Next: 1.3.5 Interface, Border and Oxide Traps Up: 1.3 Characteristic Features of HCD Previous: 1.3.3 HCD in Scaled Devices
Another characteristic feature of HCD is its strong localization near the pinch-off region (or the drain end of the gate), near the area where the electric field peaks [65,2,63,56,57,58,41]. Such a peculiarity is again related to carriers heating up to energies required to launch the bond-breakage process. Since the driving force of this acceleration is the electric field, for the sake of simplicity it is often assumed that the maximum of the interface state generation rate corresponds to the electric field peak. However, it has been long understood that the DF can follow changes in the electric field only with a certain delay [93]. Therefore, in order to improve over the electric field approximation, such quantities as the carrier temperature have been used to estimate the location of the maximum damage. However, as it was demonstrated in [94,95], the maxima of different quantities are observed at different positions and therefore the Nit peak never directly coincides with that of the electric field. Moreover, Zaka et al. showed that different simplified treatments of carrier transport employing the drift-diffusion, energy-transport, and spherical harmonics expansion methods (keeping only the 0th and 1st order polynomials) lead to spurious description of hot-carrier injection [96]. As a result, the spherical harmonics expansion method for BTE solution with a higher expansion number of the stochastic Monte Carlo-based solver must be used. This finding is very important because the Si-H bond-breakage process is described by an energy-dependent reaction cross section [98,99,30]. Hence, it is important to know the magnitude of the carrier fraction which corresponds to the given energy.