Diode with PN junction
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Page 1 of 13 3. The PN Junction Diode P and N type semiconductors are not useful in themselves. But when they are joined together to form a PN junction, this forms a very useful device called a diode. It is important to note that the P and the N type semiconductors are not physically joined together. There has to be a continuous boundary between them. This is achieved with a single Si bar, by doping the two sides of the bar with Group III and V impurities. The so formed PN junction is illustrated in the figure below. To study the phenomena that take place as soon as the PN junction is formed we consider the simpler representation of one row of the crystal lattice as shown in the figure (b). As soon as the junction is formed the, 1) conduction and valence bands in the P and N type overlap, (a) below. 2) h+ from P diffuse to N and recombine with free e-, (b) 3) e- from N diffuse to P and recombine with free h+, (b) 4) Diffusion take place due to different concentrations (P has more h+, N has more e-) 5) Diffusion of h+ and e- take place for a short time. 6) After a few recombinations near the junction a restoring force is automatically set up due to the charge depleted region, (c) 7) As a result further diffusion of h+ and e- are stopped. 8) Potential barrier exerts a repelling force on further h+ and e-, (d). At room temp, height of the potential barrier V B = 0.7V for Si. - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + minority carriers e- P N majority carriers h+ majority carriers e- minority carriers h+ - - - - - - + + + + + P N a b Donor ions Acceptor ions
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Transcript of Diode with PN junction
8/10/2019 Diode with PN junction
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