elec lecture 1

1Slide #8/20/2006 Dr. F. Nkansah – Physical Electronics

Solid State Electronics(ELEG3033)

Solid State Electronics(ELEG3033)

Dr. Franklin D. Nkansah

Electrical and Computer Engineering

Center for Micro-Fabrication Micro-Design and Materials (CM3)

Home page: http://fdnconsulting.net

Textbook : Solid State Electronic Devices (5th Ed.), written by Ben G. Streetman & Sanjay Banerjee, published by Prentice Hall


Objective and GoalObjective: To learn basics of semiconductor materials, devices, and related applications

Text book: Solid State Electronic Devices, Ben. G. Streetman and Sanjay Banerjee, 6th edition, Prentice Hall, Upper Saddle, NJ 07458, 2000ISBN # 013149726-X

Reference book: Semiconductor Device Fundamentals, Robert Pierret, Addison-Wesley, 1996, ISBN # 0201543931

Lecture Notes: I will provide you with lecture-notes web-acess, however this is not a substitute for class attendance since lectures will be posted after the lecture not before!!


Why this course is important?

Microelectronics has applications in cell-phone towers to air-planes to computers


Course Contents• Semiconductor Materials

• Atoms and Electrons

• Energy Bands and Charge Carries in Semiconductors

• Junctions

• Devices Field-Effect Transistors

Bipolar Junction TransistorsOptoelectronics DevicesMicrowave Devices

• Integrated Circuits Fabrication Overview


Career Tracks

• Conventional Microelectronics/PhotonicsElemental semiconductor (Silicon) Applications:

Device design: processing, fabrication, packaging, and testingCircuit design: packaging, and testingSystem design: packaging, and testing

Compound Semiconductor Applications:Same as abovePhotonics and high speed applications

• Display applications (Thin film display, plasma display, etc)• Microwave engineering, telecommunication and wireless

applications• CAD tools and professional software for semiconductor industry• Manufacturing tools and control system for semiconductor industry• Military and space applications• Sensors and Nanotechnology (Next generation technology)


[Chapter Lecture -1]

Crystal Properties & Growth of Semiconductors

• Semiconductor Materials

• Crystalline Lattices

• Bulk Crystal Growth

• Epitaxial Growth


What are semiconductors ?Materials with electrical conductivity in between conductors andinsulators

Semiconductors

InsulatorsMetals

Ohm’s law: R = ρ L (length)/A (area)Conductivity: σ = 1/ ρ

LA

• Conductors Metals (silver, gold, etc) 10-6-1 ohm-cm• Insulators Ceramics (quartz, alumina) > 107 ohm-cm• Semiconductors Silicon, germanium, 10-2 - 106 ohm-cm


Periodic Table

Elements in a column have similar properties which gradually change (become more metallic, less electronegative) as we move from the top to bottomEach atom has protons, electrons and neutronsNumber of electrons in outer shells determines the properties of materials

Ref. [1]


Different Semiconductor Types

• Elemental Semiconductors: Group IV (most commonly Si and Ge)

• Compound Semiconductors: IV-IV (Ex: SiC), III-V (Ex: GaN, GaAs), II-VI (ZnS, CdS)

Grouping of common elemental and compound semiconductors

Ref. [1]


Types of Semiconductors

Crystalline: long range ordered arrangement of atoms

Amorphous: no ordered arrangement of atoms

Polycrystalline: short or medium range ordered arrangement of atoms

Long term atomic arrangement determines the crystal type. Properties such as mechanical, electrical and optical are intimately tied to crystal type.Crystals (Ex: any good quality semiconductor) have periodic arrrangements of atoms in 3-dimensions. Polycrystals (Ex: semiconductors deposited on non-lattice matched substrate) have only short range ordering of the atoms. Amorphous materials (Ex: Amorphous Si) do not have any ordering at all.


Modern Semiconductor Device

50 nmGate 100 nm

Influenza Virus(Source: CDC)

Intel Transistor


Crystal and LatticeSingle Crystal Semiconductors ⇒ Periodic Arrangement of atomsCrystal lattice: Periodic arrangement of points (in 3D space) making up the crystal. Note: Each point may have a single atom or multiple atoms.

Unit Cell: Arrangement of atoms or a volume which can be moved in space by unit lattice constant in each direction to create the entire crystal lattice.

Primitive Cell: A primitive cell is the smallest Unit Cell that can be translated by unit lattice constant in each direction to form the crystal lattice

Lattice constant: Smallest distance between periodically arranged atoms in each direction

Ref. [1]


Bravais LatticeBravais Lattice:A Lattice is called Bravais if the arrangement of lattice points around one lattice point is the same as around any other point.

Any lattice can be generated by three unit vectors, and a set of integers k, l and m so that each lattice point can be identified by a vector


Lattice Types and Summary


Cubic LatticesRef. [1]

Simple Cubic Body-centered cubic Face-centered cubic

Cubic lattice types are one of the most common ones. Si and GaAs, two most common type of semiconductors have face centered cubic lattice (actually two interpenetrating FCC lattice or two bases).

Note: CRYSTAL STRUCTURE = LATTICE + BASIS. Bases determine the atoms at each lattice points.Ex: Both Si and GaAs have two bases at (0,0,0) and (¼, ¼, ¼).


Miller Indices

• To find miller indices of a plane: (1) Find the intercepts of the plane in each of the three axes in terms of the lattice constants, (2) Take reciprocals of these numbers, and (3) convert them to the smallest 3 integers having the same ratio, by multiplying with appropriate integers

• Notations: (hkl) plane; [hkl] denotes a crystal direction

Directions

Planes


Example of Miller Indices for directions

Crystal directions are represented by three integers a, b, c, with the same relations as a vector in that direction, and represented as [a, b, c]. <hkl> equivalent crystal directions i.e. <010>, <0-10>, <100> etc.

0

z

Ref. [1]

The intercepts for a vector in this direction will be 1, 1,1


Example of Miller Indices for planes

Ref. [1]1. The intercepts are 2, 4, 12. The reciprocals are ½, ¼, 13. Multiply with 4 to get the miller

indices as 2, 1 and 44. Represent the plane as (214)

Planes are represented by a set of numbers called Millers Indices (h, k, l). {hkl} ⇒planes of equivalent symmetry i.e. (001), (010), (0-10), (100) etc.

Note: Since the origin can be chosen freely and unit cell can be rotated. Therefore, in crystal lattice, some sets of planes and directions are equivalent.

elec lecture 1

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