Showing papers on "Thin film published in 2001"

Method of forming crystalline semiconductor thin film on base substrate, lamination formed with crystalline semiconductor thin film and color filter

Abstract: A method of forming a crystalline semiconductor thin film on a base material which can be prepared at a low temperature by simple step and device, the method including a processing step of applying UV-rays to an amorphous semiconductor thin film provided on a base material while keeping a temperature at not less than 25° C. and not more than 300° C. in a vacuum or a reducing gas atmosphere, as well as a substrate having the semiconductor thin film provided on the base material, a substrate for forming a color filter and a color filter using the substrate.

The Science and Engineering of Microelectronic Fabrication

Abstract: PART I: OVERVIEW AND MATERIALS 1. An Introduction to Microelectronic Fabrication 1.1 Microelectronic Technologies -- A Simple Example 1.2 Unit Processes and Technologies 1.3 A Roadmap for the Course 1.4 Summary 2. Semiconductor Substrates 2.1 Phase Diagrams and Solid Solubility 2.2 Crystallography and Crystal Structure 2.3 Crystal Defects 2.4 Czochralski Growth 2.5 Bridgman Growth of GaAs 2.6 Float Zone Growth 2.7 Water Preparation and Specifications 2.8 Summary and Future Trends Problems References PART II: UNIT PROCESSING I: HOT PROCESSING AND ION IMPLANTATION 3. Diffusion 3.1 Fick's Diffusion Equation in One Dimension 3.2 Atomistic Models of Diffusion 3.3 Analytic Solutions of Fick's Law 3.4 Corrections to Simple Theory 3.5 Diffusion Coefficients for Common Dopants 3.6 Analysis of Diffused Profiles 3.7 Diffusion in SiO2 3.8 Diffusion Systems 3.9 SUPREM Simulations of Diffusion Profiles 3.10 Summary Problems References 4. Thermal Oxidation 4.1 The Deal-Grove Model of Oxidation 4.2 The Linear and Parabolic Rate Coeffients 4.3 The Initial Oxidation Regime 4.4 The Structure of SiO2 4.5 Oxide Characterization 4.6 The Effects of Dopants During Oxidation and Polysilicon Oxidation 4.7 Oxidation Induced Stacking Faults 4.8 Alternative Gate Insulations 4.9 Oxidation Sytems 4.10 SUPREM Oxidations 4.11 Summary Problems References 5. Ion Implantation 5.1 Idealized Ion Implantation Systems 5.2 Coulomb Scattering 5.3 Vertical Projected Range 5.4 Channeling and Lateral Projected Range 5.5 Implantation Damage 5.6 Shallow Junction Formation 5.7 Buried Dielectrics 5.8 Ion Implantation Systems -- Problems and Concerns 5.9 Implanted Profiles Using SUPREM+ 5.10 Summary Problems References 6. Rapid Thermal Processing 6.1 Gray Body Radiation, Heat Exchange, and Optical Absorption 6.2 High Density Optical Sources and Chamber Design 6.3 Temperature Measurement 6.4 Temperature Measurement 6.4 Thermoplastic Stress 6.5 Rapid Thermal Activation of Impurities 6.6 Rapid Thermal Processing of Dielectrics 6.7 Silicidation and Contact Formation 6.8 Alternative Rapid Thermal Processing Systems 6.9 Summary Problems References PART III: UNIT PROCESSES 2: PATTERN TRANSFER 7. Optical Lithography 7.1 Lithography Overview 7.2 Diffraction 7.3 The Modulation Transfer Function and Optical Exposures 7.4 Source Systems and Spatial Coherence 7.5 Contact/Proximity Printers 7.6 Projection Printers 7.7 Advanced Mask Concepts 7.8 Surface Reflections and Standing Waves 7.9 Alignment 7.10 Summary Problems References 8. Photoresists 8.1 Photoresist Types 8.2 Organic Materials and Polymers 8.3 Typical Reactions of DQN Positive Photoresist 8.4 Contrast Curves 8.5 The Critical Modulation Transfer Function 8.6 Applying and Developing Photoresist 8.7 Second Order Exposure Effects 8.8 Advanced Photoresists and Photoresist Processes 8.9 Summary Problems References 9. Nonoptical Lithographic Techniques 9.1 Interactions of High Energy Beams with Matter 9.2 Direct Write Electron Beam Lithography Systems 9.3 Direct Write Electron Beam Lithography Summary and Outlook 9.4 X-Ray Sources 9.5 Proximity X-Ray Exposure Systems 9.6 Membrane Masks 9.7 Projection X-Ray Lithography 9.8 Projection Electron Beam Lithography (SCALPEL) 9.9 E-bean and X-Ray Resists 9.10 Radiation Damage in MOS Devices 9.11 Summary Problems References PART IV: UNIT PROCESSES 3: THIN FILMS 10. Vacuum Science and Plasmas 10.1 The Kinetic Theory of Gasses 10.2 Gas Flow and Conductance 10.3 Pressure Ranges and Vacuum Pumps 10.4 Vacuum Seals and Pressure Measurement 10.5 The DC Glow Discharge 10.6 RF Discharges 10.7 High Density Plasmas 10.8 Summary Problems References 11. Etching 11.1 Wet Etching 11.2 Chemical Mechanical Publishing 11.3 Basic Regimes of Plasma Etching 11.4 High Pressure Plasma Etching 11.5 Ion Milling 11.6 Reactive Ion Etching 11.7 Damage in Reative Ion Etching 11.8 High Density Plasma (HDP) Etching 11.9 Liftoff 11.10 Summary Problems References 12. Physical Deposition: Evaporation and Sputtering 12.1 Phase Diagrams: Sublimation and Evaporation 12.2 Deposition Rates 12.3 Step Coverage 12.4 Evaporator Systems: Crucible Heating Techniques 12.5 Multicomponent Films 12.6 An Introduction to Sputtering 12.7 Physics of Sputtering 12.8 Deposition Rate: Sputter Yield 12.9 High Density Plasma Sputtering 12.10 Morphology and Step Coverage 12.11 Sputtering Methods 12.12 Sputtering of Specific Materials 12.13 Stress in Deposited Layers 12.14 Summary Problems References 13. Chemcial Vapor Deposition 13.1 A Simple CVD System for the Deposition of Silicon 13.2 Chemical Equilibrium and the Law of Mass Action 13.3 Gas Flow and Boundary Layers 13.4 Evaluation of the Simple CVD System 13.5 Atmospheric CVD of Dielectrics 13.6 Low Pressure CVD of Dielectrics and Semiconductors in Hot Wall Systems 13.7 Plasma Enhanced CVD of Dielectrics 13.8 Metal CVD + 13.9 Summary Problems References 14. Exiptaxial Growth 14.1 Water Cleaning and Native Oxide Removal 14.2 The Thermodynamics of Vapor Phase Growth 14.3 Surface Reactions 14.4 Dopant Incorporation 14.5 Defects in Epitaxial Growth 14.6 Slective Growth 14.7 Halide Transport GaAs Vapor Phase Epitaxy 14.8 Incommensurate and Strained Layer Heterooepitaxy 14.9 Metal Organic Chemical Vapor Deposition (MOCVD) 14.10 Advanced Silicon Vapor Phase Epitaxial Growth Techniques 14.11 Molecular Beam Epitaxy Technology 14.12 BCF Theory 14.13 Gas Source MBE and Chemical Beam Epitaxy 14.14 Summary Problems References PART V: PROCESS INTEGRATION 15. Device Isolation, Contacts, and Metallization 15.1 Junction and Oxide Isolation 15.2 LOCOAS Methods 15.3 Trench Isolation 15.4 Silicon on Insulator Isolation Techniques 15.5 Semi-insulating Substrates 15.6 Schottky Contacts 15.7 Implanted Ohmic Contacts 15.8 Alloyed Contacts 15.9 Multilevel Metallization 15.10 Planarization and Advanced Interconnect 15.11 Summary Problems References 16. CMOS Techniques 16.1 Basic Long Channel Device Behavior 16.2 Early MOS Technologies 16.3 The Basic 3 um Technology 16.4 Device Scaling 16.5 Hot Carrier Effects and Drain Engineering 16.6 Processing for Robust Oxides 16.7 Latchup 16.8 Shallow Source/Drains and Tailored Channel Doping 16.9 Summary Problems References 17. GaAs Technologies 17.1 Basic MESFET Operation 17.2 Basic MESFET Technology 17.3 Digital Technologies 17.4 MMC Technologies 17.5 MODFETs 17.6 Optoelectronic Devices 17.7 Summary Problems References 18. Silicon Bipolar Techniques 18.1 Review of Bipolar Devices -- Ideal and Quasi-ideal Behavior 18.2 Second Order Effects 18.3 Performance of BJTs 18.4 Early Bipolar Processes 18.5 Advaned Bipolar Processes 18.6 Hot Electron Effects in Bipolar Transitions 18.7 BiCMOS 18.8 Analog Bipolar Technolgies 18.9 Summary Problems References 19. MEMS (co-authored with G. Cibuzar, University of Minnesota) 19.1 Fundamentals of Mechanics 19.2 Stress in Thin Films 19.3 Mechanical to Electrical Transduction 19.4 Mechanics of Common MEMS Devices 19.5 Bulk Micromachining Etching Techniques 19.6 Bulk Micromachining Process Flow 19.7 Surface Micromachining Basics 19.8 Surface Micromachining Process Flow 19.9 MEMS Actuators 19.10 High Aspect Ratio Microsystems Technology (HARMST) 19.11 Summary Problems References 20. Integrated Circuit Manufacturing 20.1 Yield Prediction and Yield Tracking 20.2 Particle Control 20.3 Statistical Process Control 20.4 Full Factorial Experiments and ANOVA 20.5 Design of Experiments 20.6 Computer Integrated Manufacturing 20.7 Summary Problems References APPENDICES I. Acronyms and Common Symbols II. Properties of Selected Semiconductor Materials III. Physical Constants IV. Conversion Factors V. The Complimentary Error Function VI. F Values VII. SUPREM Commands Index

Resistivity of polycrystalline zinc oxide films: current status and physical limit

Abstract: Heavily doped zinc oxide films are used as transparent and conductive electrodes, especially in thin film solar cells. Despite decades of research on zinc oxide it is not yet clear what the lower limit of the resistivity of such films is. Therefore, the electrical parameters of zinc oxide films deposited by magnetron sputtering, metal organic chemical vapour deposition and pulsed laser ablation are reviewed and related to the deposition parameters. It is found that the lowest resistivities are in the range of 1.4 to 2×10-4 Ω cm, independently of the deposition method. The highest reported Hall mobilities are about 60 cm2 V-1 s-1. The thin film electrical data are compared with the corresponding values of single crystalline zinc oxide and with that of boron and phosphorous doped crystalline silicon. From this comparison it can be seen that the dependence of the Hall mobilities on the carrier concentration n are quite similar for silicon and zinc oxide. In the region n>5×1020 cm-3, which is most important for the application of zinc oxide as a transparent and conductive electrode, phosphorous doped silicon has a mobility only slightly higher than zinc oxide. The experimental data on the electron and hole mobilities in silicon as a function of the impurity concentration have been described by a fit function (Masetti et al 1983), which can also be applied with different fitting parameters to the available zinc oxide mobility data. A comparison of the experimental data with the well known ionized impurity scattering theories of Conwell-Weisskopf (1946) and Brooks-Herring-Dingle (1955) shows that these theories are not able to describe the data very well, even if the non-parabolic band structure is taken into account. As in the case of silicon, an additional reduction of the mobility also occurs for zinc oxide for concentrations n>5×1020 cm-3, which can be ascribed qualitatively to the clustering of charge carriers connected with increased scattering due to the Z-2 dependence of the scattering cross section on the charge Z of the scattering centre. The presented review of the charge carrier transport in zinc oxide indicates that a physical limit due to ionized impurity scattering is reached for homogeneously doped layers. Due to the universal nature of this limitation it is suggested that it also applies to the other important materials indium-tin (ITO) and tin oxide. Experiments are proposed to overcome this limit.

Growth dynamics of pentacene thin films

Abstract: The recent demonstration of single-crystal organic optoelectronic devices has received widespread attention1,2,3,4. But practical applications of such devices require the use of inexpensive organic films deposited on a wide variety of substrates. Unfortunately, the physical properties of these organic thin films do not compare favourably to those of single-crystal materials. Moreover, the basic physical principles governing organic thin-film growth and crystallization are not well understood. Here we report an in situ study of the evolution of pentacene thin films, utilizing the real-time imaging capabilities of photoelectron emission microscopy. By a combination of careful substrate preparation and surface energy control, we succeed in growing thin films with single-crystal grain sizes approaching 0.1 millimetre (a factor of 20–100 larger than previously achieved), which are large enough to fully contain a complete device. We find that organic thin-film growth closely mimics epitaxial growth of inorganic materials, and we expect that strategies and concepts developed for these inorganic systems will provide guidance for the further development and optimization of molecular thin-film devices.

Micromachined metal oxide gas sensors: opportunities to improve sensor performance

Abstract: This review deals with gas sensors combining a metal oxide based sensing layer and a substrate realized by using micromachining. It starts by giving an overview of the design principles and technology involved in the fabrication of micromachined substrates examining thermal and mechanical aspects. Both kinds of micromachined substrates, closed-membrane-type and the suspended-membrane-type, are discussed. The deposition of the sensing layer is complicated by the mechanical fragility of the micromachined substrates. Different approaches used for the formation of the sensing layer such as thin film and thick film deposition techniques are reviewed. Finally, the gas sensing function of the sensitive layer is analyzed and various ways for extracting the information are presented with respect to the improvement of sensor performance brought by this new approach.

Ultrafast Electron Transfer Dynamics from Molecular Adsorbates to Semiconductor Nanocrystalline Thin Films

Abstract: Interfacial electron transfer (ET) between semiconductor nanomaterials and molecular adsorbates is an important fundamental process that is relevant to applications of these materials. Using femtosecond midinfrared spectroscopy, we have simultaneously measured the dynamics of injected electrons and adsorbates by directly monitoring the mid-IR absorption of electrons in the semiconductor and the change in adsorbate vibrational spectrum, respectively. We report on a series of studies designed to understand how the interfacial ET dynamics depends on the properties of the adsorbates, semiconductors, and their interaction. In Ru(dcbpy)2(SCN)2 (dcbpy = 2,2‘-bipyridine-4,4‘-dicarboxylate) sensitized TiO2 thin films, 400 nm excitation of the molecule promotes an electron to the metal-to-ligand charge transfer (MLCT) excited state, from which it is injected into TiO2. The injection process was characterized by a fast component, with a time constant of <100 fs, and a slower component that is sensitive to sample con...

High throughput fabrication of transition-metal-doped epitaxial ZnO thin films: A series of oxide-diluted magnetic semiconductors and their properties

Abstract: Combinatorial laser molecular-beam epitaxy method was employed to fabricate epitaxial ZnO thin films doped with all the 3d transition metal (TM) ions in a high throughput fashion The solubility behavior of TM ions was discussed from the viewpoints of the ionic radius and valence state The magneto-optical responses coincident with absorption spectra were observed for Mn- and Co-doped samples Cathodoluminescence spectra were studied for Cr-, Mn-, Fe-, and Co-doped samples, among which Cr-doped ZnO showed two sharp peaks at 297 eV and 371 eV, respectively, at the expense of the exciton emission peak of pure ZnO at 325 eV Different magnetoresistance behavior was observed for the samples codoped with n-type carriers Ferromagnetism was not observed for Cr- to Cu-doped samples down to 3 K

Composition and Microstructure of Cobalt Oxide Thin Films Obtained from a Novel Cobalt(II) Precursor by Chemical Vapor Deposition

Abstract: The present work reports the synthesis and the characterization of cobalt oxide thin films obtained by chemical vapor deposition (CVD) on indium tin oxide (ITO) substrates, using a cobalt(II) β-diketonate as precursor. The complex is characterized by electron impact mass spectrometry (EI-MS) and thermal analysis in order to investigate its decomposition pattern. The depositions are carried out in a cold wall reactor in the temperature range 350−500 °C at different oxygen pressures, to tailor film composition from CoO to Co3O4. The crystalline nanostructure is evidenced by X-ray diffraction (XRD), while the surface and in-depth chemical composition is studied by X-ray photoelectron (XPS) and X-ray excited auger electron spectroscopy (XE-AES). Atomic force microscopy (AFM) is employed to analyze the surface morphology of the films and its dependence on the synthesis conditions. Relevant results concerning the control of composition and microstructure of Co−O thin films are presented and discussed.

Optical Properties of Thin Films of Au@SiO2 Particles

Abstract: Homogeneous films of Au@SiO2 particles have been deposited on glass as a prototype 3D “artificial solid” using the LBL method. The film thickness is controlled by the number of dipping cycles and is measured by AFM. Each cycle results in approximately one monolayer of particles being deposited. The particle films are dense, but disordered. The optical properties of the resulting thin films have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness. We find that the surface plasmon peak position in films with volume fractions up to φ > 0.5 is accurately predicted by the Maxwell−Garnett model. The films exhibit remarkably uniform, transmitted colors and display metallic reflection at low angles of incidence, even at low volume fractions. The films can be annealed at T > 500 K to provide extremely stable, optical films.

Graded thin films

Abstract: Thin films are formed by formed by atomic layer deposition, whereby the composition of the film can be varied from monolayer to monolayer during cycles (301) or (450, 455, 460, 470) including alternating pulses of self-limiting chemistries. In the illustrated embodiments, varying amounts of impurity sources (306 or 460) are introduced during the cyclical process. A graded gate dielectric (72) is thereby provided, even for extremely thin layers. The gate dielectric (72) as thin as 2 nm can be varied from pure silicon oxide to oxynitride to silicon nitride. Similarly, the gate dielectric (72) can be varied from aluminum oxide to mixtures of aluminum oxide and a higher dielectric material (e.g., ZrO2) to pure high k material and back to aluminum oxide. In another embodiment, metal nitride (432) (e.g., WN) is first formed as a barrier for lining dual damascene trenches and vias. During the alternating deposition process, copper can be introduced, e.g., in separate pulses, and the copper source pulses (460) can gradually increase in frequency, forming a graded transition region (434), until pure copper (436) is formed at the upper surface. Advantageously, graded compositions in these and a variety of other contexts help to avoid such problems as etch rate control, electromigration and non-ohmic electrical contact that can occur at sharp material interfaces.

Controlled Aqueous Chemical Growth of Oriented Three-Dimensional Crystalline Nanorod Arrays: Application to Iron(III) Oxides

Abstract: The ability to create thin films of highly oriented anisotropic nanoparticles of transition metal oxides onto polycrystalline and single-crystalline substrates is demonstrated by the fabrication of large three-dimensional arrays of perpendicularly oriented nanorods of crystalline iron(III) oxides onto tin oxide and sapphire substrates. An enchanced control of the thermodynamics and kinetics of nucleation and growth processes allows one to grow such novel materials directly onto substrates from a simple aqueous solution of metal salts.

Methods of forming thin films by atomic layer deposition

Abstract: Methods of forming thin films include forming a first layer comprising a first element that is chemisorbed to a surface of a substrate, by exposing the surface to a first source gas having molecules therein that comprise the first element and a halogen. A step is then performed to expose the first layer to an activated hydrogen gas so that halogens associated with the first layer become bound to hydrogen provided by the activated hydrogen gas. The first layer may then be converted to a thin film comprising the first element and a second element, by exposing a surface of the first layer to a second source gas having molecules therein that comprise the second element.

Materials Processing by Gas Cluster Ion Beams

Abstract: This paper discusses the principles and experimental status of gas cluster ion beam (GCIB) processing as a promising surface modification technique for practical industrial applications. Theoretical and experimental characteristics of GCIB processes and of related equipment development are described from the moment of neutral cluster formation, through ionization, acceleration and impact upon a surface. The impact of an accelerated cluster ion upon a target surface imparts very high energy densities into the impact area and produces non-linear effects that are not observed in the impacts of atomic ions. Unique characteristics of GCIB bombardment have been found to offer potential for various industrial applications that cannot be achieved by conventional ion beam processing. Among prospective applications are included shallow ion implantation, high rate sputtering, surface cleaning and smoothing, and low temperature thin film formation. Sputtering effects produced by cluster ion impact are particularly interesting. High sputtering yields and lateral distribution of sputtered atoms cause surface smoothing effects which cannot be achieved with monomer ion beams. Surface smoothing to atomic levels is expected to become the first production use of GCIB.

MgB2 superconducting thin films with a transition temperature of 39 kelvin.

Abstract: We fabricated high-quality c axis-oriented epitaxial MgB2 thin films using a pulsed laser deposition technique. The thin films grown on (1 i 0 2) Al2O3 substrates have a transition temperature of 39 kelvin. The critical current density in zero field is approximately 6 x 10(6) amperes per cubic centimeter at 5 kelvin and approximately 3 x 10(5) amperes per cubic centimeter at 35 kelvin, which suggests that this compound has potential for electronic device applications, such as microwave devices and superconducting quantum interference devices. For the films deposited on Al2O3, x-ray diffraction patterns indicate a highly c axis-oriented crystal structure perpendicular to the substrate surface.

Epitaxial growth of transparent p-type conducting CuGaO2 thin films on sapphire (001) substrates by pulsed laser deposition

Abstract: Transparent p-type conducting CuGaO2 thin films were prepared on α-Al2O3 (001) single-crystal substrates by pulsed laser deposition. The films were grown epitaxially on the substrates in an as-deposited state. X-ray pole figure analysis revealed that the films were composed of two types of epitaxial grains, both with c axes oriented perpendicular to the surface and a axes rotated 60° with respect to each other around the c axis. Observation of the CuGaO2 thin films by atomic force microscopy and high-resolution transmission electron microscopy substantiated this conclusion. The films have high optical transparency (∼80%) in the visible region, and the energy gap of CuGaO2 for direct allowed transition was estimated to be 3.6 eV. p-type conductivity was confirmed by Seebeck and Hall measurements. The electrical conductivity, carrier (positive hole) density, and Hall mobility of the films at room temperature were 6.3×10−2 S cm−1, 1.7×1018 cm−3, and 0.23 cm2 V−1 s−1, respectively.

Metalorganic vapor-phase epitaxial growth and photoluminescent properties of Zn1−xMgxO(0⩽x⩽0.49) thin films

Abstract: High-quality Zn1−xMgxO(0.00⩽x⩽0.49) thin films were epitaxially grown at 500–650 °C on Al2O3(00⋅1) substrates using metalorganic vapor-phase epitaxy. By increasing the Mg content in the films up to 49 at. %, the c-axis constant of the films decreased from 5.21 to 5.14 A and no significant phase separation was observed as determined by x-ray diffraction measurements. Furthermore, the near-band-edge emission peak position showed blueshifts of 100, 440, and 685 meV at Mg content levels of 9, 29, and 49 at. %, respectively. Photoluminescent properties of the alloy films are also discussed.

Thin-Film Deposition of Organic−Inorganic Hybrid Materials

Abstract: Organic−inorganic hybrid films present special challenges and opportunities with respect to potential applications, as well as for the observation of interesting physical phenomena. Although the often disparate characteristics (e.g., solubility and thermal stability) of the two components provide a potential barrier toward forming workable and convenient film deposition strategies, recent results have demonstrated that not only is it possible to develop suitable techniques for these materials but relatively simple processes are often sufficient to yield high quality films. In the current review, some of these recent results on organic−inorganic hybrid films are discussed, with selected examples chosen from among the deposition of sol−gel materials, self-assembled hybrids, Langmuir−Blodgett films, and artificially layered materials. In addition to discussing film-deposition techniques, an effort will also be made, where appropriate, to indicate how the resulting films might be useful for applications such ...

Method of forming silicon containing thin films by atomic layer deposition utilizing trisdimethylaminosilane

Abstract: An atomic layer deposition method of forming a solid thin film layer containing silicon. A substrate is loaded into a chamber. A first portion of a first reactant is chemisorbed onto the substrate, and a second portion of the first reactant is physisorbed onto the substrate. The physisorbed portion is purged from the substrate and the chamber. A second reactant is injected into the chamber. A first portion is chemically reacted with the chemisorbed first reactant to form a silicon-containing solid on the substrate. The first reactant is preferably Si[N(CH 3 ) 2 ] 4 , SiH[N(CH 3 ) 2 ] 3 , SiH 2 [N(CH 3 ) 2 ] 2 or SiH 3 [N(CH 3 ) 2 ]. The second reactant is preferably activated NH 3 .

Lithium doping of semiconducting organic charge transport materials

Abstract: We study the effects of lithium (Li) incorporation in the cathodes of organic light-emitting devices. A thermally evaporated surface layer of metallic Li is found to diffuse through, and subsequently dope, the electron transporting organic semiconducting thin films immediately below the cathode, forming an Ohmic contact. A diffusion length of ∼700 A is inferred from analyses of the current–voltage and secondary ion mass spectrometry data. The conductivity of the Li-doped organic films is ∼3×10−5 S/cm. Photoemission spectroscopy suggests that Li lowers the barrier to injection at the organic/cathode interface, introduces gap states in the bulk of the organic semiconductor, and dopes the bulk to facilitate efficient charge transport.

Highly conductive epitaxial CdO thin films prepared by pulsed laser deposition

Abstract: Epitaxial growth of both pure and doped CdO thin films has been achieved on MgO (111) substrates using pulsed laser deposition. A maximum conductivity of 42 000 S/cm with mobility of 609 cm2/V s is achieved when the CdO epitaxial film is doped with 2.5% Sn. The pure CdO epitaxial film has a band gap of 2.4 eV. The band gap increases with doping and reaches a maximum of 2.87 eV when the doping level is 6.2%. Both grain boundary scattering and ionized impurity scattering are found to contribute to the mobility of CdO films.

Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure

Abstract: A transparent oxide semiconductor with delafossite structure, CuInO2, was found to exhibit both p-type and n-type conduction by doping of an appropriate impurity and tuning of proper film-deposition conditions. Thin films of Ca-doped or Sn-doped CuInO2 (optical band gap=∼3.9 eV) were prepared on α-Al2O3(001) single crystal substrates by pulsed laser deposition method. The films were deposited at 723 K in O2 atmosphere of 1.0 Pa for the Ca-doped films or 1.5 Pa for the Sn-doped films. The positive sign of the Seebeck coefficient demonstrated p-type conduction in the Ca-doped films, while the Seebeck coefficient of the Sn-doped films was negative indicating n-type conductivity. The electrical conductivities of Ca-doped and Sn-doped CuInO2 thin films were 2.8×10−3 S cm−1 and 3.8×10−3 S cm−1, respectively, at 300 K.

Review: Deposition of ceramic thin films at low temperatures from aqueous solutions

Abstract: Many techniques for the synthesis of ceramic thin films from aqueous solutions at low temperatures (25–100°C) have been reported. This paper reviews non-electrochemical, non-hydrothermal, low-temperature aqueous deposition routes, with an emphasis on oxide materials for electronic applications. Originally used for sulfide and selenide thin films, such techniques have also been applied to oxides since the 1970's. Films of single oxides (e.g., transition metal oxides, In2O3, SiO2, SnO2) and multicomponent films (doped ZnO, Cd2SnO4, ZrTiO4, ZrO2-Y2O3, Li-Co-O spinel, ferrites, perovskites) have been produced. The maximum thicknesses of the films obtained have ranged from 100 to 1000 nm, and deposition rates have ranged from 2 to 20,000 nm/h. Compared to vapor-deposition techniques, liquid-deposition routes offer lower capital equipment costs, lower processing temperatures, and flexibility in the choice of substrates with respect to topography and thermal stability. Compared to sol-gel techniques, the routes reviewed here offer lower processing temperatures, lower shrinkage, and (being based on aqueous precursors) lower costs and the potential for reduced environmental impact. This review emphasizes the influence of solution chemistry and process design on the microstructures and growth rates of the films. The current understanding of the mechanisms of film formation is presented, and the advantages and limitations of these techniques are discussed.

Preparation of Nb2O5 Coated TiO2 Nanoporous Electrodes and Their Application in Dye-Sensitized Solar Cells

Abstract: The preparation of a new bilayer nanoporous wide band gap semiconductor electrode and its application for solar cells are reported. This new electrode consists of an inner nanoporous TiO2 matrix covered with a thin layer of ca. 2−3 nm Nb2O5. The results presented in this study show that this Nb2O5 layer forms an inherent energy barrier at the electrode−electrolyte interface. This barrier reduces the recombination rate of the photoinjected electrons with their counter holes. A comparison of two similar dye-sensitized solar cells (DSSCs) that differ only in their nanoporous electrodes shows that the solar cells made from the new electrode are superior to the standard cells with respect to all parameters. This superiority measured with many cells results in a 35% increase of the overall conversion efficiency from 3.6 to 5.0%. Optimization of the coating process and the characterization of the coating effects are described.

Synthesis and characterization of a low bandgap conjugated polymer for bulk heterojunction photovoltaic cells

Abstract: Low optical bandgap conjugated polymers may improve the efficiency of organic photovoltaic devices by increasing the absorption in the visible and near infrared region of the solar spectrum. Here we demonstrate that condensation polymerization of 2,5-bis(5-trimethylstannyl-2-thienyl)-N-dodecylpyrrole and 4,7-dibromo-2,1,3-benzothiadiazole in the presence of Pd(PPh3)2Cl2 as a catalyst affords a novel conjugated oligomeric material (PTPTB), which exhibits a low optical bandgap as a result of the alternation of electron-rich and electron-deficient units along the chain. By varying the molar ratio of the monomers in the reaction and fractionation of the reaction product, two different molecular weight fractions (PTPTB-I and PTPTB-II, see Experimental section) were isolated, containing 5–17 and 13–33 aromatic units respectively, as inferred from matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Thin films of PTPTB-I and PTPTB-II exhibit an optical bandgap of 1.60 and 1.46 eV, respectively. Photoinduced absorption (PIA) and photoluminescence spectroscopy of blends of PTPTB-I and a methanofullerene (1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61, PCBM) gave direct spectral evidence of the photoinduced electron-transfer reaction from PTPTB-I as a donor to the fullerene derivative as an acceptor. Thin PTPTB-I:PCBM composite films were sandwiched between indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (ITO/PEDOT:PSS) and Al electrodes to prepare working photovoltaic devices, which show an open circuit voltage of 0.67 V under white-light illumination. The spectral dependence of the device shows an onset of the photocurrent at 1.65 eV (750 nm).