Spintronic nanostructures

Semiconductor spintronics has now reached a stage where the basic physical mechanisms controlling spin injection and detection are understood. Moreover, some critical technological issues involved in the growth and lithography of the magnetic semiconductors have been solved. This has allowed us to explore the physics of spintronic nanostructures. In this talk I will give examples of devices we have fabricated using two different classes of dilute magnetic semiconductors (DMSs). In II-VI semiconductors, magnetic impurities can be introduced iso-electronicallly, allowing n-and p-type doping of the material. Moreover, the layers can be grown by molecular beam epitaxy (MBE) at relatively high temperatures, so that the carrier mean free path is relatively long and devices may be constructed that rely on the typical properties of compound semiconductors, such as e.g. easily accessible confinement states. The drawback of magnetic II-VI´s is, of course, that the materials are not ferromagnets, but are paramagnets with a very high effective g-factor. Dilute magnetic III-V semiconductors are ferromagnetic. This is because the magnetic impurities now act as acceptors, and the resulting compound have large hole concentrations. The holes then intermediate in the ferromagnetic alignment of the impurities. The problem with II-V DMSs is that sizable concentrations of the magnetic impurities can only be incorporated using low-temperature MBE, which implies relatively low sample quality, and very short carrier mean free path. This implies that the devices one can construct our of such compounds are much more like the devices already known from metallic spintronics. Here, we will briefly discuss the type of devices one can fabricate from these materials.