bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Patterning by Laser Induced Localized Chemistry
Authors: Lachish-Zalait Aurélie , Zbaida David , Klein Eugenia , Elbaum Michael 
Published: April 2011

AbstractA method is described for creating microscale-patterned surfaces by direct-write lithography. A tightly focused, low-power infrared laser beam is applied to a homogeneous precursor solution containing soluble reagents. When the laser is focused directly at a glass-solution interface, it initiates the local precipitation of a solid product that attaches firmly to the substrate. Operating the laser momentarily forms isolated spots, while moving the microscope stage or the laser spot draws continuous lines. The method has been demonstrated for metallic silver and gold, for oxidized copper, and for molybdenum disulfide, suggesting a broad generality in the range of suitable materials. Silver patterns were further modified by chemical reactions. Their morphology and physical properties can be altered during deposition by the use of capping agents, which may provide a handle for further functionalization.
Enlargement of Crystal Grain Size and Significant Inclusion of Hexagonal Diamond Phase in Ultra Pure Microcrystalline Silicon
Authors: Kamei Toshihiro 
Published: April 2011

AbstractWe have shown significant effects of atmospheric impurities on crystal grain sizes of hydrogenated microcrystalline Si (μc-Si:H), the growth surface of which is totally covered by hydrogen. By reducing impurity concentrations, two growth modes emerge, bordered at 250°C. In particular, at higher temperature growth mode, strong (220) preferential growth takes place, resulting in increased grain size. Appearance of this growth mode seems to be related to surface monohydride. Sharp x-ray diffraction peak in lower angle than (111) is observed, which stems from (10-10) crystal plane of hexagonal diamond Si. Its formation is related to (220) oriented crystallites. Implication of these results is the possibility of Si polytype control.
Nucleation-Control and Enhancement of Solid-Phase-Crystallization of SiGe-Heterostructure
Authors: Yamaguchi S. , Park S. K. , Sugii N. 
Published: April 2011

AbstractThe crystallization of SiGe-heterostructure in which a thin Ge layer put between Si layers has been investigated. When the Ge layer is inside the Si layer, the crystallization phenomena are similar to those of SiGe alloy layer; Ge completely diffuses in Si layer during the crystallization. When the Ge layer is at the interface between the Si layer and the quartz substrate, significant enhancement of crystallization has been found. In this structure, decrease in surface free-energy increases the nucleation rate at the interface and causes anomalous localization of Ge at the interface. When the Ge layer is on the surface of the Si layer, the crystallization property is quite different from the other structures. The underlying Si layer has large and aligned grains when the furnace annealing is assisted by the laser-annealing.A part of this work was carried out under the ASET program supported by NEDO, Japan.
Reconciliation of the microcrystalline and the continuous random network model for amorphous semiconductors
Authors: Bording J.K. , Tafto J. 
Published: April 2011

AbstractWe show by molecular dynamics simulations, that the radial distribution function of an amorphous material does not change significantly by introducing a considerable volume fraction of nanocrystals. The nanocrystals, embedded in a continuous random network, ensure a certain degree of medium range order in the amorphous material. Our simulations, which are on germanium, show that microcrystals smaller than 2 nm can comprise at least 20 % of the volume without significantly changing the radial distribution function from that of pure continuous random network. By increasing the size of the crystals, without altering the crystal to amorphous volume ratio, the radial distribution changes. The molecular dynamics simulations show that the nanocrystals are unchanged at low temperature. At higher temperature the mobility and critical size of the grains increase, transforming the sub-critical crystalline grains into the surrounding continuous random network matrix.
Comparison of 500nm InGaN/GaN QW Emission Properties Induced by Piezoelectric Field Effect and Phase Separation
Authors: Kee Bong , Koh J.M. , Yoon Euijoon 
Published: April 2011

ABSTRACTTwo kinds of InGaN/GaN single quantum well with emission wavelength of 500nm were obtained by employing piezoelectric effect and phase separation with different growth methods. Their emission properties are studied by measuring temperature and photo-excitation power dependent photoluminescence and electrolluminescence. The 500nm luminescence from the sample obtained by piezoelectric effect shows very weak temperature and excitation power dependent, on the other hand, it shows profound band tail broadening at both high temperature and low excitation power for phase separated sample which mean the strong localized state exist. We observed highly bright spots with longer wavelength then that of matrix in the phase separation sample and we believe that high emission efficiency can be obtained from these indium rich clusters.
Current Injection UV-Emission from InAlGaN Multi-Quantum-Well Light-Emitting Diodes
Authors: Kinoshita A. , Hirayama H. , Ainoya M. , Kim J. S. , Hirata A. , Aoyagi Y. 
Published: April 2011

ABSTRACTInAlGaN quaternary material is very attractive for realizing ultraviolet (UV) emitting devices working at 300 – 350 nm wavelength range. We demonstrate current injection into 340 nm-band InAlGaN based UV light emitting diodes (LEDs), for the first time, fabricated by metal organic vapor phase epitaxy (MOVPE). We performed current injection into AlGaN/AlGaN multi quantum well (MQW), bulk InAlGaN quaternary and InAlGaN/InAlGaN MQW LEDs through Mg-doped AlGaN/GaN superlattice hole conductive layers. The injected current density was ranging 0 – 0.5 kA/cm2 under pulsed or CW operation. The intensity of both photoluminescence (PL) and electroluminescence for InAlGaN quaternary-based LED was much higher than that for AlGaN based LEDs at room temperature. From these results InAlGaN quaternary-based QWs are expected to realize high intensity UV LEDs and LDs.
Improved Optical Quality of BAlGaN/AlN MQW Structure Grown on 6H-SiC Substrate by Controlling Residual Strain Using Multi-Buffer Layer
Authors: Takano Takayoshi , Kawanishi Hideo , Kurimoto Makoto , Ishihara Yoshiyuki , Horie Masato , Yamamoto Jun 
Published: April 2011

ABSTRACTBAlGaN and (BAlGaN/AlN) multi-quantum-wells (MQWs) structure were grown on 6H-SiC substrate by a low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). Estimated boron compositions of the BAlGaN quantum wells by an Auger electron spectroscopy (AES) analysis were 0% to 13%. Photoluminescence (PL) spectra around 260 nm were observed at room temperature. The full-width at half maximum (FWHM) of PL spectra for BAlGaN/AlN MQW structure(with 2% of boron) was narrowed from 360 meV to 179 meV, as the residual strain in the BAlGaN well layer was decreased from 1.3% to 1.0% by increasing the Al content in the quantum wells.
Indium incorporation and surface segregation during InGaN growth by molecular beam epitaxy
Authors: Chen Huajie , Feenstra R. M. , Northrup J. E. , Neugebauer J. , Greve D. W. 
Published: April 2011

ABSTRACTInGaN alloys with (0001) or (000) polarities are grown by plasma-assisted molecular beam epitaxy. Scanning tunneling microscopy images, interpreted using first-principles theoretical cal- culations, show that there is strong indium surface segregation on InGaN for both (0001) and (000) polarities. The dependence on growth temperature and group III/V ratio of indium incorporation in InGaN is reported, and a model based on indium surface segregation is proposed to ex- plain the observations.
The Effect of Buffer Layers in Mocvd Growth of Gan Film on 3C-SiC/Si Substrate
Authors: Park C. I. , Kang J. H. , Kim K. C. , Lim K. Y. , Suh E.-K. , Nahm K. S. 
Published: April 2011

ABSTRACTThe growth of GaN films on Si substrates is very attractive work because of irreplaceable merits of Si wafer such as low cost, high surface quality, large area wafer availability, high conductivity and well-established processing techniques.In this work, we studied the effect of buffer layers to grow high quality GaN films on 3C- SiC/Si(111) substrates. GaN films were grown on 3C-SiC/Si(111) by metalorganic chemical vapor deposition (MOCVD) using various buffer layers (GaN, AlN, and superlattice). The surface morphology and structural and optical properties of GaN films were investigated with atomic force microscopy (AFM), x-ray diffraction (XRD), Raman spectroscopy, and Photoluminescence (PL), respectively. GaN films grown using superlattice buffer layer showed only c-oriented (0002) plane of GaN from the XRD analysis. Raman spectra showed that the E2 high mode agreed with the selection rule was well observed in all GaN films. The A1(TO) and E1(TO) mode were appeared for GaN grown without buffer layer, whereas the E1(TO) mode was additionally appeared in the GaN films grown with GaN buffer layer. In the PL spectra at low temperature, the peaks associated with band edge emission and donor-accepter pair (D0A0) were observed in GaN films grown without buffer layer or with GaN buffer layer and AlN buffer layer. GaN films grown with superlattice buffer layer showed band edge and very weak D0A0 emission. The root mean square (RMS) roughness of the GaN film grown on superlattice buffer layer was only 4.21 Å Our experimental results indicated that the buffer layer affects crucially the qualities of GaN films grown on the 3C-SiC/Si substrate. Superlattice buffer layer improved the surface morphology as well as structural and optical properties of GaN films.
Nucleation of GaN on (0001) sapphire during MOCVD growth: an atomic force and high resolution electron microscopy study
Authors: Degave F. , Ruterana P. , Nouet G. , Je J.H. , Kim C.C. 
Published: April 2011

ABSTRACTThe morphology and microstructure of GaN nucleation layers have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The nucleation layers were grown at 500°C by metalorganic chemical vapour deposition (MOCVD) on (0001) sapphire. Different deposition times were used in order to investigate the evolution of the nucleation layer and try to understand the growth mechanisms. Systematically, it was found that the thinnest layers are mainly defect free and have a cubic structure. The (111) GaN planes are parallel to (0001) sapphire. It is shown that the nucleation follows the Volmer- Weber mechanism and as the islands height increases, the transformation from cubic to wurtzite starts from the substrate surface.
Stability, diffusion, and complex formation of beryllium in wurtzite GaN
Authors: Limpijumnong Sukit , Walle Chris G. Van de , Neugebauer Jörg 
Published: April 2011

ABSTRACTWe have studied the properties of Be dopants in GaN using first principles calculations. Substitutional Be on a Ga site acts as an acceptor, but interstitial Be poses a potential problem because of its low formation energy and donor character. We study the diffusion of interstitial Be and find it to be highly anisotropic. We also study the formation of complexes between substitutional and interstitial Be, and between substitutional Be and hydrogen. We have calculated the Be-H vibrational modes to aid in experimental identification of such complexes.
Characteristics of Fielo-GaN Grown by Hydride Vapor Phase Epitaxy
Authors: Usui Akira , Sunakawa Haruo , Kobayashi Kenji , Watanabe Heiji , Mizuta Masashi 
Published: April 2011

ABSTRACTThe crystal quality of facet-initiated epitaxial lateral overgrowth (FIELO) -GaN, in particular, that in the vicinity of the GaN surface, is reported. It is shown that the surface smoothness of FIELO-GaN enables us to use it as an “epi-ready” substrate. The crystallinity of FIELO-GaN is evaluated by x-ray rocking curve (XRC) measurements. We indicate that the FWHM of XRC should be reduced with the decrease of the dislocation density. We previously reported that the dislocation behavior of FIELO-GaN causes the tilting of the c-axis in the overgrown regions. By using scanning reflection electron microscopy (SREM), however, we show that the tilting on the surface of thick FIELO-GaN was negligibly small.
Photo- and cathodoluminescence investigations of piezoelectric GaN/AlGaN quantum wells
Authors: Goldys E.M. , Godlewski M. , Phillips M.R. , Toropov A.A. 
Published: April 2011

ABSTRACTWe have examined multiple quantum well AlGaN/GaN structures with several quantum wells of varying widths. The structures had strain-free quantum wells and strained barriers. Strong piezoelectric fields in these structures led to a large red shift of the PL emission energies and long decay times were also observed. While the peak energies could be modelled using the effective mass approximation, the calculated free exciton radiative lifetimes were much shorter than those observed in experiments, indicating an alternative recombination mechanism, tentatively attributed to localised excitons. Cathodoluminescence depth profiling revealed an unusually small penetration range of electrons suggesting that electron-hole pairs preferentially remain within the multiple quantum well region due to the existing electric fields. Spatial fluctuations of the cathodoluminescence intensity were also observed.
IR-VUV Dielectric Function of Al1−xInxN determined by Spectroscopic Ellipsometry
Authors: Kasic A. , Schubert M. , Rheinländer B. , Off J. , Scholz F. , Herzinger C. M. 
Published: April 2011

ABSTRACTSpectroscopic Ellipsometry from the mid-infrared (mid-ir) to the vacuum-ultraviolet (vuv) spectral range (350 cm−1 … 8.8 eV) is used to study the optical properties of hexagonal MOVPE-grown Al1−xInxN films for 0.11 ≤ × ≤ 0.21. The AlInN E1(TO) phonon shows a onemode behavior in contrast to recent theoretical predictions [H. Grille, Ch. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Approximately 120 nm thick Al1−xInxN films grown on slightly compressively strained hexagonal GaN buffer layers reveal the influence of in-plane strain on the E1(TO) phonon mode frequencies. Al1−xInxN deposited directly on [0001] sapphire substrate possesses E1(TO) mode frequency which indicate fully relaxed film growth. For highquality Al0.890In0.110N one A1(LO) phonon mode was observed. Furthermore, we present the complex dielectric function of hexagonal Al0.872In0.128N from the mid-ir to vuv spectral range.
Growth and Characterization of Epitaxial Al1−xInxN Films Grown on Sapphire (0001) by Plasma Source Molecular Beam Epitaxy
Authors: Lukitsch M. J. , Auner G. W. , Naik R. , Naik V. M. 
Published: April 2011

ABSTRACTEpitaxial Al1−xInxN films (thickness ∼150 nm) with 0 ≤ × ≤ 1 have been grown by Plasma Source Molecular Beam Epitaxy on Sapphire (0001) at a low substrate temperature of 375°C and were characterized by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), and atomic force microscopy (AFM). Both RHEED and XRD measurements confirm the c-plane growth of Al1-xInxN films on sapphire (0001) with the following epitaxial relations: Nitride [0001] ∥ Sapphire [0001] and Nitride < 0110 > ∥ Sapphire <2110>. The films do not show any alloy segregation. However, the degree of crystalline mosaicity and the compositional fluctuation increases with increasing In concentration. Further, AFM measurements show an increased surface roughness with increasing In concentration in the alloy films.
Review of Facet Controlled Epitaxial Lateral Overgrowth (FACELO) of GaN via Low Pressure Vapor Phase Epitaxy
Authors: Hiramatsu Kazumasa , Miyake Hideto 
Published: April 2011

ABSTRACTFacet structures of GaN grown by epitaxial lateral overgrowth (ELO) via low pressure-metalorganic vapor phase epitaxy (LP-MOVPE) are controlled by growth conditions such as reactor pressure and growth temperature, where this technique is called FACELO (Facet Controlled ELO). The mechanism of the morphological change is discussed based on stability of the surface atoms. The propagation mechanism of the threading dislocations for the different GaN facet structure is also investigated. The distribution and density of the threading dislocations are observed by the growth pit density (GPD) method. Two typical models employing the FACELO are proposed; in one model, the dislocation concentrates only on the window area and, in the other model, only in the coalescence region in the center of the mask. In the latter model, the dislocation density is dramatically dropped to the order of 105−6 cm−2 with good reproducibility.
Growth and Characterization of GaN Underlying Layer Used in Blue-Violet GaN-Based Laser Diodes on Sapphire
Authors: Funato Kenji , Hino Tomonori , Tomiya Shigetaka , Miyajima Takao , Asano Takeharu , Tojyo Tsyuyoshi , Hashimoto Shigeki , Yanashima Katsunori , Uchida Shiro , Tmamura Koshi , Kobayashi Toshimasa , Ikeda Masao 
Published: April 2011

ABSTRACTThe underlying GaN layers on which laser diodes are fabricated have been improved through two steps. In the first step, GaN single layer on sapphire was investigated. The residual strain and etch pit density were measured. We found that they reflect the optical quality. We found that the threading dislocation can be reduced to 4 × 108 cm−2. The optical quality depends on the residual strain and dislocation density. In the next step, we have utilized epitaxial lateral overgrowth ELO) technique. The optimized GaN layer on sapphire with the smallest dislocation density was used as seed layer. In the wing region of ELO-GaN, the threading dislocation density was reduced to 1 × 106 cm−2. On the other hand, in the seed region, dislocation density remained 4 × 108 cm−2. Photoluminescence intensity in the wing region was three times as large as that in the seed. The laser diodes were fabricated on the ELO-GaN layer, so that the ridge stripe was fabricated over the wing region, and its properties were compared with those of laser diodes on sapphire. It was found that the lifetime can be increased by using the ELO-GaN layer as the underlying layer.
A Growth Technique to Make Extensive Atomically Flat Silicon Surfaces
Authors: Lee Doohan , Schroeder Todd , Engstrom James , Blakely Jack 
Published: April 2011

AbstractWe have carried out a series of experiments aimed at producing arrays of mesas on both Si(001) and Si(111) which are free from atomic steps. These are of interest in CMOS technology and for quantum well structures. They also provide interesting substrates for fundamental surface science experiments. In previous work we have created atomically flat regions surrounded by ridges through an evaporation method. The present work ‘inverts’ the previous process by using a pattern of trenches to define the mesas and then depositing Si to grow the atomic steps off the edges. The mesas are created on Si wafers, which are ~1° from the (111) and (001) plane by lithography and reactive ion etching. Step-free mesas were formed on Si(111) but not yet on Si(001). Both the evaporation and this new growth technique rely on step flow to move the steps to the edges of the flat areas. Although the evaporation method is simpler, an advantage of the growth technique is that it can be carried out at lower temperature. The maximum size of mesa that can be made free of atomic steps depends on the combination of temperature and deposition rate. On very large step-free terraces nucleation of islands and concentric arrays of mono-atomic steps are observed; these correspond to the vacancy pits observed with the evaporation method.
Ab initio study of Ge Adsorption on H-terminated Si(001) Surfaces
Authors: Ohno Takahisa , Nara Jun , Ezaki Takahide 
Published: April 2011

AbstractThe Ge adsorption and diffusion processes on the monohydride terminated Si(001) surface are investigated by using first-principles total-energy calculations and kinetic Monte Carlo simulations. We find that the adsorbed Ge atoms tend to exchange sites with substrate Si dimer atoms. The site exchange plays an important role, which provides the most stable geometry and the easiest diffusion pathway. The Ge adatom migrates in the subsurface region instead of on the surface. The temporal variation in the adsorption geometry during diffusion is found. The Si atoms can become the surface diffusion species instead of the Ge atoms, as a result of the site exchange.
Structural and mechanical properties of amorphous Zr–based alloy thin films
Authors: Mayr S.G. , Moske M. , Samwer K. 
Published: April 2011

AbstractThe evolution of surface structures of coevaporated and sputtered amorphous Zr65Al7.5Cu27.5films with varying deposition conditions is investigated primarily with scanning tunneling microscopy (STM). While vapor deposited thin films reveal pronounced structure formation, depending on parameters, such as substrate temperature, film composition (variation of the Al versus the Cu content) and the angle of incidence, comparable sputtered films hardly show any structure formation. With the help of a numerical analysis of the STM data, surface diffusion, self–shadowing and energy transfer in the case of sputtering can be identified as the main structure forming mechanisms. Presuming these atomic processes, it is possible to model the main experimentally observed features of amorphous thin film growth by the use of stochastic continuum growth equations, which are numerically solved. Additionally, the connection to intrinsic stress formation during film growth is discussed.
Ultrafast Magnetization Reversal Dynamics on A Micrometer-Scale Thin Film Element Studied by Time Domain Imaging
Authors: Choi B.C. , Ballentine G. , Belov M. , Hiebert W.K. , Freeman M.R. 
Published: April 2011

AbstractPicosecond time scale magnetization reversal dynamics in a 15nm thick Ni80Fe20 microstructure (10μm×2μm) is studied using time-resolved scanning Kerr microscopy. The time domain images reveal a striking change in the magnetization reversal mode, associated with the dramatic reduction in switching time when the magnetization vector is pulsed by a longitudinal switching field while a steady transverse biasing field is applied to the sample. According to the time domain imaging results, the abrupt change of the switching time is due to the change in the magnetization reversal mode; i.e., the nucleation dominant reversal process is replaced by domain wall motion if transverse biasing field is applied. Furthermore, magnetization oscillations subsequent to reversal are observed at two distinct resonance frequencies, which sensitively depend on the biasing field strength. The high frequency resonance at f=2 GHz is caused by damped precession of the magnetization vector, whereas another mode at f≈0.8 GHz is observed to arise from domain wall oscillation.
The Ehrlich-Schwoebel Effect for Vacancies: Low-Index Faces of Silver
Authors: Haftel Michael I. 
Published: April 2011

AbstractWe employ surface-embedded-atom-method potentials to investigate the diffusion barriers of vacancies diffusing over and near steps on the low index faces of silver. Barriers for vacancy terrace diffusion, diffusion over step-edges, and diffusion along step edges, including around corners, are calculated. Vacancies are significantly less mobile than adatoms and have large Ehrlich-Schwoebel (ES) barriers on all three faces. For Ag(100) the diffusion barrier for vacancies along step-edges is virtually the same (474 meV) as on the terrace. As in diffusion near the step edge, vacancies encounter a significant increase (213 meV) in the activation barrier when diffusing around the corner of a vacancy island (the corner analogue of the ES barrier), but the excess barrier around a kink all but disappears because exchange diffusion is favorable there. The consequences of the vacancy diffusion barriers on 3D pitting and on island diffusion and coarsening are discussed.