Magnetite Schottky barriers on GaAs substrates

Abstract

Carrier transport across Fe 3 O 4 / GaAs interfaces has been studied for n-and p-type GaAs͑001͒ substrates with medium ͑7.7ϫ 10 17 cm −3 ͒ to high ͑3.5ϫ 10 18 cm −3 ͒ carrier concentrations. Currentvoltage ͑I-V͒ measurements on medium-doped substrates show a rectifying behavior that is characteristic for thermionic emission/diffusion across a Schottky barrier. The n-type structure exhibits a low ideality factor of 1.3 and a Schottky barrier height of 0.58-0.63 eV. The Schottky barrier height of the p-type sample is 0.51 eV. For Fe 3 O 4 / GaAs structures with higher doping levels the I -V dependence is nearly symmetric. In this case, tunneling of electrons and holes through the Schottky barrier dominates transport between the Electrical spin injection and detection has been demonstrated between ferromagnetic and normal metals 1 and in semiconductor/͑magnetic͒ semiconductor heterostructures. 2,3 However, one of the main goals of spin electronics, to achieve spin injection from a ferromagnetic metal into a semiconductor, has been more difficult to attain. One particular obstacle is the conductivity mismatch between metals and semiconductors, which drastically limits the spin injection efficiency for ohmic contacts between metals and semiconductors. 4 For nonohmic contacts, however, the conductivity mismatch model of Schmidt et al. does not apply and it has recently been demonstrated that spin injection can be obtained by tunneling through a barrier at the semiconductor interface 5 or by using a magnetic tunnel transistor emitter. 6 An alternative route for spin injection is to use a halfmetallic ferromagnet, which has a completely spin-polarized conduction band, as the spin injector. For perfectly spinpolarized sources, the conductivity mismatch is circumvented even for ohmic contacts, and in the case of tunneling the higher polarization should give a much larger spin accumulation in the semiconductor compared to 3d transition metal injectors. Unfortunately the growth of half-metallic ferromagnets onto semiconductors tends to be more difficult than ferromagnetic transition metals, and very often the spin polarization will be determined more by disordered interfacial layers than by the bulk properties of the ferromagnet itself. Furthermore, perfect spin polarization is a zerotemperature property. The two spin states are mixed, to some extent, at finite temperature. Nonetheless, Fe 3 O 4 has a number of unusual properties that make it attractive as a spinpolarized source.As a class II B half-metal, Fe 3 O 4 is not truly a metal but it is rather a polaronic hopping conductor of minority spins. 7 The resistivity increases with decreasing temperature and goes up sharply at the Verwey transition at about 120 K. 8

Spin and orbital moments inFe3O4

“…The proposed high spin polarization, together with the magnetoresistive properties, have generated interest in using Fe 3 O 4 in various spintronic applications such as spin-polarized current injection. 10,11 There are still conflicting reports concerning the magnetism, orbital ordering, and the degree of spin polarization in Fe 3 O 4 . For example, while charge and orbital ordering have been reported, 12-14 recent work suggests that charge order is not necessarily present.…”

All oxide ferromagnet/semiconductor epitaxial heterostructures

“…Furthermore, the conductivity σ ≈ 200 Ω −1 cm −1 of Fe 3 O 4 at room temperature is low [8], while the Curie temperature T C 860 K is well above room temperature, making Fe 3 O 4 a promising material for spin injection into semiconductors. However, the Fe 3 O 4 /semiconductor heterostructures investigated so far [9,10,11,12,13,14] show that for both group IV and III-V semiconductors, it is very difficult to grow Fe 3 O 4 thin films with high crystalline quality, while preventing the formation of secondary phases at the FM/SC interface. To our knowledge, the deposition of Fe 3 O 4 onto a II-VI semiconductor has not been reported to date.…”

Electrical transport, magnetic properties of the half-metallic Fe3O4-based Schottky diode

“…The fitting curves were shown in Fig. 8 (0.63 eV) [20] and Fe 3 O 4 /STON (0.51 eV) [21] diodes, but different from the Fe 3 O 4 /amorphous Si diode [22] which was reported to be qfE0 eV and did not show any rectifying property at room temperature. I s ¼ 3 Â 10 À4 A, R ¼ 320 O, n ¼ 2.4 and Schottky barrier height qf ¼ 0.08 eV were also deduced for the I-V curves measured at 40 K.…”