Semiconductors

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Semiconductors
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Semi conductors

• A semiconductor is a material whose resistance is
  between that of a conductor and an insulator. Eg
  Silicon

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Intrinsic Semiconductor
Intrinsic conduction is conduction in a pure
semiconductor.
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Extrinsic Semiconductors
Extrinsic conduction is conduction in a doped
semiconductor.
p-type
Electrons are the majority charge carriers.
Holes are the majority charge carriers.
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Doping
Doping

• The addition of a small amount of impurity to a
  semiconductor to improve its conductivity.
• Doping produces two types of semiconductorn-type
  and p-type
• Electrons are the majority charge carriers in
  n-type material
• Holes are the majority charge carriers in p-type
  material

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Factors that affect conduction in semiconductors

• Temperature - Conductivity increases with
  temperature as the heat energy liberates
  electrons e.g. the thermistor
• Light - Conductivity increases with light
  intensity e.g. the LDR light dependent resistor

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PN Diode
Structure
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The Diode

• When p-type and n-type materials are placed in
  contact current will flow in one direction but
  not in the other
• Because of the charge movement at the junction,
  the p-type develops a negative charge and the
  n-type a positive charge A voltage is then
  created called the junction voltage.
• The depletion layer is the area between the p and
  n type material where there are no free charge
  carriers.

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PN Diode
Structure
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Forward Bias
P Type
N Type
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Reverse Bias
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A
B
Forward or reverse bias?
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Half Wave Rectifier
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Full Wave Rectifier
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Light Emitting Diode
Used to indicate that power is on in electrical
devices. Uses less power than a bulb and does not
heat up.
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Light Dependant Resistor LDR
Used in automatic street lights
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Answer the following questions

• Define the following
• Semiconductor
• Doping
• Extrinsic conduction
• Intrinsic conduction
• Diode
• Depletion layer
• Draw and label the structure of a diode.
• Draw a diagram to show the semi conductor diode
  in reverse bias and forward bias.