Modeling and optimization of Au-GaAs plasmonic nanoslit array structures for enhanced near-infrared photodetector applications

Zachary T Brawley,Joseph B Herzog,Omar Manasreh,Stephen J Bauman,Ahmad I Nusir,Grant P Abbey,Ahmad A Darweesh

doi:10.1117/1.jnp.11.016017

Abstract

This theoretical work explores how various geometries of Au plasmonic nanoslit array structures improve the total optical enhancement in GaAs photodetectors. Computational models studied these characteristics. Varying the electrode spacing, width, and thickness drastically affected the enhancement in the GaAs. Peaks in enhancement decayed as Au widths and thicknesses increased. These peaks are resonant with the incident near-infrared wavelength. The enhancement values were found to increase with decreasing electrode spacing. Additionally, a calculation was conducted for a model containing Ti between the Au and the GaAs to simulate the necessary adhesion layer. It was found that optical enhancement in the GaAs decreases for increasing Ti layer thickness. Optimal dimensions for the Au electrode include a width of 240 nm, thickness of 60 nm, electrode spacing of 5 nm, and a minimum Ti thickness. Optimal design has been shown to improve enhancement to values that are up to 25 times larger than for nonoptimized geometries and up to 300 times over structures with large electrode spacing. It was also found that the width of the metal in the array plays a more significant role in affecting the field enhancement than does the period of the array.

Highlights

Light incident on a metallic surface causes the conduction electrons of the solid to oscillate at a characteristic frequency dependent on the radiation energy and the material properties
The average optical enhancement was studied as a function of Au width and electrode spacing
Another interesting result is that the optical enhancement depends simultaneously on both s and w; since the peaks do not shift with s in Fig. 3(a), this indicates that the enhancement is not highly dependent on the specific value of the period, P 1⁄4 w þ s

Summary

Introduction

Light incident on a metallic surface causes the conduction electrons of the solid to oscillate at a characteristic frequency dependent on the radiation energy and the material properties. The quantized, collective oscillations of free electrons in a metal are known as surface plasmons, and they exhibit their own enhanced local electromagnetic fields, which may be harnessed for applications that benefit from the strengthening of electromagnetic field intensity.[1] The electromagnetic intensity in the near-field region next to plasmonic structures can be many times that of the incident radiation, making plasmonic structures useful for optical signal enhancement. Plasmonic devices can be tuned to improve sensing and photovoltaic devices. This has led to much research in determining optimal device parameters that will generate the maximum enhancement. Common geometries include nanowire and nanotoroid arrays as these structures can be accurately modeled and fabricated.[2,3]

Methods

Results

Conclusion