Periodic Reporting for period 1 - NANO-MIR (Novel 3D nano-antennas for optoelectronic applications in the mid-infrared)
Reporting period: 2018-04-01 to 2020-03-31
Extreme confinement of light on the nanoscale is today at the heart of many technological applications: confining light means confining optical energy to high densities, and this ultimately leads to drastically improved light-matter interaction. This is true, for instance, in non-linear systems, such as Raman scattering, which is proportional to the fourth power of the local electric field, and which is at the base of spectroscopic sensing of bio-molecules or gas traces. Or in photocatalysis, where high density of optical energy may lead to the splitting of stable molecules, such as water, into its constituents. In specific cases, however, light-matter interaction may also lead to exotic behaviors, such as the strong coupling regime, where photons (light) and matter excitations (such as excitons in semiconductors, i.e. transitions between valence and conduction band) may couple together to form mixed quasi-particles, called polaritons. In this particular situation, when the two excitations approach the same resonance frequency, a characteristic repulsion of modes splits the energy levels in two distinct values, yielding a gap of forbidden energy states.
The work carried out within this fellowship revolves around the study of sub-wavelength light-matter interaction in a specific environment: III/V semiconductors, and more specifically, heterostructures hosting quantum wells. Light interacting with such artificial materials can be absorbed at given frequencies, to promote a transition of an electron in the conduction band from an energy level to another: such discrete absorption mechanisms are called intersubband (ISB) transitions.
By patterning metallic nanoantennas directly on engineered heterostructures, thus achieving high electric field confinement within the active region, this MSCA Individual Fellowship addresses this last field of applied physics for both fundamental and applicative optoelectronic studies, investigating the interaction between light in the mid-infrared (mid-IR) range and the intersubband (ISB) transition in highly doped quantum wells. The goal of this proposal is to fully develop and exploit the potential of nanoantenna-enabled light confinement, funneling energy with unprecedented efficiency onto optically active materials. By taking advantage of a recently introduced novel class of vertical metallic nanoantennas, which have optimized energy harvesting properties (light is trapped and exchanged within arrays of 3D antennas in the form of oscillating ensembles of electrons), efficient layout (the out-of-plane character inherently provides a strong and conveniently oriented electric field) and a very small interaction volume (few hundreds of nanometers in diameter, which means extreme subwavelength energy confinement), this fellowship tackles two main objectives.
From one side, it explores a more fundamental aspect – the possibility of triggering and detecting strong coupling from a single nanoantenna optical resonator; from the other side, it exploits extreme subwavelength confinement to explore novel and efficient optoelectronic devices, such as quantum well infrared detectors (QWIPs) and second harmonic generation (SHG).
A new class of devices can stem from this action, yielding improved infrared cameras and detectors, or improved frequency up-conversion in non-linear optically active materials.
The work carried out within this fellowship revolves around the study of sub-wavelength light-matter interaction in a specific environment: III/V semiconductors, and more specifically, heterostructures hosting quantum wells. Light interacting with such artificial materials can be absorbed at given frequencies, to promote a transition of an electron in the conduction band from an energy level to another: such discrete absorption mechanisms are called intersubband (ISB) transitions.
By patterning metallic nanoantennas directly on engineered heterostructures, thus achieving high electric field confinement within the active region, this MSCA Individual Fellowship addresses this last field of applied physics for both fundamental and applicative optoelectronic studies, investigating the interaction between light in the mid-infrared (mid-IR) range and the intersubband (ISB) transition in highly doped quantum wells. The goal of this proposal is to fully develop and exploit the potential of nanoantenna-enabled light confinement, funneling energy with unprecedented efficiency onto optically active materials. By taking advantage of a recently introduced novel class of vertical metallic nanoantennas, which have optimized energy harvesting properties (light is trapped and exchanged within arrays of 3D antennas in the form of oscillating ensembles of electrons), efficient layout (the out-of-plane character inherently provides a strong and conveniently oriented electric field) and a very small interaction volume (few hundreds of nanometers in diameter, which means extreme subwavelength energy confinement), this fellowship tackles two main objectives.
From one side, it explores a more fundamental aspect – the possibility of triggering and detecting strong coupling from a single nanoantenna optical resonator; from the other side, it exploits extreme subwavelength confinement to explore novel and efficient optoelectronic devices, such as quantum well infrared detectors (QWIPs) and second harmonic generation (SHG).
A new class of devices can stem from this action, yielding improved infrared cameras and detectors, or improved frequency up-conversion in non-linear optically active materials.
"Part of the fellowship was committed to study one of the intriguing light-matter interactions mechanisms – strong coupling between light and matter excitations – at a very fundamental level, demonstrating polaritonic behavior on the single-resonator level. In the mid-IR range, infant, accessing the spectroscopic signature of strong coupling has never been demonstrated if not on large areas of repeated structures (double metal gratings, for instance), or on several optical resonators. Here we prove strong coupling between an ISB transition and mid-IR photons in a single cavity resonator by probing the near field with two different experimental setups. SNOM (tip-enhanced scattering)near field microscopy of the fringing fields leaking out of the optical cavity and nano-IR thermal expansion imaging of a heterostructure/polymeric bi-layer placed inside a patch antenna optical cavity.
A second part of the fellowship was committed instead to more applicative, device-oriented experiments, tackling photodetection with stacks of specifically engineered quantum wells. Such optoelectronic devices, called QWIPs, are based on two-level quantized conduction bands, the upper of which is designed to easily ""lose"" the electron into the continuous states band. In this case, detection of light – enabled by ISB transitions – can be hidden by ""dark"" (unwanted) thermal currents, which are independent of light excitation. One strategy to increase significantly detectivity is to nanotructure the active region so that only the regions involved with detection allow current to flow. This action tackled this issue by using extremely sub-wavelength vertical nano antennas as light concentrators. After developing the technology needed to obtain all necessary prerequisites (such a mid-IR transparent conductor to polarize the structures, and the suitable geometrical layouts to tune the plasmonic resonance on the ISB transition), a first prototype showing detectivity from extra sub wavelength nano resonators was tested and a proof of concept was shown. The final experiments to demonstrate the potential of this novel technology are underway.
At last, as an intermediate milestone, propedeutical to reach the results of the action, a new approach to realize devices with a double pattened active region was developed and published. It allows to either access electrically or to pump optically the epitaxial layers, freed from the growth substrate. This method has shown potential towards the design of a new class of devices, including for instance mid-IR cameras for thermal imaging."
A second part of the fellowship was committed instead to more applicative, device-oriented experiments, tackling photodetection with stacks of specifically engineered quantum wells. Such optoelectronic devices, called QWIPs, are based on two-level quantized conduction bands, the upper of which is designed to easily ""lose"" the electron into the continuous states band. In this case, detection of light – enabled by ISB transitions – can be hidden by ""dark"" (unwanted) thermal currents, which are independent of light excitation. One strategy to increase significantly detectivity is to nanotructure the active region so that only the regions involved with detection allow current to flow. This action tackled this issue by using extremely sub-wavelength vertical nano antennas as light concentrators. After developing the technology needed to obtain all necessary prerequisites (such a mid-IR transparent conductor to polarize the structures, and the suitable geometrical layouts to tune the plasmonic resonance on the ISB transition), a first prototype showing detectivity from extra sub wavelength nano resonators was tested and a proof of concept was shown. The final experiments to demonstrate the potential of this novel technology are underway.
At last, as an intermediate milestone, propedeutical to reach the results of the action, a new approach to realize devices with a double pattened active region was developed and published. It allows to either access electrically or to pump optically the epitaxial layers, freed from the growth substrate. This method has shown potential towards the design of a new class of devices, including for instance mid-IR cameras for thermal imaging."
"Any device innovation in the mid-IR range can have major impacts, from the wider field of biotechnologies (SERS and SEIRA spectroscopies use infrared sources and detectors to identify molecules at extremely low concentrations), to defense (mid-IR thermal cameras allow imaging of heat sources with very high sensitivity), from trace gas sensing (in the oil and gas industry for instance) to photocatalysis (where passive devices, concentrating optical energy in engineered hot spots, are employed to ease chemical reactions). This fellowship showed, for the first time, the detection of strong coupling between an ISB transition and mid-IR photons inside the optical cavity, detecting and identifying spatially the fields buried within the optical resonator. This was never shown experimentally before, and the only way to probe spectral characteristics aside with field distribution was by performing numerical calculations, or indirect measurements. Imaging the fields, besides, in principle allows the detection also of those ""dark"" modes which usually are hidden by far field detection methods, such as FTIR spectroscopy.
The methods explored in this action, furthermore, showed potential impact on novel devices, such as efficient QWIP photodetectors, possibly working at room temperature, and thermal cameras."
The methods explored in this action, furthermore, showed potential impact on novel devices, such as efficient QWIP photodetectors, possibly working at room temperature, and thermal cameras."