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We have analyzed and modeled the reverse-biased gate leakage current in a Schottky-gate AlGaN/GaN high electron mobility transistor. While the Poole–Frenkel emission current along conductive threading dislocations dominates at low negative gate bias, the trap-assisted tunneling of thermally energized electrons and the thermal emission of electrons from threading dislocations aided by dislocation-related states at multiple energy levels within the AlGaN bandgap are dominant at moderate to large reverse bias. Additionally, deep trap levels of high density localized near the gate/AlGaN interface cause significant leakage at 473 K at low to moderate reverse bias, which could be specific to the device we have analyzed. We extracted about 10 12 cm − 2 traps near the AlGaN/GaN interface from the difference of the barrier layer electric field profile obtained from the experimental high-frequency capacitance–gate voltage and the one needed for final matching. The thermionic- and the thermionic field-emission currents are considerably low; the latter, however, dominates in the defect-free case. Finally, the simulation framework we developed here helped us identify various conduction mechanisms contributing to the reverse-biased gate leakage and the density and electronic structure of the responsible defects. [ABSTRACT FROM AUTHOR]

An analytical expression for the decay rate of quasi-bound states (QBS) in a triangular quantum well is derived by considering the resonance scattering of particles from the triangular potential profile. Asymptotic properties of the Airy functions that are solutions to the Schrödinger equation for a linear or triangular potential and a perturbative expansion for a small broadening of the QBS are utilized to derive the expression for its location E0 as well as the decay rate Γ that further gives the net tunneling current from the well. The triangular well model is commonly used to represent the band-bending near a heterojunction due to the electrostatic field. This compact expression shows excellent agreement with a full numerical solver and improvement over Wentzel–Kramers–Brillouin based calculations is demonstrated. [ABSTRACT FROM AUTHOR]

The design of rural drinking water schemes consists of optimization of several network components like pipes, tanks, pumps and valves. The sizing and configuration of these network configurations need to be such that the water requirements are met while at the same time being cost efficient so as to be within government norms. We developed the JalTantra system to design such water distribution networks. The Integer Linear Program (ILP) model used in JalTantra and described in our previous work solved the problem optimally, but took a significant amount of time for larger networks—an hour for a network with 100 nodes. In this current work, we describe a series of three improvements of the model. We prove that these improvements result in tighter models, i.e. the set of points of linear relaxation is strictly smaller than the linear relaxation for the initial model. We test the series of three improved models along with the initial model over eight networks of various sizes and show a distinct improvement in performance. The 100-node network now takes only 49 s to solve. These changes have been implemented in JalTantra, resulting in a system that can solve the optimization of real world rural drinking water networks in a matter of seconds. The JalTantra system is free for use, and is available at https://www.cse.iitb.ac.in/jaltantra/. [ABSTRACT FROM AUTHOR]

The analysis of retention characteristics is essential for reliability assessment of any type of flash memory. A high-k (HK) material in the Interpoly dielectric (IPD) stack is known to improve the program-erase characteristics and makes the control oxide thicker for better retention time; however, it also brings-in defects along with it, creating undesirable charge loss path that plays a significant role in retention. Accurate modeling of this leakage process is important for optimizing the architecture that is less prone to oxide defects and exhibiting improved charge retention. In this paper, we present a physical model considering all possible charge leakage mechanisms that include inelastic tunneling through multiple traps in addition to direct tunneling (DT). The trap capture process is modeled as an inelastic process from nanocrystal (NC) to trap state, while the trap-to-trap tunneling is calculated by Bardeen's Transfer Hamiltonian approach. The trap emission process and DT from the spherical NC are modeled by computing the lifetime of quasi-bound states with very small decay widths in the finite-element setup. We show that a single trap model in HK cannot explain the retention characteristics. We propose a new asymmetric IPD structure that show significant improvement in retention time. [ABSTRACT FROM AUTHOR]

The program/erase process in floating gate (FG) flash memory devices is modeled by considering sequential quantum tunneling of electrons and taking into account quantum confinement in the channel and FG. We precisely determine location of quasi-bound or decaying quantum states in the inversion layer and in FG comprising a nanocrystal (NC) layer, and compute their lifetime by finding the complex eigenenergy of the resonance transmission problem. Self-consistent solutions to Poisson and Schrödinger equations are obtained for the quantum states of electrons in the inversion layer of MOS devices, and subsequently, sequential Fowler–Nordheim tunneling current to the spherical NCs is obtained using finite-element method considering open boundary conditions. The method described here is capable of determining the tunneling current accurately for arbitrary potential profiles, and can be applied for composite tunnel dielectric stacks. Our results show good agreement with the experimental data for high- $k$ interpoly dielectric flash memory devices. [ABSTRACT FROM PUBLISHER]

Motivation: Elementary (flux) modes (EMs) have served as a valuable tool for investigating structural and functional properties of metabolic networks. Identification of the full set of EMs in genome-scale networks remains challenging due to combinatorial explosion of EMs in complex networks. It is often, however, that only a small subset of relevant EMs needs to be known, for which optimization-based sequential computation is a useful alternative. Most of the currently available methods along this line are based on the iterative use of mixed integer linear programming (MILP), the effectiveness of which significantly deteriorates as the number of iterations builds up. To alleviate the computational burden associated with the MILP implementation, we here present a novel optimization algorithm termed alternate integer linear programming (AILP). Results: Our algorithm was designed to iteratively solve a pair of integer programming (IP) and linear programming (LP) to compute EMs in a sequential manner. In each step, the IP identifies a minimal subset of reactions, the deletion of which disables all previously identified EMs. Thus, a subsequent LP solution subject to this reaction deletion constraint becomes a distinct EM. In cases where no feasible LP solution is available, IP-derived reaction deletion sets represent minimal cut sets (MCSs). Despite the additional computation of MCSs, AILP achieved significant time reduction in computing EMs by orders of magnitude. The proposed AILP algorithm not only offers a computational advantage in the EM analysis of genome-scale networks, but also improves the understanding of the linkage between EMs and MCSs. [ABSTRACT FROM AUTHOR]

A standard experimental setup for Inelastic Electron Tunneling Spectroscopy (IETS) performs the measurement of the second derivative of the current with respect to the voltage ( d 2 I / d V 2 ) using a small AC signal and a lock-in based second harmonic detection. This avoids noise arising from direct differentiation of the current-voltage characteristics (I–V) by standard numerical methods. Here we demonstrate a noise-filtering algorithm based on Tikhonov Regularization to obtain IET spectra (i.e. d 2 I / d V 2 vs. V) from measured DC I–V curves. This leads to a simple and effective numerical method for IETS extraction. We apply the algorithm to I–V data from a molecular junction and a metal-insulator-semiconductor tunneling device, demonstrating that the computed first/second derivatives have a workable match with those obtained from our lock-in measurements; the computed IET spectral peaks also correlate well with reported experimental ones. Finally, we present a scheme for automated tuning of the algorithm parameters well-suited for the use of this numerical protocol in real applications. [ABSTRACT FROM AUTHOR]

Heterogeneous SiN x based charge trap flash (CTF) which has varying N/Si ratio (x) along the thickness of the charge-trapping layer (CTL) shows improved program/erase (P/E) transients. In this work, we present the P/E model invoking different nature of traps in N-rich and Si-rich CTL and investigate the physical processes behind the P/E improvement observed in heterogeneous CTF. A set of coupled equations that include Poisson's and rate equations for electrons and holes are solved considering the variation of CTL physical parameters along the thickness. The electron/hole injection current is accurately computed by including quantum effects at Si/SiO 2 interface and taking into account the field-dependent relaxation of the energetic injected carriers. The simulation results of our model are in close agreement with the experimentally observed characteristics for five different sets of CTF devices with standard, Si-rich and N-rich homogeneous, and discretely and linearly graded heterogeneous CTF. Our study points out that the improvement in program transient for the heterogeneous CTF devices is attributed to the variation of trap density and trap energy along the CTL thickness and not due to lateral tunneling between the traps. The improvement in erase saturation and speed is due to high electron emission from the traps in Si-rich layer near bottom oxide of heterogeneous CTL. • The SiN x heterogeneous trap layer has a variation of N/Si ratio (x) along the thickness. • The Program/Erase model for flash having a heterogeneous trap layer is presented for the first time. • The model shows close agreement with the experimentally observed characteristics of 5 devices. • Improved program transient is shown due to the variation of trap energy and density. • Erase transient improvement is due to the presence of a Si-rich layer near bottom oxide. [ABSTRACT FROM AUTHOR]