Intrinsic semiconductors are materials that have a natural ability to conduct electricity under certain conditions, but their conductivity is relatively low compared to conductors like metals. These materials are pure and contain no intentional dopants or impurities that would significantly alter their electrical properties.
In an intrinsic semiconductor, such as silicon (Si) or germanium (Ge), the valence electrons in the crystal lattice are shared between atoms, forming covalent bonds. At absolute zero temperature (0 Kelvin or -273.15 degrees Celsius), all electrons are in their lowest energy state, the valence band, and there are no electrons available in the conduction band to carry an electric current.
However, at higher temperatures or with the application of energy, electrons can gain enough energy to break free from their covalent bonds and move to the conduction band, creating "holes" or vacant positions in the valence band. These mobile electrons and holes are responsible for the conductivity of intrinsic semiconductors.
Key concepts related to intrinsic semiconductors:
Energy Band Diagram: This diagram illustrates the relationship between the energy levels of the valence and conduction bands. The energy gap between the two bands is called the "band gap." In intrinsic semiconductors, the band gap is relatively large, which means that a significant amount of energy is required to move an electron from the valence band to the conduction band.
Intrinsic Carrier Concentration (ni): At a given temperature, there is a certain concentration of mobile electrons and holes that exists due to thermal excitation. This concentration is known as the intrinsic carrier concentration (ni). The ni value increases with temperature due to more electrons gaining sufficient energy to move to the conduction band.
Intrinsic Conductivity: Intrinsic semiconductors have relatively low conductivity compared to metals. The conductivity (σ) of a material is related to its carrier concentration (n) and mobility (μ) of charge carriers (electrons and holes). The relationship is given by the equation σ = q * n * μ, where q is the elementary charge.
Temperature Dependence: The conductivity of intrinsic semiconductors increases with temperature. This is because higher temperatures provide more thermal energy to electrons, allowing a greater number of them to move to the conduction band.
Doping: The electrical properties of intrinsic semiconductors can be greatly modified through a process called doping, where specific impurities are intentionally introduced into the crystal lattice. Doping can increase the conductivity and tailor the semiconductor's behavior for specific electronic applications.
In summary, intrinsic semiconductors have unique electrical properties that make them useful for a variety of electronic devices, ranging from diodes and transistors to solar cells and integrated circuits. Their behavior can be modified through doping to optimize their performance in different applications.