Microcavity-Integrated Carbon Nanotube Photodetectors

Si/Organic Integrated Narrowband Near-Infrared Photodetector

Spectrally selective narrowband photodetection is critical for near-infrared (NIR) imaging applications, such as for communicationand night-vision utilities. It is a long-standing challenge for detectors based on silicon, to achieve narrowband photodetection without integrating any optical filters. Here, this work demonstrates a NIR nanograting Si/organic (PBDBT-DTBT:BTP-4F) heterojunction photodetector (PD), which for the first time obtains the full-width-at-half-maximum (FWHM) of only 26 nm and fast response of 74 µs at 895 nm. The response peak can be successfully tailored from 895 to 977 nm. The sharp and narrow response NIR peak is inherently attributed to the coherent overlapping between the NIR transmission spectrum of organic layer and diffraction enhanced absorption peak of patterned nanograting Si substrates. The finite difference time domain (FDTD) physics calculation confirms the resonant enhancement peaks, which is well consistent with the experiment results. Meanwhile, the relative characterization indicates that the introduction of the organic film can promote carrier transfer and charge collection, facilitating efficient photocurrent generation. This new device design strategy opens up a new window in developing low-cost sensitive NIR narrowband detection.

Synthesis, Sorting, and Applications of Single-Chirality Single-Walled Carbon Nanotubes

The synthesis of high-quality chirality-pure single-walled carbon nanotubes (SWCNTs) is vital for their applications. It is of high importance to modernize the synthesis processes to decrease the synthesis temperature and improve the quality and yield of SWCNTs. This review is dedicated to the chirality-selective synthesis, sorting of SWCNTs, and applications of chirality-pure SWCNTs. The review begins with a description of growth mechanisms of carbon nanotubes. Then, we discuss the synthesis methods of semiconducting and metallic conductivity-type and single-chirality SWCNTs, such as the epitaxial growth method of SWCNT ("cloning") using nanocarbon seeds, the growth method using nanocarbon segments obtained by organic synthesis, and the catalyst-mediated chemical vapor deposition synthesis. Then, we discuss the separation methods of SWCNTs by conductivity type, such as electrophoresis (dielectrophoresis), density gradient ultracentrifugation (DGC), low-speed DGC, ultrahigh DGC, chromatography, two-phase separation, selective solubilization, and selective reaction methods and techniques for single-chirality separation of SWCNTs, including density gradient centrifugation, two-phase separation, and chromatography methods. Finally, the applications of separated SWCNTs, such as field-effect transistors (FETs), sensors, light emitters and photodetectors, transparent electrodes, photovoltaics (solar cells), batteries, bioimaging, and other applications, are presented.

Single-Walled Carbon Nanotube-Germanium Heterojunction for High-Performance Near-Infrared Photodetector

In this research, we report on a high-performance near-infrared (near-IR) photodetector based on single-walled carbon nanotube-germanium (SWCNT-Ge) heterojunction by assembling SWCNT films onto n-type Ge substrate with ozone treatment. The ozone doping enhances the conductivity of carbon nanotube films and the formed interfacial oxide layer (GeOx) suppresses the leakage current and carriers’ recombination. The responsivity and detectivity in the near-IR region are estimated to be 362 mA W−1 and 7.22 × 1011 cm Hz1/2 W−1, respectively, which are three times the value of the untreated device. Moreover, a rapid response time of ~11 μs is obtained simultaneously. These results suggest that the simple SWCNT-Ge structure and ozone treatment method might be utilized to fabricate high-performance and low-cost near-IR photodetectors.

Encoding Enantiomeric Molecular Chiralities on Graphene Basal Planes

Graphene has demonstrated broad applications due to its prominent properties. Its molecular structure makes graphene achiral. Here, we propose a direct way to prepare chiral graphene by transferring chiral structural conformation from chiral conjugated amino acids onto graphene basal plane through π-π interaction followed by thermal fusion. Using atomic resolution transmission electron microscopy, we estimated an areal coverage of the molecular imprints (chiral regions) up to 64 % on the basal plane of graphene (grown by chemical vapor deposition). The high concentration of molecular imprints in their single layer points to a close packing of the deposited amino acid molecules prior to "thermal fusion". Such "molecular chirality-encoded graphene" was tested as an electrode in electrochemical enantioselective recognition. The chirality-encoded graphene might find use for other chirality-related studies and the encoding procedure might be extended to other two-dimensional materials.

Spectroscopic near-infrared photodetectors enabled by strong light-matter coupling in (6,5) single-walled carbon nanotubes

Strong light-matter coupling leads to the formation of mixed exciton-polariton states, allowing for a rigorous manipulation of the absorption and emission of excitonic materials. Here, we demonstrate the realization of this promising concept in organic photodetectors. By hybridizing the E₁₁ exciton of semiconducting (6,5) single-walled carbon nanotubes (SWNTs) with near-infrared cavity photons, we create spectrally tunable polariton states within a photodiode. In turn, we are able to red-shift the detection peak that coincides with the lower polariton band. Our photodiodes comprise a metal cavity to mediate strong coupling between light and SWNTs and utilize P3HT and PC₇₀BM as the electron donor and acceptor, respectively. The diodes are formed either via mixing of SWNTs, P3HT, and PC₇₀BM to create a bulk heterojunction or by sequential processing of layers to form flat heterojunctions. The resulting near-infrared sensors show tunable, efficient exciton harvesting in an application-relevant wavelength range between 1000 nm and 1300 nm, with optical simulations showing a possible extension beyond 1500 nm.

Chirality-Enriched Carbon Nanotubes for Next-Generation Computing

For the past half century, silicon has served as the primary material platform for integrated circuit technology. However, the recent proliferation of nontraditional electronics, such as wearables, embedded systems, and low-power portable devices, has led to increasingly complex mechanical and electrical performance requirements. Among emerging electronic materials, single-walled carbon nanotubes (SWCNTs) are promising candidates for next-generation computing as a result of their superlative electrical, optical, and mechanical properties. Moreover, their chirality-dependent properties enable a wide range of emerging electronic applications including sub-10 nm complementary field-effect transistors, optoelectronic integrated circuits, and enantiomer-recognition sensors. Here, recent progress in SWCNT-based computing devices is reviewed, with an emphasis on the relationship between chirality enrichment and electronic functionality. In particular, after highlighting chirality-dependent SWCNT properties and chirality enrichment methods, the range of computing applications that have been demonstrated using chirality-enriched SWCNTs are summarized. By identifying remaining challenges and opportunities, this work provides a roadmap for next-generation SWCNT-based computing.

Integrated Photodetectors Based on Group IV and Colloidal Semiconductors: Current State of Affairs

With the aim to take advantage from the existing technologies in microelectronics, photodetectors should be realized with materials compatible with them ensuring, at the same time, good performance. Although great efforts are made to search for new materials that can enhance performance, photodetector (PD) based on them results often expensive and difficult to integrate with standard technologies for microelectronics. For this reason, the group IV semiconductors, which are currently the main materials for electronic and optoelectronic devices fabrication, are here reviewed for their applications in light sensing. Moreover, as new materials compatible with existing manufacturing technologies, PD based on colloidal semiconductor are revised. This work is particularly focused on developments in this area over the past 5-10 years, thus drawing a line for future research.

Giga-Gain at Room Temperature in Functionalized Carbon Nanotube Phototransistors Based on a Nonequilibrium Mechanism

Achieving high gain in a photodetector is critical to detect weak light fields because of the need to amplify the signal. Here, we report the observation of a gain exceeding 10⁹ for a phototransistor composed of an array of aligned semiconducting carbon nanotubes functionalized with a nanoscale layer of poly(3-hexylthiophene-2,5-diyl) (P3HT). In contrast to the expectation based on simple band alignments, the phototransistor operates by transferring holes between the P3HT and the CNT, trapping negative charge near the nanotubes. This mechanism leads to an integrating detector that is shown to detect as little as 490 aW and to resolve as few as 8-13 photons/nanotube at room temperature. A detailed experimental and theoretical investigation of the mechanism shows that the phototransistor is most sensitive when prepared in a nonequilibrium state.

A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures (vdWHs) with other materials. Molybdenum disulfide (MoS2) atomic layers which exhibit high carrier mobility and optical transparency are very suitable for developing ultra-broadband photodetectors to be used from surveillance and healthcare to optical communication. This review provides a brief introduction to TMD-based photodetectors, exclusively focused on MoS2-based photodetectors. The current research advances show that the photoresponse of atomic layered MoS2 can be significantly improved by boosting its charge carrier mobility and incident light absorption via forming MoS2 based plasmonic nanostructures, halide perovskites-MoS2 heterostructures, 2D-0D MoS2/quantum dots (QDs) and 2D-2D MoS2 hybrid vdWHs, chemical doping, and surface functionalization of MoS2 atomic layers. By utilizing these different integration strategies, MoS2 hybrid heterostructure-based photodetectors exhibited remarkably high photoresponsivity raging from mA W-1 up to 1010 A W-1, detectivity from 107 to 1015 Jones and a photoresponse time from seconds (s) to nanoseconds (10-9 s), varying by several orders of magnitude from deep-ultraviolet (DUV) to the long-wavelength infrared (LWIR) region. The flexible photodetectors developed from MoS2-based hybrid heterostructures with graphene, carbon nanotubes (CNTs), TMDs, and ZnO are also discussed. In addition, strain-induced and self-powered MoS2 based photodetectors have also been summarized. The factors affecting the figure of merit of a very wide range of MoS2-based photodetectors have been analyzed in terms of their photoresponsivity, detectivity, response speed, and quantum efficiency along with their measurement wavelengths and incident laser power densities. Conclusions and the future direction are also outlined on the development of MoS2 and other 2D TMD-based photodetectors.

Silicon-Waveguide-Integrated Carbon Nanotube Optoelectronic System on a Single Chip

Monolithic optoelectronic integration based on a single material is a major pursuit in the fields of nanophotonics and nanoelectronics in order to meet the requirements of future fiber-optic telecommunication systems and on-chip optical interconnection systems. However, the incompatibility between silicon-based electronics and germanium or compound semiconductor-based photonics makes it very challenging to realize optoelectronic integration based on a single material. Here, the integration between silicon waveguides and a carbon nanotube (CNT) optoelectronic system is demonstrated. Waveguide-integrated photodetectors based on the CNT exhibit 12.5 mA/W photoresponsivity at 1530 nm, which presents an improvement of 97.6 times enhanced absorption efficiency compared to that without the waveguide. Multiplied output signals of cascading photodetectors are used to control the output of CNT-based logic gates, thereby demonstrating that the CNT-based optoelectronic integration system is compatible with silicon photonics. Our work indicates that carbon nanotubes have the potential for future integration between nanophotonics and nanoelectronics on a single chip.

Strain Effect Enhanced Ultrasensitive MoS2 Nanoscroll Avalanche Photodetector

Two-dimensional (2D) materials and their derived quasi one-dimensional structure provide incredible possibilities for the field of photoelectric detection due to their intrinsic optical and electrical properties. However, the photogenerated carriers in atomically thin media are poor due to the low optical absorption, which greatly limits their performance. Here, in the MoS₂ nanoscroll photodetector, we meticulously investigated the avalanche multiplication effect. The results show that by employing the nanoscroll structure, the required threshold electrical field for triggering avalanche multiplication is significantly lower than that of MoS₂ flake due to the modulation of the energy band and intervalley scattering through the strain effect. Consequently, avalanche multiplication could efficiently enhance the photoresponsivity to >10⁴ A/W. Furthermore, enhanced avalanche multiplication could be generalized to other TMDCs through theoretical prediction. The results not only are significant for the understanding of the intrinsic nature of 2D materials but also reveal meaningful advances in high-performance and low-power consumption photodetection.

Ultrathin Nano-Absorbers in Photovoltaics: Prospects and Innovative Applications

Approaching the first terawatt of installations, photovoltaics (PV) are about to become the major source of electric power until the mid-century. The technology has proven to be long lasting and very versatile and today PV modules can be found in numerous applications. This is a great success of the entire community, but taking future growth for granted might be dangerous. Scientists have recently started to call for accelerated innovation and cost reduction. Here, we show how ultrathin absorber layers, only a few nanometers in thickness, together with strong light confinement can be used to address new applications for photovoltaics. We review the basics of this new type of solar cell and point out the requirements to the absorber layer material by optical simulation. Furthermore, we discuss innovative applications, which make use of the unique optical properties of the nano absorber solar cell architecture, such as spectrally selective PV and switchable photovoltaic windows.

Nanoscale Patterning of Carbon Nanotubes: Techniques, Applications, and Future

Carbon nanotube (CNT) devices and electronics are achieving maturity and directly competing or surpassing devices that use conventional materials. CNTs have demonstrated ballistic conduction, minimal scaling effects, high current capacity, low power requirements, and excellent optical/photonic properties; making them the ideal candidate for a new material to replace conventional materials in next-generation electronic and photonic systems. CNTs also demonstrate high stability and flexibility, allowing them to be used in flexible, printable, and/or biocompatible electronics. However, a major challenge to fully commercialize these devices is the scalable placement of CNTs into desired micro/nanopatterns and architectures to translate the superior properties of CNTs into macroscale devices. Precise and high throughput patterning becomes increasingly difficult at nanoscale resolution, but it is essential to fully realize the benefits of CNTs. The relatively long, high aspect ratio structures of CNTs must be preserved to maintain their functionalities, consequently making them more difficult to pattern than conventional materials like metals and polymers. This review comprehensively explores the recent development of innovative CNT patterning techniques with nanoscale lateral resolution. Each technique is critically analyzed and applications for the nanoscale-resolution approaches are demonstrated. Promising techniques and the challenges ahead for future devices and applications are discussed.

Solution-Processing of High-Purity Semiconducting Single-Walled Carbon Nanotubes for Electronics Devices

High-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) are of paramount significance for the construction of next-generation electronics. Until now, a number of elaborate sorting and purification techniques for s-SWCNTs have been developed, among which solution-based sorting methods show unique merits in the scale production, high purity, and large-area film formation. Here, the recent progress in the solution processing of s-SWCNTs and their application in electronic devices is systematically reviewed. First, the solution-based sorting and purification of s-SWCNTs are described, and particular attention is paid to the recent advance in the conjugated polymer-based sorting strategy. Subsequently, the solution-based deposition and morphology control of a s-SWCNT thin film on a surface are introduced, which focus on the strategies for network formation and alignment of SWCNTs. Then, the recent advances in electronic devices based on s-SWCNTs are reviewed with emphasis on nanoscale s-SWCNTs' high-performance integrated circuits and s-SWCNT-based thin-film transistors (TFT) array and circuits. Lastly, the existing challenges and development trends for the s-SWCNTs and electronic devices are briefly discussed. The aim is to provide some useful information and inspiration for the sorting and purification of s-SWCNTs, as well as the construction of electronic devices with s-SWCNTs.

Carrier photogeneration, drift and recombination in a semiconducting carbon nanotube network

Charge carrier photogeneration, drift and recombination in thin film networks of polymer-wrapped (6,5)-single-wall carbon nanotubes (SWNTs) blended with phenyl-C61-butyric acid methyl ester (PCBM) have been investigated by using transient photocurrent and time-delayed collection field (TDCF) techniques. Three distinct transient photocurrent components on the nano- and microsecond timescales have been identified. We attribute the dominant (>50% of total extracted charge) ultrashort photocurrent component with a decay time below our experimental time-resolution of 2 ns to the intratube hole motion. The second component on the few microsecond timescale is attributed to the intertube hole transfer, while the slowest component is assigned to the electron drift within the PCBM phase. The hole drift distance appears to be limited by gaps in the nanotube percolation network rather than by hole trapping or recombination. Photocurrent saturation was observed when excitation densities reached more than one charge pair per nanotube; we attribute this to the local electric field screening.

Plasmonic Crystals for Strong Light-Matter Coupling in Carbon Nanotubes

Their high oscillator strength and large exciton binding energies make single-walled carbon nanotubes (SWCNTs) highly promising materials for the investigation of strong light-matter interactions in the near infrared and at room temperature. To explore their full potential, high-quality cavities-possibly with nanoscale field localization-are required. Here, we demonstrate the room temperature formation of plasmon-exciton polaritons in monochiral (6,5) SWCNTs coupled to the subdiffraction nanocavities of a plasmonic crystal created by a periodic gold nanodisk array. The interaction strength is easily tuned by the number of SWCNTs that collectively couple to the plasmonic crystal. Angle- and polarization resolved reflectivity and photoluminescence measurements combined with the coupled-oscillator model confirm strong coupling (coupling strength ∼120 meV). The combination of plasmon-exciton polaritons with the exceptional charge transport properties of SWCNTs should enable practical polariton devices at room temperature and at telecommunication wavelengths.