Unipolar spin transistor and the applications of the same

The unipolar spin transistor includes a first semiconductor region having a conductivity type and a first spin polarization, and a second semiconductor region having a conductivity type that is the same conductivity type of the first semiconductor region and a second spin polarization that is different from the first spin polarization of the first semiconductor region, and a third semiconductor region having a conductivity type that is the same conductivity type of the first semiconductor region and the first spin polarization. The unipolar spin transistor can also include a magnetic semiconductor wherein the semiconductor material is in a high-resistance state when the second spin polarization of the second region is opposite to the first spin polarization of the first and third regions, and wherein the semiconductor material is in a low-resistance state when the second spin polarization of the second region is aligned to the first spin polarization of the first and third regions.