EEE 3394 Electronic Materials Chris Ferekides FALL 2014

WHY ELECTRONIC MATERIALS

WHY ELECTRONIC MATERIALS … Moore's law: the number of transistors that can be placed on an chip (integrated circuit) doubles approximately every two years.

Chapter 1 – Short Questions Name several classes of important materials …. What is a proton? What is the atomic number Z? What is charge? What do we mean by valence electrons? What is bond or binding energy? What is a crystal? What is the difference between a crystalline and polycrystalline material? Describe the metallic bond What is a lattice parameter? What is Avogadro’s Number? What is an amorphous solid?

Short Questions Describe covalent bonding What is the coordination number? What is a crystalline defect? Give a word definition for the unit cell. How many atoms are there in a simple cubic cell? In a bcc unit cell? In a fcc unit cell? In the unit “diamond” cell? With regards to the Miller Indices, what do the following indicate? (), {}, [], <>? The lattice constant for Ge at room temperature is 5.65 x 10-8 cm. Determine the number of Ge atoms per cm3. The surface of a Si wafer is a (100) plane. Determine the number of atoms per cm2 at the surface of the wafer. (repeat for (110)) Assuming a cubic crystal, identify sketch the following planes: (001), (111), (123), (-110), (010), (-1-1-1), (221). (Note: the negative signs should be on top!)

Short Questions What is an Arrhenius equation ? What is an electron-volt … eV ? In your own words describe what causes the phenomenon of thermal expansion What is diffusion? And what causes it? i.e. what is the “driving force” behind it. Know the ideal gas law and its “significance” What is an ion ? Cation vs. anion … The term allotropy describes a material that does what ? Know the difference between the terms “solvent” and “solute Ionization energy is the energy required to do what ? Define/describe a stoichiometric compound

BONDING Covalent Bonding: sharing of electrons…. between atoms to complete outer shells; does not have to be “equal” sharing; some times electrons “spend more time around one of the atoms; strong attraction between –ve shared electrons and positive nuclei – therefore strong bond; strong bond implies high melting temperatures, hard materials; Since electrons complete outer valence by participating in covalent bond, there are no free electrons – therefore materials covalently bonded have low electrical conductivity

BONDING Metallic Bonding: atoms (of metals) give easily valence electrons to the solid; “free” electrons are shared by the now charged metal atoms (ions); negative electron “cloud” and positively charged ions attract each other – metallic bonding; non-directional bond; ions can move easily – therefore metals are ductile; “free” electrons can move easily – therefore high electrical conductivity; also high thermal conductivity as electrons can help transfer energy

BONDING Ionic Bonding: transfer of charge; i.e. electron transfer from one atom to the other creating ions; anion (-) and cation (+); coulombic attractions creates the strong ionic bond; poor electrical conductors; hard and brittle See table 1.2 on pg. 21

General Bonding Principle

ATOMIC ARRANGEMENT Crystalline (single crystal): order thorough entire solid Polycrystalline: solid segmented in ordered regions – called grains; the grain boundaries are “defective” regions; typically contain dangling bonds, leading to high recombination losses. Amorphous: no order at all……

SEM IMAGE of a POLYCRYSTALLINE FILM

Crystal Lattices Unit Cell: small portion of a crystal that can be used to reproduce the crystal; (smallest building block!) (REM: primitive cell) Lattice Constant: a unit cell dimension Crystal Systems (unit cell geometries) Cubic Tetragonal Orthorhombic Hexagonal .etc. Cubic System Simple Cubic Body centered Cubic Face centered cubic

Crystal Lattices - Diamond Diamond lattice - Si, Ge; Zincblend when two atoms GaAs, (III-V’s.) Two interpenetrating fcc’s displaced by ¼ a. Four nearest Neighboring atoms!

F a c e n t r d u b i S m p l B o y g h s R H x T C U I Y E M = 9 ° , ° , A P . N L G O ­ 2 ( < 3 ) f X ; 1 Z D -

MILLER INDICES What are they? Why do we need them?

Miller Indices Directions

Miller Indices Directions [241]

Miller Indices Planes – how do we determine plane indices? Miller Indices for a plane: identify x, y, z intercepts; i.e. 2, 1, 4 invert them; i.e. 1/2, 1/1, 1/4 reduce to lower integers; i.e. 2, 4, 1  (2 4 1) 2, 1, 4 1/2, 1/1, 1/4 (241)

Crystal Lattices – Miller Indices [hkl] direction <hkl> equivalent directions (hkl) plane {hkl} equivalent planes