Siddhartha Dhar

The Effect of General Strain on the Band Structure and Electron Mobility of Silicon

A model capturing the effect of general strain on the electron effective masses and band-edge energies of the lowest conduction band of silicon is developed. Analytical expressions for the effective mass change induced by shear strain and valley shifts/splittings are derived using a degenerate kldrp theory at the zone-boundary X point. Good agreement to numerical band- structure calculations using the nonlocal empirical pseudopotential method with spin-orbit interactions is observed. The model is validated by calculating the bulk electron mobility under general strain with a Monte Carlo technique using the full-band structure and the proposed analytical model for the band structure. Finally, the impact of strain on the inversion-layer mobility of electrons is discussed.

Electron mobility model for strained-Si devices

Strained-Si material has emerged as a strong contender for developing transistors for next-generation electronics, because this material system offers superior transport properties. We suggest a model describing the low-field bulk mobility tensor for electrons in strained-Si layers as a function of strain. Our analytical model includes the effect of strain-induced splitting of the conduction band valleys in Si, intervalley scattering, and doping dependence. Intervalley scattering has been modeled on the equilibrium electron distribution and the valley splitting for a given strain tensor. The effect of different substrate orientations is considered by performing coordinate transformations for the strain tensor and effective masses. Monte Carlo simulations accounting for various scattering mechanisms and the splitting of the anisotropic conduction band valleys due to strain in combination with an accurate ionized impurity scattering model were carried out to verify the results for the complete range of Ge contents and for a general orientation of the SiGe buffer layer. Our mobility model is suitable for implementation into a conventional technology CAD simulation tool.

Electron Mobility Model for

Stress-induced enhancement of electron mobility has primarily been attributed to the splitting of the conduction band minima. However, experiments have indicated that the mobility enhancement cannot solely be attributed to this effect, and a recent study has shown that stress along the lang110rang direction leads to a change of the effective mass. This work investigates the effect of the variation of the effective mass with stress along the lang110rang direction on the electron mobility. An improved low-field mobility model incorporating the effective mass change is presented

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The band structure of silicon (Si) under arbitrary stress/strain conditions is calculated using the empirical nonlocal pseudopotential method. The method is discussed with a special focus on the strain induced breaking of crystal symmetry. It is demonstrated that under general stress the relative movement of the sublattices has a prominent effect on the conduction band masses. This displacement, which cannot be determined from macroscopic strain, is extracted from ab initio calculations. The transport properties of strained Si are investigated by solving the semi-classical Boltzmann equation using the Monte Carlo (MC) method. It is shown that the change of the electron effective mass induced by uniaxial stress has to be included in accurate models of the electron mobility.

Stressed Silicon Including Strain-Dependent Mass

The application of mechanical stress to enhance the carrier mobility in silicon has been well established in the last few years. This paper probes into the electron conduction in biaxially and uniaxially stressed silicon in the nonlinear transport regime. The electron behavior has been analyzed for different field directions and stress/strain conditions using full-band Monte Carlo simulations. An analytical model describing the velocity components parallel and perpendicular to the electric field has been developed. The model includes the effect of strain induced valley splitting and can be applied for arbitrary directions of the electric field. The extension to different field directions has been performed using a Fourier series interpolation and a spherical harmonics interpolation for transport in two and three dimensions, respectively. The model can be implemented in a drift-diffusion-based device simulator

The effect of uniaxial stress on band structure and electron mobility of silicon

An analytical model for the low-field bulk electron mobility tensor in strained germanium is presented. The model includes the effects of strain-induced splitting of the conduction band valleys in germanium and the corresponding inter-valley scattering reduction as well as temperature and doping dependence. Bulk mobility values larger than 2.5 times the strained silicon values has been predicted. The results obtained from the model have been verified using Monte Carlo simulations

High-Field Electron Mobility Model for Strained-Silicon Devices

Application of stress to Si causes a deviation of its lattice constant from the equilibrium value, thereby modifying the electronic band structure. A phenomenological approach to calculate the mobility tensor for electrons in strained Si at high electric fields has been proposed. The model is intended for implementation in drift-diffusion based device simulators

Analytical Modeling of Electron Mobility in Strained Germanium

We have performed a detailed analysis of the electron transport at high electric field in strained Si for different field directions and stress/strain conditions using Full-band Monte Carlo simulations. A phenomeno-logical model describing the velocity-field relationship for electrons in biaxially or uniaxially strained Si has been developed. The model is suitable for incorporation into any device simulator for performing TCAD tasks.