This work investigates the use of the novel electric field assisted chemical vapour deposition (EACVD) process in the production of titanium dioxide thin films for photocatalytic applications on glass substrate. This work looks into the interaction of applied electric fields with the precursor species during the aerosol assisted chemical vapour deposition (AACVD) and atmospheric pressure chemical vapour deposition (APCVD) reaction of Titanium isopropoxide (TTIP) and Titanium (IV) Chloride (TiCl4) with different solvents. The electric field was generated by applying a potential difference between two fluorine-doped tin oxide glass sheets. The electric field was varied between 0 – 3000 Vm-1. The deposited films were analysed and characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, UV-vis spectroscopy, water-contact angles and resazurin photcatalytic testing. It was observed that the application of electric fields produced changes in the morphology, particle size, growth rate, crystal orientation and crystal phases. Generally, films produced under the influence of the electric fields showed higher photo-activity than films produced in absence of electric fields. The deposited films produced from the electric field assisted aerosol chemical vapour deposition (EAACVD) showed higher photo-activity with applied AC electric fields than with applied DC electric fields. Likewise, they showed higher photo-activity than the deposited films produced from the electric field assisted atmospheric pressure chemical vapour deposition (EAAPCVD) with applied AC electric fields. The results obtained were explained by the interaction mechanisms between the electric fields and the precursor species, which differ depending on the CVD technique used. Although titanium dioxide photo-activity is comprised by a combination of factors, it was observed that an optimum can be obtained by varying both experimental conditions and field strength. In particular, optimum results were obtained for deposited films which showed long-shaped particles, reduced particle size and high preferential orientation in the anatase (004) plane. Electric field assisted chemical vapour deposition (EACVD) shows a great potential for the improvement of commercial products available in the market such as self-cleaning and antibacterial surfaces.

The work in this thesis examines the effects of the application of oxide coatings on the performance of the single crystalline silicon photovoltaic solar cells. A variety of potential oxide materials for solar cells performance enhancement are investigated. These films are silicon oxide, titanium oxide and rare earth ion-doped gadolinium oxysulfide phosphor. This study compares the electrical characteristics, optical properties and surface chemical composition of mono-crystalline silicon cells before and after coating. The first study investigates the potential for using single and double layers of silicon oxide films produced by low-temperature Plasma Enhanced Chemical Vapour Deposition (PECVD) using tetramethylsilane as a silicon precursor and potassium permanganate oxidising agent for efficiency enhancement of solar cells at low manufacturing cost. Deposition of the films contributes to the increase of the conversion energy of the solar cells on one hand while the variety of colours obtained in this study can be of great importance for building-integrated photovoltaic application on the other hand. The obtained results demonstrated a relative enhancement of 3% in the conversion efficiency of the crystalline silicon solar cell. In the second study, the effects of using a single layer of titanium oxide and a stack of silicon oxide and titanium oxide on the performance of solar cell are demonstrated. Moreover, this study shows the use of different sputtering configurations and oxidation methods. The experimental results showed a relative enhancement of 1.6% for solar cells coated with a stack of silicon oxide/titanium oxide. In the third study, silicon cells were coated with a luminescent layer consisting of down-converting phosphor, gadolinium oxysulfide doped with erbium and terbium, and a polymeric binder of EVA using doctor-blade screen printing technique. A relative enhancement of 4.45% in the energy conversion efficiency of PV solar cell was achieved. Also, the effects of combining silicon oxide layers together with the luminescent composite are also presented in this study.

The work carried out as a part of this thesis has been focussed on understanding different aspects of the chemical vapor deposition process namely, ALD / MOCVD. A large part of the thesis is aimed at solving the problem of a single-source precursor for the MOCVD process to obtain substituted metal oxide thin films. For a chemical vapor deposition technique, it is important to understand the requisite salient features of precursor for deposition of thin films. For this purpose, not only is the structural characterization of the chemical precursor is required but also an in-depth thermal analysis of the precursor to know its vapor pressure. Vapor pressure of a metalorganic complex is one of the important properties to evaluate the applicability of a metalorganic complex as a MOCV/ALD precursor. The thesis discusses a novel approach to use thermal analysis as a tool to gauge the viability of substituted metal “single source” precursor for MOCVD/ALD. The other half deals with material characterization of thin films grown by an ALD process using hydrogen and Ti(OiPr)2(tbob)2 as precursors. The films were further studied for their potential application as high-k dielectric in DRAM applications. The first chapter is an overview of topics that are relevant to the work carried out in this thesis. The chapter focuses on the description of techniques used for thin film deposition. A detailed review of CVD-type techniques (ALD/ MOCVD) is then given. Chapter1 reviews the various process parameters involved in ALD,i.e. film growth(specifically as a function of the reactant pulse length, the nature of the chemical reactant/precursor and that of the metal precursor, and purge length) and growth temperature. Following the discussion of ALD, CVD and its growth kinetics are also discussed. Chapter 1 then outlines a holistic understanding of precursors, followed the differences in requirement for using them in ALD and MOCVD. Further, an introduction to the titanium oxide (Stoichiometric titanium dioxide and various Magneli phases) system, its phase diagram, oxide properties and their applications is given. Chapter 1 concludes by delineating the scope of the work carried out which is presented in the thesis. The second chapter deals with the synthesis of a series of substituted metal “single source” precursors to be used for MOCVD of substituted metal oxides thin films. The precursor complexes were of the type AlxCr1-x (acac)3 where 0<x<1. The complexes were synthesized using the novel approach of co-synthesis and were characterized by various spectroscopic techniques. Single crystal X-ray diffraction at low temperature was carried out to understand the substitution of metal in the complex crystallographically. The substituted metal complexes synthesized and characterized in chapter 2 were further evaluated for their viability as single source precursors for MOCVD application, using thermo-gravimetry as discussed in chapter 3. Vapor pressure of these complexes was determined by using the Langmuir equation, while the enthalpies of submission and evaporation were calculated using the Clausius-Clapeyron equation. One of the composition of the series of substituted metal complexes, viz., Al0.9Cr0.1(acac)3, was employed on MOCVD reactor as precursor to obtain thin films on three substrates, Si(100), fused silica, and polycrystalline x- alumina, simultaneously. The resultant thin films were characterized using XRD, electron microscopy, FTIR, EDS, X-ray mapping, and UV-vis spectroscopy. Chapter 4 deals with the growth of titanium oxide thin films using ALD. The metal precursor used was Ti(OiPr)2(tbob)2 and the reactant gas was hydrogen. Hydrogen, a reducing gas, was deliberately used to obtain the reduced defect oxide phases of titanium, commonly called Magneli phases. The growth rate of films grown on p-Si(100) was studied with respect to the substrate temperature, vaporizer temperature, pulse duration of metal precursor and pulse duration of the reactive gas. Also, the concept of complementarity of a reaction and self-limiting behavior in a true ALD process was illustrated. The deposition conditions such as substrate temperature and reactive gas flows have been varied to optimize the phase content and the morphology of the films. The films grown were characterized to determine the various phases of titanium oxide present using XRD, TEM, FTIR spectroscopy, Raman spectroscopy, and UV-vis spectroscopy. The presence of carbon was revealed by Raman spectroscopy. By using these characterization techniques, it was concluded that the film grown is a composite made of stiochiometric TiOx matrix embedded with crystallites of (reduced) Magneli phases. Chapter 5 deals with the electrical properties of the composite thin films grown in chapter 4. the films behave as percolative capacitor which could be used for application as novel high-k dielectric material for DRAM. The effect of change in flow rates of reactive gas (H2) on the dielectric constant (k) and leakage current of the film were studied. It was found that phase composition of the film plays an important role in tuning the dielectric properties of the film was also studied. The effect of thickness of the film also studied on the dielectric properties of the film. The trend observed was correlated to the morphology of the film as a function of its thickness and the grain growth mechanism as observed from high resolution scanning electron microscopy. Further, the effect of change in substrate temperature, metal precursor pulse length, and of the metal used as top electrode, on C-V and I-V characteristics were studied. It was interesting to see that the presence of the more conductingTi5O9 (than Ti3O5) enhances the dielectric constant, which is a requisite for a high-k material for DRAM application. On the other hand, the presence of Ti5O9 also increased the leakage current in the film, which was not desirable. It therefore suggested itself that an optimum embedment of Ti5O9 in the composite helps in enhancing the dielectric constant, while maintaining a low leakage current. Under optimum conditions, a dielectric constant of 210 at 1MHz was measured with a leakage current of 17 nA. The effect of the presence of carbon in the film was studied using Raman Spectroscopy, and it was found that a high leakage was associated with films having greater carbon content. In this chapter, electrical properties of composite thin films were also compared with those of stoichiometric titanium dioxide (a known dielectric). Further, a multilayer sandwich structure was proposed, such that it had a 53 mm thick stoichiometric TiO2 layer followed by 336nm thick composite film and again a 53nm thick stoichiometric titanium dioxide layer. The dielectric characteristics of this structure were found to be better than those of either of the other two.viz., stoichiometric titanium dioxide film or the composite thin film of titanium oxide.

This thesis describes the deposition of thin films of titanium oxide and Magnéli phases of titanium oxide by atomic layer deposition (ALD) using a novel β-ketoesterate precursor. Titanium oxide is a promising candidate for the high-k dielectric gate oxide layer for CMOS devices in microelectronic circuits. The Magnéli phases of titanium oxide are difficult to grow and stabilize, especially in the thin film form, and have useful properties. The thin film deposition of oxides by CVD/ALD requires suitable precursors, which are often metalorganic complexes. The estimation of vapour pressure using thermogravimetry is described, and employed, using an approach based on the Langmuir equation. This data is important for the evaluation of the suitability of these complexes as CVD precursors. The first chapter gives a brief introduction to the topics that will be discussed in this thesis. Part one of the thesis deals with the synthesis, characterization, and studies of the vapour pressure and partial pressures of the precursors for CVD. This part comprises of the second, third and fourth chapter. The second chapter deals with the synthesis and characterization of the various metalorganic complexes that have been synthesized and characterized to evaluate their suitability as precursors for CVD. The third chapter describes the derivation of vapour pressure of precursors for CVD and ALD, from rising temperature thermogravimetric analysis (TGA) data, using the Langmuir equation. The fourth chapter deals with the determination of partial pressure of CVD precursors using data from low-pressure thermogravimetry. Part Two of the thesis reports the deposition of titanium oxide thin films by ALD, and the detailed investigation of their properties, for application as high-k dielectric materials. Chapters five, six and seven constitute this part. The fifth chapter deals with the deposition of titanium oxide thin films by ALD. Chapter six describes the electrical characterization of the thin films of titanium oxide, for applications as high-k dielectric gate oxide layers for CMOS circuits. In the seventh chapter, the deposition of Magnéli phases of titanium by ALD is described. The dielectric properties of the films are studied.