Unipolar spin diode and the applications of the same

A unipolar spin diode and a unipolar spin transistor. In one embodiment, the unipolar spin diode includes a first semiconductor region having a conductivity type and a spin polarization, and a second semiconductor region having a conductivity type that is the same conductivity type of the first semiconductor and a spin polarization that is different from the spin polarization of the first semiconductor region. The first semiconductor region and the second semiconductor region are adjacent to each other so as to form a spin depletion layer therebetween, the spin depletion layer having a first side and an opposing second side. When a majority carrier in the first semiconductor region moves across the spin depletion layer from the first side of the spin depletion layer to the second side of the spin depletion layer, the majority carrier in the first semiconductor region becomes a minority carrier in the second semiconductor region. Moreover, when a majority carrier in the second semiconductor region moves across the spin depletion layer from the second side of the spin depletion layer moves to the first side of the spin depletion layer, the majority carrier in the second semiconductor region becomes a minority carrier in the first semiconductor region.