Circ Ctrl & Protectn, Semicond - Week 1

The 3 states of matter

solid, liquid, gas

Element

substance that cannot be reduced into a simpler substance

Compounds

two or more elements chemically combined

Molecule

two or more atoms chemically combined

The 3 subatomic particles

protons, neutrons, electrons

Negatively charged subatomic particle

electron

Positively charged subatomic particle

proton

Neutrally charged subatomic particle

neutron

The nucleus is made up of

protons and neutrons

Orbit around the nucleus

electrons

The number of protons in the nucleus

atomic number

The number of protons and neutrons in the nucleus

atomic weight

Shell nearest to the nucleus

K shell

The number of electrons each shell will contain

2(n)²

The outermost shell

valence shell

Less than 4 valence electrons

conductors

More than 4 valence electrons

insulator

Exactly 4 valence electrons

semiconductor

Two semiconductor elements

Silicon and Germanium

More electrons than protons

anion (negative ion)

Less electrons than protons

cation (positive ion)

Band Gap

difference in energy between the valence and conduction bands

Insulator band gap vs conductor band gap

insulator large gap, conductor no gap but overlap

Covalent bond

sharing of valence electrons between two atoms

Intrinsic

pure, no impurities

Recombination

when a free electron fills a hole

Hole

space that is missing an electron

Free electron

an electron in the conduction band not bound to a nucleus

Electron current in an intrinsic crystal is caused by

thermal energy

Hole current occurs in the

valence band

Doping

adding impurities to a semiconductor

Extrinsic

has impurities

Two types of impurities

n-type, p-type

n-type

pentavalent impurities added

Pentavalent atom also called

donor atom

p-type

trivalent impurities added

Trivalent also called

acceptor atom

What are the majority and minority carriers in n-type

majority: electrons minority: holes

What are the majority and minority carriers in p-type

majority: holes minority: electrons

When does a pn junction form

when a semiconductor has been doped by both p and n types

Diffusion

movement from higher to lower concentrations

Electrons diffuse across the pn junction from what region

n-region to p-region

n-region

higher concentration of electrons

p-region

higher concentration of holes

Depletion region

region with no free electrons or holes

Barrier potential

voltage that forms across the depletion region and opposes the movement of electrons and holes must be overcome for movement to occur

Silicon barrier potential

0.7V

Germanium barrier potential

0.3V