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Diodes
What is a diode?
A diode is the
simplest form of
semi conductor
device
What is a semi conductor?
A semi conductor is defined as a
solid whose electrical
conductivity can be controlled.
The Solid that is used in most
semi conductors is Silicon which
is not to be mistaken with silicone
which is used for many thing such
as caulking around doors
Silicon is the most commercially
important semiconductor used
today.
Raw Silicon is a excellent
insulator which would mean that
is a terrible choice for moving
electrons.
The atomic stucture of Raw
Silicon is transformed by a
process called Doping.
Doping is the process of
introducing small amounts of
another compond to change the
atomic structure of Silicon
Two of the most common
compounds are Boron and
Phosphorus
Phosphorus is introduced to raw
Silicon to create a compound that
has an excess of electrons which
makes it a good conductor of
electricity with negative
properties. It is classified as a
N-type semiconductor.
It is said that the electrons in
N-type Silicon are the Majority
Carriers and the holes are the
Minority Carriers
What are holes

In an abstract way holes are the
space left when an electron moves.
A good way of understanding this
is to think of removing an egg from
an egg tray. When you remove the
egg a hole is left behind.
Boron is introduced to raw
Silicon to create a compound that
has an excess of holes. This
makes it a good conductor of
electricity with positive
properties. It is classified as a
P-type semiconductor.
It is said that in P-type Silicon
the holes are the Majority
Carriers and the electrons are the
Minority Carriers

Materials with more of one type of
charge carrier than the other are
called extrinsic. The charge carrier
present in greater numbers is
called the Majority Carrier.
Materials with exactly the same
number of both types of carriers
are called intrinsic.
In the simpliest terms a diode is a
device that is comprised of two
pieces of semi conductor material
that are joined together. One
piece of silicon would be N-type
silicon and the other would be Ptype silicon
The main purpose of a diode is to
allow electrons to flow in one
direction without resistance and
restrict electrons from flowing in
the other direction.
This is the schematic symbol for a
diode
For electricity to flow through a
diode it must be forward biased.
A forward biased diode will have
the Anode connected to the more
positive side of the circuit and
the Cathode connected to the
more negative side of the circuit
For a diode to work in a forward
biased configuration it must be
turned on. To turn on a diode
requires about .7 Volts to drop
over the diode.
If a diode is placed in the circuit the
other way it is said to be reverse
biased. In this configuration
electricity will not flow
Forward bias - all current,
almost no volts.
Reverse bias - all volts,
almost no current.
Diodes are used for many
reasons. One very important
reason is to stop current flowing
the wrong way through a circuit
which can happen by placing a
battery in backwards.
Another is to convert AC Voltage
to DC Voltage
The picture below shows the
association between the schematic
picture of a diode and the colour
coding of a diode
Notice that the white band on the
diode is at the Cathode end of the
diode