In a silicon sample the electron concentration drops linearly

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In a silicon sample the electron concentration drops linearly from 10¹⁸ cm^{– 3} to 10¹⁶ cm^{– 3} over a length of 2.0 µm. The current density due to the electron diffusion current is (D_n = 35 cm²/s)—

1. 9.3 × 10⁴ A/cm²
2. 2.8 × 10⁴ A/cm²
3. 9.3 × 10⁹ A/cm²
4. 2.8 × 10⁹ A/cm²

Correct Option: B

We know that electron current density

J_n = q D_n	dn
	dx

or J_n = 1.6 × 10^–19 × 35		10¹⁸ – 10¹⁶
		2 × 10^–4

= 2.8 × 10⁴ A/ cm²
Hence alternative (B) is the correct choice.