Equivalent Ge Research Articles

Interpretation of FISH Results in the Case of Nonuniform Internal Radiation Exposure of Human Body with the Use of Model Approach

The fluorescence in situ hybridization (FISH) technique allows for the estimation of the number of stable chromosomal aberrations (translocations) in human blood T-lymphocytes decades after radiation exposure. Therefore, it is used for retrospective assessment of irradiation doses received by red bone marrow (RBM). Cytogenetic analysis of individuals exposed on the Techa River in the 1950s to 89,90Sr, locally irradiating RBM, showed that dose assessment based on FISH data led to underestimation of the actual dose estimated from measurements of whole-body 90Sr content. The purpose of current study was to evaluate the dose–effect relationship and the frequency of translocations per 1 Gy of RBM irradiation dose and T-lymphocytes dose for donors living in Techa riverside villages (n = 178; translocation yield = 2389; number of genome equivalents GE = 96 446). Irradiation doses were estimated using the latest version of the Techa River dosimetry system and the T-cell irradiation model. Statistical analysis showed that the frequency of translocations per 1000 GE per 1 Gy of RBM dose was 8.0 ± 0.7; this value was statistically significantly lower than the value estimated for Sellafield radiation workers under external exposure (11.6 ± 1.6). At the same time, the use of T-cell and their progenitor doses led to re-evaluation (increase) in the slope of the dose–response curve to 11.8 ± 1.6 per 1 Gy per 1000 GE, which agreed well with the published data. The obtained estimates of the background frequencies of translocations also were close to the published values ​​for unexposed donors. These findings demonstrate the legitimacy of using a model approach for estimation of irradiation doses in T-lymphocytes and their progenitors and the need to take into account complex T-cell dynamics in interpretation of cytogenetic data for the purposes of biodosimetry.

Modeling the threshold voltage of PNIN SSOI tunnel field‐effect transistor

AbstractIn this paper, a physically based analytical threshold voltage model for PNIN strained‐silicon‐on‐insulator tunnel field‐effect transistor (PNIN SSOI TFET) is proposed by solving the two‐dimensional (2D) Poisson equation in narrow N+ layer and intrinsic region. In the proposed model, the effect of strain (in terms of equivalent Ge mole fraction), narrow N+ layer and gate dielectric, and so on, is being considered. The validity of the proposed model is verified by comparing the model results with 2D device simulation results. It is demonstrated that the proposed model can correctly predicts the trends in threshold voltage with varying the device parameters. This proposed model can be effectively used to design, simulate, and fabricate the PNIN SSOI TFETs with the desired performance. Copyright © 2015 John Wiley & Sons, Ltd.

Exploring novel characteristics of strain compensated SiGeC nanoscale MOSFET

In the present work a precise but simple empirical model for single gate nanoscale single-layer fully depleted strained-silicon-on-insulator MOSFET is proposed. The threshold voltage is calculated by solving the two-dimensional (2D) Poisson equation under befitting boundary conditions incorporating short-channel effects, the effect of strain, strained-silicon thin film thickness, and gate work function. The proposed empirical model provides results comparable with those obtained from 2D device simulation thereby establishing the extent of accuracy of our present model. The empirical model so developed correctly exhibits that the threshold voltage is reduced with the increase of strain in the silicon thin film. We have investigated, herewith our proposed model, the influences of various device parameters like: strain (with minute amount of carbon and significant amount of Ge), strained-silicon thin-film thickness and gate work function on the threshold voltage. The extent of equivalent Ge content enhances the performance of the proposed MOSFET in terms of better speed because of the carrier mobility enhancement due to addition of carbon atoms.

Analytical drain current model for nanoscale strained‐Si/SiGe MOSFETs

PurposeThe purpose of this paper is to present an analytical drain current model for output characteristics of strained‐Si/SiGe bulk MOSFET.Design/methodology/approachA physics‐based model for current output characteristics and transconductance of strained‐Si/SiGe bulk devices has been developed incorporating the impact of strain (in terms of equivalent Ge mole fraction), strained silicon thin film thickness, gate work function, channel length and other device parameters. The accuracy of the results obtained using this model is verified by comparing them with 2D device simulations.FindingsThis model correctly predicts the output characteristics, IDS−VGS characteristics, transconductance and output conductance of the strained‐Si/SiGe MOSFET and demonstrates a significant enhancement in the drain current of the MOSFET with increasing strain in the strained‐Si thin film, i.e. with increasing equivalent Ge concentration in the SiGe bulk.Research limitations/implicationsCan be implemented in a SPICE like simulator for studying circuit behaviour containing strained‐Si/SiGe bulk MOSFETs.Practical implicationsThe model discussed in this paper can be easily implemented in a circuit simulator and used for the characterization of strained silicon devices. This complements the recent trend of investigation of new materials and device structures to maintain the rate of advancement in VLSI technology.Originality/valueThis paper presents, for the first time, a compact surface potential‐based analytical model for strained‐Si/SiGe MOSFETs which predicts the device characteristics reasonably well over their range of operation.

A simple analytical threshold voltage model of nanoscale single-layer fully depleted strained-silicon-on-insulator MOSFETs

For the first time, a simple and accurate analytical model for the threshold voltage of nanoscale single-layer fully depleted strained-silicon-on-insulator MOSFETs is developed by solving the two-dimensional (2-D) Poisson equation. In the proposed model, the authors have considered several important parameters: 1) the effect of strain (in terms of equivalent Ge mole fraction); 2) short-channel effects; 3) strained-silicon thin-film doping; 4) strained-silicon thin-film thickness; and 5) gate work function and other device parameters. The accuracy of the proposed analytical model is verified by comparing the model results with the 2-D device simulations. It has been demonstrated that the proposed model correctly predicts a decrease in threshold voltage with increasing strain in the silicon thin film, i.e., with increasing equivalent Ge concentration. The proposed compact model can be easily implemented in a circuit simulator

Electrical and Structural Properties of Heavily Ge-Doped GaAs Grown by Molecular-Beam Epitaxy

The properties of GaAs highly doped with Ge grown by molecular-beam epitaxy (MBE) and migration-enhanced epitaxy (MEE) have been studied. We report here that, although Ge doped GaAs films grown by conventional MBE at temperatures lower than 450 °C tend to become semi-insulating materials, a conductive Ge-doped GaAs film with an electron concentration as high as 2×1019 cm-3 can be grown even at 300 °C by MEE. In MBE grown samples, a transition from n-type conductivity to p-type conductivity is observed when the Ge concentration of the films exceeds 1×1020 cm-3, whereas in MEE grown layers at 300 °C only n-type conductivity is observed regardless of the Ge concentration. The lattice constants of these MEE-grown samples are much larger than those of MBE-grown samples with equivalent Ge concentrations. These results indicate that Ge incorporation mechanism is quite different in MEE at low temperatures from that at high temperatures. The large lattice constant of as-grown MEE-grown layers suggests that a substantial fraction of Ge atoms occupy interstitial sites and act as donors. Postgrowth annealing results in marked reductions in lattice constant and electron concentration in MEE samples. The resulting lattice constants are even smaller than those of the n- and p-type GaAs films grown by MBE at high temperatures. This observed result can be explained in terms of (GaAs)1-x(Ge2)x alloy formation in MEE samples during annealing.

Energy balance of winter oilseed rape ( Brassica napus L.) cropping as related to nitrogen supply and preceding crop

Data from a field experiment (1995–2000) conducted on a fertile sandy loess in the Hercynian dry region of central Germany were used to determine the energy efficiency of winter oilseed rape ( Brassica napus L.) as affected by previous crop and nitrogen (N) fertilization. Depending on the previous crop, winter oilseed rate was cultivated in two different crop rotations: (1) winter barley ( Hordeum vulgare L.)–winter oilseed rape–winter wheat ( Triticum aestivum L.), and (2) pea ( Pisum sativum L.)–winter oilseed rape–winter wheat. Fertilizer was applied to winter oilseed rape as either calcium ammonium nitrate (CAN) or cattle manure slurry. The N rates applied to winter oilseed rape corresponded to 0, 80, 160 and 240 kg N ha −1 a −1. Results revealed that different N management strategies influenced the energy balance of winter oilseed rape. Averaged across years, the input of energy to winter oilseed rape was highly variable ranging from 7.42 to 16.1 GJ ha −1. Lowest energy input occurred when unfertilized winter oilseed rape followed winter barley, while the highest value was obtained when winter oilseed rape received 240 kg N ha −1 organic fertilization and followed winter barley. The lowest energy output (174 GJ ha −1), energy from seed and straw of winter oilseed rape, was observed when winter oilseed rape receiving 80 kg N ha −1 as organic fertilizer followed winter barley. The energy output increased to 262 GJ ha −1 for winter oilseed rape receiving 240 kg N ha −1 as mineral fertilizer followed pea. The energy efficiency was determined using the parameters energy gain (net energy output), energy intensity (energy input per unit grain equivalent GE; term GE is used to express the contribution that crops make to the nutrition of monogastric beings), and output/input ratio. The most favourable N rate for maximizing energy gain (250 GJ ha −1) was 240 kg N ha −1, while that needed for minimum energy intensity (91.3 MJ GE −1) was 80 kg N ha −1 and for maximum output/input ratio (29.8) was 0 kg N ha −1.

High-resolution local vibrational mode spectroscopy of the negatively charged oxygen–vacancy complex in germanium

It was recently discovered that in irradiated germanium doped with oxygen a local vibrational mode occurs at 669cm−1 which could be ascribed to the negatively charged oxygen–vacancy (VO−) complex. In the 669cm−1 band and in another band at 731cm−1 due to a different defect, fine structure which indicated the occurrence of the Ge-isotope splitting of the modes could be partly resolved. We report here the results of high-resolution infrared measurements (res.=0.02cm−1) at liquid helium temperatures of the two bands. The oxygen-doped germanium ([Oi]=2.7×1017cm−3) was first irradiated with 2MeV electrons to increase the concentration of VO complexes. A second similar specimen received the same treatment but with subsequent anneals to obtain the 731cm−1 band. The experimentally observed splitting of the 669cm−1 band and the amplitudes of its individual components are accurately predicted using a model of a non-linear symmetric Ge–O–Ge molecule within a Ge crystal lattice, in agreement with the assignment of the mode to the VO− complex. A similar model also seems to apply to the yet unassigned 731cm−1 mode and the conclusion is made that the defect also must include a single O atom bonded to two equivalent Ge atoms. The higher annealing temperature of the unassigned band however indicates that the defect must be more complex than the VO center.

Isomers of Ge2N2: Production and infrared absorption of GeNNGe in solid N2

Crystalline germanium was ablated with light at 532 nm from a frequency-doubled Nd:YAG laser, and the resultant plume reacted with N2 before deposition onto a substrate at 20 K. Multiple absorption lines at 891.8, 890.8, 890.4, 889.9, 889.4, 888.9, 888.4, 887.9, 887.5, and 887.0 cm−1 that become enhanced after annealing of the matrix at 31 K are attributed to a species containing two Ge atoms in their isotopic variants: Ge70, Ge72, Ge73, Ge74, and Ge76. Replacing N214 with a mixture of N214 and N215 yields an additional multiplet in the region 867.1–862.1 cm−1, whereas reaction of the same mixture subjected to microwave discharge yields a further multiplet in the region 878.9–874.0 cm−1. The isotopic pattern indicates that the vibrational mode is associated with a Ge–N stretching motion that involves two equivalent Ge atoms and two equivalent N atoms. Theoretical calculations with density-functional theories (B3LYP/6-311+G* and B3LYP/aug-cc-pVTZ) predict nine stable isomers of Ge2N2, with linear GeNNGe and asymmetric angular Ge(GeNN) having the least energies. Among calculated vibrational wave numbers, IR intensities, and isotopic shifts for all isomers of Ge2N2, only those predicted for the asymmetric Ge–N stretching mode of linear GeNNGe fit satisfactorily with experimental results. GeNNGe is likely formed from direct reaction of Ge2 and N2 rather than from two-step reactions involving GeNN or GeN.

Nanometer Scale Composition Variations in Ge Quantum Dots on Si(100)

AbstractElectron-energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) was used to measure nm-scale composition variations in Ge/Si(100) islands grown by molecular beam epitaxy (MBE) at substrate temperatures 400°C ≤T ≤700°C and a growth rate of 1.4 ML/min (1 monolayer, ML=6.78x1014 atoms / cm2). These measurements were correlated with island ensemble morphology determined by atomic force microscopy (AFM). The average Si concentration of the islands and Si/Ge interface width increased monotonically with growth temperature. Integrated island volumes measured by AFM were proportional to the equivalent Ge coverage, øGe, with slopes greater than one for the higher deposition temperatures. This result confirms that the islands grow faster than the Ge deposition rate. Linear behavior of the island volume vs. øGe curves implies that the average Ge composition is independent of island size. The volume at which islands change shape from pyramids to domes correlates well with the average Ge content of the islands in the context of simple strain-scaling arguments. For T=700°C, rapid Si interdiffusion precludes formation of pure Ge pyramids for growth at 1.4 ML/min. Growth at 4.8 ML/min kinetically stabilizes pure Ge pyramid clusters, allowing their formation prior to Si interdiffusion.

Structure and formation mechanism of Ge E (') center from divalent defects in Ge-doped SiO2 glass

We have performed ab initio quantum-chemical calculations on clusters of atoms modeling a divalent Ge defect in Ge-doped SiO (2) glasses. It has been found that the divalent Ge defect interacts with a nearby GeO (4) tetrahedron, forming complex structural units that are responsible for the observed photoabsorption band at approximately 5 eV. We have shown that these structural units can be transformed into two equivalent Ge E' centers by way of the positively charged defect center.

Growth of Ge layers on Si(100) monitored by in situ ellipsometry

Ellipsometric monitoring of the growth of Ge layers on Si(100) by pyrolysis of GeH 4 at substrate temperatures of 400, 450 and 500°C was performed by using a single wavelength ellipsometer based on the four detector photopolarimeter. By coupling ellipsometric monitoring with X-ray photoelectron spectroscopy surface analysis, the changeover between bi-dimensional and tri-dimensional growth modality at 450°C was found at Ge coverage of about 1 ML. The recorded Ψ– Δ data were analysed by using a growth model based on the Effective Medium Approximation (EMA) in order to derive the fraction of voids v and the thickness of the EMA layer h EMA. The values found for v were consistent with the clustered morphology observed by Atomic Force Microscopy (AFM) analysis of the samples. A qualitative model for the island evolution and for the growth rate of the equivalent Ge layer as a function of the substrate temperature was derived from the calculated v and h EMA, in agreement with the indications given by AFM and Rutherford backscattering spectroscopy film characterisation.

Observation of lateral confinement effect in Ge quantum wires self-aligned at step edges on Si(100)

Spontaneous formation of step-edge Ge quantum wires and lateral quantum confinement effect are clearly observed in Si submonolayer-Ge/Si heterostructures grown on Si(100). By depositing submonolayer equivalent Ge (Q), the Ge atoms are found to line up in a wire-like fashion at the 〈01̄1〉 step edges as revealed by plan-view transmission electron microscopy. Photoluminescence (PL) peak energy shift with Q due to lateral quantum confinement of holes is clearly observed, and PL features characteristic of the quasi-one-dimensional system are also addressed.