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

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits3 Marks
Question
A semiconductor has equal electron and hole concentration of $2 \times 10^8/m^3$.
On doping with a certain impurity, the hole concentration increases to $4 \times 10^{10}/m^3$.
  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 $n_e = 2 \times 10^8/m^3, n_h = 4 \times 10^{10}/m^3$
  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 $= 10^6/m^3$
Hole concentration $= 4 \times 10^{10}/m^3$
  1. Energy gap decreases on doping.
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