The results of the structural and magnetic studies of the epitaxial structure prepared during the simultaneous evaporation from two iron and silicon sources on an atomically pure Si(111)7 × 7 surface...

We report on abrupt changes in dc resistance and impedance of a diode with the Schottky barrier based on the Mn/SiO₂/p-Si structure in a magnetic field. It was observed that at low temperatures the dc and ac resistances of the device change by a factor of more than 10⁶ with an increase in a magnetic field to 200 mT. The strong effect of the magnetic field is observed only above the threshold forward bias across the diode. The ratios between ac and dc magnetoresistances can be tuned from almost zero to 10⁸% by varying the bias. To explain the diversity of magnetotransport phenomena observed in the Mn/SiO₂/p-Si structure, it is necessary to attract several mechanisms, which possibly work in different regions of the structure. The anomalously strong magnetotransport effects are attributed to the magnetic-field-dependent impact ionization in the bulk of a Si substrate. At the same time, the conditions for this process are specified by structure composition, which, in turn, affects the current through each structure region. The effect of magnetic field attributed to suppression of impact ionization via two mechanisms leads to an increase in the carrier energy required for initiation of impact ionization. The first mechanism is related to displacement of acceptor levels toward higher energies relative to the top of the valence band and the other mechanism is associated with the Lorentz forces affecting carrier trajectories between scatterings events. The estimated contributions of these two mechanisms are similar. The proposed structure is a good candidate for application in CMOS technology-compatible magnetic- and electric-field sensors and switching devices.

The optical, magnetooptical, and magnetic properties of polycrystalline (Fe5Si3/SiO2/Si(100)) and epitaxial Fe3Si/Si(111) films are investigated by spectral magnetoellipsometry. The dispersion of the...

Three-layer iron-rich Fe_3+xSi_1−x/Ge/Fe_3+xSi_1−x (0.2 < x < 0.64) heterostructures on a Si(111) surface with Ge thicknesses of 4 nm and 7 nm were grown by molecular beam epitaxy. Systematic studies of the structural and morphological properties of the synthesized samples have shown that an increase in the Ge thickness causes a prolonged atomic diffusion through the interfaces, which significantly increases the lattice misfits in the Ge/Fe_3+xSi_1−x heterosystem due to the incorporation of Ge atoms into the Fe_3+xSi_1−x bottom layer. The resultant lowering of the total free energy caused by the development of the surface roughness results in a transition from an epitaxial to a polycrystalline growth of the upper Fe_3+xSi_1−x. The average lattice distortion and residual stress of the upper Fe_3+xSi_1−x were determined by electron diffraction and theoretical calculations to be equivalent to 0.2 GPa for the upper epitaxial layer with a volume misfit of −0.63% compared with a undistorted counterpart. The volume misfit follows the resultant interatomic misfit of |0.42|% with the bottom Ge layer, independently determined by atomic force microscopy. The variation in structural order and morphology significantly changes the magnetic properties of the upper Fe_3+xSi_1−x layer and leads to a subtle effect on the transport properties of the Ge layer. Both hysteresis loops and FMR spectra differ for the structures with 4 nm and 7 nm Ge layers. The FMR spectra exhibit two distinct absorption lines corresponding to two layers of ferromagnetic Fe_3+xSi_1−x films. At the same time, a third FMR line appears in the sample with the thicker Ge. The angular dependences of the resonance field of the FMR spectra measured in the plane of the film have a pronounced easy-axis type anisotropy, as well as an anisotropy corresponding to the cubic crystal symmetry of Fe_3+xSi_1−x, which implies the epitaxial orientation relationship of Fe_3+xSi_1−x (111)[0−11] || Ge(111)[1−10] || Fe_3+xSi_1−x (111)[0−11] || Si(111)[1−10]. Calculated from ferromagnetic resonance (FMR) data saturation magnetization exceeds 1000 kA/m. The temperature dependence of the electrical resistivity of a Ge layer with thicknesses of 4 nm and 7 nm is of semiconducting type, which is, however, determined by different transport mechanisms.

The growth and phase formation features, along with the influence of structure and morphology on the electronic, optical, and transport properties of Cr₂GeC and Cr_2-xMn_xGeC MAX phase thin films synthesized by magnetron sputtering technique, were studied. It was found that the Cr:Ge:C atomic ratios most likely play the main role in the formation of a thin film of the MAX phase. A slight excess of carbon and manganese doping significantly improved the phase composition of the films. Cr₂GeC films with a thicknesses exceeding 40 nm consisted of crystallites with well-developed facets, exhibiting metallic optical and transport properties. The hopping conduction observed in the Cr_2-xMn_xGeC film could be attributed to the columnar form of crystallites. Calculations based on a two-band model indicated high carrier concentrations N, P and mobility μ in the best-synthesized Cr₂GeC film, suggesting transport properties close to single crystal material. The findings of this study can be utilized to enhance the growth technology of MAX phase thin films.