Waveguide-Integrated Electrically Driven Light-Emitting Carbon Nanotubes

In this work proof-of-concept devices with light-emitting electrically driven carbon nanotubes (CNTs) integrated in nanophotonic environments are presented. Electroluminescent and incandescent CNTs can be envisioned as waveguide-integrated light sources for future on-chip data communication due to their unique structural, electrical and optical properties. The challenge thereby is to integrate and electrically contact solution processed CNTs across CMOS compatible waveguide structures and to enforce efficient coupling of light from the CNT into the waveguide. Various nanophotonic devices with versatile functionalities were fabricated and equipped with CNTs by means of site-selective dielectrophoresis. The realized electrically driven CNT-based light emitters integrated with nanophotonic circuits allow for efficient coupling and propagation of light in waveguides over centimeter distances. Furthermore, in scope of the thesis it was demonstrated how spectral properties of a CNT emitter can be controlled directly on a chip with passive devices using grating structures, Mach-Zehnder interferometers and directional couplers. Moreover, it was observed that in combination with a one-dimensional photonic crystal cavity CNT becomes an emitter with exceptionally narrow linewidths at desired adjustable wavelength. Finally, the usage of electrically driven CNTs as fast waveguide-integrated light emitters with Gbit/s response speed was shown. Therefore direct, near-field coupling of electrically generated CNT-emitted light into a waveguide, opposed to far-field fiber coupling of external light sources, opens new avenues for scalable nanoscale optoelectronic systems in a CMOS compatible framework

Directional couplers with integrated carbon nanotube incandescent light emitters

We combine on-chip single-walled carbon nanotubes (SWNTs) emitters with directional coupling devices as fundamental building blocks for carbon photonic systems. These devices are essential for studying the emission properties of SWNTs in the few photon regime for future applications in on-chip quantum photonics. The combination of SWNTs with on-chip beam splitters herein provides the basis for correlation measurements as necessary for nanoscale source characterization. The employed fabrication methods are fully scalable and thus allow for implementing a multitude of functional and active circuits in a single fabrication run. Our metallic SWNT emitters are broadband and cover both visible and near-infrared wavelengths, thus holding promise for emerging hybrid optoelectronic devices with fast reconfiguration times

An electroluminescent and tunable cavity-enhanced carbon-nanotube-emitter in the telecom band

Emerging photonic information processing systems require chip-level integration of controllable nanoscale light sources at telecommunication wavelengths. Currently, substantial challenges remain in the dynamic control of the sources, the low-loss integration into a photonic environment, and in the site-selective placement at desired positions on a chip. Here, we overcome these challenges using heterogeneous integration of electroluminescent (EL), semiconducting carbon nanotubes (sCNTs) into hybrid two dimensional – three dimensional (2D-3D) photonic circuits. We demonstrate enhanced spectral line shaping of the EL sCNT emission. By back-gating the sCNT-nanoemitter we achieve full electrical dynamic control of the EL sCNT emission with high on-off ratio and strong enhancement in the telecommunication band. Using nanographene as a low-loss material to electrically contact sCNT emitters directly within a photonic crystal cavity enables highly efficient EL coupling without compromising the optical quality of the cavity. Our versatile approach paves the way for controllable integrated photonic circuits

Contact spacing controls the on-current for all-carbon field effect transistors

All-carbon field-effect transistors, which combine carbon nanotubes and graphene hold great promise for many applications such as digital logic devices and single-photon emitters. However, the understanding of the physical properties of carbon nanotube (CNT)/graphene hybrid systems in such devices remained limited. In this combined experimental and theoretical study, we use a quantum transport model for field-effect transistors based on graphene electrodes and CNT channels to explain the experimentally observed low on currents. We find that large graphene/CNT spacing and short contact lengths limit the device performance. We have also elucidated in this work the experimentally observed ambipolar transport behavior caused by the flat conduction- and valence-bands and describe non-ideal gate-control of the contacts and channel region by the quantum capacitance of graphene and the carbon nanotube. We hope that our insights will accelerate the design of efficient all-carbon field-effect transistors

Sub-nanosecond light-pulse generation with waveguide-coupled carbon nanotube transducers

Carbon nanotubes (CNTs) have recently been integrated into optical waveguides and operated as electrically-driven light emitters under constant electrical bias. Such devices are of interest for the conversion of fast electrical signals into optical ones within a nanophotonic circuit. Here, we demonstrate that waveguide-integrated single-walled CNTs are promising high-speed transducers for light-pulse generation in the gigahertz range. Using a scalable fabrication approach we realize hybrid CNT-based nanophotonic devices, which generate optical pulse trains in the range from 200 kHz to 2 GHz with decay times below 80 ps. Our results illustrate the potential of CNTs for hybrid optoelectronic systems and nanoscale on-chip light sources

Low-temperature electroluminescence excitation mapping of excitons and trions in short channel monochiral carbon nanotube device

Single walled carbon nanotubes as emerging quantum-light sources may fill a technological gap in silicon photonics due to their potential use as near infrared, electrically driven, classical or non-classical emitters. Unlike in photoluminescence, where nanotubes are excited with light, electrical excitation of single tubes is challenging and heavily influenced by device fabrication, architecture and biasing conditions. Here we present electroluminescence spectroscopy data of ultra short channel devices made from (9,8) carbon nanotubes emitting in the telecom band. Emissions are stable under current biasing and no quenching is observed down to 10 nm gap size. Low-temperature electroluminescence spectroscopy data also reported exhibits cold emission and linewidths down to 2 meV at 4 K. Electroluminescence excitation maps give evidence that carrier recombination is the mechanism for light generation in short channels. Excitonic and trionic emissions can be switched on and off by gate voltage and corresponding emission efficiency maps were compiled. Insights are gained into the influence of acoustic phonons on the linewidth, absence of intensity saturation and exciton exciton annihilation, environmental effects like dielectric screening and strain on the emission wavelength, and conditions to suppress hysteresis and establish optimum operation conditions

Waveguide-Integrated Electrically Driven Light-Emitting Carbon Nanotubes

In this work proof-of-concept devices with light-emitting electrically driven carbon nanotubes (CNTs) integrated in nanophotonic environments are presented. Electroluminescent and incandescent CNTs can be envisioned as waveguide-integrated light sources for future on-chip data communication due to their unique structural, electrical and optical properties. The challenge thereby is to integrate and electrically contact solution processed CNTs across CMOS compatible waveguide structures and to enforce efficient coupling of light from the CNT into the waveguide. Various nanophotonic devices with versatile functionalities were fabricated and equipped with CNTs by means of site-selective dielectrophoresis. The realized electrically driven CNT-based light emitters integrated with nanophotonic circuits allow for efficient coupling and propagation of light in waveguides over centimeter distances. Furthermore, in scope of the thesis it was demonstrated how spectral properties of a CNT emitter can be controlled directly on a chip with passive devices using grating structures, Mach-Zehnder interferometers and directional couplers. Moreover, it was observed that in combination with a one-dimensional photonic crystal cavity CNT becomes an emitter with exceptionally narrow linewidths at desired adjustable wavelength. Finally, the usage of electrically driven CNTs as fast waveguide-integrated light emitters with Gbit/s response speed was shown. Therefore direct, near-field coupling of electrically generated CNT-emitted light into a waveguide, opposed to far-field fiber coupling of external light sources, opens new avenues for scalable nanoscale optoelectronic systems in a CMOS compatible framework

Contact spacing controls the on-current for all-carbon field effect transistors

All-carbon field-effect transistors, which combine carbon nanotubes and graphene hold great promise for many applications such as digital logic devices and single-photon emitters. However, the understanding of the physical properties of carbon nanotube (CNT)/graphene hybrid systems in such devices remained limited. In this combined experimental and theoretical study, we use a quantum transport model for field-effect transistors based on graphene electrodes and CNT channels to explain the experimentally observed low on currents. We find that large graphene/CNT spacing and short contact lengths limit the device performance. We have also elucidated in this work the experimentally observed ambipolar transport behavior caused by the flat conduction- and valence-bands and describe non-ideal gate-control of the contacts and channel region by the quantum capacitance of graphene and the carbon nanotube. We hope that our insights will accelerate the design of efficient all-carbon field-effect transistors

Contact spacing controls the on-current for all-carbon field effect transistors

All-carbon field-effect transistors, which combine carbon nanotubes and graphene hold great promise for many applications such as digital logic devices and single-photon emitters. However, the understanding of the physical properties of carbon nanotube (CNT)/graphene hybrid systems in such devices remained limited. In this combined experimental and theoretical study, we use a quantum transport model for field-effect transistors based on graphene electrodes and CNT channels to explain the experimentally observed low on currents. We find that large graphene/CNT spacing and short contact lengths limit the device performance. We have also elucidated in this work the experimentally observed ambipolar transport behavior caused by the flat conduction- and valence-bands and describe non-ideal gate-control of the contacts and channel region by the quantum capacitance of graphene and the carbon nanotube. We hope that our insights will accelerate the design of efficient all-carbon field-effect transistors

Sub-nanosecond light-pulse generation with waveguide-coupled carbon nanotube transducers

Carbon nanotubes (CNTs) have recently been integrated into optical waveguides and operated as electrically-driven light emitters under constant electrical bias. Such devices are of interest for the conversion of fast electrical signals into optical ones within a nanophotonic circuit. Here, we demonstrate that waveguide-integrated single-walled CNTs are promising high-speed transducers for light-pulse generation in the gigahertz range. Using a scalable fabrication approach we realize hybrid CNT-based nanophotonic devices, which generate optical pulse trains in the range from 200 kHz to 2 GHz with decay times below 80 ps. Our results illustrate the potential of CNTs for hybrid optoelectronic systems and nanoscale on-chip light sources