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Physics · 2026 · 3 marks
Semiconductor Electronics: Materials, Devices and Simple CircuitsExtrinsic Semiconductor3 marksApplyshort answer
CBSE 2026 · Region 1 · Set 2 · Q27
A semiconductor has equal electron and hole concentration of 3 × 10^8 m^-3. On doping with a certain impurity, the hole concentration increases to 6…
A semiconductor has equal electron and hole concentration of $\displaystyle 3 \times 10^{8} \mathrm{~m}^{-3}$. On doping with a certain impurity, the hole concentration increases to $\displaystyle 6 \times 10^{10} \mathrm{~m}^{-3}$.
(a)
What type of semiconductor is obtained on doping ?
(b)
Calculate the new electron concentration of the semiconductor.
(c)
How does the energy gap of semiconductor change with doping ? Draw the energy band diagram for it.
Marking-scheme solution
(a)
p type semiconductor
(b)
$\displaystyle \because \mathrm{n}_{\mathrm{e}}=\dfrac{\mathrm{n}_{\mathrm{i}}^{2}}{\mathrm{n}_{\mathrm{h}}}$
$\displaystyle \mathrm{n}_{\mathrm{e}}=\dfrac{\left(3 \times 10^{8}\right)^{2}}{6 \times 10^{10}}$
$\displaystyle \mathrm{n}_{\mathrm{e}}=1.5 \times 10^{6} \mathrm{~m}^{-3}$
(c)
Energy gap effectively decreases
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CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.