Semiconductor Definition, N-type semiconductor, and P-type semiconductor, properties of semiconductor
The material whose property lies between conductor and semiconductor is called semiconductor. When the temperature increases, the resistance of the material decreases this made it a conductor. A semiconductor material has an electrical conductivity value lies between conductor, such as metallic copper, and an insulator, like glass. Its resistance falls as its temperature rises.
To make conductors, we introducing impurities (doping) into the crystal structure of the semiconductor. Where two differently doped regions exist in the same crystal, a semiconductor junction is created between these two regions. Some examples of semiconductors are silicon, gallium, germanium, and arsenide.
After silicon, gallium and arsenide is the second most common semiconductor and these are used in solar cells, laser diodes, microwave-frequency, integrated circuits, and others. Silicon is a special element for fabricating most electronic circuits.
Semiconductor devices can show a range of useful properties such as passing current more easily in one direction than the other direction, sensitivity to light or heat and showing variable resistance. The semiconductor material can be modified by doping because of their electrical properties.
Devices made from semiconductors can be used for switching, amplification and energy conversion. The conductivity of silicon is increased by adding a small number of pentavalent impurities(antimony, phosphorus, or arsenic) or trivalent (boron, gallium, indium) impurities.
This process is known as doping. By doping the conductivity of a semiconductor can equally be improved by increasing its temperature. This is the behavior of a metal in which conductivity increases with an increase in temperature.
The property of a semiconductor relies on quantum physics that explains the movement of charge carriers in a crystal lattice. By doping the number of charge carriers within the crystal greatly increases.
Types of semiconductors
There are two types of semiconductor
- P-type semiconductor
- N-type semiconductor
When the doped semiconductor contains mostly free holes it is called p-type. In a P-type semiconductor material, there are fewer numbers of electrons, so there are holes in the crystal lattice. In this case, the holes are moving.
This can happen by creating the potential difference and the holes can be seen to flow in one direction resulting in an electric current flow. It is harder for holes to move than for free electrons to move and so the mobility of holes is less than that of free electrons. Holes are positively charged carriers.
When the doped semiconductor contains mostly free electrons it is known as n-type. In N-type semiconductor, the electrons are the charge carriers. It flows from high potential to low potential. The electrons are negatively charged carriers.
Properties of semiconductor
When two differently doped semiconducting materials are joined together Heterojunctions occur. For example, it consists of p-doped and n-doped germanium. This results in an exchange of electrons and holes between these differently doped semiconducting materials.
The n-doped germanium would have a large number of electrons, And the p-doped germanium would have a large number of holes. The transfer continuously occurs until equilibrium is reached by a process called recombination, This causes the migrating electrons from the n-type region to come in contact with the migrating holes from the p-type region.
A product of this process is charged ions due to an electric field.
Variable electrical conductivity
In a natural state, the semiconductors are poor conductors because a current requires the flow of electrons, and valence bands of semiconductors have filled, that preventing the entire flow of new free electrons.
There are several techniques that allow semiconducting materials to behave like conducting materials, such as gating or doping. These modifications of semiconductors have two outcomes: n-type semiconductor and p-type semiconductor.
These refer to the excess of electrons. An unbalanced number of electrons would allow a current to flow through the material.
In certain semiconductors, excited electrons can de-excited by emitting light instead of producing heat.
These semiconductors are used in the construction of fluorescent quantum diodes and light-emitting diodes.
A difference in electric potential on a semiconductor would cause it to leave thermal equilibrium and create a non-equilibrium situation. This introduces more numbers of electrons and holes to the system. When thermal equilibrium is unstable in a semiconducting material the number of holes and electrons changes.
Such disturbance can occur as a result of a temperature difference, which can enter the system and create electrons and holes. The processes of creation and annihilates of electrons and holes pairs are called generation and recombination.
High thermal conductivity
Semiconductors that have high thermal conductivity can be used for heat dissipation and improving the thermal management of electronics.
Silicon crystals are the most common semiconducting materials used in photovoltaics and microelectronics. A large number of elements and compounds those posses semiconducting properties, including:
- Certain pure elements are found in fourth group of the periodic table.
The most important of these elements are silicon and germanium. Silicon and germanium are used here effectively because they have four valence electrons in their outermost shell. That gives them the ability to gain or lose electrons equally at the same time.
- Binary compounds, particularly between elements in Groups three and five, such as gallium arsenide.
- Certain ternary compounds, oxides, and alloys.
- Organic semiconductors made up of organic compounds.
Most common semiconducting materials are in crystalline solids form, but liquid and amorphous semiconductors are also known.