Scientific project:

Photovoltaic is playing a major role in the energy transition, and its share in electricity generation is expected to continue rising to contribute to the net zero emission goals by 2050. 90 % of the currently produced solar panels are using silicon solar cells with gradually decreasing costs and increasing efficiency. Nevertheless, this efficiency is nearing its physical limit of 29.4 %, with 26.8 % obtained in laboratory. In order to overcome this limit, the next generation of solar cells will consist in tandem devices, that combine two materials of different bandgaps. In our laboratory in particular, III-V on silicon and perovskite on silicon devices are being produced.

Those new devices present exciting challenges: new fabrication steps, new materials and combinations of materials, new aging mechanisms and failure modes… All those aspects call for a better understanding of their working principles, through new characterization methods and data analysis. We propose in this internship to take advantage of the recognized know-how of the IPVF and the C2N in terms of luminescence characterization and state-of-the-art equipment.

In particular, we will develop a new technique based on simultaneous electrical and optical carrier injection in solar cells, with which we showed that we can access the current collection efficiency in each subcells, with a spatial resolution. In addition, we expect the intern to explore the feasibility of implementing those luminescence characterization methods in a LED solar simulator available in the laboratory, that provide high flexibility in the illumination spectrum.

This internship comprises an extensive part of experimental work in the laboratory as well as data treatment. We expect the intern to propose further developments of the techniques already existing at the laboratory, as well as to suggest the exploration of new methods. He / she will propose models to explain the observed phenomena, and design experiments for their validation, using his / her own knowledge as well as the scientific literature. He / she will take advantage of the unique luminescence characterization platform of the partner laboratories as well complementary methods (solar simulator, quantum efficiency). This environment will provide the intern various opportunities to tackle this project challenge and gain experience.

Profile :

The candidate must possess solid knowledges in material physics and characterization. He must show good project management skills, for the development of measurement procedures involving numerous parameters. He will be able to work independently and suggest innovative solutions to reach the project objectives. Collaborative work being at the core of the program, communication skills are required for team working as well as regular presentation of work progress in internal meetings.

More information in the attached file

Scientific project: Saturation of the light-matter interaction is a general nonlinear feature of material systems, be they atoms or semiconductors [1]. A saturable absorber exhibits an absorption coefficient that depends on the incident intensity. In semiconductors, the possibility of judiciously controlling saturation phenomena is of great importance for fundamental physics as well as applications. A seminal example is the development of the semiconductor saturable absorption mirror (SESAM) [2] based on interband transitions in quantum wells, that revolutionized the field of ultra-fast lasers in the vis/near-IR spectral range, allowing ultra-fast lasers pulses (see picture). Ultra-fast lasers based on SESAMs find applications in several domains, and even in quantum phenomena.

In the mid-IR (λ~10 µm), the intensity required to reach saturation is very high, about 1 MW/cm². This very high value explains why saturable absorbers, SESAM mirrors, bistable systems are missing from the current toolbox of mid-IR opto-electronic devices: they could only be used with extremely high power laser sources and are incompatible with the output power levels of typical mid-IR semiconductor lasers such as quantum cascade lasers (QCLs).

The host team has recently proposed that absorption saturation can be engineered if the system operates in the so called strong light-matter coupling regime [3], and has also provided its experimental proof [4]. In this regime, the response is governed by coupled light-matter states called polaritons. In particular, they designed a SESAM with ultra-low saturation intensities, that are compatible – for the first time – with table-top QCLs.

The goal of this internship is to demonstrate ultra-low power nonlinear mirrors in the mid-IR, supported by the recent results obtained by the host team [4]. The experiments will be performed by optical pumping with a tunable, commercial QCL. Two experiments will be performed.

In the first, already implemented experimental configuration, the device reflectivity spectrum will be measured using the tunable QCL at different incident powers. The theoretical outcome of the experiment is shown panel (a): the low intensity spectrum (blue) shows two polariton resonances. Increasing the laser intensity leads to the collapse of the light-matter coupling towards the purple curv: this is the manifestation of saturation. In a second experiment, the QCL power is varied while the wavelength is fixed: a typical outcome is in panel (b). This experiment permits to gauge the saturation threshold to be compared with simulations, for further device optimization. If time permits, charac-terizations in the time domain will be performed too. This project, that evolves in the context of a running ANR grant,  opens up exciting perspectives in the realization of ultrafast, mode-locked mid-IR fiber and semiconductor lasers.

[1] R. W. Boyd, Nonlinear Optics, 3rd ed. (Elsevier, Amsterdam, 2008).

[2] U. Keller, et al., Opt. Lett. 17, 505 (1992) and U. Keller, Nature 424, 831 (2003)

[3] M. Jeannin, JM Manceau, R. Colombelli, Phys. Rev. Lett 127, 187401 (2021)

[4] M. Jeannin, E. Cosentino, et al., Appl. Phys. Lett. 122, 241107 (2023)

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Scientific project:  Applications relying on mid-infrared radiation (MIR, l = 3-12 μm) have progressed at a rapid pace recently, stimulated by scientific and technological breakthroughs. For instance MIR cameras have enabled thermal imaging and the invention of the quantum cascade laser (QCL) has enabled a vast range of applications in spectroscopy, metrology, medicine. In addition to the generation and detection of light, a key functionality for most photonic systems is the possibility to electrically control the amplitude, phase, and polarization of a laser beam up to ultrashort time scales. Contrary to the visible and near-IR range, in the MIR range passive or active integrated components such as modulators and directional couplers do not exist, but recent experiments [1] have revealed propagation losses less that 1dB/cm at l=5.2µm. In this context, the host team has recently developed passive integrated waveguides on III-V semicondutor plaforms (InGaAs/InP and AlGaAs/GaAs), and identified the opportunity of greatly improving the propagation losses at longer wavelengths.

But du stage/internship objectives: The goal of the internship is to develop mid-infrared integrated optical resonators based on a low loss integrated waveguide geometry. The perspective student will perform the design of the optical cavities such as ring or racetrack resonators. The material systems that will be investigated are GaAs/AlGaAs-on-GaAs and InGaAs/InP-on-InP. The subtle design of optical waveguide features such as optical refractive index contrast, free carrier absorption and geometric parameters will be a primordial element that will be taken into account. Operation will be optimized for the 8-9 mm wavelength range, in the center of an atmospheric transparency region. The sample characterizations will take place with a dedicated end fire coupling setup equipped with a variety of mid-IR laser sources (allowing to control the injected wavelength, power and polarization) and detectors. She/he will benefit from the experience of the host team (https://odin.c2n.universite-paris-saclay.fr/en/activities/mir-thz-devices/) in quantum and electromagnetic design of opto-electronic devices, of cleanroom fabrication, and device opto-electronic characterizations [2].

Qualités du candidat(e) requises/ required skills: Basic knowledge in optics and electromagnetics, semiconductor physics, optoelectronics, ability to work in groups, interest for experimental work.

Relevant References:[1]  Kevin Zhang, Gerhard Böhm, Mikhail A. Belkin; Mid-infrared microring resonators and optical waveguides on an InP platform. Appl. Phys. Lett. 7 February 2022; 120 (6): 061106. https://doi.org/10.1063/5.0077394 

[2]    S. Pirotta et al., "Fast amplitude modulation up to 1.5 GHz of mid-IR free-space beams at room-temperature", Nat. Commun. 12, 799 (2021).   https://www.nature.com/articles/s41467-020-20710-2 

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Mid-infrared (mid-IR) spectroscopy is a nearly universal way to identify chemical and biological substances and to perform non-intrusive diagnostics. Indeed, the mid-IR spectral range contains the so-called “fingerprint” region (wavelength from 6 to 15 µm) in which most molecules have vibrational and rotational resonances. This wavelength range can, hence, be exploited to detect small traces of environmentally hazardous and toxic substances for a variety of applications including defense, security and industrial monitoring. A challenging task is to make mid-IR spectroscopy accessible in remote areas, driving the development of compact and cost-effective solutions to replace table-top systems.

            The development of mid-IR photonics circuits thus benefited from a burst of research activity in the recent years. Different solutions are explored for the development of an integrated mid-IR sensing platform. Among them silicon (Si) photonics can have a major impact for the development of mid-IR photonics by leveraging the reliable and high-volume fabrication technologies already developed for microelectronic integrated circuits. As a key point for optical spectroscopy and molecular sensing, the optical functions that will be developed using Si photonics circuits should offer the capability of retrieving the spectrum of a light beam after interaction with the substance to be analyzed, to detect the presence and quantify the concentration of the molecular compounds.

            Ge-rich SiGe photonics has been developed in our group in the recent years, in strong collaboration with Politecnico Di Milano. It has been demonstrated that graded index SiGe waveguide can be used in a large wavelength range in the mid-IR, and a large range of passive building bloc including Mach Zehnder interferometers [1] or integrated resonators have been obtained [2]. Then, the demonstration of large bandwidth optical source on chip based on non-linear optical effects of SiGe waveguides[3], and the realization of optoelectronic devices (modulator and photodetector) [4,5] complete the photonics platform.

            In this context, the goal of the internship position is to participate in the development of high speed electro-optic modulator and photodetector, operating in the mid-IR wavelength range, using  Ge-rich SiGe photonic devices.

The research activity will include:

- Modeling of the photonics devices (optical, electro-optical simulation using commercially available software and developing code interfaces (python/matlab)

- Design and fabrication of the devices in in-house clean room in collaboration with the group members.

- Experimental characterizations of the devices, using a mid-IR optical bench already developed in the group

The work is done in the framework of EU ERC Electrophot project (2023-2028), in collaboration with Politecnico Di Milano. PhD position will be discussed during the internship.

Air pollution poses a great environmental risk to health, accounting for nearly half a million premature deaths each year in Europe. Ubiquitous, real-time air quality monitoring could reduce the negative impact of pollution. However, air pollution monitoring generally relies on costly (k€ range), complex stationary equipment, that limits its widespread deployment. The Silicon Photonics team at C2N leads a new European project, SYMPHONY that aims at developing a new technology combining different silicon photonics platforms and silicon microelectronics to enable the implementation of dense networks of cloud-connected, low-cost (< 100 €), and portable (5-80 cm³ size) easy-to-use smart sensors, capable of multi-target detection in air pollution monitoring.

Conversion between electrical and optical signals enabled the use of near-infrared (near-IR) photons for high data rate transmission through optical fibre networks. Likewise, coherent conversion between microwave and optical photons stands as a promising solution to transfer quantum states between remote quantum processors, thus enabling the development of large-scale quantum networks. However, the vast frequency difference between microwave (GHz) and near-IR (200 THz) optical photons hampers direct coherent conversion. The Silicon photonics team at C2N leads a new ERC project, SPRING, that aims at demonstrating phonon-mediated transduction between microwave and near-IR signals at the quantum regime.

The goal of this internship is the exploration of machine learning algorithms for the development of silicon photonic devices with improved performance and advanced functionalities. Deep learning methodologies (e.g. variational autoencoders) will be combined with optimizaiton techniques to both alleviate the large amount of input data required by classical algorithms and to efficiently optimize device designs. Devices will then be fabricated in the C2N cleanroom and tested to demonstrate their performance.

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Neuromorphic photonics is an expanding field of research at the heart of recent progresses in analog computation and machine learning. Its goal is to investigate new ways to process optical information or to compute using brain-inspired physical concepts.

We propose to investigate the physics and applications of coupled spiking photonic nodes implementing artificial spiking neural networks. Each node (optical neuron) is materialized by a micropillar laser with integrated saturable absorber, whose neuromimetic properties have already been explored in the team. In neurons, information is coded with spikes (electrical pulses) which are excited in an all-or-none fashion provided input stimuli to the neuron soma exceed a given threshold. This generic property is called excitability and has been demonstrated in micropillar lasers with optical spikes [1]. Though, the optical spikes emitted by these latter are more than one millions times shorter in duration than biological action potentials. Hence, photonic neurons could in principle be interesting to build ultrafast artificial neural networks with low power consumption.

The objective of the internship will be to take part to the projects developed in the group to fabricate and study neuromorphic architectures, understand the physics involved in the dynamics of these coupled microlasers and demonstrate ultrafast analog computation. The work will mainly involve experimental and modeling activities, with nanofabrication aspects. The internship will take place at the C2N (Palaiseau) which hosts a first-class nanofabrication facility.

The applicant should have a background in physics, optics, laser physics, semiconductor physics. Background in semiconductor lasers and/or nonlinear dynamics and/or machine learning is appreciated but not compulsory.

Website: https://toniq.c2n.universite-paris-saclay.fr/fr/activites/smila/

Reference

[1] Micro-lasers for neuromorphic computing V. A. Pammi, S. Barbay, Photoniques 104, 26-29 (2020) https://doi.org/10.1051/photon/202010426

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Context :

Mid-infrared (mid-IR) spectroscopy is a nearly universal way to identify chemical and biological substances and to perform non-intrusive diagnostics. Indeed, the mid-IR spectral range contains the so-called “fingerprint” region (wavelength from 6 to 15 µm) in which most molecules have vibrational and rotational resonances. This wavelength range can, hence, be exploited to detect small traces of environmentally hazardous and toxic substances for a variety of applications including defense, security and industrial monitoring. A challenging task is to make mid-IR spectroscopy accessible in remote areas, driving the development of compact and cost-effective solutions to replace table-top systems.

            The development of mid-IR photonics circuits thus benefited from a burst of research activity in the recent years. Different solutions are explored for the development of an integrated mid-IR sensing platform. Among them silicon (Si) photonics can have a major impact for the development of mid-IR photonics by leveraging the reliable and high-volume fabrication technologies already developed for microelectronic integrated circuits. As a key point for optical spectroscopy and molecular sensing, the optical functions that will be developed using Si photonics circuits should offer the capability of retrieving the spectrum of a light beam after interaction with the substance to be analyzed, to detect the presence and quantify the concentration of the molecular compounds.

            Ge-rich SiGe photonics has been developed in our group in the recent years, in strong collaboration with Politecnico Di Milano. It has been demonstrated that graded index SiGe waveguide can be used in a large wavelength range in the mid-IR, and a large range of passive building bloc including Mach Zehnder interferometers [1] or integrated resonators have been obtained [2]. Then, the demonstration of large bandwidth optical source on chip based on non-linear optical effects of SiGe waveguides[3], and the realization of optoelectronic devices (modulator and photodetector) [4,5] complete the photonics platform.

Objectives of the internship :

            In this context, the goal of the internship position is to participate in the development of high speed electro-optic modulator and photodetector, operating in the mid-IR wavelength range, using  Ge-rich SiGe photonic devices.

The research activity will include:

- Modeling of the photonics devices (optical, electro-optical simulation using commercially available software and developing code interfaces (python/matlab)

- Design and fabrication of the devices in in-house clean room in collaboration with the group members.

- Experimental characterizations of the devices, using a mid-IR optical bench already developed in the group

The work is done in the framework of EU ERC Electrophot project (2023-2028), in collaboration with Politecnico Di Milano. PhD position will be discussed during the internship.

poursuite en thèse envisageable

Non-equilibrium Bose-Einstein condensation of exciton-polaritons have become a vast playground for fascinating phenomena previously reserved to ultracold atomic gases. In particular, it has led to the demonstration of superfluidity, topological lasing and non-Hermitian effects. In these polaritonic systems the fundamental energy scale is intrinsically fixed by the interband transition of the underlying material, limiting flexibility and also the magnitude of the Rabi splitting. Conversely, the transition energy of intersubband (ISB) polaritons in doped semiconductor quantum well (QW) structures can be freely tuned by varying the QW width and doping to reach the mid-IR and Far-IR range of the electromagnetic spectrum. As their excitonic counter-part, it has been predicted that they can show exotic quantum behavior such as final state stimulation and condensation. This would open interesting perspectives of a condensate operating at much lower energy scale and interacting with a 2D gas of electrons to form Fermi-Bose mixtures. Our team has made major progresses towards that goal in the recent years. Starting with dispersion engineering [1], we developed a clear roadmap towards condensation [2] and confirmed the existence of a spontaneous process based on ISB polariton - LO phonon scattering [3]. More recently, in the frame of an international collaboration, we demonstrated for the first time polariton-polariton interaction in the regime of final state stimulation (see figure) [4]. In this pump-probe experiment, we have shown an amplification process occurring on an ultrafast time scale; this is the key ingredient towards condensation.
In this continuity, this internship aims at exploring the nonlinearities of a novel polaritonic scheme based on the strong coupling regime of bound-to-continuum transition and a microcavity [5]. Such novel polaritonic scheme has been demonstrated recently by our team and hold great promises for the demonstration of condensation with polaritons issued from a 2D gas of electrons. The main task of the candidate will be the exploration of the saturation process in such systems, using already existing samples. The candidate will have to use the optical MIR pump-probe setup recently built in the team and characterized the reflectance of the system as a function of the pump fluence. The candidate will then record the dynamic of the system on an ultrafast time scale to fully capture the nonlinearities at play. Finally, she/he will use an in-house numerical code to simulate the polaritons scattering dynamic and amplification process within the novel polaritonic architectures that was characterized earlier on.
Furthermore, and if time allows, the candidate will also be invited to follow the different steps of the fabrication process of the samples in clean room. The project offers a global view of the different activities led in our team from the numerical design, the fabrication in cleanroom and the optical characterization.
[1] J.-M. Manceau et al., Mid-Infrared Intersubband Polaritons in Dispersive Metal-Insulator-Metal Resonators, Appl. Phys. Lett. 105, 8 (2014).
[2] R. Colombelli and J.-M. Manceau, Perspectives for Intersubband Polariton Lasers, Phys. Rev. X 5, 1 (2015).
[3] J.-M. Manceau et al., Resonant Intersubband Polariton-LO Phonon Scattering in an Optically Pumped Polaritonic Device, APL. 112, 19 (2018).
[4] M. Knorr, J.-M. Manceau et al., Intersubband Polariton-Polariton Scattering in a Dispersive Microcavity, Phys. Rev. Lett. 128, 247401 (2022).
[5] E. Cortese, et al., “Excitons bound by photon exchange,” Nat. Phys., (2020)

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Scientific description: Ferroelectrics (FE) are fascinating multifunctional materials with a spontaneous electric polarization P which can be controlled by applied electric field (Fig. 1(a)). In addition, the coupling of electric polarization to strain make FEs good piezoelectrics for the development of microelectromechanical systems (MEMS), such as actuators and sensors. For devices applications, thin films are preferred because they can show improved performance when they are epitaxially grown. However, most of the piezoelectric thin films integrated in MEMS are based on Pb, which is toxic. The search for alternative lead-free FE is thus crucial, and, among them, BiFeO3 appears as a very promising candidate thanks to its lead-free composition, very large remanent polarization, and low dielectric constant.
Recently, we have reported the first investigation of the piezoelectric response in epitaxial BiFeO3 microcantilevers (Fig.1(b)), demonstrating larger electromechanical performance than that of Pb-based state-of-the-art piezoelectric MEMS. A strong asymmetry in the properties was observed with the voltage polarity (Fig.1(c)), which points towards a significant contribution from the flexoelectric effect (electrical polarization induced by strain gradient).

More information in the attached file

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General framework

SEEDs team has long standing know-how in synthesis and characterisation of group-IV semiconductor. At the moment we are especially investigating different ways to synthesize the very promising hexagonal SiGe-2H phase (an allotrope of the standard diamond cubic 3C structure) which exhibits a direct band gap and excellent light emission capabilities [1] with a tuneable emission wavelength in the mid infrared between 1.8-3.5 μm by a concentration range of 0-40% of Si. This material may therefore provide additional photonic functionality to the silicon technology and fill the gap between electronics and photonics industry. We aim at
integrating SiGe-2H light sources on silicon on insulator in a CMOS compatible way.
We have pioneered an original method to achieve a shear induced phase transformation in Ge and Si nanowires NWs resulting in unprecedented heterostructures with quasi periodic embedded 2H domains distributed all along the nanowire (fig). The process is described in refs [2,3]. Using Si/Ge/Si heterostructures enables promoting and localising the transformed domain in the Ge section.
We propose to combine this strain-induced process with selective epitaxial growth on the transformed SiGe-2H seed. We aim at developing a highly selective etching method to remove the cubic untransformed top part and uncover the 2H transformed domain which is expected to serve as a seed for further epitaxy in order to subsequently increase the volume of the 2H segment.

Objectives and work plan
The student is expected to contribute to :
- participate to the realization of Ge thin layers in Si using UHV-CVD
- selective etching of the cubic Si top part to uncover the Ge-2H surface
- develop the seeded epitaxial regrowth on the Ge-2H

More information in the attached file

Contact :

Laetitia Vincent, C2N, CNRS / Université Paris-Saclay, Département Matériaux / Equipe SEEDs

Surface acoustic waves (SAWs) are elastic waves that propagate at the surface of a solid. On piezoelectric materials, they can be generated with interdigitated transducers (IDTs). Beyond their widespread use in electronic filtering, they can modulate a light field through the acousto-optical (AO) interaction, and especially imprint on it a sinusoidal phase variation. This concept is widely used in AO modulators using bulk acoustic waves in a crystal to diffract a light beam. Recent research has shown the extreme potential of SAWs in integrated photonics, where they can be used to modulate complex photonic circuits. Innovative devices have recently been proposed using a SAWs and integrated photonic circuits to demonstrate AO modulation in semiconductor waveguides, but also much more complex functions such as optical isolation [1]. The current state-of-the-art is confined to the near-infrared spectral range where photonic integrated circuits are mature and can rely on a plethora of materials. On the contrary, such devices do not exist in the mid-infrared (mid-IR) part of the spectrum (3 μm < λ < 12 μm). This wavelength range is of particular interest for many applications from industrial control and pollution detection, optical communication to astronomical sciences. The field of integrated mid-IR photonics is currently booming, sustained by recent breakthroughs in integrated Si-photonics and III-V semiconductor platforms. Advanced integrated devices are needed, amongst which optical phase modulators.

To design and characterize efficient AO photonic circuits, a visualization of the SAW propagation is a valuable tool. This internship constitutes a first step on this ambitious project: building an optical interferometer allowing the mapping of SAW on GaAs substrate. The idea is to measure the out-of-plan vibration of the semiconductor surface with sub-nm precision in a modified Michelson interferometer [2]. This allows directly imaging the propagation of the SAW with unprecedented precision: the lateral resolution is given by the laser spot size (< 1 μm) and the amplitude is a fraction of the wavelength, with the Angstrom as a first target. After building the interferometer, characterizations of SAWs on GaAs substrates will be performed. Time will be dedicated to interface the instrument to a computer to automatize measurements through a home-made Python interface tool. If time permits, numerical simulations of novel SAW devices will be initiated, as well as first cleanroom fabrication steps.

Starting date: March 2024. More information on the attached file.

[1] Sarabalis et al., Optica 8, 477 (2021)
[2] Knuuttila et al., Optics Lett. 25, 613 (2000)

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