SEMICONDUCTOR
MATERIALS
To familiarize students with
semiconductors
OBJECTIVE
To learn about semiconductor
materials
To learn about the importance of
semiconductor materials
Semiconductors
Semiconductors are Common elements Silicon is the best
materials that such as carbon, and most widely
essentially can be used
silicon, and
conditioned to act as semiconductor
good conductors, or germanium are
good insulators, or semiconductors
any thing in between.
SEMICONDUCTOR
VALENCE ORBIT
•The main characteristic of a semiconductor
element is that it has four electrons in its outer
or valence orbit.
CRYSTAL LATTICE
STRUCTURE
• The unique capability of
semiconductor atoms is their ability
to link together to form a physical
structure called a crystal lattice.
• The atoms link together with one
another sharing their outer electrons.
• These links are called covalent
bonds
SEMICONDUCTORS CAN BE INSULATORS
If the material is pure
Since the outer valence
semiconductor material like
electrons of each atom are
silicon, the crystal lattice Good insulating
tightly bound together with one
structure forms an excellent semiconductors material is
another, the electrons are
insulator since all the atoms are referred to as intrinsic.
difficult to dislodge for current
bound to one another and are
flow.
not free for current flow.
Silicon in this form is a great Semiconductor material is
insulator. often used as an insulator.
To make the semiconductor conduct
electricity, other atoms called impurities
must be added.
DOPING
“Impurities” are different elements.
This process is called doping.
SEMICONDUCTORS CAN
BE CONDUCTORS
• An impurity, or element like
arsenic, has 5 valence electrons.
• Adding arsenic (doping) will allow
four of the arsenic valence
electrons to bond with the
neighboring silicon atoms.
• The one electron left over for each
arsenic atom becomes available to
conduct current flow
RESISTANCE EFFECT OF DOPING
If you use lots of arsenic
If you use only a few boron
atoms for doping, there will
atoms, there will be fewer By controlling the doping
be lots of extra electrons so
free electrons so the amount, virtually any
the resistance of the
resistance will be high and resistance can be achieved
material will be low and
less current will flow.
current will flow freely.
ANOTHER WAY
TO DOPE
• You can also do a semiconductor material with
an atom such as boron that has only 3 valence
electrons.
• The 3 electrons in the outer orbit do form
covalent bonds with its neighboring
semiconductor atoms as before. But one
electron is missing from the bond.
• This place where a fourth electron should be
Instead referred to as a hole
• The hole Assumes a positive charge so it can
attract electrons from some other source.
• Holes become a type of current carrier like the
electron to support current flow
The silicon dope with extra electrons is called an N
type semiconductor.
“N” is for a negative which is the charge of an
TYPES OF electron
SEMICONDUCTOR
MATERIALS Silicon dope with material missing electrons that
produced locations called holes is called “p.type”
semiconductor
“P” is for positive which is the charge of a hole.
CURRENT FLOW IN N
TYPE SEMICONDUCTORS
• The DC voltage source has a positive
terminal that attracts the free electrons in
the semiconductor it pulls them away from
their atoms leaving the atoms charged
positively.
• Electrons from the negative terminal of the
supply enter the semiconductor material
and are attracted by the positive charge of
the atoms missing one of their electrons.
• Current (electrons) flows from the positive
terminal to the negative terminal
CURRENT FLOW IN P
TYPE SEMICONDUCTOR
• Electrons from the negative supply
terminals are attracted to the positive holes
and fill them.
• The positive terminal of the supply pulls
the electrons from the holes leaving the
holes to attract more electrons .
• Current electrons flow from negative
terminal to the positive terminal .
• Inside the semiconductor current flow is
actually the movement of the holes from
positive to negative
