Littérature scientifique sur le sujet « Degree Of Polarization of the Photoluminescence (DOP PL) »

AbstractObjectivesMonolayer transition metal dichalcogenides (TMDCs) have been regarded as promising candidates for the future light-emitting devices. To date, though the modulation of emission intensity and directionality in monolayer TMDCs has received considerable scholarly attention, there has been no systematic investigation on the underlying critical polarization. The intensity, directionality and robust polarization are highly favorable and pivotal for the future on-chip optoelectronic emission devices based on TMDCs.MethodsWe explore the emission features of the monolayer TMDCs in the photonic crystal (PhC) platform at room temperature. A monolayer tungsten disulfide (WS2) is specifically integrated with a tailored PhC structure. Angle-resolved photoluminescence (PL), time-resolved PL and polarized PL measurements are carried out to study the enhanced emission and polarization properties.ResultsThe photoluminescence (PL) of WS2 is greatly enhanced by over 300-fold, resulting from a ∼fivefold enhancement (from 1.5 to 7.2%) of the PL efficiency with accelerated spontaneous emission rates. Additionally, the overall polarized emission is obtained with the degree of linear polarization (DLP) up to 60%, which is independent of the excitation polarization. Moreover, two branched directional emissions with horizontal polarization are also achieved at a divergency angle of only 3.5°, accompanied by a surprising near-100% DLP at ±8° directions.ConclusionsThis comprehensive study sets out to assess the feasibility of the high-performance light emission device based on the monolayer TMDCs and PhC structures.

Optical properties of InAs binary quantum dot (bi-QD) molecules grown on the (001) GaAs substrate were measured by means of temperature- and excitation-power-dependent photoluminescence (PL) spectroscopy. It was observed that the shape and peak position of the PL spectra changed with the temperature and with the excitation power. It was also found that the linear polarization degree of the bi-QD PL signal changed with temperature. The temperature-dependent PL described that the linear polarization degree of bi-QDs is closely related to the carrier dynamics.

The development of future valley based electronics or valleytronics requires a high degree of valley polarization (VP) in large area monolayer (1L)-MoS2. Though it is possible to synthesize 1L-MoS2 films with large area coverage, VP property of as-grown films is found to be very poor. Here, we investigate the role of physisorbed air molecules and strain on the luminescence and the VP characteristics of large area monolayer MoS2 grown on various substrates by a microcavity based chemical vapor deposition (CVD) technique. The study shows that the removal of adsorbates from sulfur vacancy ( VS) sites not only suppresses the broad sub-bandgap luminescence feature that typically dominates low temperature photoluminescence (PL) spectra of these films but also significantly enhances VP. Post-growth transfer of the 1L-MoS2 film from sapphire to a SiO2/Si substrate by a polystyrene assisted process is found to be highly effective in improving the polarization characteristic (∼80%) of K-valleys through relaxation of the biaxial tensile strain and the removal of physisorbed air molecules from the VS sites. The process is also found to provide long lasting protection for MoS2 films from air. The finding, thus, creates much needed opportunity to use CVD grown large area 1L-MoS2 for realization of valleytronics of the future.

ABSTRACTWe report on deposition and properties of m-plane GaN/InGaN/AlInN structures on LiAlO2 substrates grown by metal organic vapor phase epitaxy (MOVPE). At first, two different buffer structures, one of them including an m-plane AlInN interlayer, were investigated concerning their suitability for the subsequent coalesced single-phase m-plane GaN growth. A series of quantum well structures with different well thickness based on one of these buffers showed absence of polarization-induced electric fields verified by room temperature photoluminescence (RT PL) measurements at different excitation intensities. Furthermore, polarization-resolved PL measurements revealed a high degree of polarization (DoP) of the emitted light with an intensity ratio of 8:1 between light polarized perpendicular and parallel to the c-axis.

ABSTRACTSome optoelectronic effects in porous Si (PS) have been investigated in relation to the visible luminescence mechanism. As regards photoluminescence (PL), particular emphasis is placed on the relationship between photoconduction (PC) and PL excitation (PLE) spectra, the interaction of external electric field and PL emission, and polarization properties of PL Main subjects of electroluminescence (EL) studies reported here are the dynamic behavior of EL operation and the formation of a large-area contact by a conducting polymer (polypyrrole: PP). The observed experimental results (almost complete coincidence of PC spectra with PLE ones, linear polarization memory of PL definite correlation between the polarization degree and the PL efficiency, and comparable response time of electrical PL quenching and EL to the PL decay time) are consistent with our hypothesis that the major process of PL takes place within Si nanocrystallites. The electrical characterization of light-emitting PS diodes with PP contacts ensures the usefulness of the contact formation by electropolymerization as a technique for uniform and efficient carrier injection into PS.

ABSTRACTHigh quality quantum wire (QWR) structures with an emitting wavelength in the 1.5-μm range were self-organized in an In0.65Ga0.35As/In0.52Al0.48As quantum well layer grown on a (775)B-oriented InP substrate by molecular beam epitaxy. Photoluminescence (PL) from the (775)B In0.65Ga0.35As/In0.52Al0.48As QWRs with a nominal well width of 4.8 nm was observed at 1.43 μm at 12 K, which corresponds to a PL wavelength of about 1.5 μm at room temperature. The PL peak was considerably polarized along the wire direction with a polarization degree of P [= (I∥ - I⊥) / (I∥ + I] ⊥)] = 0.14, indicating its good one-dimensionality. The FWHM of the PL peak was as small as 17 meV, which is the best value for InGaAs QWRs on InP substrates.

Abstract Transition metal dichalcogenide (TMD) monolayers (1L) in the 2H-phase are two-dimensional semiconductors with two valleys in their band structure that can be selectively populated using circularly polarized light. The choice of the substrate for monolayer TMDs is an essential factor for the optoelectronic properties and for achieving a high degree of valley polarization at room temperature (RT). In this work, we investigate the room-temperature valley polarization of monolayer WS2 on different substrates. A degree of polarization of photoluminescence (PL) in excess of 27% is found from neutral excitons in 1L-WS2 on graphite at room temperature, under resonant excitation. Using chemical doping through photochlorination we modulate the polarization of the neutral exciton emission from 27% to 38% for 1L-WS2/graphite. We show that the valley polarization strongly depends on the interplay between doping and the choice of the supporting layer of TMDs. Time-resolved PL measurements, corroborated by a rate equation model accounting for the bright exciton population in the presence of a dark exciton reservoir support our findings. These results suggest a pathway towards engineering valley polarization and exciton lifetimes in TMDs, by controlling the carrier density and/or the dielectric environment at ambient conditions.

With complex coupling of multiple degrees of freedom, transition metal oxides (TMOs) provide a promising platform to tune the magnetic property in heterostructures via the magnetic proximity effect. Recent realization of freestanding TMO thin films allows further extension of this technique to novel two-dimensional heterostructures by mechanically stacking with van der Waals materials. Here, we demonstrate the presence of significant magnetic exchange interactions in a heterostructure of 8 nm freestanding LaMnO3 and monolayer WS2. The high magnetization in freestanding LaMnO3 leads to valley degeneracy breaking in WS2, resulting in unbalanced valley polarization in the photoluminescence (PL). Further temperature-dependent PL measurements reveal the same transition behavior as the magnetization in the freestanding LaMnO3 film. Our results unlock new approaches for tuning the magnetism and the valley degree of freedom in ultrathin two-dimensional heterostructures.

AbstractSingle spin-defects in 2D transition-metal dichalcogenides are natural spin-photon interfaces for quantum applications. Here we report high-field magneto-photoluminescence spectroscopy from three emission lines (Q1, Q2, and Q*) of He-ion induced sulfur vacancies in monolayer MoS2. Analysis of the asymmetric PL lineshapes in combination with the diamagnetic shift of Q1 and Q2 yields a consistent picture of localized emitters with a wave function extent of ~3.5 nm. The distinct valley-Zeeman splitting in out-of-plane B-fields and the brightening of dark states through in-plane B-fields necessitates spin-valley selectivity of the defect states and lifted spin-degeneracy at zero field. Comparing our results to ab initio calculations identifies the nature of Q1 and Q2 and suggests that Q* is the emission from a chemically functionalized defect. Analysis of the optical degree of circular polarization reveals that the Fermi level is a parameter that enables the tunability of the emitter. These results show that defects in 2D semiconductors may be utilized for quantum technologies.

Les couches minces à base de nitrure de silicium (SiNx) ont été reconnus comme des diélectriques essentiels dans l'industrie microélectronique et optoélectronique en raison de leurs propriétés intéressantes. Dans cette thèse, nous décrivons comment contrôler l'indice optique et les propriétés mécaniques des couches de SiNx et d'oxynitrure de silicium (SiOyNx) en ajustant les paramètres du processus de dépôt. Nous utilisons deux types de réacteurs de dépôt chimique en phase vapeur assisté par plasma : un réacteur standard à couplage capacitif avec excitation radiofréquence et un réacteur à résonance cyclotron électronique avec excitation micro-onde. Nous discutons de la fabrication et de la caractérisation des structures multicouches comme application optique de nos couches minces. Nous focalisons sur la caractérisation et la compréhension des propriétés optiques de ces couches minces grâce à l’ellipsométrie spectroscopique. Nous étudions également expérimentalement leurs propriétés mécaniques en utilisant la technique de mesure de la courbure des substrats, la fabrication de microstructures et les mesures de nanoindentation. Enfin, nous montrons des mesures précises de la distribution des contraintes induites dans le GaAs lorsque de tels couches minces sont structurés sous forme de rubans allongées de largeur variable, en utilisant la lithographie optique et la gravure au plasma. Pour cela, nous cartographions la déformation anisotrope, en mesurant le degré de polarisation de la photoluminescence (PL) à intégration spectrale générée au sein du GaAs par excitation avec un laser rouge. La PL des semi-conducteurs cubiques massifs tels que le GaAs n'est pas polarisé, tandis que sous une contrainte anisotrope un certain degré de polarisation est produit. Ces cartographies ont été mesurées soit à partir de la surface du semi-conducteur, soit à partir de sections transversales clivées. Ils fournissent une image détaillée et complète de la déformation cristalline au voisinage de la couche contrainte structurée. Ensuite, nous avons effectué des simulations par éléments finis en essayant de reproduire les cartographies expérimentales. Nous pensons que notre schéma de simulation est utile pour la conception des composants photoniques, par exemple pour prédire les changements locaux de l'indice de réfraction dus à l'effet photoélastique
Due to their attractive properties, silicon nitride (SiNx) based films have been recognized as essential dielectric films in the microelectronic and optoelectronic industries. In this PhD thesis, we describe how we can control the refractive index and the mechanical properties of SiNx and silicon oxynitride (SiOyNx) films by tuning the deposition process parameters. We use two different plasma-enhanced chemical vapor deposition reactors: a standard capacitively coupled reactor with radiofrequency excitation and an electron cyclotron resonance reactor with microwave excitation. We discuss the fabrication and characterization of multilayer structures as an optical application of our thin films. We focus on characterizing and understanding these thin films’ optical properties through spectroscopic ellipsometry. We also study their mechanical properties experimentally using the wafer curvature measurement technique, microstructure fabrication, and nanoindentation measurements. Finally, we show accurate measurements of the strain distribution induced within GaAs wafers when such thin films are structured in the shape of elongated stripes of variable width, using standard optical lithography and plasma etching. For this, we map the anisotropic deformation, measuring the degree of polarization of the spectrally integrated photoluminescence (PL) generated within GaAs by excitation with a red laser. PL from bulk cubic semiconductors such as GaAs is unpolarized, whereas anisotropic strain produces some degree of polarization. These maps were measured either from the semiconductor surface or from cleaved cross-sections. They provide a detailed and complete image of the crystal deformation in the vicinity of the structured stressor film. Then, we performed some finite element simulations trying to reproduce the experimental maps. We believe our simulation scheme is helpful for designing the photonic components, e.g., to predict the local changes in the refractive index due to the photoelastic effect