Spin injection efficiency in spin electronic devices

Abstract We examine the comparative importance of spin injection efficiency in different types of spin electronic devices. We analyse the devices using a “pseudo-density of states” treatment of spin currents coupled to the principle of spin balance. This approach affords a generality that readily encompasses both metal and semiconductor direct spin injection systems. This implies that the various spin electronic devices have differing criteria for assessing the quality of their performance and that in turn these criteria determine the importance of implementing high-efficiency spin injection. We examine the factors which determine the obtainable spin injection performance in each case. We conclude that for CPP trilayer devices with semiconductor interlayers, obtaining efficient spin injection should not be a problem so long as the semiconductor layer thickness is small compared with its own spin diffusion length. Direct-injected and tunnel-injected spin LEDs are predicted to have similar spin efficiencies. However, direct-injected SPICE-type spin transistors have superior spin performance to their tunnel-injected counterparts.