POISSON's equation (2.14) can be rewritten as

Since the current relations were introduced by using two separate subsystems it is convenient to also split up the current continuity equation eqn. (2.18) into two equations by introducing a formal separation parameter

can be interpreted as the net recombination rate defined as

where / and / are the recombination/generation rates for electrons and holes, respectively.

By summarizing POISSON's equation (2.38), the current continuity equations (2.39) and (2.40), and the current relations (2.35) and (2.36), the set of basic semiconductor equations is obtained. This set of equations was first presented by VANROOSBROECK in 1950 [10].