Highly compact optical waveguides with a novel pedestal geometry

Chaudhari, Amar D.; West, Lawrence C.; Roberts, Charles W.; Lu, Yicheng

doi:10.1109/68.384532

Cited by 15 publications

(3 citation statements)

References 8 publications

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“…The timedomain finite-element software used in the present research has been applied by other investigators to a number of systems of practical interest, including the determination of lightscattering properties of features on silicon wafers 16 and evaluation of the performance of integrated optical devices 17 and waveguides. [18][19][20] The finite-element models in the present study are constructed in Cartesian coordinate systems by specifying edge dimensions, the finite-element mesh density, particle position(s) and shape(s), and the optical properties of the constituent materials at the wavelength of interest. Typical models contain 1-2 million elements.…”

Section: (1) Finite-element Approachmentioning

confidence: 99%

Light‐Scattering Properties of Representative, Morphological Rutile Titania Particles Studied Using a Finite‐Element Method

Thiele

French

1998

Journal of the American Ceramic Society

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The light-scattering performance of TiO 2 pigment depends intimately upon particle size, size distribution, shape and dispersion quality. TiO 2 particles exhibit complex shapes and have anisotropic optical constants, and particulate dispersions of TiO 2 are characterized by complicated microstructures such as aggregates and agglomerates. Despite this complexity, the theoretical understanding of light scattering by white pigment has been based upon Mie theory, which is restricted to the case of a single, optically isotropic sphere. We utilize a finite-element method which produces rigorous solutions to Maxwell's equations to determine computationally the light-scattering properties of complex particulate microstructures. This represents a significant step beyond the restrictions of Mie theory, providing a method to determine quantitatively the effects of particle shape, optical anisotropy, and interactions between neighboring particles upon the light-scattering properties of white pigments in coatings. In the present study, we use the finite-element method first to compute the light-scattering properties of a single, morphological rutile particle with a representative size and shape. These results are compared to the light-scattering properties of the optically isotropic, equivalent volume sphere using Mie theory. Neither the average index nor the weighted sum approximation offers clear advantages in this case. Second, the far-field lightscattering properties of two such particles interacting at near field are determined as a function of the interparticle separation. The agglomerated pair of particles exhibits a 20% decrease relative to the single particle in the scattering parameter associated with the hiding power of a paint film. The basis for this decrease is the same as for the crowding effect observed in extensive paint films. The results of both sets of computations are compared to Mie theory to determine the sizes of spherical particles with equivalent scattering cross sections. These comparisons highlight the inherent difficulties in using Mie theory to evaluate particle size by light-scattering methods.

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Section: (1) Finite-element Approachmentioning

confidence: 99%

Light‐Scattering Properties of Representative, Morphological Rutile Titania Particles Studied Using a Finite‐Element Method

Thiele

French

1998

Journal of the American Ceramic Society

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“…The high hole mobility of Ge has a large potential for high-speed heterobipolar Ge/GaAs transistors, 11 strong absorption in the 1.0-1.5 m range explains why the Ge-GaAs system is widely used in solar cells, 12 and transparency in the midinfrared 3-10 m range makes it a good waveguide in GaAs-based integrated electro-optics. [13][14][15] In view of such promising features of Si/GaAs and Ge/ GaAs heterostructures, and the strong interrelation between the growth microstructures and their physical properties, there are surprisingly few publications concerned with the detailed analysis of their respective growth characteristics. 16 -22 Bratina et al 18 have used molecularbeam epitaxy to grow Si on GaAs͑001͒-͑2ϫ4͒ ͑prepared by oxide desorption at 580°C at As 4 overpressure͒, and found that a ͑3ϫ1͒-reconstructed Si layer grew two-dimensionally up to 3-4 monolayers, after which initiation of threedimensional ͑3D͒ growth was detected in reflection highenergy electron diffraction ͑RHEED͒.…”

Section: Introductionmentioning

confidence: 99%

Molecular-beam epitaxy of Ge on GaAs(001) and Si capping

Goldfarb

Azar

Grisaru

et al. 2003

Journal of Applied Physics

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Epitaxial quality of Ge layers on GaAs͑001͒, as well as the quality of the Si capping layers, were investigated in situ by reflection high-energy electron diffraction during growth and, subsequently, by scanning electron and scanning probe microscopies. Ge was grown on the ͑1ϫ1͒-GaAs͑001͒ surface prepared by oxide desorption at 580°C in an As-free ultrahigh vacuum; its morphology, varying from reasonably flat layers with only atomic scale roughness to relatively large three-dimensional asperities, was found to crucially depend on the GaAs surface quality and growth temperature. The data presented in this work also account for the apparent discrepancies between various groups regarding the Ge/GaAs reconstruction; our detailed analysis proves that, at least under the experimental conditions described herein, it is a mixture of ͑1ϫ2͒ and ͑2ϫ1͒, rather than a ͑2ϫ2͒ or c(2ϫ2). Smooth Si growth was mainly impeded by a large lattice mismatch with the underlying Ge, initially replicating the morphology of the Ge layer and eventually forming discrete three-dimensional islands and continuous undulations. The study shows that flat epitaxial Si capping of GaAs should be possible by employing graded silicon-germanium buffers.

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“…The heteroepitaxial growth of Ge on GaAs substrate has been investigated for applications such as solar cells, 7 heterobipolar transistors, 8 and waveguides for electro-optic integrated circuits. 9 However, there is no demonstration of MOS devices on a thin layer of Ge formed on GaAs. For MOS device application, the as-grown Ge epi layer should meet the following criteria ͑i͒ it must have excellent single crystalline quality and be free of dislocations and defects, ͑ii͒ it should be very flat because large surface roughness in the channel region can degrade the effective carrier mobility, and ͑iii͒ the Ge layer should be relatively thin to avoid the lithography issue because of the different depths of focus.…”

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confidence: 99%

Fabrication of p-MOSFETs on Germanium Epitaxially Grown on Gallium Arsenide Substrate by Chemical Vapor Deposition

Zhu

Chin

Samudra

et al. 2008

J. Electrochem. Soc.

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We demonstrate a p-MOSFET fabricated on Ge/GaAs heterostructure. The Ge layer was epitaxially grown on GaAs substrate by high vacuum chemical vapor deposition. High-quality single crystalline Ge film confirmed by X-ray diffraction and transmission electron microscopy was achieved with a very low root-mean-square roughness of 5 Å measured by atomic force microscopy. Secondary ion mass spectrometry results indicate that no Ga and As out-diffusion to Ge epi layer can be observed. By employing silane passivation, Ge p-MOSFET with TaN/HfO 2 gate stack was fabricated on Ge/GaAs heterostructure. The resultant transistor exhibited excellent subthreshold swing of 86 mV/dec and I on /I off ratio greater than four orders. Additionally, ϳ1.7 times hole mobility enhancement over the universal curve of Si was achieved.

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Highly compact optical waveguides with a novel pedestal geometry

Cited by 15 publications

References 8 publications

Light‐Scattering Properties of Representative, Morphological Rutile Titania Particles Studied Using a Finite‐Element Method

Light‐Scattering Properties of Representative, Morphological Rutile Titania Particles Studied Using a Finite‐Element Method

Molecular-beam epitaxy of Ge on GaAs(001) and Si capping

Fabrication of p-MOSFETs on Germanium Epitaxially Grown on Gallium Arsenide Substrate by Chemical Vapor Deposition

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