Bonds and Bands in Semiconductors

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.

Contenu

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

Fermi Levels

Band Bending

Metal-Semiconductor Contacts

p-n Junctions

Carrier Injection and Trapping

Junction Transistors

Tunnel Diodes

Avalanche Diodes

Why Si?

Microwave Evolution

Luminescence

Junction Lasers

Intervalley Transfer Oscillators

Semiconductors and Materials Science

References

Author Index

Subject Index