bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of High-k Dielectrics by Combined Spectroscopic Ellipsometry (SE) and X-Ray Reflectometry (XRR)
Authors: Sun L. , Defranoux C. , Stehle J.L. , Boher P. , Evrard P. , Bellandi E. , Bender H. 
Published: April 2011

ABSTRACTAt present, new high-k dielectric materials are being intensively investigated to replace the silicon dioxide as gate dielectric for the next generation of electronic devices. Several candidate materials (such as ZrO2, HfO2, Al2O3) and deposition processes are currently under investigation. Because the layer thickness which is required in the next generations of devices is of the order of few nanometers, a precise determination and control of layer thickness will be mandatory. Although spectroscopic ellipsometry (SE) is well established non-contact, non-destructive and precise technique for determining thickness and optical properties of thin films, it becomes more difficult to obtain this information unambiguously and simultaneously for ultra-thin films with traditional SE alone because of possible high correlations between film structure and optical properties. The grazing x-ray reflectometry (XRR) is a complementary nondestructive optical technique and can be used to unambiguously determine ultra thin film thickness accurately. Combined with ellipsometry technique together, it will provide a promising way to characterize high-k gate dielectrics including thickness, roughness, interfacial layers and material composition information etc. In this paper, the principles for both SE and XRR will be briefly reviewed and limitation of each technique will be discussed. Following the high-k gate dielectric exploration and development, examples of using the combined SE/XRR techniques will be presented.
Atomic Layer Deposition of Silica and Group IV Metal Oxides Nanolaminates
Authors: Zhong Lijuan , Chen Fang , Campbell Stephen A. , Gladfelter Wayne L. 
Published: April 2011

ABSTRACTWith alternating exposure of Si (100) substrates to tri (t -butoxy) silanol and anhydrous zirconium nitrate, mixed films of zirconia and silica were deposited at 162°C. The films were atomically smooth and their thickness was uniform across the entire substrate. The maximum growth rate of 12 Å/cycle implies deposition of more than one monolayer per cycle. A singular reflection in the low angle X-ray scattering pattern indicates an ordered bi-layer structure. Similar nanolaminate structures were also formed using anhydrous nitrates of hafnium and tin.
Atomic Scale Modeling of ZrO2 and HfO2 Atomic Layer Deposition on Silicon: Linking Density Functional Theory and Kinetic Monte Carlo
Authors: Estève A. , Jeloaica L. , Mazaleyrat G. , Dkhissi A. , Djafari Rouhani M. , Ali Messaoud A. , Fazouan N. 
Published: April 2011

ABSTRACTThe present paper establishes some required elements from both Quantum calculations and Kinetic Monte Carlo Modeling to perform full atomic scale simulations of Zirconia and Hafnia Atomic Layer Deposition (ALD) on Silicon technology process. In this view, we present quantum cluster calculations that investigate reaction pathways being part of the chemical reactions taking place at the different stages of the ALD growth. In particular, we detail ongoing research effort on the hydrolysis of adsorbed HfCl3 and ZrCl3 on ultra-thin SiO2. At very low water dose, the hydrolysis appears to be un-favourable. The complete reaction pathways with their associated activation barrier are detailed. We then show that actual available mechanisms emanating from quantum calculations are not sufficient to give a coherent picture of the layer structuring through a Kinetic Monte Carlo technique with the hope of giving new directions for further quantum studies.
Electronic structure of Zn(Mn)O surface alloy - a resonant photoemission study
Authors: Guziewicz E. , Kopalko K. , Sadowski J. , Guziewicz M. , Golacki Z. 
Published: April 2011

ABSTRACTElectronic structure of Mn/ZnO system has been investigated by synchrotron radiation photoemission. Manganese vacuum deposition was done at room temperature onto a ZnO(0001) single crystal for coverage ΘMn < 4 ML. Photoemission spectra taken near Mn3p-Mn3d absorption edge after each deposition step show resonant enhancement of Mn3d states within 10 eV of the Fermi level. The experimentally deduced partial Mn3d density of states for Θ > 1.2 ML shows at least three features: a major Mn3d structure at 3.8–4.5 eV below the Fermi energy, a valence structure at lower binding energy (1–3 eV) and a broad satellite in the 5.5 – 9 eV range. The branching ratio of satellite/main structure increases with deposition from 0.33 for 0.4 ML to 0.65 for 4 ML. After annealing up to 500 C the satellite/main ratio decreases to 0.43 indicating a high degree of hybridization between the Mn3d states and valence band of ZnO. After annealing no manganese cap layer was found at the crystal surface as was confirmed by the lack of metallic Fermi edge in photoemission spectra and by scanning Auger spectroscopy experiment. The photoemission Mn3p core level spectra taken after annealing consist of two components separated by about 4eV. It is evidence that at least two manganese states are observed in the Mn-ZnO interface region.
Photo- and Thermal Annealing-Induced Processes in Carbon Nanotube Transistors
Authors: Shim Moonsub , Siddons Giles P. , Jeong Jae Kyeong , Merchin David 
Published: April 2011

ABSTRACTPhotoinduced conductivity changes and effects of thermal annealing in carbon nanotube transistors have been examined. Low-intensity ultraviolet light significantly reduces the p-channel conductance while simultaneously increasing the n-channel conductance. A combination of optical absorption and electron transport measurements reveals that these changes occur without variations in dopant concentrations. Measurements with different metals reveal that UV induces oxygen desorption from the electrodes rather than from nanotubes. In Ti-nanotube contact where the Schottky barrier plays an important role, photodesorption of oxygen mainly occurs from the native oxide of Ti electrodes. Decrease in the p-channel conductance arises from the metal work function change which causes larger hole Schottky barrier. Non-Schottky Pd-contacted nanotube transistors do not show photodesorption effects with low intensity UV. Thermal annealing of nanotube transistors with Ti/Au electrodes also leads to the disappearance of the photodesorption effects. However, a noticeable p-doping is observed to upon air exposure after thermal annealing.
Observation of Size Confinement Effects of Excitons in AgX Nanocrystals by Cryo-Energy-Filtering TEM/EELS
Authors: Oleshko Vladimir P. 
Published: April 2011

ABSTRACTThe non-uniform size-dependent contrast of AgBr0.95I0.05 nanocrystals (NCs) ranging from 22 to 80 nm in equivalent diameter (dc) observed by cryo-energy-filtering TEM is referred to predominant excitations at the surfaces and near the edges. When the fields due to surface losses reach throughout the structure, they couple and the probability for their generation becomes periodic in the NC size. Since electronic sum rules must be satisfied, the surface excitations reduce the strength of the bulk excitations. Coupling of surface and volume losses may cause oscillations of the image intensities with the NC size. The appearance of such oscillations demonstrates a size confinement of excitations of valence electrons due to contributions to the energy-level structure from carrier confinement and surface states. The imaginary part of relative dielectric permittivity derived from electron energy-loss spectra shows an enhanced intensity of the band at 4 eV for NCs with dc = 50±4 nm as compared to those of 109±7 nm in size, while the bands at 7 eV and at 10 eV appear to be suppressed. An increase of the intensity of exciton-assisted direct interband transition at 4 eV (Γ8-, Γ6- → Γ6) correlates with the size-dependent enhancement of free exciton luminescence from AgBr NCs, when their size is less than 100 nm.
Crystallographically-Oriented Electrochemically-Deposited Bismuth Nanowires
Authors: Rabin Oded , Chen Gang , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTBismuth nanowires 200 nm in diameter were synthesized via electrochemical deposition into the pores of anodic alumina templates. A near neutral pH solution and a special sample holder were employed. Both polycrystalline and (012) oriented bismuth nanowire arrays were prepared. The electrical resistance of the samples versus temperature was measured in the range 2–300 K, and the results were fitted to a transport model. Despite the crystallographic alignment of the nanowire array, the model calculations suggest the dominance of a temperature independent scattering mechanism (such as grain boundary or nanowire boundary scattering). The results are compared to the electrical resistance of nanowires formed by impregnation techniques.
Effect of K/Bi ordering on the electronic structure of K2Bi8Se13
Authors: Bilc Daniel I , Larson Paul , Mahanti S.D. , Kanatzidis M.G. 
Published: April 2011

ABSTRACTK2Bi8Se13 belongs to a class of complex chalcogenides which show potential for superior thermoelectric performance. This compound forms in two distinct phases, α and β. The β-phase, which has several sites with mixed K/Bi occupancy is a better thermoelectric. To understand the origin of this difference we have carried out electronic structure calculations within ab initio density functional theory using full potential linearized augmented plane wave (FLAPW) method. The generalized gradient approximation was used to treat the exchange and correlation potential. Spin-orbit interaction (SOI) was incorporated using a second variational procedure. The α-phase is found to be a semiconductor with an indirect band gap of 0.47eV compared to 0.76eV for the observed direct optical gap. For the β-phase we have chosen two different ordered structures with full occupancies of K and Bi atoms at the “mixed sites”. The system is a semi-metal for both the ordered structures. To incorporate the effect of mixed occupancy we have chosen a 1x1x2 supercell with an alternative K/Bi occupancy at the “mixed sites”. The superlattice ordering gives a semiconductor with an indirect gap of 0.38eV. Mixed occupancy is crucial for the system to be a semiconductor because the Bi atoms at the “mixed sites” stabilize the p orbitals of the neighboring Se atoms by lowering their energy, and opening up a gap at the chemical potential.
Extended Huckel electronic calculations for PrFe4P12
Authors: Galvan D. H. , Samaniego J. C. 
Published: April 2011

ABSTRACTElectronic structure calculations were performed on PrFe4P12 filled skutterudite, in order to provide more information regarding its properties. The energy bands yielded information regarding the metallic behavior as well as a mini gap of 0.02 eV. Total and projected Density of States (DOS) yielded information for the existence of a hybridization between Pr -f, Fe -d and P -p orbitals. Hence, this compound could be considered a likely candidate as a thermoelectric compound.
Irreversible Tensile Stress Development in PECVD Silicon Nitride Films
Authors: Hughey Michael P. , Cook Robert F. 
Published: April 2011

ABSTRACTThe thermo-mechanical behavior of plasma-enhanced chemical vapor deposited (PECVD) silicon nitride films are investigated during thermal cycling and annealing. It is well known that PECVD films have a large amount of incorporated hydrogen that evolves on heating. This reduction in hydrogen is shown to be directly responsible, via constrained volume decrease, for irreversible increases in tensile stress. It is demonstrated that no stress equilibrium is attained during very long time anneals. The thermal cycling behavior of PECVD films can be modeled by chemical reaction theory, with the irreversible development of film stress a mechanical consequence. The model assumes first-order reaction kinetics of Si-H and N-H bonds, which react to form molecular hydrogen and reformed network bonds. The activation energy of reaction is not single-valued, indicative of the strong influence that the local bonding environment has on bond energies. If the incorporated hydrogen reactant pairs are assumed to be normally distributed with activation energy, irreversible stress development is well modeled, and the mean activation energy ranges from 2.44 to 2.93 eV for 150 to 300 °C deposited films.
Solutions and Discussions of thin film Undergoing the Nonlinear Peeling
Authors: Wei Yueguang , Shu Siqi , LNM Ying Du 
Published: April 2011

ABSTRACTBased on the bending model, three double-parameter criteria characterizing thin film peeling process are introduced and analyzed in detail. Three double-parameter criteria include: (1) the interfacial fracture toughness and the separation strength, (2) the interfacial fracture toughness and the interfacial crack tip slope angle of thin film, and (3) the interfacial fracture toughness and the critical von Mises effective strain of thin film at crack tip. Based on the three double-parameter criteria, the thin film nonlinear peeling problems are solved analytically for each case. The results show that the solutions of thin film nonlinear peeling based on the bending model are very sensitive to the model parameter selections. Through analyses and comparisons for different solutions, a connection between solutions based on the bending models and based on the two-dimensional elastic-plastic finite element analysis is obtained.
Stress-assisted Copper-induced Lateral Growth of Polycrystalline Germanium
Authors: Hekmatshoar B. , Shahrjerdi D. , Mohajerzadeh S. , Khakifirooz A. , Robertson M. , Afzali-Kusha A. 
Published: April 2011

ABSTRACTLateral growth of poly-Ge at temperatures as low as 150°C is reported. External mechanical stress has been properly manipulated to drive the low temperature Cu-induced crystallization of poly-Ge wherever Cu is deposited to form the crystallization seed for lateral growth. Uniaxial compressive stress has been externally applied to the Ge layer by bending the flexible PET substrate inward. A 10-hour period thermo-mechanical post-treatment in the presence of 0.05% equivalent compressive strain leads to a growth rate of 2.5 μm/hour in the direction of the applied stress and 1.8 μm/hour in the perpendicular direction, as confirmed by SEM analysis. We believe that partial growth of the Cu-seeded poly-Ge region in the form of tetragonal structures is the key feature which leads to the lateral growth of the pure-Ge strip. Elimination of the compressive stress hinders the lateral growth completely, even at reasonably high temperatures.
Microstructural aspects of fracture in nanolayered TiAlCrN thin films
Authors: Santana A. E. , Karimi A. , Derflinger V. H. , Schütze A. 
Published: April 2011

ABSTRACTThis paper studies the effects of bilayer thickness and chromium content on the microstructure and mechanical properties of nanolayered TiAlN/CrN thin films. By rotation of samples holder and control of targets activity, a variety of multilayers and chemically modulated thin films were grown on WC-Co substrates using cathodic arc PVD. Conventional and high resolution TEM showed that aluminum contributes to refinement of structure while chromium favors the formation of coarse columnar morphology. Consequently, TiAlN layers periodically interrupt the formation of columns in CrN layers in multilayer films, while in chemically modulated samples the columns are not interrupted leading thus to the formation of strongly columnar films. Both Cr content and bilayer thickness contribute to hardness enhancement. Effect of Cr arises from the formation of hard fcc-(CrAl)N phase to the detriment of softer wurtzite-like hcp-AlN. The contribution of bilayer thickness is explained by the grain refinement based on Hall-Petch effect and the formation of highly stressed columnar structures with (111) preferred orientation. Such structural modifications strongly influence crack modes and morphologies as observed using AFM and FIB cross-section of indents. Thin bilayer films exhibit well-organized straight cracks parallel to the contact edge between indenter and film, while large bilayer films show a network of discontinuous irregular mud cracks attributed to grain boundary sliding. Refinement of structure favours crack meandering and branching that prevents the propagation of large cracks with more dramatic effects.
Microstructure Evolution of On-substrate NiTi Shape Memory Alloy Thin Films
Authors: Wang Xi , Lai Ann , Vlassak Joost J. , Bellouard Yves 
Published: April 2011

ABSTRACTWhen deposited at room temperature, sputtered NiTi thin films are amorphous and need to be crystallized before they can be used as a functional material. We present the results of an annealing study on substrate-constrained NiTi shape memory thin films. Amorphous films of a NiTi shape memory alloy were deposited by UHV sputtering. Films of thickness 1.0 μm were grown on (100) Si wafers both with and without an LPCVD SiNx barrier. The as-deposited films were annealed in vacuum at temperatures ranging from 500°C to 800°C. The microstructure of the annealed films was characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and Rutherford back scattering (RBS).
Thermal Activation of Beryllium in GaN Grown by RF-Plasma Molecular Beam Epitaxy
Authors: VanMil B. L. , Lee Kyoungnae , Wang Lijun , Giles N. C. , Myers T. H. 
Published: April 2011

ABSTRACTDifferences in the optical activity of Be in GaN epilayers grown on different surface polarities by rf-plasma molecular beam epitaxy are investigated. Nitrogen-polar GaN doped with Be exhibits a significantly higher intensity of donor-acceptor pair (DAP) photoluminescence (PL) than similarly doped Ga-polar GaN, indicating the Be is incorporating at microscopically different sites, or possibly is forming different compensating complexes. Highly Be-doped Ga-polar GaN apparently forms isolated polarity-inverted regions which then incorporate Be via the N-polar mechanism resulting in the DAP PL. High temperature annealing of the Ga-polar layers both under nitrogen/hydrogen mixtures and under pure nitrogen atmospheres activates the DAP PL.
Effects of growth interruption on the structural and optical properties of GaN self-assembled quantum dots
Authors: Hoshino K. , Kako S. , Arakawa Y. 
Published: April 2011

ABSTRACTWe report the effects of thermal annealing and growth interruption on the formation of GaN self-assembled quantum dots (QDs) grown by low-pressure metalorganic chemical vapor deposition (MOCVD). For the uncapped QD structures, atomic force microscopy (AFM) analysis shows that the density of the QDs rapidly increases and then decreases with increasing the annealing time. This is due to the combined effect of the QD formation process and the ripening process. The size of the QDs increases with increasing the annealing time. We have also investigated the photoluminescence (PL) property of the AlN capped QD structures with different growth interruption times. The PL from the QDs showed a red-shift with increasing the growth interruption time. In contrast, the PL from the wetting layer (WL) shows a blue-shift. These results indicate that the formation of the QDs is proceeding at the expense of the WL, which is consistent with the AFM analysis of the thermal annealing effect. These results show that the growth interruption plays an important role in the formation of the QDs.
Intersubband Absorptions in Doped and Undoped GaN/AlN Quantum Wells at Telecommunication Wavelengths Grown on Sapphire and 6H-SiC Substrates
Authors: Helman A. , Tchernycheva M. , Lusson A. , Warde E. , Julien F. H. , Monroy E. , Fossard F. , Si Dang Le , Daudin B. 
Published: April 2011

ABSTRACTIn this paper we present experimental and theoretical study of intersubband transitions at telecommunication wavelengths in GaN/AlN hexagonal-phase quantum wells grown by molecular beam epitaxy on sapphire substrates. Crossed structural and photoluminescence experiments show that strong in-plane carrier localization occurs due to thickness fluctuations at GaN/AlN interfaces. Fourier transform infrared spectroscopy and photo-induced absorption spectroscopy performed on doped and undoped samples reveal a systematic blue-shift of the e1-e2 transitions with doping due to many body interactions. A good agreement is achieved between experiments and self-consistent Schrödinger-Poisson calculations.
TEM investigation of defect reduction and etch pit formation in GaN
Authors: Vennemann Angelika , Dennemarck Jens , Kröger Roland , Böttcher Tim , Hommel Detlef , Ryder Peter 
Published: April 2011

ABSTRACTGaN samples of this study were chemically wet etched to gain easier access to the dislocation sturcture. The scanning electron microscopy and transmission electron microscopy investigations revealed four different types of etch pits. After brief etching, several dislocations with screw component showed large etch pits, which may be correlated with the core of the screw dislocation. By means of SiNx micromasking the dislocation density could be reduced by more than one order of magnitude. The reduction of threading dislocations in the SiNx region in GaN grown on 〈0001〉 sapphire is due to bending of the threading dislocations into the {0001} plane, such that they form dislocation loops if they meet dislocations with opposite Burgers vectors. Accordingly, the achievable reduction of the dislocation density is limited by the probability that these dislocations interact. Edge dislocations bend more easily on account of their low line tension. This results in a preferential bending and reduction of dislocations with edge character.
Strain evolution and phonons in AlN/GaN superlattices
Authors: Darakchieva V. , Paskov P. P. , Schubert M. , Valcheva E. , Paskova T. , Arwin H. , Monemar B. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTAlN/GaN superlattices (SLs) with different periods grown on GaN buffer layers were studied by infrared spectroscopic ellipsometry (IRSE), Raman scattering (RS) and highresolution reciprocal space mapping (RSM). The lattice parameters and the degree of strain in the GaN buffer and the SL constituents were determined. Phonon modes originating from the buffer layer and the SL sublayers were identified and their frequency shifts were correlated with the strain state of the films.
MOCVD Growth of InAlAsSb Layer for High-Breakdown Voltage HEMT Applications
Authors: Yokoyama Haruki , Sugiyama Hiroki , Oda Yasuhiro , Sato Michio , Watanabe Noriyuki , Kobayashi Takashi 
Published: April 2011

ABSTRACTThis paper studies the decomposition characteristic of group-III sources during InAlAsSb growth on InP substrates by metalorganic chemical vapor deposition (MOCVD) using trimethylindium (TMI), trimethylaluminum (TMA), trimethylantimony (TMSb) and arsine (AsH3). A composition analysis of InAlAsSb layers shows that the group-III compositions in the InAlAsSb layer change remarkably when the flow rate of the group-V source is varied. To clarify the reason for this phenomenon, the growth rates of InAsSb and AlAsSb component are examined. Their changes indicate that TMSb suppresses the decomposition of TMA while AsH3 enhances it. Moreover, the HEMT structure with InP/InAlAsSb Schottky barrier layer, whose InP layer acts as a recess-etch-stop layer, is fabricated for the first time. The I-V characteristics of a fabricated Schottky barrier diode indicate that the reverse leakage current of InP/InAlAsSb is about one order of magnitude smaller than that of commonly used InP/InAlAs.