1. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -1 Copyright © 2002 Barry Fell 23 September 2002 ECEE 302: Electronic Devices Lecture 1B. Solid State Device Materials and Material Growth 23 September 2002

2. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -2 Copyright © 2002 Barry Fell 23 September 2002 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. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -3 Copyright © 2002 Barry Fell 23 September 2002 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. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -4 Copyright © 2002 Barry Fell 23 September 2002 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. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -5 Copyright © 2002 Barry Fell 23 September 2002 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. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -6 Copyright © 2002 Barry Fell 23 September 2002 Periodic Table Column IV Materials Elemental Semi-conductors –Si –Ge IV Compound Semi-Conductors –SiC –SiGe

7. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -7 Copyright © 2002 Barry Fell 23 September 2002 Binary III-V Compound Semi-Conductors AlP AlAs AlSb GaP GaAs GaSb InP InAs InSb

8. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -8 Copyright © 2002 Barry Fell 23 September 2002 Binary II-VI ZnS ZnSe ZnTe CdS CdSe CdTe

9. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -9 Copyright © 2002 Barry Fell 23 September 2002 Ternary and Quaternary Compound Semi- Conductors Ternary (3 element) –GaAsP –HgCdTe –AlGaAs Quaternary (4 element) –InGaAsP

10. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -10 Copyright © 2002 Barry Fell 23 September 2002 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. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -11 Copyright © 2002 Barry Fell 23 September 2002 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. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -12 Copyright © 2002 Barry Fell 23 September 2002 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) a a b a b c

13. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -13 Copyright © 2002 Barry Fell 23 September 2002 Unit Cell / Primitive Cell Smallest number of atoms needed to re-produce the regular solid lattice structure Examples Unit Cell

14. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -14 Copyright © 2002 Barry Fell 23 September 2002 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 1 1 1 1 2

15. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -15 Copyright © 2002 Barry Fell 23 September 2002 Direction Indices The vector that is perpendicular to the plane of interest Examples 1 1 1 1 2 Miller Indices Direction Indices

16. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -16 Copyright © 2002 Barry Fell 23 September 2002 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 k d =(C S /C L) –Seed Crystal –Doping

17. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -17 Copyright © 2002 Barry Fell 23 September 2002 Impurities: distribution coefficient k d k d describes the ratio of concentration of the impurity to the melt

18. ECEE 302 Electronic Devices Drexel University ECE Department BMF-Lecture 2-092302-Page -18 Copyright © 2002 Barry Fell 23 September 2002 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)