Semiconductor
Semiconductor device fabrication |
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MOSFET scaling (process nodes) |
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A semiconductor is a material that has an
The conductivity of silicon is increased by adding a small amount (of the order of 1 in 108) of pentavalent (antimony, phosphorus, or arsenic) or trivalent (boron, gallium, indium) atoms. This process is known as doping, and the resulting semiconductors are known as doped or extrinsic semiconductors. Apart from doping, the conductivity of a semiconductor can be improved by increasing its temperature. This is contrary to the behavior of a metal, in which conductivity decreases with an increase in temperature.
The modern understanding of the properties of a semiconductor relies on
A few of the properties of semiconductor materials were observed throughout the mid-19th and first decades of the 20th century. The first practical application of semiconductors in electronics was the 1904 development of the
Properties
Variable electrical conductivity
Semiconductors in their natural state are poor conductors because a
Heterojunctions
Excited electrons
A difference in electric potential on a semiconducting material would cause it to leave thermal equilibrium and create a non-equilibrium situation. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion. Whenever thermal equilibrium is disturbed in a semiconducting material, the number of holes and electrons changes. Such disruptions can occur as a result of a temperature difference or photons, which can enter the system and create electrons and holes. The processes that create or annihilate electrons and holes are called generation and recombination, respectively.[6]
Light emission
In certain semiconductors, excited electrons can relax by emitting light instead of producing heat.[7] Controlling the semiconductor composition and electrical current allows for the manipulation of the emitted light's properties.[8] These semiconductors are used in the construction of light-emitting diodes and fluorescent quantum dots.
High thermal conductivity
Semiconductors with high thermal conductivity can be used for heat dissipation and improving thermal management of electronics. They play a crucial role in electric vehicles, high-brightness LEDs and power modules, among other applications.[9][10][11]
Thermal energy conversion
Semiconductors have large
Materials
A large number of elements and compounds have semiconducting properties, including:[13]
- Certain pure elements are found in group 14 of the periodic table; the most commercially important of these elements are silicon and germanium. Silicon and germanium are used here effectively because they have 4 valence electrons in their outermost shell, which gives them the ability to gain or lose electrons equally at the same time.
- Binary compounds, particularly between elements in groups 13 and 15, such as gallium arsenide, groups 12 and 16, groups 14 and 16, and between different group-14 elements, e.g. silicon carbide.
- Certain ternary compounds, oxides, and alloys.
- Organic semiconductors, made of organic compounds.
- Semiconducting metal–organic frameworks.[14][15]
The most common semiconducting materials are crystalline solids, but
Preparation of semiconductor materials
Almost all of today's electronic technology involves the use of semiconductors, with the most important aspect being the
A high degree of crystalline perfection is also required, since faults in the crystal structure (such as dislocations, twins, and stacking faults) interfere with the semiconducting properties of the material. Crystalline faults are a major cause of defective semiconductor devices. The larger the crystal, the more difficult it is to achieve the necessary perfection. Current mass production processes use crystal ingots between 100 and 300 mm (3.9 and 11.8 in) in diameter, grown as cylinders and sliced into wafers.
There is a combination of processes that are used to prepare semiconducting materials for ICs. One process is called
The etching is the next process that is required. The part of the silicon that was not covered by the
The last process is called diffusion. This is the process that gives the semiconducting material its desired semiconducting properties. It is also known as doping. The process introduces an impure atom to the system, which creates the p–n junction. To get the impure atoms embedded in the silicon wafer, the wafer is first put in a 1,100 degree Celsius chamber. The atoms are injected in and eventually diffuse with the silicon. After the process is completed and the silicon has reached room temperature, the doping process is done and the semiconducting material is ready to be used in an integrated circuit.[3][6]
Physics of semiconductors
Energy bands and electrical conduction
Semiconductors are defined by their unique electric conductive behavior, somewhere between that of a conductor and an insulator.
High conductivity in material comes from it having many partially filled states and much state delocalization. Metals are good electrical conductors and have many partially filled states with energies near their Fermi level.
A pure semiconductor, however, is not very useful, as it is neither a very good insulator nor a very good conductor. However, one important feature of semiconductors (and some insulators, known as semi-insulators) is that their conductivity can be increased and controlled by doping with impurities and gating with electric fields. Doping and gating move either the conduction or valence band much closer to the Fermi level and greatly increase the number of partially filled states.
Some wider-bandgap semiconductor materials are sometimes referred to as semi-insulators. When undoped, these have electrical conductivity nearer to that of electrical insulators, however they can be doped (making them as useful as semiconductors). Semi-insulators find niche applications in micro-electronics, such as substrates for HEMT. An example of a common semi-insulator is gallium arsenide.[19] Some materials, such as titanium dioxide, can even be used as insulating materials for some applications, while being treated as wide-gap semiconductors for other applications.
Charge carriers (electrons and holes)
The partial filling of the states at the bottom of the conduction band can be understood as adding electrons to that band. The electrons do not stay indefinitely (due to the natural thermal
For partial filling at the top of the valence band, it is helpful to introduce the concept of an electron hole. Although the electrons in the valence band are always moving around, a completely full valence band is inert, not conducting any current. If an electron is taken out of the valence band, then the trajectory that the electron would normally have taken is now missing its charge. For the purposes of electric current, this combination of the full valence band, minus the electron, can be converted into a picture of a completely empty band containing a positively charged particle that moves in the same way as the electron. Combined with the negative effective mass of the electrons at the top of the valence band, we arrive at a picture of a positively charged particle that responds to electric and magnetic fields just as a normal positively charged particle would do in a vacuum, again with some positive effective mass.[18] This particle is called a hole, and the collection of holes in the valence band can again be understood in simple classical terms (as with the electrons in the conduction band).
Carrier generation and recombination
When ionizing radiation strikes a semiconductor, it may excite an electron out of its energy level and consequently leave a hole. This process is known as electron-hole pair generation. Electron-hole pairs are constantly generated from thermal energy as well, in the absence of any external energy source.
Electron-hole pairs are also apt to recombine. Conservation of energy demands that these recombination events, in which an electron loses an amount of energy larger than the band gap, be accompanied by the emission of thermal energy (in the form of phonons) or radiation (in the form of photons).
In some states, the generation and recombination of electron-hole pairs are in equipoise. The number of electron-hole pairs in the
As the probability that electrons and holes meet together is proportional to the product of their numbers, the product is in the steady-state nearly constant at a given temperature, providing that there is no significant electric field (which might "flush" carriers of both types, or move them from neighbor regions containing more of them to meet together) or externally driven pair generation. The product is a function of the temperature, as the probability of getting enough thermal energy to produce a pair increases with temperature, being approximately exp(−EG/kT), where k is
The probability of meeting is increased by carrier traps – impurities or dislocations which can trap an electron or hole and hold it until a pair is completed. Such carrier traps are sometimes purposely added to reduce the time needed to reach the steady-state.[20]
Doping
The conductivity of semiconductors may easily be modified by introducing impurities into their
A 1 cm3 specimen of a metal or semiconductor has the order of 1022 atoms.[24] In a metal, every atom donates at least one free electron for conduction, thus 1 cm3 of metal contains on the order of 1022 free electrons,[25] whereas a 1 cm3 sample of pure germanium at 20 °C contains about 4.2×1022 atoms, but only 2.5×1013 free electrons and 2.5×1013 holes. The addition of 0.001% of arsenic (an impurity) donates an extra 1017 free electrons in the same volume and the electrical conductivity is increased by a factor of 10,000.[26][27]
The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. In general, dopants that produce the desired controlled changes are classified as either electron
For example, the pure semiconductor
During manufacture, dopants can be diffused into the semiconductor body by contact with gaseous compounds of the desired element, or ion implantation can be used to accurately position the doped regions.
Amorphous semiconductors
Some materials, when rapidly cooled to a glassy amorphous state, have semiconducting properties. These include B, Si, Ge, Se, and Te, and there are multiple theories to explain them.[31][32]
Early history of semiconductors
The history of the understanding of semiconductors begins with experiments on the electrical properties of materials. The properties of the time-temperature coefficient of resistance, rectification, and light-sensitivity were observed starting in the early 19th century.
A unified explanation of these phenomena required a theory of
Agreement between theoretical predictions (based on developing quantum mechanics) and experimental results was sometimes poor. This was later explained by John Bardeen as due to the extreme "structure sensitive" behavior of semiconductors, whose properties change dramatically based on tiny amounts of impurities.[34] Commercially pure materials of the 1920s containing varying proportions of trace contaminants produced differing experimental results. This spurred the development of improved material refining techniques, culminating in modern semiconductor refineries producing materials with parts-per-trillion purity.
Devices using semiconductors were at first constructed based on empirical knowledge before semiconductor theory provided a guide to the construction of more capable and reliable devices.
The first semiconductor devices used galena, including German physicist Ferdinand Braun's crystal detector in 1874 and Indian physicist Jagadish Chandra Bose's radio crystal detector in 1901.[38][39]
In the years preceding World War II, infrared detection and communications devices prompted research into lead-sulfide and lead-selenide materials. These devices were used for detecting ships and aircraft, for infrared rangefinders, and for voice communication systems. The point-contact crystal detector became vital for microwave radio systems since available vacuum tube devices could not serve as detectors above about 4000 MHz; advanced radar systems relied on the fast response of crystal detectors. Considerable research and development of silicon materials occurred during the war to develop detectors of consistent quality.[34]
Early transistors
Detector and power rectifiers could not amplify a signal. Many efforts were made to develop a solid-state amplifier and were successful in developing a device called the
The first working
In 1954,
See also
- Deathnium
- Semiconductor device fabrication
- Semiconductor industry
- Semiconductor characterization techniques
- Transistor count
References
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- ^ a b c d Feynman, Richard. Feynman Lectures on Physics.
- ^ "2.4.7.9 The "hot-probe" experiment". ecee.colorado.edu. Archived from the original on 6 March 2021. Retrieved 27 November 2020.
- ISBN 978-0-88275-382-9.
- ^ a b c d e f g Neamen, Donald. "Semiconductor Physics and Devices" (PDF). Elizabeth A. Jones.
- ^ By Abdul Al-Azzawi. "Light and Optics: Principles and Practices." 2007. March 4, 2016.
- ^ "Electrical Property of Semiconductor - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-12-14.
- ISBN 978-953-51-2637-9, retrieved 2024-01-24
- ^ Arik, Mehmet, and Stanton Weaver. "Chip-scale thermal management of high-brightness LED packages." Fourth International Conference on Solid State Lighting. Vol. 5530. SPIE, 2004.
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- ^ "How do thermoelectric coolers (TECs) work?". ii-vi.com. Retrieved 2021-11-08.
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- ^ Nave, R. "Doped Semiconductors". Retrieved May 3, 2021.
- ^ Y., Roshni (5 February 2019). "Difference Between Intrinsic and Extrinsic Semiconductors". Retrieved May 3, 2021.
- ^ "Lesson 6: Extrinsic semiconductors" (PDF). Archived from the original (PDF) on January 28, 2023. Retrieved January 28, 2023.
- ^ "General unit cell problems". Retrieved May 3, 2021.
- ^ Nave, R. "Ohm's Law, Microscopic View". Archived from the original on May 3, 2021. Retrieved May 3, 2021.
- ^ Van Zeghbroeck, Bart (2000). "Carrier densities". Archived from the original on May 3, 2021. Retrieved May 3, 2021.
- ^ "Band strcutre and carrier concentration (Ge)". Retrieved May 3, 2021.
- ^ "Doping: n- and p-semiconductors". Retrieved May 3, 2021.
- ^ Nave, R. "Silicon and Germanium". Retrieved May 3, 2021.
- ^ Honsberg, Christiana; Bowden, Stuart. "Semiconductor Materials". Retrieved May 3, 2021.
- ^ "Amorphous semiconductors 1968" (PDF).
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- ^ ISBN 9780863412271– via Google Books.
- ^ a b Lidia Łukasiak & Andrzej Jakubowski (January 2010). "History of Semiconductors" (PDF). Journal of Telecommunication and Information Technology: 3. Archived from the original (PDF) on 2013-06-22. Retrieved 2012-08-03.
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- ^ Überlingen.), Josef Weiss (de (July 22, 1910). "Experimentelle Beiträge Zur Elektronentheorie Aus dem Gebiet der Thermoelektrizität, Inaugural-Dissertation ... von J. Weiss, ..." Druck- und Verlags-Gesellschaft – via Google Books.
- ^ "Timeline". The Silicon Engine. Computer History Museum. Retrieved 22 August 2019.
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- ^ "1947: Invention of the Point-Contact Transistor". The Silicon Engine. Computer History Museum. Retrieved 23 August 2019.
- ^ "1954: Morris Tanenbaum fabricates the first silicon transistor at Bell Labs". The Silicon Engine. Computer History Museum. Retrieved 23 August 2019.
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Further reading
- A. A. Balandin & K. L. Wang (2006). Handbook of Semiconductor Nanostructures and Nanodevices (5-Volume Set). American Scientific Publishers. ISBN 978-1-58883-073-9.
- ISBN 978-0-471-05661-4.
- Turley, Jim (2002). The Essential Guide to Semiconductors. Prentice Hall PTR. ISBN 978-0-13-046404-0.
- Yu, Peter Y.; Cardona, Manuel (2004). Fundamentals of Semiconductors: Physics and Materials Properties. Springer. ISBN 978-3-540-41323-3.
- Sadao Adachi (2012). The Handbook on Optical Constants of Semiconductors: In Tables and Figures. World Scientific Publishing. ISBN 978-981-4405-97-3.
- G. B. Abdullayev, T. D. Dzhafarov, S. Torstveit (Translator), Atomic Diffusion in Semiconductor Structures, Gordon & Breach Science Pub., 1987 ISBN 978-2-88124-152-9