Monte Carlo study of non-quasiequilibrium carrier dynamics in III–N LEDs

Hot carrier effects have been observed in recent measurements of III–Nitride (III–N) light-emitting diodes. In this paper we carry out bipolar Monte Carlo simulations for electrons and holes in a typical III–N multi-quantum well (MQW) LED. According to our simulations, significant non-quasiequilibrium carrier distributions exist in the barrier layers of the structure. This is observed as average carrier energies much larger than the 1.5kBT1.5kBT corresponding to quasi-equilibrium. Due to the small potential drop over the MQW being modest, the non-quasiequilibrium carriers can be predominantly ascribed to nnp and npp Auger processes taking place in the QWs. Further investigations are needed to determine the effects of hot carriers on the macroscopic device characteristics of real devices

Physical Simulation of Si-Based Resistive Random-Access Memory Devices

We present a newly-developed three-dimensional (3D) physical simulator suitable for the study of resistive random-access memory (RRAM) devices. We explore the switching behavior of Si-rich silica (SiOx) RRAM structures, whose operation has been successfully demonstrated experimentally at ambient conditions [1]. The simulator couples self-consistently a simulation of oxygen ion and electron transport to a self-heating model and the `atomistic' simulator GARAND. The electro-thermal simulation model provides many advantages compared to the classical phenomenological models based on the resistor breaker network. The simulator is validated with respect to experimental data and captures successfully the memristive behavior of the simulated SiOx RRAMs, by reconstructing the conductive filament formation and destruction phenomena in the 3D space. The simulation framework is useful for exploring the little-known physics of SiOx RRAMs, and providing efficient designs, in terms of performance, variability and reliability, for both memory devices and circuits

Self-consistent physical modeling of SiOx-based RRAM structures

We apply a unique three-dimensional (3D) physics-based atomistic simulator to study silicon-rich (SiOx, x<;2) resistive switching nonvolatile memory (RRAM) devices. We couple self-consistently a simulation of ion and electron transport to the `atomistic' simulator GARAND and a self-heating model to explore the switching processes in these structures. The simulation model is more advanced than other available phenomenological models based on the resistor breaker network. The simulator is calibrated with experimental data, and reconstructs accurately the formation and rupture of the conductive filament in the 3D space. We demonstrate how the simulator is useful for exploring the little-known physics of these promising devices, and show that switching is an intrinsic property of the SiOx layer. In general, the simulation framework is useful for providing efficient designs, in terms of performance, variability and reliability, for memory devices and circuits. The simulator validity is not limited to SiOx-based devices, and can be used to study other promising RRAM systems based, e.g., on transition metal oxides

A Hierarchical Model for CNT and Cu-CNT Composite Interconnects: From Density Functional Theory to Circuit-Level Simulations

No abstract available

Influence of photo-generated carriers on current spreading in double diode structures for electroluminescent cooling

Current crowding close to electrical contacts is a common challenge in all optoelectronic devices containing thin current spreading layers (CSLs). We analyze the effects of current spreading on the operation of the so-called double diode structure (DDS), consisting of a light emitting diode (LED) and a photodiode (PD) fabricated within the same epitaxial growth process, and providing an attractive platform for studying electroluminescent (EL) cooling under high bias conditions. We show that current spreading in the common n-type layer between the LED and the PD can be dramatically improved by the strong optical coupling between the diodes, as the coupling enables a photo-generated current through the PD. This reduces the current in the DDS CSL and enables studying EL cooling using structures that are not limited by the conventional light extraction challenges encountered in normal LEDs. The current spreading in the structures is studied using optical imaging techniques, electrical measurements, simulations, as well as simple equivalent circuit models developed for this purpose. The improved current spreading leads further to a mutual dependence with the coupling efficiency, which is expected to facilitate the process of optimizing the DDS. We also report a new improved value of 63% for the DDS coupling quantum efficiency (CQE).Peer reviewe

Bipolar Monte Carlo Simulation of Hot Carriers In III-N LEDs

We carry out bipolar Monte Carlo (MC) simulations of electron and hole transport in a multi-quantum well light-emitting diode with an electron-blocking layer. The MC simulation accounts for the most important interband recombination and intraband scattering processes and solves self-consistently for the non-quasiequilibrium transport. The fully bipolar MC simulator results in better convergence than our previous Monte Carlo-drift-diffusion (MCDD) model and also shows clear signatures of hot holes. Accounting for both hot electron and hot hole effects increases the total current and decreases the efficiency especially at high bias voltages. We also present our in-house full band structure calculations for GaN to be coupled later with the MC simulation in order to enable even more detailed predictions of device operation

Advanced physical modeling of SiOx resistive random access memories

We apply a three-dimensional (3D) physical simulator, coupling self-consistently stochastic kinetic Monte Carlo descriptions of ion and electron transport, to investigate switching in silicon-rich silica (SiOx) redox-based resistive random-access memory (RRAM) devices. We explain the intrinsic nature of resistance switching of the SiOx layer, and demonstrate the impact of self-heating effects and the initial vacancy distributions on switching. We also highlight the necessity of using 3D physical modelling to predict correctly the switching behavior. The simulation framework is useful for exploring the little-known physics of SiOx RRAMs and RRAM devices in general. This proves useful in achieving efficient device and circuit designs, in terms of performance, variability and reliability

One-Dimensional Multi-Subband Monte Carlo Simulation of Charge Transport in Si Nanowire Transistors

In this paper, we employ a newly-developed one-dimensional multi-subband Monte Carlo (1DMSMC) simulation module to study electron transport in nanowire structures. The 1DMSMC simulation module is integrated into the GSS TCAD simulator GARAND coupling a MC electron trajectory simulation with a 3D Poisson-2D Schrödinger solver, and accounting for the modified acoustic phonon, optical phonon, and surface roughness scattering mechanisms. We apply the simulator to investigate the effect of the overlap factor, scattering mechanisms, material and geometrical properties on the mobility in silicon nanowire field-effect transistors (NWTs). This paper emphasizes the importance of using 1D models that include correctly quantum confinement and allow for a reliable prediction of the performance of NWTs at the scaling limits. Our simulator is a valuable tool for providing optimal designs for ultra-scaled NWTs, in terms of performance and reliability

Investigation of resistance switching in SiOx RRAM cells using a 3D multi-scale kinetic Monte Carlo simulator

We employ an advanced three-dimensional (3D) electro-thermal simulator to explore the physics and potential of oxide-based resistive random-access memory (RRAM) cells. The physical simulation model has been developed recently, and couples a kinetic Monte Carlo study of electron and ionic transport to the self-heating phenomenon while accounting carefully for the physics of vacancy generation and recombination, and trapping mechanisms. The simulation framework successfully captures resistance switching, including the electroforming, set and reset processes, by modeling the dynamics of conductive filaments in the 3D space. This work focuses on the promising yet less studied RRAM structures based on silicon-rich silica (SiOx) RRAMs. We explain the intrinsic nature of resistance switching of the SiOx layer, analyze the effect of self-heating on device performance, highlight the role of the initial vacancy distributions acting as precursors for switching, and also stress the importance of using 3D physics-based models to capture accurately the switching processes. The simulation work is backed by experimental studies. The simulator is useful for improving our understanding of the little-known physics of SiOx resistive memory devices, as well as other oxide-based RRAM systems (e.g. transition metal oxide RRAMs), offering design and optimization capabilities with regard to the reliability and variability of memory cells

Impact of Strain on the Performance of Si Nanowires Transistors at the Scaling Limit: A 3D Monte Carlo/2D Poisson Schrodinger Simulation Study

In this work we investigate the correlation between channel strain and device performance in various n-type Si-NWTs. We establish a correlation between strain, gate length and cross-section dimension of the transistors. For the purpose of this paper we simulate Si NWTs with a <110> channel orientation, four different ellipsoidal channel cross-sections and five gate lengths: 4nm, 6nm, 8nm, 10nm and 12nm. We have also analyzed the impact of strain on drain-induced barrier lowering (DIBL) and the subthreshold slope (SS). All simulations are based on a quantum mechanical description of the mobile charge distribution in the channel obtained from a 2D solution of the Schrödinger equation in multiple cross sections along the current path, which is mandatory for nanowires with such ultra-scale dimensions. The current transport along the channel is simulated using 3D Monte Carlo (MC) and drift-diffusion (DD) approaches