- 2070 Chaitra · 8 marks
Si cube with As and B per million
Short answer
For pure Si, σi=ni e(μe+μh)=4.176×10⁻⁶ S cm⁻¹, R_i=1/σ_i≈2.39×10⁵ Ω. With As (1 per 10⁹) and B (1 per 10⁶), compensation makes p≈Na−Nd=4.995×10¹⁶ cm⁻³, σ≈e p μh=3.596 S cm⁻¹, R≈0.278 Ω.
Calculate the resistance of pure silicon cubic crystal of 1 cm³ at room temperature. What will be the resistance of the cube when it is doped with 1 arsenic in 10⁹ silicon atoms and 1 boron atom per million silicon atoms? Atomic concentration of silicon is 5×10²² cm⁻³. Use other required data from above given list.
The cube is 1 cm³, so L = 1 cm, A = 1 cm² and equals numerically.
Data used (the "list" in the paper): , , , C, Si atoms .
Pure silicon
Doped with As and B
, so the cube is p-type (compensated):
| Sample | Carriers (cm⁻³) | R (Ω) |
|---|---|---|
| Pure Si | ||
| As only (for comparison) | 92.6 | |
| As + B | 0.278 |
Answer: pure cube ; doped cube (about times smaller). Boron dominates because it is 1000 times more concentrated than arsenic.
✓ Answer checked by Claude Opus 5.5 (high effort)
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