Methods for operating a unipolar spin transistor and applications of same

A unipolar spin transistor includes a semiconductor material having a first region, a second region, and a third region. The first region is adjacent to the second region so as to form a first domain between the first region and the second region, and the second region is adjacent to the third region so as to form a second domain between the second region and the third region. A first voltage is provided between the first region and the second region to cause carriers to move across the first domain from the first region to the second region. A second voltage is generated between the second region and the third region to cause the carriers move across the second domain from the second region to the third region. The second voltage has an amplitude different from that of the first voltage. The first region and the third region have a first spin polarization, and the second region has a second spin polarization which may be different from the first spin polarization.