Plasmonic structures can be used to enhance electromagnetic radiation, and nanoscale (<5 nm) gaps can increase this
enhancement even further. Fabrication of these desired structures involves using a relatively new, previously developed
self-aligned process to overcome typical electron beam lithography resolution limits. The resulting nanogap structures
have been shown to exhibit enhanced optical emission. This technique enables the fabrication of a large-area two-dimensional
matrix of such nanostructures which could prove useful for photovoltaics, plasmonically enhanced Raman
spectroscopy, biosensing, and other optoelectronic applications. Computational electromagnetic simulations of the
structures will prove useful for predicting behavior upon interaction with light and for experimental comparison.
Plasmonic nanostructures have been shown to act as optical antennas that enhance optical devices. This study focuses on
computational electromagnetic (CEM) analysis of GaAs photodetectors with gold interdigital electrodes. Experiments
have shown that the photoresponse of the devices depend greatly on the electrode spacing and the polarization of the
incident light. Smaller electrode spacing and transverse polarization give rise to a larger photoresponse. This
computational study will simulate the optical properties of these devices to determine what plasmonic properties and
optical enhancement these devices may have.
The models will be solving Maxwell’s equations with a finite element method (FEM) algorithm provided by the
software COMSOL Multiphysics 4.4. The preliminary results gathered from the simulations follow the same trends that
were seen in the experimental data collected, that the spectral response increases when the electrode spacing decreases.
Also the simulations show that incident light with the electric field polarized transversely across the electrodes produced
a larger photocurrent as compared with longitudinal polarization. This dependency is similar to other plasmonic devices.
The simulation results compare well with the experimental data. This work also will model enhancement effects in
nanostructure devices with dimensions that are smaller than the current samples to lead the way for future nanoscale
devices. By seeing the potential effects that the decreased spacing could have, it opens the door to a new set of devices
on a smaller scale, potentially ones with a higher level of enhancement for these devices.
In addition, the precise modeling and understanding of the effects of the parameters provides avenues to optimize the
enhancement of these structures making more efficient photodetectors. Similar structures could also potentially be used
for enhanced photovoltaics as well.