Most metallic elements have a crystal structure that is either body-centered cubic (bcc), face-centered close packed, or hexagonal packed. If the bcc lattice thermodynamically most stable structure, close-packed structures usually are dynamically unstable, i.e., elastic constants violating Born stability conditions or, more generally, phonons with imaginary frequencies. Conversely, tends to be unstable if equilibrium This striking regularity essentially went unnoticed until ab initio...

GeSn is predicted to exhibit an indirect direct band gap transition at alloy Sn composition of 6.5% and biaxial strain effects are investigated in order further optimize structure for optoelectronics high speed electronic devices. A theoretical model has been developed based on the nonlocal empirical pseudopotential method determine germanium tin (GeSn) alloys. Modifications virtual crystal potential accounting disorder induced fluctuations incorporated reproduce large bowing observed

The success of silicon as a dominant semiconductor technology has been enabled by its moderate band gap (1.1 eV), permitting low-voltage operation at reduced leakage current, and the existence SiO2 high-quality "native" insulator. In contrast, other mainstream semiconductors lack stable oxides must rely on deposited insulators, presenting numerous compatibility challenges. We demonstrate that layered two-dimensional (2D) HfSe2 ZrSe2 have gaps 0.9 to 1.2 eV (bulk monolayer) technologically...

The structures and energies of oxygen-deficient rutile ${\text{TiO}}_{2}$ were calculated using density-functional theory. electronic interactions are described within the $\text{LDA}+U$ formalism, where on-site Coulomb corrections applied on $3d$ orbital electrons Ti atoms $({U}^{d})$ $2p$ O $({U}^{p})$. We show that ${U}^{d}$ parameter affects only character conduction band values higher than 7 eV produce an unphysical description interactions. results dramatically improved, when...

The electronic properties of rutile TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with an ordered arrangement oxygen vacancies show a transition from resistive to conductive oxide as function vacancy ordering. Vacancy ordering along two different directions [110] and [001], studied by the density functional theory, predicts that geometries in which vacancy-to-vacancy interaction is strongest, within nearest neighbor coordination,...

First principles study showed indicated band gap of Ge can be tuned by alloying with Sn and metastable GeSn alloys synthesized at or above room temperature. Subsequently, high quality layers were grown using low temperature MBE. PL good crystal material a reduced direct bandgap. Challenges involved in CMOS processing on addressed through effective surface cleaning thermal budget process flow. To the best our knowledge this work is first demonstration high-κ pMOSFET 3% as channel showing 20%...

The structural and electronic implications of cation anion vacancies in NiO are assessed using density functional theory conjunction with the local-density approximation employing on-site Coulomb corrections within $\text{LDA}+U$ method. Electronic band-structure data supports $p$-type semiconducting oxide character. calculated formation energies identify stability charged vacancy states consistent experimental reports. We present a microscopic model for rupture an electrically active...

We study the ON-OFF switching mechanism of oxide-based resistive–random–access–memories using theoretical calculations. Electron deficient vacancies (VO) up to 1+ charge states would stabilize a cohesive filament, while further electron removal will disrupted VO configurations with 2+ charges. The cohesion-isolation transition upon carrier injection and is shown be strong driving force in process. also propose that bipolar or unipolar behavior determined by how carriers are injected into VO....

Resistance change random access memory (RRAM) cells, typically built as MIM capacitor structures, consist of insulating layers I sandwiched between metal M, where the insulator performs resistance switching operation. These devices can be electrically switched two or more stable states at a speed nanoseconds, with long retention times, high endurance, low read voltage, and large windows. They are attractive candidates for next-generation non-volatile memory, particularly flash successor,...

The scaling and 3-D integration issues of NbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with threshold switching characteristics were investigated for ReRAM selector device. To avoid the process problems Pt electrode, we tested devices conventional electrodes (TiN W). By adopting 10nm-thick TiN bottom electrode low thermal conductivity, could significantly reduce current insulator-metal transition (I-M-T) due to heat confinement...

Through ab initio calculations, we propose that the conductive filaments in Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt resistive random access memories are due to HfO xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> suboxides, possibly tetragonal, where x ≤ 1.5. The electroforming process is initiated by a continuous supply of oxygen Frenkel defect pairs through an electrochemical process. accumulation vacancies leads...

We report that V${}_{\mathrm{O}}$ cohesion-isolation transition caused by carrier injection/removal is a generalized resistance switching mechanism of binary-oxide-based resistive random-access memories (ReRAMs). propose universal guiding principles which ReRAM with unipolar and bipolar operations can be designed controlling electrode work functions. found first-principles calculations structural phase the physical origin ReRAM. Based on our theory, we principle toward stable high function...

Doping techniques have been widely investigated to improve the performance and reliability of resistive random-access memory. In this paper, oxide phases, non-stoichiometry, dopant concentrations are identified as three critical factors that affect characteristics doped HfOx. Using ab initio calculations, their effects on Al, Ti, Si dopants thoroughly compared with experimental studies. particular, inconsistent observations regarding Al forming voltages explained by variation oxygen...

Doping has often been considered for performance improvement of resistive memories (ReRAM), but the effects many different dopants have not distinguished. To obtain a systematic understanding doping effects, density functional theory calculations are performed to investigate 9 metal in TiO2 ReRAM. The dopants' on both electronic structures and vacancy-formation stability single vacancy conductive filament discussed detail. Trends physical properties using various revealed well explained by...

The impacts of charge trapping and filament-induced anisotropy on the resistive switching mechanism in hafnia are formulated quantified. Using ab initio calculations, we find energetics kinetics oxygen vacancies hafnium oxide random access memory strongly influenced by at vacancy sites as well local crystal structure presence nearby conductive filaments.

We theoretically study an oxygen vacancy (VO) diffusion in Al2O3-based resistive-random-access-memories (ReRAMs). find that the activation energy of VO Al2O3 strongly depends on charge state VO. In ReRAM, can be easily changed by applying voltage and lowest is observed at q = 2+. The operation ReRAM close to 2+, indicating diffuses with doubly positive state. Moreover, 0 bulk Al2O3, which explains discrepancy between previous experimental theoretical studies.

Monovacancy diffusion alone dominates over due to divacancies and interstitials in Al for all temperatures up the melting point. Deviations from a single Arrhenius dependence are anharmonicity. The conclusion is based on combination of theoretical methods, density functional theory thermodynamic integration, without fitting experimental data. calculated rate agrees with data 11 orders magnitude.

We present a comprehensive study of the thermodynamic and electronic properties intrinsic point defects in solar energy conversion materials $\mathrm{C}{\mathrm{u}}_{2}\mathrm{ZnSnS}{\mathrm{e}}_{4}$ $\mathrm{CuInS}{\mathrm{e}}_{2}$ based on screened-exchange hybrid density functional theory. A comparison between defect transition levels for reveals that $\mathrm{C}{\mathrm{u}}_{2}\mathrm{ZnSnS}{\mathrm{e}}_{4}$, $\mathrm{S}{\mathrm{n}}_{\mathrm{Cu}}$ $\mathrm{S}{\mathrm{n}}_{\mathrm{Zn}}$...

A new model of work function variability (WFV) based on grain orientation differences the polycrystalline metal gate is reported. Our predicts that at 22 nm technology node, among three device sources: random dopant fluctuation (RDF), line edge roughness (LER) and WFV, WFV will cross over RDF becomes dominating factor. The SRAM circuit analysis shows write/read failures are underestimated by 9 orders magnitude area weighted averaged model.

We present a detailed theoretical analysis to motivate GeSn for CMOS logic. High quality films have been obtained on Ge-on-Si using CVD process. A novel surface passivation scheme is presented achieve record low trap densities at high-κ/GeSn interface. Using the method, combined with thermal budget device fabrication process, n-channel MOSFETs channel Sn content as high 8.5% demonstrated first time.

We address the role of Ti/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface on conductive filament (CF) formation within context oxide-based resistive random access memories (OxRRAMs). investigate oxygen defects and diffusion at through ab initio calculations. The calculated energy barriers compare well with available experimental data. Through region charge analysis associated energies O defect migration into Ti, our results...

Ge channel is one of the promising performance boosters for replacing Si in future complementary metal-oxide-semiconductor technology. The uniaxial stress technology can further enhance MOSFETs. In this paper, effect on NMOSFETs was experimentally and theoretically investigated. gate dielectric fabricated by using novel radical oxidation technique. high quality allowed vertical field mobility measurements. By applying mechanical NMOSFETs, enhancement obtained. physical mechanism under such...

We report on the electronic roles in filamentary-type switching of binary oxide-based resistive random access memories using ab initio calculations. show that charge injection and removal determine thermodynamic stability vacancy filament diffusion memory devices; electron induces cohesion stabilizes filament, whereas these electrons favors isolation destabilizes filament; makes energy barrier processes small enough to be overcome by joule heating. The cohesion-isolation are induced leads...

Semiconducting germanium tin (GeSn) alloy has recently emerged as a candidate for optoelectronic and high performance CMOS devices because of its tunable direct gap potential electron hole mobilities. High mobility in GeSn channel pMOSFETs already been demonstrated [1, 2]. However, nMOSFETs not yet explored. In this work we perform detailed theoretical analysis to gauge the benefits over Ge nMOSFETs. Our predicts outperform Ge. n-channel have successfully fabricated factors limiting performance.