TF EIM Chapt3

Semiconductor physics

There are 5 states of matter: Solid, liquid, gas, plasma (ionized gas) , and a Bose-Einstein condensate (quantum effects on a macroscopic scale).

Crystal Lattice

Semiconductor physics focuses on the solid state of matter in the form of crystals.

Crystals are formed when atoms are arranged in repeating structures called the crystal lattice. The recurrent structure which forms the crystal lattice is referred to a a cell.

Some popular cell names are

(SC) Simple Cubic	(BCC) Body Centered Cubic	(FCC) Face Centered Cubic

The above images are suppose to represent the distribution of electrons in the crystal lattice cell.

To understand this structure more let's consider the structure of a 1-D crystal of atoms

A single free atom will have electrons bound to the atom due to the coulomb force. The bound electrons are found in various energy levels.

Notice

When you add the atoms to form the lattice, the potential barrier is lowered. This allows the electrons in the higher (more valence) states to become shared among adjacent atoms.( Delocalized)

There are 14 different Bravais lattice configurations

Crystal System	Lattice type
Cubic	Simple, Face Centered, Body Centered
Tetragonal	Simple, Body Centered
Orthorhombic	Simple, Face Centered, Body Centered, End Centered
Monoclinic	Simple, End Centered
Rhombohedral	Simple
Triclinic	Simple
Hexagonal	Simple

Most Semiconductors are made from Silicon and GaAs.

Silicon is a Face Centered Cubic cell

Silicon is an insulator if in pure form with 4 weakly bound (valence) electrons.

If you replace silicon atoms in the lattice with atoms that have either 3 valance or 5 valence electrons (doping) your can create sites with either a deficient number of electrons (a missing bond) or extra electrons (complete bond with a free electron)

By Doping silicon you can create sites with extra electrons (n-type) or sites with a deficient number of electrons (vacancies or holes ) (P-type)

Forest_Electronic_Instrumentation_and_Measurement