μ= Ev+E+kln(m/m) The chemical potential is close to the center of the band gap, slightly shifted toward the band with the lighter effective mass. At room temperature, we have an intrinsic electron density of: nsi = 1.45 × 1016 m-3 nGaAs =1.8 × 1012 m-3 for silicon for GaAs Exercise 3: Obtain the carrier densities for electrons and holes and dependence of the chemical potential on temperature.

Lake Ontario has a volume of approximately V =1600 km3. It is heavily polluted by a certain pollutant with a concentration of co = 0.1%.As a part pollution control, the pollutant concentration of the inflow is reduced to cin = 0.02%. The inflow and outflow rates Qin = Qout = Q = 500 km3 per year. Suppose that pollutant from the inflow is well mixed with the lake water before leaving the lake. How long will it take for the pollutant concentration in the lake to reduce to 0.05%?