Search

GaAs0.51Sb0.49 is lattice-matched to InP and finds electron transport applications in base or absorber layers in high-speed heterostructure bipolar transistors or photodiodes, because its staggered ("type-II") band alignment with InP favors electron injection across abrupt heterojunctions. Little remains known about electron transport properties and band structure details of GaAsxSb1−x near x = 0.5. Particularly, based on the Γ-L intervalley separation in binary constituents (ΔΓL = 84 meV in GaSb and 290 meV in GaAs at 300 K), interpolation suggests a low Γ-L separation in GaAs0.51Sb0.49 before considering energy gap bowing effects. To gain insight into electron transport in GaAs0.51Sb0.49, we characterized experimental Hall electron mobilities vs carrier concentration at 300 and 77 K in n-type GaAs0.51Sb0.49, Ga0.47In0.53As, and Ga0.76In0.24As0.67Sb0.33 alloys nearly matched to InP. In marked contrast to the other two alloys, GaAs0.51Sb0.49 exhibits a sharp rise in 77 K electron mobility, which evidences L-valley de-population for lower electron concentrations. A two-band transport analysis reveals a Γ-L valley separation ΔΓL = 91 meV at 77 K, significantly lower than values recommended in the literature. Based on the reported temperature variations of ΔΓL in GaAs and GaSb, 84 < ΔΓL < 95 meV is expected at 300 K. The corresponding GaAsxSb1−x L-valley bowing parameter is cL = 1.63 eV, significantly higher than the 1.1–1.2 eV recommended in the literature. In contrast to GaAsxSb1−x, GaInAsSb grown on InP displays a strong alloy scattering, which limits its low-temperature electron mobility. [ABSTRACT FROM AUTHOR]

The Kirk effect mechanism is studied in type-II InP/GaAsSb/InP NpN double heterojunction bipolar transistors (DHBTs) both experimentally and through two-dimensional hydrodynamic numerical simulations. We show that the large valence band discontinuity ΔEV at the GaAsSb–InP base/collector heterojunction does not allow hole injection into the InP collector as is the case in homojunction collectors. Instead, a blocking barrier is electrostatically induced in the base layer at high collector current densities: this barrier increases base recombination and decreases the current gain. We show that tunneling transport must be considered at the base/collector heterojunction and that the induced barrier depends on the base layer doping level—effectively, InP/GaAsSb DHBTs display high-current limitations that are also controlled to some extent by the base doping level. [ABSTRACT FROM AUTHOR]

HEMT small-signal equivalent-circuit (SSEC) extractions are of great utility in device characterization, as well as in the design of low-noise amplifiers. Despite the importance of low-noise HEMTs in cryogenic applications, the literature shows little or no work on the temperature dependence of SSEC extractions. This work addresses the question in detail. We recently reported a robust nondestructive accurate room-temperature extraction procedure that we presently apply to InP HEMTs between 5 and 350 K. The extracted SSEC reproduces measured S-parameters well as a function of temperature without the need for optimization. As well, extrinsic resistance and inductive element values exhibit physically correct temperature variations and thereby support the suitability of the present procedure down to cryogenic temperatures. Our work provides a detailed characterization of HEMT SSEC extractions over the broadest temperature range published to date. [ABSTRACT FROM PUBLISHER]

In early 2011, Assimpredil ANCE (Association of construction firms and related industries in the provinces of Milan, Lodi, Monza and Brianza), together with the Muicipality of Milan, the Milano Chamber of Architects, IN/ARCH Lombardia and FederlegnoArredo, organized a competition to form a directory for high-performance, low-cost housing buildings proposals. Aim of the competition was to promote architectural quality, research and innovation in the housing sector by offering practical examples of high-performance, low-cost housing designs that fulfill the specific requirements. Participants were invited to submit designs on two themes: a 12 floors tower building and a 5 floors horizontal building, both intended with a GFA of about 5,000 sqm. The proposal were asked to deal with: • Prefabricated and/or traditional construction system with high performance standards. • Attention to the building's life cycle and its operating and management costs from the perspective of environmental sensitivity. • Control and containment of costs and construction times with the contractor guaranteeing completion. • Optimal usability and design flexibility. • Optimization of energy efficiency and acoustic performance, low CO2 emissions, minimization of indoor and outdoor pollution. • Milanese architectural identity given a contemporary sensibility. • Aggregability and flexibility of the apartments' building solutions. • Use of innovative components. After the selection made by the technical jury, 125 projects were admitted to the directory. A book has been published containing all projects told through images, technical drawings and a dashboard that summarizes, for each project, the technical performance and the assessment made by the qualitative jury. Editing the book, we had the opportunity to analyse in detail all projects, their structural characteristics, their performance and their architectural features. This paper aims to relate the results of this analysis, reporting, through a series of comparative studies, the state of the art of the Italian residential construction sector, its strengths and its weaknesses, the typological design strategies put in place and the available technologies. [ABSTRACT FROM AUTHOR]

HEMT performance critically depends on contact resistance, particularly in cryogenic applications, where the semiconductor resistance contributions are reduced, thanks to lower optical phonon scattering rates. The literature offers little about the temperature dependence of contact resistances in HEMTs. We report a temperature-dependent comparison of the annealed and nonannealed ohmic contacts for low-noise InP HEMTs. Contact resistances of annealed Ge/Au/Ni/Au and nonannealed Ti/Pt/Au ohmic contacts were characterized as a function of temperature between 5 and 350 K. Side-by-side comparison exposes the differences of nonannealed versus annealed structures with respect to the contact and sheet resistance. Whereas both contact types show equivalent performances at cryogenic temperatures for recessed cap structures reminiscent of practical HEMTs, our annealed contacts display a significant increase in contact resistance with increasing temperature, in marked contrast to the near temperature independence found in our nonannealed contacts. The finding is of importance since the source resistance directly enters the transistor minimum noise figure F\min in field-effect transistors. Additional contributions to the parasitic sheet resistance of ohmic, overlay, and electroplated interconnect metals are also characterized as a function of temperature. [ABSTRACT FROM PUBLISHER]

In this paper, a thorough evaluation of calibration residual uncertainty of on-wafer load-pull systems at millimeter-wave frequencies, with actual comparisons between real-time and non-real-time load-pull systems, is reported for the first time. Two figures of merit for uncertainty evaluation are taken into account, showing the differences between the two methodologies. In the case of non-real-time systems, based on a simulation tool developed for the purpose, typical values of uncertainties to be expected at millimeter-wave frequencies are shown. Finally, a methodology to reduce calibration residual uncertainty of non-real-time load-pull measurements, based on the optimization of a thru load-pull map, is for the first time introduced, and its effects on actual measurements of microwave HBTs at 40 GHz are shown. [ABSTRACT FROM PUBLISHER]

In order to assess possible human effects associated with glyphosate formulations used in the Colombian aerial spray program for control of illicit crops, a cytogenetic biomonitoring study was carried out in subjects from five Colombian regions, characterized by different exposure to glyphosate and other pesticides. Women of reproductive age (137 persons 15-49 yr old) and their spouses (137 persons) were interviewed to obtain data on current health status, history, lifestyle, including past and current occupational exposure to pesticides, and factors including those known to be associated with increased frequency of micronuclei (MN). In regions where glyphosate was being sprayed, blood samples were taken prior to spraying (indicative of baseline exposure), 5 d after spraying, and 4 mo after spraying. Lymphocytes were cultured and a cytokinesis-block micronucleus cytome assay was applied to evaluate chromosomal damage and cytotoxicity. Compared with Santa Marta, where organic coffee is grown without pesticides, the baseline frequency of binucleated cells with micronuclei (BNMN) was significantly greater in subjects from the other four regions. The highest frequency of BNMN was in Boyaca, where no aerial eradication spraying of glyphosate was conducted, and in Valle del Cauca, where glyphosate was used for maturation of sugar cane. Region, gender, and older age (≥35 yr) were the only variables associated with the frequency of BNMN measured before spraying. A significant increase in frequency of BNMN between first and second sampling was observed in Narino, Putumayo, and Valle immediately (<5 d) after spraying. In the post-spray sample, those who reported direct contact with the eradication spray showed a higher quantitative frequency of BNMN compared to those without glyphosate exposure. The increase in frequency of BNMN observed immediately after the glyphosate spraying was not consistent with the rates of application used in the regions and there was no association between self-reported direct contact with eradication sprays and frequency of BNMN. Four months after spraying, a statistically significant decrease in the mean frequency of BNMN compared with the second sampling was observed in Narino, but not in Putumayo and Valle del Cauca. Overall, data suggest that genotoxic damage associated with glyphosate spraying for control of illicit crops as evidenced by MN test is small and appears to be transient. Evidence indicates that the genotoxic risk potentially associated with exposure to glyphosate in the areas where the herbicide is applied for coca and poppy eradication is low. [ABSTRACT FROM AUTHOR]

Abstract: Degenerative ocular diseases are widespread in the population and represent a major cause of reversible and irreversible blindness. Scientific evidences have been accumulating supporting the role of genotoxic damage and gene environment interactions in the pathogenesis of these diseases mainly including glaucoma, age-related macular degeneration, and cataract. Glaucoma, in its degenerative form, is characterized by the degeneration of the trabecular meshwork, the tissue of the anterior chamber of the eye devoted to aqueous-humour outflow. Such a degenerative process results in intra-ocular pressure increase and progressive damage of optic nerve head. Oxidative stress and DNA damage play an important role in inducing the degeneration of these well differentiated target tissues in which DNA damage results in a progressive cell loss. Macular degeneration is a common age-related disease affecting the central regions of the retina inducing progressive accumulation of oxidized lipoproteins and neovascularization. Environmental genotoxic risk factors include diet, light, and cigarette smoke paralleled by individual susceptibility as determined by adverse genetic assets. Cataract is a progressive opacity of the crystalline lens resulting from molecular damages induced by various risk factors including UV-containing light. This disease has been related to a failure in antioxidant defences. Experimental study provides evidence that cataract patients possess higher basal level of DNA damage, as evaluated by Comet test, in lymphocytes than controls. This finding is paralleled by the higher susceptibility to oxidative stress observed in the same patients. These novel experimental data further support the role of DNA damage as a main factor contributing to cataract onset. In conclusion, the examined degenerative ocular diseases recognise environmental risk factors often displaying genotoxic attitudes. Whenever these factors target individuals who are susceptible due their genetic assets the results is the onset of a specific eye disease depending on the affected ocular tissue. [Copyright &y& Elsevier]

AlGaN/GaN high-electron mobility transistor ‘hot’ parasitic source and drain resistances RS,D are determined under operating biases through wideband S-parameter measurements, without the use of ‘ColdFET’ biasing conditions. Both RS and RD are found to increase dramatically over ColdFET values, both for biases approaching threshold and for open-channel conditions. Parasitic resistance values have a significant effect on the extracted small-signal equivalent circuit model elements, as well as on the apparent device linearity. The bias dependence of access resistances modifies the understanding of the transistor physical operation: A revised delay time analysis accounting for the bias dependence of parasitic resistances shows that the effective average electron velocity in the AlGaN/GaN two-dimensional electron-gas channel is approximately equal to 1.9 × 107 cm/s. This new value of channel velocity is also consistent with the CGS/gMO ratio obtained when the bias dependence of RS and RD is accounted for during the extraction of the transistor small-signal equivalent circuit model. [ABSTRACT FROM AUTHOR]

While current collapse affects AlGaN/GaN heterojunction field-effect transistors (HFETs) around room temperature, it gradually gives place to a current enhancement with cooling—below 200 K, electrically stressed devices do show higher currents than in their prestressed state. This behavior can be explained by increased levels of channel impact ionization at lower temperatures. The positive hole charge generated by impact ionization compensates (and eventually dominates) the parasitic negative charge that is responsible for current collapse at higher temperatures (i.e., the “virtual gate charge”). Cooling of AlGaN/GaN HFETs may potentially alleviate some of the nonidealities that have so far plagued this technology. [ABSTRACT FROM AUTHOR]

We report on the tradeoff between current gain β and the base sheet resistance RSH in metalorganic chemical vapor deposition-grown NpN InP/GaAs1-xSbx/InP double-heterojunction bipolar transistors (DHBTs) with heavy base carbon-doping levels resulting in hole concentrations NB ranging from 4×1019 to 12×1019 /cm3. In contrast to Ga0.47In0.53As and GaAs–based transistors, which both display gain variations proportional to 1/(NB×WB)2 due to Auger recombination at high doping levels, neutral base recombination in InP/GaAsSb/InP DHBTs is not limited by Auger processes, and the measured current gain is proportional to 1/(NB×WB). We show that GaAs1-xSbx base layers offer a growing lifetime advantage over Ga0.47In0.53As with increasing doping levels. Potential explanations for the observed suppression of Auger recombination in the InP–GaAsSb system are proposed. [ABSTRACT FROM AUTHOR]

We report on the implementation of InAs-channel heterostructure-field-effect transistors (HFETs) fabricated with InAs/AlSb short-period superlattice barriers. The InAs/AlSb superlattice barrier structure is advantageous for InAs/AlSb HFETs because of its improved chemical stability against oxidation when compared to pure AlSb, and its compatibility with silicon as an n-type dopant during growth by molecular beam epitaxy. The structures examined here consist of a 200-A˚-wide InAs quantum well inserted between 25/25 A˚ InAs/AlSb superlattice barriers that provide a 0.5 eV conduction band discontinuity between the quantum well and the superlattice barrier. Fabricated HFET devices display complete channel modulation, confirming the field-effect operation at room temperature. In addition, we demonstrate the modulation doping of an InAs quantum well clad by silicon-doped InAs/AlSb superlattice barriers. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this letter we report the Arrhenius-type dependence of the valley current density on inverse temperature in a triple-well asymmetric resonant tunneling diode. The activation energy is found to be equal to the effective phonon energy representing the AlAs and GaAs-like mode of AlAs in the AlxGa1-xAs barrier layers of a triple well asymmetric resonant tunneling (RT) diode operating at temperatures as high as 350 K. The data presented here correlate the longitudinal optical phonons to the excess valley current found in AlxGa1-xAs/GaAs RT devices between 200 and 350 K and raise the possibility of phonon spectroscopy of high quality barrier layers via resonant tunneling transport experiments. [ABSTRACT FROM AUTHOR]

Current collapse in AlGaN/GaN HEMTs is normally attributed to charged surface states which deplete the channel in the extrinsic gate-to-drain region due to the highest electric fields in the devices. It is demonstrated that the gate-source region also plays a significant role in current collapse through the selective passivation of transistors using evaporated Al2O3 patterned via a lift-off process. The approach allows discriminating between the respective contributions of the source and drain regions to the current collapse. [ABSTRACT FROM AUTHOR]

Current collapse in (Al,Ga)N/GaN HFETs is generally associated with electrical stresses in the gate-to-drain region. It is demonstrated through pulsed I-V measurements that the source access region can also give rise to severe current collapse in (Al,Ga)N/GaN HFETs. The effect is of significance to the design of (Al,Ga)N/GaN HFET highefficiency power amplifiers and transmit/receive (T/R) switches because such circuits often result in electrical stresses to the gatesource region. [ABSTRACT FROM AUTHOR]

Background:The cytokinesis-block micronucleus test (MNT), as a marker of chromosomal mutagen sensitivity, was applied in a number of studies enrolling breast cancer (BC) patients and subjects with known or putative genetic predisposition to BC. The large majority of them involve the evaluation of induced micronuclei (MN) frequency in peripheral lymphocytes, after the in vitro challenge with ionising radiations.Methods:The aim of the present systematic review and meta-analysis is to investigate the role of MN assay in the identification of individuals at increased risk of BC and its potential use as prescreening test in women with a family history (FH) of BC.Results:Twelve studies were included in the meta-analysis, covering a time interval 1998-2007, and including 752 cases and 593 controls. Among the cases, 629 are cancer patients and 123 are cancer-free subjects, including 32 first-degree relatives of the susceptible subjects and 91 BRCA1/2 mutation carriers. Our meta-analysis reveals a significant increase of baseline MN frequency related to cancer status, but the association with FH of BC and specifically with BRCA mutations is not clear. A larger difference in MN frequency between cases and controls was observed after in vitro challenge, but response to radiation exposure doesn't appear to better discriminate cancer-susceptible subjects.Conclusion:Our study suggests the presence of some bias affecting many of these studies, reinforcing the suggestion that a more rigorous study design is needed in this area. [ABSTRACT FROM AUTHOR]

Abstract: The paper outlines a 2-tier approach for wide-scale biomonitoring programmes. To obtain a high level of standardization, we suggest the use of caged organisms (mussels or fish). An “early warning”, highly sensitive, low-cost biomarker is employed in tier 1 (i.e. lysosomal membrane stability (LMS) and survival rate, a marker for highly polluted sites). Tier 2 is used only for animals sampled at sites in which LMS changes are evident and there is no mortality, with a complete battery of biomarkers assessing the levels of pollutant-induced stress syndrome. Possible approaches for integrating biomarker data in a synthetic index are discussed, along with our proposal to use a recently developed Expert System. The latter system allows a correct selection of biomarkers at different levels of biological organisation (molecular/cellular/tissue/organism) taking into account trends in pollutant-induced biomarker changes (increasing, decreasing, bell-shape). A selection of biomarkers of stress, genotoxicity and exposure usually employed in biomonitoring programmes is presented, together with a brief overview of new biomolecular approaches. [Copyright &y& Elsevier]

Abstract: Peptide nucleic acids (PNAs) are synthetic homolog of nucleic acids in which the phosphate-sugar polynucleotide backbone is replaced by a flexible polyamide. They bind complementary polynucleotide sequences with higher affinity and specificity than their natural counterparts. PNAs linked to the appropriate nuclear localization signal (NLS) peptide have been used to selectively down-regulate the expression of several genes in viable cells. For example in Burkitt''s lymphoma (BL) cells the c-myc oncogene is translocated in proximity to the Eμ enhancer of the Ig gene locus and upregulated. PNAs complementary to the second exon of c-myc or to the Eμ enhancer sequence (PNAEμ-NLS), selectively and specifically block the expression of the c-myc oncogene and inhibit cell growth in vitro and in vivo. PNAEμ-NLS administration to mice did not exhibit toxic effects even at the highest concentration allowed by the experimental conditions. Because of the accumulating data confirming PNAEμ-NLS potential therapeutic value, PNAEμ-NLS was evaluated for the inability to induce mutations in tester strains of Salmonella typhimurium, Escherichia coli, and at the hprt locus in Chinese hamster ovary cells (CHO). Moreover, the induction of chromosomal aberrations in CHO cells and of micronuclei in human lymphocytes were investigated. We may conclude that PNAEμ-NLS neither induces mutations nor has clastogenic effects as detectable by treatment under the standard test conditions. [Copyright &y& Elsevier]

Surface recombination effects are studied in non-passivated non-self-aligned and self-aligned NpN InP-GaAsSb-InP double heterostructure bipolar transistors (DHBTs) down to sub- micrometer emitter dimensions, and over current densities ranging from 10 A/cm² to 100 kA/cm². The present study is motivated by the drive to scale InP DHBTs for higher speeds and integration densities. Self-aligned InP-GaAsSb-InP DHBTs are characterized by weak emitter size effects (ESEs), and periphery recombination currents are found to be very nearly identical to published results for InP-GaInAs SHBTs despite the major differences in emitter junction band alignments ("type-II" versus "type-I") and injection mechanisms (thermal versus hot electron injection). The correspondence of measured periphery currents in both systems indicates that ESEs are dominated by a mechanism common to InP-GaAsSb and InP-GaInAs devices: this requirement is fulfilled by the direct electron injection from the InP emitter mesa sidewalls onto the extrinsic base surface. Consideration of band alignments and surface depletion effects at the extrinsic base surface is used to explain the commonality of emitter size effects in InP-GaAsSb and InP-GaInAs devices. [ABSTRACT FROM AUTHOR]

Type-II InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with a 15-nm base were fabricated by contact lithography: 0.73 × 11 μm² emitter devices feature fT = 384 GHz (fMAX = 262 GHz) and BVCEO = 6 V. This is the highest fT ever reported for InP/GaAsSb DHBTs, and an "all-technology" record fT × BVCEO product of 2304 GHz·V. This result is credited to the favorable scaling of InP/GaAsSb/InP DHBT breakdown voltages (BVCEO) in thin collector structures. [ABSTRACT FROM AUTHOR]

Current collapse in AlGaN/GaN field-effect transistors subjected high rf drive levels and/or to bias stresses is attributed to the presence of surface trapping levels whose nature remains to be identified. Although current collapse manifestations can be alleviated with various surface films, the exact passivation mechanism remains a matter of debate. We show that slow transient current collapse can be eliminated by a short ozone exposure, unambiguously tying current collapse to the sample surface, without invoking strain or dielectric encapsulation arguments. We assert that the surface states responsible for slow collapse arise where dislocations intersect the sample surface, and propose an alternative current collapse mechanism wherein individual dislocation lines result in multiple discrete virtual gates that locally deplete the transistor channel access regions. [ABSTRACT FROM AUTHOR]

We characterize the resistivity of InP buffer layers deposited by metal-organic vapor-phase epitaxy for the fabrication of Al-free GaInP/GaInAs high electron mobility transistors (HEMTs). Achieving highly-resistive InP buffer layers on semi-insulating (SI) InP:Fe substrates has long been recognized to be challenging. This is particularly true in HEMT applications because such devices are especially sensitive to the deleterious effects of buffer leakage currents. Our experiments show that impurities arising from the SI InP substrate as well as from reactor parts produce an overall n-type doping concentration of n=1-10×1016 cm-3 near the buffer/substrate interface, which decays exponentially to a level of 4×1014 cm-3 after approximately 1 μm of InP growth. This nonintentional impurity incorporation leads to a parasitic channel in the buffer and a current leakage path for the HEMT structures, regardless of the growth conditions used. Highly-insulating buffer layers could however be obtained with InP doped by Fe at a concentration of 6×1016 cm-3 in a thin region near the InP:Fe substrate. The sheet resistance consequently increased from RS=3 000 Ω/□ for the not intentionally doped InP layers to RS=9.4×107 Ω/□ when Fe-doping is used in the buffer layers, a value suitable for the realization of high-speed HEMTs. As a demonstration vehicle, Al-free pseudomorphic T-gate GaInP/GaInAs HEMTs with a 100 nm footprint were fabricated and achieved a cutoff frequency of fT=fMAX∼250 GHz based on a still nonoptimized channel structure featuring a mobility and sheet carrier concentration of 10 000 cm2/V s and 1012 cm-2, respectively. The present work differentiates itself from previous Fe doping studies of InP by clarifying and quantifying the physical processes leading to parasitic conduction in not intentionally doped InP buffer layers grown on InP:Fe substrates. [ABSTRACT FROM AUTHOR]

Optimum device performance in terms of noise and gain of AlInAs/GaInAs/InP High Electron Mobility Transistors (HEMTs) requires minimizing the contact resistance ${R} _{C}$. In several HEMT fabrication steps in device manufacturing it is common to expose highly doped semiconductors layers to heated solvents for prolonged periods of time. It is shown here that even a small amount of water or water vapor present during photoresist removals, metal lift-offs or related processes can dramatically affect the final device performance by promoting electrochemical etching of the semiconductor layers adjacent to metal stacks. In this paper, the impact of metal lift-off on erosion of HEMT epitaxial layers and Ohmic contact resistance is studied with respect to different layer doping levels, compositions and metal stacks forming the Ohmic contacts. [ABSTRACT FROM AUTHOR]

GaInAs/InAs composite channels in InP-based pHEMTs enable wideband and/or low-noise performances because of their superior carrier transport properties. To date, the influence of the InAs inset design details on transistor performance has not been parametrized in the literature. We present a systematic study of the effects of the InAs channel inset thickness on transistor characteristics and cutoff frequencies versus temperature, and on the noise performance at 300 K. The epitaxial layer structures considered here incorporate 2 to 5-nm InAs insets in a fixed total composite channel thickness. All layers exhibit excellent electron mobilities (from 40 200 to 54 800 cm2/Vs at 77 K). Thicker InAs insets improve both the current gain cutoff frequency (${f}_{\text {T}}$) and the maximum oscillation frequency (${f}_{\text {MAX}}$). However, they also result in higher gate leakage currents and increased channel impact ionization. 50-nm gate length pHEMTs with a 5-nm InAs inset feature the highest simultaneous ${f}_{\text {T}} / {f}_{\text {MAX}} \ge {390}$ /675 (455/800) GHz at 300 (15) K for a low-noise bias but exhibit the poorest minimum noise figure ${NF}_{\text {MIN}}$. Whereas higher ${f}_{\text {T}}$ (and/or ${f}_{\text {MAX}}$) values have traditionally been associated with improved noise performances, this is no longer the case. [ABSTRACT FROM AUTHOR]

Presents a Raman scattering study of strained layer superlattices. Application of molecular beam epitaxy in the growth of the superlattices; Determination of structural parameters by Rutherford backscattering and x-ray diffraction; Experimental details; Result of the study.

A Pt/Ti/Pt/Au gate electrode stack is commonly used in AlInAs/GaInAs/InP high electron mobility transistors due to the high Schottky barrier height of Pt on AlInAs and the fact that Pt can be controllably diffused through semiconductor layers thereby enabling vertical scaling. We show here that the Pt-AlInAs reaction is not only controlled by the annealing time and temperature—the annealing ambient and the thermal ramp rate also affect the diffusion of Pt through the underlying semiconductor layers and impact the DC and RF device performance. Following the gate metal deposition, one process split was rapid thermal annealed at 250 °C and subsequently passivated by atomic layer deposition (ALD) at 180 °C. For the second process split, the Pt gate sink-in process was carried out in the ALD system at 250 °C simultaneously with the gate passivation. Despite identical gate sink-in temperatures, the two process splits exhibit different characteristics suggesting different gate-to-channel distances. The distance of the Pt gate to the GaInAs channel was therefore confirmed through high-resolution cross-sectional scanning transmission electron microscopy analysis. The results presented here reveal that both the suitable ramp rate and the sink-in ambient are necessary to achieve a fully sunken Pt gate. [ABSTRACT FROM AUTHOR]

Analysis of cEVTs (n = 19) DNA content showed a fold change of 1.47, consistent with triploid karyotype. Partial hydatiform moles (PHM) are mainly derived from a dispermic fertilisation of the oocyte and the karyotype is 90% of the time triploid and either 69,XXX or 69,XXY or 69,XYY. Therefore, three different DNA ploidy statuses were assessed and the results clearly showed that the ploidy that best shapes the copy-number signal correspond to a triploid status with a 69,XXY karyotype, that was subsequently confirmed by cytogenetic analysis on chorionic villi. [Extracted from the article]

As expected, the 3 monochorionic pregnancies showed only one genetic profile; 3/5 known dizygotic pregnancies and 2/2 dichorionic pregnancies showed 2 profiles. EP15.08: Single circulating extravillous trophoblasts for non-invasive cell-based prenatal testing in twin pregnancies Multifetal pregnancies are at increased risk for pregnancy complications and adverse outcomes. [Extracted from the article]

We present a complete methodology to evaluate the accuracy of the microwave transistor figures-of-merit fT (current gain cutoff frequency) and fMAX (maximum oscillation frequency). These figures-of-merit are usually extracted from calibrated S-parameter measurements affected by residual calibration and measurement uncertainties. Thus, the uncertainties associated with fT and fMAX can be evaluated only after an accurate computation of the S-parameters uncertainties. This is done with the aid of two recently released software tools. In the uncertainty propagation, the standard de-embedding techniques are assumed to be error free, but still contribute to the final uncertainty budget via their measurement uncertainty. We also present an analysis of how different interpolation/extrapolation methodologies affect uncertainty. In addition, an overview of the possible causes of errors and suggestions on how to avoid them are given. With the continued rise of reported fT/fMAX values, this work has become necessary in order to evaluate the accuracy of these figures-of-merit both by adding confidence intervals to their values and by identifying possible extraction errors. [ABSTRACT FROM PUBLISHER]

We report the large-signal performance of high electron mobility transistors (HEMTs) fabricated on GaN- and AlN-capped AlInN/GaN epilayers grown on semi-insulating SiC substrates. Large-signal measurements at 10 and 40 GHz are presented with both gate and drain dynamic loadlines to clarify the factors limiting the high-power performance. Devices fabricated with AlN-capped epilayers show a marginal advantage in terms of higher current and reduced dispersion, but GaN-capped epilayers perform better in terms of reduced short-channel effects and better channel control. In large-signal operation at 40 GHz, both device types delivered power densities in excess of 4.5 W/mm. A maximum power density of 5.8 W/mm is achieved on GaN-capped devices which is, to the best of our knowledge, the highest power density reported at 40 GHz in AlInN/GaN-based HEMTs. [ABSTRACT FROM AUTHOR]

Abstract-Type-II n-p-n InP/GaAsSb/InP double heterostructure bipolar transistors (DHBTs) that are fabricated by optical lithography with a 0.6 × 5 μm² emitter on a 20-nm compositionally uniform GaAszSb1-x carbon-doped base with x = 0.60 and a 75-nm InP collector show current-gain cutoff frequencies as high as 423 GHz at 10 mA/μm2 and feature a BVCEO = 4 V. The pseudomorphic As-rich InP/GaAsSb DHBTs feature a high maximum dc current gain of > 160, owing to the reduction of the type-II conduction band discontinuity ΔEc and the associated recombination at the InP/GaAsSb emitter-base interface. This brief demonstrates that the InP/GaAsSb DHBT technology can combine high gain, wide bandwidths, high-current drivability, and structural simplicity. [ABSTRACT FROM AUTHOR]

Objective: Dietary supplementation with guar gum or fructose has been reported to reduce the postprandial glycemic response to an oral glucose challenge. As a result of the poor palatability of most foods containing guar gum, a novel low-viscosity beverage with guar gum was developed that becomes viscous in vivo through an enzymatic induction. The primary study objective was to determine the effect of an amylase-induced viscosity (I-V) product, with or without supplemental fructose, on the postprandial glycemic response to a high glycemic index test meal in healthy nondiabetic subjects. Design: The study was a four-treatment, placebo-controlled, double-blind, randomized block protocol. Setting: The study was performed at Glycaemic Index Testing, Inc., Toronto, Ontario, Canada. Subjects: A total of 30 healthy nondiabetic volunteers (13 male, 17 female, mean ± s.e.m. age of 51 ± 3 y and body mass index of 24.2 ± 0.4 kg/m²) participated in the study. Intervention: In the morning after an overnight fast, subjects participated in four 3-h meal glucose tolerance tests on separate occasions. The test meals contained 50 g of available carbohydrate from maltodextrin and white bread (control) or the same meal with either 5 g of guar gum (3.6 g galactomannan), 5 g of fructose, or 5 g of guar gum + 5 g of fructose. Results: Treatments containing guar gum had a reduced (P<0.01) baseline-adjusted peak glucose response and incremental area under the glucose curve. In contrast to previous studies, fructose increased (P<0.05) the baseline-adjusted peak glucose concentration. Conclusions: Guar gum incorporated into an amylase I-V product provided a means to stabilize blood glucose levels by reducing the early phase excursion and then by appropriately maintaining the later phase excursion in healthy nondiabetic humans. [ABSTRACT FROM AUTHOR]

• Micronucleus experiments are the most widely used approach in human biomonitoring. • Many published studies have severe methodological shortcomings. • The article describes important quality criteria which should be fulfilled. • It contains relevant information concerning the group size and number of cells to be scored. Micronucleus (MN) analyses in peripheral blood lymphocytes and exfoliated cells from different organs (mouth, nose, bladder and cervix) are at present the most widely used approaches to detect damage of genetic material in humans. MN are extranuclear DNA-containing bodies, which can be identified microscopically. They reflect structural and numerical chromosomal aberrations and are formed as a consequence of exposure to occupational, environmental and lifestyle genotoxins. They are also induced as a consequence of inadequate intake of certain trace elements and vitamins. High MN rates are associated with increased risk of cancer and a range of non-cancer diseases in humans. Furthermore, evidence is accumulating that measurements of MN could be a useful tool for the diagnosis and prognosis of different forms of cancer and other diseases (inflammation, infections, metabolic disorders) and for the assessment of the therapeutic success of medical treatments. Recent reviews of the current state of knowledge suggest that many clinical studies have methodological shortcomings. This could lead to controversial findings and limits their usefulness in defining the impact of exposure concentrations of hazardous chemicals, for the judgment of remediation strategies, for the diagnosis of diseases and for the identification of protective or harmful dietary constituents. This article describes important quality criteria for human MN studies and contains recommendations for acceptable study designs. Important parameters that need more attention include sufficiently large group sizes, adequate duration of intervention studies, the exclusion of confounding factors which may affect the results (sex, age, body mass index, nutrition, etc.), the evaluation of appropriate cell numbers per sample according to established scoring criteria as well as the use of proper stains and adequate statistical analyses. [ABSTRACT FROM AUTHOR]

We present a novel multistep method to enrich and isolate circulating fetal extravillous trophoblasts (fEVTs) for molecular characterisation. Genetic analysis of fetal cells from 131 women resulted in identification of 15 cases with common chromosomal abnormalities, with 100% concordance with standard karyotyping following invasive diagnostic sampling. Conclusions This novel, fully automated, non-invasive method for isolation and testing of individual fetal cells could enable the routine detection of clinically relevant genomic alterations. [Extracted from the article]

We report on the low-temperature growth of heavily Si-doped (>1020 cm-3) n -type GaN by 4 N-rich ammonia molecular beam epitaxy (MBE) with very low bulk resistivity (<4 x 10-4 Ω x cm). This is applied to the realization of regrown ohmic contacts on InAlN/GaN high electron mobility transistors. A low n+-GaN/2 dimensional electron gas contact resistivity of 0.11 Ω x mm is measured, provided an optimized surface preparation procedure, which is shown to be critical. This proves the great potentials of ammonia MBE for the realization of high performance electronic devices. [ABSTRACT FROM AUTHOR]

Approximately 165,000 and 311,000 individuals die annually from urothelial (UC) and cervical (CC) cancer. The therapeutic success of these cancers depends strongly on their early detection and could be improved by use of additional diagnostic tools. We evaluated the current knowledge of the use of micronucleus (MN) assays (which detect structural and numerical chromosomal aberrations) with urine- (UDC) and cervix-derived (CDC) cells for the identification of humans with increased risks and for the diagnosis of UC and CC. Several findings indicate that MN rates in UDC are higher in individuals with inflammation and schistosomiasis that are associated with increased prevalence of UC; furthermore, higher MN rates were also found in CDC in women with HPV, Candidiasis and Trichomonas infections which increase the risks for CC. Only few studies were published on MN rates in UDS in patients with UC, two concern the detection of recurrent bladder tumors. Strong correlations were found in individuals with abnormal CC cells that are scored in Pap tests and histopathological abnormalities. In total, 16 studies were published which concerned these topics. MN rates increased in the order: inflammation < ASC-US/ASC-H < LSIL < HSIL < CC. It is evident that MNi numbers increase with the risk to develop CC and with the degree of malignant transformation. Overall, the evaluation of the literature indicates that MNi are useful additional biomarkers for the prognosis and detection of CC and possibly also for UC. In regard to the diagnosis/surveillance of UC, further investigations are needed to draw firm conclusions, but the currently available data are promising. In general, further standardization of the assays is needed (i.e. definition of optimal cell numbers and of suitable stains as well as elucidation of the usefulness of parameters reflecting cytotoxicity and mitotic activity) before MN trials can be implemented in routine screening. [ABSTRACT FROM AUTHOR]

We have measured the Raman spectra of heavily carbon doped (p > 10[sup 19] cm[sup -3]) GaSb and GaAsSb. A local vibrational mode (LVM) due to carbon residing on group-V lattice sites was observed at 540 cm[sup -1] for GaSb and 568 cm[sup -1] for GaAs[sub 0.44]Sb[sub 0.56]. A gap mode at 164 cm[sup -1] was observed for GaSb. The frequency of the LVM as well as the gap mode is in quantitative agreement with recent theoretical predictions. [ABSTRACT FROM AUTHOR]

We have detected three- and six-fold lateral ordering in undoped and carbon-doped GaAs[sub 1-x]Sb[sub x] films (0.4

Reported is the first experimental microwave noise characterisation of 0.9×11.5 µm2 emitter AlInAs/GaAsSb/InP double heterojunction bipolar transistors with a ‘type-I’ AlInAs emitter. The devices feature cutoff frequencies of fT=210 GHz and fMAX=127 GHz, and achieve a minimum noise figure NFmin<3 dB with an associated gain GA=12 dB at 10 GHz. [ABSTRACT FROM AUTHOR]

The realisation of 0.1 µm gate AlGaN/GaN high electron mobility transistors grown on high-resistivity silicon substrates is reported. A maximum current density of 750 mA/mm and an extrinsic transconductance of 225 mS/mm are achieved. The devices feature a record current gain cutoff frequency as high as fT=90 GHz, the highest value ever reported from a GaN-based device grown on a silicon substrate. The results demonstrate the great potential of GaN-on-silicon technology for low-cost millimetre-wave applications. [ABSTRACT FROM AUTHOR]

We characterize a KOH-based ultraviolet (UV) photoassisted wet etching technique using K[sub 2]S[sub 2]O[sub 8] as the oxidizing agent. The solution provides a well-controlled etch rate and produces smooth high-quality etched surfaces with a minimal degradation in surface roughness as measured by atomic force microscopy. The evolution of the solution pH upon exposure to UV radiation is identified as key to obtaining smooth etched surfaces and a controlled etch rate: Unless steps are taken to maintain the pH above 12.0, the etch rate displays a sharp drop that coincides with a gross roughening of the etched surface. The applicability of the present technique is demonstrated by the fabrication of high-quality mesa-isolated AlGaN/GaN hetrostructure field-effect transistors. In addition, the etch presented here features a high selectivity to C-doped layers which should prove useful in the fabrication of AlGaN/GaN hetrostructure bipolar transistors. The method is well adapted to device processing applications because it does not require connection to the sample to an external electrochemical cell. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The optical properties of lattice-matched GaAsSb/InGaAs/InP heterostructures with a varying InGaAs layer thickness (0–900 Å) were investigated. These structures display strong low temperature type II luminescence, the energy of which varies with the InGaAs layer thickness and ranges from 0.453 to 0.63 eV. The type II luminescence was used to determine directly and accurately the conduction band offset of these structures. The values obtained herein are 0.36 and 0.18 eV at 4.2 K for the GaAsSb/InGaAs and GaAsSb/InP heterojunctions, respectively, with the GaAsSb conduction band higher in energy. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]