Bonds and Bands in Semiconductors deals with bonds and bands in semiconductors and covers a wide range of topics, from crystal structures and covalent and ionic bonds to elastic and piezoelectric constants. Lattice vibrations, energy bands, and the thermochemistry of semiconductors are also discussed, along with impurities and fundamental optical spectra. Comprised of 10 chapters, this book begins with an overview of the crystal structures of the more common and more useful semiconductors, together with bonding definitions and rules; bond energy gaps and band energy gaps; tetrahedral coordination; and bond lengths and radii. The discussion then turns to the effects of covalent and ionic bonds on crystal structures and cohesive energies of semiconductors, paying particular attention to the electronic configurations of atoms, ionicity, and homopolar energy gaps. Subsequent chapters introduce the reader to elastic and piezoelectric constants as well as lattice vibrations, energy bands, impurities, and fundamental optical spectra. The book also examines the thermochemistry of semiconductors before concluding with a concise qualitative description of barriers, junctions, and devices, with emphasis on the physical and chemical principles behind their operation. This monograph will be of interest to physicists, chemists, and materials scientists.

Preface

1 Crystal Structures


What Is a Semiconductor?


Energy Bands


Metals, Insulators, and Semiconductors


Allowed and Forbidden Energies


Valence Bonds


Bond Counting


Atomic Orbitals


Hybridized Orbitals


Bonding Definitions and Rules


Bond Energy Gaps and Band Energy Gaps


Tetrahedral Coordination


Layer Structures


Fluorite Bonds


Relativistic Structures


Chalcogenides


Defect and Excess Compounds


Transition Metal Semiconductors


Bond Lengths and Radii


Rationalized Radii


Impurity Radii


Layer Bonds


Summary


References


2 Covalent and Ionic Bonds


Electronic Configurations of Atoms


Core d Electrons


Universal Semiconductor Model


Covalent and Ionic Character


Symmetric and Antisymmetric Potentials


Coulson Definition of Ionicity


Pauling Definition of Ionicity


Extension of Pauling's Definition to Crystals


Limitations of Pauling's Definition


The Middle Way


Homopolar Energy Gaps


Complex Energy Gaps and Resonance


Heteropolar Energy Gaps


Modern Definition of Ionicity


Statistical Test of Definitions of Ionicity


Borderline Crystals


True (Undistorted) Scales


Cohesive Energies


Itinerant Character of Covalent Binding


Core Corrections


Electronegativity Table


Historical Note


Summary


References


3 Elastic and Piezoelectric Constants


Stresses and Strains


Harmonic Strain Energy


Invariance Conditions


Model Force Fields


Diamond Lattice


Zincblende Lattice


Shear Constants and Ionicity


Internal Strains


Piezoelectric Constants


Origin of Piezoelectric Effects


Wurtzite Crystals


Chalcopyrite Crystals


Summary


References


4 Lattice Vibrations


Brillouin Zones


Experimental Determination of (k)


Normal Modes


Mode Descriptions


Sum Rules


Optically Active Modes


Infrared Modes and Effective Charges


Raman Active Modes


Polaritons


Dispersion Curves of Diamond-Type Semiconductors


Electrostatic Models


Zincblende-Type Dispersion Curves


Metallization in Gray Sn


Thermal Expansion


Vibrations of Impurity Atoms


Summary


References


5 Energy Bands


The Language of Band Theory


Nearly Free Electron Model


Valence Bands of Silicon


Jones Zone


Simplified Bands


Isotropic Model


Secular Equation


Dielectric Function of Isotropic Model


Important Anisotropies


Conduction Bands


Band-Edge Curvatures


Perturbation Theory


Special Cases


Atomic Orbitals


Specific Band Structures


Diamond and Silicon


Germanium and Gallium Arsenide


Indium Antimonide and Arsenide


Gray Tin and the Mercury Chalcogenides


Effective Mass Parameters


The PbS Family


Summary


References


6 Pseudopotentials and Charge Densities


Atomic Wave Functions


Atomic Pseudopotentials


Crystal Potential


Crystal Wave Functions


Pseudoatom Form Factors


Metallic Binding


Covalent Binding


Ionic Binding


Semiconductor Wave Functions


Pseudocharge Densities


Atomic Charges


Bond Charges


Partially Ionic Charge Distributions


Conduction Band States


Pressure Dependence of Band Edges


Temperature Dependence of Energy Gaps


Summary


References


7 Fundamental Optical Spectra


One-Electron Excitations


Line and Continuum (Band) Spectra


Dielectric Function


Sum Rules


Direct Thresholds


Germanium


Photoemission


Derivative Techniques


Interband Energies


Core d Electrons


Spectroscopic Definitions of Valence


Chemical Trends in Interband Energies


Spin-Orbit Splittings


Crystal Field Splittings


Nonlinear Susceptibilities


Summary


References


8 Thermochemistry of Semiconductors


Cohesive Energies


Pauling's Description


Ionicity and Metallization


Heats of Formation


Entropies of Fusion


The PbS or ANB10-N Family


Pressure-Induced Phase Transitions


Ideal Solutions


Regular Solutions


Pseudobinary Alloys


Bowing Parameters


Crystallization of Pseudobinary Alloys


Virtual Crystal Model


Optical Transitions in Elemental Alloys


Energy Gaps in Pseudobinary Alloys


Summary


References


9 Impurities


Crystal Growth and Perfection


Stoichiometry of Compound Semiconductors


Shallow and Deep Impurity States


Diffusion of Interstitial and Substitutional Impurities


Distribution Coefficients


Donors and Acceptors


Isovalent Impurities


Spherical (Hydrogenic) Models


Band-Edge Degeneracies


Valleys Anisotropies


Chemical Shifts and Central Cell Corrections


Impurity States in Compound Semiconductors


Free and Bound Excitons


Donor-Acceptor and Isovalent Pairs


Self-Compensation


Polyvalent Impurities


Transition Metal Impurities


Summary


References


10 Barriers, Junctions, and Devices
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