adminINTRINSIC SEMICONDUCTORS
An intrinsic semiconductor is a pure or un-doped semiconductor crystal with no significant impurities.
At very low temperature (i.e. absolute zero), it behaves like an insulator but as the temperature rises, thermal energy excites electrons from the valence band to the conduction band , creating equal numbers of free electrons and holes thereby enabling conducting and electron flow.
There are two main types of intrinsic semiconductors and they are; elemental and compound intrinsic semiconductors.
Elemental intrinsic semiconductors are made from a single element in the periodic table, typically group IV elements with four valence electrons, allowing covalent bonding in a diamond cubic structure. Example of elemental intrinsic semiconductors includes; silicon (Si), germanium (Ge), carbon (diamond form), Tin (grey/alpha-Sn), selenium (Se) etc.
Compound intrinsic semiconductors combine two or more different elements, typically from group III and group V (III-V compounds or group II and group VI (II-VI compounds). The bonding of compound intrinsic semiconductors are largely covalent but with some ionic character. Example of compound intrinsic semiconductors includes; the binary compounds gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), cadmium sulfide (CdS), cadmium telluride (CdTe) and the tenary/quaternary or advanced compounds such as aluminum gallium arsenide (AlGaAs), indium Gallium nitride (InGaN), mercury cadium telluride (HgCdTe) etc.
The advantages of intrinsic semiconductors are; since intrinsic semiconductors are pure their electrical behavior are predictable. Intrinsic semiconductors have high electron mobility thereby enhancing their electron flow efficiently. Intrinsic semiconductors exhibit low noise level in operation, making them suitable for highly sensitive applications. Intrinsic semiconductors can operate at high temperatures without significant degradation.
The disadvantages of intrinsic semiconductors are; intrinsic semiconductors have limited conductivity which can make them unsuitable for high current applications. Intrinsic semiconductors are sensitive to impurities, which can alter their electrical properties. Intrinsic semiconductors are difficult to dope with impurities, which can limit their use in certain applications. Intrinsic semiconductors require extremely high purity (often 99.9999% or higher) to behave as theoretically predicted, thereby driving up manufacturing costs and complexity.
Intrinsic semiconductors find application in the following; intrinsic semiconductors such as gallium arsenide (GaAs) and indium phosphide(InP) are used in high frequency devices such as microwave amplifiers, millimeter wave devices etc.. high purity intrinsic semiconductors such as germanium and silicon are used in radiation detectors (i.e. gamma-ray spectrometers). Intrinsic semiconductors such as silicon (Si) and gallium arsenide (GaAs) are being researched for their potential quantum computing applications.
The future of intrinsic semiconductors is based on the advances and development of the following technologies; ultra-pure crystal growth advancement will continue to push purity levels even higher, benefiting intrinsic semiconductor use and applications. Diamond, silicon carbide (SiC) and gallium nitride (GaN) in their intrinsic forms are being explored for extreme environment electronics. 2D intrinsic semiconductor material like grapheme, molybdenum disulfide (MoS2) and others are being researched in their un-doped forms for ultra-thin flexible and transparent electronics. Intrinsic semiconductors nanostructures are being explored as qubit hosts and single photon sources for quantum information systems. Also continued refinement of high purity germanium and silicon detectors is ongoing for medical imaging, nuclear security and astrophysics instrumentation applications. Research into intrinsic semiconductors made from more abundant, less toxic elements to reduce dependence on rare or hazardous materials particularly for solar energy applications.
SOURCES:
- Semiconductor physics and devices by Donald A. Neamen.
- Semiconductor: A modern materials perspective by Peter Y. Yu and Manuel Cardona.
- The physics of semiconductors by Walter A. Harrison.
- Introduction to semiconductor devices by M.S Tyagi.
- Semiconductor physics: An introduction by Karlheinz Seeger.
