Simulation of Capacitance-Voltage characteristics of Ultra-thin Metal-Oxide-Semiconductor Structures with Embedded Nanoc
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1071-F02-11
Simulation of Capacitance-Voltage characteristics of Ultra-thin Metal-OxideSemiconductor Structures with Embedded Nanocrystals Mosur Rahman1, Bo Lojek2, and Thottam Kalkur3 1 University Of Colorado at Colorado Springs, Colorado Springs, CO, 80933-7150 2 Atmel Corporation, Colorado Springs, CO, 80907 3 Electrical and Computer Engineering Dept., University of Colorado at Colorado Springs, Colorado Springs, CO, 80933-7150 Abstract This paper presents an approach to model and simulate quantum mechanical (QM) effects in solid-state devices such as Metal Oxide Semiconductor (MOS) capacitor with and without nanocrystal in the oxide. This QM model is developed to understand finite inversion layer width and threshold voltage shift. It allows a consistent determination of the physical oxide thickness based on an agreement between the measured and modeled CV curves. However, as for thinner oxides finite inversion layer width effects become more severe, QM model predicts higher threshold voltage than the classical model. The inversion-layer charge density and MOS capacitance in multidimensional MOS structures are simulated with various substrate doping profiles and gate bias voltages. The effectiveness of the QM correction method for modeling quantum effects in ultrathin oxide MOS structures is also investigated. The CV characteristic is used as a tool to compare results of the Schrödinger–Poisson (SP) solution i.e. the QM model with that of the QM correction, the Classical solution and measured data. The change in C-V characteristics indicative of threshold voltage shift for Si nanocrystal embedded in oxide is also investigated. I. INTRODUCTION Quantum mechanics have played a significant role primarily in compound semiconductor devices. However, due to the shrinking feature size of CMOS devices toward tens of nanometers in gate length, the QM effects manifest even in the conventional silicon devices [1-4]. The electrical properties of nanoscale semiconductor devices and structures are typically determined by quantum confinement that strongly affects the density of states of electrons and holes. When energy bands are bent strongly near a semiconductor-insulator interface a potential well formed by the interface barrier and the electrostatic potential in the semiconductor can be narrow enough that quantummechanical effects become important. So the shrinking dimensions of the devices require suitable device models in view of physics and mathematics for accurate simulation. Since the operation of the nanoscale MOS is primarily based on controlling the electron density by varying the confining potential, the modeling of the potential distribution and the electronic states is important. Using an initial value calculated from charge neutrality for potential, potential and charge density profiles in equilibrium are computed by solving the set of nonlinear partial differential equations described by the Poisson’s equation. The electronic states in the quantum dot are subsequently determined from solutions of the Schrödinge
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