 The scheme considers two physical stages of the device and model them using two coupled systems, i.e., a Poisson-drift-diffusion (DD) system describing the nonequilibrium steady state, and a Maxwell-DD system describing the transient stage.
<clarity>  The scheme considers two physical stages of the device and model them using two coupled systems, i.e., a Poisson-drift-diffusion (DD) system describing the nonequilibrium steady state, and a Maxwell-DD system describing the transient stage.
 The scheme considers two physical stages of the device and model them using two coupled systems, i.e., a system of Poisson and drift-diffusion equations describing the nonequilibrium steady state, and a Maxwell-DD system describing the transient stage.