La société ESSILOR est à l’origine d’un nouveau concept ophtalmique : « l’optique digitale ». Ce concept s’appuie sur la discrétisation du verre en pixels et l’introduction, dans ces structures micrométriques, de liquides fonctionnels. Les axes de recherche de cette thèse sont issus des besoins et contraintes de cette thématique et ils concernent principalement : l’élaboration de couches minces polymères par un procédé CVD (Chemical Vapor Deposition) et les dépôts de films sur des substrats liquides. Un bâti commercial de CVD avec un mode d’activation thermique a permis la réalisation contrôlée et la caractérisation de couches minces conformes d’un matériau polymère aux propriétés en adéquation avec le cahier des charges industriel : le parylène. Des études sur le mécanisme mis en jeu ont révélé un mode de croissance original de ce matériau et pouvant être décrit par différents modèles complémentaires dans les informations qu’ils apportent. Nous avons également imaginé un dispositif de modulation des propriétés surfaciques des films de parylène par une fonctionnalisation en voie sèche. Le second procédé CVD qui a été étudié met en œuvre l’activation photonique. Il s’agit d’un bâti de photo-CVD innovant et très modulable, développé au CIRIMAT, pour répondre au mieux aux besoins de ce projet « verre digital » et en particulier à la nécessité de déposer des couches de divers polymères sur des liquides fonctionnels à une pression se rapprochant de la pression atmosphérique. / ESSILOR society is investigating a new ophthalmologic concept: “the digital optic”. This concept is based on the discretization of the ocular glass in pixels, and the insertion, in those micrometric structures, of functional liquids. The research work of this PhD thesis aims to satisfy the requirements and constraints of this topic. They principally concerns: the elaboration of thin polymeric films by a CVD (Chemical Vapor Deposition) process and the deposition on liquid substrates. A commercial CVD reactor thermally activated has permitted the controlled production and the characterization of conform polymeric thin films whose properties are in good adequacy with the industrial specifications: the parylene. Studies on the mechanism have revealed an original growth mechanism of this material which can be described with some complementary and informative models. We also have developed a functionalization method by a dry process to modulate the surface properties of parylene films. The second CVD process studied uses a photonic activation. It is an innovative and very flexible photo-CVD process designed in the CIRIMAT in order to satisfy the “digital glass” project and in particular the necessity to deposit various polymer films on functional liquids at a pressure near the atmospheric pressure.

The method of coating near-ultraviolet light with phosphor powders is one of the main trends in the current development of white light-emitting diodes (LEDs). It a long time for the development of Ce3+ doped phosphor materials. The Ce3+ has one outer 4f1 electron. And this electron can be excited to 5d. The luminescence wavelength of Ce3+ doped phosphor materials different from the different host lattice. First part of this paper is about the growth of cerium doped LiGaO2 crystal by conventional Czochralski melt pulling method. The dose of cerium is 0.2ppm. The growth were operated in the ambient pressure, with the pull rate of 2.0 mm/hour and the rotation rate of 10~20 RPM. LiGaO2 crystal of 200 mm in length was grown under these conditions. We found a yellow to green peak on 505 nm from the measurement of photoluminescence spectra. It showed that LiGaO2 can emit phosphorescence by the doped of cerium. Second part of this paper is growth of Gallium nitride (GaN) thin films. GaN possess vast application potential in the fields of optoelectronics and microelectronics for its wide band gap, high thermal stability and high chemistry stability. GaN mostly grow on large lattice mismatch substrates, for the difficulty growth of GaN bulk single crystal and scarce of lattice match heteroepitaxial substrates. This result in great dislocation defects density in the GaN films. To lower the dislocation density of GaN films and improve the crystal quality is an important point of GaN research fields. In this study, the GaN thin films were grown on £^-LiAlO2(100) substrates by Chemical Vapor Deposition(CVD). We found that the growth direction and structure of GaN were influenced by growth parameter. The GaN¡]10-10¡^ thin films were grown by the adjust of growth temperature and pressure.

This thesis aims to develop a chemical vapor deposition (CVD) process for the new directions in both silicon carbon (SiC) and gallium nitride (GaN) epitaxial growth. The properties of the grown epitaxial layers are investigated in detail in order to have a deep understanding. SiC is a promising wide band gap semiconductor material which could be utilized for fabricating high-power and high-frequency devices. 3C-SiC is the only polytype with a cubic structure and has superior physical properties over other common SiC polytypes, such as high hole/electron mobility and low interface trap density with oxide. Due to lack of commercial native substrates, 3C-SiC is mainly grown on the cheap silicon (Si) substrates. However, there’s a large mismatch in both lattice constants and thermal expansion coefficients leading to a high density of defects in the epitaxial layers. In paper 1, the new CVD solution for growing high quality double-position-boundaries free 3C-SiC using on-axis 4H-SiC substrates is presented. Reproducible growth parameters, including temperature, C/Si ratio, ramp-up condition, Si/H2 ratio, N2 addition and pressure, are covered in this study. GaN is another attractive wide band gap semiconductor for power devices and optoelectronic applications. In the GaN-based transistors, carbon is often exploited to dope the buffer layer to be semi-insulating in order to isolate the device active region from the substrate. The conventional way is to use the carbon atoms on the gallium precursor and control the incorporation by tuning the process parameters, e.g. temperature, pressure. However, there’s a risk of obtaining bad morphology and thickness uniformity if the CVD process is not operated in an optimal condition. In addition, carbon source from the graphite insulation and improper coated graphite susceptor may also contribute to the doping in a CVD reactor, which is very difficult to be controlled in a reproducible way. Therefore, in paper 2, intentional carbon doping of (0001) GaN using six hydrocarbon precursors, i.e. methane (CH4), ethylene (C2H4), acetylene (C2H2), propane (C3H8), iso-butane (i-C4H10) and trimethylamine (N(CH3)3), have been explored. In paper 3, propane is chosen for carbon doping when growing the high electron mobility transistor (HEMT) structure on a quarter of 3-inch 4H-SiC wafer. The quality of epitaxial layer and fabricated devices is evaluated. In paper 4, the behaviour of carbon doping using carbon atoms from the gallium precursor, trimethylgallium (Ga(CH3)3), is explained by thermochemical and quantum chemical modelling and compared with the experimental results. GaN is commonly grown on foreign substrates, such as sapphire (Al2O3), Si and SiC, resulting in high stress and high threading dislocation densities. Hence, bulk GaN substrates are preferred for epitaxy. In paper 5, the morphological, structural and luminescence properties of GaN epitaxial layers grown on N-face free-standing GaN substrates are studied since the N-face GaN has advantageous characteristics compared to the Ga-face GaN. In paper 6, time-resolved photoluminescence (TRPL) technique is used to study the properties of AlGaN/GaN epitaxial layers grown on both Ga-face and N-face free-standing GaN substrates. A PL line located at ~3.41 eV is only emerged on the sample grown on the Ga-face substrate, which is suggested to associate with two-dimensional electron gas (2DEG) emission.

Zinc oxide (ZnO) has gained many interests in the research of wide band-gap semiconductor materials nowadays. ZnO has attracted much attention because of its high excition bound energy (60meV), and it¡¦s promising to gain application in the field of optoelectronic such as ultraviolet light emitting devices (UV-LED) and laser diode (LD) etc. This study aims to investigate the growth condition of ZnO and to control the growth direction. ZnO was grown on LiAlO2 (LAO) (100) substrates by chemical vapor deposition (CVD) with zinc source Zn(C5H7O2)2. The different reacting temperature from 500¢J to 650¢J and the flow rate of oxygen were studied. In the result of scanning electron microscope (SEM), the surface morphology of ZnO showed two different structures, hexagonal structure and non-hexagonal film structure. And the side view of hexagonal structure showed double layers. The key factor for the transformation of double layers from film to column structure is the equilibrium of growth temperature and substrate stress. The crystals structures and epitaxial relationship were studied by X-ray Diffraction Pattern (XRD), Electron Backscattering Diffraction (EBSD). There are two kinds of ZnO epitaxial growth on LiAlO2 (100) substrate, one is c-plane of ZnO(0001)// LiAlO2 (100) and another one is m-plane of ZnO(10 0)// LiAlO2 (100), the latter one has a smaller lattice mismatch. The results of the strong UV and green emission peaking were shown in photoluminescence (PL) spectrum. Under the control of substrate temperature, c-plane polarized ZnO films were grown at 500 ¢J, and m-plane nonpolar ZnO films were grown at 650¢J. Rectangular structure could be formed between 550¢J and 650¢J. With the increase of substrate temperature, the size of rectangular became larger. At last, uniformed film would be formed at 650¢J. In addition to benefit the formation of m-plane structure, high temperature helps the sideward growth to form uniform film. In the experiment of oxygen flow, we found that c-plane hexagonal structure appeared on the m-plane film while the oxygen flow lowered to 50 sccm. And there were large numbers of oxygen vacancies measured by PL. The oxygen flow of 100 sccm is more suitable to obtain higher quality m-plane film than 400 and 50 sccm. At last, the growth time experiments were done under the growth temperament of 600¢J.Island structures of c-plane and m-plane ZnO combined with the growth time increased, and the island become larger. The XRD measurement showed that crystallinity of ZnO become better with the growth time increased.

One-dimension (1D) nanostructures such as wires, rods, belts and tubes have become the focus of intensive researches for investigating structure-property relationships and related scientific and technological applications. Few-walled carbon nanotubes (FWNTs), a special type of small diameter multi-walled carbon nanotubes with superb structural perfection, are first discovered in our laboratory and systemically studied in this dissertation, including the synthesis by chemical vapor deposition (CVD) method, the purification and their applications. Moreover, iron phosphide nanorods/nanowires with controlled structures have been synthesized in solution phase and their magnetic properties have been investigated. The first parts of this dissertation are mainly focused on the studies of FWNTs synthesized by CVD method using binary catalyst Co (or Fe) with Mo (or W) supported on MgO made by modified combustion method. The structures of as-grown FWNTs can be controlled by three basic growth parameters: temperature, catalyst composition and carbon feeding rate. It is found that the as-grown FWNT materials prepared from W-containing catalysts are much more easily purified than those from Mo-containing catalysts. Both raw and purified FWNTs show enhanced electron field emission characteristics compared to other current commercial nanotubes. The highly pure FWNTs are then used to prepare composite materials with polymers and noble metal nanocrystals. Furthermore, the structures of FWNTs are attempted to be controlled by adjusting the growth parameters of carbon monoxide CVD. Highly pure DWNTs (over 95%) are obtained and well characterized by TEM, Raman and fluorescence spectrum. The optical properties of DWNTs and their application in bio-imaging are primarily investigated. In addition, conducing films are fabricated using highly pure FWNTs and the relationship between the structure and the conductivity is surveyed and further possible improvements are discussed. The second parts of this dissertation describe a solution-phase route for the preparation of single-crystalline iron phosphide nanorods and nanowires. The mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP) which are commonly used as the solvents for semiconductor nanocrystal synthesis is not entirely inert. TOP serves as phosphor source and reacts with Fe precursors to generate iron phosphide nanostructures with large aspect ratios. In addition, the morphology of the produced iron phosphide structures can be controlled by the ratio of TOPO/TOP. A possible growth mechanism is discussed. / Dissertation

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The study aims at growing nonpolar GaN film on LiGaO2 substrate by chemical vapor deposition (CVD). Metallic gallium and NH3 are the sources of Ga and N. There are two sets of experiment: add NH3 when raising the temperature, and set different reacting pressure at each experiment; add N2 when raising the temperature, and set different reacting temperature at each experiment, while reach the reacting temperature add NH3. Analyze the reacted samples with X-ray diffraction, scanning electron microscope, electron back-scattered diffraction, atomic force microscope and transmission electron microscopy to know the growing direction, morphology, roughness, optical property, and the microstructure of GaN growing situation. Under the experimental conditions, add NH3 when raising the temperature and set the reacting pressure in the range of 50 torr ~ 400 torr at 950¢XC with NH3 flow rate 450sccm for 60 minutes, m-plane GaN can be obtained; setting different reacting temperature(900¢XC ~ 1000¢XC) at 50 torr with N2/NH3 flow rate 450/30sccm for 60 minutes can also get m-plane GaN. Besides, the thin film of pure m-plane GaN can be obtained when setting the reacting temperature at 1000¢XC, but the film peels off seriously. After reacting under the conditions of the first set experiments, the inside LGO substrate become damaged, pores can be observed easily; and the circumstances of LGO is better in second set experiment.

In this thesis, we investigated the growth of nonpolar (11-20) GaN films on LiGaO2 substrate by a simple chemical vapor deposition (CVD) process. Metallic gallium, NH3 and ultra-purity nitrogen were used as Ga, N sources and carrier gas. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to study the influence of growth conditions such as reaction pressure, growth temperature and deposition time on the GaN epilayer¡¦s orientation and surface morphology. It¡¦s found that GaN epilayers have different surface morphology grown on LiGaO2 substrates by the change of growth pressures (50 torr ~ 400 torr) under temperature of 950 ¢XC, NH3 gas flow of 450 sccm and the growth time of 60 minutes, and uniform a-plane GaN epilayers are found with growth pressures 50, 200 and 300 torr. In addition, we obtain uniform a-plane GaN epilayers with different surface morphology by the change of growth temperatures (900 ¢XC ~ 975 ¢XC) under pressure of 50 torr, N2/NH3 gas flow of 450/30 sccm and the growth time of 60 minutes. Furthermore, we obtain flatter a-plane GaN epilayer by a longer growth time (120 mins) under temperature of 950 ¢XC, pressure of 50 torr and N2/NH3 gas flow of 450/30 sccm. The orientation relationship between GaN and LiGaO2 was determined as (11-20)GaN // (010)LiGaO2 and (1-100)GaN // (100)LiGaO2 by TEM analysis.

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