A semiconductor bar of length 8 µm and cross-sectional area 2 µm² is uniformly doped with donors with a much higher concentration than the intrinsic concentration (10(11) cm³) such that

the ionized impurity scattering causes its majority carrier mobility to decrease with the doping density Na (cm³). 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.