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In tunnel field-effect transistors, trap-assisted tunneling (TAT) is one of the probable causes for degraded subthreshold swing. The accurate quantum-mechanical (QM) assessment of TAT currents also requires a QM treatment of phonon-assisted tunneling (PAT) currents. Therefore, we present a multi-band PAT current formalism within the framework of the quantum transmitting boundary method. An envelope function approximation is used to construct the electron-phonon coupling terms corresponding to local Fröhlich-based phonon-assisted inter-band tunneling in direct-bandgap III-V semiconductors. The PAT current density is studied in up to 100 nm long and 20 nm wide p-n diodes with the 2- and 15-band material description of our formalism. We observe an inefficient electron-phonon coupling across the tunneling junction. We further demonstrate the dependence of PAT currents on the device length, for our non-self-consistent formalism which neglects changes in the electron distribution function caused by the electron-phonon coupling. Finally, we discuss the differences in doping dependence between direct band-to-band tunneling and PAT current. [ABSTRACT FROM AUTHOR]

In the quantum mechanical simulation of exploratory semiconductor devices, continuum methods based on a k ⋅ p/envelope function model have the potential to significantly reduce the computational burden compared to prevalent atomistic methods. However, full-zone k ⋅ p/envelope function simulation approaches are scarce and existing implementations are not self-consistent with the calculation of the electrostatic potential due to the lack of a stable procedure and a proper normalization of the multi-band envelope functions. Here, we therefore present a self-consistent procedure based on a full-zone spectral k ⋅ p/envelope function band structure model. First, we develop a proper normalization for the multi-band envelope functions in the presence of transmitting boundary conditions. This enables the calculation of the free carrier densities. Next, we construct a procedure to obtain self-consistency of the carrier densities with the electrostatic potential. This procedure is stabilized with an adaptive scheme that relies on the solution of Poisson's equation in the Gummel form, combined with successive underrelaxation. Finally, we apply our procedure to homostructure In 0.53 Ga 0.47 As tunnel field-effect transistors (TFETs) and staggered heterostructure GaAs 0.5 Sb 0.5 /In 0.53 Ga 0.47 As TFETs and show the importance of self-consistency on the device predictions for scaled dimensions. [ABSTRACT FROM AUTHOR]

The time-dependent dielectric breakdown in thin gate oxides is studied and a new methodology is proposed that is applicable to a wide range of gate stacks for extracting soft breakdown (SBD) and post-SBD wear-out (WO) parameters from measuring the time to hard breakdown ([t.sub.HBD) only. A new complete reliability prediction model is proposed that has included SBD and WO.

The article presents various different techniques that can be employed for the evaluation of the threshold voltage shift induced by the negative bias temperature instability (NBTI). The effects of sensing and recovery are shown to be the major factors that need to be considered during the process of voltage evaluation.