Quantum-Mechanical Study on Surrounding-Gate Metal-Oxide-Semiconductor Field-Effect Transistors

As the channel length of metal-oxide-semiconductor field-effect transistors （MOSFETs） scales into the nanometer regime, quantum mechanical effects are becoming more and more significant. In this work, a model for the surrounding-gate （SG） nMOSFET is developed. The SchrSdinger equation is solved analytically. Some of the solutions are verified via results obtained from simulations. It is found that the percentage of the electrons with lighter conductivity mass increases as the silicon body radius decreases, or as the gate voltage reduces, or as the temperature decreases. The eentroid of inversion-layer is driven away from the silicon-oxide interface towards the silicon body, therefore the carriers will suffer less scattering from the interface and the electrons effective mobility of the SG nMOSFETs will be enhanced.

Analytical Modeling of Quantum Mechanical Tunneling in Germanium Nano-MOSFETS

A simple analytical model has been developed to study quantum mechanical effects （QME） in a germanium substrate MOSFET （metal oxide semiconductor field effect transistor）, which includes gate oxide tunneling considering the energy quantization effects in the substrate. Some alternate high dielectric constant materials to reduce the tunneling have also been studied. By comparing with the numerically reported results, the results match well with the existing reported work.

Quantum Boltzmann equation solved by Monte Carlo method for nano-scale semiconductor devices simulation

A two-dimensional （2D） full band self-consistent ensemble Monte Carlo （MC） method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to extend the MC method to the study of nano-scale semiconductor devices with obvious quantum mechanical （QM） effects. The quantum effects both in real space and momentum space in nano-scale semiconductor devices can be simulated. The effective mobility in the inversion layer of n and p channel MOSFET is simulated and compared with experimental data to verify this method. With this method 50nm ultra thin body silicon on insulator MOSFET are simulated. Results indicate that this method can be used to simulate the 2D QM effects in semiconductor devices including tunnelling effect.

Quantum compact model for thin-body double-gate Schottky barrier MOSFETs

Nanoscale Schottky barrier metal oxide semiconductor field-effect transistors （MOSFETs） are explored by using quantum mechanism effects for thin-body devices. The results suggest that for small nonnegative Schottky barrier heights, even for zero barrier height, the tunnelling current also plays a role in the total on-state current. Owing to the thin body of device, quantum confinement raises the electron energy levels in the silicon, and the tradeoff takes place between the quantum confinement energy and Schottky barrier lowering （SBL）. It is concluded that the inclusion of the quantum mechanism effect in this model, which considers an infinite rectangular well with a first-order perturbation in the channel, can lead to the good agreement with numerical result for thin silicon film. The error increases with silicon thickness increasing.

Quantum mechanical compact modeling of symmetric double-gate MOSFETs using variational approach

A physics-based analytical model for symmetrically biased double-gate（DG） MOSFETs considering quantum mechanical effects is proposed.Schrodinger＇s and Poisson＇s equations are solved simultaneously using a variational approach.Solving the Poisson and Schrodinger equations simultaneously reveals quantum mechanical effects（QME） that influence the performance of DG MOSFETs.The inversion charge and electrical potential distributions perpendicular to the channel are expressed in closed forms.We systematically evaluated and analyzed the potentials and inversion charges,taking QME into consideration,in Si based double gate devices.The effect of silicon thickness variation in inversion-layer charge and potentials are quantitatively defined.The analytical solutions provide good physical insight into the quantization caused by quantum confinement under various gate biases.

Analytical Modeling of Source-to-Drain Tunneling in Nanoscale Silicon MOSFET

Sub-10-nm bulk n-MOSFET （metal-oxide -semiconductor field effect transistor） direct source-to- drain tunneling current density using Wentzel- Krammers-Brillouin 0NKB） transmission tunneling theory has been simulated. The dependence of the source-to-drain tunneling current on channel length and barrier height is examined. Inversion layer quantization, band-gap narrowing, and drain induced barrier lowering effects have been included in the model. It has been observed that the leakage current density increases severely below 4 nm channel lengths, thus putting a limit to the scaling down of the MOSFETs. The results match closely with the numerical results already reported in literatures.

Heat transport in low-dimensional materials: A review and perspective

Heat transport is a key energetic process in materials and devices. The reduced sample size, low dimension of the problem and the rich spectrum of material imperfections introduce fruitful phenomena at nanoscale. In this review, we summarize recent progresses in the understanding of heat transport process in low-dimensional materials, with focus on the roles of defects, disorder, interfaces, and the quantum- mechanical effect. New physics uncovered from computational simulations, experimental studies, and predictable models will be reviewed, followed by a perspective on open challenges.

Comparative Study of Energy Quantization Approaches in Nanoscale MOSFETs

An analytical model has been developed to study inversion layer quantization in the ultra thin oxide MOS （metal oxide semiconductor） structures using variation and triangular well approaches.Accurate modeling of the inversion charge density using the continuous surface potential equations has been done.No approximation has been taken to model the inversion layer quantization process.The results show that the variation approach describes inversion layer quantization process accurately as it matches well with the BSIM 5 （Berkeley short channel insulated gate field effect transistor model 5） results more closely compared with triangular well approach.

New strategy of modeling inversion layer characteristics in MOS structure for ULSI applications

With the development of ULSI silicon technology, metal oxide semiconductor field effect transistor (MOSFET) devices are scaling down to nanometer regime. Energy of carriers in inversion layer in MOS structure is quantized and consequently, the physics and then the transport characteris-tics of inversion layer carriers are different from those in semi-classical theory. One essential matter is that the widely used concept of conduction band (valence band as well) effective density-of-states is no longer valid in quantized inversion layer. In this paper, an alternative concept, called surface layer effective density-of-states, is used to model the characteristics of MOS structure including threshold voltage, carrier sheet density, surface potential as well as capacitance.

Generalized Coherent States for Position-Dependent Effective Mass Systems

A generalized scheme for the construction of coherent states in the context of position-dependent effective mass systems has been presented. This formalism is based on the ladder operators and associated algebra of the system which are obtained using the concepts of supersymmetric quantum mechanics and the property of shape invariance. In order to exemplify the general results and to analyze the properties of the coherent states, several examples have been considered.