Optical and electrical properties of nanostructured metallic electrical contacts

Victor J Toranzos,W Luis Mochán,Jorge O Zerbino,Guillermo P Ortiz

doi:10.1088/2053-1591/aa58bd

Abstract

We study the optical and electrical properties of silver films with a graded thickness obtained through metallic evaporation in vacuum on a tilted substrate to evaluate their use as semitransparent electrical contacts. We measure their ellipsometric coefficients, optical transmissions and electrical conductivity for different widths, and we employ an efficient recursive method to calculate their macroscopic dielectric function, their optical properties and their microscopic electric fields. The topology of very thin films corresponds to disconnected islands, while very wide films are simply connected. For intermediate widths the film becomes semicontinuous, multiply connected, and its microscopic electric field develops hotspots at optical resonances which appear near the percolation threshold of the conducting phase, yielding large ohmic losses that increase the absorptance above that of a corresponding homogeneous film. Optimizing the thickness of the film to maximize its transmittance above the percolation threshold of the conductive phase we obtained a film with transmittance T = 0.41 and a sheet resistance . We also analyze the observed emission frequency shift of porous silicon electroluminescent devices when Ag films are used as solid electrical contacts in replacement of electrolytic ones.

Highlights

Transparent electric contacts are needed in a widespread variety of optoelectronic applications
For thick films experiment agrees roughly with the values of ψ and δ calculated for a locally homogeneous film of width h with a dielectric function εAg taken from [28] and deposited over glass, with dielectric response obtained from [29], but they don’t agree for thinner films (h < 20 nm) for which the film inhomogeneities lead to a strong dependence of the optical response with the film morphology
Resistance In figure 4 we show our measurements of the sheet resistance Rs at various positions on sample S2, prepared with a larger angle α and a smaller mass m than sample S1, so that for each position the corresponding film is thinner

Summary

Introduction

Transparent electric contacts are needed in a widespread variety of optoelectronic applications. An alternative for the design of semitransparent electrical contacts is the use of nanostructured metallic-dielectric composites. Extraordinary optical transmission [2] in perforated metallic films with nanoperforations has been explained in terms of bulk and surface plasmons in nanostructured films [3] and is promising for the control of optical properties [4]. Analyzing the optical and electrical properties of semicontinuous Ag films with a graded thickness we have searched for an optimum film, with an adequate conductivity in the low frequency range and a relatively high transmittance in the VIS.

Experimental

Results

Applications

Conclusions