Electrical performance of III-V gate-all-around nanowire transistors

The performance of III-V inversion-mode and junctionless nanowire field-effect transistors are investigated using quantum simulations and are compared with those of silicon devices. We show that at ultrascaled dimensions silicon can offer better electrical performance in terms of short-channel effects and drive current than other materials. This is explained simply by suppression of source-drain tunneling due to the higher effective mass, shorter natural length, and the higher density of states in the confined channel. We also confirm that III-V junctionless nanowire transistors are more immune to short-channel effects than conventional inversion-mode III-V nanowire field-effect transistors. (C) 2013 AIP Publishing LLC

Simulation of multigate SOI transistors with silicon, germanium and III-V channels

In this work by employing numerical three-dimensional simulations we study the electrical performance and short channel behavior of several multi-gate transistors based on advanced SOI technology. These include FinFETs, triple-gate and gate-all-around nanowire FETs with different channel material, namely Si, Ge, and III-V compound semiconductors, all most promising candidates for future nanoscale CMOS technologies. Also, a new type of transistor called “junctionless nanowire transistor” is presented and extensive simulations are carried out to study its electrical characteristics and compare with the conventional inversion- and accumulation-mode transistors. We study the influence of device properties such as different channel material and orientation, dimensions, and doping concentration as well as quantum effects on the performance of multi-gate SOI transistors. For the modeled n-channel nanowire devices we found that at very small cross sections the nanowires with silicon channel are more immune to short channel effects. Interestingly, the mobility of the channel material is not as significant in determining the device performance in ultrashort channels as other material properties such as the dielectric constant and the effective mass. Better electrostatic control is achieved in materials with smaller dielectric constant and smaller source-to-drain tunneling currents are observed in channels with higher transport effective mass. This explains our results on Si-based devices. In addition to using the commercial TCAD software (Silvaco and Synopsys TCAD), we have developed a three-dimensional Schrödinger-Poisson solver based on the non-equilibrium Green’s functions formalism and in the framework of effective mass approximation. This allows studying the influence of quantum effects on electrical performance of ultra-scaled devices. We have implemented different mode-space methodologies in our 3D quantum-mechanical simulator and moreover introduced a new method to deal with discontinuities in the device structures which is much faster than the coupled-mode-space approach

Effect of strain and diameter on electronic and charge transport properties of indium arsenide nanowires

The impact of uni-axial compressive and tensile strain and diameter on the electronic band structure of indium arsenide (InAs) nanowires (NWs) is investigated using first principles calculations. Effective masses and band gaps are extracted from the electronic structure for relaxed and strained nanowires. Material properties are extracted and applied to determine charge transport through the NWs described within the effective mass approximation and by applying the non-equilibrium Green’s function method. The transport calculations self-consistently solve the Schrödinger equation with open boundary conditions and Poisson’s equation for the electrostatics. The device structure corresponds to a metal oxide semiconductor field effect transistor (MOSFET) with an InAs NW channel in a gate-all-around geometry. The channel cross sections are for highly scaled devices within a range of 3 × 3–1 × 1 nm2. Strain effects on the band structures and electrical performance are evaluated for different NW orientations and diameters by quantifying subthreshold swing and ON/OFF current ratio. Our results reveal for InAs NW transistors with critical dimensions of a few nanometer, the crystallographic orientation and quantum confinement effects dominate device behavior, nonetheless strain effects must be included to provide accurate predictions of transistor performance

Influence of surface stoichiometry and quantum confinement on the electronic structure of small diameter InxGa1-xAs nanowires

Electronic structures for InxGa1-xAs nanowires with [100], [110], and [111] orientations and critical dimensions of approximately 2 nm are treated within the framework of density functional theory. Explicit band structures are calculated and properties relevant to nanoelectronic design are extracted including band gaps, effective masses, and density of states. The properties of these III-V nanowires are compared to silicon nanowires of comparable dimensions as a reference system. In nonpolar semiconductors, quantum confinement and surface chemistry are known to play a key role in the determination of nanowire electronic structure. InxGa1-xAs nanowires have in addition effects due to alloy stoichiometry on the cation sublattice and due to the polar nature of the cleaved nanowire surfaces. The impact of these additional factors on the electronic structure for these polar semiconductor nanowires is shown to be significant and necessary for accurate treatment of electronic structure properties

Influence of surface passivation on indium arsenide nanowire band gap energies

The interplay between surface chemistry and quantum confinement on the band gap energies of indium arsenide (InAs) nanowires is investigated by first principle computations as the surface-to-volume ratio increases with decreasing cross section. Electronic band structures are presented as determined by both density functional and hybrid density functional theory (DFT) calculations; the latter are used to provide improved band gap energy estimates over those from standard approximate DFT methods. Different monovalent chemical species with varying electron affinity are used to eliminate surface states to enable direct comparison between surface chemistry and quantum confinement. The influence of these effects on energy band gaps and electron effective masses is highlighted. It is found that many desirable properties in terms of electronic properties and the elimination of surface states for nanoscale field effect transistors fabricated using [100]-oriented InAs can be achieved. © 2019, The Minerals, Metals & Materials Society

Comparison of three primer pairs included: novel primers IS711, universal primers B4 - B5 and 16SrRNA in the diagnosis of human brucellosis in suspected patients in Iran

The genus Brucella is a worldwide distributed intracellular bacteria, which infects animals and human. Currently, this zoonosis has been diagnosed by microbiological and serological laboratory tests. Different PCR protocols with various primer pairs and different target genes have been published for the detection of Brucella, but only a few of these primers have been used in human samples. This study aimed to evaluate and compare the sensitivity and specificity of three primer pairs in the PCR technique, each of which separately amplifies three different regions in the Brucella genome, to determine which are more comfortable for the detecting of Brucella DNA in human clinical samples. 49 clinical serum samples were isolated from suspected patients in different cities in Iran from October 2017 to July 2018. The suspected patients with brucellosis-compatible symptoms were checked. These primers amplified 3 distinctive fragments in BCSP 31 gene (B4/B5), Designed IS711 primers, and a sequence of 16SrRNA of Brucella melitensis. The results showed that the B4/B5 primer pair had the highest sensitivity and specificity for the detection of both positive and negative samples (100%). The designed IS711 primer pair detected 94% of samples, whereas the 16SrRNA primer pair was the least sensitivity, being able to detect only 30.64% of samples. The specificity of 3 techniques was 100%. The B4/B5 primers were able to detect the smallest number of bacteria 0.05 CFU/reaction whereas IS711 was able to detect 2 CFU/reaction and 16SrRNA was able to detect 2×105 CFU/reaction. &nbsp

Improvement of carrier ballisticity in junctionless nanowire transistors

In this work we show that junctionless nanowire transistor (JNT) exhibits lower degree of ballisticity in subthreshold and higher ballisticity above threshold compare to conventional inversion-mode transistors, according to quantum mechanical simulations. The lower degradation of the ballisticity above threshold region gives the JNT near-ballistic transport performance and hence a high current drive. On the other hand, lower ballisticity in subthreshold region helps reducing the off-current and improves the subthreshold slope. A three-dimensional quantum mechanical device simulator based on the nonequilibrium Green's function formalism in the uncoupled mode-space approach has been developed to extract the physical parameters of the devices. (C) 2011 American Institute of Physics. (doi:10.1063/1.3559625

Bipolar effects in unipolar junctionless transistors

In this work, we analyze hysteresis and bipolar effects in unipolar junctionless transistors. A change in subthreshold drain current by 5 orders of magnitude is demonstrated at a drain voltage of 2.25 V in silicon junctionless transistor. Contrary to the conventional theory, increasing gate oxide thickness results in (i) a reduction of subthreshold slope (S-slope) and (ii) an increase in drain current, due to bipolar effects. The high sensitivity to film thickness in junctionless devices will be most crucial factor in achieving steep transition from ON to OFF state. (C) 2012 American Institute of Physics. (http://dx.doi.org/10.1063/1.4748909

Characterization of a junctionless diode

A diode has been realised using a silicon junctionless (JL) transistor. The device contains neither PN junction nor Schottky junction. The device is measured at different temperatures. The characteristics of the JL diode are essentially identical to those of a regular PN junction diode. The JL diode has an on/off current ratio of 10(8), an ideality factor of 1.09, and a reverse leakage current of 1 x 10(-14) A at room temperature. The mechanism of the leakage current is discussed using the activation energy (E-A). The turn-on voltage of the device can be tuned by JL transistor threshold voltage. (C) 2011 American Institute of Physics. (doi: 10.1063/1.3608150

Field-effect mobility extraction in nanowire field-effect transistors by combination of transfer characteristics and random telegraph noise measurements

A technique based on the combined measurements of random telegraph-signal noise amplitude and drain current vs. gate voltage characteristics is proposed to extract the channel mobility in inversion-mode and accumulation-mode nanowire transistors. This method does not require the preliminary knowledge of the gate oxide capacitance or that of the channel width. The method accounts for the presence of parasitic source and drain resistance effect. It has been used to extract the zero-field mobility and the field mobility reduction factor in inversion-mode and junctionless transistors operating in accumulation mode. (C) 2011 American Institute of Physics. (doi:10.1063/1.3626038