H.F. Arrand

Porous silicon multilayer optical waveguides

Optical waveguiding is demonstrated in porous silicon multilayers. Depth variations in porosity, and therefore refractive index, are achieved by switching between high and low current densities during the anodic etch process. Planar waveguiding has been demonstrated at λ = 1.28 μm. The wavelength range has been extended to the visible (λ = 0.6328 μm) by oxidising the samples to produce layered porous oxide structures. Two-dimensional strip-loaded waveguides have been produced, for both the visible and infrared, by etching into each top layer through a pre-deposited photolithographically-defined mask.

Novel liquid sensor based on porous silicon optical waveguides

The introduction of solvents into the pores of optical waveguides formed using porous silicon is shown to dramatically reduce the interfacial scattering loss of the waveguides (by as much as 34-dB cm/sup -1/ in one example), in a reversible manner. The degree of loss reduction is dependent on the type of solvent introduced. These observations, combined with the fact that a substantial portion of the guided-mode field interacts with the solvent introduced into the pores, indicate that an enhanced sensitivity for sensor applications may be achievable across a broad range of operational wavelengths.

The application of porous silicon to optical waveguiding technology

The porosification of silicon can be achieved by the partial electrochemical dissolution (anodization) of the surface of a silicon wafer. The degree of porosity is dependent on the anodization parameters and can generally be controlled within the constraints imposed by substrate dopant type and concentration. Control of porosity leads to control of refractive index, and therein lies the concept of using porous silicon as an optical waveguide. We discuss porous silicon wavegides, for the visible to the infrared, produced by a number of approaches: 1) epitaxial growth onto porous silicon (where the porous layer acts as a substrate for a higher refractive index waveguide epilayer); 2) ion implantation (where either selective areas of high electrical resistivity can be produced, which act as a barrier against porosification, or where the surface of a porosified layer is amorphised to form a waveguide; 3) porous silicon multilayers (where the anodization parameters are periodically varied to produce alternate layers of different porosity and thus refractive index); and 4) oxidation of porous silicon (where a porosified layer is oxidized to form a graded-index, dense or porous, oxide waveguide).

Progress towards achieving integrated circuit functionality using porous silicon optoelectronic components

Porous silicon offers many potential advantages for the realisation of optoelectronic circuits and systems. This paper assesses some of the technologies available for the fabrication of porous silicon waveguides for visible and infrared applications. The unique physical and chemical properties of the material enable additional functionality over other silicon-based optoelectronic technologies. As an example, optical sensing of solvents and vapours is discussed using both optical waveguides and multi-layer reflector stacks.

Optical waveguides in porous silicon pre-patterned by localised nitrogen implantation

FIPOS technology forms islands of silicon isolated from a silicon substrate by (oxidised) porous silicon. The larger refractive index of the silicon islands suggests their use as optical waveguides. Sets of these silicon islands have been fabricated and the anticipated waveguiding has been observed at wavelengths of 1.15 and 1.3 μm in the silicon islands. However, the dominant waveguiding in these FIPOS structures is observed in the porous silicon between the silicon islands, close to the sample surface. A simple dynamic model of the anodisation process has been developed to explain the origin of this unexpected waveguiding.

Formation Features of Deposits during a Cathode Treatment of Porous Silicon in Aqueous Solutions of Erbium Salts

The chemical processes that occur during the electrochemical treatment of a porous silicon cathode in aqueous solutions of erbium salts are studied. The results obtained show that (i) erbium ions do not take place in the electrochemical reactions and (ii) erbium-containing deposits are formed by chemical reactions at the cathode. The chemical composition and structure of the deposits can be varied by controlling the electrolysis conditions. These observations facilitate the future design of process cells suitable for the effective incorporation of erbium and other rare earth elements into oxidized porous silicon waveguides for optical amplifier applications.