Epitaxial ferromagnetic Fe3Si∕Si(111) structures with high-quality heterointerfaces

Abstract

To develop silicon-based spintronic devices, we have explored high-quality ferromagnetic Fe3Si/silicon (Si) structures. Using low-temperature molecular beam epitaxy at 130 • C, we realize epitaxial growth of ferromagnetic Fe3Si layers on Si (111) with keeping an abrupt interface, and the grown Fe3Si layer has the ordered DO3 phase. Measurements of magnetic and electrical properties for the Fe3Si/Si(111) yield a magnetic moment of ∼ 3.16 µB/f.u. at room temperature and a rectifying Schottky-diode behavior with the ideality factor of ∼ 1.08, respectively. PACS numbers:Semiconductor spintronic devices such as spin-field effect transistors (spin FET) are one of the possible candidates to substitute for existing silicon-based complementary metal-oxide-semiconductor devices. [1,2,3,4] To realize operations of the spin FET, an electrical spin injection from ferromagnets into semiconductors is an essential technology. For III-V semiconductor devices, several groups have demonstrated highly efficient spin injection and detection using an epitaxial Fe thin film and tailored Schottky tunnel barriers so far. [5,6,7] From these facts, it is necessary for semiconductor spintronics to develop crystal growth techniques of ferromagnets on semiconductors with keeping high-quality interfaces. In particular, it will become key to build epitaxial growth of ferromagnets on silicon (Si) from the viewpoint of application to existing silicon large-scale integrated circuit (LSI) technologies. [8] Moreover, for spintronics, Si has been regarded as an ideal material because of a long spin relaxation time due to weak spin-orbit interaction, weak hyperfine interaction and lattice inversion symmetry, which will give rise to a long spin diffusion length in the devices. Recently, spin transport in Si conduction channels was experimentally demonstrated although their operations were limited at low temperatures. [9,10,11] This means that the spin degree of freedom can be introduced into Si-based electronic devices.To date, ferromagnetic MnAs thin films have been grown epitaxially on Si (001), [12] but electrical spin injection from MnAs into Si across a Schottky tunnel barrier has never been demonstrated unfortunately. Also, the Curie temperature of MnAs is ∼ 315 K, [13] which may be relatively low for an operation temperature of future LSIs. Thus, possibilities of other high-Curie temperature materials compatible with Si should be explored. Here we select a ferromagnetic Heusler alloy Fe 3 Si thin film, which has a high Curie temperature above 800 K, a relatively high spin polarization of ∼ 45 % and a small coercive field of ∼ 7.5 Oe. [14] In this letter, we achieve highly

Electrical injection and detection of spin-polarized electrons in silicon through an Fe3Si/Si Schottky tunnel barrier

“…[9,10] By low-temperature molecular beam epitaxy (LTMBE), we recently demonstrated highly epitaxial growth of a binary Heusler alloy Fe 3 Si on Si and obtained an atomically abrupt heterointerface. [11] In this letter, inserting a heavily doped n + -Si layer near the abrupt interface between Fe 3 Si and n-Si, we achieve an effective Shottky tunnel barrier for spin injection into Si. Using nonlocal signal measurements, we demonstrate electrical injection and detection of spin-polarized electrons in Si conduction channels though the Schottky-tunnel-barrier contacts.…”

Magnetic, morphological and structural investigations of CoFe/Si interfacial structures

“…In recent years, several studies have been performed on epitaxial growth of FM metal thin film on III-V and IV group SCs. [2][3][4][5][6][7] For such type of devices, transition metals and their alloys are of great interest. Among various types of transition metals and alloys, CoFe magnetic alloy is of interest due to its soft magnetic properties.…”

Giant enhancement of spin pumping efficiency using Fe3Si ferromagnet

“…Here, we focus on single-crystal Fe 3 Si, which has desirable properties such as a smaller damping constant and a larger resistivity than those for Ni 80 Fe 20 (Py), the most commonly used spin source. 19 Moreover, high-quality single-crystal Fe 3 Si can be easily grown on semiconducting substrates such as Si, Ge and GaAs with atomically flat interfaces. [19][20][21] This means that Fe 3 Si can be applied to a wide variety of materials, allowing the development of novel semiconductor-based spintronic devices in addition to metal-based devices.…”

“…19 Moreover, high-quality single-crystal Fe 3 Si can be easily grown on semiconducting substrates such as Si, Ge and GaAs with atomically flat interfaces. [19][20][21] This means that Fe 3 Si can be applied to a wide variety of materials, allowing the development of novel semiconductor-based spintronic devices in addition to metal-based devices. In the present study, a significant enhancement of spin-injection efficiency is demonstrated by using a single-crystal Fe 3 Si layer.…”

“…19,20 A 5-nm-thick Pd layer was then formed by electron beam (EB) evaporation at room temperature. Two contact wires (separated by w=1.0 mm gap) for measuring the DC electromotive force were attached to the edge of the Pd film using Ag paste.…”