Quantum size effect and tunneling magnetoresistance in ferromagnetic-semiconductor quantum heterostructures

We report on the resonant tunneling effect and the increase of tunneling magnetoresistance induced by it in ferromagnetic-semiconductor GaMnAs quantum-well (QW) heterostructures. The resonant tunneling effect was observed when the GaMnAs QW thickness was from 3.8 to 20 nm, which indicates that highly coherent tunneling occurs in these heterostructures. The observed quantum levels of the GaMnAs QW were successfully explained by the valence-band k.p model and the p-d exchange interaction. It was also found that the Fermi level of the electrode injecting carriers is important to observe resonant tunneling in this system.