In this work we explore the microscopic mechanisms responsible for Random Telegraph Noise (RTN) current fluctuations in HfOx Resistive Random Access Memory (RRAM) devices. The statistical properties of the RTN current fluctuations are analyzed in a variety of reading conditions by exploiting the Factorial Hidden Markov Model (FHMM) to decompose the complex RTN traces in a superimposition of two-level fluctuations. We investigate the physical mechanisms that could be responsible for the RTN current fluctuations by considering two options that are the Coulomb blockade effect and the metastable-to-stable transition of defect assisting the Trap- Assisted-Tunneling (TAT) charge transport. Physics-based simulations show that both options allow reproducing the RTN current fluctuations. The electron TAT via oxygen vacancy defects, responsible for the current in High Resistive State (HRS), is significantly altered by the electric field caused by electron trapping at defects (i.e. neutral interstitial oxygen), not directly involved in charge transport. Similarly, the transition of oxygen vacancies into a stable-slow defect configuration (still unidentified in HfOx) can temporarily switch off the current, thus explaining the RTN

Starting from experimental findings and interface growth problems in Si/Ge superlattices, we have investigated through ab initio methods the concurrent and competitive behavior of strain and defects in the second-harmonic generation process. Interpreting the second-harmonic intensities as a function of the different nature and percentage of defects together with the strain induced at the interface between Si and Ge, we found a way to tune and enhance the second-harmonic generation response of these systems.

Second-harmonic generation is described by the second-order nonlinear susceptibility χ(2) which, in the\ud electric-dipole approximation, requires a noncentrosymmetric medium. It is very challenging and of high\ud technological interest to search whether it is possible to find away to break inversion symmetry in centrosymmetric\ud crystals in order to induce second-order nonlinearities. A new intriguing way to observe second-order nonlinear\ud phenomena is strain. Here, we present a detailed analysis of the correlation between the strain and the χ(2) in\ud both centrosymmetric and noncentrosymmetric materials. We considered Si and SiC as test materials and we\ud studied different types of strain (tensile/compressive), in different directions (uniaxial/biaxial) and for different\ud light-polarization directions.We found which is the type of strain necessary in order to induce, tune, and enhance\ud second-harmonic generation in different energy regions for centrosymmetric and noncentrosymmetric materials

We combine Density Functional Theory and Many Body Perturbation Theory to investigate the electronic properties of Si(100) and Ge(100) surfaces terminated with halogen atoms (-I, -Br, -Cl, - F) and...