published in Advanced Optical Materials. Let's have a look back on some of the high points of 2015. One highlight was definitely the special issue on “Optical Materials for Spectral Management” guest-edited by Ralf Wehrspohn and Stefan Schweizer. This compilation included review articles on different spectral converters as fluoride hosts and methods to tune the fluorescence of phosphors and their applications in photovoltaics, scintillator materials, and solid-state lighting. Furthermore, many new results on materials for up- and down-conversion were published, three examples being novel energy-transfer materials presented by Andries Meijerink et al., an innovative topotactic transformation synthetic route from Hongpeng You and colleagues, and persistent and photostimulated red emission in nanophosphors presented by John Capobianco. The whole issue can be found here. We were also very proud to be able to present a very special article series dedicated to celebrate the International Year of Light. The topics of the featured review articles, written by experts in their fields, span carbon nanotube photodetectors and photonic structures for light harvesting to micro-transfer printing and plasmonic nanoparticles. You can find all of the contributions in the table below or online at www.advopticalmat.de/IYL. In the past two years the Best of Advanced Optical Materials editions were very well received by the community. Therefore, this year we also selected some of the most outstanding articles from all original articles published in the twelve issues of 2015. The collection can be found at www.best-of-advanced-optical-materials-2015.com and gives you a good impression of the high quality and broad scope of the content published in Advanced Optical Materials. The excellent research published in Advanced Optical Materials has contributed to the journal's first one-year impact factor of 4.062, which is a very promising result underlining the position among the top optics journals. Citations and impact factors are not the only measures of a journal's performance and the quality of the presented research; but this inaugural value, together with our 2015 Immediacy Index of 1.132, provides a solid foundation on which to build in future years. We would like to take this opportunity to thank our Editorial Advisory Board members for their help and advice over the last year, all authors who submitted to the journal, and last but certainly not least all of the more than 1200 reviewers who help to maintain the standards of the journal. We would especially like to mention our most frequent reviewers—Hongbing Fu, Jianfang Wang, Dai-Sik Kim, Hirohiko Fukagawa, Paul Braun, Yong Sheng Zhao, Timothy Bunning, and He Tian—for their generous contributions to the success of the journal. Thank you very much! For the coming year of 2016 we wish you great success and hope that we can contribute to it through our continuous publishing efforts and dedication to good customer service. P.S.: For any kind of feedback please contact us at advopticalmat@wiley-vch.de.

Room Temperature Broadband Infrared Carbon Nanotube Photodetector with High Detectivity and Stability

Room Temperature Broadband Infrared Carbon Nanotube Photodetector with High Detectivity and Stability

Infrared Camera Using a Single Nano-Photodetector

Infrared (IR) cameras have versatile applications; however, the low performance and high cost of conventional photodetectors have prevented their widespread utilization in various fields. Nano-materials have recently emerged as possible sensing elements of nano-photodetectors, and have exhibited data that may outperform their conventional counterparts. Carbon nanotube (CNT), a promising nano-material with excellent optical properties, has been employed to develop high performance photodetectors with low noise, tunable bandgap, and noncryogenic cooled operation. However, it is difficult to fabricate a large scale CNT photodetector array that can be integrated into traditional IR camera structures. In order to take advantage of the outstanding performance of the nano-photodetectors and overcome the fabrication difficulties to achieve high resolution and efficient imaging, we present a compressive sensing-based IR camera using a single pixel CNT photodetector. A photonic cavity is developed to integrate with the CNT photodetector so as to increase the absorption area of the device. The camera system uses the CNT photodetector to compressively sample the linear projections of the images onto binary random patterns. Employing the compressive sensing algorithm, high resolution imaging can be achieved with many fewer samples than the original image dimension. The camera is demonstrated effectively in order to observe the dynamic movement of a laser spot. By adaptively adjusting the camera setup, a zooming technique is developed to image small features. To our knowledge, this is the first demonstration of an IR camera using a nano-size photodetector. Our work shows that compressive sensing-based cameras have the potential to complement or selectively replace conventional IR imaging systems.

Progress on the development of a silicon–carbon nanotube photodetector

The properties of carbon nanotubes (CNTs), the new allotropic status of carbon discovered in 1991, have been widely investigated in all possible application field. This new material in fact can be easily obtained chemically by CVD (Chemical Vapour Deposition) as a layer of nanotubes growth on a wide variety of materials. When growth on a silicon surface, CNTs create a semiconductor heterojunction with peculiar photoresponsivity properties. We studied this heterojunction with the purpose to realize a large photocathode with high quantum efficiency in a large wavelength range from UV to IR. Results obtained up to day allowed us to build a new kind of photodetector very cheap, stable and easy to manage. Recently this new device has been proposed as one of candidates for the beam monitor system of SuperB.

Optical immunosensor using carbon nanotubes coated with a photovoltaic polymer

In this work, an on-chip optical immunosensor using an individually assembled carbon nanotube (CNT) coated with a photovoltaic polymer has been proposed, developed, characterized, and applied for the detection of cardiac biomarkers. An individual CNT was self-assembled on a nickel (Ni)-patterned electrode by magnetically attracting the residual iron catalyst at one end of the CNT. After the CNT self-assembled electrode was prepared, it was coated with a photovoltaic polymer to implement a CNT photodetector. Under an incident light, the photovoltaic polymer generated electrons that changed the conductivity of the CNT. The CNT photodetector was finally insulated with parylene to prevent interruptions of charged molecules in a sample solution, such as non-specifically bound proteins and various ions. Chemiluminescent immunoassay was directly performed on the CNT photodetector for an on-chip detection of cardiac troponin T (cTnT) with a detection limit of 12pg/mL. High sensitivity and reliable selectivity have been achieved through the use of on-chip measurement of chemiluminescent light by the CNT photodetector. As a result, the developed device is envisaged as a new platform for optical immunosensing using the individually self-assembled CNT for point-of-care (POC) clinical diagnostics.

Plasmonic-Resonant Bowtie Antenna for Carbon Nanotube Photodetectors

The design of bowtie antennas for carbon nanotube (CNT) photodetectors has been investigated. CNT photodetectors have shown outstanding performance by using CNT as sensing element. However, detection wavelength is much larger than the diameter of the CNT, resulting in small fill factor. Bowtie antenna can confine light into a subwavelength volume based on plasmonic resonance, thus integrating a bowtie antenna to CNT photodetectors can highly improve photoresponse of the detectors. The electric field enhancement of bowtie antennas was calculated using the device geometry by considering fabrication difficulties and photodetector structure. It is shown that the electric field intensity enhancement increased exponentially with distance reduction between the CNT photodetector to the antenna. A redshift of the peak resonance wavelength is predicted due to the increase of tip angles of the bowtie antennas. Experimental results showed that photocurrent enhancement agreed well with theoretical calculations. Bowtie antennas may find wide applications in nanoscale photonic sensors.