Book Description
Les propriétés optiques des couches épitaxiées de GaN dopées aux terres rares ont attiré l'attention pour des applications optoélectroniques tels que la signalisation, [la] lumière blanche et [les] communications optiques. Nous avons étudié les propriétés optiques et structurales des couches minces de GaN dopées aux terres rares (Er3+, Eu3+, Tm3+), réalisées par GSMBE (Gas Source Molecular Beam Epitaxy). La totalité du spectre de la lumière visible a été observé, du GaN:Eu (Rouge : 622 nm) au GaN:Tm (Bleu : 477 nm), en passant par le GaN:Er (Vert : 537 nm, 558 nm). La diffraction de rayons X a été utilisée pour étudier la qualité cristalline des couches. La microscopie électronique en transmission (TEM) a été utilisée pour étudier les défauts dus à l'incorporation d'ions de terres rares dans la matrice de GaN. Des mesures AFM ont aussi été utilisées pour étudier les effets de la température de croissance et de la concentration de terres rares sur la morphologie de la surface des couches dopées. Les études structurales sur les couches de GaN dopées aux terres rares ont montré que les défauts participent au mécanisme de transfert d'énergie de la matrice vers les ions de terres rares, ce qui accroît l'émission de lumière relative aux transitions intra-4f des terres rares, observées par photoluminescence.
Author: Lu Jiao Publisher: Open Dissertation Press ISBN: 9781361011973 Category : Science Languages : en Pages : 118
Book Description
This dissertation, "Growth of Transition Metal Dichalcogenide Thin Films by Molecular Beam Epitaxy" by Lu, Jiao, 焦璐, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Atomically thin transition metal dichalcogenides (TMD) have attracted intensive research interests due to their extraordinary properties and potential applications in electronics and optoelectronics. In this thesis, epitaxial growths of two-dimensional (2D) MoSe2 and WSe2 thin films were carried out in Molecular Beam Epitaxy (MBE). Multiple characterization techniques were employed to investigate thin films' structural, morphological, electronic and optical properties. A series of submonolayer MoSe2 coverage samples have been grown on highly ordered pyrolytic graphite (HOPG) substrate. Growth temperature and post-growth annealing temperature were seen to have obvious impacts on film's morphology and crystal quality. Layer-by-layer growth mode has been identified for the Van der Waals epitaxy of MoSe2 on HOPG. Dense networks of inversion domain boundaries (IDBs) have been observed in as-grown MoSe2 epifilms by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM), and their density can be tuned by changing the MBE conditions. Scanning tunneling spectroscopy (STS) measurements reveal mid-gap electronic states associated with the IDB defects. STS measurements also reveal energy bandgaps of monolayer (ML) and bilayer (BL) MoSe2. ML WSe2 thin films were also grown at varying conditions on HOPG substrates through the Van der Waals epitaxy process and the growth characteristics were found similar to that of MoSe2. However, differences are also noted, particularly about the IDB defects. Contrary to MoSe2, as-grown WSe2 films do not contain the line defects. The reason behind such differences will be discussed. Finally, besides the STM/S studies about the morphological and electronic properties of MBE MoSe2 and WSe2 films, high quality samples have been synthesized on graphene-on-SiC substrate with reduced defect density and well-controlled thicknesses for some ex situ characterizations by photoluminescence and Raman spectroscopy methods. The results will be summarized and discussed in this thesis. Subjects: Molecular beam epitaxy Metallic films
Author: Rashin Basiri Namin Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Rare earth doping is one of the main approaches to enhance the optical properties of silicon-based materials. In this work, a set of europium doped silicon oxide (Eu[subscript x]Si[subscript y]O[subscript z]) thin films are fabricated using an integrated magnetron sputtering electron cyclotron resonance plasma enhanced chemical vapor deposition (IMS-ECR-PECVD) system. The thin film composition was studied by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) measurements verifying high control over the Eu content by changing the sputtering power. Variable Angle spectroscopic ellipsometry (VASE) was conducted, delivering the refractive index and thickness. Using a UV laser (325 nm) excitation source, Photoluminescence (PL) measurements were performed, and it was confirmed that Eu[superscript 3+] transition which is associated with the red light emission is successfully achieved even at annealing temperatures as low as 300°C. Performing X-ray diffraction (XRD) analysis, the structural properties of the thin films were studied and the formation of Eu[subscript x]Si[subscript y]O[subscript z] crystals was confirmed for the samples annealed at elevated temperatures.
Author: Lee Sang a Publisher: LAP Lambert Academic Publishing ISBN: 9783659638916 Category : Languages : en Pages : 136
Book Description
In this study we report on structural and electric properties of -Ga2O3 on Si and GaN substrates. Since Ga2O3 has a band-gap of 4.8 eV at room temperature and a dielectric constant of 10.2 14.2, Ga2O3 can be a potential candidate dielectrics for MIS devices. -Ga2O3 has been deposited using various techniques such as radio-frequency sputtering, plasma enhanced atomic layer deposition (PEALD), and pulsed laser deposition (PLD). In particular, epitaxial Ga2O3 thin films grown on n-GaN/Al2O3 substrate by PLD technique have a monoclinc -Ga2O3 phase and peaks were indexed as (-2 0 1) and higher order diffractions. Optical transmittance of the epitaxial -Ga2O3 film was more than 90% from UV to visible spectral regions and the optical band-gap of the -Ga2O3 was calculated to be about 4.8 eV. Moreover, we have fabricated MFIS capacitors using Ga2O3 and Ba0.5Sr0.5TiO3 (BST) thin films on GaN/Al2O3 substrate by pulsed laser deposition. The epitaxial growth, structural analysis, and dielectric properties of the Ga2O3 films and BST thin films will be discussed.
Author: Muhammad Monzur Morshed Publisher: ISBN: 9781321551297 Category : Optoelectronic devices Languages : en Pages : 118
Book Description
Mgx Zn1-x O thin film was developed to realize optoelectronic devices in the ultraviolet region. The alloy was grown without any phase separation and characterized with different methods, such as, photoluminescence, absorption, x-ray diffraction etc. to confirm the structural properties. P-type doping of Mg x Zn1-x O thin film was investigated. Antimony (Sb) and nitrogen (N) were used as the p-type dopant. It was found that incorporation of Sb degrades the optical quality of the film. On the other hand, N-doped p-type Mgx Zn1-x O thin film was demonstrated without any degradation of the optical quality. Temperature dependent photoluminescence of nitrogen doped p-type Mgx Zn1-x O nano crystalline thin films grown on c -plane sapphire substrate by rf plasma assisted molecular beam epitaxy were examined. P-type behavior was confirmed by both Hall effect and Seebeck measurements. However, structural defect related bound excitonic emission peak was distinguished in the low temperature photoluminescence spectra. Also, typical 'S shape' behavior of energy position versus temperature is observed due to polarization induced internal field. Nitrogen related acceptor ionization energy was calculated to be ~180-200meV.
Author: Che Woei Chin Publisher: LAP Lambert Academic Publishing ISBN: 9783844392678 Category : Languages : en Pages : 124
Book Description
Various techniques have been used to grow III-nitride heterostructures including metalorganic vapor deposition, hydride vapor epitaxy and molecular beam epitaxy (MBE). Among these techniques, MBE presents a number of advantages such as precise control of layer thickness and composition. MBE is a highly sophisticated system which thin film quality is sensitive to the growth parameters. From the literature, a systematic growth procedure has not been well-documented. This book presents an in depth understanding of MBE growth mechanism which is essential for thin film quality improvement. Detailed study on the growth mechanism allows the acquisition of the fundamental knowledge in growing precise optoelectronics device structures. This book focuses on the study of III-nitride thin films grown by MBE on various aspects, supported by analysis using a variety of structural and optical characterization techniques. The book starts with the introduction of the MBE architecture, follows by the detailed growth procedures. The characterization and analysis of various III-nitride thin films grown on Si and sapphire will be presented in the last part of the book.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The present work is devoted to the experimental study of the MI transition in V2O3 thin films, grown on different substrates. The main goal of the work was to develop a technology of growth of V2O3 thin films on substrates with different electrical and structural properties (diamond and LiNbO3), designed for specific applications. The structural and electrical properties of the obtained films were characterized in detail with a special focus on their potential applications. The MIT of V2O3 was investigated by SAW using first directly deposited V2O3 thin film onto a LiNbO3 substrate.
Author: Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
Optical properties of erbium ions in MBE-grown GaN-thin films are reported. Three types of sites were identified using site selective laser excitation. The main center is ascribed to the Er3+ ions substituted in the Ga sub-lattice while the two other centers are assigned to Er-related defects. The lifetimes of the 4S3/2 and 4I13/2 multiplets of the main center are strongly quenched with increasing Er concentration. The complex decay profile of the visible fluorescence and its concentration dependence were modeled and interpreted using the diffusion-limited model. The dynamics of the infrared emission at 1.54 m from the 4I13/2 multiplet after excitation in the visible range is discussed. The crystal field strength of Er3+ in GaN was deduced from the overall crystal field splitting of the ground multiplet. Comparison of the results with those obtained in inorganic materials indicates that the rare earth is well embedded in the semiconductor host and not in a impurity oxide phase.
Author: Georgios Halambalakis
Author: Lu Jiao
Author: Rashin Basiri Namin
Author: Lee Sang a
Author: Muhammad Monzur Morshed
Author: Che Woei Chin
Author: Peter W. Deelman
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