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ECEE 302: Electronic Devices

23 September 2002. ECEE 302: Electronic Devices. Lecture 1B. Solid State Device Materials and Material Growth. Outline. Physical States of Matter (Solid, Liquid, Gas, Plasma) Electrical Classification of Materials (Conductor, Insulator, Semi-conductor) Semi-Conductor Materials

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ECEE 302: Electronic Devices

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  1. 23 September 2002 ECEE 302: Electronic Devices Lecture 1B. Solid State Device Materials and Material Growth

  2. Outline • Physical States of Matter (Solid, Liquid, Gas, Plasma) • Electrical Classification of Materials (Conductor, Insulator, Semi-conductor) • Semi-Conductor Materials • Mathematical Description of Crystal Lattices • primitive cell • simple cubic/body centered cubic/face centered cubic • Diamond Lattice/Zincblende • Close Packing • Miller Indices/direction indices • Crystal Growth • Bulk Crystal Growth • Doping • Epitaxial Crystal Growth • Lattice Matching • Liquid Phase • Vapor Phase • Molecular Beam Epitaxy

  3. Physical States of Matter • Solid State - Rigid structure. Strong coupling between atoms. Fixed relation between atoms. Periodic arrangement of atoms. Shape is fixed by structure • Liquid State - Loose Structure. Weak coupling between molecules. No Fixed relation between molecules. Shape is determined by shape of vessel that contains liquid. • Gaseous State - No over-arching structure. Collection of individual molecules or atoms. No shape associated with a gas. • Plasma State - Atoms are broken into individual constituants: ions (positively charged) and electrons (negatively charged)

  4. Electrical Description of Materials • Three basic solid materials • Conductor (of electricity or heat) • Insulator (of electric current or heat) • semi-conductor (properties depend on Temperature/Doping/etc) • Physical Characteristics of Solid Materials are understood by the “Band Theory of Solids” • This course will focus on “Semi-Conductors” • Conductors - easy to pass a current, relatively low loss. • Insulators - high resistance, will not pass appreciable electric current • Semi-Conductors • Described by Electron Band Theory of Solids • Can be a good conductor or an insulator based on properties of the bands and temperature • Quantum Mechanics describes the theory and mechanisms of semi-conductors

  5. Semi-Conductor Materials • Semi-conductor properties are determined by electron mobility (ease of movement) • Electron mobility determined by valance of atom • Semi-conductor material is from the periodic table column IV or mixtures of Column III+IV or Column II+VI • Doping (addition of other atoms to the crystal structure) enhances the desired properties of semi-conductors

  6. Periodic Table Column IV Materials • Elemental Semi-conductors • Si • Ge • IV Compound Semi-Conductors • SiC • SiGe

  7. Binary III-V Compound Semi-Conductors • AlP • AlAs • AlSb • GaP • GaAs • GaSb • InP • InAs • InSb

  8. Binary II-VI • ZnS • ZnSe • ZnTe • CdS • CdSe • CdTe

  9. Ternary and Quaternary Compound Semi-Conductors • Ternary (3 element) • GaAsP • HgCdTe • AlGaAs • Quaternary (4 element) • InGaAsP

  10. Crystal Structure • Description of Solids is made possible for two reasons • Translational symmetry Properties • Rotational Symmetry Properties • Crystal Structure Representation • Translational Axes - directions within the crystal that describe the atomic positions • Unit Cell - cell that repeats itself within the crystal structure • Primitive Cell - smallest unit cell • Types of solids • Crystalline - uniform distribution of atoms • Amorphous - random position of atoms • Polycrystalline - Multiple, randomly oriented, crystals

  11. Close Packing • Assuming atoms are hard spheres, what percentage of a solid volume is occupied by the atoms. • Example: What is percentage of volume taken up by Si structure

  12. a b a a c b Crystalline Basis Vectors • Basis Vectors are special directions within the crystal • Linear progression of atoms • Linear progression of lines of atoms (planes) • Linear progression of planes (volume)

  13. Unit Cell / Primitive Cell • Smallest number of atoms needed to re-produce the regular solid lattice structure • Examples Unit Cell

  14. Miller Indices • Method of identifying planes within a Solid • Procedure • Find intercepts of planes in x, y, z axis • Take reciprocals • Multiply through to get smallest set of whole numbers • Examples 2 1 1 1 1

  15. Direction Indices 2 • The vector that is perpendicular to the plane of interest • Examples 1 1 1 1 Miller Indices Direction Indices

  16. Crystal Growth (1 of 2) • Bulk Crystal Formation • Growth from Melt • Czochralski Method • Liquid Encapsulated Czochralski (LEC) Method • Localized Heating • Zone Refining and Floating Zone Growth • distribution coefficient kd=(CS/CL) • Seed Crystal • Doping

  17. Impurities: distribution coefficient kd • kd describes the ratio of concentration of the impurity to the melt

  18. Crystal Growth (2 of 2) • Epitaxy • Chemical Vapor Deposition (CVD) • Liquid Phase Epitaxy (LPE) • Metal-organic vaper-phase epitaxy (MOVPE or OMVPE) • Molecular Beam Epitaxy (MBE) • solid source • chemical beam • gas source MBE • Lattice Matching • lattice matched • lattice mismatched • pseudomorphic layers • strained-layer super lattice (SLS)

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