An intrinsic semiconductor is a pure semiconductor material with no intentional impurities added through the process of doping. It's composed of a single-element crystal such as silicon (Si) or germanium (Ge) in its pure form. In this state, the semiconductor possesses its own unique electrical properties.
Properties of Intrinsic Semiconductor:
1. Electron-Hole Generation:
- At absolute zero temperature (0 K), an intrinsic semiconductor acts as an insulator because all electrons are tightly bound to their atoms.
- As temperature increases, some electrons gain enough thermal energy to break free from their covalent bonds, leaving behind holes (vacancies in the crystal lattice).
2. Carrier Generation:
- Electrons that break free from the covalent bonds become free electrons available for conduction.
- The holes, created due to the absence of electrons, act as positive charge carriers.
3. Electron-Hole Recombination:
- Electrons and holes can recombine: a free electron can fall into a hole, neutralizing both and releasing energy in the form of heat or light.
4. Intrinsic Carrier Concentration (ni):
- At a certain temperature, thermal energy promotes electrons to the conduction band, creating electron-hole pairs.
- Intrinsic carrier concentration represents the density of electrons and holes in an intrinsic semiconductor at thermal equilibrium.
5. Band Gap:
- The energy difference between the valence band (where electrons are tightly bound) and the conduction band (where electrons are free to move) is known as the band gap.
- For silicon, the band gap is approximately 1.1 eV, while for germanium, it's around 0.7 eV.
6. Electrical Conductivity:
- Intrinsic semiconductors exhibit moderate electrical conductivity due to the presence of both electrons and holes, which contribute to charge transport.
7. Temperature Dependence:
- As temperature increases, more electron-hole pairs are generated, leading to an increase in conductivity.
Intrinsic vs. Extrinsic Semiconductors:
- Intrinsic Semiconductor:
- Pure semiconductor material with no intentional impurities.
- Conductivity arises due to thermal excitation of electrons across the band gap.
- Extrinsic Semiconductors:
- Doped semiconductor with intentional impurities (P-type or N-type).
- Conductivity is significantly enhanced by introducing dopants that increase the density of charge carriers.
Applications:
- Basis for Semiconductor Devices:
- Intrinsic semiconductors form the foundation for various semiconductor devices like diodes, transistors, and integrated circuits.
- Extrinsic semiconductors (P-type and N-type) are essential for creating the desired electronic properties in these devices through controlled doping.
Understanding intrinsic semiconductors is crucial as it forms the starting point for comprehending the behavior of doped or extrinsic semiconductors used in modern electronic devices and circuits.
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