The electrical performance of silicon carbide metal-oxide-semiconductor field effect transistors (4H-SiC MOSFETs) are strongly related to the presence of interface states at the silicon dioxide (SiO2)/4H-SiC interface, whose density is much higher than in the Si/SiO2 system. In particular, the charged interface states determine a degradation of the carrier mobility in the channel of the MOSFET with respect to the bulk mobility. A reliable and consistent method for the evaluation of the interface state density (D (it)) and the effective channel mobility (mu (ch)) in these devices is presented in this work. The two quantities are simultaneously extracted by a combined fit of the current-voltage (I-V) and capacitance-voltage (C-V) electrical characteristics collected on a single device. The simultaneous fit of the I-V and C-V characteristics, which can be easily measured on the same device, noticeably improve the reliability of D (it) and mu (ch) estimation. The results obtained at different temperatures indicate an increase of the mu (ch) with T, in agreement with a dominance of the Coulomb scattering effect as the degradation mechanism of the carrier channel mobility induced by the presence of charged interface states.

Innovative applications in light signal sensing require flexibility, lightweight, low-cost and low temperature processability, as well as high sensitivity and quantitative photoresponse. We report on flexible organic photo transistors (OPTs) with excellent reproducibility in the detection of outstandingly low light intensities of few nW cm(-2). The optical response of the phototransistor was thoroughly characterized as a function of the wavelength, the incident optical intensity and the electrical polarizations. The photodetectors work reliably under bending and pulse cycling in different environmental conditions, at low polarizations down to the range 0.1-5 V. Based on these outcomes, arrays for broadband or multiple wavelength detection were implemented and successfully tested. The proposed device structure, derived from a layered p-p heterojunction, was developed to be easily implementable in each wavelength of interest. These results show a prospect of highly sensitive flexible OPT arrays for both experimental research and innovative optoelectronic systems.

While it is known that a resonant amplification of Tc in two-gap superconductors can be driven by using the Fano-Feshbach resonance tuning the chemical potential near a Lifshitz transition, little is known on tuning the Tc resonance by cooperative interplay of the Rashba spin-orbit coupling (RSOC) joint with phonon mediated (e-ph) pairing at selected k-space spots. Here, we present first-principles quantum calculation of superconductivity in an artificial heterostructure of metallic quantum wells with 3 nm period where quantum size effects give two-gap superconductivity with RSOC controlled by the internal electric field at the interface between the nanoscale metallic layers intercalated by insulating spacer layers. The key results of this work show that fundamental quantum mechanics effects including RSCO at the nanoscale [Mazziotti et al., Phys. Rev. B, 103, 024523 (2021)] provide key tools in applied physics for quantitative material design of unconventional high temperature superconductors at ambient pressure. We discuss the superconducting domes where Tc is a function of either the Lifshitz parameter (?) measuring the distance from the topological Lifshitz transition for the appearing of a new small Fermi surface due to quantum size effects with finite spin-orbit coupling and the variable e-ph coupling g in the appearing second Fermi surface linked with the energy softening of the cut off ?0.

The electrothermal behavior of gallium nitride (GaN) HEMTs has been simulated by using a hybrid approach in which the problem is solved by coupling together an effective model (for the electrical part) and a 3-D finite element model (for the thermal part). The effective model relies on the estimation of the channel current at different temperatures in the absence of thermal gradients. This regime occurs in real devices only during the very initial stage of bias pulses, when self-heating effects are not yet developed, for time intervals shorter than 1 ns. Virtual output electrical characteristic, in which self-heating effects are negligible, have been derived from pulsed measurements of the electrical output characteristics and electrothermal transient simulations. The maximum temperature because of self-heating evaluated by using the virtual output characteristic are substantially higher than those obtained using the short time-pulsed measurements directly. The results have been validated by a comparison with temperature measurements obtained using Raman thermography. This approach has proven to be numerically very efficient and fast, allowing the analysis of realistic complex structures and circuits.

In this work we study the electrical stability under both gate bias stress and gate and drain bias stress of short channel (L = 5 mu m) bottom contact/top gate OTFTs made on flexible substrate with solution-processed organic semiconductor and fluoropolymer gate dielectric. These devices show high field-effect mobility ( mu(FE)> 1 cm(2)V(-1)s(-1)) and excellent stability under gate bias stress (bias stress V-ds = 0V). However, after prolonged bias stress performed at high drain voltage, V-ds, the transfer characteristics show a decreased threshold voltage, degradation of the subthreshold slope and an apparent increase in the field effect mobility. Furthermore, the output characteristics show an asymmetry when measured in forward and reverse mode. These experimental results can be explained considering that the bias stress induces the damage of a small part of the device channel, localized close to the source contact. The analysis of the experimental data through 2D numerical simulations supports this explanation showing that the electrical characteristics after bias stress at high V-ds can be reproduced considering the creation of donor-like interface states and trapping of positive charge into the gate dielectric at the source end of the device channel. In order to explain this degradation mechanism, we suggest a new physical model that, assuming holes injection from the source contact into the channel in bounded polarons, envisages the defect creation at the interface near the source end of the channel induced by injection of holes that gained energy from both the high longitudinal electric fields and the polaron dissolution.

The control of Covid 19 epidemics by public health policy in Italy during the first and the second epidemic waves has been driven by using reproductive number Rt(t) to identify the supercritical (percolative), the subcritical (arrested), separated by the critical regime. Here we show that to quantify the Covid-19 spreading rate with containment measures there is a need of a 3D expanded parameter space phase diagram built by the combination of Rt(t) and doubling time Td(t). In this space we identify the Covid-19 dynamics in Italy and its administrative Regions. The supercritical regime is mathematically characterized by (i) the power law of Td vs. [Rt(t) - 1] and (ii) the exponential behaviour of Td vs. time, either in the first and in the second wave. The novel 3D phase diagram shows clearly metastable states appearing before and after the second wave critical regime. for loosening quarantine and tracing of actives cases. The metastable states are precursors of the abrupt onset of a next nascent wave supercritical regime. This dynamic description allows epidemics predictions needed by policymakers interested to point to the target "zero infections" with the elimination of SARS-CoV-2, using the Finding mobile Tracing policy joint with vaccination-campaign, in order to avoid the emergence of recurrent new variants of SARS-CoV-2 virus, accompined by recurrent long lockdowns, with large economical losses, and large number of fatalities.

The maximum critical temperature for superconductivity in pressurized hydrides appears at the top of superconducting domes in T c vs pressure curves at a particular pressure, which is not predicted by standard superconductivity theories. The high-order anisotropic Van Hove singularity near the Fermi level observed in band-structure calculations of pressurized sulfur hydride, typical of a supermetal, has been associated with the array of metallic hydrogen wire modules forming a nanoscale heterostructure at an atomic limit called the superstripe phase. Here, we propose that pressurized sulfur hydrides behave as a heterostructure made of a nanoscale superlattice of interacting quantum wires with a multicomponent electronic structure. We present first-principles quantum calculation of a universal superconducting dome where T c amplification in multi-gap superconductivity is driven by the Fano-Feshbach resonance due to a configuration interaction between open and closed pairing channels, i.e., between multiple gaps in the BCS regime, resonating with a single gap in the BCS-Bose-Einstein condensation crossover regime. In the proposed three dimensional phase diagram, the critical temperature shows a superconducting dome where T c is a function of two variables: (i) the Lifshitz parameter ( eta) measuring the separation of the chemical potential from the Lifshitz transition normalized by the inter-wire coupling and (ii) the effective electron-phonon coupling (g) in the appearing new Fermi surface including phonon softening. The results will be of help for material design of room-temperature superconductors at ambient pressure.</p>

While the mathematical laws of uncontrolled epidemic spreading are well known, the statistical physics of coronavirus epidemics with containment measures is currently lacking. The modelling of available data of the first wave of the Covid-19 pandemic in 2020 over 230 days, in different countries representative of different containment policies is relevant to quantify the efficiency of these policies to face the containment of any successive wave. At this aim we have built a 3D phase diagram tracking the simultaneous evolution and the interplay of the doubling time, T (d), and the reproductive number, R (t) measured using the methodological definition used by the Robert Koch Institute. In this expanded parameter space three different main phases, supercritical, critical and subcritical are identified. Moreover, we have found that in the supercritical regime with R (t) > 1 the doubling time is smaller than 40 days. In this phase we have established the power law relation between T (d) and (R (t) - 1)(-nu) with the exponent nu depending on the definition of reproductive number. In the subcritical regime where R (t) < 1 and T (d) > 100 days, we have identified arrested metastable phases where T (d) is nearly constant.

In this paper we analyze the effect of the top metal overlap associated to the drain contact, that can be present in thin film transistors (TFTs) with bottom-gate staggered configuration. It is shown that the effect of the top metal contact at the drain, overlapping the passivation or etch stopper layer (ESL), increases the drain current. Results from numerical simulations show that this top metal overlap acts as a second gate to the device, partially located near the drain contact. The overall effect on the device current will depend on the semiconductor doping, as well as on the thickness and dielectric constants of the gate dielectric and passivation/ESL layers. The effect is more significant as the channel length of the devices is reduced.

Organic material deposition by gravure printing is a promising pathway for the realization of large area flexible electronic devices. Nevertheless, in order to achieve high performance it is required to improve the electronic ink printability, operating on the fluid dynamic mechanisms involved during the process. In this work, this issue has been faced working on ink characteristics for a conductive and a dielectric material. The suitable ink features have been defined studying the influence on the printability of the different forces that act in the fluid during the printing process, using an experimental approach. Properly defined ink formulations have been printed, considering different shapes and dimensions of the cells on the gravure cliche to fit the ink features. The printing outcomes have been compared and analysed through the evaluation of several significant fluid dynamic parameters and the rheological characterization of the materials. Finally, exploiting the results of this study, high performance fully printed organic thin film transistors have been realized.

We present a compact model for the DC and small signal AC analysis of Organic Thin Film Transistors (OTFTs). The DC part of the model assumes that the electrical current injected in the OTFT is limited by the presence of a metal/organic semiconductor junction that, at source, acts as a reverse biased Schottky junction. By including this junction, modeled as a reverse biased gated diode at source, the DC model is able to reproduce the scaling of the electrical characteristics even for short channel devices.

Recent experiments have reported the emergence of high-temperature superconductivity with critical temperature T-c between 43K and 123K in a potassium-doped aromatic hydrocarbon para-Terphenyl or p-Terphenyl. This achievement provides the record for the highest T-c in an organic superconductor overcoming the previous record of T-c = 38K in Cs3C60 fulleride. Here we propose that the driving mechanism is the quantum resonance between superconducting gaps near a Lifshitz transition which belongs to the class of Fano resonances called shape resonances. For the case of p-Terphenyl our numerical solutions of the multigap equation shows that high T-c is driven by tuning the chemical potential by K doping and it appears only in a narrow energy range near a Lifshitz transition. At the maximum critical temperature, T-c = 123 K, the condensate in the appearing new small Fermi surface pocket is in the BCS-BEC crossover while the T-c drops below 0.3K where it is in the BEC regime. Finally, we predict the experimental results which can support or falsify our proposed mechanism: a) the variation of the isotope coefficient as a function of the critical temperature and b) the variation of the gaps and their ratios 2 Delta/T-c as a function of T-c. Copyright (C) EPLA, 2017

A compensation model for semi-insulating CdTe: Cl based on a single dominant deep level 0.725 eV above the valence band is proposed. The model is corroborated by experimental evidence: resistivity measurements as a function of temperature on bulk crystals and stationary electric field distributions in Ohmic/Schottky radiation detectors, obtained by the Pockels effect. The latter are in close agreement with the numerical solutions of transport equations when considering the deep centre concentration in the range 2 - 4 x 10(12) cm(-3), and a compensation ratio R = 2.1, this one being consistent with an original ambipolar analysis of resistivity. More generally, the approach elucidates the role of electrical contacts and deep levels in controlling the electric fields in devices based on compensated materials.

This work introduces a compact DC model developed for organic thin film transistors (OTFTs) and its SPICE implementation. The model relies on a modified version of the gradual channel approximation that takes into account the contact effects, occurring at nonohmic metal/organic semiconductor junctions, modeling them as reverse biased Schottky diodes. The model also comprises channel length modulation and scalability of drain current with respect to channel length. To show the suitability of the model, we used it to design an inverter and a ring oscillator circuit. Furthermore, an experimental validation of the OTFTs has been done at the level of the single device as well as with a discrete-component setup based on two OTFTs connected into an inverter configuration. The experimental tests were based on OTFTs that use small molecules in binder matrix as an active layer. The experimental data on the fabricated devices have been found in good agreement with SPICE simulation results, paving the way to the use of the model and the device for the design of OTFT-based integrated circuits.

We studied, by 2D numerical simulations, the effects of poor semiconductor morphology near the source and drain contacts of BGBC-OTFTs. The variations of the electrical characteristics and of the path of the injected carriers in the transistor channel have been analyzed considering different defective regions, parameters (mobility, density of states) and contact thicknesses. The results showed that 100 nm wide defective regions can induce high contact resistance, resulting in large variation in the electrical characteristics. However, the typical S-shape in the low-Vds output characteristics is clearly observed only considering a combination of highly defected regions and Schottky barrier at the contacts. Furthermore, the simulations showed that most of the current is injected and extracted, at the source and drain contact, within a few nanometers from the semiconductor- dielectric interface. This explains the small influence of the contact thickness on the simulated electrical characteristics, at least for a contact thickness down to 10 nm.

We propose the implementation of graphene-based field effect transistor (FET) as radiation sensor. In the proposed detector, graphene obtained via chemical vapor deposition is integrated into a Si-based field effect device as the gate readout electrode, able to sense any change in the field distribution induced by ionization in the underneath absorber, because of the strong variation in the graphene conductivity close to the charge neutrality point. Different 2-dimensional layered materials can be envisaged in this kind of device.

We have investigated the stability of the electrical performances in staggered organic thin film transistors (OTFTs) manufactured by using a CYTOP fluoropolymer as a gate dielectric, after the devices underwent reliability cycles in a high moisture and temperature controlled environment chamber. The results of such testing cycles showed a very high stability against the environmental conditions that might be related to the device top-gate structure, working as an efficient encapsulation, and to the hydrophobic properties of the fluoropolymer used as gate dielectric.

In thiswork,we simulated and experimentally assessed the possibility to detect, through electrical transduction, hybridization of DNA molecules onMOS-like devices, having different dielectrics: SiO2, Si3N4 and SiO2/Si3N4/SiO2 (ONO). The electrical characterization was performed after the various functionalization steps, consisting of dielectric activation, silanization, DNA spotting and anchoring, and after the hybridization process, to test the devices effectiveness as DNA recognition biosensors. The experimental results were used to validate device simulations. The comparison shows the ability to determine a priori the DNA probe density needed to maximize the response. The results confirm that the structures analyzed are sensitive to the immobilization of DNA and its hybridization.

A unified drain current model of complementary (p- and n-type) organic thin film transistors (OTFTs) is presented. The model is physically based and takes into account the detailed properties of the organic semiconductor through the density of states (DOS). The drain current depends on the geometrical and physical parameters of the transistor, on the applied gate, drain and source voltages, and on the surface potential at the source and drain contacts. An analytical expression of the surface potential is derived. The proposed model is validated with the numerical calculations and the measurements of both p- and n-type OTFTs fabricated in a printed complementary technology. The provided analyses show that the model is continuous, accurate, and includes the main physical effects taking place in complementary organic transistors. Thanks to its analytical and symmetric formulation, it is suitable for the design of organic integrated circuits. Moreover, the unified physical picture provided by the model enables the extraction of the OTFTs physical parameters, thus it is a very powerful tool for the technology characterization.

In multiband superconductivity, the case where the single electron hopping between different Fermi surface spots of different symmetry is forbidden by selection rules is recently attracting a large interest. The focus is addressed to superconductivity made of multiple condensates with different symmetry where the chemical potential crosses a 2.5 Lifshitz transition. This can now be investigated experimentally by fine-tuning of the chemical potential in the range of tens meV around a band edge using gate voltage control. We discuss here the case of a superconducting two-dimensional electron gas (2DEG), at the interface between two insulating oxides confined within a slab of 5 nanometers thickness, where the electronic structure is made of subbands generated by quantum size effects. We obtain shape resonances in the superconducting gaps, characterisc gaps to T-c ratios and the BCS-BEC crossover in the upper subband for different pairing strength in the shallow Fermi surface, pointing toward the best configurations for enhanced superconductivity in 2DEG.