170,110 research outputs found
Dependence of photoluminescence induced by carbon contamination on GeSi structure
No full textWe studied the dependence of photoluminescence induced by carbon contamination on the Ge/GeSi structure. It is found that a carbon and silicon defect complex may be formed in a special structure by opening the in situ high-energy electron diffraction test during growth. There is an important difference in the dependence of photoluminescence on the temperature between the defect complex in our samples and in bulk Si. where the impurity-active center is generated by high-energy electron (about several MeV) irradiation. The quenching temperature of the photoluminescence from the impurity-active center is higher in our Ge/GeSi structure than in bulk Si. The defect complex may serve as an impurity-active center for a possible application in making Si-based light-emitting diodes whose wavelength is around 1.3 mu m in the window of optical communication. (C) 1998 Elsevier Science B.V. All rights reserved
Rapid Thermal Oxidation of GeSi Strained Layers
No full textABSTRACTA cold-wall rapid thermal processor is used for the oxidation of commensurately grown GexSi1−x layers on Si substrates. It is shown for dry oxidation that the oxidation rate of GeSi is the same as that of Si. The dry oxidationrate of GeSi is independent of Ge concentration (up to 20 % considered in this study) in the GeSi layer. For wet oxidation, however, the rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the Ge concentration in GexSi1−x layer. Employing highfrequency and quasistatic Capacitance-Voltage measurements, it is found for a thin oxide that a fixed negative oxide charge density in the range of 1011 – 1012/cm2, and the interface trap level density (in the mid-gap region) of about 1012 /cm2.eV are present. Further, the density of this fixed oxide charge at the SiO2 /GeSi interface is found.to increase with the Ge concentration in the commensurately grown GeSi layers.</jats:p
GeSi photodetectors and EA modulators for silicon EPIC
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (p. 185-188).The silicon electronic-photonic integrated circuit (EPIC) has emerged as a promising technology to break through the interconnect bottlenecks in telecommunications and on-chip interconnects. High performance photonic modulators and photodetectors compatible with Si complimentary metal oxide semiconductor (CMOS) devices are indispensable to achieve this goal. A photonic modulator generates optical "1" and "0" signals by switching the light on and off, while a photodetector converts the optical signals to electrical ones so that they can be processed by a CMOS circuit. Due to its compatibility with Si CMOS processing and adequate optoelectric properties, epitaxial GeSi material has been considered as a promising candidate to achieve this goal. This thesis investigates epitaxial GeSi photodetectors and electro-absorption (EA) modulators integrated with high index contrast Si(core)/Si02(cladding) waveguides to form an EPIC circuit on a Si platform with CMOS compatibility. Tensile strain is introduced into the GeSi material to enhance its optoelectronic properties. The effect of tensile strain on the band structure of Ge is systematically studied, and the deformation potential constants of Ge are derived from the experimental results with relatively high accuracy.(cont.) Methods to engineer the tensile strain in Ge are demonstrated. Tensile strain in small, selectively grown Ge mesas and stripes with at least one dimension 50 GHz has been designed with the material composition and device structure optimized for operations around 1550 nm. The same material and device structure can be also used for waveguide-integrated photodetectors with a responsivity of 1.1 A/W at 1550 nm and a bandwidth >35 GHz. A method to monolithically integrate GeSi modulators, photodetectors and Si/SiO2 waveguides is proposed and the expected performance is evaluated. Waveguide-integrated GeSi photodetectors and EA modulators are fabricated on a standard 180 nm CMOS production line based on the design. We demonstrate a waveguide-integrated GeSi photodetector with a responsivity of 1.0 A/W at 1518 nm and a bandwidth >4.5 GHz, as well as a GeSi EA modulator with an extinction ratio of -0.3 dB. While the device performance of the EA modulator is far from ideal due to fabrication issues, the preliminary results demonstrate the feasibility of the electronic-photonic integration on a Si platform with GeSi modulator and detector devices. The problems in this first device processing are identified, and solutions are proposed and partially tested. The device performance could be greatly enhanced with improved processing technique.by Jifeng Liu.Ph.D
L'apomorfina induce morte cellulare di tipo apoptotico nelle cellule di ovaio di hamster cinese (CHO)
No full textGiornate Pisane dei Giovani Cultori delle Neurosciez
Strain relaxation of GeSi alloy with low dislocation density grown on low-temperature Si buffers
No full textWe have developed a low-temperature (LT) growth technique. Even with Ge fraction x upto 90%, the total thickness of fully relaxed GexSi1-x buffers can he reduced to 1.7 mu m with dislocation density lower than 5 x 10(6) cm(-2). The surface roughness is no more than 6 nm. The strain relaxation is quite inhomogeneous From the beginning. Stacking faults generate and form the mismatch dislocations in the interface of GeSi/LT-Si. (C) 1999 Elsevier Science B.V. All rights reserved
Nanometer-Scale Oxide Particles in Gesi Films Grown by Wet Oxidation
No full textABSTRACTAmorphous GeSi films with different thicknesses and oxygen contents were electron beam evaporated onto Si (KK)) wafers and wet oxidized at 900 °C for 30 Min. If there was no oxygen in the as-deposited film, an epitaxial GeSi film would be grown after wet oxidation. For the samples with oxygen, epitaxial growth broke down when the thickness of the epitaxy exceeded about 200 A and polycrystalline GeSi films were formed. A dedicated STEM (scanning transmission electron Microscope) was used to characterize the sample after oxidation. STEM BF (bright field), ADF (annular dark field), and energy filtered images revealed the presence of small oxide particles in the polycrystalline GeSi films. X-ray microprobe analysis with a windowless detector was employed to identify the oxide particles. The failure of the epitaxy is explained by the random nucleation and growth of GeSi grains on the oxide particles.</jats:p
Confinement of Threading Dislocations in Simox with a GeSi Strained Layer
No full textABSTRACTWe have investigated improving the crystalline quality of epitaxial silicon grown on SIMOX by confining threading dislocations in the original Si top layer using a GeSi strained layer. Epitaxial Si/GeSi/Si structures were grown by CVD on SIMOX and Si substrates with a GeSi alloy layer about 1000 − 1500 angstroms thick with Ge concentrations of about 0−20%. A Ge concentration in the alloy layer of about 5.5% or higher appears to be necessary in order to bend any of the threading dislocations from the original SIMOX top layer. For a higher Ge concentration of about 16%, most of the threading dislocations appear to be bent and confined by the GeSi layer. In addition, the GeSi strained layers grown by CVD (at about 1000°C) appear to be high quality and no misfit dislocations were observed in the regions studied by XTEM and plane view TEM.</jats:p
Ion Irradiation of GeSi/Si Strained-Layer Heterostructures
No full textAbstractThe strain in GeSi/Si strained layer heterostructures is studied as a function of ion-irradiation and thermal annealing conditions and correlated with the defect microstructure in the GeSi alloy layer. For room temperature irradiation, compressive strain within the alloy layer increases with increasing ion fluence for both low (projected range of ions within the alloy layer) and high energy (projected range of the ions greater than alloy thickness) irradiation. In contrast, elevated temperature irradiation results in an increase in strain for low-energy irradiation, but a decrease for high-energy irradiation. For example, strain relaxation is observed in layers irradiated with I MeV 28Si+ at 253 °C. During subsequent annealing to 750 °C, the strain is partially recovered but relaxes again at temperatures > 750°C. This behavior is shown to be consistent with the evolution of intrinsic (vacancy-type) defects within the alloy layer.</jats:p
Dislocation Velocities In Gesi Bulk Alloys
No full textAbstractThe mechanical strength and dislocation velocities in single crystal Ge1−xSix alloys grown by the Czochralski method were investigated by compressive deformation and by the etch pit technique, respectively. In the temperature range 450 – 700 °C and the stress range 3 – 20 MPa, the dislocation velocity in the GeSi alloys with x = 0.004 – 0.053 decreases monotonously with an increase in the Si content, reaching about a quarter of that in Ge at x = 0.053, and can be expressed as a function of the stress and the temperature. The yield stress of the GeSi alloy increases with increasing Si content from x = 0 to 0.4 and is temperature-insensitive at high temperatures, showing that the flow stress of alloy has an athermal component which is absent in elemental or compound semiconductors.</jats:p
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