(2.29) | ||

(2.30) |

where and are the diffusion coefficients for electrons and holes, respectively, and are the respective particle flux densities, which have to be multiplied by the charge of the particle to get the electrical current density

(2.31) | ||||

(2.32) |

For conditions close to thermal equilibrium and for non-degenerate carrier systems (BOLTZMANN statistics), the diffusion coefficients are related to the mobilities by the EINSTEIN relation

(2.33) | |

(2.34) |

where is BOLTZMANN's constant.

Superposition of the current components yields the drift-diffusion current relations