The electron concentration in a sample of uniformly doped n-type silicon at 300 K varies linearly from 10¹⁷/cm³ at x = 0 to 6 $\times$10¹⁶/cm³ at x = 2 $\mu$m. Assume a situation that electrons are supplied to keep this concentration gradient constant with time. If electronic charge is 1.6$\times$10^-19 coulomb and the diffusion constant Dn = 35 cm²/s, the current density in the silicon, if no electric field is present, is