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Direct wafer bonding of β-Ga2O3 and N-polar GaN at a low temperature was achieved by acid treatment and atmospheric plasma activation. The β-Ga2O3/GaN surfaces were atomically bonded without any loss in crystalline quality at the interface. The impact of post-annealing temperature on the quality of bonding interfaces was investigated. Post-annealing at temperatures higher than 700 °C increases the area of voids at bonded interfaces probably due to the difference in the coefficient of thermal expansion. The integration of β-Ga2O3 on the GaN substrate achieved in this work is one of the promising approaches to combine the material merits of both GaN and Ga2O3 targeting the fabrication of novel GaN/β-Ga2O3 high-frequency and high-power electronics as well as optoelectronic devices. [ABSTRACT FROM AUTHOR]

Recently, the crystallographic phases of HfO2 and ZrO2, including the polar phases, have been well characterized, and also the total and free energies have been calculated. However, less is known about the structure and energy of the crystalline coherent interface—also called the interphase. The formation of domain and phase boundaries is determined by interphase energies and properties, and their knowledge is indispensable to better understand the phase formation and phase stability. We have calculated the interphase energy for HfO2 and ZrO2 at T = 0 K for the relevant phase pairs with two methods, which are in good agreement. The method is applicable to any crystalline material with metastable phases. The values range in a few 100 mJ/m2, which is consistent with previous estimates from room temperature but too large for estimates from high-temperature processes. We propose a temperature dependence of interphase energy such that it becomes small close to the phase transition. [ABSTRACT FROM AUTHOR]

It has been shown recently that the perovskite oxide SrVO3 is a transparent conductor with optical and electrical properties outreaching those of the most used material indium tin oxide (ITO). These properties, observed in the crystalline phase, imply the strong potential of SrVO3 for use as a lower cost alternative to ITO, but the possible integration of this perovskite oxide material in actual electronic devices is still an open question. One of the possible approaches for the integration of oxide materials is the use of amorphous thin films, allowing low thermal budgets to preserve the performances of the electronic device. Therefore, in this study, the electrical and optical properties of amorphous or poorly crystallized thin SrVO3 films are investigated. [ABSTRACT FROM AUTHOR]

Polarization properties and dielectric relaxations were investigated in single crystalline Mn-substituted YFeO3. Thermally stimulated depolarization currents (TSDC) were observed at Tm ≈ 110 K along all three orthorhombic directions but with different magnitudes. These anisotropic behaviors were also observed in temperature dependent dielectric responses. Electric field sweep polarization measurements down to 10 K showed neither hysteresis nor remanent polarization. Based on the result of the temperature- and frequency-dependent dielectric measurements and the relaxation analysis of the TSDC, we suggest that previously reported pyroelectric currents at ~110 K are not due to a ferroelectric phase transition but due to the formation of frozen defect dipoles which are induced by the localized charge carriers. [ABSTRACT FROM AUTHOR]

We report the fabrication of a Si(111) crystalline thin film on graphene by the aluminum-induced crystallization (AIC) process. The AIC process of Si(111) on graphene is shown to be enhanced compared to that on an amorphous SiO2 substrate, resulting in a more homogeneous Si(111) thin film structure as revealed by X-ray diffraction and atomic force microscopy measurements. Raman measurements confirm that the graphene is intact throughout the process, retaining its characteristic phonon spectrum without any appearance of the D peak. A red-shift of Raman peaks, which is more pronounced for the 2D peak, is observed in graphene after the crystallization process. It is found to correlate with the red-shift of the Si Raman peak, suggesting an epitaxial relationship between graphene and the adsorbed AIC Si(111) film with both the graphene and Si under tensile strain. [ABSTRACT FROM AUTHOR]

We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc2O3/Y2O3/Si(111) substrates. Using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we find that ScN films grown at 600 °C are single crystalline, twin-free with rock-salt crystal structure, and exhibit a direct optical band gap of 2.2 eV. A high degree of crystalline perfection and a very good lattice matching between ScN and GaN (misfit<0.1%) makes the ScN/Sc2O3/Y2O3 buffer system a very promising template for the growth of high quality GaN layers on silicon. [ABSTRACT FROM AUTHOR]

We demonstrate Pb(Mg1/3Nb2/3)O3-PbTiO3 cylinders with ~98% h100iC texture along the radial direction. A giant enhancement in the magnitude of electromechanical coupling factor (k31=kh=0.60, and kl=0.7) was obtained for textured cylinder, and d31×g31 was measured to be 6766×10–15 m2/N which is 3–6 times higher than that of commercial Pb(Zr,Ti)O3 compositions. The crystallographic grain orientation in the textured cylinder was visualized by electron backscatter diffraction, and the domain structure was characterized by piezoresponse force microscopy. Using these results, we explain the mechanism for this enhanced performance of radially textured piezoelectrics. [ABSTRACT FROM AUTHOR]

Strain relaxation behavior of epitaxial SrRuO3 thin films on (001) LaAlO3 substrates was investigated using high resolution X-ray diffraction. Lattice distortion and dislocation densities were systematically studied with samples under different growth conditions. Reciprocal space maps reveal different strain relaxation behavior in SrRuO3 thin films grown at different temperatures. Two kinds of strain relaxation mechanisms were proposed to understand the growth dynamics, including the evolution of threading dislocations and the tilt of crystalline planes. [ABSTRACT FROM AUTHOR]

Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces. [ABSTRACT FROM AUTHOR]

The electrical properties of amorphous-crystalline interfaces in phase change materials, which are important for rewritable optical data storage and for random access memory devices, have been investigated by surface scanning potential microscopy. Analysis of GeSb systems indicates that the surface potential of the crystalline phase is ∼30-60 mV higher than that of the amorphous phase. This potential asymmetry is explained qualitatively by the presence of a Schottky barrier at the amorphous-crystalline interface and supported also by quantitative Schottky model calculations. [ABSTRACT FROM AUTHOR]

Information regarding the conductivity type of Si/GeOx/Ni structures with various stoichiometry has been obtained using experiments on injection of minority carriers from n- and p-type silicon. Results show that non-stoichiometric GeOx films exhibit bipolar conductivity, that is, holes as well as electrons contribute to the charge transport. Stoichiometric GeO2 films exhibit unipolar electron conductivity. [ABSTRACT FROM AUTHOR]

We report the photoluminescence (PL) and cathodoluminescence (CL) study of nanostructured poly-crystalline silicon surface fabricated by lithography-less, reactive ion etching process. Photoluminescence in visible range at room temperature with peak position between 630 nm and 720 nm is observed without any oxidation or annealing steps. X-ray photoemission (XPS) and Auger electron spectroscopy (AES) revealed the presence of silicon oxide. The observed cathodoluminescence in green and red regions of the visible spectrum are due to nano-scaled tips and their coating with nonstoichiometric silicon oxide. [ABSTRACT FROM AUTHOR]

In this letter, we propose an atmospheric pressure-chemical vapor deposition technique to grow metastable GeSn epitaxial layers on Ge. We report the growth of defect free fully strained undoped and in-situ B doped GeSn layers on Ge substrates with Sn contents up to 8%. Those metastable layers stay fully strained after 30 min anneal in N2 at 500 °C; Ge-Sn interdiffusion is seen at 500 °C but not at lower temperature. B is 100% active in the in-situ GeSn:B layers up to a concentration of 1.7 × 1019 cm-3. GeSn:B provides slightly lower Hall hole mobility values than in pure p-type Ge especially for low B concentrations. [ABSTRACT FROM AUTHOR]

Crystalline silicon surface passivation by amorphous silicon deposited by three different chemical vapor deposition (CVD) techniques at low (T∼130 °C) temperatures is compared. For all three techniques, surface recombination velocities (SRVs) are reduced by two orders of magnitude after prolonged thermal annealing at 200 °C. This reduction correlates with a decreased dangling bond density at the amorphous-crystalline interface, indicating that dangling bond saturation is the predominant mechanism. All three deposition methods yield excellent surface passivation. For a-Si:H layers deposited by radio frequency plasma enhanced CVD, we obtain outstanding carrier lifetimes of 10.3 ms, corresponding to SRVs below 1.32 cm/s. [ABSTRACT FROM AUTHOR]

The nanopatterned sapphire substrates (NPSSs) with aspect ratio that varied from 2.00 to 2.50 were fabricated by nanoimprint lithography. We could improve the epitaxial film quality and enhance the light extraction efficiency by NPSS technique. In this work, the aspect ratio effects on the performances of GaN-based light-emitting diodes (LEDs) with NPSS were investigated. The light output enhancement of GaN-based LEDs with NPSS was increased from 11% to 27% as the aspect ratio of the NPSS increases from 2.00 to 2.50. Owing to the same improvement of crystalline quality by using various aspect ratios of NPSS, these results indicated that the aspect ratio of the NPSS is strongly related to the light extraction efficiency. [ABSTRACT FROM AUTHOR]

We analyze the dependence of the interface defect density Dit in amorphous/crystalline silicon (a-Si:H/c-Si) heterojunctions on the microscopic properties of ultrathin (10 nm) undoped a-Si:H passivation layers. It is shown that the hydrogen bonding and network disorder, probed by infrared- and photoelectron spectroscopy, govern the initial Dit and its behavior upon a short thermal treatment at 200 °C. While the initial Dit is determined by the local and nonequilibrated interface structure, the annealed Dit is defined by the bulk a-Si:H network strain. Thus it appears that the equilibrated a-Si:H/c-Si interface does not possess unique electronic properties but is governed by the a-Si:H bulk defects. [ABSTRACT FROM AUTHOR]

We investigated and compared the photoelectric behavior of the Pt sandwiched (Bi3.7Nd0.3)Ti3O12 (BNT) and Pb(Zr0.2Ti0.8)O3 (PZT) films deposited by sol-gel method. Based on the analysis of the photocurrent and I-V characteristics, the top and bottom Pt/film interface Schottky barriers are found to be more symmetric in BNT, compared to that in PZT. The photocurrents originated from the depolarization field due to the alignment of ferroelectric polarization are different, although the polarizations of the two films are about the same. The mechanism behind the origin of the different photocurrent behaviors between Pt/BNT/Pt and Pt/PZT/Pt capacitors was discussed. [ABSTRACT FROM AUTHOR]

The piezoelectric properties of [001]c poled 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 single crystals were greatly enhanced by controlling their domain configurations. Contrary to the interpretation of charged domain walls being the main contributor to the piezoelectric enhancement, we found that smaller domain size and more neutral domain walls were the main contributors for the piezoelectric enhancement of these multidomain crystals. The properties of 109° neutral domain walls in 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 single crystals were extracted by using a piezoelectric domain wall model. [ABSTRACT FROM AUTHOR]

Highly conducting interfaces of transition metal oxide heterolayers could provide a promising access to transition metal oxide based electronic devices similar to those based on semiconductor heterostructures. Recently, metallic conductivity has been reported at the LaAlO3/SrTiO3 heterointerface. Here we report the observation of diodelike behavior and the formation of a random diode network in thin films of LaVO3 deposited on as-polished SrTiO3 substrates. Depending on films annealing conditions we observed linear or nonlinear I-V characteristic below 50 K. [ABSTRACT FROM AUTHOR]

Atomic migration under an electric field, electromigration, in molten and crystalline Ge2Sb2Te5 was studied using a pulsed dc stress to an isolated line structure. Under a single pulse (∼10-3 s), Ge2Sb2Te5 was melted by Joule heating, and an electrostatic force-induced drift of Ge and Sb toward the cathode and Te toward the anode was observed. Effective charge numbers were calculated to be 0.28, 0.38, and -0.29 for Ge, Sb, and Te, respectively. Electromigration in the crystalline state was studied by applying a 10 MHz pulsed dc; constituent elements migrated toward the cathode, which suggests a hole wind-force operating in this phase. [ABSTRACT FROM AUTHOR]

Band offsets of the Ge/GeO2 interface are calculated through a hybrid density functional scheme. We first generate a model of disordered GeO2 through ab initio molecular dynamics to describe the oxide component. For addressing the interface, we then consider an atomistic model in which amorphous GeO2 is connected to crystalline Ge through a suboxide transition region showing regular structural parameters. The band offsets are obtained through the application of an alignment scheme, which reproduces the experimental band gaps of the interface components. The calculated valence band offset of 3.7 eV favors the low-energy side of the range of measured offsets. [ABSTRACT FROM AUTHOR]

We have employed the “3ω method” to determine the thermal conductivities of the amorphous and crystalline phases of the technologically important materials Ge2Sb2Te5, nitrogen-doped Ge2Sb2Te5, Ag- and In-doped Sb2Te, and Ge15Sb85. We used the “3ω voltage” as a monitor of thermal conductivity that allowed us to observe the amorphous-to-crystalline phase transition as the material was annealed. For these materials, our results reveal that the thermal conductivity κ is related to the electrical conductivity σ by an empirical relationship of the form κ=σLT+0.175 W/m K, where L is the Lorenz number and T is temperature. [ABSTRACT FROM AUTHOR]

Although a high electric energy density was recently reported for defect-modified poly(vinylidene fluoride) (PVDF) copolymers at millisecond discharge, they usually deliver less energy at a high pulse rate. In this letter, a low loss polystyrene (PS) was grafted as side chains onto the P(VDF-chlorotrifluoroethylene) main chain. After PVDF crystallization, dielectric PS side chains were segregated to the crystalline-amorphous interface, forming a finite confinement layer for ferroelectric PVDF crystals. We speculated that less space charge was induced during electric poling because of the nanoscale confinement effect. Consequently, a fast discharge speed and a relatively high energy density were achieved. [ABSTRACT FROM AUTHOR]

Single crystalline Nd2O3 based capacitors with proper forming gas annealing treatment are fabricated. By elevating the temperature of substrate to 100 °C, near interface oxide traps are observed according to the quasistatic C-V obtained at low frequency. Two types of traps, interface traps and near interface oxide traps, are demonstrated in this gate stack. Using the low-high frequency method, the interface trap density at flatband voltage condition and the near interface oxide trap density are estimated to be 5.17×1011 eV-1 cm-2 and 3.75×1012 cm-2, respectively. The interface trap density is then further confirmed by the conductance method. [ABSTRACT FROM AUTHOR]

Epitaxial Bi(111) films on the Si(100)-(2×1) surface were studied by two different scanning probe techniques, to obtain information on the buried interface. Ballistic electron emission microscopy reveals that the transmission across the Schottky barrier depends on the type of substrate terrace. The thermovoltage in scanning tunneling microscopy exhibits alternating signals for substrate step edges, which can be related to SA and SB steps, characteristic for the uncovered Si(100)-(2×1) surface. In addition to information about the growth mode of Bi, it was found that typical features of the Si(100)-(2×1) surface reconstruction are maintained. [ABSTRACT FROM AUTHOR]

This letter introduces a modified effective medium formulation for composites where the characteristic length of the inclusion is on the order of or smaller than the phonon mean free path. The formulation takes into account the increased interface scattering in the different phases of the nanocomposite and the thermal boundary resistance between the phases. The interface density of inclusions is introduced and is found to be a primary factor in determining the thermal conductivity. The predictions are in good agreement with results from Monte Carlo simulations and solutions to the Boltzmann equation. [ABSTRACT FROM AUTHOR]

The plastic deformation in copper-zirconium nanocrystalline-amorphous nanolaminates is investigated by means of stress-relaxation experiments at a range of initial stress levels. Progressive multistep relaxation cycles reveal that the onset of plastic deformation occurs at a much lower stress level in nanocrystalline-amorphous nanolaminate than in crystalline-crystalline nanolaminates or other nanostructured materials. The derived activation volumes and strain rate sensitivities imply interfacial dislocation mechanisms, consistent with the observations from postmorterm transmission electron microscopy. This indicates that the crystalline-amorphous interfaces may be the preferred source for dislocation nucleation and/or emission. [ABSTRACT FROM AUTHOR]

Using grazing-incidence x-ray scattering technique the authors have investigated the evolution of the damage profile of the transition layer between the ion-induced ripplelike pattern on top surface and the ripples at buried crystalline interface in silicon created after irradiation with 60 keV Ar+ ions under 60°. The transition layer consists of a defect-rich crystalline part and a complete amorphous part. The crystalline regions are highly strained but relaxed for low dose and high dose irradiations, respectively. The appearance of texture in both cases shows that the damage of the initial crystalline structure by the ion bombardment takes place along particular crystallographic directions. [ABSTRACT FROM AUTHOR]

First-principles calculations of the atomic and electronic structure of crystalline CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) are performed to understand the effect of B on spin-dependent transport in these junctions. The authors find that it is energetically favorable for B atoms to reside at the crystalline CoFeB/MgO interface rather than remain in the bulk of the crystalline CoFeB electrode. The presence of B at the interfaces is detrimental to tunneling magnetoresistance (TMR) because it significantly suppresses the majority-channel conductance through states of Δ1 symmetry. Preventing B segregation to the interfaces during annealing should result in an enhanced TMR in CoFeB/MgO/CoFeB MTJs. [ABSTRACT FROM AUTHOR]

The effect of the sputtered Ni layer thickness (7–14 nm) on the silicide phase transition was studied at 260 °C. In 7-nm-thick layers, the complete mixing of Ni and Si occurring during deposition produces stable Ni2Si transrotational structures which further evolve into similar NiSi domains within 50 min of annealing. In 14-nm-thick layers, the residual unmixed Ni atoms diffuse towards the interface and speed up the transition from Ni2Si to NiSi (25 min) by promoting the nucleation of polycrystaline NiSi grains. A competition between NiSi trans- and poly-structures occurs, and the resulting layer morphology depends on the reaction temperature. [ABSTRACT FROM AUTHOR]

In this work the authors introduce and provide details on the stoichiometrically controlled self-driven formation of freestanding single crystal platelets in Zn3As2 by a direct self-catalytic vapor-solid growth mechanism. The platelets feature dimensions of up to ∼1 cm and mirrorlike microscopically flat top surfaces. A coherent formation of pyramids and wires has been further observed on some of the platelet top surfaces, the growth mechanism of which is discussed. This study might open pathways for facile engineering of high-performance semiconductor via a direct vapor-solid conversion of polycrystalline semiconductor powders into single crystal substrates on a large scale and with low cost. [ABSTRACT FROM AUTHOR]

We report a relaxorlike modification in the ferroelectric poly(vinylidene fluoride-trifluorethylene) copolymer using ultraviolet (UV) irradiation. This behavior is clearly demonstrated by dielectric measurements. Besides the relaxor feature, the ferroelectric character of the material is retained, also exhibiting Curie transition at barely diminished temperatures. UV-Vis absorption measurements suggests that the UV radiation induces conjugated C==C bonds in the copolymer chains. The coexistence of both relaxor and ferroelectric behavior, the lack of chain cross-linking, and a weak reducing in the crystallinity suggest that the UV-induced defects are not sufficient to completely break up the polarization domains. [ABSTRACT FROM AUTHOR]

In this study, free standing crystalline ZnSe nanorings and nanowires have been fabricated on Au coated Si substrates by simple thermal evaporation of ZnSe powders. Ring- or wirelike morphology can be achieved in a controllable manner by using different reactor pressures during growth, while all the other conditions remain the same. Our results show that the ZnSe nanorings are wurtzite phase instead of the zinc-blende phase, observed in typical one-dimensional ZnSe nanostructures. The growth mechanism of the nanorings has been discussed, and the cathodoluminescence of the nanorings has been described. [ABSTRACT FROM AUTHOR]

In this work, we investigate the electronic and optical properties of self-assembled InN/GaN quantum dots. The one-particle states of the low-dimensional heterostructures are provided by a tight-binding model that fully includes the wurtzite crystal structure on an atomistic level. Optical dipole and Coulomb matrix elements are calculated from these one-particle wave functions and serve as an input for full configuration interaction calculations. We present multiexciton emission spectra and discuss in detail how Coulomb correlations and oscillator strengths are changed by the piezoelectric fields present in the structure. Vanishing exciton and biexciton ground state emission for small lens-shaped dots is predicted. [ABSTRACT FROM AUTHOR]

We suggest an approach to the fabrication of versatile nanocomponents designed deliberately by selective Ga+ focused-ion-beam etching or Ar+ ion milling of single-crystalline Au nanoplates synthesized by the chemical reaction. The nanocomponents have various shapes like gear, wheel, dumbbell, square and letter “A” with in-plane size of about 400 nm and thickness of 40–50 nm. They can be picked up or moved freely one by one to be assembled into sophisticated nanodevices or micromachines. The applicability of our approach both to the fundamental research and to the applied research is discussed. [ABSTRACT FROM AUTHOR]

Single-crystalline alpha silicon–nitride nanowires have been achieved with large scale by the reaction of Mg3N2 and SiCl4 at 600 °C. Electron microscopy analyses have revealed that the nanowires have only ∼35 nm in diameter, up to 5 μm in length, and a preferred [001] growth direction. The nanowires exhibit the quantum size effect in optical properties, showing the redshift of an infrared band and the blueshift of the photoluminescence band. The growth mechanism of the nanowires have been properly discussed. [ABSTRACT FROM AUTHOR]

Different types of waveguides and connections between them were fabricated in a three-dimensional (3D) layer-by-layer photonic crystal. The waveguides were formed by removing either a single rod or a series of rod fragments running in three mutually orthogonal directions. This provides the potential of forming a 3D network of waveguide channels with cross sectional dimensions on the order of one lattice constant. The propagation behavior of guided modes in these waveguide networks was probed using a network analyzer. High transmission efficiency (with loss below 0.5 dB) through various waveguide bends and networks with carefully designed geometries has been achieved. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An InAs/GaP/InGaP rectifier has been fabricated using a semiconductor-semiconductor “Schottky” junction to utilize the thermal stability of the semiconductor-semiconductor interface. The InAs/GaP/InGaP system demonstrates rectifying characteristics with an ideality factor of 2.3 and a current–voltage extracted barrier height of 0.96 eV. It exhibits low reverse bias leakage current and achieves breakdown electric field of 0.6 MV/cm. The InAs/GaP/InGaP system maintains the rectifying characteristics up to 600 °C. Further improvement of the thermal stability is expected to be achieved by reducing the diffusion of Si dopant atoms across the InAs/GaP interface at high temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The correlation between the vicinal properties of SrTiO[sub 3] (001) substrates and the twinning in YBa[sub 2]Cu[sub 3]O[sub 7-x] thin films grown by pulsed-laser deposition is studied using x-ray diffraction with reciprocal space mapping. The vicinal properties, i.e., angle and in-plane orientation, play a significant role in the anisotropic strain starting at the interface between substrate surface and film, and affect the twin behavior of YBa[sub 2]Cu[sub 3]O[sub 7-x]. On substrates having an [110] in-plane orientation of the step edges, a completely preferred twin pair is observed if the vicinal angle is increased to 0.60°. Whereas on substrates having their step edges oriented along one of the crystallographic axis, the films exhibit a detwinning as the vicinal angle increases. For α=1.10° a maximum detwinned, i.e., monocrystalline film is obtained. At this angle, the diffusion length of YBa[sub 2]Cu[sub 3]O[sub 7-x] during the growth matches the terrace length of SrTiO[sub 3]. Up to this specific angle, the films are grown perpendicular to the optical instead of the crystallographic surface. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

4H-polytype AlN has been grown on a 4H-SiC substrate with the (1120) face via plasma-assisted molecular-beam epitaxy. The microscopic structure of the AlN/4H-SiC interface was examined using high-resolution transmission electron microscopy, and the polytype replication of the 4H structure from the 4H-SiC(1120) substrate was evidently confirmed. The x-ray rocking curve of (1120) diffraction for the single crystalline 4H-AlN epilayer exhibited a very small linewidth of 90 arc sec, suggesting noticeably small tilting around the [1120] direction. The excellent crystalline quality is probably owing to the polytype matching between the 4H-AlN epilayer and the 4H-SiC substrate, which resulted in remarkable reduction of defects at the interface. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have measured the density of Pd[sub 40]Ni[sub 40-x]Cu[sub x]P[sub 20] (x=0–40) alloys in the amorphous and crystalline states. For x>30, the alloys are denser in the amorphous than in the crystalline states, which is contrary to the behavior of all known metallic glasses. For Pd[sub 40]Ni[sub 40-x]Cu[sub x]P[sub 20] and all other bulk metallic glasses where density data are available in both the amorphous and crystalline states, we find a correlation between the stability of the supercooled liquids and the difference between the molar volumes of the glassy and crystalline phases. The supercooled liquid region is largest for those alloys that show no change in molar volume upon crystallization. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Efficient polymer-fullerene photovoltaic devices require close proximity of the two materials to ensure photoexcited electron transfer from the semiconducting polymer to the fullerene acceptor. We describe studies in which a bilayer system consisting of spin-cast 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene copolymer (MEH-PPV) and sublimed C[sup 60] is heated above the MEH-PPV glass transition temperature in an inert environment, inducing an interdiffusion of the polymer and the fullerene layers. With this process, a controlled, bulk, gradient heterojunction is created bringing the fullerene molecules within the exciton diffusion radius of the MEH-PPV throughout the film to achieve highly efficient charge separation. The interdiffused devices show a dramatic decrease in photoluminescence and concomitant increase in short circuit currents, demonstrating the improved interface. [ABSTRACT FROM AUTHOR]

We report measurements of the ultrafast dynamics of interracial electric fields in semiconductor multilayers using pump-probe second-harmonic generation (SHG). A pump beam was tuned to excite carriers in all the layers in GaAs/GaSb and GaAs/GaSb/InAs heterostructures. The resulting carrier dynamics manifests itself via electric fields created by charge separation due to carrier redistribution at the interfaces. The evolution of interfacial fields is monitored by a probe beam through an eletric-field-induced SHG signal. We distinguish between several stages of dynamics originating from redistribution of carriers between the layers. We also find a strong enhancement of the induced electric field caused by hybridization of the conduction and valence bands at the GaSb/InAs interface. [ABSTRACT FROM AUTHOR]

The origin of the difference in the optimum processing temperature of microcrystalline silicon (μc-Si:H) solar cells depending on the device structure has been studied. The two different type structures have been compared with each other, a superstrate-type cell, and a substrate-type cell where the order of the deposited layer is p-i-n and n-i-p, respectively on the substrate. We fabricate μc-Si:H solar cells at various deposition temperatures of the i layer under contamination-free conditions using an ultrahigh vacuum system. We found that the optimum temperature for the superstrate-type cell is lower than that for the substrate-type cell and that a significant degradation of the cell performance occurs during the deposition of the i layer at higher temperatures. We ascribed the degradation to the formation of the defect at the p/i interface due to the enhanced diffusion of the boron from the underlying layer to the intrinsic layer. We also found that this degradation and the enhanced diffusion do not take place for phosphorous or postdeposition annealing. We speculate that the enhanced boron diffusion is mediated by the Si—Si bond breaking and its accompanying structural relaxation caused by atomic hydrogen. [ABSTRACT FROM AUTHOR]

The growth of epitaxial InSb layers on highly lattice-mismatched semi-insulating GaAs substrates has been achieved via traditional liquid-phase epitaxy. Scanning and transmission electron microscopy show sharp interfaces even at 35 nm resolution. High-resolution x-ray diffraction studies reveal reflections even up to 2θ=153° with distinct layer and substrate peaks, indicating structural coherence. The films grown were n type and the highest electron mobility obtained was 3.96 x 10[sup 4] cm²/Vs at room temperature. The band gap varies from 0.17 to 0.23 eV in the temperature range of 300-10 K and is consistent with the expected variation. These results indicate that the films grown are comparable to those grown by other sophisticated techniques in terms of structural, optical and electrical properties. [ABSTRACT FROM AUTHOR]

We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co[sub 20](Cu[sub 1-x]Ge[sub x])[sub 80] ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co[sub 3]Ge[sub 2] compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co[sub 3]Ge[sub 2]/Co junctionlike configuration. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A direct wafer bonding process has been developed to accurately control both the bonding interface twist and tilt angles between a monocrystalline layer and a bare monocrystalline wafer. This process is based on the bonding of twin surfaces produced by splitting a single wafer, using for instance the Smart Cut® process. A targeted control of ±0.005° is obtained for the twist angle without any crystallographic measurement. Moreover, pure twist-bonded interfaces have been artificially made between two (001) bonded silicon surfaces. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a formula for exploring the effects of misfit dislocation distribution and capping layer on excess stress. Introduction of a parameter denoting the ratio of the density of misfit dislocations from the upper to the lower interface; Extension of threading dislocation along the direction of the crossover if strain relaxation takes place.

Examines copper (Cu) silicide formation on SiGeC/Si and SiGe/Si layers. Investigation of Cu reaction with epitaxial SiGeC/Si layers; Comparison between reaction to SiGeC/Si and SiGe/Si layers of Cu; Sequence phase formation of Cu reaction with monocrystalline silicon; Factors influencing the slow supply of Cu atoms to silicide/Si interface.

The morphology of the crystalline–amorphous interface is studied during solid-phase epitaxial crystallization of amorphous GeSi alloy layers with depth-dependent Ge distributions. The interface is shown to undergo an initial strain-induced roughening transition when the Ge concentration exceeds 6.6 at. %. As crystallization continues in strain-relaxed material the interface is shown to further roughen or smooth in response to changes in the Ge distribution. This evolution of the interface morphology is shown to be a consequence of kinetic effects whereby the differential velocity between the leading and trailing edges of the rough interface increases in regions of increasing Ge concentration and decreases in regions of decreasing Ge concentration. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]