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

摘要

Ferromagnetic semiconductors (FMSs), which inherit the properties of both semiconductors and ferromagnets, are essential for spin-based electronic applications. Among various FMS materials, (In,Fe)As is the first n-type electron-induced Ⅲ-Ⅴ FMS and particularly promising due to its unique properties such as the large s-d exchange interaction energy, large spontaneous spin splitting in the conduction band, and high coherency of electron carriers. We found that, in (In,Fe)As ultrathin films, the band gap energies at the critical points E_1(L point) and E_2 (X point) are increased with decreasing the film thickness, which is caused by the quantum size effect (QSE). However, this previous work was performed by using magnetic circular dichroism (MCD) with visible – ultraviolet light (wavelength λ = 200 - 900 nm, photon energy E_(ph) = 1.4 – 6 eV), and thus unable to reveal the effect of QSE on the band structure at the conduction band (CB) bottom (Γ point, band gap 0.42 eV) of (In,Fe)As, which is most crucial for the transport properties.