This article will discuss the function and construction of semiconductors and upcoming semiconductor innovations that are set to promote a more efficient and electronically connected future.
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A semiconductor material is one that has a variable conductivity and resistivity value depending on temperature, besides other features such as crystal arrangement, which are specific to the material, but generally fall between that of conductive copper and insulating glass. A semiconductor electronic component, therefore, is constructed from one or more semiconducting materials such as silicon, germanium, or gallium arsenide, often modified chemically in a method known as “doping” in order to fine-tune the resistive properties of the semiconductor.
What are Semiconductors Made From?
Semiconductors are typically constructed from silicon, as it is low cost compared to competitor materials and can be fairly easily fabricated into wafers. Metals such as germanium and several gallium crystals are also often used but are generally more difficult to fabricate into large wafers than silicon, though in some cases offer specific benefits that make their use viable.
For example, gallium nitride has a band gap three times larger than silicon and conducts electrons 1,000 times more efficiently, as well as possessing higher strength and thermal conductivity, making it useful in light-emitting diodes and radiofrequency components. Germanium was actually discovered earlier than silicon as a useful semiconducting material in 1886 but was quickly replaced owing to cost. In more recent decades, a plethora of more complex semiconductor materials have been investigated, leading to a number of semiconductor innovations.
The number of valence electrons available in a semiconductor material determines its conductivity; silicon has four, while gallium arsenide has eight, three from gallium, and five from arsenic. Tin oxide has 16 valence electrons and has increasingly been explored for applications in thin-film transistors owing to high carrier mobility, useful in flat panel displays and similar low-profile devices.
Speed is not the only consideration when it comes to semiconductors; one must also consider the frequency of the electrical signal which is similarly influenced by semiconductor material. For example, most communication is via radiowaves in the high MHz to GHz region, which silicon semiconductor components can interpret. As 5G is rolled out, capable of 100 GHz, silicon-only semiconductors may be unable to keep pace as high-power receivers and need to be replaced with mixed element semiconducting materials such as gallium nitride.
What Future Semiconductor Innovations Are Expected?
Nano-conductive components such as gold nanowires or graphene are increasingly incorporated with advanced semiconductor innovations in the generation of novel electronic devices. Graphene is a two-dimensional network of sp2 hybridized carbon atoms in a hexagonal structure, with a delocalized electron cloud connected by π-conjugation.
Graphene has high electrical conductivity and extremely fast electron mobility, large surface area, good optical transmittance, and is much stronger than steel in a mass-for-mass comparison while maintaining flexibility. Graphene itself is a zero-gap semiconductor, in that the conduction and valence band energies are touching, and thus there is no threshold energy requirement for promoting an electron, while the resistivity of the material is influenced by conditions such as temperature, flex, number of graphene layers, pressure, the presence of magnetic fields, or by traditional doping.
The use of bilayer graphene allows changes in band structure to be induced by the electric field effect between the two layers, which has allowed graphene to see use in flexible sensors and similar technologies. Traditional semiconductors can also be incorporated with graphene-based electronics to produce novel semiconductor innovations, taking advantage of the unique properties of graphene in conventional electronics.
Graphene may be set to replace silicon as the go-to material for semiconductors, as the iterant improvements made to silicon semiconductors over the last 50 years, which roughly followed Moore’s law, wherein the number of transistors on a circuit board doubles every two years (the year number has varied), appear to have slowed significantly.
The power of newly designed computer processors has plateaued since around 2010 compared to previous decades, and squeezing additional performance from silicon-based semiconductors is becoming increasingly costly with regard to research and development. Part of the reason for this limitation is the extremely close packing of transistors, to such an extent that quantum effects such as tunneling can occur, wherein an electron is able to pass the potential energy barrier and jump to an adjacent transistor.
This and other quantum phenomena are exploited in quantum computing, drastically improving computation speed over traditional processors by allowing superpositioning to occur, i.e., in binary coding, qubits can be 0 and 1 simultaneously. Graphene is of great interest as a semiconductor material in quantum computing, partially owing to its potentially multi-layered structure if engineered with gating structures connecting the layers. For example, quantum dots are semiconductor nanocrystals, often constructed from materials such as cadmium and selenium, germanium, gold, and even carbon, which can be placed between graphene layers as an electron transfer agent.
Future semiconductors are likely to be constructed from new and innovative materials such as graphene and advanced metal-ceramics where applications demand more power and higher frequencies than silicon is able to handle. The broad availability of silicon will ensure that it is to be used at least for decades to come, however, and semiconductor innovations surrounding silica alloys continue to be produced in spite of a slowing pace of improvements, even with useful applications in quantum computing.
What is the Role of the Depletion Region in a Semiconductor PN Junction?
References and Further Reading
Jing, F., Zhang, Z., Qin, G., Luo, G., Cao, G., Li, H., Song, X., & Guo, G. (2022). Gate‐Controlled Quantum Dots Based on 2D Materials. Advanced Quantum Technologies, 5(6), 2100162. https://doi.org/10.1002/qute.202100162
Obeng, Y. & Srinivasan, P. (2011). Graphene: Is It the Future for Semiconductors? An Overview of the Material, Devices, and Applications. The Electrochemical Society. https://www.electrochem.org/dl/interface/spr/spr11/spr11_p047-052.pdf
International roadmap for devices and systems. Semiconductor Materials. https://irds.ieee.org/topics/semiconductor-materials
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