  The terahertz current generated by a photoconductive device (PCD) saturates
as the power of the input optical pump is increased. This behavior is induced
by various screening effects that stem from the interactions between
electromagnetic (EM) fields and semiconductor carriers. In this work, these
screening effects are numerically analyzed for the first time using a
fully-coupled multiphysics approach. Unlike the previously developed simulation
frameworks, this approach rigorously models the nonlinear coupling between the
EM fields and the carriers and therefore is capable of accounting for the
screening effects. It is demonstrated that the results obtained using this
multiphysics approach and actual experiments are in excellent agreement. The
optical- and radiation-field screening effects are identified in the simulation
results and the optical-field screening is found to play a more dominant role
in the saturation of the PCD output under high optical pump power levels.
