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The deposition of homogeneous thin films on porous substrates has been investigated. The thin film deposition of Ta(N) by physical vapor deposition on porous films with different average pore sizes and material compositions has been studied. The continuity of Ta(N) films on top of porous low-k dielectrics is evaluated by means of ellipsometric porosimetry combined with sheet resistance and atomic force microscopy measurements. Interface reactions are analyzed by x-ray photoelectron spectroscopy profiling. It has been observed that the minimal Ta(N) thickness required to obtain a continuous metal layer on top of the porous film depends, on the one hand, on the porosity and pore size and, on the other hand, on the chemical interaction of the thin film with the porous substrate. The sealing of pores is favored by the presence of carbon in the dielectric matrix. This is explained through a mechanism of local enhancement of the degree of crosslinking in the dielectric matrix, catalyzed by Ta.

We examine the influence of surface and grain-boundary scattering on the total electrical resistivity of copper as dimensions are reduced close to the bulk electron mean free path (39 nm). Through resistivity and grain size characterization on copper wires with sizes down to 95×130 nm2 in a temperature range of 4.2 to 293 K, it was found that the influence of surface scattering is less than previously speculated, while grain-boundary scattering is dominant. A reduction of the background scattering length due to small grains accounts for the observed behavior. The reflection coefficient varies as expected from impurity enrichment in the grain boundaries.

A detailed investigation of the electrical transport in (100) CoSi2/Si contacts is presented. The transport properties of epitaxial CoSi2 films, obtained both by ion‐beam synthesis and by solid‐state reaction of a Ti/Co bimetallic layer, are compared with the transport properties of conventional polycrystalline CoSi2 layers. The electrical resistivity, the magnetoresistance, and the Hall effect are measured on Hall bars for temperatures ranging from 1.2 to 300 K and magnetic fields up to 5 T. Very high values of the order parameter kFL0 are observed, indicating that the investigated samples are of very high purity and crystalline order. In addition, the electric transport at the CoSi2/Si interface is studied by current‐voltage and capacitance‐voltage measurements on Schottky diode structures for temperatures ranging from 173 to 333 K. Ideality factors close to unity are observed for the highest temperatures, for the lower temperatures the ideality factors are found to increase with decreasing temperatures...

The ohmic contact formation mechanism in furnace alloyed Ni/Au/Te/Au/GaAs structures is investigated by the combined application of x‐ray diffraction and Raman spectroscopy. It was found that the Ni top layer promotes a more uniform dissociation of the GaAs substrate by the formation of a ternary Nix GaAs phase in the initial stages of contact formation (T=350 °C). At an alloy temperature T=550 °C, which induces low resistive electrical behavior, the formation of epitaxial Ga2Te3 was observed, indicating the formation of a Ga2Te3/GaAs heterojunction. After alloying at 600 °C, Ga2Te3 was still found to be present in the contact zone. In addition, evidence for a regrowth of GaAs crystallites could be derived from an increase of the intensity ratio ITO/ILO of the GaAs Raman signals. No indication for the presence of a high density of shallow donors (≳1019 cm−3) in the GaAs top layers could be adduced.

We investigate the effect of methane/hydrogen (CH4/H2) reactive ion etching (RIE) and a subsequent annealing process on AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs heterostructures. We use low temperature Hall, Shubnikov–de Haas, and photoluminescence measurements. We observe that the electron density and mobility of the two‐dimensional electron gas in the heterostructure is strongly reduced by the RIE process. After annealing the electron density fully recovers for both types of structures, whereas the electron mobility responds differently. While for the pseudomorphic AlGaAs/InGaAs/GaAs heterostructures thermal annealing restores the electron mobility completely, for the AlGaAs/GaAs heterostructures the electron mobility recovers only to 60% of the original value. This indicates that in the AlGaAs/GaAs heterostructures the structural damage induced by reactive ion etching is not fully removed by thermal annealing. This is confirmed by photoluminescence measurements at low temperatures.

The line shape of N 1s photoemission spectra in a certain type of amorphous carbon nitride is shown to depend strongly on the polar angle of photoelectron emission. This effect is explained in terms of photoelectron forward scattering due to preferential orientation of bonds near the surface. An alternative model based on different indepth distributions for each of the nitrogen chemical species does not provide a satisfactory explanation of the observed angular dependence. The changes with polar emission angle of the photoelectron and Auger electron spectra are compared to elucidate the nature of each of the N 1s photoemission peaks.

Back side Raman measurements were performed on Ge/Pd/n‐GaAs ohmic contacts. The analysis was carried out on as‐deposited and annealed Ge/Pd/60 nm GaAs structures, and complemented by measurements on isolated 60 nm GaAs slabs. Ohmic behavior is found to coincide with the presence of a confined, highly doped (∼1–3×1019/cm3) region in the GaAs surface layers. This result can be interpreted as giving direct experimental evidence for the importance of doping in the ohmic behavior for this contact.

It is commonly accepted that interface states at the passivation surface of AlGaN/GaN heterostructures play an important role in the formation of the 2DEG density. Several interface state models are cited throughout literature, some with discrete levels, others with different kinds of distributions, or a combination of both. The purpose of this article is to compare the existing interface state models with both direct and indirect measurements of these interface states from literature (e.g., through the hysteresis of transfer characteristics of Metal-Insulator-Semiconductor High Electron Mobility Transistors (MISHEMTs) employing such an interface in the gate region) and Technology Computer Aided Design (TCAD) simulations of 2DEG densities as a function of the AlGaN thickness. The discrepancies between those measurements and TCAD simulations (also those commonly found in literature) are discussed. Then, an alternative model inspired by the Disorder Induced Gap State model for compound semiconductors is proposed. It is shown that defining a deep border trap inside the insulator can solve these discrepancies and that this alternative model can explain the origin of the two dimensional electron gas in combination with a high-quality interface that, by definition, has a low interface state density.

The lateral dimensions of resonant tunneling AlGaAs‐GaAs double barrier heterostructures have been restricted by hydrogen plasma exposure. Ohmic contacts to the submicron diodes have been made by solid phase epitaxial growth of Ge on GaAs. The current‐voltage characteristics show a fine structure splitting that is inversely proportional to the lateral size of the diode. The results are interpreted as resonant tunneling through zero‐dimensional states in the quantum box confined by the AlGaAs barriers and a harmonic lateral confining potential.

The ohmic contact formation mechanism in pulsed laser beam mixed Au/Te/Au/GaAs structures has been investigated by 129I Mossbauer spectroscopy. Low‐resistance, ohmic contact structures, on both n‐ and p‐type GaAs, were found to be correlated to the formation of a high density of defect complexes consisting of tellurium atoms quasi‐substitutional on arsenic sites with a gallium vacancy in the first neighbor shell. Correspondingly, the ohmic conduction is suggested to occur according to the amorphous heterojunction model, i.e., by a multi‐step recombination‐tunneling process.

Gaseous precursors for the atomic layer deposition (ALD) process can penetrate and deposit inside porous dielectrics. Understanding the relationship between the substrate porosity and the size and shape of precursor molecules used for the ALD of dielectric or metal films on these substrates is crucial for the formation and fabrication of reliable nanostructures. Sealing the surface pores is highly desirable to prevent the deposition of gaseous ALD precursors inside the porous network. In this study, in-diffusion of precursors is investigated using x-ray reflectivity, transmission electron microscopy, and Rutherford backscattering spectrometry for different porous substrates and binary (TaN) and ternary (WNC) ALD systems. Experimental observations are complemented with computational molecular modeling performed in the framework of the density-functional-theory formalism to determine the size and shape of ALD precursors. Pore sealing treatments are used to prevent a precursor penetration and to provide a suitable starting surface for the nucleation and growth of ALD films.

On nanoscale laminate structures, the interface cannot be identified any longer as the separation between two films of bulk materials. The formation of the interface defines the final composition and structure of the laminate structure. As such, the characterization of the interface becomes an important challenge. In this work the nanoscale laminate structures were formed by atomic layer deposition (ALD) of tungsten nitride carbide and tantalum nitride thin films on dense dielectrics [silicon carbide and silicon oxide (SiO2)]. The laminates were studied using x-ray reflectivity. The starting substrate surface is a primary factor in determining the density of the ALD layer. Moreover, in some cases, electron-density perturbations are observed in the vicinity of the interfacial region. A characterization strategy, using a density contrast layer between the silicon substrate and the SiO2 dielectric is presented. Depending on the chemical nature of precursors and substrate, ALD processes can either form specific interfacial organization or induce dielectric modifications, in any case, leading to unexpected metal-dielectric interactions. (C) 2005 American Institute of Physics.

We report fabrication and electro‐optic measurement of In0.52Al0.48As/In0.53Ga0.47As modulation‐ doped field‐effect transistors. The devices are monolithically integrated with coplanar stripline fixtures incorporating photoconductive switches. The switching time for a 0.35 μm T‐gate device is 4.2 ps and the delay is 3.2 ps. This is the fastest directly measured switching in a three‐terminal device reported to date.

The location of a half monolayer of ordered hydrogen adatoms on Ni(111) has been analyzed by Low‐Energy Electron Diffraction (LEED), Thermal Desorption Spectroscopy (TDS), and Work Function (Δφ) measurements. It is found that the hydrogen atoms are arranged in an overlayer of graphitic structure with a (2×2) unit cell with respect to the substrate unit cell. In the ordered regions, the hydrogen adatoms occupy both types of three fold hollow sites without a detectable difference in the Ni–H bond lengths between the two sites. The Ni–H bond length is found to be 1.84±0.06 A, corresponding to an overlayer‐substrate spacing of 1.15±0.1 A. The relation between this structure and its observed order–disorder phase diagram as a function of temperature and hydrogen coverage is discussed. The disorder is discussed in detail, and a novel ’’atomic band structure’’ interpretation is given.

We report an extensive study of the TiW/GaAs interface after rapid thermal annealing between 750 and 1050 °C. Characterization of the interface was performed by secondary ion mass‐spectroscopy (SIMS), Auger, Rutherford backscattering spectroscopy (RBS), x‐ray diffraction, transmission electron microscopy, and electrical measurements. Schottky barrier heights extracted from I‐V and C‐V data show a continuous increase with annealing temperatures up to 950 °C. The reverse I‐V measurements exhibit a transition from tunneling to avalanche breakdown. SIMS, Auger, and RBS show significant motion of the Ti, resulting in surface accumulation, as well as Ti diffusion into the GaAs substrate. Interface doping by Ti produces an artificial enhancement of the Schottky barrier height.

Adsorption of CO on a Pd(100) surface was studied in detail mainly by LEED, UPS, work function and thermal desorption measurements. Analysis of the ordered c(2√2×√2) R 45° structure occurring at Θ=0.5 revealed that in this phase each CO molecule is bridge bonded to 2 Pd atoms with Pd–C distances of 1.93±0.07 A and a C–O bond length of 1.15±0.1 A, the molecular axis being oriented normal to the surface. The mutual configuration of the adsorbed molecules is explained in terms of a short‐range repulsive interaction model, which is supported by the observation that the isosteric heat of adsorption (Ead=38.5 kcal/mole) is constant up to a coverage of Θ?0.45. The photoelectron spectra exhibit two maxima at 7.9 (5σ+1π level) and 10.8 eV (4σ level) below the Fermi level which are in agreement with the observations with other Pd planes. This also holds for an electronic excitation associated with an energy of 13.5 eV as observed by electron energy loss spectroscopy. The variation of the sticking coefficient with coverage is described in terms of a second‐order precursor state model with repulsive interactions. The pre‐exponential factor for desorption (3×1016 sec−1) varies only little with coverage. The dipole moment of the adsorbate remains constant up to Θ?0.35 (0.17 D) where the overlayer starts to order, and exhibits an appreciable higher value near Θ=0.5. The maximum work function increase is Δφmax=0.93 V at Θ=0.5. The differential entropy of the adsorbed layer around 450 K was derived from the experimental adsorption isotherms. Up to Θ=0.35 the data fall well between the limits of two theoretical models for localised and delocalised adsorption of noninteracting particles. Deviations at higher coverages reflect again the onset of ordering. The energetic and work function data are in some variance to results reported earlier which is ascribed to the fact that these quantities may be sensitively influenced by spurious amounts of carbon impurities on the surface.