Semiconductors

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

Intrinsic Semiconductor Intrinsic conduction is conduction in a pure semiconductor.

Extrinsic Semiconductors p-type n-type Pb Extrinsic conduction is conduction in a doped semiconductor. Electrons are the majority charge carriers. Holes are the majority charge carriers.

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

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

PN Diode Structure Symbol Depletion layer

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.

PN Diode Structure Symbol

Forward Bias P TypeN Type

Reverse Bias P TypeN Type

A B Forward or reverse bias?

Half Wave Rectifier

Full Wave Rectifier

Light Emitting Diode Used to indicate that power is on in electrical devices. Uses less power than a bulb and does not heat up.

Light Dependant Resistor LDR Used in automatic street lights

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.