Nanomaterials for Optoelectronics group

Semiconductor nanostructures for optics

Silicon is the material of choice for microelectronics. However, it is a poor optical transmitter because of its electronic structure that is characterized by an indirect band gap. Achieving all-silicon optoelectronics is a
major challenge for many applications in the fields of information transfer, communications, and energy. Thus, the group is developing different strategies to bring optical properties to silicon-based materials:

• Quantum confinement of charge carriers in nanostructures
• Optical doping with rare earth ions
• Nanocrystal elecronic doping
• 2D Materials

Semiconductor nanocrystals, also known as quantum dots, have remarkable properties due to the quantum confinement of the carriers. These make it possible to control the energy of the photons emitted, which is linked to object size. For some semiconductors, such as silicon, confinement considerably increases the probability of radiative transitions compared to the bulk material.

Doping of bulk semiconductors is now well mastered for many materials. In contrast, doping of nanocrystals is still relatively unknown and raises many fundamental and technological questions. One major difficulty is linked to the synthesis of doped nano-objects because of the thermodynamics of these systems that tends to favour the exclusion of dopants from the nanocrystal core. The fundamental questions the group is interested in include:

• the localization of dopants, in interstitial or substitution sites,
• the levels of the electronic states created by the dopants,
• the activation energies of the dopants,
• the solubility threshold for impurities,
• the possibility of obtaining electronic collective oscillations (plasmons).

To answer these questions, the group is studying the model system of silicon nanocrystals doped with boron or phosphorus. In particular, it is implementing out-of-equilibrium elaboration processes for the synthesis of doped nano-objects, structural and chemical analysis techniques at the nanoscale, as well as analyses by optical spectroscopy.

Some IV/V type binary alloys such as SiP are extremely high-potential materials provided that it is possible to synthesize them in 2 dimensions. Electronic structure calculations have shown that SiP is an indirect gap semiconductor in the bulk state, but that it becomes a direct gap in the 2D form. This alloy is also a lamellar material that can be exfoliated, which should make it possible to obtain a 2D material that is potentially very interesting for new applications in silicon optoelectronics. The group is implementing different synthesis pathways of this 2D material for its spectroscopic study and its development for optical applications.

Projects:

• ANR DONNA, Doping at the Nanoscale, 2018-2022
• Région Grand Est NanoDop, Doping of semiconductor nanocrystals: development of model systems at the nanoscale, 2019-2020

Thesis:

• Fatme TRAD, 2017-2020
• Alix VALDENAIRE, 2019-2022
• Sébastien GEISKOPF, 2015-2019
• Rosalie NZANG MINTSA, 2022-2025

Collaborations:

• National: CEMES, GPM, LAAS, CEATECH-LETI, IBS, LCPME, ICube, IPCMS, GDR NACRE
• International: Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, Skolkovo Institute of Science and Technology, Moscow

Articles:

• Formation of SiP2 Nanocrystals Embedded in SiO2 from Phosphorus Rich SiO1.5 thin Films, Journal of Physical Chemistry C 124, 7973–7978 (2020), S. Geiskopf, M. Stoffel, X. Devaux, E. André, C. Carteret, A. Bouché, M. Vergnat, H. Rinnert.
   
• Direct Insight into Ce-Silicates/Si-Nanoclusters Snowman-Like Janus Nanoparticles Formation in Ce-Doped SiOx Thin Layers, G. Beainy et al., J. Phys. Chem. C 121, 12447-12453 (2017)
   
• Observation of a nanoscale phase separation in blue-emitting Ce-doped SiO1.5 thin films, J. Weimmerskirch-Aubatin et al., J. Mater. Chem. C 3, 12499-12506 (2015)
   
• Influence of phosphorus on the growth and the photoluminescence properties of Si-NCs formed in P-doped SiO/SiO2 multilayers, Nanoscale 13, 19617-19625 (2021), F. Trad, A. E. Giba, X. Devaux, M. Stoffel, D. Zhigunov, A. Bouché, S. Geiskopf, R. Demoulin, P.Pareige, E. Talbot, M. Vergnat, H. Rinnert”

Spintronics with semiconductors

Spin-dependent electronic transport and spin injection into semiconductors may pave the way for a new generation of electronic and optoelectronic components. The group is especially interested in the following issues:

• Spin-dependent transport in group IV and 2D semiconductors
• Spin Injection Light Emitting Diodes (Spin LEDs)
• Spin-photodiodes
• Spintronics with organic ferroelectric materials

The use of electron spin in semiconductors is particularly attractive because the coherence length of the spin is three orders of magnitude longer than in metallic systems. The characteristic times correspond to an electron spin precession frequency ranging from GHz to THz, which makes it possible to generate a spin current.
In addition, it is possible to integrate information storage and communication operations in the same technology. The group has studied spin-dependent transport in 2D materials, and has demonstrated for the first time the electrical injection/detection of spin in the conduction band of a multi-layer MoS2, using a two-terminal spin valve. The spin diffusion length is of the order of 230 nm. This could open up prospects for spintronics applications based on the use of transition metal dichalcogenide multilayers.
Spin-dependent transport has also been studied in Si. A molecular bonding technique under ultra-high vacuum has been developed to achieve vertical metal/semiconductor/metal structures. In the case of CoFeB/MgO/Si/Pt structures, the group demonstrated spin current injection and perpendicular transport over a distance greater than 2 μm in n-Si at room temperature. This work highlights the importance of the electronic states located at the MgO/Si interface for the generation of a spin current.

By injecting a spin-polarized current into a light-emitting diode or laser, the spin polarization of the charge carriers can be converted into the circular polarization (CP) of the emitted photons. The use of CP light could replace current technologies that are based on light switching. The CP can be changed extremely quickly simply by changing the direction of the spin injector magnetization. Such components would also make it possible to obtain 3D holographic images without polarizing glasses. To develop all these applications, it is essential to make spin injectors with a magnetic anisotropy that is perpendicular to the plane of the thin film. Since 2014, the group has developed a new spin injector based on an ultra-thin layer of CoFeB (1.2 nm)/MgO (2.5 nm) with perpendicular magnetic anisotropy. When this injector is deposited on a light-emitting diode containing GaAs quantum wells, CP of 13% at 25K and 8% at 300K are obtained, without an applied magnetic field. The group also deposited the CoFeB/MgO injector on a light-emitting diode containing InAs/GaAs quantum wells. Polarization-resolved electroluminescence measurements performed on a single quantum dot showed an extremely high polarization of up to 35% without an applied magnetic field. This remarkable result was highlighted on the CNRS site.

New communication protocols could be developed if we can manipulate and detect the circular polarization (CP) of light without the need for external optics. The spin-photodiode is a ferromagnetic metal/insulator/semiconductor heterojunction that allows CP light to be analysed using spin-polarized current. The group deposited a CoFeB/MgO injector with perpendicular magnetic anisotropy on a Ge(001) substrate before performing a spin-photodiode. The latter shows an asymmetry of photocurrent helicity of the order of 0.9% at 9K and even 0.1% at room temperature, at a wavelength of 1310 nm, without an external magnetic field. The demonstration of a spin-photodiode operating at a wavelength used in telecommunications without an external magnetic field is of great interest for future applications based on the optical transport of spin information.

Hybrid ferromagnetic metal/organic material structures, also called "spinterfaces", can exhibit very efficient spin filtering properties and are likely to be promising for future spintronic devices. The spin polarization at the spinterface at Fermi may be different from, or even opposite in sign to, that of the adjacent ferromagnetic electrode. Using an organic ferroelectric such as PVDF (polyvinylidene fluoride) as a barrier, the group has constructed a multiferroic organic junction for the first time and has also shown that spin polarization at the organic ferroelectric/ferromagnetic interface can be controlled by changing the polarization of the organic ferroelectric.

Funded Projects:

• ANR SIZMO2D, Spin Injection/detection at Zero Magnetic field in spin Optronics devices based on 2D Semiconductors, Grant No. ANR-19-CE24-0005-02, 2019-2023.
   
• Carnot ICEEL International SHATIPN, Spin Hall Angle with Topological Insulator pn Junctions, Grant No. 9-IN, 2020-2022.
   
• ANR FEOrgSpin, Ferroelectric control of organic/ferromagnetic spinterface, Grant No. ANR-18-CE24-0017-01, 2018-2022.

Theses:

Pambiang Abel DAINONE, 2021-2024

Co-directed Theses:

• Ziqi ZHOU, 2019-2021
• Yuan CAO, 2019-2021
• Xue Gao, 2017-2019

Collaborations:

National:

• Unité Mixte de Physique CNRS/Thales and Université Paris-Sud
• Institut Physique de Rennes
• LPCNO, INSA-CNRS-UPS, Toulouse
• Institut des Nanosciences de Paris, CNRS-Universités Paris 6
• SPINTEC, CEA-INAC/CNRS/UJF-Grenoble
• CEA-LETI, Grenoble
• Université d’Artois, Lens

International:

• University of Minnesota, Electrical and Computer Engineering, Minneapolis, USA
• Washington State University, ISP/Applied Sciences Laboratory, Spokane, USA
• Institute of Problems of Chemical Physics, Moscow, Russia
• Hitachi Cambridge Laboratory, Cambridge, United Kingdom
• Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
• Institute of Semiconductor, Chinese Academic of Sciences, Beijing, China
• Institute of Physics, Chinese Academic of Sciences, Beijing, China
• Department of physics, University of Science and Technology of China, Hefei, China
• Tongji University, Shanghai, China; Fert Beijing Institute, Beihang University, Shanghai, China
• Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academic of Sciences, Suzhou, China
• Ningbo Institute of Materials Technology & Engineering, Chinese Academic of Sciences, Ningbo, China
• Department of physics, Tsinghua University, Beijing, China
• Department of physics, Peking University, Beijing, China

Articles:

• Electrical spin injection and detection in molybdenum disulfide multilayer channel, S. Liang et al., Nature Communications 8, 14947 (2017)
   
• Evidence of Pure Spin-Current Generated by Spin Pumping in Interface Localized States in Hybrid Metal-Silicon-Metal Vertical Structures, C. Cerqueira et al., Nano Lett. 19, 90 (2019)
   
• Large and robust electrical spin injection into GaAs at zero magnetic field using an ultrathin CoFeB/MgO injector, S.H. Liang et al., Physical Review B, 90, 085310 (2014)
   
• Co-Fe-B/MgO/Ge Spin Photodiode Operating at Telecommunication Wavelength with Zero Applied Magnetic Field, A. Djeffal et al., PRA 10, 044049 (2018)
   
• Electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field, F. Cadiz at al., Nano Letters 18, 2381 (2018)

Development

• Development of thin films by reactive evaporation, molecular beam epitaxy and sputtering. Synthesis of oxides or nitrides of group IV elements, doping, growth of ferromagnetic layers. The chambers for deposing are coupled to the DAUM ultra-high vacuum tube
• Conventional heat treatments under ultra-high vacuum, fast annealing up to 1100 °C
• Micro and nano synthesis

Characterisation

• Time-resolved and steady state photoluminescence optical spectroscopy. Photoluminescence excitation spectroscopy. Low temperature measurements with helium cryostats. Quantum emission efficiency measurements. Electroluminescence resolved in polarization
• Transmission Electron Microscopy. High resolution. Energy-filtered electron microscopy. EELS (electron energy loss spectroscopy) and EDS (energy dispersive x-ray spectroscopy). EELS and EDS imaging
• Electronic transport, characteristic current-voltage, magnetic field measurements
• Ellipsometric spectroscopy
• Magnetic measurements
• Vibrational spectrometry, infrared absorption and Raman diffusion (link towards optical laser CC)

CNRS researchers

• Xavier DEVAUX
• Yuan LU

Professors, assistant professors

• Thomas EASWARAKHANTHAN
• Hervé RINNERT
• Mathieu STOFFEL
• Michel VERGNAT

PhD students

• Pambiang DAINONE
• Clavel Berclis KENGNE CHOUMELE
• Samuel MATHIEU
• Rosalie NZANG MINTSA

Post-doctoral researchers

• Tongxin CHEN