STANDARDPhysics-Semiconductors
STANDARD Physics Doping MCQ Question
Type: MCQ-numerical-Medium
A pure Si crystal has 5 × 10²² atoms m⁻³. It is doped by 1 ppm concentration of pentavalent impurity. The number of holes is (nᵢ² = nₕnₑ) (Take nᵢ = 1.5 × 10¹⁶ m⁻³)
A
4.5 × 10⁹ m⁻³
B
4.5 × 10⁶ m⁻³
C
2.5 × 10⁹ m⁻³
D
2.5 × 10⁶ m⁻³
Correct Answer
Option A
Detailed Explanation
Note that thermally generated electrons (nᵢ = 10¹⁶ m⁻³) are negligibly small as compared to those produced by doping. Therefore, nₕ ≈ Nᴰ. Since nₕnₑ = nᵢ², nₑ = (nᵢ² / Nᴰ) = (1.5 × 10¹⁶)² / 5 × 10¹⁶ = 4.5 × 10⁹ m⁻³.
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