2. Semiconductors
A material with four free or valence electrons
Usually silicon or germanium, these
materials do not allow the free flow of
electrons like a conductor, but also do not
prevent electron flow like an insulator
3. Semiconductor Doping
Silicon and germanium start out as a pure
semiconductor crystal
In order to be useful, the crystalline
structure must be “doped”
Doping replaces some of the atoms in the
crystal with atoms from different elements
These “replacement” atoms contain more or
less free electrons than the pure
semiconductor material
4. Semiconductor Doping
If atoms with more free electrons are used, N-Type
material is created
The added free electrons in N-Type material are
called carriers
If atoms with fewer free electrons are used, P-Type
material is created
The missing free electrons in P-Type material are
called holes
5. Semiconductor Properties
Once their internal structure has been altered,
semiconductors can act as an insulator or a
conductor
This property is controlled with current, and
allows the semiconductor device to either
block almost all of the current, or allow
almost all of the current to pass through
(semiconductor can act as an insulator or
conductor)
6. Diodes
Diodes only allow current to travel in one direction
A diode is made of an anode (+) and a cathode (-)
The diode will permit current flow when it is forward
biased (anode connected to + and cathode connected
to -)
The diode will prevent current flow when it is reverse
biased (anode connected to - and cathode connected to
+)
7. Diodes
Internally the diode is composed of two differently
doped materials, N-material and P-material.
In between these two materials is a thin layer called
the “depletion region”
The depletion region is neither P nor N, but made
up of the pure crystalline semiconductor structure
8. Forward Bias
When a positive charge is on the anode (P-
material) and a negative charge is on the cathode
(N-material) the diode will
conduct
This occurs because likes
repel each other, and the
N-Type & P-Type close
over the depletion region
9. Reverse Bias
When a negative charge is on the anode (P-
material) and a positive charge is on the cathode
(N-material) the diode will
not conduct
This occurs because
opposites attract each other,
and the N-Type & P-Type
widen the depletion region
10. Forward Operating Voltage &
PIV
All semiconductor devices require a forward operating
voltage.
This is the amount of forward bias voltage required for the
component to start conducting
Germanium ~ 0.3vdc
Silicon ~ 0.6vdc
Diodes also have a Peak Inverse
Voltage Rating (PIV)
This is the amount of reverse bias
voltage a diode can handle without
breaking down
A higher voltage will cause the
diode to conduct in reverse bias
(avalanche current)
11. Rectification
One of the most common uses of diodes is for
rectification
Rectification is changing AC to DC
A single diode can be used to transform AC into a
rough DC signal (only converts half of the AC
signal to DC)
12. Bridge Rectifier
Because a single diode produces such a crude DC
signal, a bridge rectifier is more commonly used
A bridge rectifier allows all of the AC signal to be
converted into DC
Bridge rectifiers still produce
a pulsating DC signal, so a
filter (cap) must be used to
further improve the signal
13. LED’s
LED stands for Light Emitting Diode
Like a diode, an LED will only allow current flow in
one direction
LED’s can only handle a limited amount of current
(must include a current limiting resistor)
14. Review
Semiconductors have how many valence electrons?
What procedure is used to produce N-Type and P-Type
material?
What are N-Type & P-Type?
What is a depletion region?
What is forward bias?
What is reverse bias?
What is forward operating voltage?
What is PIV?
What is rectification?
What is an LED?
