jeudi 23 novembre 2017

Solar energy advantages and disadvantages

Solar power technologies pros and cons

Controversy over alternative energy  (part 2)

Voltaic cells production 

   From an electric point of view, a photo-voltaic cell is the equivalent of a power generator to which a diode has been added. In a photo-voltaic cell, a semiconductor is exposed to the light, a photon with a sufficient energy pulls off an electron from the matrix of the semiconductor, creating a hole. The principle of the voltaic cell is to force the electrons and the holes to go toward the opposite side of the material and created a difference of potential, a voltage in between the two faces like in a battery.
   A semiconductor is generally made of silicon because of its properties, cheap price and its abundance in nature. In the semiconductor's production, the introduction of small impurities into the intrinsic semiconductor is made for the purpose of modulating its electrical properties. The dope material is referred to as extrinsic semiconductor.
  In the superior layer of a semiconductor doped N voltaic cell exists a larger quantity of free electrons compared to the intrinsic material (non-doped), hence the name superconductor doping N, for electron negative. The doping N production consisted of increasing the density of electrons in the semiconductor. The atoms or the elements needed generally have 5 valence electrons to participate in the chemical bond, and they are usually in the IV column of the periodic table chart: P, As, Sb, are commonly used in the production… Those atoms embedded in the crystal lattice will present 4 covalent bonds and a free electron. This electron who's weakly bound to the atom can easily be excited toward the conductive band. When the doping N is sufficient, the number of electrons surpass by far the number of holes, and they become majority carriers. 
   The doped P semiconductors production consists of creating a deficit of electrons and to increase the density of holes in the matrix. And then the semiconductor will be considered positively charged, hence its name superconductor doped P for positive charge. To do this, we include a certain number of atoms low in electrons in the semiconductor. For silicon semiconductors, trivalent atoms will be embedded in the intrinsic (pure) matrix and it is boron atoms that are used most often in the fabrication of the P semiconductors. This atom: boron with his 3 valence electrons can only produce 3 covalent bonds with his 4 neighbours, creating holes in the structure. Holes who will be filled with electrons from silicon neighbours; thus displacing the holes. When the doping P is sufficient, holes surpass by far the number of electrons, and holes become majority carriers.

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