2.4.4.2 Electric Conductivity

The isothermal electric conductivity of the electrons (holes) $\sigma_n$ ($\sigma_p$) describes the electron (hole) current $\mathbf{J_n}$ ( $\mathbf{J_p}$) driven by a gradient of the quasi Fermi level; the inverse of $\sigma_n$ ($\sigma_p$) is defined as

$$\sigma_{n,p}^{-1} = - \frac{\mathbf{J_{n,p}} \cdot \nabla \phi_{n,p}} {\vert\mathbf{J_{n,p}}\vert^2} \quad \nabla T = 0$$ (2.8)