Barrier-height non-uniformities of PtSi/Si(111) Schottky diodes

The forward current-voltage characteristics of PtSi Schottky contacts on epitaxial n-type Si (111) is studied in the temperature range from 100 to 300 K. A current contribution in excess to that predicted by thermionic emission diffusion theory is caused by a few thousand patches of reduced Schottky barrier height in a device area of 3.14 mm². The typical lateral extent of these patches is 70–250 nm. It correlates with the size of surface bumps observed. The number of patches is reduced upon increasing the silicidation temperature up toT _siI=550°C. Possible non-uniformities of the typical crystallite grain size of 20 nm are not resolved due to effective pinch-off.     

Nonlinear optical spectroscopy of suboxides at oxidized Si(111) interfaces

Native oxidation of the Si(111)(1 x 1)H surface causes the appearance and disappearance of second-harmonic generation (SHG) resonances related to specific bonding configurations of Si atoms at the interface. Resonances at 3.52 eV two-photon energy observed in p-polarized SHG spectra are indicative of a Si suboxide configuration present in a partially oxidized Si surface bilayer. Similar resonances are observed in spectra of thermally oxidized Si(111) and point to Si2+ suboxide states at the buried interface.     

Quantum oscillations in Pb/Si (111) heterostructure system

This paper summarizes our recent work on the study of quantum size effects (QSE) and novel physical properties of the Pb/Si (111) heterostructure. Two different types of samples were investigated. One is wedge-shaped Pb islands, and the other is atomically flat Pb thin films. With scanning tunneling microscopy (STM) manipulation, we observed an intriguing morphology dynamics of the islands that swings between two extreme energy states, like that in a classical pendulum. We show that the dynamics is a result of the competition between the QSE and the classical step free energy minimizing effect. For the second type of the samples, the QSE is studied in terms of thickness-dependent film stability, electronic structure and physical properties by using STM, angle-resolved photoemission spectroscopy (ARPES) and transport measurement. The results consistently reveal the formation of quantum well states (QWS) due to electron confinement in the films. This size effect could greatly modify the electronic structure near the Fermi level and lead to quantum oscillations in superconductivity, electron-phonon coupling and thermal expansion. The work unambiguously demonstrates the possibility of quantum engineering of physical properties of thin films by exploiting well-controlled and thickness-dependent QSE.     

Optical characteristics of an epitaxial Fe3Si/Si(111) iron silicide film

The dispersion of the relative permittivity ? of a 27-nm-thick epitaxial Fe₃Si iron silicide film has been measured within the E = 1.16–4.96 eV energy range using the spectroscopic ellipsometry technique. The experimental data are compared to the relative permittivity calculated in the framework of the density functional theory using the GGA-PBE approximation. For Fe₃Si, the electronic structure and the electronic density of states (DOS) are calculated. The analysis of the frequencies corresponding to the transitions between the DOS peaks demonstrates qualitative agreement with the measured absorption peaks. The analysis of the single wavelength laser ellipsometry data obtained in the course of the film growth demonstrates that a continuous layer of Fe₃Si iron silicide film is formed if the film thickness achieves 5 nm.     

Current transport in Pd2Si/n-Si(100) Schottky barrier diodes at low temperatures

The forward current-voltage (I–V) characteristics of Pd₂Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height ( _b0) and an increase of the ideality factor () with decreasing temperature. Further, the changes in _b0 and become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and T ₀-effect fail to account for the temperature dependence of the barrier parameters. The 1n(I _s /T ²) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd₂Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 10⁴ A m^–2 K^–2 against the theoretical value of 1.12 × 10⁶ A m^–2 K^–2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.     

"Devil's staircase" in Pb/Si(111) ordered phases

With scanning tunneling microscopy we have found that ordered phases in Pb/Si(111) are one of the best examples of the "devil's staircase" phase diagram. Phases within a narrow coverage range (1.2相似文献   

Study of the structural and magnetic characteristics of epitaxial Fe3Si/Si(111) films

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 at a substrate temperature of 150°C have been presented. The epitaxial structure has been identified as a single-crystal Fe₃Si silicide film with the orientation Si[111]‖Fe₃Si[111] using methods of the X-ray structural analysis, transmission electron microscopy, and reflection high-energy electron diffraction. It has been established that the epitaxial Fe₃Si film at room temperature has magnetic uniaxial anisotropy (H _a = 26 Oe) and a relatively narrow uniform ferromagnetic resonance line (ΔH = 11.57 Oe) measured at a pump frequency of 2.274 GHz.     

Magnetic and magnetoresistive properties of epitaxial Co/Cu/Co trilayers on Si(111)

Giant magnetoresistance of the epitaxial Co/Cu/Co trilayers grown on vicinal Si(111) was determined as a function of Cu spacer coverage in the range from 0 to 7 ML. The first maximum of giant magnetoresistance and antiferromagnetic coupling was detected at 3.0 ML coverage of the Cu spacer. The portion of antiferromagnetic coupling in the first antiferromagnetic maximum was estimated as 17%. 3D growth mode of the Cu spacer leads to the simultaneous occurrence of the ferromagnetically and antiferromagnetically coupled areas between the Co layers.