Total Number Of Carriers Research Articles

Recovering the carrier number conservation in SPICE simulation of PIN diodes and IGBT devices

In SPICE simulations of PIN diodes and IGBT devices using finite difference method, one discretizes an undepleted N− region into several equally spaced nodes with a time-dependent distance of Δx(t), and then transforms the ambipolar diffusion equation, a time–space partial differential equation, into a set of time-dependent ordinary differential equations. However, the time-dependent property of Δx(t) destroys the carrier number conservation. In this paper, we propose an approach to correct the effect of the Δx(t) by introducing an auxiliary system. It has the same total current and the total carrier number in the undepleted N− region as the real system, but has different electron and hole current components. The difference is caused by adding compensation current terms with the equal amplitude and opposite sign to the electron and hole current terms in the auxiliary system. These compensation current terms are proportional to the boundary speed of the undepleted N− region and do not change the total current. The auxiliary system can be easily solved using SPICE behavior models and its carrier density is a good approximation to the real one. Our simulations show that the compensation current correction is important for fast switching PIN diodes, but may not be very important in IGBT devices due to their large gate-related capacitance.

High‐Performance Back‐Channel‐Etched Thin‐Film Transistors with an InGaO/InZnO Stacked Channel

Back‐channel‐etched (BCE) thin‐film transistors (TFTs) with an InGaO/InZnO stacked channel are developed, in which the InGaO and InZnO provide a highly acid‐resistant back channel and a high‐mobility front channel, respectively. The electrical performance of the TFT is optimized by adjusting the InGaO thickness. The best performance is achieved for the TFT with 10 nm thick InGaO. A thinner InGaO layer leads to inferior performance due to damage during the back‐channel‐etching process, while a thicker InGaO layer results in a hump effect and significant negative shifts in the threshold voltage (Vth) and turn‐on voltage (Von), which should be ascribed to the large total carrier number in the channel. The optimal TFT exhibits a high saturated field‐effect mobility of 28.9 cm2 V−1 s−1, a near‐zero Vth of −0.17 V, a Von of −0.49 V, a low subthreshold swing of 0.12 V dec−1, a high on‐to‐off current ratio of 3.5 × 109, and a low contact resistance between the source/drain (S/D) electrodes and channel. The TFT also exhibits high stability under bias thermal stress.

Addition of triple negativity of breast cancer as an indicator for germline mutations in predisposing genes increases sensitivity of clinical selection criteria

BackgroundBreast cancer is the most common cancer in women. 12–15% of all tumors are triple-negative breast cancers (TNBC). So far, TNBC has been mainly associated with mutations in BRCA1. The presence of other predisposing genes seems likely since DNA damage repair is a complex process that involves several genes. Therefore we investigated if mutations in other genes are involved in cancer development and whether TNBC is an additional indicator of mutational status besides family history and age of onset.MethodsWe performed a germline panel-based screening of 10 high and low-moderate penetrance breast cancer susceptibility genes (BRCA1, BRCA2, ATM, CDH1, CHEK2, NBN, PALB2, RAD51C, RAD51D and TP53) in 229 consecutive individuals affected with TNBC unselected for age, family history or bilateral disease. Within this cohort we compared the number of mutation carriers fulfilling clinical selection criteria with the total number of carriers identified.ResultsAge at diagnosis ranged from 23 to 80 years with an average age of 50.2 years. In 57 women (24.9%) we detected a pathogenic mutation, with a higher frequency (29.7%) in the group manifesting cancer before 60 years. Deleterious BRCA1 mutations occurred in 14.8% of TNBC patients. These were predominantly recurrent frameshift mutations (24/34, 70.6%). Deleterious BRCA2 mutations occurred in 5.7% of patients, all but one (c.1813dupA) being unique.While no mutations were found in CDH1 and TP53, 10 mutations were detected in one of the six other predisposition genes. Remarkably, neither of the ATM, RAD51D, CHEK2 and PALB2 mutation carriers had a family history. Furthermore, patients with non-BRCA1/2 mutations were not significantly younger than mutation negative women (p = 0.3341). Most importantly, among the 57 mutation carriers, ten (17.5%) would be missed using current clinical testing criteria including five (8%) with BRCA1/2 mutations.ConclusionsIn summary, our data confirm and expand previous studies of a high frequency of germline mutations in genes associated with ineffective repair of DNA damage in women with TNBCs. Neither age of onset, contralateral disease nor family history were able to discern all mutation positive individuals. Therefore, TNBC should be considered as an additional criterion for panel based genetic testing.

Trends in the total numbers of HBV and HCV carriers in Japan from 2000 to 2011.

We estimated the total number of undiagnosed HBV and HCV carriers and patients with hepatitis virus-related disease in Japan according to 6 different groups classified by their natural histories during 2011. In 2011, the total number of carriers and patients infected with HBV or HCV was estimated according to 6 groups using government reports and reports from the hepatitis epidemiology research group of The Ministry of Health, Labor and Welfare in Japan. In 2011, the total number of hepatitis virus carriers was estimated to be 2090128-2840128 in which the estimated number of undiagnosed HCV and HBV carriers was 776826 (HBV: 481470; HCV: 295356). The total number of treated patients, as either inpatients or outpatients, was estimated to be 811588 (HBV: 303366; HCV: 520600) in 2011. It is presumed that many carriers shirk consultation for many reasons, such as patients' misunderstanding, lack of awareness and forgetfulness of their positive status. The numbers of infected patients who did not seek treatment increased gradually to 501714-1251714 (HBV: 333791-483791; HCV: 167923-767923) in 2011. Compared to 2000, the number of undiagnosed carriers was significantly reduced in 2011 probably because of the well-organized, effective national hepatitis virus screening system that has been launched by the Japanese government since 2002. Moreover, the increase in the number of untreated persons who are aware of their positive status shows that more effort should be invested in improving the referral system from screening centres to core hospitals.

Evaluating the breast cancer predisposition role of rare variants in genes associated with low-penetrance breast cancer risk SNPs

BackgroundGenome-wide association studies (GWASs) have identified numerous single-nucleotide polymorphisms (SNPs) associated with small increases in breast cancer risk. Studies to date suggest that some SNPs alter the expression of the associated genes, which potentially mediates risk modification. On this basis, we hypothesised that some of these genes may be enriched for rare coding variants associated with a higher breast cancer risk.MethodsThe coding regions and exon-intron boundaries of 56 genes that have either been proposed by GWASs to be the regulatory targets of the SNPs and/or located < 500 kb from the risk SNPs were sequenced in index cases from 1043 familial breast cancer families that previously had negative test results for BRCA1 and BRCA2 mutations and 944 population-matched cancer-free control participants from an Australian population. Rare (minor allele frequency ≤ 0.001 in the Exome Aggregation Consortium and Exome Variant Server databases) loss-of-function (LoF) and missense variants were studied.ResultsLoF variants were rare in both the cases and control participants across all the candidate genes, with only 38 different LoF variants observed in a total of 39 carriers. For the majority of genes (n = 36), no LoF variants were detected in either the case or control cohorts. No individual gene showed a significant excess of LoF or missense variants in the cases compared with control participants. Among all candidate genes as a group, the total number of carriers with LoF variants was higher in the cases than in the control participants (26 cases and 13 control participants), as was the total number of carriers with missense variants (406 versus 353), but neither reached statistical significance (p = 0.077 and p = 0.512, respectively). The genes contributing most of the excess of LoF variants in the cases included TET2, NRIP1, RAD51B and SNX32 (12 cases versus 2 control participants), whereas ZNF283 and CASP8 contributed largely to the excess of missense variants (25 cases versus 8 control participants).ConclusionsOur data suggest that rare LoF and missense variants in genes associated with low-penetrance breast cancer risk SNPs may contribute some additional risk, but as a group these genes are unlikely to be major contributors to breast cancer heritability.

How Carrier Size and Valency Modulate Receptor-Mediated Signaling: Understanding the Link between Binding and Endocytosis of ICAM-1-Targeted Carriers.

Targeting of drug carriers to endocytic cell receptors facilitates intracellular drug delivery. Carrier size and number of targeting moieties (valency) influence cell binding and uptake. However, how these parameters influence receptor-mediated cell signaling (the link between binding and uptake) remains uncharacterized. We studied this using polymer carriers of different sizes and valencies, targeted to endothelial intercellular adhesion molecule-1 (ICAM-1), a marker overexpressed in many pathologies. Unexpectedly, induction of cell signals (ceramide and protein kinase C (PKC) enrichment and activation) and uptake, were independent of carrier avidity, total number of carriers bound per cell, cumulative cell surface area occupied by carriers, number of targeting antibodies at the carrier-cell contact, and cumulative receptor engagement by all bound carriers. Instead, "valency density" (number of antibodies per carrier surface area) ruled signaling, and carrier size independently influenced uptake. These results are key to understanding the interplay between carrier design parameters and receptor-mediated signaling conducive to endocytosis, paramount for intracellular drug delivery.

Performance of standard and double‐sided 3D‐radiation detectors under the impact of a temperature pulse

In this Letter, a comparison of the electrical performances of a standard and a double-sided 3D-radiation detectors using TCAD simulations is performed. The transient simulation is used to investigate the charge collection performance by swamping the detector with a uniform concentration of EHPs (75 e-h pairs/µm), chosen to give the same total number of carriers as a minimum ionising particle. Both detectors can be biased with the same voltage level of the readout circuitry in the standard 0.35 µm BiCMOS technology, but the standard full 3D structure is preferred for its high collection charge which means high signal to noise ratio. Finally, the impact of a temperature (300−400 K) pulse with fast transition times is studied. The impact has no significant effect on the collection current waveform of the standard but it has a big influence of the current waveform of the double-sided 3D-detectors. This makes the standard 3D-detector favourable than the double-sided 3D-detector in a harsh environment.

A Highly Efficient Computational Model for FDTD Simulations of Ultrafast Electromagnetic Interactions With Semiconductor Media With Carrier Heating/Cooling Dynamics

We report a new computational model to incorporate carrier heating/cooling effects for the finite-difference time-domain (FDTD) simulation of electromagnetic interactions with semiconductor media. The model is formulated to be computationally efficient enough to be applied to FDTD simulations of photonic devices of complex structural geometry. The model developed here is built on top of a previous multi-level multi-electron (MLME) model we presented and the new model is called MLME-dynamical temperature (MLMEDT) model. The key developments here include the following. 1) Intraband transition terms with electron and hole temperature parameters that vary with time and space are introduced. 2) Rate equations for the explicit update of carrier temperature are formulated. A computationally efficient method is used to evaluate these carrier temperature rate equations which circumvent iterative procedures as well as the need to dynamically compute the chemical potential by presolving the relational functions required using dimensionless fitting functions. The temporal update of these fitting functions only needs the total carrier number densities, which are already obtained in the MLME model computation. 3) The changes in the total carrier kinetic energy density and carrier number density due to all interband processes such as stimulated emission/absorption and intraband processes such as free carrier absorption are tracked to drive the carrier temperature rate equations. 4) The thermal relaxation of the electron and hole temperatures to the lattice temperature and the thermal relaxation between electrons and holes are also included. In order to validate the approach, simulations of thermalization of nonequilibrium carrier distributions and nonlinear gain and refractive index dynamics in semiconductor optical amplifiers (SOA) are presented. Quantitative agreement with nonlinear gain dynamics experiments of SOA directly verifies the accuracy of the current approach. Additionally, a 2-D simulation of a microdisk laser is presented to depict how FDTD can be used to visualize the spatial profile of carrier temperatures. The computational time of the MLMEDT model is found to be only ~10% more than that of the MLME model, thus showing high computational efficiency.

Indium Oxide Thin-Film Transistors Fabricated by RF Sputtering at Room Temperature

Thin-film transistors (TFTs) were fabricated using an indium oxide (In2O3) thin film as the n-channel active layer by RF sputtering at room temperature. The TFTs showed a thickness-dependent performance in the range of 48-8 nm, which is ascribed to the total carrier number in the active layer. Optimum device performance at 8-nm-thick In2O3 TFTs had a field-effect mobility of 15.3 cm2 · V-1 · s-1, a threshold voltage of 3.1 V, an ON-OFF current ratio of 2.2 × 108, a subthreshold gate voltage swing of 0.25 V · decade-1, and, most importantly, a normally OFF characteristic. These results suggest that sputter-deposited In2O3 is a promising candidate for high-performance TFTs for transparent and flexible electronics.

Analysis of Resistance Asymmetry Due to p-n Junctions in Graphene FETs

AbstractFor graphene FETs, asymmetry in the drain current transfer characteristics has been observed. It has been proposed that asymmetry is due to additional resistances from p-n transition regions along the channel [1,2]. Calculations of the additional resistance have been received attention for small p-n transition lengths [3,4]. In this paper, we analyze the resistance of graphene FETs with p-n junctions when transition lengths are long compared with energy and momentum relaxation lengths, as is found in many experimental FETs. We employ a two dimensional device simulator to determine the electric field and channel conductivity variations in the vicinity of the FET gate, assuming rapid electron/hole equilibration. The simulations show added resistances in the range of 50-500 Ω μm p-n junction. We also extract the additional p-n resistance ΔR from experimental results by plots of Vd/Id vs. 1/|Vg-Vt|. Values of ΔR of order 450 Ω μm were extracted from FET results reported in [2]. Epitaxial graphene FETs fabricated on a SiC substrate [5] gives additional resistance of 620 Ωum. Both results are in reasonable agreement with the simulations.The physically-based device simulator Atlas of Silvaco with parameters modified for graphene was used to obtain carrier distributions. A graphene FET on SiO2 substrate with a global back gate and 0.3μm gate/drain and gate/source gaps was studied. The carrier density in the gap region was controlled by back gate bias (Vbg) while the channel region under the top gate was modulated by top and back gate simultaneously. A long channel device at Vds=10mV was used to minimize the lateral electric field effect.From the simulated carrier distribution, we can obtain the resistivity along the channel by ρ=1/[qμ(n+p)]. Mobility is assumed to be equal for electrons and holes, and depends on carrier concentration Ns, μ=μ0 (N0/Ns)1/2 where N0 and μ0 are intrinsic carrier concentration and peak mobility, respectively. Under positive Vbg, the graphene layer becomes n-type in the gap region and channel region. Proper top gate bias (Vg) may be applied to make channel region intrinsic, p-type or n-type. Therefore, various configurations along the channel such as npn or nnn structures may be created. In the p-n transition region, the total number of carriers reduces to N0 and resistivity shows a peak. The additional resistance of a p-n junction can be calculated by integrating the difference of the resistivity vs. channel position for the nnn and npn structures. The integrated resistance value is impacted by the peak height and peak width. The peak height is controlled by Vg-Vt; the resistivity reaches a maximum at the threshold condition, where the electron and hole densities reach their intrinsic levels. The peak width is also controlled by Vg, via fringing field of the gate.

The Genetics of High-Density Lipoprotein Metabolism: Clinical Relevance for Therapeutic Approaches

The risk for coronary artery disease (CAD) is inversely correlated with high-density lipoprotein (HDL) cholesterol plasma levels. These plasma HDL cholesterol levels are influenced by the activity of a number of enzymes and receptors, and therefore, variations in the genes encoding for these proteins may consequently result in an altered CAD risk. Identification of such pivotal players in HDL cholesterol metabolism that are also strongly associated with CAD risk is crucial for the materialization of novel therapeutic modalities. A large amount of knowledge has been obtained by studies involving families with extreme HDL phenotypes specific to molecular defects. In fact, thus far, monogenetic defects have been described in the genes coding for apolipoprotein A-I, adenosine triphosphate-binding cassette transporter A1, cholesterol ester transfer protein, the lack of endothelial lipase (LIPG), phospholipid transfer protein, and lecithin-cholesterol acyltransferase. Despite the fact that the total number of carriers of such mutations is rather small, much can be gained by extensively studying the metabolic and vascular consequences of these mutations. Surrogate markers for atherosclerosis have proved to be useful to overcome this sample size limitation and have been widely exploited to study families with decreased or increased HDL cholesterol levels in order to correlate HDL cholesterol phenotypes to atherosclerotic burden in cases and controls. Apart from such extreme phenotype approaches, novel population-based genome-wide association studies have been used to decipher the link between genetic loci and HDL cholesterol levels, and the identification of novel HDL cholesterol-related genes is eagerly awaited. These might be instrumental in the ongoing fight against atherosclerosis.

On the Hooge relation in semiconductors and metals

The expressions describing the low frequency noise caused by defects in semiconductors and metals have been obtained in the framework of a general unified approach for both fluctuations in the number of carriers and their mobility. When fluctuations in the number of carriers are responsible for noise, the spectral noise density is inversely proportional to the carrier concentration squared and to the volume of the sample. The spectral density of the noise caused by mobility fluctuations is inversely proportional to the sample volume, and does not depend either on carrier concentration or on the total number of carriers. In the case when both mechanisms contribute to noise and they are correlated, the dependence of the noise on the number of carriers depends on the relative contribution of these two noise mechanisms. The expressions obtained can be associated with corresponding cases of the 1/f noise. The physical basis and limitations of the Hooge formula are discussed.

Plasma nanosheath formation with carrier accumulation and enhanced localized spontaneous emission at “quantum wedges” in textured GaN

It is shown that spontaneous and piezoelectric polarization fields, inherent in GaN lattices, combined with constrained carrier motion along the quantum wells, give rise to equilibrium plasma nanosheaths. Induced potentials are localized within nm Debye lengths with peak voltages much larger than the thermal carrier energy. The associated energy band-bending causes enhanced carrier accumulation at quantum wedges and quantum tips formed by intersecting quantum wells. The total carrier number over an entire quantum well (QW) also increases, compared to flat bands, manifesting spontaneous intrinsic pumping due to polarization. It follows that the spontaneous emission is localized at quantum wedges, and the total emission exceeds that from a flat quantum well of similar parameters, as experimentally observed. The sheath potentials are sufficiently high for 1D or 0D carrier localization at quantum wedges and quantum tips.

Spin dynamics of carrier generation in a photoconductive C 60-doped poly( N-vinylcarbazole) film

The magnetic field effects on the carrier yield have been studied to clarify the spin dynamic process during photoinduced carrier generation in a fullerene (C 60)-doped poly( N-vinylcarbazole) (PVCz) film. The charge transfer (CT) complex of C 60 and the carbazole (Cz) chromophore is selectively excited. The total number of carriers that escaped from the geminate pairs decreases in the presence of magnetic fields, which arises from a hyperfine mechanism of the distant ion pairs involving C 60 - and Cz +. Time-resolved EPR measurements verify that the excited triplet state of C 60 is produced via its excited singlet state generated from the contact ion pair. The competitive formation processes of distant ion pairs and the excited states of C 60 from the contact ion pair are discussed.

Effects of Pauli blocking on semiconductor laser intensity and phase noise spectra

In this paper we derive the intensity and phase noise spectra of a single-mode semiconductor laser on the basis of an operatorial Langevin set of equations that includes the dynamics of the microscopic variables, i.e., the carrier polarization and their distribution over the k states. In particular we take into account the fact that the carriers pumped into the active layer are subject to the blocking determined by Pauli exclusion principle. We demonstrate that, due to the fastness of the carrier scattering and polarization dephasing processes, the noise spectra can be determined on the basis of a macroscopic linearized set of three equations for the two quadrature components of the laser intensity and the total carrier number. A formal comparison with the paradigmatic results of [Yamamoto et al. Phys. Rev. A 34, 4025 (1986)] allows to deduce that the only essential difference arises from Pauli-induced pump blocking, which has the effect of increasing the low-frequency branch of the intensity noise spectrum. We demonstrate that, even for very small amounts of pump blocking, the low-frequency intensity noise steeply rises with the stationary value of the carrier density in the active layer, which depends on a great number of parameters. This result can explain the erratic behavior of the experimental findings and their discrepancy with the standard theoretical predictions.

1/f noise in metal–oxide–semiconductor transistors biased in weak inversion

An approach to model 1/f noise in the weak inversion range of metal–oxide–semiconductor transistors (MOST) is proposed, based on Hooge’s theory (mobility fluctuation model). Starting from conduction equations in the subthreshold regime, a method to evaluate the total number of carriers under the gate is presented and allows us to deduce the Hooge parameter αH. This model is applied to p-channel MOSTs. With the proposed model, the value of αH obtained in weak inversion is quite similar to this extracted in strong inversion allowing a unique description of the 1/f noise.

Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors

We predict the existence of an anomalous crossover between thermal and shot noise in macroscopic diffusive conductors. We first show that, besides thermal noise, these systems may also exhibit shot noise due to fluctuations of the total number of carriers in the system. Then we show that at increasing currents the crossover between the two noise behaviors is anomalous, in the sense that the low-frequency current spectral density displays a region with a superlinear dependence on the current up to a cubic law. The anomaly is due to the nontrivial coupling in the presence of the long-range Coulomb interaction among the three time scales relevant to the phenomenon, namely, diffusion, transit, and dielectric relaxation time.

1/f noise considerations for the design and process optimization of piezoresistive cantilevers

Piezoresistive cantilevers are limited by two major noise sources: Johnson noise, which is independent of frequency, and conductance fluctuation noise, which has a 1/f spectrum. The 1/f fluctuations of piezoresistive cantilevers are shown to vary inversely with the total number of carriers in the piezoresistor, as formulated by Hooge in 1969. Therefore, while 1/f noise is reduced for large heavily doped cantilevers, sensitivity considerations favor thin lightly doped cantilevers. Balancing these conflicting constraints produces optima for many design and processing parameters. For a cantilever with specified spring constant and bandwidth requirements, optima are identified for the beam thickness and length, and it is shown that the legs should be between 1/3 and 2/3 of the total length with a doping depth that is 1/3 of the beam thickness. Additionally, an optimal doping concentration is identified as a function of the cantilever volume and the measurement bandwidth. Annealing reduces 1/f noise, but causes a loss in sensitivity due to dopant diffusion, and an optimal anneal is computed with a typical diffusion length 10/sup -8/ cm. The analysis, methods, and some of the conclusions of this paper are also applicable to other types of piezoresistive sensors.

Carrier Redistribution in Graded-Band-Gap Multilayer Semiconductor Structures Caused by Electric Current

The paper theoretically investigates peculiarities of the carrier redistribution in periodic homogeneously doped semiconductor graded-band-gap multilayer structures with linear coordinate dependence of the energy gap which are caused by electric current in the direction perpendicular to the layers. It is shown that at strong electric fields a practically constant carrier concentration is set up in almost the whole volume of the structure except for the thin regions in the vicinity of the interfaces. In the case of asymmetric structures carrier redistribution can give rise to a change of the total number of carriers.

Doping-induced change of optical properties in underdoped cuprate superconductors

We report on the ab-plane optical reflectance measurements of single crystals of Y-doped and Pr-doped over a wide frequency range from 80 to (10 meV-5 eV) and at temperatures between 20 and 300 K. Y and Pr doping both decrease the hole concentration in the planes. This has allowed us to investigate the evolution of ab-plane charge dynamics at doping levels ranging from heavily underdoped to nearly optimally doped. Our results of the low-frequency optical conductivity and spectral weight do not show any features associated with the normal-state pseudogap. Instead, one-component analysis for the optical conductivity shows the low-frequency depression in the scattering rate at , signalling entry into the pseudogap state. Alternatively, no clear indications of the normal-state pseudogap are detected in the temperature-dependent zero-frequency free-carrier scattering rate by using two-component analysis. In the superconducting state, there is also no convincing evidence of superconducting gap absorption in all spectra. We find that there is a `universal correlation' between the numbers of carriers and the transition temperature. This correlation holds whether one considers the number of carriers in the superfluid or the total number of carriers.