- Examples: Carbon, Silicon, Germanium. Carbon is commonly used to make resistors, whereas Silicon and Germanium are commonly used in the manufacturing of transistors and integrated circuits.
- These are solids which have electrical conductivity between the insulators and conductors at room temperature. The charge carriers are free electrons and holes. Electrical conduction is due to the movement of the free electrons and holes.
Generally, for semi-conductors, resistance decreases with temperature.
- Collision frequency of the electrons with the lattice increases, which causes an increase in resistance.
- There will be an increase in number of charge carriers (electrons are more likely to have sufficient energy to escape from the atoms when temperature is high). This is generally more significant hence causing a decrease in resistance.
- Example: Saltwater solution or copper sulphate solution
- The charge carriers are cations (positive charge) and anions (negative charge). Electric current consists of these mobile cations and anions drifting in opposite direction.
- Example: Gas discharge tube and fluorescent lamp.
- The charge carriers are the ionized gas molecules and/or the free electrons from the ionized gas molecules. Electric current consists of the movement of these carriers.