Vortex flows in semiconductor device quantum channels: time-dependent simulation

It has been proposed that the formation of blocking quantum vortices embedded in the open current flows between source and drain plays a significant role in determining the current-voltage characteristics of nano-scaled semiconductor devices. These studies were based on time-independent quantum transport models. The vortices are associated with angular momentum generation at non-uniformities in the channel, quantum interference with atomistic impurity distributions and surface roughness scattering. We find that generally the vortex cores lie on curved lines in three dimensions which thread the through the channel either as closed loops or open lines. In the present paper we report investigation of the physics of formation of vortices in time-dependent flows. This problem is crucial to quasi-ballistic channels where transient response is a more appropriate model for the current and density fields than asymptotic stationary state analysis. The present work understands how the stationary vortex flows at different energies superpose to produce the net flow in both the steady-state and time-dependent regimes. Preliminary results are presented for the onset of vortices when the fluctuation potential landscape of a rough interface is marginally changed for example by charge trapping. Preliminary results of application to ultra-small MOSFET devices are also reported.