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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 R=ρL/AR = \rho L/A equals ρ\rho numerically.

Data used (the "list" in the paper): ni=1.45×1010 cm−3n_i = 1.45\times10^{10}\ \text{cm}^{-3}, μe=1350\mu_e = 1350, μh=450 cm2V−1s−1\mu_h = 450\ \text{cm}^2\text{V}^{-1}\text{s}^{-1}, e=1.6×10−19e = 1.6\times10^{-19} C, Si atoms 5×1022 cm−35\times10^{22}\ \text{cm}^{-3}.

Pure silicon

σi=nie(μe+μh)=1.45×1010×1.6×10−19×(1350+450)=4.176×10−6 S cm−1Ri=1σi=2.39×105 Ω\begin{aligned} \sigma_i &= n_ie(\mu_e+\mu_h)\\ &= 1.45\times10^{10}\times1.6\times10^{-19}\times(1350+450)\\ &= 4.176\times10^{-6}\ \text{S cm}^{-1}\\ R_i &= \frac{1}{\sigma_i} = 2.39\times10^{5}\ \Omega \end{aligned}

Doped with As and B

Nd=5×1022109=5×1013 cm−3,Na=5×1022106=5×1016 cm−3N_d = \frac{5\times10^{22}}{10^9} = 5\times10^{13}\ \text{cm}^{-3},\qquad N_a = \frac{5\times10^{22}}{10^6} = 5\times10^{16}\ \text{cm}^{-3}

Na≫NdN_a \gg N_d, so the cube is p-type (compensated):

p=Na−Nd=4.995×1016 cm−3,n=ni2p=4.2×103 cm−3p = N_a - N_d = 4.995\times10^{16}\ \text{cm}^{-3},\qquad n = \frac{n_i^2}{p} = 4.2\times10^{3}\ \text{cm}^{-3} σ=e(nμe+pμh)≈epμh=1.6×10−19×4.995×1016×450=3.596 S cm−1R=13.596=0.278 Ω\begin{aligned} \sigma &= e(n\mu_e + p\mu_h) \approx ep\mu_h\\ &= 1.6\times10^{-19}\times4.995\times10^{16}\times450\\ &= 3.596\ \text{S cm}^{-1}\\ R &= \frac{1}{3.596} = 0.278\ \Omega \end{aligned}
SampleCarriers (cm⁻³)R (Ω)
Pure Sin=p=1.45×1010n = p = 1.45\times10^{10}2.39×1052.39\times10^{5}
As only (for comparison)n=5×1013n = 5\times10^{13}92.6
As + Bp=4.995×1016p = 4.995\times10^{16}0.278

Answer: pure cube R≈2.39×105 ΩR \approx 2.39\times10^{5}\ \Omega; doped cube R≈0.278 ΩR \approx 0.278\ \Omega (about 8.6×1058.6\times10^5 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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