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Understanding the interaction between hydrogen (H) and helium-vacancy (He-V) complexes in tungsten (W) is important for the development of plasma-facing materials in fusion reactors. H trapping by HexVy complexes in bulk W, as well as the H solution behavior and H trapping by HexV complexes near W(100), W(111), and W(110) surfaces, has been investigated by first-principles computer simulations using density function theory. The results show that the sequential H binding energies to HexV complexes in bulk W decrease with the increasing number of H and He. For the HexV2 complexes in bulk W, H prefers to trap at interstitial sites near the junction of the di-vacancy, where the H can minimize the isosurface of optimal charge density. The most stable interstitial sites for H below W surfaces are dependent on the surface orientation. Our calculations indicate that H atoms tend to prefer a depth of 0.3 nm below the W(100) and W(111) surfaces due to the surface reconstruction. The binding energy of H to a HeV complex near W surfaces has the most significant orientation dependence below the W(111) surface, followed by the W(100) and W(110) surfaces. Compared with the bulk value, the largest difference in the average binding energy of H to the stable HexV complexes at the three W surfaces is about 0.2 eV. Furthermore, the effect of surfaces on the H binding energy to HexV complexes can be ignored for depths greater than 0.65 nm. [ABSTRACT FROM AUTHOR]

Density function theory calculations have been performed to study the stability of small helium-vacancy (He-V) complexes near tungsten (W) surfaces of different orientations. The results show that the stability of vacancies and He-V complexes near W surfaces depends on surface orientation. However, as the depth below the surface increased beyond about 0.65–0.8 nm, the stability of He-V complexes is similar to the bulk. The formation energies of single vacancies and di-vacancies at depths less than 0.2 nm below the W(110) surface are higher than for W(100) or W(111) surfaces, but have lower energies at depths between 0.2 and 0.65 nm. The formation energies of He-V complexes below W surfaces are sensitive to the geometric orientation of the He and vacancy, especially below the W(111) surface. Within about 0.2 nm of the top layer of the three W surfaces, neither a vacancy nor a di-vacancy can trap He. Because of the lower formation energy of He-V complexes and higher He binding energy to vacancies below the W(110) surface, the He desorption from the W(110) surface is less likely to occur than from the W(100) and W(111) surfaces. Our results provide fundamental insight into the differences in surface morphology changes observed in single W crystals with different surface orientations under He plasma exposure. [ABSTRACT FROM AUTHOR]

A metal–interlayer–semiconductor (MIS) structure that is realized by inserting an ultrathin interlayer between a contact metal and a semiconductor has been investigated recently as a low-resistance non-alloyed contact structure. However, a comprehensive and systematical investigation of Schottky barrier height (SBH) modulation through the insertion of an interlayer depending on the contact surface orientation has not been conducted despite its importance for its use in multi-gate transistors. Therefore, in this work, the SBH modulation of the MIS contact structure for different contact surface orientations is systematically investigated, and a comprehensive analysis platform of the MIS contact structure is suggested. Two factors, (1) alleviation of Fermi-level pinning due to metal-induced gap states and interface states and (2) formation of the interface dipole, contribute to the SBH modulation in the MIS contact structure. Their contributions depending on the contact surface orientation are evaluated through a comparison of the contact structures on (100)- and (110)-oriented germanium (Ge). These factors and how they should be considered for a certain contact surface in Ge-channel multi-gate transistors are investigated. The investigation and the proposed analysis platform will contribute to the design of high-performance non-alloyed contact schemes for next-generation multi-gate transistors. [ABSTRACT FROM AUTHOR]

Measurements have been made near normal incidence of the two-dimensional spatial coherence of the acoustic field scattered from the lakebed in Seneca Lake, New York. In the test region, the lakebed consists of a series of sediment layers created by a sequence of distinct depositional processes. The spatial coherence length of the scattered field is shown to be dependent on the structure of the underlying sediment sequences. Significant ping-to-ping variability in the spatial coherence surface was also observed for each sediment sequence. This variability is quantified by a two-dimensional spatial coherence metric that measures the coherence lengths and asymmetric coherence surface orientation. The ping-to-ping variation of the surface asymmetry appears to be linked to the spatial isotropy of the sediment scattering strength. The scattering strength of the deepest observed sequence in the sub-bottom is the most spatially isotropic and the ping-to-ping variability of the coherence lengths and surface orientations are random. The scattering strength of the shallower sequences is spatially anisotropic and the coherence lengths and surface orientations show intervals of non-random ping-to-ping behavior. [ABSTRACT FROM AUTHOR]

The selective epitaxial growth of Si1-xGex and the related strain properties were studied. Epitaxial Si1-xGex films were deposited on (100) and (110) orientation wafers and on patterned Si wafers with recessed source and drain structures via ultrahigh vacuum chemical vapor deposition using different growing steps and Ge concentrations. The stepwise process was split into more than 6 growing steps that ranged in thicknesses from a few to 120 nm in order to cover the wide stages of epitaxial growth. The growth rates of SiGe on the plane and patterned wafers were examined and a dependence on the surface orientation was identified. As the germanium concentration increased, defects were generated with thinner Si1-xGex growth. The defect generation was the result of the strain evolution which was examined for channel regions with a Si1-xGex source/drain (S/D) structure. [ABSTRACT FROM AUTHOR]

We investigated the dependence of absolute SnS band-edge energies on surface orientation using density functional theory and GW method for all surfaces with Miller indices -3 ≤ h; k; l ≤ 3 and found variations as large as 0.9 eV as a function of (hkl). Variations of this magnitude may affect significantly the performance of photovoltaic devices based on polycrystalline SnS thin-films and, in particular, may contribute to the relatively low measured open circuit voltage of SnS solar cells. X-ray diffraction measurements confirm that our thermally evaporated SnS films exhibit a wide distribution of different grain orientations, and the results of Kelvin force microscopy support the theoretically predicted variations of the absolute band-edge energies. [ABSTRACT FROM AUTHOR]

Two high-k dielectric materials (Al2O3 and HfO2) were deposited on n-type (100) and (110) InAs surface orientations to investigate physical properties of the oxide/ semiconductor interfaces and the interface trap density (Dit). X-ray photoelectron spectroscopy analyses (XPS) for native oxides of (100) and (110) as-grown n-InAs epi wafers show an increase in As-oxide on the (100) surface and an increase in InOx on the (110) surface. In addition, XPS analyses of high-k (Al2O3 and HfO2) on n-InAs epi show that the intrinsic native oxide difference between (100) and (110) epi surfaces were eliminated by applying conventional in-situ pre-treatment (TriMethyAluminium (TMA)) before the high-k deposition. The capacitance-voltage (C-V) characterization of HfO2 and Al2O3 MOSCAPs on both types of n-InAs surfaces shows very similar C-V curves. The interface trap density (Dit) profiles show Dit minima of 6.1 × 1012/6.5 × 1012 and 6.6 × 1012/7.3 × 1012 cm-2 eV-1 for Al2O3 and HfO2, respectively for (100) and (110) InAs surfaces. The similar interface trap density (Dit) on (100) and (110) surface orientation were observed, which is beneficial to future InAs FinFET device with both (100) and (110) surface channel orientations present. [ABSTRACT FROM AUTHOR]

The authors report the compositional dependence of the direct and indirect band gaps of pseudomorphic Ge1−x−ySixSny alloys on Ge and GaAs with (001) surface orientation determined from deformation potential theory and spectroscopic ellipsometry measurements. The effects of alloying Ge with Si and Sn and the strain dependence of the band gaps at the Γ, Δ, and L conduction band minima are discussed. Deformation potential theory predicts an indirect to direct crossover in pseudomorphic Ge1−y−xSixSny alloys on Ge or GaAs only for very high Sn concentrations between 15% and 20%. No indirect to direct cross-over in pseudomorphic Ge1−ySny alloys (x = 0) on Ge or GaAs was found for practically approachable Sn compositions (y < 25%). The predictions for the compositional dependence of the E0, E1, and E1 + Δ1 band gaps were validated for pseudomorphic Ge1−ySny alloys on Ge using spectroscopic ellipsometry. The complex pseudodielectric functions of pseudomorphic Ge1−ySny alloys grown on Ge by molecular beam epitaxy were determined from Fourier transform infrared and ultraviolet-visible ellipsometry in the 0.1–6.6 eV energy range of Sn contents up to 11%, to investigate the compositional dependence of the band gaps. Critical point energies and related parameters were obtained by analyzing the second derivative spectra of the dielectric function of the Ge1−ySny epilayers. Sn composition, thickness, and strain of the Ge1−ySny epilayers on Ge were characterized by high resolution x-ray diffraction. The E0, E1, and E1 + Δ1 band gaps of pseudomorphic Ge1−ySny alloys on Ge obtained from ellipsometry are in good agreement with the theoretical predictions. [ABSTRACT FROM AUTHOR]

Valence band structure and surface states of InN with (0001), (000-1), (1-100), and (11-20) orientation were investigated in situ after growth using photoelectron spectroscopy. Depending on surface orientation, different occupied surface states are identified and differentiated from bulk contributions. For N-polar, m-plane, and a-plane InN, the surface states are located at the valence band maximum, while In-polar InN features surface states close to the Fermi level. The surface band alignment correlates with the position of surface states. For InN(0001), a much larger surface downward band bending is observed compared to N-polar, m-plane, and a-plane InN, where almost flat band conditions occur. [ABSTRACT FROM AUTHOR]

AlSb is grown by molecular beam epitaxy. The evolution and the relaxation of the deposited AlSb layer is investigated by synchrotron-based in situ grazing incidence x-ray diffraction (GID), and the analysis of the real space distribution is performed by atomic force microscopy. AlSb forms islands with (111)A polarity and {110} surface orientations with different side facets following the Volmer-Weber growth mode. GID investigations reveal facet rods originating from AlSb{110} islands. It is shown that a concentration of only 0.7% AlSb{110} oriented domains influences the diffraction pattern in such a way that additional crystal truncation rods parallel to the surface appear. [ABSTRACT FROM AUTHOR]