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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits3 Marks
Question
A semiconductor has equal electron and hole concentration of 2 × 108/m3. On doping with a certain impurity, the hole concentration increases to 4 × 1010/m3.
  1. What type of semiconductor is obtained on doping?
  2. Calculate the new electron and hole concentration of the semiconductor.
  3. How does the energy gap vary with doping?
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Answer

Given ne = 2 × 108/m3, nh = 4 × 1010/m3

  1. The majority charge carriers in doped semiconductor are holes, so semiconductor obtained is p-type semiconductor.

$\text{n}_\text{e}\text{n}_h=\text{n}^2_\text{i}$

$\Rightarrow\text{n}_\text{h}=\frac{\text{n}^2_\text{i}}{\text{n}_\text{h}}$

$=\frac{(2\times10^8)^2}{4\times10^{10}}=10^6/\text{m}^3$

  1. New electron concentration = 106/m3

Hole concentration = 4 × 1010/m3

  1. Energy gap decreases on doping.

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