SPIN FILTERING IN MAGNETIC HETEROSTRUCTURES

Several techniques were proposed to achieve solid state spin filtering such as magnetic tunnel junctions comprised of half-metallic compounds or solid state Stern-Gerlach apparatus. Another alternative consists in using spin-dependent resonant tunneling through magnetically active quantum wells. Recent advances in molecular beam epitaxial growth made it possible to fabricate exotic heterostructures comprised of magnetic films or buried layers (ErAs, GaxMn1-xAs) integrated with conventional semiconductors (GaAs) and to explore quantum transport in these heterostructures. It is particularly interesting to study spin-dependent resonant tunneling in double-barrier resonant tunneling diodes (RTD) with magnetic elements such as GaAs/AlAs/ErAs/AlAs/ErAs/AlAs/GaAs, GaxMn1-xAs/AlAs/GaAs/AlAs/GaAs, and GaAs/AlAs/GaxMn1-xAs/AlAs/GaAs. We present the results of our theoretical studies and computer simulations of transmission coefficients and current-voltage characteristics of resonant tunneling diodes based on these double-barrier structures. Resonant tunneling of holes (GaxMn1-xAs-based RTDs) is considered. Our approach is based on k·p perturbation theory with exchange splitting effects taken into account. We analyze exchange splitting of different resonant channels as a function of magnetization as well as spin polarization of the transmitted current as a function of bias. We found that resonant tunneling I – V characteristics of the double-barrier magnetic hererostructures strongly depend on the doping level in the emitter as well as on the orientation of the magnetization.