Semiconductor spintronics using ferromagnetic semiconductor heterostructures

Summary form only given. Modern information technology utilizes the charge degree of freedom of electrons to process information in semiconductors and the spin degree of freedom for mass storage of information in magnetic materials. New functionalities are expected from semiconductor devices that make use of both charge and spin degrees of freedom in semiconductors. Carrier-induced ferromagnetism in transition metal doped Ill-V compounds offers integration of ferromagnetism with the existing nonmagnetic III-V heterostructures. These structures allow us to explore spin-dependent phenomena in semiconductor heterostructures, which may lead us to a new form of electronics, spintronics, where both the spin and charge degrees of freedom play critical roles. Here, I review the recent development in the field of III-V ferromagnetism and spin-dependent phenomena in its heterostructures. A mean-field theory based on exchange between carrier spin and Mn spin is shown to be capable of explaining the ferromagnetic transition temperatures, strain-dependent easy axis, and peculiar temperature dependence of magnetic circular dichroism, when realistic band structure is incorporated. Magnetic/nonmagnetic trilayer structures based on HI-V´s have been shown to exhibit spin-dependent scattering, tunnel magnetoresistance as well as interlayer coupling due to the carrier polarization. Electrical spin injection across a ferromagnetic/nonmagnetic heterojunction and into an InGaAs quantum well (QW) has been demonstrated using ferromagnetic (Ga,Mn)As as a source of spin polarized carriers. Electrical electron spin injection has also been realized in a spin Esaki diode structure. By the use of insulating-gate field-effect transistor structures, we can electrically switch the ferromagnetic phase transition. We are thus beginning to learn how to control and utilize the spin degree of freedom in semiconductors. Routes to room temperature ferromagnetism by realizing new surface stabilized ferrom- gnetic compounds compatible with semiconductor heterostructures will also be discussed.