An Efficient Discontinuous Galerkin Scheme for Simulating Terahertz Photoconductive Devices with Periodic Nanostructures

Abstract

Photoconductive devices (PCDs) enhanced with nanostructures have shown a significantly improved optical-to-terahertz conversion efficiency. While the experimental research on the development of such devices has progressed remarkably, simulation of these devices is still challenging due to the high computational cost resulting from modeling and discretization of complicated physical processes and intricate geometries. In this work, a discontinuous Galerkin (DG) method-based unit-cell scheme for efficient simulation of PCDs with periodic nanostructures is proposed. 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. 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 composed of these coupled equations and boundary conditions is discretized and solved using DG methods. The boundary conditions are enforced weakly through the numerical flux of DG. Numerical results show that the proposed DG-based unit-cell scheme models the device accurately but is significantly faster than the DG scheme that takes into account the whole device.