Selective epitaxial growth of III-V semiconductor heterostructures on Si substrates for logic applications

in ECS Transactions (2010), 33

We have deposited III-V alloys on 200 mm Si miscut wafers with an oxide pattern. The selective epitaxial growth (SEG) of GaAs in large windows defined by SiO2 lines on a thick strained-relaxed Ge buffer ... [more ▼]

We have deposited III-V alloys on 200 mm Si miscut wafers with an oxide pattern. The selective epitaxial growth (SEG) of GaAs in large windows defined by SiO2 lines on a thick strained-relaxed Ge buffer layer served as a test vehicle which allowed us to demonstrate the integration of a III-V material deposition process step in a Si manufacturing line using an industrial reactor. High quality GaAs layers with high wafer-scale thickness uniformity were achieved. In a subsequent step, SEG of InP was successfully performed on wafers with a 300 nm shallow trench isolation pattern. The seed layer morphology depended on the treatment of the Ge surface and on the growth temperature. The orientation of the trench with respect to the substrate miscut direction had an impact on the quality of the InP filling. Despite of the challenges, such an approach for the integration of III-V materials on Si substrates allowed us to obtain extended-defect-free epitaxial regions suitable for the fabrication of high-performance devices. [less ▲]

Selective epitaxial growth of III-V semiconductor on large-area Si substrate for advanced logic CMOS technologies

Conference (2010)

The continued downscaling of the metal-oxide semiconductor (MOS) transistor for sub-22 nm logic circuits with boosted performance will require the introduction of new channel materials with carrier ... [more ▼]

The continued downscaling of the metal-oxide semiconductor (MOS) transistor for sub-22 nm logic circuits with boosted performance will require the introduction of new channel materials with carrier mobility higher than that of Si, such as Ge for pMOS. The use of III-V compounds for nMOS devices poses however additional challenges related to the hetero-epitaxial growth of a polar semiconductor on a non-polar surface. Furthermore, these high-mobility materials have to be fabricated on large-area Si substrates, in the perspective of application in a standard low-cost very-large-scale integration scheme. In this work, we report on the successful growth of GaAs on 200 mm Si wafers by means of metal-organic vapor deposition using a modified Crius Close-Coupled Showerhead system from AIXTRON AG. We used Si (100) wafers with off-axis orientation (6° miscut towards <111>) in order to avoid the formation of anti-phase domains which lead to Ga-Ga and As-As bonds at their boundaries that have strong detrimental effects on the electrical conduction. In our approach, based on Ge virtual substrates with low threading dislocation (TD) density, the lattice mismatch between Si and GaAs is accommodated and, thus, no additional TD is introduced in the deposited III-V film. Our results show that smooth GaAs layers can be epitaxially grown on large-area Si substrates with high wafer-scale thickness uniformity. The excellent quality of the deposited GaAs was confirmed by photoluminescence and electron microscopy. Our process also demonstrates very high selectivity on patterned wafers with SiO2 mask and enabled the fabrication of capacitor structures using an integration process flow very similar to standard high volume Si manufacturing lines. The capacitance-voltage characteristics were similar to the ones obtained on a bulk GaAs substrate, and showed extremely tight within-wafer and wafer-to-wafer distributions as is standard to Si manufacturing. [less ▲]

Selective gravitational microlensing and line profile variations in the BAL quasar H 1413+117

in Astronomy and Astrophysics (1993), 280

In order to interpret the spectral differences observed between the four images of the gravitationally lensed broad absorption line (BAL) quasar H 1413+117, we have investigated the effect on the line ... [more ▼]

In order to interpret the spectral differences observed between the four images of the gravitationally lensed broad absorption line (BAL) quasar H 1413+117, we have investigated the effect on the line profiles of the selective magnification of individual BAL clouds by gravitational microlenses. Since microlenses magnify both the selected cloud and the whole BAL region, this effect is only differential, and general constraints on its capability to produce spectral variations have been derived. Considering simple but realistic models for the microlenses, we find that the selective magnification of a relatively large optically thick BAL cloud can be at the origin of the spectral differences reported between the components of H 1413+117. However, a very precise configuration is needed: the magnified cloud must be at the border of the BAL region which must itself partially lie in a region of strong de-magnification. The fine tuning of the parameters mecessary to reproduce the observations either seriously questions this kind of interpretation or puts strong constraints on the lensing models. Another interpretation of the observed line profile differences in terms of effects due to microlensing is also briefly discussed. [less ▲]

Selective inhibition of AP-1 activity in airway immune cells ameliorates experimental asthma

in Proceedings: The American Thoracic Society (2005)

Selective interaction of ethidium derivatives with quadruplexes: An equilibrium dialysis and electrospray ionization mass spectrometry analysis

in Biochemistry (2003), 42(35), 10361-10371

The telomeric G-rich single-stranded DNA can adopt in vitro an intramolecular quadruplex structure, which has been shown to directly inhibit telomerase activity. The reactivation of this enzyme in ... [more ▼]

The telomeric G-rich single-stranded DNA can adopt in vitro an intramolecular quadruplex structure, which has been shown to directly inhibit telomerase activity. The reactivation of this enzyme in immortalized and most cancer cells suggests that telomerase is a relevant target in oncology, and telomerase inhibitors have been proposed as new potential anticancer agents. In this paper, we have analyzed the selectivity of four ethidium derivatives and ethidium itself toward different G-quadruplex species, with electrospray mass spectrometry and competitive equilibrium dialysis and evaluated their inhibitory properties against telomerase. A selectivity profile may be obtained through electrospray ionization mass spectrometry (ESI-MS), which is in fair agreement with competitive equilibrium dialysis data. It also provides unambiguous data on the number of binding sites per nucleic acid (maximal number of two ethidium derivatives per quadruplex, in agreement with external stacking). Our experiments also demonstrate that one compound (4) is the most active and selective G-quadruplex ligand within this series and the most selective telomerase inhibitor in a modified TRAP-G4 assay. [less ▲]

Selective localization of carbon black in immiscible polymer blends : a useful tool to design electrical conductive composites

in Macromolecules (1994), 27(7), 1972-1974

Selective osteopontin knockdown exerts anti-tumoral activity in a human glioblastoma model.

in International Journal of Cancer = Journal International du Cancer (2010), 126

Osteopontin (OPN), a member of the SIBLING (Small Integrin-Binding LIgand N-linked Glycoprotein) family, is overexpressed in human glioblastoma. Higher levels of OPN expression correlate with increased ... [more ▼]

Osteopontin (OPN), a member of the SIBLING (Small Integrin-Binding LIgand N-linked Glycoprotein) family, is overexpressed in human glioblastoma. Higher levels of OPN expression correlate with increased tumor grade and enhanced migratory capacity of tumor cells. Based on these observations, we explored the possibility that knocking down OPN expression in glioblastoma cells could exert an anti-tumoral activity using an avian in vivo glioblastoma model that mimics closely human gliobastoma. Human U87-MG glioma cells transfected with specific anti-OPN small interfering RNAs (siRNAs) were grafted onto the chicken chorio-allantoic membrane (CAM). OPN-deficient U87-MG cells gave rise to tumors that were significantly smaller than tumors formed from untransfected cells (paired t-test, p<0.05). Accordingly, the amount of proliferating cells in OPN-deficient tumors showed a six-fold reduction when compared to control tumors. However, OPN inhibition did not affect significantly tumor-associated angiogenesis. In vitro, OPN-silenced U87-MG and U373-MG cells showed decreased motility and migration. This is the first demonstration that OPN inhibition blocks glioma tumor growth, making this invasion-related protein an attractive target for glioma therapy. (c) 2009 UICC. [less ▲]

Selective recognition of pyrimidine–pyrimidine DNA mismatches by distance-constrained macrocyclic bis-intercalators

in Nucleic Acids Research (2008), 36

Binding of three macrocyclic bis-intercalators, derivatives of acridine and naphthalene, and two acyclic model compounds to mismatch-containing and matched duplex oligodeoxynucleotides was analyzed by ... [more ▼]

Binding of three macrocyclic bis-intercalators, derivatives of acridine and naphthalene, and two acyclic model compounds to mismatch-containing and matched duplex oligodeoxynucleotides was analyzed by thermal denaturation experiments, electrospray ionization mass spectrometry studies (ESI-MS) and fluorescent intercalator displacement (FID) titrations. The macrocyclic bis-intercalators bind to duplexes containing mismatched thymine bases with high selectivity over the fully matched ones, whereas the acyclic model compounds are much less selective and strongly bind to the matched DNA. Moreover, the results from thermal denaturation experiments are in very good agreement with the binding affinities obtained by ESI-MS and FID measurements. The FID results also demonstrate that the macrocyclic naphthalene derivative BisNP preferentially binds to pyrimidine– pyrimidine mismatches compared to all other possible base mismatches. This ligand also efficiently competes with a DNA enzyme (M.TaqI) for binding to a duplex with a TT-mismatch, as shown by competitive fluorescence titrations. Altogether, our results demonstrate that macrocyclic distance- constrained bis-intercalators are efficient and selective mismatch-binding ligands that can interfere with mismatch-binding enzymes. [less ▲]

Selective thermal denaturation of Pisum sativum L. proteins using salt.

Poster (2007, October 11)

Selectivity enhancement for enantiomeric separations in capillary electrophoresis using dual cyclodextrin systems

Conference (1999)