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We present an efficient method to include full-band-structure effects for the case of a silicon conduction band in a deterministic Boltzmann equation solver based on the high-order spherical harmonics expansion method. This method employs the exact density of states and the group velocity obtained from band structure calculations, and it eliminates the modulus of the wave vector in the formulation such that an explicit invertible dispersion relation is not required. While the present method does not require additional central-processing-unit time and memory, compared with the analytic band model, the simulation results are significantly improved and in excellent agreement with those from the full-band Monte Carlo simulations and from an approach based on an invertible anisotropic band that matches several moments of the group velocity of the full band structure. [ABSTRACT FROM PUBLISHER]

Abstract: With the constant-matrix-element approach we have calculated the impact ionization (II) rates for uniaxially/biaxially strained Si and biaxially strained SiGe. Energy and momentum are exactly conserved during the calculation of the six-dimensional integral in k-space over four conduction and three valence bands. The wave-vector space is discretized with a very fine grid with a spacing of up to , where a is the lattice constant. II coefficient and quantum yield for relaxed Si, strained Si and strained SiGe are calculated through full-band Monte Carlo simulations. Good agreement between simulation and experimental data for relaxed Si is obtained. [Copyright &y& Elsevier]

In this paper, a new deterministic approach to electron noise based on a spherical harmonics expansion (SHE) of the Langevin—Boltzmann equation in the frequency domain is presented for silicon devices. Compared to the standard Monte Carlo (MC) approach, the SHE method has many advantages. It can handle the full frequency range from zero to terahertz, low current levels, and slow processes, and it gives more insight into the physics of noise. This is demonstrated for HF noise in a nanoscale silicon N+NN+ structure and an n-p-n bipolar junction transistor, for which not only the terminal-current fluctuations are investigated but also the spatial origin of the noise, which is not possible by MC simulation. With respect to numerics, the new approach is similar to classical device simulation (e.g., drift-diffusion model), and the same well-known methods can be used (e.g., adjoint method, ac analysis, harmonic-balance technique, linear solvers, maximum entropy dissipation stabilization, box integration, etc.). [ABSTRACT FROM AUTHOR]

A 2D hydrodynamic model based on modified Langevin forces for terminal current noise in the RF range is presented for Si and SiGe devices, where all transport and noise parameters are generated by full-band Monte Carlo simulations under bulk conditions and stored in lookup tables. Since these tables have to be built only once, the accuracy of the noise model is improved without increasing the CPU time compared to models based on analytical expressions for the parameters. The accuracy of the noise model is assessed by comparison with the Monte Carlo device model and good agreement of both models is found for diffusion and generation noise. The terminal current noise of a realistic SiGe HBT is investigated and it is found that hole diffusion noise has a strong impact on the collector current noise. The limitations of the thermodynamic model, a compact model for noise, are explored by comparison with the hydrodynamic model. [ABSTRACT FROM AUTHOR]

Presents langevin-type two-dimensional bipolar drift-diffusion and hydrodynamic noise models for silicon and silicon germanium devices. Discussion on momentum-based noise models; Inclusion of different noise sources; Descriptions of the Monte Carlo technique for the evaluation of the noise parameters.

Presents information on a study which analyzed the stochastic error of Monte Carlo (MC) device simulations. Background on the MC simulation method; Estimation of the value of an MC variable; Results; Conclusions.

Abstract: A global additional uniaxial stress ranging from −1GPa to 1GPa along different directions has been applied to SiGe HBTs in order to improve the high-frequency performance of these devices. Two transistors have been investigated: a slow one (peak f T =110GHz) and a fast one (peak f T =750GHz). The results from full-band Monte Carlo simulations show that the cutoff frequency of both devices can be improved by more than 30 percent under suitable stress conditions. A spherical-harmonics-expansion simulator is also used to investigate the spatial origin of this improvement, where it is found that the transit times are reduced in all regions (base, collector, emitter). [Copyright &y& Elsevier]

Abstract: A vertical impact ionization MOSFET (IMOS) with a thin layer of biaxially strained SiGe in the impact ionization (II) region near the drain and in the channel is thoroughly investigated by Full-Band Monte Carlo (FB-MC) and Hydrodynamic simulations. An anisotropic II model based on the constant matrix element approximation is integrated into the FB-MC to simulate II in relaxed-Si- and strained-SiGe-Vertical-IMOSs. The II generation currents obtained by FB-MC are, in turn, used to calibrate the II model of the Hydrodynamic simulator. The final results show that the reduction of the energy barrier caused by the strained SiGe layer in the channel improves the IMOS characteristic by lowering the threshold voltage. However, when the strained SiGe layer is placed in the region with the highest II near the drain, an improvement of the vertical IMOS by a higher II rate of the strained layer is not observed. [Copyright &y& Elsevier]