Bipolar spin transistors and the applications of the same

A bipolar spin transistor is provided. In one embodiment of the present invention, the bipolar spin transistor includes a first semiconductor region having a first conductivity type, a second semiconductor region having a second conductivity type that is different from the first conductivity type and also having a spin polarization, and a third semiconductor region having a conductivity type that is the same conductivity type of the first semiconductor region. The first semiconductor region and the second semiconductor region are adjacent to each other so as to form a first charge depletion layer therebetween, the first charge depletion layer having a first side facing the first semiconductor region and an opposing second side facing the second semiconductor region. Additionally, the second semiconductor region and the third semiconductor region are adjacent to each other so as to form a second charge depletion layer therebetween, the second charge depletion layer having a first side facing the second semiconductor region and an opposing second side facing the third semiconductor region.