Nonballistic two-channel Datta-Das spin field effect transistor

Scattering by impurities is believed to be harmful for a Datta- Das spin field effect transistor (SFET). We present a quantum mechanical analysis of a nonballistic SFET in the small width limit, where only two (two from spin) channels are allowed, and find that the SFET can show diverse behaviors depending on relative magnitudes of various important energy scales. We identify these scales and show that the nonballistic SFET can operate successfully in certain regimes of the energy scales.