Semiconductors were thought from long ago, thought to be first mentioned by the physicist Volta in 1728 and further investigated by Faraday. They were finally invented by John Bardeen (who you may remember from my Superconductors post), William Shockley and Walter Brattain, in the form of the all-important transistor! They are what the name suggests: not full conductors, only half ones (can only partially conduct). Then "why use them?" I hear you say. If you need to conduct, conductors do a much better job at it. And if you need to insulate, insulators are there. But the problem with conductors is that they conduct too much, making the current a bit hard to control. Semiconductors make it easier to do so. Semiconductors also have a higher resistance so can boost the voltage by reducing current. And finally, they can also be used to create semiconductor junctions, which can isolate two different currents until some energy is given to overcome this.
So how do they work? In a normal conductor, the outer shell is called the valence orbit and has only one electron in it, which makes it easy to move the electron about and therefore conduct electricity. However, in the valence orbit of a non metal such as silicon, there are four electrons in the valence orbit. This makes it hard for them to conduct and makes them an insulator. These non-metals can form bonds covalent bonds with other atoms like them that are around it by sharing electrons with the surrounding electrons. When these atoms are arranged into a structure, they are called crystals. Here there is a technique called doping that makes these crystals (typically made of silicon) into superconductors. It involves making impurities in the crystals by injecting other elements into them. There are two types of semiconductors.
The first type are N-type semiconductors. This is when an element with a higher number of electrons in the valence orbit than of the element in the crystal is injected into the crystal as an impurity. Here, lets just say that the crystal is made of silicon and the impurity (aka dopant) is phosphorus. Feel free to sketch out the bond diagram as it will help you visualise the concept better. The four electrons in the valence orbit of silicon form covalent bonds with four of the five electrons in the phosphorus atom. This leaves out one electron, which is lonely. This one electron is free to move about, just like the free electrons in a metal (conductor) and so make the semiconductor able to conduct.
The second type is P-type conductors. This is when an element with a lower number of electrons in the valence orbit than of the element in the crystal becomes the dopant. In this case, let the dopant be boron. So the three electrons of boron will form a covalent bond with three electrons in the valence orbit of silicon. But the fourth electron from silicon will remain as unstable and can easily escape, given a little energy. So, when a current is applied, this electron will be displaced and create a hole. Now, the silicon will become an ion (as it has less electrons than protons and will have a positive charge) and the hole is act as the positive charge. So, the electrons from other atoms that have been displaced will come to fill this hole, then be displaced again, effectively making a flow of electrons. This is how P-type semiconductors work.
Thanks for reading this week's topic! Come back next week for more physics topics!
So how do they work? In a normal conductor, the outer shell is called the valence orbit and has only one electron in it, which makes it easy to move the electron about and therefore conduct electricity. However, in the valence orbit of a non metal such as silicon, there are four electrons in the valence orbit. This makes it hard for them to conduct and makes them an insulator. These non-metals can form bonds covalent bonds with other atoms like them that are around it by sharing electrons with the surrounding electrons. When these atoms are arranged into a structure, they are called crystals. Here there is a technique called doping that makes these crystals (typically made of silicon) into superconductors. It involves making impurities in the crystals by injecting other elements into them. There are two types of semiconductors.
The first type are N-type semiconductors. This is when an element with a higher number of electrons in the valence orbit than of the element in the crystal is injected into the crystal as an impurity. Here, lets just say that the crystal is made of silicon and the impurity (aka dopant) is phosphorus. Feel free to sketch out the bond diagram as it will help you visualise the concept better. The four electrons in the valence orbit of silicon form covalent bonds with four of the five electrons in the phosphorus atom. This leaves out one electron, which is lonely. This one electron is free to move about, just like the free electrons in a metal (conductor) and so make the semiconductor able to conduct.
The second type is P-type conductors. This is when an element with a lower number of electrons in the valence orbit than of the element in the crystal becomes the dopant. In this case, let the dopant be boron. So the three electrons of boron will form a covalent bond with three electrons in the valence orbit of silicon. But the fourth electron from silicon will remain as unstable and can easily escape, given a little energy. So, when a current is applied, this electron will be displaced and create a hole. Now, the silicon will become an ion (as it has less electrons than protons and will have a positive charge) and the hole is act as the positive charge. So, the electrons from other atoms that have been displaced will come to fill this hole, then be displaced again, effectively making a flow of electrons. This is how P-type semiconductors work.
Thanks for reading this week's topic! Come back next week for more physics topics!
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