- Materials can be placed into three groups according to their electrical resistance:
- Conductors: silver, copper, iron, graphite
- Semiconductors: silicon, germanium, gallium arsenide, indium antimonide
- Insulators: wood, paper, plastic
In IBDP Physics, Insulators and pure semiconductors have a very high resistance, while conductors have a very low resistance. The addition of heat, light or a voltage to pure semiconductors causes a few electrons to escape from their atoms, leaving behind ‘holes’. This decreases the resistance and a small current can exist.
- Doping: the deliberate addition of impurities into a semiconductor decreases its resistance.
N- type Semi-conductors
InIBDP Physics, the pure semiconductor with four electrons in its outer shell is doped with an impurity with five electrons in its outer shell. Four of the electrons in the outer shell of the impurity are ‘used up’ in bonding with the surrounding atoms, but the fifth electron is a free charge carrier.
N-type material: the majority of the free charge carriers are negative
The pure semiconductor and impurity are both electrically neutral; the n-type material is also electrically neutral.
P- type Semi-conductors
The pure semiconductor with four electrons in its outer shell is doped with an impurity with three electrons in its outer shell. The three electrons of the impurity are ‘used up’ in bonding with the surrounding atoms and there is a ‘hole’ where the ‘missing’ electron should be.
P-type material: the majority of the free charge carriers are positive
- The resistance of the semiconductor is reduced because there are free charge carriers.
- In IBDP Physics, the pure semiconductor and impurities are both electrically neutral so the n-type and p-type materials are also .
This is the end of this topic.