Minority-spin impurity band in n -type (In,Fe)As: A materials perspective for ferromagnetic semiconductors

Abstract

Fully understanding the properties of n-type ferromagnetic semiconductors (FMSs), complementary to the mainstream p-type ones, is a challenging goal in semiconductor spintronics because ferromagnetism in n-type FMSs is theoretically nontrivial. Soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) is a powerful approach to examine the mechanism of carrier-induced ferromagnetism in FMSs. Here our SX-ARPES study on the prototypical n-type FMS (In,Fe)As reveals the entire band structure, including the Fe-3d impurity bands (IBs) and the host InAs ones, and provides direct evidence for electron occupation of the InAs-derived conduction band (CB). A minority-spin Fe-3d IB is found to be located just below the conduction-band minimum (CBM). The IB is formed by the hybridization of the unoccupied Fe 3d states with the occupied CBM of InAs in a spin-dependent way, resulting in the large spin polarization of CB. The band structure with the IB is varied with band filling, which cannot be explained by the rigid-band picture, suggesting a unified picture for realization of carrier-induced ferromagnetism in FMS materials.

Ultrafast Subpicosecond Magnetization of a 2D Ferromagnet

“…However, the generated photoelectrons reside in bands 1.0 eV higher than the conduction band bottom and thus cannot directly participate in the s-d exchange interaction with the Fe spins, which form an impurity band immediately below the conduction band bottom, [47][48][49][50][51][52][53][54] as illustrated in the left panel of Figure 3a. Relaxation of the photoelectrons to the conduction band bottom generally requires several tens of ps, [3] which thus cannot explain the sub-ps enhancement of M. Moreover, because there are only minority-spin Fe-related impurity bands above the Fermi level, [54] excitation of electrons to these d-orbital impurity bands would lead to a decrease in the Fe spin moments; but clearly this is not consistent with the experimental observations. On the other hand, no photocarriers are generated in the AlSb buffer layer due to the large direct band gap (2.2 eV), which excludes superdiffusive current [55][56][57][58][59] from the bottom AlSb layer toward the (In,Fe)As QW as a possible origin.…”

“…Irradiation with fs-laser pulses with a photon energy of 1.55 eV (wavelength 798 nm) instantly generates a large amount of photocarriers (electrons and holes) in the (In,Fe)As QW. However, the generated photoelectrons reside in bands 1.0 eV higher than the conduction band bottom and thus cannot directly participate in the s-d exchange interaction with the Fe spins, which form an impurity band immediately below the conduction band bottom, [47][48][49][50][51][52][53][54] as illustrated in the left panel of Figure 3a. Relaxation of the photoelectrons to the conduction band bottom generally requires several tens of ps, [3] which thus cannot explain the sub-ps enhancement of M. Moreover, because there are only minority-spin Fe-related impurity bands above the Fermi level, [54] excitation of electrons to these d-orbital impurity bands would lead to a decrease in the Fe spin moments; but clearly this is not consistent with the experimental observations.…”

“…Relaxation of the photoelectrons to the conduction band bottom generally requires several tens of ps, [ 3 ] which thus cannot explain the sub‐ps enhancement of M . Moreover, because there are only minority‐spin Fe‐related impurity bands above the Fermi level, [ 54 ] excitation of electrons to these d ‐orbital impurity bands would lead to a decrease in the Fe spin moments; but clearly this is not consistent with the experimental observations. On the other hand, no photocarriers are generated in the AlSb buffer layer due to the large direct band gap (2.2 eV), which excludes superdiffusive current [ 55–59 ] from the bottom AlSb layer toward the (In,Fe)As QW as a possible origin.…”

Computational investigation of high Curie temperature in a new N‐type ferromagnetic diluted magnetic semiconductors, especially iron‐doped on GaSb

“…Both p-type and n-type semiconductor materials are required in pairs for most real-spin electronic semiconductor devices, such as spin light-emitting diodes, field effect transistors, and p-n junction diodes, to do work effectively. [36][37][38] To fill this gap, we initiated a study of the ferromagnetic properties of (Ga,Fe)Sb. The potential applications of (Ga,Fe)Sb diluted magnetic semiconductors are used for new spintronics devices such as the p-d zener model, [39] determination of nitrogen incorporation, [40] soft x-ray, [41] photo emission spectroscopy, [41] magnetic field sensors, [42] nonvolatile spin, [43] spin pumping and electrical spin injection, [44] spin valve magneto resistance (GMR and TMR), [43] spin pumping measurement devises, [41] light irradiation, electrical gating, and wave function manipulation.…”

“…This indicates that this work is novel compared to prior studies and more applicable for spintronic devices than other developments. The total spin quantum of Fe 3 + is S = 2.5, Fe ion concentration from 13.9% to 20%, a = 6.09$${A}^0$$, and n = × $${10}^{18}{\mathrm{cm}}^{ - 3}$$6–2.2 × 1 × $${10}^{22}{\mathrm{cm}}^{-3}$$ [ 16,28,35,36,37,38,44,46,56–59,63–66,68,69,71 ] have been used in this studies.…”