Influence of Traps and Carriers on Reliability in HfSiON/ $hbox{SiO}_{2}$ Stacks

The influence of traps and current on the degradation in HfSiON has been studied. Different characteristics of activation energy for TDDB between thick and thin HfSiON, where the Poole Frenkel (PF) and tunnel currents mainly flow, respectively, were observed in the same temperature range. It was indicated that the current could promote the breakdown in HfSiON. Furthermore, we investigated the correlation between pre-existing traps and trap generation in HfSiON/$hbox{SiO}_{2}$ stacks with fluorine incorporation. It was found that the nature of generated traps correspond to that of pre-existing traps. From these results, it was considered that the interaction between traps and carriers causes the degradation in HfSiON.      

Positive Bias Temperature Instability Effects in nMOSFETs With $hbox{HfO}_{2}/hbox{TiN}$ Gate Stacks

The Positive Bias Temperature Instability (PBTI) and the stress-induced leakage current (SILC) effects are thoroughly examined in nFETs with $hbox{SiO}_{2}/hbox{HfO}_{2}/hbox{TiN}$ dual-layer gate stacks under a wide range of bias and temperature stress conditions. Experimental evidence of the SILC increase with time is obtained suggesting the activation of a trap generation mechanism. Threshold voltage $(V_{rm T})$ instability is found to be the result of a complicated interplay of two separate mechanisms; filling of preexisting electron traps versus trap generation each one dominating at different stress condition regimes. Furthermore, $V_{rm T}$ instability relaxation experiments, undertaken at judiciously chosen conditions, show that the preexisting and stress-induced traps exhibit similar detrapping kinetics indicating that both types of traps may have similar characteristics. Finally, it is shown that the role of the SILC effect (and the associated trap generation component) on $V_{rm T}$ instability is process dependent and that SILC reduction is accompanied by enhancement of the PBTI device lifetime.      

$hbox{NO}_{rm x}$ Aftertreatment Using Thermal Desorption and Nitrogen Nonthermal Plasma Reduction

In this paper, the results of two experiments are reported. First, the performances of various types of nonthermal plasma reactors for $hbox{NO}_{rm x}$ reduction were compared. It was shown that the surface-discharge reactors have as high $ hbox{NO}_{rm x}$ reduction capabilities as pulse-powered wire–cylinder reactors. Second, $hbox{NO}_{rm x}$ treatment using the surface-discharge reactor with a NO-adsorbent zeolite 13X was performed. Thermal desorption was employed for the regeneration of the zeolite. The $hbox{NO}_{rm x}$ of 350 ppm was kept lower than 18 ppm for at least 11 h, whereas it degraded to 75 ppm in the absence of the regeneration. The result suggested the possibility of an aftertreatment system that employed thermal desorption by utilizing the waste heat of diesel engine exhaust and $hbox{NO}_{rm x}$ reduction by using a surface-discharge reactor.      

Time-Dependent Dielectric Breakdown of 4H-SiC/$ hbox{SiO}_{2}$ MOS Capacitors

Time-dependent dielectric breakdown (TDDB) is one of the major issues concerning long-range reliability of dielectric layers in SiC-based high-power devices. Despite the extensive research on TDDB of $hbox{SiO}_{2}$ layers on Si, there is a lack of high-quality statistical TDDB data of $hbox{SiO}_{2}$ layers on SiC. This paper presents comprehensive TDDB data of 4H-SiC capacitors with a $ hbox{SiO}_{2}$ gate insulator collected over a wide range of electric fields and temperatures. The results show that at low fields, the electric field acceleration parameter is between 2.07 and 3.22 cm/MV. At fields higher than 8.5 MV/cm, the electric field acceleration parameter is about 4.6 cm/MV, indicating a different failure mechanism under high electric field stress. Thus, lifetime extrapolation must be based on failure data collected below 8.5 MV/cm. Temperature acceleration follows the Arrhenius model with activation energy of about 1 eV, similar to thick $hbox{SiO}_{2}$ layers on Si. Based on these experimental data, we propose an accurate model for lifetime assessment of 4H-SiC MOS devices considering electric field and temperature acceleration, area, and failure rate percentile scaling. It is also demonstrated that temperatures as high as 365 $^{circ}hbox{C}$ can be used to accelerate TDDB of SiC devices at the wafer level.      

Preparation and Luminescence Properties of Glass Ceramics Precipitated With $hbox{M}_{bf 2}hbox{MgSi}_{bf 2}hbox{O}_{bf 7}{:},hbox{Eu}^{bf 2+}$ (M = Sr, Ca) Phosphor for White Light Source

$hbox{Eu}^{2+}$-doped silicate glasses were prepared in the system $42hbox{SiO}_{2}$– $gamma hbox{CaO}$– $(38gamma)hbox{SrO}$–$20hbox{MgO}$– $0.2hbox{EuO} (gamma = 0, 10, 20, 30, 38)$ by melting under reducing atmosphere. Glass ceramics precipitated with $hbox{M}_{2}hbox{MgSi}_{2}hbox{O}_{7}{:}hbox{Eu}^{2+}$ (M = Sr, Ca) phosphor were obtained by heat-treatment of the glass. They showed broad emission band due to the 5d $rightarrow$ 4f transition of $hbox{Eu}^{2+}$. The peak wavelength shifted from 470 to 530 nm with increasing CaO content. Their emission wavelength can be controlled by changing the compositional ratio of Ca and Sr. Their color coordinates were widely changed from blue to yellowish green region. We have successfully obtained glass ceramic phosphors with excellent durability for a high-power white LED based on near-UV LED.      

PM and $hbox{NO}_{rm x}$ Removal for Diesel Engine Emission Using Ozonizer and Chemical Hybrid Reactor

Over the years, we have investigated particulate matter (PM) and $ hbox{NO}_{rm x}$ reduction using nonthermal plasma-chemical hybrid processes without using catalysts. Among nonthermal plasma hybrid processes, the ozonizer combined with the chemical hybrid reactor was investigated using a 479 cc (5.5 kW) power generation diesel engine. The PM deposited on the diesel particulate filter can be incinerated by ozone and $hbox{NO}_{2}$ in a wide range of flue gas temperature. The NO was oxidized to form $hbox{NO}_{2}$ by ozone, and $hbox{NO}_{2}$ was reduced by the 3% $hbox{Na}_{2}hbox{SO}_{3}$ chemical reactor. As the results, PM deposited on both metal and ceramic filters were successfully removed even at ambient temperature. The rate of PM incineration depends on the amount of ozone injected and was significantly higher than the rate of PM generation. Using 2.4% ozone concentration with a flow rate of 10 L/min, 82% of NO having 720 L/min was oxidized to $hbox{NO}_{2}$, and 78% of $ hbox{NO}_{rm x}$ was removed as a chemical scrubber. However, $ hbox{NO}_{rm x}$ removal was deteriorated about 10% after 1-h operation. This was attributed to $hbox{Na}_{2}hbox{SO}_{3}$ oxidation by air, which was evidenced by the reduction of pH in the chemical reactor.      

Highly Stable 1.3-$muhbox{m}$ -Wavelength Lasers With p- and n-InP Buried Heterostructure

Highly stable 1.3-$muhbox{m}$-wavelength Fabry–Perot lasers with a p- and n-type InP buried heterostructure have been achieved at an ambient temperature of 85 $^{circ}hbox{C}$. The $t^{0.5}$ deterioration (second-stage degradation) property does not appear clearly within 6000 h, and the saturated first-stage degradation property remains. It is confirmed that the fabricated 1.3-$muhbox{m}$ FP lasers have a different optical-beam-induced-current characteristic from lasers suffering from $t^{0.5}$ deterioration. The first-stage degradation is due to the deterioration of the active layer and is attributed to the fact that some nonradiative recombination centers are generated in the active layer.      

Analog and RF performance of doping-less tunnel FETs with $$\hbox {Si}_{0.55} \hbox {Ge}_{0.45}$$ source

This paper reports studies of a doping-less tunnel field-effect transistor (TFET) with a \(\hbox {Si}_{0.55} \hbox {Ge}_{0.45}\) source structure aimed at improving the performance of charge-plasma-based doping-less TFETs. The proposed device achieves an improved ON-state current (\(I_{{\mathrm{ON}}} \sim {4.88} \times {10}^{-5}\,{\mathrm{A}}/\upmu {\mathrm{m}}\)), an \(I_\mathrm{ON}/I_\mathrm{OFF}\) ratio of \({6.91} \times {10}^{12}\), an average subthreshold slope (\(\hbox {AV-SS}\)) of \(\sim \) \({64.79}\,{\mathrm{mV/dec}}\), and a point subthreshold slope (SS) of 14.95 mV/dec. This paper compares the analog and radio of frequency (RF) parameters of this device with those of a conventional doping-less TFET (DLTFET), including the transconductance (\(g_{{\mathrm{m}}}\)), transconductance-to-drain-current ratio \((g_\mathrm{m}/I_\mathrm{D})\), output conductance \((g_\mathrm{d})\), intrinsic gain (\(A_{{\mathrm{V}}}\)), early voltage (\(V_{{\mathrm{EA}}}\)), total gate capacitance (\( C_{{\mathrm{gg}}}\)), and unity-gain frequency (\(f_{{\mathrm{T}}}\)). Based on the simulated results, the \(\hbox {Si}_{0.55}\hbox {Ge}_{0.45}\)-source DLTFET is found to offer superior analog as well as RF performance.     

Delta-doped tunnel FET (D-TFET) to improve current ratio ($$I_\mathrm{ON}/I_\mathrm{OFF}$$) and ON-current performance

A two dimensional (2D) analytical drain current model has been developed for a delta-doped tunnel field-effect transistor (D-TFET) that can address the ON-current issues of the conventional TFET. Insertion of a highly doped delta layer in the source region paves the way for improved tunneling volume and thus provides high drain current as compared with TFETs. The present model takes into account the effects of the distance between the delta-doping region and the source–channel interface on the subthreshold swing (SS), current ratio, and ON-current performance. The D-TFET is predicted to have a higher current ratio \(\left( {\frac{I_\mathrm{ON} }{I_\mathrm{OFF} }\cong 10^{11}} \right) \) compared with TFETs \(\left( {\frac{I_\mathrm{ON} }{I_\mathrm{OFF} }\cong 10^{10}} \right) \) with a reasonable SS \(\left( {{\sim }52\,\mathrm{mV/dec}} \right) \) and \(V_\mathrm{th}\) performance at an optimal position of 2 nm from the channel. The surface potential, electric field, and minimum tunneling distance have been derived using the solution of the 2D Poisson equation. The accuracy of the D-TFET model is validated using the technology computer aided design (TCAD) device simulator from Synopsys.     

$hbox{1}/f$ Noise Characterization of n- and p-Type Polycrystalline-Silicon Thin-Film Transistors

This paper presents a study of low-frequency-noise properties of n- and p-type polycrystalline-silicon (poly-Si) thin-film transistors (TFTs). The $hbox{1}/f$ noise behavior of these devices prompted the use of the carrier number with correlated mobility fluctuation model for data analysis. From this model, trap densities in this study were found to range from $hbox{3.5} times hbox{10}^{16}$ to $hbox{4} times hbox{10}^{17} hbox{states/eV} cdot hbox{cm}^{3}$, which is indicative of a good top surface of the channel and interface between the oxide and poly-Si. The normalized current noise of the p-channel TFTs changes with the inverse of current, independent of the width $(W)$ -to-length $(L)$ ratio of the channel; the normalized current noise of the n-channel TFTs also changes with the inverse of current, but not independent of the $W/L$ ratio. For smaller currents, noise is caused by traps at or near the oxide/semiconductor interface, whereas for larger currents, the larger contribution to the noise is believed to originate from the bulk.      

Comparative study on interfacial properties of Mo,Nb, and W contacts with monolayer $$\hbox {MoS}_{2}$$

In this work, we make a comparative study on the interfacial properties of top contact for Mo, Nb, and W metals with monolayer \(\hbox {MoS}_{2 }\,(\hbox {mMoS}_{2})\) by employing first-principles based on density functional theory (DFT) calculations. We evaluate the heights of Schottky barrier (SBH) and orbital overlap of the three models by carefully observing band structure and the density of the states relative to the Fermi level. Also, the tunnel barriers and electron densities of the three systems are analyzed. In accordance with the DFT simulations, \(\hbox {mMoS}_{2}\) forms an n-type Schottky contact with Mo, Nb, and W electrodes with electron SBH of 0.28, 0, and 0.6 eV, respectively. Besides, \(\hbox {Nb-mMoS}_{2}\) contact exhibits higher average electron density and lower tunneling barriers, demonstrating that Nb can form a better top contact with \(\hbox {mMoS}_{2}\) and should have prior electron injection efficiency and backgated regulation of current compared to the \(\hbox {mMoS}_{2}\) contacts with Mo and W.     

High-Power $hbox{Yb}^{{bm 3}{bm +}}$-Doped Phosphate Fiber Amplifier

We report on the development of novel high-power light sources utilizing a $hbox{Yb}^{3+}$-doped phosphate fiber as the gain element. This host presents several key benefits over silica, particularly much higher $hbox{Yb}_{2} hbox{O}_{3}$ concentrations (up to 26 wt%), a 50% weaker stimulated Brillouin scattering (SBS) gain cross section, and the absence of observable photodarkening even at high population inversion. These properties result in a greatly increased SBS threshold compared to silica fibers, and therefore, potentially much higher output powers out of either a multimode large mode area or a single-mode fiber, which means in the latter case a higher beam quality. To quantify these predictions, we show through numerical simulations that double-clad phosphate fibers should produce as much as $sim$700 W of single-frequency output power in a step index, single-mode core. As a step in this direction, we report a short phosphate fiber amplifier doped with 12 wt% $hbox{Yb}_{2} hbox{O}_{3}$ that emits 16 W of single-frequency single-mode output. We also describe a single-mode phosphate fiber laser with a maximum output power of 57 W. The laser slope efficiency is currently limited by the fairly high fiber loss ( $sim$3 dB/m). Measurements indicate that 77% of this loss originates from impurity absorption, and the rest from scattering.      

Filament-to-dielectric band alignments in $$\hbox {TiO}_{2}$$ and $$\hbox {HfO}_{2}$$HfO2 resistive RAMs

The next-generation nonvolatile memory storage may well be based on resistive random access memories (RRAMs). \(\hbox {TiO}_{2}\) and \(\hbox {HfO}_{2}\) have been widely used as the resistive switching layer for RRAM devices. However, the electronic properties of the filament-to-dielectric interfaces are still not well understood yet, compared to those of the electrodes and the dielectric. In this work, we study the electronic structures of three typical filament and dielectric structures, \(\hbox {Ti}_{4}\hbox {O}_{7}/\hbox {TiO}_{2}\), \(\hbox {Hf}_{2}\hbox {O}_{3}/\hbox {HfO}_{2}\) and \(\hbox {Hf}/\hbox {HfO}_{2}\), using ab initio calculations. We implement the GGA-1/2 method, which rectifies the band gaps of GGA through self-energy correction. Our calculation predicts an ohmic contact for the \(\hbox {Ti}_{4}\hbox {O}_{7}/\hbox {TiO}_{2}\) interface, where the defective \(\hbox {Ti}_{4}\hbox {O}_{7}\) phase was experimentally identified as the filament composition in \(\hbox {TiO}_{2}\). However, there is a finite Schottky barrier existing in either \(\hbox {Hf}_{2}\hbox {O}_{3}/\hbox {HfO}_{2}\) interface (1.96 eV) or \(\hbox {Hf}/\hbox {HfO}_{2}\) interface (0.61 eV), the two probable filament–dielectric configurations in hafnia-based RRAM. Our results suggest that the distinct filament-to-dielectric band alignments in \(\hbox {TiO}_{x}\) and \(\hbox {HfO}_{x}\) systems account for the much larger resistance window for the latter.     

Composition dependence of fundamental properties of $$\hbox {Cd}_{\mathrm{1-x}}\hbox {Co}_\mathrm{x}$$Te magnetic semiconductor alloys

Ab initio calculations based on density functional theory have been performed using the full-potential augmented-plane-wave method so as to investigate the composition dependence of the electronic structure and fundamental properties of hypothetical zinc-blende \(\hbox {Cd}_{\mathrm{1-x}}\hbox {Co}_{\mathrm{x}}\hbox {Te}\) magnetic semiconductor alloys at low Co concentrations. To treat the exchange and correlation energies, the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof has been used. In addition, the modified Becke–Johnson exchange potential with the GGA approach is used for the band structure providing high accuracy. It is found that the addition of a small amount of Co atoms in the \(\hbox {Cd}_{\mathrm{1-x}}\hbox {Co}_{\mathrm{x}}\hbox {Te}\) makes the latter less compressible, ferromagnetic and exhibiting a half metallic character. Besides, the composition dependence of the real and imaginary parts of the dielectric function has been examined and discussed. The information derived from the present study may be useful for spintronics technological applications.     

First-principles investigation on transport properties of $$\hbox {Zn}_{2}\hbox {SnO}_{4}$$ molecular device and response toward $$\hbox {NO}_{2}$$NO2 gas molecules

The transport properties of a \(\hbox {Zn}_{2}\hbox {SnO}_{4}\) device along with adsorption properties of \(\hbox {NO}_{2}\) gas molecules on \(\hbox {Zn}_{2}\hbox {SnO}_{4}\) (ZTO) molecular devices are investigated with density functional theory using the non-equilibrium Green’s function technique. The transmission spectrum and device density of states spectrum confirm the changes in HOMO–LUMO energy level due to transfer of electrons between the ZTO-based material and the \(\hbox {NO}_{2}\) molecules. I–V characteristics demonstrate the variation in the current upon adsorption of \(\hbox {NO}_{2}\) gas molecules on the ZTO device. The findings of the present study clearly suggest that ZTO molecular devices can be used to detect \(\hbox {NO}_{2}\) gas molecules in the trace level.     

Optimal design of the multiple-apertures-GaN-based vertical HEMTs with $$\hbox {SiO}_{2}$$ current blocking layer

Gallium nitride (GaN) based vertical high electron mobility transistor (HEMT) is very crucial for high power applications. Combination of advantageous material properties of GaN for high speed applications and novel vertical structure makes this device very beneficial for high power application. To improve the device performance especially in high drain bias condition, a novel GaN based vertical HEMT with silicon dioxide \((\hbox {SiO}_{2})\) current blocking layer (CBL) was reported recently. In this paper, effects of the thickness of CBL layer and the aperture length on the electrical and breakdown characteristics of GaN vertical HEMTs with \(\hbox {SiO}_{2}\) CBL are simulated by using two-dimensional quantum-mechanically corrected device simulation. Intensive numerical study on the device enables us to optimize and conclude that devices with \(0.5\hbox {-}\upmu \hbox {m}\)-thick \(\hbox {SiO}_{2}\) layer and \(1\hbox {-}\upmu \hbox {m}\)-long aperture will be beneficial considerations to improve the device performance. Notably, using the multiple apertures can effectively reduce the on-state conducting resistance of the device. On increasing the number of apertures, the drain current is increased but the breakdown voltage is decreased. Therefore, device with four apertures is taken as an optimized result. The maximum drain current of 84 mA at \(\hbox {V}_\mathrm{G}= 1\,\hbox {V}\) and \(\hbox {V}_\mathrm{D}= 30\,\hbox {V}\), and the breakdown voltage of 480 V have been achieved for the optimized device.     

Structural,electrical and optical properties of $$\hbox {InGaZnO}_{4}$$ and $$\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}$$In29Sn3O48: a first-principles study

First-principles calculations were performed to investigate the electrical and optical properties of \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) with Sn-doped \(\hbox {In}_{2}\hbox {O}_{3}\) and \(\hbox {InGaZnO}_{4}\) (IGZO). The band structure, density of states, optical properties including dielectric function, loss function, reflectivity and absorption coefficient are calculated. The calculated total energy shows that the most stable crystal structures are type III for \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and type II for \(\hbox {InGaZnO}_{4}\). The band structure indicates the both \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and \(\hbox {InGaZnO}_{4}\) are direct gap semiconductors. The intrinsic band gap of \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) is much narrower than that of \(\hbox {InGaZnO}_{4}\), and results in a better electrical conductivity for \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\). The density of states shows the main hybridization occurring between In-4d and O-2p states for \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) while between In-4d In-5p, Zn-4s and O-2p states for \(\hbox {InGaZnO}_{4}\) near the valence band maximum. The reflectivity index \(R({\omega })\) shows that the peak value of \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and \(\hbox {InGaZnO}_{4}\) appears only in the ultraviolet range, indicating that these two materials have all excellent transparency. In addition, the absorption coefficient \({\alpha }({\omega })\) of both \(\hbox {In}_{29}\hbox {Sn}_{3}\hbox {O}_{48}\) and \(\hbox {InGaZnO}_{4}\) is high in the ultraviolet frequency range, and therefore they show, a high UV absorption rate.     

Numerical analysis of transmission coefficient,LDOS, and DOS in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ resonant tunneling MODFETs

Numerical analysis of the transmission coefficient, local density of states, and density of states in superlattice nanostructures of cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) resonant tunneling modulation-doped field-effect transistors (MODFETs) using \(\hbox {next}{} \mathbf{nano}^{3}\) software and the contact block reduction method is presented. This method is a variant of non-equilibrium Green’s function formalism, which has been integrated into the \(\hbox {next}\mathbf{nano}^{3}\) software package. Using this formalism in order to model any quantum devices and estimate their charge profiles by computing transmission coefficient, local density of states (LDOS) and density of states (DOS). This formalism can also be used to describe the quantum transport limit in ballistic devices very efficiently. In particular, we investigated the influences of the aluminum mole fraction and the thickness and width of the cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N}\) on the transmission coefficient. The results of this work show that, for narrow width of 5 nm and low Al mole fraction of \(x = 20\,\%\) of barrier layers, cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) superlattice nanostructures with very high density of states of 407 \(\hbox {eV}^{-1}\) at the resonance energy are preferred to achieve the maximum transmission coefficient. We also calculated the local density of states of superlattice nanostructures of cubic \(\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}\) to resolve the apparent contradiction between the structure and manufacturability of new-generation resonant tunneling MODFET devices for terahertz and high-power applications.     

Atomistic tight-binding simulations of quaternary-alloyed $$\hbox {Zn}_{x}\hbox {Cd}_{1-x}\hbox {S}_{y}\hbox {Se}_{1-y}$$ nanocrystals

Advancement of alloyed nanocrystals with attractive structural and optical properties for use in a wide range of physical, chemical, and biological applications represents a growing research field. Employing atomistic tight-binding theory combined with the virtual crystal approximation, the electronic structure and optical properties of quaternary-alloyed \(\hbox {Zn}_{{x}}\hbox {Cd}_{1-{x}} \hbox {S}_{{y}}\hbox {Se}_{1-{y}}\) nanocrystals with experimentally synthesized compositions (x and y) and sizes were investigated. Analysis of the results shows that the physical properties are mainly sensitive to the concentrations (x and y) and the diameter. With decreasing x and y contents, the optical bandgap is reduced because the contributions of the materials with narrower bulk bandgap (ZnSe and CdSe) is mostly promoted. The optical bandgap is reduced with increasing diameter due to the quantum confinement effect. The optical bandgap calculated based on tight-binding calculations shows discrepancy of less than 0.4 eV from experiment. Most importantly, the optical emission is continuously tunable across the entire visible spectrum. The conduction and valence bands are predominantly contributed by cation and anion atoms, respectively. The optical properties are obviously improved in Cd- and Se-rich quaternary \(\hbox {Zn}_{{x}}\hbox {Cd}_{1-{x}} \hbox {S}_{{y}}\hbox {Se}_{1-{y}}\) nanocrystals with large diameter. The atomistic electron–hole interactions can be hybrid-engineered by tuning either the contents (x and y) or diameter. The Stokes shift becomes more pronounced with decreasing alloy concentrations (x and y) and diameter, as described by the trend of the atomistic electron–hole exchange interaction. The present systematic study provides a new avenue to understand the unique size- and composition-dependent structural and optical properties of quaternary-alloyed \(\hbox {Zn}_{{x}}\hbox {Cd}_{1-{x}} \hbox {S}_{{y}}\hbox {Se}_{1-{y}}\) nanocrystals for broad use in multicolor bioimaging, biosensing, light-emitting diodes, solar cells, and other nanodevice applications.     

$${ SIM}^2{ RRAM}$$: a physical model for RRAM devices simulation

In the last few years, resistive random access memory (RRAM) has been proposed as one of the most promising candidates to overcome the current Flash technology in the market of non-volatile memories. These devices have the ability to change their resistance state in a reversible and controlled way applying an external voltage. In this way, the resulting high- and low-resistance states allow the electrical representation of the binary states “0” and “1” without storing charge. Many physical models have been developed with the aim of understanding the mechanisms that control the resistive switching. In this work, we have compiled the main theories accepted as well as their corresponding models for the conduction characteristics. In addition, simulation tools play a very important role in the task of checking these theories and understanding these mechanisms. For this reason, the simulation tool called \(\hbox {SIM}^{2}\hbox {RRAM}\) has been presented. This simulator is capable of replicating the global behavior of RRAM cell based on \(\hbox {HfO}_{x}\).