For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon. Recently, however, a continuous-wave Raman silicon laser was demonstrated; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, chi(2) approximately 15 pm V(-1), makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative.

Abstract:We demonstrate a concept for tailoring the group velocity and dispersion properties for light propagating in a planar photonic crystal waveguide. By perturbing the holes adjacent to the waveguide core it is possible to increase the useful bandwidth below the light-line and obtain a photonic crystal waveguide with either vanishing, positive, or negative group velocity dispersion and semi-slow light. We realize experimentally a silicon-on-insulator photonic crystal waveguide having nearly constant group velocity ~c 0 /34 in an 11-nm bandwidth below the silica-line.

Diffusion coefficients and activation energies have been determined for Ge diffusion in strain-relaxed Si(1)-(x)Ge(x) with x = 0.00, 0.10, 0.20, 0.30, 0.40, and 0.50. The activation energy drops from 4.7 eV in Si and Si(0.90)Ge(0.10) to 3.2 eV at x = 0.50. This value compares with the literature value for Ge self-diffusion in Ge, suggesting Ge-like diffusion already at x approximately equal to 0.5. The effect of strain on the diffusion was also studied showing a decrease in diffusion coefficient and an increase in activation energy upon going from compressive over relaxed to tensile strain.

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The diffusion of boron and phosphorus has been investigated in SiGe grown by molecular beam epitaxy. The analysis was done in relaxed Si 1Ϫx Ge x for xϭ0, 0.01, 0.12, and 0.24 for B and x ϭ0, 0.07, 0.12, 0.24, and 0.40 for P. B diffusion in relaxed samples shows little effect of changing the Ge content while for P diffusion, increasing Ge content increases the diffusion coefficient from Si up to Si 0.76 Ge 0.24 . This is explained by a pairing of B and Ge atoms retarding the diffusion. B diffusion in compressively strained Si 0.88 Ge 0.12 and Si 0.76 Ge 0.24 and tensile strained Si and Si 0.88 Ge 0.12 was also investigated. Compressive strain was found to decrease the diffusion coefficient of B and tensile strain to increase it.