The document discusses the basics of semiconductor materials. It begins by reviewing the atomic model and how electrons are arranged in energy levels. Intrinsic semiconductors like silicon have electrons that can be excited into the conduction band to allow current flow. Semiconductor crystals form a lattice structure through covalent bonding. Doping introduces impurities to semiconductors to improve electrical properties by adding extra electrons or holes. A p-n junction forms the basis of semiconductor devices like diodes, which allow current to flow in one direction depending on bias polarity.

1. Semi-conductor Material
Presenter : Damion Lawrence

2. Review of
Basic Atomic
Model
 Atoms are comprised of
electrons, neutrons, and
protons.
 Electrons are found orbiting
the nucleus of an at atom at
specific intervals, based
upon their energy levels.
 The outermost orbit is the
valence orbit.

3. Energy Levels
 Valence band electrons
are the furthest from the
nucleus and have
higher energy levels
than electrons in lower
orbits.
 The region beyond the
valence band is called
the conduction band.
 Electrons in the
conduction band are
easily made to be free
electrons.

4. Intrinsic Semiconductors
 Silicon, germanium, and gallium arsenide are
the primary materials used in semiconductor
devices.
 Silicon and germanium are elements and are
intrinsic semiconductors.
 In pure form, silicon and germanium do not
exhibit the characteristics needed for practical
solid-state devices.

5. Semiconductor Crystals
 Tetravalent atoms such as silicon, gallium
arsenide, and germanium bond together to
form a crystal or crystal lattice.
 Because of the crystalline structure of
semiconductor materials, valence electrons
are shared between atoms.
 This sharing of valence electrons is called
covalent bonding. Covalent bonding makes it
more difficult for materials to move their
electrons into the conduction band.

6. Electron Distribution
 As more energy is applied to a
semiconductor, more electrons will move into
the conduction band and current will flow
more easily through the material.
 Therefore, the resistance of intrinsic
semiconductor materials decreases with
increasing temperature.
 This is a negative temperature coefficient.

7. Semiconductor Doping
 Impurities are added to intrinsic
semiconductor materials to improve the
electrical properties of the material.
 This process is referred to as doping and the
resulting material is called extrinsic
semiconductor.
 There are two major classifications of doping
materials.
 Trivalent - aluminum, gallium, boron
 Pentavalent - antimony, arsenic, phosphorous

8. Atomic Outer Electron Shells
Silicon
Tetravalent
Boron
Trivalent
“Acceptor”
Phosphorus
Pentavalent
“Donor”

9. Forward Biased Junction
 An external source can either oppose or aid the barrier
potential.
 If the positive side of the voltage is connected to the p-
type material, and the negative side to the n-type material,
then the junction is said to be forward biased.

10. Forward Biased Junction
 In a forward biased junction, the following
conditions exist:
 Forward bias overcomes barrier potential.
 Forward bias narrows the depletion region.
 There is maximum current flow with forward
bias.

11. Reverse Biased Junction
 Reverse bias occurs
when the negative
source is connected
to the p-type
material and the
positive source is
connected to the n-
type material.
 Reverse bias
strengthens the
barrier potential.
 Reverse bias widens
the depletion region.
 Current flow is
minimum.

12. Reverse Biased Junction
 A reversed biased junction has zero current
flow (ideally).
 Reverse current is temperature dependent.
 If reverse biased is increased enough, the
reverse current increases dramatically.
 This breakdown is called junction breakdown.
The voltage required to reach this point is the
reverse breakdown voltage.
 As the breakdown occurs, avalanche may
occur and destroy the device if uncontrolled.

13. DIODE
 diode = “biased p-n junction”, i.e. p-n junction
with voltage applied across it
 “forward biased”: p-side more positive than n-
side;
 “reverse biased”: n-side more positive than p-
side;

14.  forward biased diode:
 the direction of the electric field is from p-side
towards n-side
 ⇒ p-type charge carriers (positive holes) in p-
side are pushed towards and across the p-n
boundary,
 n-type carriers (negative electrons) in n-side are
pushed towards and across n-p boundary
⇒ current flows
across p-n boundary

16. The Diode: a tiny P-N Junction
A diode comprises a section of N-type material
bonded to a section of P-type material, with
electrodes on each end. This arrangement
conducts electricity in only one direction.

17.  When no voltage is applied, to the diode,
electrons from the N-type material fill
holes from the P-type material along the
junction between the layers, forming a
depletion zone. In a depletion zone, the
semiconductor material is returned to its
original insulating state -- all of the holes are
filled, so there are no free electrons or empty
spaces for electrons, and charge can't flow.