- Semiconductor is a material with electrical conductivity better than an insulator but weaker than a conductor.
- At low temperature, a pure semiconductor conducts electricity very poorly and acts as an insulator.
- At higher temperature, the electrons receive more kinetic energy and vibrate faster. Thus, conductivity increases.
Doping of semiconductors
- Doping is the process known as adding small amount of impurities into crystalline lattice of semiconductor.
- This is to increase the conductivity of semiconductor.
n-type conductor
- free electrons as majority and holes as minority
- Phosphorous is added acts as pentavalent atom.
- When a pentavalent atom is added, there will be one extra electron and four complete covalent bonds. The free electron will act as charge carrier.
p-type conductor
- holes as majority and electrons as minority
- Boron acts as trivalent atom
- When trivalent atom is added, there will be one electron less and form 3 complete bonds, leaving a vacancy. The vacancy is a hole acts as charge carrier.
Diode
- A diode is an electric component that allows current to flow in only one direction.
Forward bias:
1. The anode (p-type) is connected to positive terminal and cathode (n-type) connected to negative terminal.
2. The electrons from n-type and holes from p-type drift to the p-n junction and produces a narrow depletion layer.
3. The electrons and holes combine together to ensure the flow of current.
Reverse bias:
1. The anode (p-type) connected to negative terminal and cathode (n-type) connected to positive terminal.
2. The electrons from n-type and holes from p-type pulled away from p-n junction and produces a wide depletion layer.
3. The resistant of diode is high as depletion layers widen. Hence electrical cannot flow in the circuit.
