Bihar BoardEnglish MediumSTD 12 SciencePhysicsSEMICONDUCTOR ELECTRONICS: MATERIALS, DEVICES AND SIMPLE CIRCUITS2 Marks
Question
What is doping ? - Explain.
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Answer
→"The deliberate addition of a desired impurity is called doping. And the impurity atoms are called dopants. Such a material is also called a doped semiconductor (or extrinsic semiconductors or impurity semiconductors.)". →The dopant atom (impurity atom) has to be such that it does not distort the original pure semiconductor lattice. →It occupies only a very few of the original semiconductor sites in the crystal. A necessary condition to attain this is that the sizes of the dopant and the semiconductor atoms should be nearly same. →Generally a small amount, say, a few parts per million (ppm), of a suitable impurity is added to the pure semi-conductor. Due to the added impurity atoms, the conductivity of the semiconductor is increased manifold. →There are two types of dopants used in doping the tetravalent $S i$ or Ge: (i) Pentavalent (Valency 5) : like Arsenic (As), Antimony (S $b$ ), Phosphorous ( P ), etc. (ii) Trivalent (Valency 3) : like Indium (I $n$ ) Boron (B), Aluminium $( A l$ ) etc.
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