Diodes are the simplest devices that can be made with semiconductors. In diodes, current is able to flow in one direction but not the other.
This device is formed when a P-type and an N-type semiconductor are put together. The combination of these semiconductors does not itself conduct electricity. Instead, negative electrons from one side are attracted to the positive terminal of a battery and current can flow when a battery is attached.
However, if the battery is flipped and hooked up in the opposite direction, no current flows because there is no movement of electrons across the P-N junction because the electrons move straight through the wire to the battery instead of crossing the gap.
Diodes are used in many circuits, as well as being a component of light emitting diodes that are being used more and more in residential lighting. Another major use of a P-N junction and semiconductors is in photovoltaic cells , the main component of solar panels. These solar cells are what allows solar energy from the Sun to be converted into electricity. Transistors are another device that use semiconductors. In transistors, there are three layers of semiconducting material that create a "sandwich" with two similar types of semiconductor N-type or P-type surrounding a semiconducting material of the other type.
Insulators do not conduct electricity easily. That means the electrical conductivity of insulator is very poor. Semiconductor crystal used for IC etc. Depending on the added impurities, they become n-type and p-type semiconductors. Pentavalent phosphorus P or arsenic As are added to high purity silicon for n-type semiconductors. These impurities are called donors. The energy level of the donor is located close to the conduction band, that is, the energy gap is small.
Then, electrons at this energy level are easily excited to the conduction band and contribute to the conductivity.
On the other hand, trivalent boron B etc. This is called an acceptor. The energy level of the acceptor is close to the valence band. Since there are no electrons here, electrons in the valence band are excited here. As a result, holes are formed in the valence band, which contributes to the conductivity. Properties of semiconductors.
Energy Band An atom is consisting of a nucleus and electrons orbiting the nucleus. Carbon, silicon and germanium germanium, like silicon, is also a semiconductor have a unique property in their electron structure -- each has four electrons in its outer orbital.
This allows them to form nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance. In a silicon lattice, all silicon atoms bond perfectly to four neighbors, leaving no free electrons to conduct electric current. This makes a silicon crystal an insulator rather than a conductor.
Metals tend to be good conductors of electricity because they usually have "free electrons" that can move easily between atoms, and electricity involves the flow of electrons. While silicon crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can't move around. A pure silicon crystal is nearly an insulator -- very little electricity will flow through it. Similarly, gallium has one electron lesser than silicon in its valence shell.
On its addition, due to the deficiency of electrons, the electron-deficient layer is created. And these layers are organized in such a way that they lie next to one another. And when sunlight falls over them, then electrons flow strongly which in return produces an electric field.
Silicon has a bandgap of 1. These electrons leave behind holes while flowing which gets filled with preceding electrons flowing across the lattice. The holes and electrons are known as carriers in the working of the solar cells.
In this way, electricity is produced by solar energy. When solar cells were used commercially in the s, its efficiency was limited only up to 6 percent. But over the decades, there are a lot of improvements done in the Silicon for the efficient working of the solar cells.
One such improvement is adding impurities in silicon to increase the capability of capturing sunlight. Another improvement in solar panels came with black silicon. Black Silicon is made black by some process named as etching. The advantages of black silicon used in a solar panel are that the sunlight is absorbed throughout the day.
Crystalline silicon captures sunlight optimally during the peak hours as photon particle falls perpendicularly on the surface of silicon, but, black silicon has a greater capacity of sunlight absorption at all angles of photons striking on black silicon.
Black silicon is done by an etching process which is a single-sided process and a smooth surface on another side can be used for some productive layout. The other benefit of black silicon is also that it does not require anti-reflecting coating. Solar panels are usually expensive because they require a proper installation which is fairly high.
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