What are semiconductors?
Semiconductors can be defined as those substances which have a conductivity between conductors and non-conductors or insulators. They can be compounds such as gallium arsenide, germanium or silicon.
Semiconductors are those materials which have properties of both normal conductors and insulators. Semiconductors are of two types:
- Intrinsic semiconductors- It is made of only one type of material. Examples are silicon and germanium. They are also called ‘undoped semiconductors’ or ‘i-type semiconductors’.
- Extrinsic semiconductors- They are intrinsic semiconductors in which other substances are added to change their properties. In other words, they have been doped with other elements. An extrinsic semiconductor can be divided into:
When a pure semiconductor of silicon or germanium is doped by pentavalent impurity (p, As, Sb, Bi) then, bonding of four electrons out of five valence electron bonds happens with the four electrons of Ge or Si.
The fifth electron of the dopant is released. Hence, the atom which is impure gives a free electron for conduction in the lattice and is called “Donar”.
As free electron increases due to the addition of impurity atoms, the negative charge carriers increase. That is why, it is called n-type semiconductor.
When a pure semiconductor is doped with a trivalent impurity (B, Al, In, Ga), then bonding of three valence electrons happens with three of the four valence electrons of the semiconductor.
This will create an absence of electron (hole) in the impurity. These impurity atom which are ready to receive bonded electrons are called ‘Acceptors’.
When the number of impurities increases, holes or the positive charge carriers also increases. That is why, it is called p-type semiconductor.
Holes and electrons in semiconductors
Holes and electrons are charge carriers which are responsible for the flow of current in semiconductors. Holes or valence electrons are positively charged carrier and electrons are negatively charged carriers. Holes and electrons are equal in magnitude but they are opposite in polarity.
Mobility of electrons and holes
In a semiconductor, the mobility of electrons is higher than that of holes due to the different band structures and scattering mechanisms.
Electrons traverses in the conduction band and hole traverses in the valence band.
The mobility of a particle is more in a semiconductor when the effective mass of particles is less and the time between the scattering events is more.
Conduction band and valence band in semiconductors
The energy band which involves the energy levels of valence electrons is called as the valence band. It is the highest energy band. If it is compared with insulators, then the band gap in semiconductors is small. It lets the electrons in the valence band to move to the conduction band when it receives any external energy.
It is the lowest unoccupied band which has energy levels of positive (holes) or negative (free electrons) charge carriers. The conduction band has high energy level and are empty. The conduction band in semiconductors takes the electrons from the valence band.
Properties of semiconductors
- Semiconductors can conduct electricity under suitable conditions or circumstances. This property makes it the best material to conduct electricity under preferable conditions or circumstances.
- Semiconductors behaves like an insulator at Zero Kelvin. When the temperature increases, it acts as a conductor.
- Since semiconductors have very good electrical properties, they can be doped to make semiconductor devices for energy conversion, switches, and amplifiers.
- There is less loss of power.
- The size of semiconductors is small and they are light in weight.
- The resistivity pf semiconductors are higher than conductors and lesser than insulators.
- The resistance of semiconductor decreases when there is an increase in temperature and the resistance increases when there is a decrease in temperature.
Applications of semiconductors
Semiconductors are used in our daily life in almost all devices. Semiconductors are used in transistors, photosensors, integrated chips, diodes, microcontrollers.
Uses of semiconductors in everyday life
- Semiconductors are used in temperature sensors.
- It is used in 3D printing machines.
- It is used in microchips and self-driving cars.
- It is also used in calculator, computers and other electronic devices.
Industrial uses of semiconductors
Due to the physical and chemical properties of semiconductors, it is used for designing technological wonders like microchips, transistors, LEDs, solar cells, etc.
The microprocessor used in space vehicles, trains, robots, etc. is made up of transistors and other controlling devices, manufactured by semiconductors materials.
Importance of semiconductors
- Since they are smaller in size, they are super portable.
- They need less input power.
- They are shockproof.
- They have longer durability.
- When they are operating, it makes no noise.
Interesting question, solve this: The conductivity of a semiconductor increases with increase in temperature because?