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Physics · 2024 · 2 marks
Semiconductor Electronics: Materials, Devices and Simple CircuitsExtrinsic Semiconductor2 marksApplyvery short answer
CBSE 2024 · Region 3 · Set 1 · Q21
Suppose a pure Si crystal has 5 × 10^28 atoms m^-3. It is doped by 1 ppm concentration of boron. Calculate the concentration of holes and electrons,…
Suppose a pure Si crystal has $\displaystyle 5 \times 10^{28}$ atoms $\displaystyle \mathrm{m}^{-3}$. It is doped by $\displaystyle 1$ ppm concentration of boron. Calculate the concentration of holes and electrons, given that $\displaystyle \mathrm{n}_{\mathrm{i}}=1.5 \times 10^{16} \mathrm{~m}^{-3}$. Is the doped crystal n -type or p-type ?
Marking-scheme solution
Calculation of concentration of holes & ele \[\begin{gathered}
\mathrm{n}_{e} \mathrm{n}_{h}=\mathrm{n}_{\mathrm{i}}^{2} \\
\mathrm{n}_{h} \approx 5 \times 10^{22} / \mathrm{m}^{3} \\
\mathrm{n}_{e}=\frac{\mathrm{n}_{\mathrm{i}}^{2}}{\mathrm{n}_{h}} \\
\mathrm{n}_{e}=\frac{\left(1.5 \times 10^{16}\right)^{2}}{5 \times 10^{22}} \\
\mathrm{n}_{e}=4.5 \times 10^{9} / \mathrm{m}^{3}
\end{gathered}
\]
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