A semiconductor bar of length 8 um and cross-sectional area 2 um is uniformly doped with donors with a much higher concentration than the intrinsic concentration (10" em) such that the ionized impurity scattering causes its majority carrier mobility to decrease with the doping density Na (cm). using the following relation. This relation was found to be If the electron drift current for an applied voltage of 160 V is 10 mA, calculate the doping concentration in the bar. \mu=\frac{800}{\sqrt{\frac{N_{d}}{10^{20} \mathrm{~cm}^{-3}}}} \mathrm{~cm}^{2} /(\mathrm{V} \cdot \mathrm{s})

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