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Semiconductors play a dynamic character in nearly every arena of modern integrated circuit technology, and they enable the manufacturing of everything from receivers to computers and microprocessors. The most significant applications for semiconductor materials comprises their use in the creation of transistors, which are solid-state electronic devices that form the derivation for a vast array of electronic systems and paraphernalia, particularly integrated circuits. The mainstream of semiconductor and transistor components are made up of silicon, which is extremely valuable for its distinct electroic structure and is one of the most profuse element. By changing the electron arrangement in silicon or similar elements through the involvement of supplementary particles, it is possible to regulate the conductivity and resistivity levels of a material formed from these elements to create a semiconductor.
As its name proposes, a semiconductor features resistivity level on an array between those of a conductor and an insulator. Decent conductors, such as metals, have electrical resistivity ratings in the lower range of 10-6 ohms per centimeter and good insulators have resistivity in the much greater range of 1012 ohms per centimeter semiconductor resistivity usually falls in between 10-4 and 104ohms per centimeter. For semiconductors resistivity is typically dependent on the presence of additional particles known as dopants that are used to selectively replace atoms within the base semiconductor material in order to alter its electrical properties.
An intrinsic semiconductor is in a pure state without any dopants added. Its material contains thermal energy that can release covalent bonds and free electrons to move through a solid mass, augmenting electrical conductivity levels. The remaining covalent bonds that have lost their electrons have vacancies that influence the semiconductor’s electrical properties. Electrons in a covalent bond can move easily into a neighboring vacancy, creating a hole in the initial covalent bond and restarting the vacancy process, holes can be said to pass through a semiconductor material, adding to conductivity by exhibiting features of a positive charge equal to electron charge magnitude. Unbound electrons and holes are the two-principal moving electrical charge carriers in a semiconductor, and are notable for being generated and recombined in equal numbers, as well as having matching populations.
Unlike intrinsic types, extrinsic, or doped, semiconductors have added particles that are specially used for altering a material’s electrical conductivity properties. In silicon, the most common semiconductor material, each atom shares four valence electrons through covalent bonds with the four nearest atoms. If the silicon atom is replaced with a dopant element that has five valence electrons, such as phosphorus, four of them will be bonded while the fifth will remain free. These dopants that carry more than four valence electrons are known as donors because they provide an influx of free electrons that move through the semiconductor. The extra electrons remove the equilibrium between holes and electrons, and when the electrons outnumber the holes the material becomes an N-type semiconductor. In N-types, the electrons are majority carriers while holes are minority carriers, meaning that the concentration of electrons is normally must higher than that of holes. HyperPhysics offers additional information on the dopants used in semiconductor technology.
A P-type semiconductor is another type of extrinsic semiconductor that also relies on dopants to alter its composition and uses the same principles as N-types to achieve an inverse effect. When a dopant atom with fewer than four valence electrons, such as a three-valence boron atom, is substituted for a silicon particle, three of the four covalent bonds are filled, while the fourth bond remains empty. An electron from a neighboring atom may easily join the empty bond, creating vacancy in its former atom. These types of dopants are known acceptors due to their capacity for receiving electrons and creating holes. The increase in holes disrupts the equilibrium, resulting in more holes than electrons and producing a P-type semiconductor. P-types have holes serving as majority carriers, while electrons are minority carriers. As expected, the concentration of holes is typically greater than that of electrons.
An important feature of semiconductors is that through selective doping various states of conductivity can be produced in different regions of a single semiconductor. For example, a crystal silicon semiconductor can have donor dopants create an N-type state on one side of the material and acceptor dopants create a P-type state on the other. The transitional state between the two sides is known as the P-N junction. The difference in concentration between electron and hole carriers can cause charge carriers to flow across the junction, allowing the N-type section to gain a positive charge relative to the P-type side. The charge level results in an electric potential barrier, or hill, at the P-N junction. When there is an equilibrium, the flow of majority carrier holes from the P-type side decreases until it is equal to that of the minority carrier holes from the N-type side.
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