An electron injection model for time-dependent simulators of nanoscale devices with electron confinement: Application to the comparison of the intrinsic noise of 3D-, 2D- and 1D-ballistic transistors

For ballistic (quasi-ballistic) devices, the noise is mainly determined by the rate of injection of electrons from the contacts. Thus, the computation of the noise can be very sensible to the boundary conditions imposed on the simulators. An algorithm for the injection of electrons in nanoscale devices with (or without) electron confinement for degenerate (or non-degenerate) conditions is presented. The injection model is conceptually similar to the boundary conditions used in the Landauer approach, but it is developed for time-dependent simulators. For a simple ballistic two-terminal device, as a test, it is shown that the injection model directly reproduces the average current and the noise obtained by the Landauer-Buttiker formalism. Finally, the injection model is applied to compute noise in nanoscale transistors (without self-consistence with the Poisson equation). The results predict an increase of the Fano factor when electron confinement is present. In addition, it is also shown that other electron injection models without correlation between the injection of consecutive electrons increase the noise of nanoscale transistors unrealistically, when degenerate conditions are present.