TABLE OF CONTENTS Many unipolar or bipolar spintronic devices have been proposed in recent years. Their modeling is not always easy but advantage can be taken from the fact that unipolar diodes and transistors made from FM semiconductors with different magnetization directions, such as the majority spin carriers on one side are the minority carriers on the other side, behave similarly to nonmagnetic bipolar p- n diodes or transistors [55]. The major difference between these two classes of devices is that the interface between layers in a p- n diode with two types of oppositely charged carriers is a charge depletion layer, whereas in a unipolar spin diode it is a spin depletion layer. Another difference is that, whether the barriers for both electrons and holes moving across the junction are reduced under forward bias and increased for reverse bias, leading to rectification of charge current, in spin diodes under both forward and reverse biases the barrier for one spin polarization is increased and for the other is decreased.
Spin filters are devices that filter spins with a definite orientation from an otherwise unpolarized spin distribution, and can therefore act as spin-polarized sources for other devices. The vast majority of spin filter configurations are based on electron tunneling through resonant structures, although it was theoretically demonstrated that atomically ordered and suitably oriented interfaces between some FM metals and some semiconductors can act as ideal spin filters. They can transmit electrons only from the...
