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MHT CET 2023 (10 May, Shift 2) · Intrinsic & Extrinsic Semiconductors

Intrinsic & Extrinsic Semiconductors question from MHT CET 2023 (10 May, Shift 2)

Q32MHT CET 2023 · 10 MAY · SHIFT 2Medium

Intrinsic & Extrinsic Semiconductors

A pure $\text{Si}$ crystal has $4 \times 10^{28}$ atoms per $\text{m}^{3}$ . It is doped by 1 ppm concentration of antimony. The number of free electrons available will be

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Answer: (c)

Each Sb (pentavalent) atom donates one free electron, so $n_e \approx N_D$ .
1 ppm means 1 dopant atom per $10^{6}$ Si atoms: $N_D = \dfrac{4 \times 10^{28}}{10^{6}} = 4 \times 10^{22}\ \text{m}^{-3}$
So the answer is (c) $4 \times 10^{22}\ \text{m}^{-3}$ .

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