Abstract
Current status of III-V based ferromagnetic semiconductors, especially (Ga, Mn)As, a GaAs based diluted magnetic semiconductor, is reviewed. Low solubility of magnetic elements was overcome by low temperature nonequilibrium molecular beam epitaxial growth to realize successfully (Ga, Mn)As as well as (In, Mn)As. Magnetization measurements showed that GaAs based (Ga, Mn) As is ferromagnetic with Curie temperature TC as high as 110 K. Magnetotransport measurements of (Ga, Mn) As epitaxial films revealed that the p-d exchange N0β is 3 eV. This strong interaction was shown to be large enough to explain the high TC by the RKKY interaction. Multilayer heterosturctures including superlattices and resonant tunneling diodes (RTD's) were also successfully fabricated. The magnetic coupling between two ferromagnetic (Ga, Mn)As films separated by a nonmagnetic GaAs (or AlGaAs) layer was found to be a function of thickness and composition of the intermediary layer, indicating the critical role of the holes on the magnetic coupling. This observation of magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin dependent tunneling in RTD's, showed the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.
