Theory of Diode

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DIODE Theory of PN Junction Diode P-N junction diode – when two different layers P–type and N–type are joined and pressed together (this is sometimes called as hermetic sealing of PN layers) a PN junction diode is formed. The joint of P & N layers is called junction. When the junction is formed, some of the electrons near the surface of N–layer cross the junction and occupy holes in P–layer. Some of the atoms in N–layer loose their electrons and they become +ve ions. At the same time, some of the atoms accept these electrons, so they become –ve ions. In this way, opposite types of ions are accumulated near the edge of junction. Now these ions oppose the process further and it stops. This opposing force of ions along the junction is called as potential barrier and this area of ions is called as depletion layer. To overcome (i.e. to jump across) this barrier and pass the electrons through it the potential of battery must be ≥ 0.7V for any Silicon diode. The two terminals from P and N layers are called anode and cathode respectively. When a single semiconductor crystal is doped with trivalent impurity atoms on one side and with pentavalent impurity atoms on the other side, a p-n junction is formed between the resultant p and n regions. A semiconductor device which utilizes the unique properties that result from such a junction is called a p-n diode. In an unbiased p-n junction diode (not connected to an external voltage source), a so called depletion region exists on both sides of the junction, which is depleted or devoid of any charge carriers (free electrons and holes). A potential energy barrier exists across this region which prevents the flow of carriers across the junction after equilibrium has been reached. Thus the diode does not conduct. When the diode is forward biased (the p side being connected to the +ve terminal of an external battery and the n

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