Basic Electronics and its introduction to semiconductor devices, Essays (university) of Basic Electronics

Download Basic Electronics and its introduction to semiconductor devices and more Essays (university) Basic Electronics in PDF only on Docsity!

EE 152: Basic Electronics

(Semiconductor Basics)

Outline

• Introduction
• Basic Semiconductor Concepts

▫Intrinsic

▫Doping

▫Extrinsic

◦N-type

◦P-type

▫Carrier movement

Conductors, semiconductors and insulators

Conductors

• Good conductors have low resistance so electrons flow through them with ease.
• Best element conductors include: ▫ Copper, silver, gold, aluminum, & nickel
• Alloys are also good conductors: ▫ Brass & steel
• Good conductors can also be liquid: ▫ Salt water

Insulators

• Insulators have a high resistance so current does not flow in them.
• Good insulators include: ▫ Glass, ceramic, plastics, & wood
• Most insulators are compounds of several elements.
• The atoms are tightly bound to one another so electrons are difficult to strip away for current flow.

Semiconductors

• Semiconductors are materials that essentially

can be conditioned to act as good conductors,

or good insulators, or any thing in between.

• Common elements such as carbon, silicon ,

and germanium are semiconductors.

• Silicon is the best and most widely used

semiconductor.

(Ge)

+3 +4 +

Group III Group IV (^) Group V

Boron (B) Carbon (C) Nitrogen (N)

Aluminium (Al) (^) Silicon (Si) Phosphorus (P)

Gallium (Ga) Germanium^ Arsenic (As)

Indium (In) Tin (Sn) Antimony (Sb)

Semiconductor Elements in the Periodic Table

Semiconductor Valence Orbit

• The main

characteristic of a

semiconductor

element is that it has

four electrons in its

outer or valence

orbit.

11

3D Crystal Lattice Structure

13

Silicon

• Atomic density: 5 x 10^22 atoms/cm^3
• Each silicon atom has an outer shell with four valence electrons and four vacancies (It is a tetravalent element).
• In intrinsic (pure) silicon, atoms join together by forming covalent bonds. Each atom shares its valence electrons with each of four adjacent neighbours effectively filling its outer shell.
• When temperature goes up, electrons can become free to move about the Si lattice.

• Thermal ionization  Valence electron--- each silicon atom has four valence electrons  Covalent bond--- two valence electrons from different two silicon atoms form the covalent bond  Be intact at sufficiently low temperature  Be broken at room temperature  Free electron--- produced by thermal ionization, move freely in the lattice structure.  Hole--- empty position in broken covalent bond, can be filled by free electron, positive charge
• Carriers A free electron is negatively charge and a hole is positively charge. Both of them can move in the crystal structure. They can conduct electric circuit.

• Recombination

Some free electrons filling the holes results in the disappearance of free electrons and holes.

• Thermal equilibrium

At a certain temperature, the recombination rate is equal to the ionization rate. So the concentration of the carriers is able to be calculated.

Semiconductors can be Insulators

• If the material is pure semiconductor material like silicon, the crystal lattice structure forms an excellent insulator since all the atoms are bound to one another and are not free for current flow.
• Good insulating semiconductor material is referred to as intrinsic.
• Since the outer valence electrons of each atom are tightly bound together with one another, the electrons are difficult to dislodge for current flow.
• Silicon in this form is a great insulator.
• Semiconductor material is often used as an insulator.

Intrinsic Semiconductors