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Give reason : ( a ) Why is Frenkel defect found in AgCl ? ( b ) What is the difference between phosphorus doped and Gallium doped semiconductors ? |
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Answer» Solution :(a) Frenkel defect is shown by substances where there is a large difference in the size of ions . In the case of AgCl, there is a large difference in the SIZES of Ag and C ions . Hence , AgCl shows Frenkel defect . Here `Ag^(+)` ions are dislocated from the normal position and are located at interstitial sites . (b) In phosphorus doped semiconductors , phosphorus is linked to say FOUR Si atoms by means of four electrons , the FIFTH electron (P has 5 electrons in the valence shell) is AVAILABLE for conducting electrons . It is an n - type semiconductor . In gallium doped semiconductor , gallium occupies one of the lattice positions . Gallium has only three valence electrons . This creates an electron hole at this position. To compensate this , an electron from the neighbouring Si atom migrates to this Ga atom . This in turn creates an electron hole at the position of Si . This process continues on PASSING electricity. The electron hole (positively charged) moves towards the negatively charged plate . Such semiconductors are called p - semiconductors . |
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