Metalorganic Chemical Vapour Deposition (MOCVD) is a versatile technique for the deposition of thin films of oxide materials as it offers advantages, such as deposition over large surface area, conformal coverage, selective area deposition, and a high degree of compositional control. The MOCVD process uses metalorganic (MO) complexes, such as β-diketonate and alkoxide-based complexes, as precursors. These complexes are stable and moderately volatile. Because of the direct bond between metal and oxygen, MO complexes are natural precursors for oxide coatings. As the process involves chemical reactions taking place on the substrate surface, growth of thin films by MOCVD depends on various parameters such as the chemical nature and concentration of precursors, reaction pressure, reaction temperature, and the nature of the substrate. Such a large parameter space of the CVD process, when combined with the dynamics (thermodynamics and fluid dynamics) and kinetics, makes it rather complex. This complexity allows one to make thin films of metastable phases, including amorphous materials. One of the important findings of the work is that MOCVD process is capable of making composite coatings of carbonaceous metal oxide. Manganese is multivalent and forms various stable oxides, such as MnO, Mn2O3, Mn3O4 and MnO2. There are various potential applications of manganese oxides. MnO2 is a very well studied material for its electrochemical applications in dry cells, lithium-ion batteries, and in supercapacitors. Hence, it becomes pertinent to explore the properties of thin films of manganese oxides prepared by MOCVD for various electrochemical and other applications. The thesis work is divided into two parts. Part 1 describes the synthesis of manganese complexes, their characterization, and their application to the CVD of coatings, especially those of carbonaceous MnO. Part 2 is devoted to a detailed study of electrochemical aspects of the carbonaceous MnO coatings, followed by a report on their unusual transport properties. Chapter 1 begins with a brief introduction to thin film deposition processes. In particular, the CVD process is described with reference to various parameters such as carrier gas flow, pressure, temperature and most importantly, the CVD precursor. The chapter ends with a description of the scope of the work undertaken for the present thesis. Chapter 2 deals with “Synthesis and Characterization of MO complexes”. It begins with a description of the classification of CVD precursors with the description of MO complexes such as β-diketonates, which are generally subliming crystalline solids. Manganese β-diketonate complexes are discussed in detail. Due to the multivalent nature of Mn, there are two possible complexes namely Mn(acac)2(H2O)2 and Mn(acac)3. These complexes have been synthesised and characterized (confirmed) by various techniques, such as elemental analysis (CHN), X-ray diffraction (XRD), FTIR spectroscopy, and mass spectroscopy. Thermal analysis of the complexes shows that they are suitable as MOCVD precursors. We have used Mn(acac)2(H2O)2 as a precursor in the present work. Metalorganic complexes, where metal ion is directly bonded with both nitrogen and oxygen, can be potential candidates for the precursor for oxynitrides coatings. We have therefore studied solid crystalline anthranilate complexes of various metal ions, such as Mn2+, Co2+, Cu2+ and Zn2+ and confirmed their formation. Thermal analysis shows that anthranilate complexes are fairly volatile below 250oC and decompose below 500oC. These complexes were pyrolysed in open air and in sealed tube at different temperatures, and the resulting powder product examined by XRD, SEM, EDAX and FTIR. This preliminary study shows that anthranilate complexes yield different oxides of Mn, Co and Cu under different pyrolysis conditions, with very interesting morphological features. Pyrolysis of Zn(aa)2 in a sealed tube leads to the formation of a nanocomposite of carbon and zinc oxide (wuerzite), rich in carbon, with potential for applications in catalysis. On the other hand, the pyrolysis of Zn(aa)2 in air at the same temperature leads to leads to crystalline, nanostructured zinc oxide (wuerzite). However, no attempt has been made to use these anthranilates as CVD precursors. Chapter 3 deals with “MOCVD of Manganese Oxides and their Characterization”. It begins with a brief review of various manganese oxides and their properties. This is followed by description of the CVD reactor used for the present work, together with the conditions employed for the deposition of MnOx films. Depositions have been carried out on different substrates such as SS-316, ceramic alumina and Si (111), while varying various deposition parameters, viz., substrate, reactor pressure, carrier gas (argon) flow rate, and the duration of deposition. Significantly, depositions are divided into two categories: one, carried out in argon ambient, in the absence of a supply of oxygen (or any other oxidant) and the second one, under oxygen flow, using argon as carrier gas. The films deposited in the absence of oxygen flow are thick, black in colour, and electrically conducting, indicating the presence of carbon. The growth rate follows a typical thermal pattern, with activation energy of ~ 1.7 eV. Detailed characterization by XRD, TEM/ED, Raman, FTIR and XPS (X-ray photoelectron spectroscopy) shows that these films are composed of MnO in a carbon-rich amorphous matrix. High-resolution SEM (fig. 1) reveals a fractal pattern of cauliflower morphology, comprising very fine particles (4 – 10 nm), characteristic of very large specific surface area of the film, which is confirmed by volumetric BET measurement (~2000 m2/g). We conclude that growth in argon ambient leads to a homogenous nanocomposite film of hydrated MnO in carbon-rich matrix. Thus, our study reveals that MOCVD is a novel one-step chemical method to produce homogenous composite thin films, wherein all components of the nanocomposite film emerge from the same chemical precursor. Carbon incorporation is generally avoided by empirical process design, as it is viewed as an impurity. The potential advantages of carbon incorporation are thus not examined and the composite nature of carbonaceous films not recognized in the literature. Carbonaceous nanocomposite film can be significant as an electrode in supercapacitors, as discussed in part 2 of the thesis. Chapter 3 describes films deposited under oxygen flow, which are no longer black and are highly resistive, indicating the absence of carbon in the film, as confirmed by Raman spectroscopy. XRD, FTIR and Raman spectroscopy reveal that the films obtained under oxygen flow are more crystalline than the ones obtained in the absence of oxygen flow, and that the films are generally nanocrystalline composites of two manganese oxides, such as MnO and Mn3O4. Given the context of the carbonaceous MnO films described above, chapter 4 begins with a review of electrochemical capacitors (also called supercapacitors or ultracapacitors), which are emerging as important energy storage devices. Until now, in the Mn-O system, hydrated MnO2 has been well-studied as an electrode material due to its low cost and environmental compatibility, but the low electrical conductivity of MnO2, together with irreversible redox reactions, reduces its performance. In electrochemical capacitor applications, metal-oxide/carbon composites are finding importance. Chapter 4 deals with “MnO/C Nanocomposite Coatings as Electrodes for Electrochemical Capacitor”. In this chapter, we have examined the novel EM, i.e., the hydrated MnO/C nanocomposite coating prepared by the MOCVD process on a conducting substrate (current collector) such as SS-316 as an electrode. Electrochemical measurements have been carried out for both the 3-electrode assembly (for basic aqueous electrolyte) and 2-electrode assembly (for gel polymer electrolyte) using cyclic voltammetry (CV), AC impedance and charge-discharge techniques. The studies lead to a maximum specific capacitance of 230 – 270 F/g at 1 mA/cm2 discharge current density for the MnO/C nanocomposite coating grown at 680oC. The Bode plot shows a maximum phase angle of around 74 – 82o, indicating capacitive behaviour. The MnO/C nanocomposite film shows a very small time constant (0.5 – 3 msec), which is good for high frequency applications. The pulse power figure of merit is found to be 650 – 2000 W/g. Capacitance determined for a large number of charge-discharge cycles (~20000), and at large current densities (50 mA/cm2) show promising results. The energy density (5 - 32 Wh/kg) and power density (2 – 4 kW/kg) estimated from charge-discharge data at 1 mA/cm2 shows the potential of the nanocomposite MnO/C as electrode for superior capacitor devices. Gel polymer electrolytes (GPE) offer the advantage of large electrochemical potential window due to its structural and chemical stability. Studies have been carried out to show that the MnO/C nanocomposite film is compatible with gel polymer electrolytes based on poly(methyl methacrylate) (PMMA) and poly(acrylonitrile) (PAN) with salts of magnesium triflate and magnesium perchlorate, respectively) and plasticizers (ethylene carbonate (EC) + propylene carbonate (PC)), in a 2-electrode assembly. Chapter 5 deals with “Magnetoconductance in MnO/C Nanocomposite Coatings on Alumina”. Amorphous systems, such as MnO/C composites wherein carbon is amorphous and MnO is nearly so, are highly symmetric condensed phases, which do not possess long range translational or orientational order. Disorder in the system creates Anderson localized states just above the valence band, which lead to reduced electrical conductivity. Amorphous systems show either a small negative magnetoresistance (~ 5%) or a small positive magnetoconductance (~ 7%) at very low temperatures (~ 10 K). As such, the transport properties of the MnO/C nanocomposite film have been investigated, and are reported in chapter 5. Transport and magnetotransport measurements have been made on the MnO/C nanocomposite film grown on alumina. It is found that the MnO/C nanocomposite coating exhibits a giant negative MR (22.3%) at a temperature as high as 100 K, which is unusual because pure MnO is anti-ferromagnetic and does not ordinarily show any magnetoresistance (MR), while amorphous carbon is known to show a small MR at very low temperatures (~7 K), due to weak-localization. The present results mean that a mechanism other than weak-localization plays a role in this nanocomposite material. Further study of this material is called for, which can perhaps lead to giant magnetoresistance (GMR) at room temperature in a metal-oxide/carbon nanocomposite. A summary of the work and an outlook for further research are given in the concluding chapter 6.

Doctor of Philosophy / Department of Physics / Hongxing Jiang / InGaN based, blue and green light emitting diodes (LEDs) have been successfully produced over the past decade. But the progress of these LEDs is often limited by the fundamental problems of InGaN such as differences in lattice constants, thermal expansion coefficients and physical properties between InN and GaN. This difficulty could be addressed by studying pure InN and In[subscript]xGa[subscript]1-xN alloys. In this context Ga-rich In[subscript]xGa[subscript]1-xN (x≤ 0.4) epilayers were grown by metal organic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) measurements showed In[subscript]xGa[subscript]1-xN films with x= 0.37 had single phase. Phase separation occurred for x ~ 0.4. To understand the issue of phase separation in Ga-rich In[subscript]xGa[subscript]1-xN, studies on growth of pure InN and In-rich In[subscript]xGa[subscript]1-xN alloys were carried out. InN and In-rich In[subscript]xGa[subscript]1-xN (x~0.97- 0.40) epilayers were grown on AlN/Al[subscript]2O[subscript]3 templates. A Hall mobility of 1400 cm[superscript]2/Vs with a carrier concentration of 7x1018cm[superscript]-3 was observed for InN epilayers grown on AlN templates. Photoluminescence (PL)emission spectra revealed a band to band emission peak at ~0.75 eV for InN. This peak shifted to 1.15 eV when In content was varied from 1.0 to 0.63 in In-rich In[subscript]xGa[subscript]1-xN epilayers. After growth parameter optimization of In- rich In[subscript]xGa[subscript]1-xN alloys with (x= 0.97-0.40) were successfully grown without phase separation. Effects of Mg doping on the PL properties of InN epilayers grown on GaN/Al[subscript]2O[subscript]3 templates were investigated. An emission line at ~ 0.76 eV, which was absent in undoped InN epilayers and was about 60 meV below the band edge emission peak at ~ 0.82 eV, was observed to be the dominant emission in Mg-doped InN epilayers. PL peak position and the temperature dependent emission intensity corroborated each other and suggested that Mg acceptor level in InN is about 60 meV above the valance band maximum. Strain effects on the emission properties of InGaN/GaN multiple quantum wells (MQWs) were studied using a single blue LED wafer possessing a continuous variation in compressive strain. EL emission peak position of LEDs varies linearly with the biaxial strain; a coefficient of 19 meV/GPa, characterizes the relationship between the band gap energy and biaxial stress of In[subscript]0.2Ga[subscript]0.8N/GaN MQWs.

The InGaN system provides the opportunity to fabricate light emitting devices over the whole visible and ultraviolet spectrum due to band-gap energies E[subscript g] varying between 3.42 eV for GaN and 1.89 eV for InN. However, high In content in InGaN layers will result in a significant degradation of the crystalline quality of the epitaxial layers. In addition, unlike other III-V compound semiconductors, the ratio of gallium to indium incorporated in InGaN is in general not a simple function of the metal atomic flux ratio, f[subscript Ga]/f[subscript In]. Instead, In incorporation is complicated by the tendency of gallium to incorporate preferentially and excess In to form metallic droplets on the growth surface. This phenomenon can definitely affect the In distribution in the InGaN system. Scanning electron microscopy, room temperature photoluminescence, and X-ray diffraction techniques have been used to characterize InGaN layer grown on InN and InGaN buffers. The growth was done on c-plane sapphire by MOCVD. Results showed that green emission was obtained which indicates a relatively high In incorporation. / Singapore-MIT Alliance (SMA)

This thesis presents the development of III-nitride materials for deep-ultraviolet (DUV) light emitting devices. The goal of this research is to develop a DUV laser diode (LD) operating at room temperature. Epitaxial structures for these devices are grown by metalorganic chemical vapor deposition (MOCVD) and several material analysis techniques were employed to characterize these structures such as atomic force microscopy, electroluminescence, Hall-effect measurement, photoluminescence, secondary ion mass spectrometry, transmission electron microscopy, transmission line measurement, and X-ray diffraction. Each of these will be discussed in detail. The active regions of III-nitride based UV emitters are composed of AlxGa1-xN alloys, the bandgap of which can be tuned from 3.4 eV to 6.2 eV, which allows us to attain the desired wavelength in the DUV by engineering the molar fraction of aluminum and gallium. In order to emit photons in the DUV wavelength range (> 4.1 eV), high aluminum molar fraction AlxGa1-xN alloys are required. Since aluminum has very low ad-atom mobility on the growth surface, a very low group V to group III precursor ratio (known as V/III ratio), high growth temperature, and low growth pressure is required to form a smooth surface and subsequently abrupt heterointerfaces. The first part of this work focuses on developing high-quality multi-quantum well structures using high aluminum molar fraction ([Al] > 60%) AlxGa1-xN alloys. Optically pumped DUV lasers were demonstrated with threshold power density as low as 250 kW/cm² for the emission wavelength as short as 248.3 nm. Transverse electric (TE) -like emission dominates when the lasers were operating above threshold power density, which suggests the diode design requires the active region to be fully strained to promote better confinement of the optical mode in transverse direction. The second phase of this project is to achieve an electrically driven injection diode laser. Owing to their large bandgap, low intrinsic carrier concentration, and relatively high dopant activation energy, the nature of these high aluminum molar fraction materials are highly insulating; therefore, efficiently transport carriers into active region is one of the main challenges. Highly conducting p-type material is especially difficult to achieve because the activation energy for magnesium, a typical dopant, is relatively large and some of the acceptors are compensated by the hydrogen during the growth. Furthermore, due to the lack of a large work function material to form a p-type ohmic contact, the p-contact layer design is limited to low aluminum molar fraction material or gallium nitride. Besides the fabrication challenges, these low aluminum molar fraction materials are not transparent to the laser wavelength causing relatively high internal loss (αi). In this work, an inverse tapered p-waveguide design is employed to transport holes to active region efficiently while the graded-index separate-confinement heterostructure (GRINSCH) is employed for the active region design. Together, a multi-quantum well (MQW) ultraviolet emitter was demonstrated.

No description available.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-01-05T09:56:54Z No. of bitstreams: 1 leonadasilvaflores.pdf: 7703560 bytes, checksum: 6e5f7330b9f5bb6e7d5e649e91d606e6 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-01-25T16:05:33Z (GMT) No. of bitstreams: 1 leonadasilvaflores.pdf: 7703560 bytes, checksum: 6e5f7330b9f5bb6e7d5e649e91d606e6 (MD5) / Made available in DSpace on 2016-01-25T16:05:33Z (GMT). No. of bitstreams: 1 leonadasilvaflores.pdf: 7703560 bytes, checksum: 6e5f7330b9f5bb6e7d5e649e91d606e6 (MD5) Previous issue date: 2015-08-21 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste trabalho foi o de sintetizar MOFs com ligantes mistos, N- e O- doadores, utilizando alguns cátions metálicos da primeira série de transição como conectores de rede. Foram obtidas as redes de coordenação CoPDC2D e ZnPDC2D, que são isoestruturas as quais se estendem bi-dimensionalmente. Essas formam laços com 16-circuitos (circuitos mais curtos que contemplam 16 átomos), e incluem apenas o ligante 2,5-piridinodicarboxilato 2,5-pdc e os cátions (Co2+ e Zn2+) na coordenação. Algumas diferenças entre as sínteses aqui reportadas e aquelas publicadas são mostradas. Este trabalho também reporta brevemente o estudo topológico dessas redes bidimensionais. Todavia, foi obtida uma nova rede de coordenação ZnPDC1D, envolvendo a formação de laço (circuitos mais curtos de átomos), os quais se estendem unidimensionalmente, e envolvem os cátions Zn2+ e o ligante 2,5-pdc. Além disso, foi reportada uma série de novos complexos CuPDC0D, MnPDC0D, CuPDC0Dq e CuPDC0Dr, aniônicos, envolvendo apenas o ligante 2,5-pdc e os íons Cu2+ e Mn2+. Estes sistemas formam monômeros, MnPDC0D e CuPDC0Dr, ou dímeros oxo-metalatos, CuPDC0D e CuPDC0Dq, e contemplam cátions etilenodimina na rede cristalina, formando complexos metálicos (no caso do CuPDC0Dq. Finalmente, faz-se uma discussão sobre os ligantes nitrogenados 1,2-bis(2-piridil)etilenediamina 2-bpen e 1,2-bis(4-piridil)etilenediamina 4-bpen, que foram sintetizados, porém não foi observada a coordenação destes em nenhum dos sistemas aqui reportados. Tal fato foi atribuído à hidrólise dos ligantes nitrogenados (Bases de Schiff) e, portanto, foi proposto um mecanismo para essa hidrólise nos sistemas obtidos. A estrutura cristalina do ligante 2-bpen, ainda não reportada na literatura, foi discutida. / The aim of this work was the synthesis of MOFs with mixed ligands N- and O- donors from some metal cations of first series transition, as connectors of the net. In this work has been obtained coordination networks CoPDC2D and ZnPDC2D, that are iso-structures, which extend two-dimensionally forming loops with 16-shortest circuits, including the ligand 2,5-pyridinedicarboxylate 2,5-pdc and the Co2+ and Zn2+ cations, respectively. Both structures were recently published, however there some differences between the syntheses and the yield. Moreover, this work reports briefly the topological study of these two-dimensional networks. Additionally, were obtained a new coordination network ZnPDC1D, including loops formation, which extend one-dimensionally containing the cation Zn2+ and 2,5-pdc ligand. Here, were reported a series of new complexes CuPDC0D, MnPDC0D, CuPDC0Dq and CuPDC0Dr, anionic, including just the 2-5-pdc ligand and some this having Cu2+ e Mn2+ ions. This systems are monomers MnPDC0D and CuPDC0Dr or oxometalates dimmers CuPDC0D and CuPDC0Dq, including etilenodiamine on the crystalline network and, in some cases, participating on coordination CoPDC0Dq. Finally, are discussed about the nitrogenous ligands 1,2-bis(2-pyridil)etilenediamine 2-bpen and 1,2-bis(4-pyridil)etilenediamine 4-bpen, that were synthesized and characterized but not was observed the coordination in any system here reported. This has been attributed to the hydrolysis of nitrogenous ligands and, therefore, was proposed a mechanism for hydrolysis of these systems. The crystal structure of ligand 2-bpen, not yet reported in literature, was discussed.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22449号 / 工博第4710号 / 新制||工||1736(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 野田 進, 教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Die vorliegende Arbeit beschäftigt sich mit homogenkatalytisch gesteuerten Dehydrierungsreaktionen unter Verwendung von fluorierten und hochfluorierten Metallkomplexen. Reaktivitätsuntersuchungen wurden vorrangig in einem perfluorierten Lösungsmittel durchgeführt, in dem die hochfluorierten Komplexe besondere Löslichkeit aufwiesen. Ferner fand in überkritischem Kohlenstoffdioxid ebenfalls homogen katalysiert die Hydrierung eines Alkens mit hoher Umsatzzahl statt. Die Aktivierung der Katalysatorvorläufer erfolgte in allen Fällen photolytisch. Die Modifizierung bekannter Strukturmotive metallorganischer Komplexe wurde durch die Einfuhr unterschiedlich langer fluorierter Ketten der Art Rf = CH2CH2CnF2n+1 (2n+1 = 13, 17 bzw. 21 → Rf13, Rf17 bzw. Rf21) vorgenommen und somit die Fluorophilie beeinflusst. Es wurden Dicarbonylkomplexe der Art [M(pentahapto-C5H4Rf)(CO)2] (M = Rh, Ir) synthetisiert. Die Rhodiumverbindungen zeigten eine latente Instabilität und bildeten höhernukleare Zersetzungsprodukte. Unterschiedliche Substrate wie Methyliodid und primäre Silane konnten erfolgreich mit den mononuklearen Spezies umgesetzt und die Komplexe [Rh(pentahapto-C5H4Rf13)(COMe)(I)(CO)] und [Rh(pentahapto-C5H4Rf13)(H)(SiEt3)(CO)] isoliert sowie auf Reaktivität untersucht werden. Durch die Reaktion der Dicarbonylkomplexe mit ausgewählten Phosphanen waren Phosphan-basierte Spezies der Art [M(pentahapto-C5H4Rf)(CO)(PR3)] (M = Rh, Ir; R = Et, Ph, Rf13) zugänglich. Die Verbindungen mit Triethylphosphanliganden zeigten gute Löslichkeit in Perfluormethylcyclohexan und Reaktivität in der C‒H-Bindungsaktivierung unterschiedlicher Cycloalkane. Die höchste Reaktivität in einer Dehydrierung von Cyclooktan konnte unter Verwendung von [Rh(pentahapto-C5H4Rf21)(CO)(PRf13)3] beobachtet werden. Gelöst in überkritischem CO2 zeigte dieser Komplex ebenfalls katalytische Reaktivität bei der Hydrierung von 3,3-Dimethyl-1-buten. / This work involves studies with homogeneous catalytically dehydrogenation reactions in use of fluorinated and highly fluorinated metalorganic compounds. Reactivity test were primarily carried out in perfluorinated solvents in use of highly fluorinated complexes with particularly high solubility. Furthermore, the hydrogenation of an alkene was possible under homogeneous conditions in supercritical carbon dioxide with high turnover numbers. Activation of all catalytic precursors was made photolytic. Influence on fluorophilic characteristics of known metalorganic compound motivs was made by substitution of fluorinated sidechains such as Rf = CH2CH2CnF2n+1 (2n+1 = 13, 17 or 21 → Rf13, Rf17 or Rf21). Thus complexes with two carbonyl ligands were available in use of rhodium and iridium [M(pentahapto-C5H4Rf)(CO)2] (M = Rh, Ir). Compounds with rhodium center were potential instable and higher nuclear species are formed due to decomposition. Substrates like methyliodide and primary silanes have been successfully activated at the mononuclear species and the complexes [Rh(pentahapto-C5H4Rf13)-(COMe)(I)(CO)] und [Rh(pentahapto-C5H4Rf13)(H)(SiEt3)(CO)] have been isolated and examined for reactive properties. In the reaction of biscarbonylic compounds and samples of free phosphines complexes such as [M(pentahapto-C5H4Rf)(CO)(PR3)] (M = Rh, Ir; R = Et, Ph, Rf13) with different phosphine ligands were available. All compounds bearing the triethylphosphine ligand are showing good solubility in perfluor(methylcyclohexane) and also showing reactivity towards C‒H bonds at different cycloalkanes. Highest reactivity in dehydrogenation reactions were carried out with [Rh(pentahapto-C5H4Rf21)(CO)(PRf13)3] towards cyclooctane. Further, dissolved in supercritical carbon dioxide it shows catalytic reactivity in the hydrogenation of 3,3-dimethyl-1-butene.

Thin films and coatings of oxides are used in various fields of science and technology, such as semiconductor and optoelectronic devices, gas sensors, protective and wear resistant coatings etc. Of late, there has been a tremendous interest in pure and doped vanadium dioxide as thermoelectric switch material. VO2 has been doped with hetero-atoms such as W, Mo, Nb, Ti etc. and effects of doping have been correlated with feasibility of being used as a smart window material. The oxide Al2O3 has been studied as an alternative gate dielectric. Ga2O3 is also a contender for replacing SiO2 as a dielectric material. Atomic layer deposition (ALD) is a technique for the deposition of thin films of various materials and is found to be of considerable scientific and technological importance. In particular, using β-diketonate complexes as precursors is very useful in preparing thin films of oxides, as these precursors already contain a metal-oxygen bond. In this thesis, β-diketonate complexes have been used as precursors for deposition of thin films. The thesis has been divided into two parts: First part deals with deposition and characterization of thin films of VO2 on glass and fused quartz. The second part deals with synthesis and chemical and thermal characterization of bimetallic Al-Ga acetylacetonates along with thin film deposition using the same. Chapter 1 presents a brief introduction to application of thin films of oxides in various fields of science and technology. A brief introduction to the ALD reactor used for the current work is also presented. The importance of thermal analysis of precursors for CVD is briefly reviewed. Chapter 2 deals with the instruments and methods used for the work done for this thesis. In Chapters 3 and 4 of the thesis, a detailed study of deposition of VO2 films on glass and fused quartz has been presented. The films deposited have been analyzed using a host of techniques, for their texture, microstructure and electrical properties. In spite of chemical similarities, considerable differences in structure and properties have been observed between the films deposited on the two substrates. These differences have been explained on the basis of the small chemical differences between the two substrates. Chapters 5, 6 and 7 deal with synthesis, thermal characterization and use of bimetallic Al-Ga precursors, respectively. The bimetallic acetylacetonates have been synthesized using ‘homogenization in solution’ approach. Chemical characterization of the precursors revealed that nominal percentages of Al and Ga are retained in the solid precursors. Single crystal structure confirmed the observation. Thermal analysis of the precursors showed that the precursors, which are solid solutions of Al and Ga acetylacetonates, show negative deviation from the Raoult’s Law. Films were deposited using these precursors and were found to near completely retain the composition of the precursors. Chapter 8 of the thesis presents the conclusions of the current work and proposes future directions.

The material and device characteristics of InGaN/GaN heterojunction bipolar transistors (HBTs) grown by metalorganic chemical vapor deposition are examined. Two structures grown on sapphire with different p-InxGa1-xN base-region compositions, xIn = 0.03 and 0.05, are presented in a comparative study. In a second experiment, NpN-GaN/InGaN/GaN HBTs are grown and fabricated on free-standing GaN (FS-GaN) and sapphire substrates to investigate the effect of dislocations on III-nitride HBT epitaxial structures. The performance characteristics of HBTs on FS-GaN with a 20×20 m2 emitter area exhibit a maximum collector-current density of ~12.3 kA/cm2, a D.C. current gain of ~90, and a maximum differential gain of ~120 without surface passivation. For the development of deep-ultraviolet optoelectronics, several various structures of optically-pumped lasers at 257, 246, and 243 nm are demonstrated on (0001) AlN substrates. The threshold-power density at room temperature was reduced to as low as 297 kW/cm2. The dominating polarization was measured to be transverse electric in all cases. InAlN material was developed to provide lattice matched, high-bandgap energy cladding layers for a III-N UV laser structure. This would alleviate strain and dislocation formation in the structure, and also mitigate the polarization charge. However, a gallium auto-doping mechanism was encountered which prevents the growth of pure ternary InAlN, resulting instead in quaternary InAlGaN. This phenomenon is quantitatively examined and its source is explored.