Longwave plasmonics on doped silicon and silicides

Richard Soref,Robert E Peale,Walter Buchwald

doi:10.1364/oe.16.006507

Abstract

The realization of plasmo-electronic integrated circuits in a silicon chip will be enabled by two new plasmonic materials that are proposed and modeled in this article. The first is ion-implanted Si (n-type or p-type) at the surface of an intrinsic Si chip. The second is a thin-layer silicide such as Pd(2)Si, NiSi, PtSi(2) WSi(2) or CoSi(2) formed at the Si chip surface. For doping concentrations of 10(20) cm(-3) and 10(21) cm(-3), our dispersion calculations show that bound surface plasmon polaritons will propagate with low loss on stripe-shaped plasmonic waveguides over the 10 to 55 microm and 2.8 to 15 microm wavelength ranges, respectively. For Pd(2)Si/Si plasmonic waveguides, the wavelength range of 0.5 to 7.5 microm is useful and here the propagation lengths are 1 to 2300 microm. For both doped and silicided guides, the SPP mode field extends much more into the air above the stripe than it does into the conductive stripe material.

Highlights

Plasmonics refers to the technology in which surface plasmons are launched, transmitted, modulated, detected, etc, on sub-wavelength conducting structures formed on or within dielectrics or semiconductors
The surface plasma polaritons (SPPs) can be launched “electronically” by an electron beam [1,2] or by a MOSFET [3]. The latter case is most interesting because, as we described earlier [4], it will lead to silicon-based plasmo-electronic integrated circuits (PEICs) in which MOSFETs on the perimeter of a planar
The SPP properties that can be calculated from the permittivity include the complex wavevector, the propagation length L for the SPP intensity along the surface, the SPP spatial confinement as determined by the distance Lair that the field extends into air above the waveguide surface and by the field penetration Lcond into the doped or silicided conductor

Summary

Introduction

Plasmonics refers to the technology in which surface plasmons are launched, transmitted, modulated, detected, etc, on sub-wavelength conducting structures formed on or within dielectrics or semiconductors. We propose and analyze two new plasmonic materials that are probably more compatible with optoelectronics than are silver or gold films These materials are highly doped-silicon embedded in undoped silicon, and a silicide film (e.g. PtSi2, NiSi, Pd2Si, WSi2, CoSi2) created in the undoped silicon surface. The wavelengths for prior-art metal-delectric-metal SPP based waveguides are in the near infrared, but as we shall show in this article, the doped-Si and silicided-Si offer low-loss performance not in the NIR, but rather in the mid-wave, longwave and very longwave infrared. The organization of this paper is as follows: we first propose striped and slotted structures for channel waveguides, we compile the relevant surface plasmon properties calculated from the complex permittivity These properties include the dispersion curves with their bound and free modes, the propagation losses within feasible longwave regions, and the mode profiles with estimated penetration depths into the air and the conductive medium

Waveguide structures

Complex permittivity data

Bound SPPs for plasmonic waveguides

Mode propagation loss

Mode profile

Conclusion