An intrinsic semiconductor is a pure form of semiconductor material without any significant impurities added. Common materials used as intrinsic semiconductors include silicon (Si) and germanium (Ge). In their pure state, these materials have an electrical conductivity that is neither high like conductors nor low like insulators, but somewhere in between.
Semiconductors are materials that possess electrical conductivity between that of insulators and conductors, making them indispensable in modern electronics. This article delves into intrinsic semiconductors, providing a comprehensive understanding of their definition, working mechanism, key properties, Fermi level, and applications.
Definition of Intrinsic Semiconductor
An intrinsic semiconductor is a pure semiconductor without any significant impurities. It is typically made from crystalline silicon or germanium. Unlike extrinsic semiconductors, which contain impurities (dopants) that alter their electrical properties, intrinsic semiconductors are used in their pure form. This purity allows for the study of the semiconductor’s true electrical properties.
An intrinsic semiconductor is a type of semiconductor that is not doped with any impurities. It is also known as a pure semiconductor, updoped semiconductor or an i-type semiconductor.
Working Mechanism of Intrinsic Semiconductor
The working mechanism of intrinsic semiconductors is governed by the generation and recombination of electron-hole pairs. At absolute zero temperature, intrinsic semiconductors behave like insulators because all the valence electrons are bound, and the conduction band is empty. However, as the temperature rises, some electrons gain enough energy to jump from the valence band to the conduction band, leaving behind holes in the valence band. This process is known as thermal generation.
The electrons that jump to the conduction band become free to conduct electricity. At the same time, the holes they leave behind also contribute to electrical conductivity by moving from one place to another within the valence band. This dual contribution to conductivity from electrons and holes is a unique characteristic of semiconductors.
Properties of Intrinsic Semiconductor
- Electrical Conductivity: Intrinsic semiconductors have lower conductivity than extrinsic semiconductors because their conductivity relies solely on the thermal generation of carriers.
- Temperature Dependence: The conductivity of intrinsic semiconductors increases with temperature as more electron-hole pairs are generated.
- Band Gap: Intrinsic semiconductors typically have a moderate band gap, which allows for the generation of carriers at practical temperatures but remains sufficient to control carrier generation effectively.
Fermi Level in Intrinsic Semiconductors
The Fermi level in an intrinsic semiconductor is particularly important because it represents the energy level at which the probability of finding an electron is 50%. In intrinsic semiconductors, the Fermi level is approximately midway between the conduction and valence bands at absolute zero. This central position changes slightly with temperature due to the slight asymmetry in the density of states in the conduction and valence bands.
Examples of Intrinsic Semiconductor
Here are some common examples of intrinsic semiconductors:
- Silicon (Si)
- Germanium (Ge)
- Gallium Arsenide (GaAs)
- Indium Antimonide (InSb)
- Silicon Carbide (SiC)
- Boron arsenide (BAs)
- Gray tin (α-Sn)
Uses of Intrinsic Semiconductor
Intrinsic semiconductors find applications in areas where high purity and controlled electrical properties are necessary:
- Photovoltaic Cells: Used in solar cells, where pure semiconductors are required to effectively convert sunlight into electricity.
- Detectors and Imaging Devices: Employed in the fabrication of sensors and imaging devices that require sensitive response to light or radiation.
- High-Purity Semiconductor Devices: Used in certain high-frequency and high-temperature semiconductor devices where the introduction of impurities might degrade performance.
- They are used in the manufacturing of diodes and transistors. Impurities are added to the intrinsic semiconductor to increase its conductivity; this process is called doping.
Conclusion
Intrinsic semiconductors, with their unique properties and mechanisms, play a crucial role in the foundation of semiconductor physics and technology. Understanding these materials is essential for advancing electronic technology, particularly in developing devices that require high levels of purity and precision. Whether in solar cells, sensors, or advanced computing elements, intrinsic semiconductors continue to be a key component of innovative electronic solutions.