A5035783092- 2D Materials and Applications
- Quantum and electron transport phenomena
- Perovskite Materials and Applications
- Semiconductor Quantum Structures and Devices
- Magnetic properties of thin films
- Chalcogenide Semiconductor Thin Films
- Semiconductor materials and devices
- Quantum Dots Synthesis And Properties
- Nanowire Synthesis and Applications
- Advancements in Semiconductor Devices and Circuit Design
- Graphene research and applications
- Advanced Chemical Physics Studies
- MXene and MAX Phase Materials
- Strong Light-Matter Interactions
- Semiconductor materials and interfaces
- Neural Networks and Reservoir Computing
- Photocathodes and Microchannel Plates
- Organic and Molecular Conductors Research
- Electron and X-Ray Spectroscopy Techniques
- Advanced biosensing and bioanalysis techniques
- Advanced Semiconductor Detectors and Materials
- Mechanical and Optical Resonators
- Photonic and Optical Devices
- Atomic and Subatomic Physics Research
- Physics of Superconductivity and Magnetism
École Polytechnique
2015-2025
Laboratoire de Physique Théorique de la Matière Condensée
2015-2025
Laboratoire de physique de la matière condensée
2015-2025
Centre National de la Recherche Scientifique
2014-2023
Université Paris-Saclay
2017-2022
Université Toulouse III - Paul Sabatier
2016-2020
Laboratoire de Physique et Chimie des Nano-Objets
2016-2020
Université de Toulouse
2016-2020
Institut National des Sciences Appliquées de Toulouse
2017
The strong light matter interaction and the valley selective optical selection rules make monolayer (ML) MoS2 an exciting 2D material for fundamental physics optoelectronics applications. But so far transition linewidths even at low temperature are typically as large a few tens of meV contain homogenous inhomogeneous contributions. This prevented in-depth studies, in contrast to better-characterized ML materials MoSe2 WSe2. In this work we show that encapsulation hexagonal boron nitride can...
We have investigated the exciton dynamics in transition metal dichalcogenide mono-layers using time-resolved photoluminescence experiments performed with optimized time-resolution. For MoSe2 monolayers, we measure $\tau_{rad}=1.8\pm0.2$ ps that interpret as intrinsic radiative recombination time. Similar values are found for WSe2 mono-layers. Our detailed analysis suggests following scenario: at low temperature (T $\leq$ 50 K), oscillator strength is so large entire light can be emitted...
The optical selection rules for interband transitions in WSe2, WS2, and MoSe2 transition metal dichalcogenide monolayers are investigated by polarization-resolved photoluminescence experiments with a signal collection from the sample edge. These measurements reveal strong polarization dependence of emission lines. We see clear signatures emitted light electric field oriented perpendicular to monolayer plane, corresponding an forbidden at normal incidence used standard spectroscopy...
Charged excitons, or X$^{\pm}$-trions, in monolayer transition metal dichalcogenides have binding energies of several tens meV. Together with the neutral exciton X$^0$ they dominate emission spectrum at low and elevated temperatures. We use charge tunable devices based on WSe$_2$ monolayers encapsulated hexagonal boron nitride, to investigate difference energy between X$^+$ X$^-$ fine structure. find regime, accompanied lower by a strong peak close longitudinal optical (LO) phonon energy....
The intricate interplay between optically dark and bright excitons governs the light-matter interaction in transition metal dichalcogenide monolayers. We have performed a detailed investigation of ``spin-forbidden'' ${\mathrm{WSe}}_{2}$ monolayers by optical spectroscopy an out-of-plane magnetic field ${\mathrm{B}}_{\mathrm{z}}$. In agreement with theoretical predictions deduced from group theory analysis, magnetophotoluminescence experiments reveal zero-field splitting...
The direct gap interband transitions in transition metal dichalcogenide monolayers are governed by chiral optical selection rules. Determined laser helicity, either the K+ or K− valley momentum space induced. Linearly polarized excitation prepares a coherent superposition of states. Here, we demonstrate control exciton coherence monolayer WSe2 tuning applied magnetic field perpendicular to plane. We show rotation this states angles as large 30° fields up 9 T. This on ps time scale could be...
Abstract Excitons, Coulomb bound electron–hole pairs, are composite bosons and their interactions in traditional semiconductors lead to condensation light amplification. The much stronger interaction transition metal dichalcogenides such as WSe 2 monolayers combined with the presence of valley degree freedom is expected provide new opportunities for controlling excitonic effects. But so far bosonic character exciton scattering processes remains largely unexplored these two-dimensional...
The optical properties of ${\mathrm{MoS}}_{2}$ monolayers are dominated by excitons, but for spectrally broad transitions in exfoliated directly onto ${\mathrm{SiO}}_{2}$ substrates detailed information on excited exciton states is inaccessible. Encapsulation hexagonal boron nitride (hBN) allows approaching the homogenous linewidth, interferences van der Waals heterostructures make direct comparison between spectra with different oscillator strength more challenging. Here we reveal...
Gallium arsenide and related compound semiconductors lie at the heart of optoelectronics integrated laser technologies. Shaped micro- nanoscale, they allow strong interaction with quantum dots wells, promise stunning optically active devices. However, gallium optical structures presently exhibit lower performance than their passive counterparts based on silicon, notably in nanophotonics, where surface plays a chief role. Here, we report advanced control miniature resonators using two...
We have combined spatially-resolved steady-state micro-photoluminescence ($\mu$PL) with time-resolved photoluminescence (TRPL) to investigate the exciton diffusion in a WSe$_2$ monolayer encapsulated hexagonal boron nitride (hBN). At 300 K, we extract an length $L_X= 0.36\pm 0.02 \; \mu$m and coefficient of $D_X=14.5 \pm 2\;\mbox{cm}^2$/s. This represents nearly 10-fold increase effective mobility excitons respect several previously reported values on nonencapsulated samples. cryogenic...
The optical response of traditional semiconductors depends on the laser excitation power used in experiments. For two-dimensional (2D) semiconductors, effects are anticipated to be vastly different due complexity added by their ultimate thinness, high surface volume ratio, and laser-membrane interaction effects. We show this article that under properties 2D materials undergo irreversible changes vacuum. Most surprisingly these take place even at low steady state excitation, which is commonly...
$\mathrm{MoT}{\mathrm{e}}_{2}$ belongs to the semiconducting transition-metal dichalcogenide family with certain properties differing from other well-studied members $(\mathrm{Mo},\mathrm{W}){(\mathrm{S},\mathrm{Se})}_{2}$. The optical band gap is in near-infrared region, and both monolayers bilayers may have a direct gap. We first simulate single-particle structure of monolayer bilayer density-functional-theory-$GW$ calculations. find (indirect) electronic for (bilayer). By solving addition...
Monolayers of transition metal dichalcogenides are ideal materials to control both spin and valley degrees freedom either electrically or optically. Nevertheless, optical excitation mostly generates excitons species with inherently short lifetime spin/valley relaxation time. Here we demonstrate a very efficient pumping resident electrons in n-doped WSe2 WS2 monolayers. We observe that, using continuous wave laser appropriate doping densities, negative trion doublet lines exhibit circular...
Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission well-defined energies. In as-exfoliated MoS2 MLs, the photoluminescence (PL) spectra even at low temperature consist typically of broad, overlapping contributions from neutral, charged excitons (trions) localized states. Here, we show that superacid treated PL intensity increases by up to 60 times room temperature. The neutral exciton...
Despite decades of research, demonstration all-optical detection and control free electron spins in silicon remains elusive. Here, we directly probe the spin properties bulk by measuring polarization luminescence following circularly polarized light excitation. The experiments performed for both direct indirect gap excitation allow not only an experimental determination optical selection rules different phonon-assisted transitions but they also lead to measurement relaxation electrons...
Abstract The roadmap of future innovative device developments foresees the reduction material dimensions down to nanometer scale and incorporation novel degrees freedom. For instance, electrons holes in 2D semiconductors like MoS 2 monolayers exhibit a unique coupling between spin crystal momentum, also referred as valley. A crucial requirement for applications is therefore possibility initialise spin/valley degree freedom these materials. Here we investigate optical initialisation valley...
The emission of circularly polarized light from a single quantum dot relies on the injection carriers with well-defined spin polarization. Here we demonstrate electroluminescence (EL) circular polarization degree up to 35% at zero applied magnetic field. spin-polarized electrons is achieved by combining ultrathin CoFeB electrodes top spin-LED device p-type InGaAs dots in active region. We measure an Overhauser shift several microelectronvolts field for positively charged exciton (trion X+)...
A new approach is demonstrated for investigating charge and spin diffusion as well surface bulk recombination in unpassivated doped semiconductors. This consists using two complementary, conceptually related, techniques, which are time-resolved photoluminescence (TRPL) spatially resolved microluminescence (μPL) applied here to p+ GaAs. Analysis of the sole TRPL signal limited by finite risetime. On other hand, it shown that joint μPL can be used determine constant, time, relaxation time. As...
A self-consistent expression for the surface recombination velocity $S$ and Fermi level unpinning energy as a function of light excitation power ($P$) is presented n- p-type semiconductors doped above 10$^{16}$ cm$^{-3}$ range. Measurements on GaAs films using novel polarized microluminescence technique are used to illustrate two limiting cases model. For naturally oxidized described by law in $P$ whereas passivated $S^{-1}$ varies logarithmically with $P$. Furthermore, variation state...
Images of the steady-state luminescence passivated GaAs self-standing films under excitation by a tightly focussed laser are analyzed as function light power. While unipolar diffusion photoelectrons is dominant at very low power, an increased power results in decrease constant near center image due to onset ambipolar diffusion. The agreement with numerical solution equations and physical analysis intensity centre image, which permits determination electron concentration.
In ${p}^{+}$ GaAs thin films, the effect of photoelectron degeneracy on spin transport is investigated theoretically and experimentally by imaging polarization profile as a function distance from tightly focused light excitation spot. Under electron gas (high concentration, low temperature), dip at center appears with maximum about $2\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ center. This counterintuitive result reveals that diffusion depends spin, direct consequence Pauli...
In view of future spintronic and spin-optronic devices, such as spin light-emitting diodes lasers, it is important to understand the dependence electrical injection on bias in bipolar devices based GaAs. Focusing efficiency Co-Fe-B/MgO injectors, authors investigate influence MgO growth process this dependence, using tunnel barriers fabricated by different techniques. The efficiency, compromise between high intensity circular polarization electroluminescence, depend strongly characteristics...
Spin-polarized transport of photoelectrons in bulk, $p$-type GaAs is investigated the Pauli blockade regime. In contrast to usual spin diffusion processes which polarization decreases with distance traveled due relaxation, images polarized photoluminescence reveal a spin-filter effect increases during over first $2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ from 26% 38%. This shown be direct consequence principle and associated quantum degeneracy pressure results spin-dependent increase...