Ce mémoire porte sur les mécanismes de relaxation et de fuite des excitons dans des systèmes de boîtes quantiques(BQs) d’InAs/InP. Les systèmes sont composés d’un sub- strat volumique d’InP, appelé matrice (M), d’un puits quantique d’InAs, nommé couche de mouillage (CM), et des familles de BQs d’InAs. La distinction entre les familles est faite par le nombre de monocouche d’épaisseur des boîtes qui sont beaucoup plus larges que hautes. Une revue de littérature retrace les principaux mécanismes de relaxation et de fuite des excitons dans les systèmes. Ensuite, différents modèles portant sur la fuite thermique des excitons des BQs sont comparés. Les types de caractérisations déjà produites et les spécifications des croissances des échantillons sont présentés. L’approche adoptée pour ce mémoire a été de caractériser temporellement la dynamique des BQs avec des mesures d’absorbtion transitoire et de photoluminescence résolue en temps (PLRT) par addition de fréquences. L’expérience d’absorption transitoire n’a pas fait ressortir de résultats très probants, mais elle est expliquée en détails. Les mesures de PLRT ont permis de suivre en température le temps de vie effectif des excitons dans des familles de BQs. Ensuite, avec un modèle de bilan détaillé, qui a été bien explicité, il a été possible d’identifier le rôle de la M et de la CM dans la relaxation et la fuite des excitons dans les BQs. Les ajustements montrent plus précisément que la fuite de porteurs dans les BQs se fait sous la forme de paires d’électrons-trous corrélées. / This thesis focuses on the mechanisms of relaxation and leakage of excitons in systems of quantum dots (QDs) InAs / InP. The systems are composed of a substrate of InP volume, called matrix (M), of a quantum well of InAs, named wetting layer (CM), and of QD families of InAs. The distinction between the families can be explained by the number of monolayer-thick boxes that are wider than high. A literature review highlights the main relaxation mechanisms and leakage of excitons in systems. Then, different models on the thermal leakage of the QD excitons are compared.Then, a presentation of the different types of characterizations already and of the specifications on the samples growths. The approach used for this thesis is to temporarily characterize the dynamic of the QDs with transient absorption and upconversion. The transient absorption experiment’s results are not very convincing, but are minutely explained. PLRT measures were used to follow in temperature the excitons effective lifetime in the QDs families. Then, with a detailed balance model, which has been well explained, it was possible to identify the role of theMand CM in relaxation and leakage of excitons in QDs. As shown by the adjustement, the escape of carriers in the QDs is made in a correlated electron-hole pairs form.

Mittels Photolumineszenz(PL)-Spektroskopie werden die Lumineszenzeigenschaften von wurtzitischen MgZnO-Dünnfilmen mit Mg-Konzentrationen im Bereich von 0 ≤ x ≤ 0,35 experimentell untersucht und die gefundenen Zusammenhänge anhand mehrerer im Rahmen dieser Arbeit entwickelter Modelle theoretisch beschrieben. Dabei werden Erklärungen für verschiedene Auswirkungen der Mischkristallunordnung auf die Lumineszenz dieses ternären Mischhalbleiters vorgestellt, welche in der Literatur bisher nicht bzw. nur unvollständig untersucht wurden. Aufgrund der Mischkristallverbreiterung überlagern sich in MgZnO für x > 0,02 die Lumineszenzbeiträge von störstellengebundenen, freien und in Potentialmulden lokalisierten Exzitonen. Sie können daher mittels zeitintegrierter PL nicht spektral getrennt werden. In dieser Arbeit wird gezeigt, dass die verschiedenen Übergänge dennoch durch zeitaufgelöste PL-Messungen unterschieden und identifiziert werden können. Die gemessenen PL-Transienten werden angepasst und die Linienform der Lumineszenzabklingkurven in Abhängigkeit von der PL-Energie analysiert. Die Bewegung der Exzitonen im Mischkristall wird unter Verwendung eines Effektiv-Masse-Modells quantenmechanisch beschrieben und der Einfluss der Mischkristallunordnung auf die optischen Übergänge qualitativ untersucht. Dabei wird insbesondere auf die Mischkristallverbreiterung sowie auf das nichtexponentielle Abklingen der Lumineszenz eingegangen. Daneben wird ein Tunnelmodell vorgestellt, mit welchem die zeitverzögerten PL-Spektren von MgZnO quantitativ reproduziert werden können. Dabei wird die asymmetrische Linienform sowie die zeitabhängige Rotverschiebung des Emissionsmaximums modelliert und die Parameter auf mikroskopische Eigenschaften der Exzitonen zurückgeführt. Außerdem wird die für Mischkristalle typische S-förmige Verschiebung des temperaturabhängigen PL-Maximums durch ein modifiziertes Arrheniusmodell erklärt.

Ce mémoire porte sur les mécanismes de relaxation et de fuite des excitons dans des systèmes de boîtes quantiques(BQs) d’InAs/InP. Les systèmes sont composés d’un sub- strat volumique d’InP, appelé matrice (M), d’un puits quantique d’InAs, nommé couche de mouillage (CM), et des familles de BQs d’InAs. La distinction entre les familles est faite par le nombre de monocouche d’épaisseur des boîtes qui sont beaucoup plus larges que hautes. Une revue de littérature retrace les principaux mécanismes de relaxation et de fuite des excitons dans les systèmes. Ensuite, différents modèles portant sur la fuite thermique des excitons des BQs sont comparés. Les types de caractérisations déjà produites et les spécifications des croissances des échantillons sont présentés. L’approche adoptée pour ce mémoire a été de caractériser temporellement la dynamique des BQs avec des mesures d’absorbtion transitoire et de photoluminescence résolue en temps (PLRT) par addition de fréquences. L’expérience d’absorption transitoire n’a pas fait ressortir de résultats très probants, mais elle est expliquée en détails. Les mesures de PLRT ont permis de suivre en température le temps de vie effectif des excitons dans des familles de BQs. Ensuite, avec un modèle de bilan détaillé, qui a été bien explicité, il a été possible d’identifier le rôle de la M et de la CM dans la relaxation et la fuite des excitons dans les BQs. Les ajustements montrent plus précisément que la fuite de porteurs dans les BQs se fait sous la forme de paires d’électrons-trous corrélées. / This thesis focuses on the mechanisms of relaxation and leakage of excitons in systems of quantum dots (QDs) InAs / InP. The systems are composed of a substrate of InP volume, called matrix (M), of a quantum well of InAs, named wetting layer (CM), and of QD families of InAs. The distinction between the families can be explained by the number of monolayer-thick boxes that are wider than high. A literature review highlights the main relaxation mechanisms and leakage of excitons in systems. Then, different models on the thermal leakage of the QD excitons are compared.Then, a presentation of the different types of characterizations already and of the specifications on the samples growths. The approach used for this thesis is to temporarily characterize the dynamic of the QDs with transient absorption and upconversion. The transient absorption experiment’s results are not very convincing, but are minutely explained. PLRT measures were used to follow in temperature the excitons effective lifetime in the QDs families. Then, with a detailed balance model, which has been well explained, it was possible to identify the role of theMand CM in relaxation and leakage of excitons in QDs. As shown by the adjustement, the escape of carriers in the QDs is made in a correlated electron-hole pairs form.

In this thesis ultrafast exciton dynamics of several colloidal quantum dots have been studied using visible transient absorption spectroscopy. The resultant transient decays and differential transmission spectra were analysed to determine the ultrafast relaxation channels, multiple exciton generation (MEG) efficiency and multi-exciton interactions in the observed materials. All QDs were preliminarily optically characterized using steady state absorption and photoluminescence spectroscopies. In addition, a high repetition infrared femtosecond pump probe experiment was designed and built to detect the picosecond intraband carrier relaxations in quantum dots. Picosecond carrier dynamics of type-II ZnTe/ZnSe and of CuInSe2 and CuInS2 type-I quantum dots were investigated. The common feature of these materials is that they are eco-friendly materials, being alternatives to the toxic Cd- and Pb- based materials. It was found that surface trapping occurred in both cases for electrons in the hot states, and in the minimum of the conduction band for ZnTe/ZnSe core/shell materials. Trion formation was observed in ZnTe/ZnSe core/shell dots at high power and unstirred conditions. The hot and cold electron trapping processes in type-II dots and CuInS2 and CuInSe2 dots shifted, distorted and moderately cancelled the bleach features. In addition, intra-gap hole trapping was observed in CuInS2 and CuInSe2 dots which results in a long decay feature in the recorded transients. MEG competes with Auger cooling, surface mediated relaxation and phonon emission. To enhance the MEG quantum yield, the rival mechanisms were suppressed in well-engineered CdSe/CdTe/CdS and CdTe/CdSe/CdS core/shell/shell and CdTe/CdS core/shell type-II quantum dots. The MEG slope efficiency and threshold for a range of different core size and shell thickness were found to be (142±9)%/Eg and (2.59±0.16)Eg, respectively. The observed threshold was consistent with the literature, whereas, the obtained slope efficiency was about three times higher than the previously reported values. The biexciton interaction energy of the dots stated in the previous paragraph was also studied. To date, time-resolved photoluminescence (TRPL) has been employed to study exciton interactions in type-II quantum dots and large repulsive biexciton interaction energy values between 50-100 meV have been reported. However, unlike the TRPL method, the TA experiment ensures that only two excitons remain in the band edge of the dot. Using this method, large attractive biexciton interaction energies up to ~-60 meV was observed. These results have promising implications regarding enhancing the MEG quantum yield.

Orientador: Fernando Iikawa / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-21T01:34:49Z (GMT). No. of bitstreams: 1 Girardi_TiagoIllipronti_M.pdf: 2091533 bytes, checksum: 1e5e58f3f5149c97c47c1bf44b7aa186 (MD5) Previous issue date: 2012 / Resumo: Neste trabalho, estudamos o efeito de diferentes condições de interface de InP/GaAs nas propriedades ópticas de pontos quânticos auto-organizados, crescidos por epitaxia de feixe químico, no modo Stranskii-Krastanov. Espera-se que os pontos quânticos de InP/GaAs apresentem alinhamento de bandas do tipo II, e somente os elétrons ficam confinados, enquanto os buracos ficam localizados nas camadas de GaAs em volta do ponto quântico, atraídos pelo elétron. No entanto, devido ao efeito de mistura de átomos nas interfaces o perfil de potencial nas interfaces pode ser alterado significativamente, afetando, com isso, as propriedades ópticas dos pontos quânticos. Foram estudadas amostras com as seguintes condições de interface entre a camada de InP e as camadas de GaAs: inclusão ou não de uma camada de InGaP em uma ou nas duas interfaces. O InGaP gera uma barreira para ambos os tipos de portadores de carga em uma junção tanto com o GaAs como InP e evita a difusa de As das camadas de GaAs para a de InP. Através de medidas de fotoluminescência resolvida no tempo, observamos a variação do tempo de decaimento da emissão óptica associada aos pontos quânticos de acordo com as diferentes condições de interface. Foi observado um tempo curto de decaimento em amostras sem a inclusão de InGaP e com a inclusão apenas na interface superior, enquanto foi observado um tempo longo quando incluímos camadas de InGaP em ambas as interfaces. O tempo de decaimento curto é incompatível com o alinhamento de bandas do tipo II, que deveria separar espacialmente o elétron do buraco. A partir desses resultados e estudos anteriores a esse trabalho, pudemos concluir que o tempo curto se deve à mistura de átomos nas regiões de ambas as interfaces, gerando ligas que localizam os portadores próximos um ao outro. O tempo longo na amostra contendo InGaP nas duas interfaces é atribuído à separação espacial do elétron e do buraco. O efeito de mistura de átomos nas interfaces, neste caso, não forma uma liga na interface que localize os dois tipos de portadores próximos um ao outro. Isso pode ser uma alternativa de preparação de pontos quânticos de InP/GaAs onde se mantém separados espacialmente o elétron e o buraco / Abstract: We studied the effect of different interface conditions on the optical properties of InP/GaAs self-assembled quantum dots grown by chemical beam epitaxy in the Stranskii-Krastanov mode. InP/GaAs quantum dots is expected to present type II band alignment, and only electrons are confined, whereas the holes are localized in the GaAs layers around the quantum dot, attracted by the electron. However, due to the atomic intermixing effect in the interface the potential profile can be strongly changed, affecting the optical properties of the quantum dots. We studied samples with the following conditions at the interfaces between the InP layer and GaAs layers: the inclusion, or the lack of, a InGaP layer at one of or both interfaces. InGaP generates a barrier for both types of carriers in a junction with GaAs and InP, and avoid the diffusion of As from the GaAs layers to the InP one. Using time-resolved photo-luminescence, we observed a change of the optical emission decay times associated to the quantum dots as the interface condition is changed. We observed a short decay lifetime in samples without InGaP layers and with the inclusion in the top interface only, whereas we observed a long decay time when we included InGaP layers in both interfaces. The short decay lifetime is incompatible with the type II band alignment, where the electron and the hole should be spatially separated. Using these and other previous results, we concluded that the short decay lifetime is due to the atomic intermixing in both interfaces regions, forming alloys that localize the carriers near each other. The long lifetime observed for sample containing InGaP in both interfaces is attributed to the large electron-hole spatial separation. In this case intermixing effects at the interfaces do not form a potential well to localize the carries near each other / Mestrado / Física / Mestre em Física

In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on the optical properties of InGaN/GaN single and multiple QW structures, measured at high excitation power densities. I show a correlation exists between the reduction in PL efficiency at high excitation power densities, the phenomenon so-called ``efficiency-droop'', and a broadening of the PL spectra. I also show a distinct change in recombination dynamics, measured by time-resolved photoluminescence (PL), which occurs at the excitation power densities for which efficiency droop is measured. The broadening of the PL spectra at high excitation power densities is shown to occur due to a rapidly redshifting, short-lived high energy emission band. The high energy emission band is proposed to be due to the recombination of weakly localised/delocalised carriers occurring as a consequence of the progressive saturation of the local potential fluctuations responsible for carrier localisation, at high excitation power densities. I report on the effects of varying threading dislocation (TD) density on the optical properties of InGaN/GaN multiple QW structures. No systematic relationship exists between the room temperature internal quantum efficiency (IQE) and the TD density, in a series of nominally identical InGaN/GaN multiple QWs deposited on GaN templates of varying TD density. I also show the excitation power density dependence of the PL efficiency, at room temperatures, is unaffected for variation in the TD density between 2 x107 and 5 x109 cm-2. The independence of the optical properties to TD density is proposed to be a consequence of the strong carrier localisation, and hence short carrier diffusion lengths. I report on the effects of including an InGaN underlayer on the optical and microstructural properties of InGaN/GaN multiple QW structures. I show an increase in the room temperature IQE occurs for the structure containing the InGaN underlayer, compared to the reference. I show using PL excitation spectroscopy that an additional carrier transfer and recombination process occurs on the high energy side of the PL spectrum associated with the InGaN underlayer. Using PL decay time measurements I show the additional recombination process for carriers excited in the underlayer occurs on a faster timescale than the recombination at the peak of the PL spectrum. The additional contribution to the spectrum from the faster recombination process is proposed as responsible for the increase in room temperature IQE.

In dieser Dissertation wird zum einen die ultraschnelle Ladungsträgerkinetik in einem Galliumnitrid (GaN)-basierten Übergitter, zum anderen die piezoelektrische Elektron-Phonon-Wechselwirkung kohärenter zonengefalteter Phononen in Galliumarsenid (GaAs)-basierten Übergittern behandelt. Mittels spektral- und zeitaufgelöster Photolumineszenzmessungen an einem n-dotierten GaN/Al0,18Ga0,82N Übergitter mit Parametern ähnlich derer in optoelektronischen Bauelementen wurde die defektbedingte Ladungsträgerkinetik untersucht, die innerhalb von ca. 150 ps durch den Einfang in tiefe, nichtstrahlende Rekombinationszentren beeinflusst wird. Die Untersuchung einer Passivierung mit Siliziumnitrid zur Verhinderung von Degradationseffekten zeigte ein stabiles optisches Langzeitverhalten bei gleichzeitiger Zunahme nichtstrahlender Defekte. Ferner wurde mit spektral aufgelöster Anrege-Abfrage-Spektroskopie eine Einfangkinetik auf einer Zeitskala von 150 - 200 fs in Defektzustände nahe der Übergitterbandkante gemessen, gefolgt von der Abkühlung der Ladungsträger durch Phononemission innerhalb weniger Pikosekunden bei Raumtemperatur und 35 ps bei 5 K. Kohärente zonengefaltete Phononen wurden mit Anrege-Abfrage-Spektroskopie an zwei AlAs/GaAs-Übergittern untersucht, die in [100]-, bzw. [111]-Richtung gewachsen wurden. Dies ermöglicht die (gezielte) Untersuchung der piezoelektrischen Elektron-Phonon-Kopplung, da diese für longitudinal-akustischen Phononen nur in der [111]-Probe existiert. Die Amplitude kohärenter Phononen mit einem Wellenvektor von q=0 in der [111]-Probe fällt verglichen mit denen in der [100]- und der [111]-Probe mit q≠0 signifikant schneller ab. Kohärente Phononen verursachen in der [111]-Probe bei q=0 ein makroskopisches piezoelektrisches Feld, welches Ladungsträger beschleunigt, die durch Reibung kohärente Phononen dämpfen. Bei hohen Ladungsträgerdichten unterdrückt die Abschirmung der induzierten piezoelektrischen Felder diese zusätzliche Dämpfung. / In this dissertation, the ultrafast carrier dynamics in a gallium nitride (GaN)-based superlattice as well as the piezoelectric electron-phonon-coupling of coherent zone-folded phonons in gallium arsenide (GaAs)-based superlattices are addressed. Using spectrally and time-resolved photoluminescence experiments on an exemplary n-doped GaN/Al0.18Ga0.82N superlattice with parameters similar to those in optoelectronic devices, we investigated the defect-related carrier kinetics, that are affected by trapping in saturable nonradiative recombination centers on time scales of ~150 ps. The investigation of a passivation with silicon nitride to prevent degradation effects show a long-term optical stability with a concomitant increase in non-radiative defect densities. Furthermore, spectrally resolved pump-probe spectroscopy was used to measure trapping kinetics into defect states near the conduction band minimum on a time scale of 150 – 200 fs. These kinetics are followed by carrier cooling through phonon emission within a few picoseconds at room temperature and within 35 ps at 5 K. Coherent zone-folded phonons were studied with pump-probe spectroscopy on two AlAs/GaAs superlattices grown in [100] and [111] direction, respectively. This allows the specific investigation of the piezoelectric electron-phonon interaction, since this exists for longitudinal acoustic phonons only in the [111] sample. The amplitude of coherent phonons with a wave vector of q=0 in the [111] sample decays significantly faster than in the [100] and the [111] samples with q≠0. Coherent phonons in the [111] sample cause a macroscopic piezoelectric field to which the photogenerated electron-hole plasma couples. Friction of the accelerated carriers provides the additional damping mechanism. High carrier densities screen the induced piezoelectric field, thus reducing the damping mechanism via the piezoelectric interaction.

Mittels Photolumineszenz(PL)-Spektroskopie werden die Lumineszenzeigenschaften von wurtzitischen MgZnO-Dünnfilmen mit Mg-Konzentrationen im Bereich von 0 ≤ x ≤ 0,35 experimentell untersucht und die gefundenen Zusammenhänge anhand mehrerer im Rahmen dieser Arbeit entwickelter Modelle theoretisch beschrieben. Dabei werden Erklärungen für verschiedene Auswirkungen der Mischkristallunordnung auf die Lumineszenz dieses ternären Mischhalbleiters vorgestellt, welche in der Literatur bisher nicht bzw. nur unvollständig untersucht wurden. Aufgrund der Mischkristallverbreiterung überlagern sich in MgZnO für x > 0,02 die Lumineszenzbeiträge von störstellengebundenen, freien und in Potentialmulden lokalisierten Exzitonen. Sie können daher mittels zeitintegrierter PL nicht spektral getrennt werden. In dieser Arbeit wird gezeigt, dass die verschiedenen Übergänge dennoch durch zeitaufgelöste PL-Messungen unterschieden und identifiziert werden können. Die gemessenen PL-Transienten werden angepasst und die Linienform der Lumineszenzabklingkurven in Abhängigkeit von der PL-Energie analysiert. Die Bewegung der Exzitonen im Mischkristall wird unter Verwendung eines Effektiv-Masse-Modells quantenmechanisch beschrieben und der Einfluss der Mischkristallunordnung auf die optischen Übergänge qualitativ untersucht. Dabei wird insbesondere auf die Mischkristallverbreiterung sowie auf das nichtexponentielle Abklingen der Lumineszenz eingegangen. Daneben wird ein Tunnelmodell vorgestellt, mit welchem die zeitverzögerten PL-Spektren von MgZnO quantitativ reproduziert werden können. Dabei wird die asymmetrische Linienform sowie die zeitabhängige Rotverschiebung des Emissionsmaximums modelliert und die Parameter auf mikroskopische Eigenschaften der Exzitonen zurückgeführt. Außerdem wird die für Mischkristalle typische S-förmige Verschiebung des temperaturabhängigen PL-Maximums durch ein modifiziertes Arrheniusmodell erklärt.

Recombination mechanisms in gallium arsenide have been studied using temperature-dependent time-resolved photoluminescence-decay. New analytical methods are presented to improve the accuracy in bulk lifetime measurement, and these have been used to resolve the temperature-dependent lifetime. Fits to temperature-dependent lifetime yield measurement of the radiative-efficiency, revealing that samples grown by the Czochralski and molecular-beam-epitaxy methods are limited by radiative-recombination at 77K, with defect-mediated nonradiative-recombination becoming competitive at 300K and above. In samples grown with both doping types using molecular-beam-epitaxy, a common exponential increase in capture cross-section characterized by a high value of E_infinity=(258 +/- 1)meV was observed from the high-level injection lifetime over a wide temperature range (300-700K). This common signature was also observed from 500-600K in the hole-lifetime observed in n-type Czochralski GaAs where E_infinity=(261 +/- 7)meV was measured, which indicates that this signature parametrizes the exponential increase in hole-capture cross-section. The high E_infinity value rules out all candidate defects except for EL2, by comparison with hole-capture cross-section data previously measured by others using deep-level transient spectroscopy. / Thesis / Doctor of Philosophy (PhD)

<p dir="ltr">In the realm of two-dimensional (2D) materials, monolayer (ML) transition metal dichalcogenides (TMDCs) have gained significant interest due to their direct bandgap transition, high carrier mobility, strong light-matter interaction, and robust spin and valley degrees of freedom, starkly contrasting their bulk counterparts. Owing to their large surface-to-volume ratio, the integration of ML TMDCs with other various 2D semiconductors and microcavities offers opportunities to study fundamental photo-physics processes at the heterointerfaces, paving the way for implementation of next-generation devices.</p><p dir="ltr">Chapter 1 provides a concise introduction to 2D materials, particularly TMDCs, and their fascinating optical and electronic properties. It examines the role of excitons in 2D materials, and the impact of energy transfer (ET) and charge transfer (CT) on exciton’s properties in TMDC through the construction of 2D van der Waals (vdW) heterostructures and coupling with optical microcavities. This chapter also delves into the potential enhancement of TMDCs’ optical properties by integrating 2D hybrid lead halide perovskites and ultra-thin three-dimensional (3D) halide perovskites with TMDCs. Furthermore, it sets the general context for light-matter interaction, another form of ET, considering both weak and strong coupling regimes.</p><p dir="ltr">Chapter 2 outlines the optical techniques employed to gather data for this work. A focus is placed on ultrafast optical techniques like transient absorption spectroscopy, which allow for direct probing and analysis of ET and CT dynamics at the heterointerface.</p><p dir="ltr">Photoinduced interfacial CT plays a critical role in the field of energy conversion involving vdW heterostructures constructed by inorganic nanostructures and organic materials. However, the control of atomic-scale stacking configurations to modulate charge separation at interfaces remains challenging. Chapter 3 aims to illustrate tunability of interfacial charge separation in a Type-II heterojunction between ML-WS₂ and an organic semiconducting molecule by rational design of relative stacking configurations using 2D perovskites as scaffoldings. This chapter investigates how different molecular stacking, face-to-face versus face-to-edge, affects CT at the heterointerface. Our findings reveal that the CT process heavily depends on the relative stacking configurations at the organic-TMDCs heterointerface, with charge separation being notably slowed down for face-to-edge configuration compared to face-to-face configuration. These investigations open new opportunities for designing efficient charge separation processes in energy conversion applications by judiciously engineering interfaces between organic and inorganic semiconductors, using 2D perovskites as scaffolds.</p><p dir="ltr">Though TMDCs’ large surface-to-volume ratios make them excellent platforms for studying interfacial properties, the presence of bulky ligands on the surface of 2D perovskite poses a challenge, impeding direct interfacial coupling in their heterostructures. Chapter 4 details the fabrication of ML-WS₂ and ultra-thin CH₃NH₃PbX₃ (MAPbX₃, X=Br, I) heterostructures with tunable energy levels, to study the dynamics of CT and ET at these hybrid interfaces. Notably, heterojunctions of WS₂ with pure MAPbBr₃ and MAPbI₃ were elucidated as Type-I and Type-II respectively, using photoluminescence (PL) and time-resolved photoluminescence (TR-PL) measurements. Transit absorption (TA) spectroscopy investigations unambiguously revealed a rapid ET facilitated by CT in the WS₂/MAPbBr₃ heterostructure, with a time constant of ~20 ps, and a predominantly CT in the WS₂/MAPbI₃ heterostructure with a time constant of ~50 femtosecond (fs). The successful interfacing of low-dimensional perovskites with an extensive array of traditional 2D materials such as TMDCs opens up possibilities for novel optoelectronic properties and applications within the field of 2D material systems. Furthermore, the ultrafast and efficient ET and CT processes hold promise for the creation of advanced energy conversion devices.</p><p dir="ltr">In the last chapter, we successfully fabricated a ML-WS₂ in conjunction with a silver (Ag) nanoparticle (NP) array. Our findings affirmed a weak light-matter coupling between ML-WS₂ and the Ag NP array, as evidenced by angle-resolved photoluminescence spectroscopy. Furthermore, an enhancement in the bright exciton emission from ML-WS₂ was observed at reduced temperatures. The analysis of PL enhancement factor at varying temperatures suggested that an upper bound of the enhancement factor for the bright exciton could reach ~51 or even higher at 7 K, given the imperfect uniformity of the electric filed generated around the NPs. This discovery carries significant implications for the manipulation of excitons in TMDCs and expands their potential applications in the field of optoelectronics.</p>