Hetero-epitaxial EuO interfaces studied by analytic electron microscopy

Abstract

With nearly complete spin polarization, the ferromagnetic semiconductor europium monoxide could enable next-generation spintronic devices by providing efficient ohmic spin injection into silicon. Spin injection is greatly affected by the quality of the interface between the injector and silicon. Here, we use atomic-resolution scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy to directly image and chemically characterize a series of EuO|Si and EuO|YAlO 3 interfaces fabricated using different growth conditions. We identify the presence of europium silicides and regions of disorder at the EuO|Si interfaces, imperfections that could significantly reduce spin injection efficiencies via spin-flip scattering. a These authors contributed equally to this work.

Direct Epitaxial Integration of the Ferromagnetic Semiconductor EuO with Silicon for Spintronic Applications

“…The presence of a band gap adds to the resistance of the surface to oxidation [47] although one should note that both theory [48] and experiments [49] predict the silicide to become partly oxidized with formation of M-O-Si bonds. This (21) reconstruction is routinely used for the growth of AO and ABO 3 compounds on Si, including EuO [18,30,42]. Both our results and other reports show the presence of impurity phases in such EuO/Si structures.…”

“…Being doped, though, at high temperature, these materials typically enter into dominant states that are not spatially homogeneous due to formation of magnetic polarons -few-body systems comprised of electron and local magnetic moments of the host [20,[24][25][26][27]. However, this unwanted formation does not take place when magnetisation of the lattice is significant, leaving the host material perfectly homogeneous in the region of its employment as a spin injector [25][26][27].Owing its outstanding magnetic and transport properties among other MS, EuO has recently attracted much attention as having tremendous potential for semiconductor spintronics, in particular, when integrated with Si [18,[28][29][30]. Not only does doped EuO exhibit a spin polarization close to 100% due to enormous (~0.6 eV) spin splitting of its conduction band but also it can be conductance-matched with Si by doping with oxygen vacancies or trivalent rare-earth atoms such as Gd, La or Lu [18,[30][31][32][33].…”

“…An intermediate layer, however, reduces the probability of spin-polarized carriers injection exponentially. In particular, an enormous band gap of about 6 eV in SrO makes injection of spin-polarized carriers into Si rather ineffective.The continuing attempts to grow EuO/Si heterojunctions [28][29][30]43,44] are checked by the presence of large amounts of impurity phases at the interface. These phases are not only detrimental to the growth of EuO films; they also prevent spin injection due to spin-flip scattering.…”

“…Owing its outstanding magnetic and transport properties among other MS, EuO has recently attracted much attention as having tremendous potential for semiconductor spintronics, in particular, when integrated with Si [18,[28][29][30]. Not only does doped EuO exhibit a spin polarization close to 100% due to enormous (~0.6 eV) spin splitting of its conduction band but also it can be conductance-matched with Si by doping with oxygen vacancies or trivalent rare-earth atoms such as Gd, La or Lu [18,[30][31][32][33].…”

“…Not only does doped EuO exhibit a spin polarization close to 100% due to enormous (~0.6 eV) spin splitting of its conduction band but also it can be conductance-matched with Si by doping with oxygen vacancies or trivalent rare-earth atoms such as Gd, La or Lu [18,[30][31][32][33]. Its Heisenberglike magnetism (7 μ B per Eu 2+ ion) arises from the half-filled 4f states which constitute the top of the valence band [33].…”