  Exact solution of the linearized equations for steady-state transport in
semiconductors yields two modes that vary exponentially in space, one involving
screening (without entropy production) and one involving diffusion and
recombination (with entropy production). Neither mode is quasineutral. For
constant surface photoexcitation with generation of electrons and holes, the
steady-state response is a linear combination of these modes, subject to global
electroneutrality. The resultant charge separation produces a voltage
difference across the sample (the Dember effect).
