Electronic Processes on Semiconductor Surfaces During Chemisorption

ISBN-13: 9780306110290 / Angielski / Twarda / 1991 / 444 str.

F. F. Vol'kenshtein; T. Wolkenstein

Opis

"Hands are useless if there are no eyes to see what is obvious." -M. V. Lomonosov Dear Reader, I invite you to open this book and step on the semiconductor surface, where the processes that form the subject of the book come into play. The surface of the semiconductor is attracting more and more interest among researchers, in fact researchers in two different fields. These are notably the physicists and engineers engaged in research in semi conductor physics and the making of semiconductor devices. The entire industry of semiconductor instruments hinges on the problem of the surface. The quality of semiconductor devices, whose use is growing steadily, depends essentially on the properties of the surface. The instability of these properties and their uncon trollable alterations with temperature and under the influence of environmental conditions result in a lack of stability in the performance of semiconductor devices, hence the high percentage of waste in their industrial production. The methods used in factory laboratories to prevent such waste are largely empirical. The properties of the surface, the nature of the physicochemical processes that take place on it, and the role of environmental factors still remain obscure. A major task of the semiconductor industry is to learn to control the properties of the surface."

Spis treści

1. Electrons and Holes in a Semiconductor.- 1.1. Order and Disorder in Crystals.- 1.1.1. Types of Defects.- 1.1.2. Properties of Defects.- 1.2. Electrical Conduction of Nonmetallic Crystals.- 1.2.1. Factors Influencing Conduction.- 1.2.2. Types of Electrical Conduction.- 1.3. The Mechanism of n- and p-type Conduction.- 1.3.1. Free Electrons, Holes, and Excitons in a Lattice.- 1.3.2. Energy Levels of Electrons and Holes.- 1.4. The Energy Spectrum of an Electron in an Infinite Crystal Lattice.- 1.4.1. Statement of the Problem.- 1.4.2. Eigenfunctions and Eigenvalues.- 1.4.3. A Three-Dimensional Lattice.- 1.4.4. The Energy Spectrum of a Hole.- 1.5. The Energy Spectrum of an Electron in a Finite Crystal Lattice.- 1.5.1. Statement of the Problem.- 1.5.2. Eigenfunctions and Eigenvalues.- 1.5.3. Tamm and Shockley Surface Levels.- 1.6. Statistics of Electrons and Holes in Semiconductors.- 1.6.1. The Fermi-Dirac Distribution Function.- 1.6.2. n- and p-type Semiconductors.- 1.6.3. Statistics of Local States.- 1.6.4. The Position of the Fermi Level.- 1.7. Limits of the Band Theory of Semiconductors.- 1.7.1. Characteristic Features of the Band Theory.- 1.7.2. The Validity of the Band Theory.- 1.7.3. The Valence Band.- 2. The Various Types of Adsorption.- 2.1. The Main Laws of Adsorption.- 2.1.1. The Main Prerequisites for Langmuir’ s Theory.- 2.1.2. The Kinetics of Adsorption.- 2.1.3. Adsorption Equilibrium.- 2.2. Physical and Chemical Adsorption.- 2.2.1. The Difference between Physical and Chemical Adsorption.- 2.2.2. Calculating the Adsorption Minimum.- 2.2.3. Activated Adsorption.- 2.2.4. The Nature of the Activation Barrier.- 2.3. “Strong” and “Weak” Bonds in Chemisorption.- 2.3.1. “Weak” and “Strong” Donor and “Strong” Acceptor Fonns of Chemisorption.- 2.3.2. The Various Forms of Chemisorption on Jonic Crystals.- 2.3.3. Examples.- 2.4. Radical and Valence-Saturated Forms of Chemisorption.- 2.4.1. Free Valences of a Surface.- 2.4.2. The Reactivity of Chemisorbed Particles.- 2.4.3. Examples of Radical and Valence-Saturated Forms of Chemisorption.- 2.4.4. The Dissociation of Molecules in Adsorption and the Recombination of Chemisorbed Atoms.- 2.5. The One-Electron Bond in Chemisorption.- 2.5.1. Statement of the Problem.- 2.5.2. Eigenfunctions and Eigenvalues.- 2.5.3. The Polarization of a Chemisorbed Atom.- 2.6. The Two-Electron Bond in Chemisorption.- 2.6.1. Statement ofthe Problem.- 2.6.2. Eigenfunctions and Eigenvalues.- 2.6.3. Free Lattice Electrons as Adsorption Centers.- 2.6.4. Allowing for “Weak” Bonding.- 2.7. Quantum-Mechanical Calculations in Adsorption Theory.- 2.7.1. The Cluster Approximation.- 2.7.2. “Covalent” Clusters for Oxide Lattices.- 2.7.3. “Ionic” Clusters for Oxide Lattices.- 3. Electron Transitions in Chemisorption.- 3.1. Transitions between Various Forms of Chemisorption.- 3.1.1. Transitions between Energy Levels.- 3.1.2. Transitions between Adsorption Curves.- 3.1.3. Equilibrium of Various Forms of Chemisorption.- 3.1.4. The Notion of Electron Transitions in Chemisorption Theories.- 3.2. Adsorption Equilibrium.- 3.2.1. Adsorptivity of a Surface.- 3.2.2. Surface Charging in Adsorption.- 3.3. The Kinetics of Adsorption.- 3.3.1. Statement of the Problem.- 3.3.2. Adsorption at a Constant Surface Potential: The General Case.- 3.3.3. Adsorption at a Constant Surface Potential: Particular Cases.- 3.3.4. Adsorption with a Varying Surface Potential.- 3.4. The Kinetics of Desorption.- 3.4.1. Desorption with Electronic Equilibrium.- 3.4.2. Violation of Electronic Equilibrium in Desorption.- 3.4.3. Incomplete Desorption.- 3.5. The Role of the Fermi Level in Chemisorption.- 3.5.1. The Fermi Level as Regulator of the Chemisorptive Properties of a Surface.- 3.5.2. The Origin of non-Langmuiran Relations.- 3.5.3. The Approximations of the “Boundary Layer Theory”.- 4. The Interaction of the Surface with the Bulk in a Semiconductor.- 4.1. The Connection between Surface and Bulk Properties of a Semiconductor.- 4.1.1. The Connection between the Position of the Fermi Levels at the Surface and in the Bulk of a Semiconductor.- 4.1.2. The Surface Potential.- 4.1.3. The Dependence of the Surface Potential on Various Factors.- 4.2. Effects due to the Charging of the Surface.- 4.2.1. Effect of Adsorption on Work Function.- 4.2.2. Surface Conduction.- 4.2.3. Effect of External Field and Adsorption on Conduction.- 4.3. The “Quasiisolated” Surface.- 4.3.1. The Notion of a “Quasiisolated” Surface.- 4.3.2. Some Properties of “Quasiisolated” Surfaces.- 4.3.3. The Continuous and Quasicontinuous Spectra of Surface States.- 4.4. Adsorptive Properties of a Charged Semiconductor.- 4.4.1. The Adsorptivity of a Charged Semiconductor.- 4.4.2. The Electroadsorptive Effect.- 4.4.3. Adsorption lons on a Semiconductor.- 4.5. The Influence of the Surface on the Impurity Distribution inside a Semiconductor.- 4.5.1. Statement of the Problem.- 4.5.2. Impurity Distribution in the Surface Layer of Semiconductors.- 4.5.3. Effect of Impurity on the Adsorptivity of Semiconductors.- 4.5.4. Irreversible Adsorption.- 4.6. The Adsorptivity of Semiconductor Films on Metals.- 4.6.1. The Variation of the Potential in the Film.- 4.6.2. The Adsorptivity of the Film for a Positively Charged Surface.- 4.6.3. The Adsorptivity of the Film for a Negatively Charged Surface.- 4.7. Growth of a Semiconductor Film on a Metal.- 4.7.1. Statement of the Problem.- 4.7.2. The Electric Field in the Film.- 4.7.3. The Logarithmic Law of Film Growth.- 4.7.4. The Parabolic and Linear Laws of Film Growth.- 4.7.5. Succession of Laws of Film Growth with Temperature and Pressure Variation.- 5. The Catalytic Effect of a Semiconductor.- 5.1. The Basics.- 5.1.1. Semiconductors as Catalysts of Chemical Reactions.- 5.1.2. The Activity and Selectivity of a Catalyst.- 5.1.3. The Activation Energy.- 5.1.4. The Electronic Theory of Catalysis.- 5.2. The Role of the Fermi Level in Catalysis.- 5.2.1. Radical Mechanisms of Heterogeneous Reactions.- 5.2.2. Acceptor and Donor Reactions.- 5.3. Electronic Mechanisms of Catalytic Reactions.- 5.3.1. Oxidation of Hydrogen.- 5.3.2. Decomposition of Alcohol.- 5.3.3. Oxidation of Carbon Monoxide.- 5.3.4. Hydrogen-Deuterium Exchange.- 5.4. The Relationship between the Catalytic Activity of a Semiconductor and Its Electronic Properties.- 5.4.1. The Origin ofthe Relationship between Catalytic Activity, Work Function, and Electrical Conductivity.- 5.4.2. Experimental Results.- 5.4.3. Variations in Electrical Conductivity and Work Function in the Course of a Reaction.- 5.4.4. Correlation between Catalytic Activity and the Forbidden Gap Width in the Energy Spectrum of a Semiconductor.- 5.5. The Effect of Various Factors on Catalytic Activity.- 5.5.1. The Effect of an Extemal Electric Field.- 5.5.2. Catalytic Properties of a Semiconductor Film on a Metal.- 5.5.3. The Mechanism of the Action of an Impurity.- 5.5.4. The Experimental Data on the Effect of Impurities.- 5.5.5. The Compensation Effect.- 6. Processes on a Real Surface.- 6.1. Deviations from Langmuir’s Theory on a Real Surface.- 6.1.1. The Concept of an In homogeneous Surface.- 6.1.2. The Concept of Interaction.- 6.2. The Adsorption-Heat Distribution Function.- 6.2.1. Inhomogeneity due to Irregularities in the Impurity Distribution.- 6.2.2. The Relation between the Impurity Concentration Gradient and the Adsorption-Heat Distribution Function.- 6.2.3. Examples of Inhomogeneous Surfaces.- 6.3. The Role of Surface Structural Defe.- 6.3.1. Adsorption on a Structural Defect.- 6.3.2. Adsorption on Defects of Thermal Origin.- 6.3.3. Adsorption on the Surface of a Disordered Semiconductor.- 6.4. Adsorption on Dispersed Semiconductors.- 6.4.1. Adsorptive Properties of a Dispersed Semiconductor.- 6.4.2. The Compensation Effect on Dispersed Semiconductors.- 6.5. Controlling the Stoichiometry of Crystals.- 6.5.1. Theoretical Aspects of the Problem.- 6.5.2. Experimental Results.- 7. The Effect of Illumination on the Adsorptive and Catalytic Properties of a Semiconductor.- 7.1. The Photoadsorption Effect.- 7.1.1. Positive and Negative Photoadsorption Effects.- 7.1.2. The Photoadsorption Effect on Ideal and Real Surfaces.- 7.1.3. Review of Basic Experimental Data.- 7.2. The Photoadsorption Effect at an Ideal Surface.- 7.2.1. The Effect of Illumination on the Amount of Various Forms of Chemisorption.- 7.2.2. Allowing for the Annihilation of Excitons at Chemisorbed Particles.- 7.2.3. The Mechanism of the Influence of Illumination on the Adsorptivity of a Surface.- 7.2.4. The Magnitude of the Photoadsorption.- 7.3. The Sign and Absolute Value ofthe Photoadsorption Effect at an Ideal Surface.- 7.3.1. Statement of the Problem.- 7.3.2. Solution for a Simplified Potential Function.- 7.3.3. The Case of the Excitonic Mechanism of Light Absorption.- 7.3.4. A Graphic Representation of the Results.- 7.3.5. The Case of High Excitation.- 7.4. Adsorption Centers in Photoadsorption.- 7.4.1. The Nature of Adsorption Centers.- 7.4.2. The Concentration of Adsorption Centers.- 7.4.3. Variation of Adsorption Center Concentration under Illumination.- 7.5. The Photoadsorption Effect at a Real Surface.- 7.5.1. Adsorption after lllumination.- 7.5.2. The Sign and Magnitude of the Photoadsorption Effect.- 7.5.3. “Direct” Photodesorption.- 7.5.4. The Aftereffect.- 7.6. Comparison of the Theory of the Photoadsorption Effect with the Experimental Data.- 7.6.1. Influence of lllumination on the Adsorptivity of a Surface.- 7.6.2. “Memory” Effects in Photoadsorption.- 7.6.3. Some Theoretical Predictions.- 7.7. The Photocatalytic Effect.- 7.7.1. The Mechanism of the Photocatalytic Effect.- 7.7.2. Hydrogen-Deuterium Exchange.- 7.7.3. Oxidation ofCarbon Monoxide: The Experimental Data and the Reaction Mechanism.- 7.7.4. Oxidation of CO: Comparison of Theoretical Results with Experimental Data.- 7.7.5. Synthesis ofHydrogen Peroxide: The Experimental Data and the Reaction Mechanism.- 7.7.6. Synthesis of Hydrogen Peroxide: Comparison of Theoretical Results with Experimental Data.- 8. Adsorption and Luminescence.- 8.1. Basic Facts on Luminescence of Crystals.- 8.1.1. The Various Types of Luminescence.- 8.1.2. Luminescence Center.- 8.1.3. Traps and Quenching Centers.- 8.2. The Effect of Adsorption on Luminescence.- 8.2.1. The Various Mechanisms of Influence of Adsorption on Photoluminescence.- 8.2.2. Recombination Luminescence: Statement of the Problem.- 8.2.3. Recombination Luminescence: Limiting Cases.- 8.2.4. Recombination Luminescence: Experimental Data.- 8.2.5. Excitonic Luminescence: Statement of the Problem.- 8.2.6. Excitonic Luminescence: A Discussion.- 8.3. The Basic Laws of Radical-Recombination Luminescence.- 8.3.1. The Spectral Composition ofRadical-Recombination Luminescence Emission.- 8.3.2. The Effect of Temperature on Intensity of RRL Spectra.- 8.3.3. The Effect of Electric Field on Intensity of RRL Spectra.- 8.3.4. The Effect of lllumination on RRL Intensity.- 8.4. The Mechanism of Radical-Recombination Luminescence.- 8.4.1. The Excitation Mechanism.- 8.4.2. The Mechanism of Luminescence.- 8.4.3. The Dependence of RRL Intensity on the Position of the Fermi Level.- 8.4.4. The Dependence of RRL Intensity on an External Electric Field.- 8.4.5. The Temperature Dependence of RRL Intensity.- 8.4.6. Radical Photoluminescence.- 8.5. Adsorption Luminescence.- 8.5.1. The Fundamentals of Adsorption Luminescence.- 8.5.2. The Mechanism and Kinetics of Adsorption Luminescence.- 8.5.3. Adsorption Luminescence at Adsorption Equilibrium.- 8.5.4. Adsorption Luminescence and the Adsorption Emission of Electrons.- 8.5.5. Luminescence Emission Accompanying Catalytic Reactions at Surfaces.- 9. Conclusion.- 9.1. The “Local” and “Collective” Effects in Chemisorption and Catalysis.- 9.2. The Basic Concepts of the Electronic Theory of Chemisorption.- 9.3. The Electronic Theory of Chemisorption and Experiment.- References.