Dominant Charge Carriers Research Articles

Dual-gate operation and carrier transport in SiGe p–n junction nanowires

We investigate carrier transport in silicon–germanium nanowires with an axial p–n junction doping profile by fabricating these wires into transistors that feature separate top gates over each doping segment. By independently biasing each gate, carrier concentrations in the n- and p-side of the wire can be modulated. For these devices, which were fabricated with nickel source–drain electrical contacts, holes are the dominant charge carrier, with more favorable hole injection occurring on the p-side contact. Channel current exhibits greater sensitivity to the n-side gate, and in the reverse biased source–drain configuration, current is limited by the nickel/n-side Schottky contact.

Recent progress on the high-pressure studies of FeSe single crystal

Among the iron-based superconductors, the structurally simplest FeSe and FeSe-derived materials have attracted enormous research interest recently due to its unusual electronic properties and the great tunability of the superconducting transition temperature <italic>T</italic>_c. For the bulk FeSe single crystal, it shows a relatively low <italic>T</italic>_c<x content-type=symbol>»</x>8 K within the unusual nonmagnetic nematic phase below <italic>T</italic>_s<x content-type=symbol>»</x>90 K. It has been reported that the application of high pressure can induce a long-range antiferromagnetic order below <italic>T</italic>_m<x content-type=symbol>»</x>20 K at <italic>P</italic><x content-type=symbol>»</x>1 GPa, and then achieve a high <italic>T</italic>_c<x content-type=symbol>»</x>37 K at <italic>P</italic><x content-type=symbol>»</x>8 GPa. It remains unclear how the high-<italic>T</italic>_c superconductivity is achieved in FeSe under pressure. In this regard, a detailed temperature-pressure phase diagram mapping out the exact relationship between the high-<italic>T</italic>_c superconductivity and the normal-state nematic order and the pressure-induced antiferromagnetic order is indispensable for achieving a better understanding. By taking advantage of the cubic anvil cell apparatus that can maintain an excellent hydrostatic pressure condition up to 15 GPa, we recently undertook a comprehensive high-pressure magnetotransport study on high-quality FeSe single crystals and obtained important results. In this article, we give a brief review on the recent progresses about the high-pressure studies of FeSe. By tracking the characteristic resistivity anomalies at the nematic order, the pressure-induced antiferromagnetic order, and the superconducting transition, we constructed for FeSe a comprehensive temperature-pressure phase diagram, which depicts explicitly the detailed evolution of these competing electronic orders. We observed a dome-shaped antiferromagnetic phase boundary <italic>T</italic>_m(<italic>P</italic>), and revealed the competitive relationship between these electronic orders. The superconducting <italic>T</italic>_c experiences two successive step increases at the critical pressures when the nematic order and the antiferromagnetic order are respectively suppressed, and finally the highest <italic>T</italic>_c^max=38.5 K is realized near <italic>P</italic>_c≈6 GPa when the antiferromagnetic order just collapses. We further measured the Hall effect of FeSe to extract the electronic structure information under high pressure. Our Hall data show that the Fermi surface of FeSe in the normal state undergoes a reconstruction at <italic>P</italic><x content-type=symbol>»</x>2 GPa, when the nematic order is suppressed and the antiferromagnetic order just emerges. The dominant charge carriers for the transport properties in the normal state change from the electron to the hole type. In addition, in the high-<italic>T</italic>_c phase near the optimal<italic> </italic><italic>T</italic>_c^max at <italic>P</italic>_c<x content-type=symbol>»</x>6 GPa, the Hall coefficient experiences a dramatic enhancement and the magnetoresistance exhibits anomalous scaling behaviors, signaling the presence of strongly enhanced inter-band spin fluctuations. These results suggest that the critical antiferromagnetic fluctuations play an important role for achieving the high-<italic>T</italic>_c superconductivity in FeSe. Aided by the first-principles calculations, we further confirmed that both electron-like and hole-like Fermi surfaces are present in FeSe under high pressures, in favor of the Fermi surface nesting scenario as in the FeAs-based high-<italic>T</italic>_c<italic> </italic>superconductors. These above results on FeSe suggest great similarities with other FeAs-based superconductors, and thus constitute an important step toward a unified understanding of iron-based superconductivity.

Comparison of dehydration in kaolin and illite using DC conductivity measurements

Temperature dependencies of the DC conductivity of kaolin and illite are measured from 20°C up to 450°C using “as received” samples and samples after heating to 400°C and 450°C. Release of physically bound water (PBW) from green kaolin shows two maxima, at 55°C and 298°C. Release of the PBW from green illite takes place in 3 steps at 72°C, 186°C, and 298°C. Up to 200°C, the dominant charge carriers are H+ and OH– ions in both materials. At higher temperatures, alkali ions (both Na+ and K+ in kaolin, prevalently K+ in illite) are the dominant charge carriers with the conduction activation energy of 1.19±0.02eV in kaolin and of 1.12±0.02eV in illite. Above 400°C, dehydroxylation runs in illite. Due to this process, the DC conductivity of illite increases; in partly dehydroxylated illite, higher conduction activation energy (1.22eV) indicates that alkali metal ions are moving in a more disordered structure. In kaolin, dehydroxylation starts only above 450°C.

Polaron Disproportionation Charge Transport in a Conducting Redox Polymer

Herein we report a mechanistic study of the charge transport in poly-3-((2,5-hydroquinone)vinyl)-1H-pyrrole by conductance measurements at various temperatures performed in situ during doping of the polypyrrole backbone in contact with an aqueous electrolyte. Charge transport was found to occur by electron hopping with associated electron transfer activation energies in the range of 0.08–0.2 eV. In situ electron paramagnetic resonance experiments indicated polarons as the dominant charge carriers and the charge transport was found to follow a second-order dependence with respect to the number of accumulated charges. Based on the findings, we present a polaron comproportionation/disproportionation model for electron conduction in poly-3-((2,5-hydroquinone)vinyl)-1H-pyrrole, thus, providing a complement to existing models for charge propagation in conducting polymers.

Magnetic and transport properties of half-Heuslers, RPdSb (R = Gd and Tb)

We present the results of our studies on rare–earth half-Heuslers, RPdSb (R = Gd and Tb), crystallizing in a LiGaGe–type hexagonal structure, by means of magnetization, heat capacity, electrical resistivity, Seebeck coefficient, thermal conductivity and magnetoresistance measurements. The compounds exhibit antiferromagnetic order with transition temperatures of 17 and 2.5 K for Gd and Tb samples, respectively. The results of electrical transport measurements establish a metallic behavior for both the samples while the deviation from the linear temperature dependence was explained based on the additional contribution from the s-d inter-band scattering. Moreover, thermal transport measurements also indicate the contribution due to the s-d interaction where both the types of charge carriers involved in scattering. The positive sign of Seebeck coefficient confirms the dominant charge carriers as holes with the carrier concentration of ∼1021 cm−3 at room temperature while the magnitude decreases with temperature non-linearly. The most interesting feature is the observation of giant positive and non-saturating magneto-resistance at low temperatures which is essentially linear at higher fields and resembles the behavior of charge compensated materials. These results were explained on the basis of the temperature dependent changes in the population of electrons and holes.

Fabrication of p-type lithium niobate crystals by molybdenum doping and polarization

The lack of p-type lithium niobate limits it serving as an active material. A series of Mo-doped and pure congruent lithium niobate crystals were grown by Czochralski method under different polarization conditions. Their dominant carrier species were characterized by holographic experiment. The results showed dominant charge carrier species may be changed from electrons to holes when lithium niobate crystal was doped with Mo ions and polarized under the current of 70mA for 30 minutes. It indicated that p-type lithium niobate crystal could be fabricated by Mo-doping and suitably controlling the polarization condition. Mo-doped lithium niobate crystals can be a promising candidate for active components.

NH4NO3 as charge carrier contributor in glycerolized potato starch-methyl cellulose blend-based polymer electrolyte and the application in electrochemical double-layer capacitor

Potato starch (PS)-methyl cellulose (MC) blend solid biopolymer electrolytes infused with ammonium nitrate (NH4NO3) and glycerol as plasticizer are made via the solution cast technique. Fourier transform infrared (FTIR) spectroscopy indicates that NH4NO3 has interacted with the polymer blend host. The addition of 40 wt% glycerol in the highest conducting plasticizer free electrolyte has improved the conductivity to the order of ∼10−3 S cm−1. The thermal stability of the electrolytes is identified by thermogravimetric analysis (TGA). Result from X-ray diffraction (XRD) analysis shows that the electrolyte with maximum conductivity value has the lowest degree of crystallinity. Differential scanning calorimetry (DSC) analysis reveals that the highest conducting plasticized electrolyte possesses the lowest glass transition temperature (T g) of −27.5 °C. Conductivity trend is further verified by dielectric analysis. Transference numbers of ion (t ion) and electron (t e) for the highest conducting electrolyte are identified to be 0.98 and 0.02, respectively, confirming that ions are the dominant charge carriers. Linear sweep voltammetry (LSV) evaluates that the potential window for the electrolyte is 1.88 V. The internal resistance of the electrochemical double-layer capacitor (EDLC) is between 29 and 64 Ω. From the charged-discharged measurement, the value of C s is 31 F g−1. The EDLC is stable over 1000 cycles.

High temperature thermopower of sol–gel processed Zn1−x−y Al x Me y O (Me: Ga, In)

In this study, dually doped samples of Zn1−x−y Al x Me y O (Me: Ga, In) were prepared by sol–gel process followed by hot isostatic pressing for high temperature thermoelectric applications. Material characterizations were performed with differential thermal analysis-thermogravimetry, Fourier transform infrared spectroscopy and X-ray diffraction on the target phases. Successful doping of the samples was confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. Thermopower values of the samples are found to be relatively high in analogy to semiconducting behavior in which negative values indicate electrons are the dominant charge carriers (n-type). Substitution of Zn2+ by Ga3+ and In3+ for Zn1−x−y Al x Me y O (Me: Ga, In) increases electron concentration in the samples and thereby decreases the thermopower values compared to Zn0.98Al0.02O. Considering the absolute values, In doped samples have higher thermopower (α max = −162 µV/K at 585 °C for Zn0.96Al0.02In0.02O) compared to the Ga doped sample. Al and In dually doped Zn0.96Al0.02In0.02O could be considered as a promising n-type thermoelectric material for high temperature applications.

Intrinsic Conductivity in Magnesium-Oxygen Battery Discharge Products: MgO and MgO2

Non-aqueous magnesium-oxygen (or ‘Mg-air’) batteries are attractive next generation energy storage devices due to their high theoretical energy densities, low cost, and potential for rechargeability. Prior experiments identified magnesium oxide, MgO, and magnesium peroxide, MgO2, as the primary discharge products in a Mg/O2 cell. Charge transport within these nominally-insulating compounds is expected to limit battery performance, yet these transport mechanisms are either incompletely understood (MgO2) or remain a matter of debate (MgO). The present study characterizes the conductivity associated with intrinsic (point) defects within both compounds using first-principles calculations. For MgO, negative Mg vacancies and hole polarons localized on oxygen anions were identified as the dominant charge carriers. Nevertheless, the large formation energies associated with these carriers suggest that their equilibrium concentrations are low. Furthermore, a large asymmetry exists in the carrier mobility: Mg vacancies are essentially immobile at room temperature, while hole polarons are highly mobile. Importantly, the calculated formation and mobility data for MgO are in remarkable agreement with the three “Arrhenius branches” observed in conductivity experiments, and thus clarify the long-debated transport mechanisms within these regimes. In the case of MgO2, electronic charge carriers alone – electron and hole polarons – are the most prevalent. Similar to MgO, the concentration of carriers in MgO2 is low, and poor mobility further limits conductivity. We conclude that: (i.) sluggish charge transport in MgO or MgO2 will limit battery performance when these compounds cover the cathode support, and (ii.) what little conductivity exists is primarily electronic in nature (i.e., polaron hopping). Artificially increasing the carrier concentration is suggested as a strategy for improving battery performance.

Intrinsic Conductivity in Magnesium–Oxygen Battery Discharge Products: MgO and MgO2

Nonaqueous magnesium–oxygen (or “Mg-air”) batteries are attractive next generation energy storage devices due to their high theoretical energy densities, projected low cost, and potential for rechargeability. Prior experiments identified magnesium oxide, MgO, and magnesium peroxide, MgO2, as the primary discharge products in a Mg/O2 cell. Charge transport within these nominally insulating compounds is expected to limit battery performance; nevertheless, these transport mechanisms either are incompletely understood (in MgO2) or remain a matter of debate (in MgO). The present study characterizes the equilibrium conductivity associated with intrinsic (point) defects within both compounds using first-principles calculations. For MgO, negative Mg vacancies and hole polarons—the latter localized on oxygen anions—were identified as the dominant charge carriers. However, the large formation energies associated with these carriers suggest low equilibrium concentrations. A large asymmetry in the carrier mobility is...

Spectral Response Behavior in Single-Layer Organic Semiconductor Devices in Relation to its Absorption Spectrum

Improved understanding of spectral response in organic semiconductor devices can be useful for building better performing devices as well as using them for newer optoelectronic applications. The nature of the spectral response for single-layer organic semiconductor devices depends on the dominant charge carrier (either electron or holes) in the absorbing layer. The exponential dependence of charge carrier mobility on electric field means that the applied bias and absorption layer thickness can affect and possibly help tune the spectral response of the device. In this paper, the spectral response for such devices has been modeled and the parameters and conditions determining either antibatic or symbatic response with respect to the absorption spectrum of the active layer have been presented. The spectral responses in a donor-type poly (3-hexylthiophene-2, 5-diyl) as well as an acceptor-type fullerene- C 60 single-layer devices have been analyzed with the help of the model. Besides giving insight into the optoelectronic phenomenon, the results point to the ability to tune organic semiconductor device spectral response that can be useful for optical demultiplexing applications.

Ionic conductivity of alkali nitrites

A comparative study of ionic conductivity in a series of alkali metal nitrites was carried out. Experimental results were interpreted in terms of the classical model of Schottky defect formation in ionic crystals when the cationic vacancies are the dominating charge carriers. The point defect formation and migration parameters were evaluated by fitting of the theoretical model to the experimental data. It was demonstrated that in a series of alkali nitrites both the defect formation and the migration enthalpies decrease with the cationic radius leading to the increase in the conductivity as a function of the cationic size. As a result, the cesium nitrite has the highest conductivity among alkali nitrites.

Ba0.5Gd0.8La0.7Co2O6-δ Infiltrated in Porous BaZr0.7Ce0.2Y0.1O3 Backbones as Electrode Material for Proton Ceramic Electrolytes

Several porous backbone layers of proton conducting BaZr1-x-yCexYyO3-δ (BZCY) were prepared by spray-coating or painting on BaZr0.7Ce0.2Y0.1O2.95 (BZCY72) button cells followed by high temperature firing in air. This step enabled to produce ceramic backbones with various grain and pore sizes. The backbones were further infiltrated with mixed conducting double perovskite Ba0.5Gd0.8La0.7Co2O6-δ (BGLC587) suspensions and annealed in air. The resulting composite layers were tested as oxygen/steam side electrodes for proton ceramic fuel cells and electrolysers (PCFCs-PCEs). The results confirm that a high performing electrode material such as BGLC587 with partial proton conductivity and high thermal expansion can be applied on a proton conducting electrolyte with low thermal expansion by use of backbone infiltration without losing electrochemical functionality. Indeed, the electrodes display an apparent polarization resistance of only 0.03 Ω cm2 at 700°C in oxygen humidified with 2.7% H2O. We further extracted and parameterized the impedances associated with the charge and mass transfer reactions in a system where protons are the dominating charge carriers at intermediate to low temperatures and oxide ions dominate the overall transport at high temperature. The fitting revealed to what extent the charge and mass transfer reactions are short-circuited by electronic leak current across the sample at high temperatures and pO2’s. The acquired activation energies and pre-exponential values were used to explain materials-specific and micro-structural differences between the different electrode architectures.

Type-inversion as a working mechanism of high voltage MAPbBr3(Cl)-based halide perovskite solar cells.

Using several metals with different work functions as solar cell back contact we identify majority carrier type inversion in methylammonium lead bromide (MAPbBr3, without intentional doping) as the basis for the formation of a p-n junction. MAPbBr3 films deposited on TiO2 are slightly n-type, whereas in a full device they are strongly p-type. The charge transfer between the metal electrode and the halide perovskite (HaP) film is shown to determine the dominant charge carrier type of the HaP and, thus, also of the final cells. Usage of Pt, Au and Pb as metal electrodes shows the effects of metal work function on minority carrier diffusion length and majority carrier concentration in the HaP, as well as on built-in voltage, band bending, and open circuit voltage (VOC) within a solar cell. VOC > 1.5 V is demonstrated. The higher the metal WF, the higher the carrier concentration induced in the HaP, as indicated by a narrower space charge region and a smaller minority carrier diffusion length. From the analysis of bias-dependent electron beam-induced currents, the HaP carrier concentrations are estimated to be ∼ 1 × 1017 cm-3 with Au and 2-3 × 1018 cm-3 with Pt. A model in which type-inversion stretches across the entire film width implies formation of the p-n junction away from the interface, near the back-contact metal electrode. This work highlights the importance of the contact metal on device performance in that contact engineering can also serve to control the carrier concentration in HaP.

The effect of NH4NO3 towards the conductivity enhancement and electrical behavior in methyl cellulose-starch blend based ionic conductors

Solid polymer electrolytes based on methyl cellulose (MC)-potato starch (PS) blend doped with ammonium nitrate (NH4NO3) are prepared by solution cast technique. The interaction between the electrolyte’s materials is proven by Fourier transform infrared (FTIR) analysis. The thermal stability of the electrolytes is obtained from thermogravimetric analysis (TGA). The room temperature conductivity of undoped 60 wt.% MC-40 wt.% PS blend film is identified to be (1.04 ± 0.19) × 10−11 S cm−1. The addition of 30 wt.% NH4NO3 to the polymer blend has optimized the room temperature conductivity to (4.37 ± 0.16) × 10−5 S cm−1. Conductivity trend is verified by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dielectric analysis. Temperature-dependence of conductivity obeys Arrhenius rule. Conductivity is found to be influenced by the number density (n) and mobility (μ) of ions. From transference number measurements (TNM), ions are found to be the dominant charge carriers.

Polarization currents in illite at various temperatures

Polarization effects, which take place when an external electrical field is applied, play an important role in ceramics. The polarization currents were measured in illite samples in the temperature range 450°C–1200°C, for 150–300min. Since the polarization current does not reach a zero value even after a long time, it was deduced that both the ions and electrons are the charge carriers. However, the ionic component is dominant in polarization currents in illite. Power functions, which describe the time dependence of the currents, suggest several polarization mechanisms. They are ascribed to local hopping or migration of K+, H+, and OH– ions which are dominant charge carriers in various temperature ranges. The polarization is a long-lasting process also at high temperatures.

Diameter-driven crossover in resistive behaviour of heavily doped self-seeded germanium nanowires.

The dependence of the resistivity with changing diameter of heavily-doped self-seeded germanium nanowires was studied for the diameter range 40 to 11 nm. The experimental data reveal an initial strong reduction of the resistivity with diameter decrease. At about 20 nm a region of slowly varying resistivity emerges with a peak feature around 14 nm. For diameters above 20 nm, nanowires were found to be describable by classical means. For smaller diameters a quantum-based approach was required where we employed the 1D Kubo–Greenwood framework and also revealed the dominant charge carriers to be heavy holes. For both regimes the theoretical results and experimental data agree qualitatively well assuming a spatial spreading of the free holes towards the nanowire centre upon diameter reduction.

Graphene Oxide for Proton Exchange Membrane and Anion Exchange Membrane Fuel Cells

Graphene is increasingly being studied for fuel cell catalysis because of its high conductivity, large surface, and chemical stability.[1,2] Graphene oxide (GO) is a monolayer carbon material with carboxyl, hydroxyl and epoxy oxygen functional groups on the surface and edges. These make GO hydrophilic, and the sp2/sp3-hybridization is believed to make it insulating to electrons.[3] Fuel cell membranes have several important requirements. They must be insulating to electrons, have significant ionomer conductivity, provide sufficient barrier to prevent hydrogen/methanol crossover, and have the mechanical strength to be able to support the cell. GO could potentially fulfil these requirements. [4,5] Here, we investigate the suitability of GO for fuel cell membranes by measuring the gas barrier properties, proton conductivity, anion conductivity, electronic conductivity, tensile strength, and fuel cell performance. Initially we reported the characterization of a graphene oxide membrane fuel cell (GOMFC).[6] Free-standing flexible GO membranes were prepared from GO dispersion in water by vacuum-filtration. GO was found to have higher tensile strength and water uptake compared with Nafion. The power density of a fuel cell with a 30 μm thick GO membrane was 35 mW/cm2 at 30°C, despite the fact that the proton conductivity is several orders of magnitude lower than Nafion. The device had a very high open circuit voltage >1 V indicating low crossover. This indicates that thinner membranes compared with Nafion can be utilized, reducing the overall cell resistance. Indeed, by changing the fabrication method to further reduce the thickness of the GO membranes to several microns, we recently achieved improved power density of up to 80 mW/cm2. We also have performed a detailed study on the through-plane conductivity and permittivity of GO membranes over a wide temperature and humidity range.[7] It was found that the proton conductivity is strongly dependant on humidity, and that under dry warm conditions significant electronic conductivity is observed. This opens the opportunity for tuneable mixed ionic-electronic conductivity and may be extremely useful in sensing application. In addition, we performed in-situ scanning electron microscopy (SEM) and electron energy loss spectroscopy (EELS) on humidified and dried GO membranes, directly observing expansion and contraction (“breathing”) of the membranes.[8] Even after drying and under high vacuum conditions, the EELS signal for crystalline ice was observed after freezing, suggesting that water is extremely strongly bound to GO, which may have implications for proton conductivity. Finally, a novel class of alkaline anion exchange membrane (AAEM) is presented, in the form of KOH-modified multilayer graphene oxide paper (GOKOH).[9] SEM investigations showed that the morphology of GO changes after KOH-treatment, whilst X-ray photoelectron spectroscopy (XPS) measurements and X-ray diffraction (XRD) analysis confirmed successful chemical modification. The hydrogen gas permeability was several orders of magnitude lower than conventional polymer-based ionomer membranes. The maximum anion conductivity was 6.1 mS/cm at 70 °C, and the dominant charge carrier was confirmed to be OH− by utilization of anion and proton-conducting blocking layers. The ion exchange capacity was 6.1 mmol/g, measured by titration. A water-mediated reverse Grotthuss-like mechanism is proposed as the main diffusion mode of OH− ions. A prototype AAEM fuel cell was fabricated using a GOKOH membrane, confirming the applicability to real systems.

Favorable Combination of Schottky Barrier and Junctionless Properties in Field-Effect Transistors for High Temperature Applications

High-temperature transistors are of great interest for industrial applications, for instance, oil&gas and geothermal exploration, avionic, space, automotive and energy conversion. Especially, energy conversion electronics using wide-bandgap power transistors, i.e. SiCFET, in combination with high-temperature silicon gate-driver circuits can significantly increase system efficiency and reduce costs [1]. Our improved planar virtually dopant-free silicon-based double gate SOI FET with Ni and WTiN front-gate electrodes demonstrates ultra-low drain leakage currents at high-temperatures opening a path to record operating temperatures for silicon-based FET devices. Device Structure The long-channel device fabrication relies on a standard CMOS-compatible prototyping process using SOITEC Smart-Cut™ SOI-substrates with the lowest commercially available boron background doping of 1E15cm-3 enabling high carrier mobilities. Mid-gap Schottky barrier (SB) contacts are fabricated via nickel silicidation. The metal front-gate (FG) electrode consist of reactively sputtered WTiN for NMOS or Nickel for PMOS operation on a 8nm thick SiO2 gate dielectric. Channel height (CH) is approximated to 15nm. The back-gate (BG) formed by the silicon handle wafer is insulated by 145nm buried SiO2 (BOX) (Fig.1). Device Operation The device is modeled as a combination of two interacting FETs, one fully ambipolar Schottky barrier backside FET and a second unipolar junctionless (JL) topside FET [2,3]. The BG influences the whole body layer including the S/D Schottky barriers forming an ambipolar enhancement mode SBFET. Therefore, the dominant charge carrier type, i.e. electrons (VBG»0V) or holes (VBG«0V) in the channel region is defined by the BG polarity. In this configuration, the channel is located close to the body silicon to BOX interface (Fig.3). The charge carriers originate from the mid-gap NiSi SB contacts and enter the body layer at room temperature mainly by thermionic field emission (TFE) and at elevated temperatures by thermionic emission (TE) (Fig.2). In contrast, the depletion mode JLFET formed by the FG electrode only locally affects the charge carrier density in the middle of the channel and controls the current flow between source and drain with excellent electrostatic control as illustrated by the carrier density simulation in Fig.3. The combination of the enhancement and depletion mode operation in one device can appositely be summarized as enhancement suppression or dehancement mode operation (DeFET). Results & Discussion P- and NMOS transistor behavior is realized by applying the appropriate BG polarity to the very same device enabling transistor level reconfigurability (Fig.4). Maximum on-state current and threshold voltage are proportional to the magnitude of VBG (Fig.4). The work function difference between Ni and WTiN metal front-gate devices as well as process variations result in a significant threshold shift (Fig.4). The channel height (Fig.1) is a crucial parameter in device fabrication as it directly affects the off-state leakage current and threshold voltage [7]. Regarding high-temperature performance, the use of the SOI substrate eliminates bulk drain leakage while the introduction of SB contacts minimizes the band-to-band tunneling effect in comparison to classic steep S/D pn-junctions. For rising operating temperatures up to 470K, the on-state current increases from 8 to 46µA as TFE and TE increase allowing an overcompensation of the temperature dependent carrier mobility degradation effect (Fig.5,right). At the same time the drain leakage current is only increasing from <100fA to 2nA from 300 to 470K due to the high potential barrier induced by the FG (Fig.5,left). Gate leakage currents are <6pA during all measurements. Furthermore, PMOS behavior with nickel metal front-gate follows the same trends. Device simulations predict that reducing the channel height and introducing mid-κ gate dielectrics, i.e. Al2O3, renders record operating temperatures possible even for scaled devices limited only by reliability. Comparing the here presented DeFET generation with previous generations and other long-channel Si-based high-temperature FET structures illustrates the clear advantage of our device concept in suppressing drain leakage currents at high temperatures (Fig.6) [4-7]. Conclusion In this contribution, we demonstrate by means of experimental measurement data and device simulations the significantly improved drain leakage suppression at high operating temperatures of the planar dehancement mode FET CMOS technology in comparison to our previously published results in [7]. The combination of SB and JLFET properties opens a possible path for silicon based FET operation up to temperatures of 700K for various industrial applications.

Influence of electron beam irradiation on electrical, structural, magnetic and thermal properties of Pr0.8Sr0.2MnO3 manganites

In this communication, the effect of electron beam (EB) irradiation on the structural, electrical transport and thermal properties of Pr0.8Sr0.2MnO3 manganites has been investigated. Rietveld refinement of XRD data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). It is observed that the orthorhombic deformation increases with EB dosage. The Mn–O–Mn bond angle is found to increase with increase in EB dosage, presumably due to strain induced by these irradiations. Analysis on the measured electrical resistivity data indicates that the small polaron hopping model is operative in the high temperature region for pristine as well as EB irradiated samples. The electrical resistivity in the entire temperature region has been successfully fitted with the phenomenological percolation model which is based on phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit positive values, indicating that holes is the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism governs the thermoelectric transport in the high temperature region. In addition, Seebeck coefficient data also is well fitted with the phenomenological percolation model. The behavior in thermal conductivity at the transition is ascribed to the local anharmonic distortions associated with small polarons. Specific heat measurement indicates that electron beam irradiation enhances the magnetic inhomogeneity of the system.