Semiconductor materials have the same conductive properties as that of insulators and conductors. They can be comprised of pure elements like silicon or germanium or can be compounded between two elements, such as gallium arsenide or cadmium selenide. Semiconductor materials can be doped by adding impurities to pure semiconductors, which alters their conductive properties.
Semiconductor devices can display a range of useful properties such as showing variable resistance, passing current more easily in one direction than the other, and reacting to light and heat. Their actual function includes the amplification of signals, switching, and energy conversion.
Therefore, they find widespread use in almost all industries, and the companies that manufacture and test them are considered to be excellent indicators of the health of the overall economy.
The semiconductor industry is a hugely important sector for both the U.S. and world economies, with semiconductor components found in a wide range of consumer and commercial products from vehicles to computers to mobile devices and personal electronics.
Because silicon covers 28% of Earth’s surface, it is considered a common material, with an atomic number of 14. Figure 1 shows silicon’s atomic structure: There are four electrons, known as valence electrons, in silicon’s outer ring. In some cases, these valence electrons can bond with the valence electrons of other atoms. When this happens, a covalent bond is formed, resulting in the formation of a lattice crystalline structure.
The most common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are also known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium, and tellurium in a variety of proportions. These compounds share with better-known semiconductors the properties of intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance. Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon. They are generally used in thin film structures, which do not require material of higher electronic quality, being relatively insensitive to impurities and radiation damage.
Pure silicon is a good insulator, meaning no electrical conduction can take place through it. However, if some impurities are added to a pure silicon structure, the conduction properties of this semiconductor can be modified.
In the doping process, impurities are added to a pure semiconductor material, making it extrinsic (versus a pure semiconductor, which is intrinsic). Some of the most common types of impurities are trivalent (three valence electrons), such as boron and gallium, and pentavalent (five valence electrons), such as arsenic and antimony.
Let’s say a pure silicon semiconductor is doped with arsenic, a pentavalent impurity. Four valence electrons of arsenic will form a covalent bond with the four valence electrons of silicon, while one electron from the arsenic remains free. In this example, arsenic essentially “donated” a free electron to the silicon structure.
All pentavalent impurities “donate” free electrons and are known as donor impurities. As a result, in the structure formed (see Figure 2), conduction takes place by electrons and the crystal is called an N-type crystal.
Trivalent impurities can use only three electrons to form covalent bonds; thus, one more electron will be needed to complete the lattice structure and a hole will remain in the place of the missing electron. Because this hole can accept an electron, a trivalent impurity is called an acceptor impurity. In the resulting structure, conduction takes place by positive holes and the crystal is called a P-type crystal.
A large number of elements and compounds have semiconducting properties, including|:
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.
An n-type semiconductor is an impurity mixed semiconductor that uses pentavalent impure atoms like phosphorus, arsenic, antimony, and bismuth.
A p-type semiconductor is a type of extrinsic semiconductor that contains trivalent impurities such as boron and aluminum which increases the level of conductivity of a normal semiconductor made purely of silicon.
An intrinsic or pure semiconductor is a semiconductor that does not have any impurities or dopants added to it, as in the case of p-type and n-type semiconductors. In intrinsic semiconductors, the number of excited electrons and the number of holes are equal: n = p.
In P-type semiconductors, Group III elements of the periodic table are added as the dopant element, while in N-type semiconductors, the Group V element acts as the dopant element. In P-type semiconductors, the majority carriers are holes and the minority carriers are electrons.
The p–n junction is an interface composed of two differently doped semiconductor types. In the P zone, there are trivalent doping elements with one more gap (more positive charge) than the semiconductor of which the junction is formed, while in the N zone, there are pentavalent doping elements with an electron more (more negative charge).
“Junction” refers to the region where the two types of doping (P and N) connect. Therefore, if the P-type and N-type layers are put close together, an emptying zone is created in the junction. This takes place as the holes in the P zone tend to approach the N layer and the electrons in the N zone tend to move toward the P zone. The emptying area, therefore, appears to be devoid of charges as the neighboring ones neutralize each other.
As a result, in the junction, an electric field is created that goes from right to left (from plus to minus) and a difference in potential delta V with the opposite direction to the electric field.
The P zone of the semiconductor is also called the acceptor zone, as it accepts electrons into its zone, while the N zone is also called the donor zone, as it donates electrons to the P zone.
Let’s say a p–n junction was electronically connected with a battery, as shown in Figure 3. If the P area of the junction was connected to the positive pole of the battery and the N area to the negative pole of the battery, it can be said that the p–n junction is connected in direct polarization.
In this instance, the p–n junction will be crossed by a current, as the negative charges of the N area get attracted to the positive pole of the battery. As this takes place, after having overcome the potential difference of the junction, they reach the positive pole of the battery. Simultaneously, at the same time, the holes get neutralized by the electrons.
Furthermore, if the p–n junction gets connected in reverse polarization, the connection should be to the P area with the negative pole of the battery and the N area with the positive pole of the battery. During this period, no current will circulate inside the junction, as the emptying area will widen, not allowing any charge to pass through it.
The diode is a passive, non-linear electronic component with two terminals whose function is to be crossed by the current only in one direction, the direct polarization, and not to be crossed by the current when polarization is inverse.
Broadly speaking, semiconductors fall into four main product categories:
Memory chips serve as temporary storehouses of data and pass information to and from computer devices’ brains. The consolidation of the memory market continues, driving memory prices so low that only a few giants like Toshiba, Samsung, and NEC can afford to stay in the game.
These are central processing units that contain the basic logic to perform tasks. Intel’s domination of the microprocessor segment has forced nearly every other competitor, with the exception of Advanced Micro Devices, out of the mainstream market and into smaller niches or different segments altogether.
Sometimes called “standard chips”, these are produced in huge batches for routine processing purposes. Dominated by very large Asian chip manufacturers, this segment offers razor-thin profit margins that only the biggest semiconductor companies can compete for.
“System on a Chip” is essentially all about the creation of an integrated circuit chip with an entire system’s capability on it. The market revolves around the growing demand for consumer products that combine new features and lower prices. With the doors to the memory, microprocessor, and commodity integrated circuit markets tightly shut, the SOC segment is arguably the only one left with enough opportunity to attract a wide range of companies.
Here we have discussed some advantages of semiconductors which makes them highly useful everywhere.
1. The energy of a photon of sodium light (λ = 589 nm) equals the bandgap of semiconducting material. Find:
2. A P-type semiconductor has an acceptor level 57 meV above the valence band. What is the maximum wavelength of light required to create a hole? (217100 A0)
Success in the semiconductor industry depends on creating smaller, faster, and cheaper products. The benefit of being tiny is that more power can be placed on the same chip. The more transistors on a chip, the faster it can do its work. This creates fierce competition in the industry and new technologies lower the cost of production per chip.
This gave rise to the observations called Moore’s Law, which states that the number of transistors in a dense integrated circuit doubles approximately every two years. The observation is named after Gordon Moore, the co-founder of Fairchild Semiconductor and Intel, who wrote a paper describing it in 1965.7 Nowadays, the doubling period is often quoted as 18 months—the figure cited by Intel executive David House.
As a result, there is constant pressure on chipmakers to come up with something better and even cheaper than what was defined as state-of-the-art only a few months beforehand. Therefore, semiconductor companies need to maintain large research and development budgets. The semiconductor market research association IC Insights reported semiconductor companies are expected to increase the research and development budgets by 9% in 2022. They also forecasted the compound annual growth rate (CAGR) will also grow by about 5.5% between 2022 and 2026.
Semiconductors literally make the world go ’round these days. Without semiconductors, we wouldn’t have computers, the internet, mobile phones, or flat-screen TVs. It is no surprise then that the semiconductor industry plays a prominent role in the global economy. The sector also remains a hub of innovation, as Moore’s law continues to work its magic, producing more powerful microchips that are cheaper to produce over time.
Source: en.wikipedia.org . powerelectronicsnews.com . .investopedia.com
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