Observation of quantum size effect at the conduction band bottom of n-type ferromagnetic semiconductor (In,Fe)As thin films

We study the quantum size effect (QSE) in the spin-dependent electronic structure at the conduction band (CB) bottom (Γ point) of an n-type ferromagnetic semiconductor (In0.92,Fe0.08)As ultrathin films (thickness t = 8-14 nm), by performing magnetic circular dichroism (MCD) spectroscopy in an infra-red photon energy range (E = 0.62-1.8 eV). The t-dependence of MCD peaks are well explained by the optical transitions from the valence band top to the quantized levels at the CB bottom of (In,Fe)As obtained from self-consistent calculations. These findings provide new possibilities of spin-device applications utilizing QSE in nm-scale (In,Fe)As thin films.