  Incorporation of plasmonic nanostructures in the design of photoconductive
devices (PCDs) has significantly improved their optical-to-terahertz conversion
efficiency. However, this improvement comes at the cost of increased complexity
for the design and simulation of these devices. Indeed, accurate and efficient
modeling of multiphysics processes and intricate device geometries of
nanostructured PCDs is challenging due to the high computational cost resulting
from multiple characteristic scales in time and space. In this work, a
discontinuous Galerkin (DG)-based unit-cell scheme for efficient simulation of
PCDs with periodic nanostructures is proposed. The scheme considers two
physical stages of the device and models them using two coupled systems: a
system of Poisson and drift-diffusion equations describing the nonequilibrium
steady state, and a system of Maxwell and drift-diffusion equations describing
the transient stage. A "potential-drop" boundary condition is enforced on the
opposing boundaries of the unit cell to mimic the effect of the bias voltage.
Periodic boundary conditions are used for carrier densities and electromagnetic
fields. The unit-cell model described by these coupled equations and boundary
conditions is discretized using DG methods. Numerical results demonstrate that
the proposed DG-based unit-cell scheme has the same accuracy in predicting the
THz photocurrent as the DG framework that takes into account the whole device,
while it significantly reduces the computational cost.
