Datta-Das-type spin-field-effect transistor in the nonballistic regime

We analyzed the applicability of original Datta-Das proposal for spin-field-effect transistor (spin-FET) to nonballistic regime based on semiempirical Monte Carlo simulation for spin transport. It is demonstrated that the spin helix state in two-dimensional electron gas system is sufficiently robust against D'yakonov-Perel' spin relaxation to allow an operation of Datta-Das-type spin-FET in the nonballistic transport regime. It is also shown that the spin diffusion length of the spin helix state can be increased with an in-plane electrical field along the [1 (1) over bar0] direction. In marked contrast to early proposals for nonballistic spin-FETs, the on and off states are characterized by a 180 degrees phase difference in the spin precession motions, which is highly advantageous in terms of device flexibility.