P-N Junctions and Semi-Conductors

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Q1 – Valence electrons : The electrons in the outermost shell of an atom are called valence electrons; They are the reason why chemical reactions can happen and they also determine the electrical nature of a material. In solid state electronics, either pure silicon or germanium may be used as the intrinsic semiconductor which forms the starting point for fabrication. Silicon is more widely used semiconductor for electronics, partly because it can be used at much higher temperatures than germanium. Solid state electronics arises from the unique properties of this important material (silicon) each of matter having four valence electrons and which form crystal lattices in which (dopants) can dramatically change the electrical properties. SILICON LATTICE Silicon atoms form covalent bonds and can crystallize into a regular lattice. The picture below is the actual crystal structure of silicon is a diamond lattice. This crystal is called an intrinsic semiconductor and it is capable to conduct a small amount of current. The lesson to observe from this is that a silicon atom has four electrons which it can share in covalent bonds with its neighbors , therefore The atoms are usually arranged into giant regular lattices . They are extremely strong structures because of the bonds involved. Silicon has a similar structure to diamond. It is also hard and has a high melting point. The fact that it is a semi-conductor makes it immensely useful in the electronics industry: most transistors are made of silica. Pn junction semiconductors are greatly benefitted today. We use them in production of solar cells to transform solar energy into electrical energy, transistors , rectifier diodes , light emminiting diodes and etc .. The basic idea behind a PN Junction : To increase the practical utility of a P or N type semiconductor, a PN junction

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