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Physics Question on Semiconductor electronics: materials, devices and simple circuits

Mobilities of electrons and holes in a sample of intrinsic germanium at room temperature are 0.36 m2V−1s−10.36\,m^2V^{-1}s^{-1} and 0.17 m2V−1s−10.17\,m^2V^{-1}s^{-1}. The electron and hole densities are each equal to 2.5×1019m32.5 \times 10^{19} m^3. The electrical conductivity of germanium is

A

4.24 S m−14.24 \,S\,m^{-1}

B

2.12 S m−12.12\, S\,m^{-1}

C

1.09 S m−11.09\, S\,m^{-1}

D

0.47 Sm−10.47\, Sm^{-1}

Answer

2.12 S m−12.12\, S\,m^{-1}

Explanation

Solution

Electrical conductivity, σ=1ρ=ρ(μene+μnnn)\sigma=\frac{1}{\rho}=\rho\left(\mu_{e} n_{e}+\mu_{n} n_{n}\right) =1.6×10−19[0.36+017](2.5×1019)]\left.=1.6 \times 10^{-19}[0.36+017]\left(2.5 \times 10^{19}\right)\right] =2.12 Sm−1=2.12\, Sm ^{-1}