Analysis of Screening Effects on Terahertz Photoconductive Devices Using a Fully-Coupled Multiphysics Approach

Abstract

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.

Multiphysics Analysis of Screening Effects on Terahertz Photoconductive Devices

“…The distance between the electrodes is 10 μm . The material properties are the same as these in [3]. The unit-cell model [7] is used to reduce the computational cost.…”

“…The interactions between electromagnetic field and semiconductor charge carriers in optoelectronic materials are described by a coupled system of the Maxwell and the DD equations [3]…”

“…This issue is even more pronounced for the recently emerged nanostructured PCDs due to the local enhancement of the optical fields. The saturation behavior has been attributed to several screening effects: space-charge screening, radiation-field screening, and optical-field screening [3]. Most studies investigating the these effects use phenomenological and heuristic models since their detailed experimental characterization requires access to the electromagnetic fields and the semiconductor carrier densities inside the device.…”