High quality Fe3−δO4∕InAs hybrid structure for electrical spin injection

Abstract

Single crystalline Fe 3−␦ O 4 ͑0 ഛ ␦ ഛ 0.33͒ films have been epitaxially grown on InAs ͑001͒ substrates by molecular beam epitaxy using O 2 as source of active oxygen. Under optimum growth conditions, in situ real time reflection high-energy electron diffraction patterns, along with ex situ atomic force microscopy, indicate that ͑001͒ Fe 3−␦ O 4 can be grown under step-flow-growth mode with a characteristic ͑ ͱ 2 ϫ ͱ 2͒R45 surface reconstruction. X-ray photoelectron spectroscopy demonstrates the possibility of obtaining iron oxides with compositions ranging from Fe 3 O 4 to ␥-Fe 2 O 3 . Measurements with a superconducting quantum interference device magnetometer at 300 K show good magnetic properties, suggesting that iron-based oxides may be promising for spintronic applications. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2713784͔ During the last decade, there has been a considerable increase of studies on hybrid structures combining both semiconductors and magnetic materials. These studies are motivated by possible applications in the nascent field of spintronics, since the electron spin degree of freedom in hybrid structures is believed to be a source of a rich array of new physical phenomena. Different approaches have been adopted for the selection of adequate spin injectors including ferromagnetic metals, 1,2 dilute magnetic semiconductors, 3 and Heusler alloys. 4 The use of magnetic semiconductors in this field presents the formidable task of increasing the Curie temperature. Ferromagnetic metal and Heusler alloys on the other hand suffer from structural and interfacial problems during their growth. Quite surprisingly, there are few reports on iron oxide based half metals, which exhibit a large polarization at the Fermi level making them very attractive for spin injection into semiconductors.Fe 3 O 4 or magnetite belongs to a large family of ironbased oxides commonly called ferrites. Our choice for this material as a possible efficient spin injector into semiconductors stems from its physical properties, which are attractive in many respects. ͑i͒ It has half metallic character with a large spin polarization at the Fermi level. 5,6 ͑ii͒ It possesses an electrical resistivity of the same order of magnitude as a semiconductor, making the conductivity mismatch problem less severe than in the case of metals. ͑iii͒ It has a Curie temperature of about 850 K, well above room temperature. This study will combine the use of magnetite with InAs substrates. InAs is used because of high room temperature electron mobility and, more importantly, because of its large and tunable spin-orbit coupling strength ͑small ratio between the Rashba and Dresselhauss terms͒, important for spin-based devices. 7 Although the growth of iron oxides on metallic and oxide based substrates is a very well documented subject, 8 there are only few reports on the growth of iron oxides on semiconducting substrates.The purpose of the present letter is to extend the only work available 9 on the growth of Fe 3 O 4 on InAs with special emp...

Probing the interface ofFe3O4/GaAsthin films by hard x-ray photoelectron spectroscopy

“…Recent interest has been directed at the use of semiconducting substrates. [10][11][12][13][14][15] However, there are only sparse experimental reports 10,13 on interface chemistry and interface reactions, although based on thermodynamic considerations such interfaces might not be stable. 16 In this work, we examine this problem and investigate the chemical nature of Fe 3 O 4 films grown on GaAs͑100͒ substrates and their respective interfaces.…”

Change of Magnetic Properties and Structure in Fe<SUB>3</SUB>O<SUB>4</SUB> Films on Si Substrates with Annealing Temperature

“…[21][22][23] It has been reported that asdeposited films have not only a Fe 3 O 4 phase but also the other phase such as an iron or an iron oxide according to their deposition conditions. 22,24,25) It has also been found that epitaxial Fe 3 O 4 films on the MgO show peculiar magnetic properties, 15,21) and that a polycrystalline Fe 3 O 4 film on the Si exhibits a large magnetoresistance of $ 7:4% at room temperature. 23) Additionally, epitaxial Fe 3 O 4 films have been prepared by post oxidation of an iron film.…”

“…Up to now, high oriented, epitaxial or polycrystalline Fe 3 O 4 films have been obtained by various deposition techniques such as NO 2 or O 2 assisted molecular beam epitaxy (MBE), 14,15) electron beam ablation, 16) pulsed laser deposition from -Fe 2 O 3 17,18) or Fe 3 O 4 19,20) as a target, and reactive sputtering from an iron target with the argon and oxygen mixture gas flow. [21][22][23] It has been reported that asdeposited films have not only a Fe 3 O 4 phase but also the other phase such as an iron or an iron oxide according to their deposition conditions.…”

Evolution of pyramid morphology during InAs(001) homoepitaxy

“…8 Epitaxial thin films for post complementary metal-oxide-semiconductor digital integrated circuits 9 and high performance spin devices [10][11][12] require the surfaces to be atomically smooth with low defect densities in critical conditions. However the formation of 3D structures or islands on the III-V surfaces is found to be an important study to explore the growth mechanism.…”

“…6,22 Oxide removal process of InAs substrate and the growth chamber are exactly same as reported in our previous publication. 12 With reference to the surface reconstruction diagram, 300-nm-thick InAs layer was grown under As-pressure with a beam-equivalent-pressure ratio of As to In of about 12. The As-pressure is almost between 5.8 ϫ 10 −6 to 6.2ϫ 10 −6 Torr throughout all the growth experiments.…”