Unusual features in the bias dependence of spin transport are observed in a Co/Au/NiFe spin valve fabricated on a highly textured Cu(100)/Si(100) Schottky interface, exploiting the local probing capabilities of a Ballistic electron magnetic microscop
e (BEMM). This arises due to local differences in the strain and the presence of misfit dislocations at the Schottky interface that enhances spin flip scattering and broadens the energy and angular distribution of the transmitted electrons. Cumulatively, these enable the transmitted hot electrons to probe the different conduction band minima in Si, giving rise to such bias dependent features in the magnetocurrent. This study reveals new insights into the spin dependence of transmission in an indirect band gap semiconductor as Si and highlights the unique capabilities of BEMM in probing local differences in spin transport across such textured interfaces.
Hot electron transport of direct and scattered carriers across an epitaxial NiSi_2/n-Si(111) interface, for different NiSi_2 thickness, is studied using Ballistic Electron Emission Microscopy (BEEM). We find the BEEM transmission for the scattered ho
t electrons in NiSi_2 to be significantly lower than that for the direct hot electrons, for all thicknesses. Interestingly, the attenuation length of the scattered hot electrons is found to be twice larger than that of the direct hot electrons. The lower BEEM transmission for the scattered hot electrons is due to inelastic scattering of the injected hot holes while the larger attenuation length of the scattered hot electrons is a consequence of the differences in the energy distribution of the injected and scattered hot electrons and the increasing attenuation length, at lower energies, of the direct hot electrons in NiSi_2.
The hot-electron attenuation length in Ni is measured as a function of energy across two different Schottky interfaces viz. a polycrystalline Si(111)/Au and an epitaxial Si(111)/NiSi_2 interface using ballistic electron emission microscopy (BEEM). Fo
r similarly prepared Si(111) substrates and identical Ni thickness, the BEEM transmission is found to be lower for the polycrystalline interface than for the epitaxial interface. However, in both cases, the hot-electron attenuation length in Ni is found to be the same. This is elucidated by the temperature-independent inelastic scattering, transmission probabilities across the Schottky interface, and scattering at dissimilar interfaces.
We investigate electron transport across a complex oxide heterointerface of La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) on Nb:SrTiO$_3$ (Nb:STO) at different temperatures. For this, we employ the conventional current-voltage method as well as the technique
of Ballistic Electron Emission Microscopy (BEEM), which can probe lateral inhomogeneities in transport at the nanometer scale. From current-voltage measurements, we find that the Schottky Barrier height (SBH) at the LSMO/Nb:STO interface decreases at low temperatures accompanied by a larger than unity ideality factor. This is ascribed to the tunneling dominated transport caused by the narrowing of the depletion width at the interface. However, BEEM studies of such unbiased interfaces, do not exhibit SBH lowering at low temperatures, implying that this is triggered by the modification of the interface due to an applied bias and is not an intrinsic property of the interface. Interestingly, the SBH at the nanoscale, as extracted from BEEM studies, at different locations in the device is found to be spatially homogeneous and similar both at room temperature and at low temperatures. Our results highlight the application of BEEM in characterizing electron transport and their homogeneity at such unbiased complex oxide interfaces and yields new insights into the origin of the temperature dependence of the SBH at biased interfaces.
