bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of the Inter-Subband Scattering in Modulation-Doped AlxGa1-xN/GaN Heterostructures
Authors: Zheng Z. W. , Shen B. , Jiang C. P. , Guo S. L. , Liu J. , Zhou H. M. , Zhang R. , Shi Y. , Zheng Y. D. , Zheng G. Z. , Chu J. H. , Someya T. , Arakawa Y. 
Published: April 2011

AbstractMagnetotransport properties of Al0.22Ga0.78N/GaN modulation-doped heterostructures have been studied at low temperatures and high magnetic fields. The inter-subband scattering of the two-dimensional electron gas was observed. The inter-subband scattering is very weak and depends weakly on temperature when temperature is between 1.3 K and 10 K and becomes stronger with increasing temperature when temperature is higher than 10 K. The strain relaxation of the Al0.22Ga0.78N layer influences the inter-subband scattering. It is suggested that the inter-subband scattering is dominant by the elastic scattering when temperature is lower than 10 K, and changes to be dominant by the inelastic scattering of the acoustic phonons when temperature is higher than 10 K.
Electrical and Optical Studies of Si-Implanted GaN
Authors: Fellows James A. , Yeo Yung Kee , Hengehold Robert L. , Krasnobaev Leonid 
Published: April 2011

AbstractThe electrical and optical properties of Si-implanted GaN have been investigated as a function of ion dose, anneal temperature, and implantation temperature using Hall-effect measurements and photoluminescence. Implantation of 200 keV Si ions was made at room temperature and 800°C into MBE-grown GaN capped with 500 Å AlN at six different doses ranging from 1x1013 to 5x1015 cm-2. The samples were proximity cap annealed from 1050 to 1350°C for 5 min to 20 s using either a conventional furnace or rapid thermal annealing. For a given dose, electrical activation efficiencies and mobilities increase as the anneal temperature increases from 1050 to 1350°C. Generally, the higher the dose, the greater the activation efficiency for any given anneal temperature. For a sample implanted with a dose of 1x1015 cm-2 and annealed at 1350°C for 20 s, an electrical activation efficiency of 100% was obtained. Exceptional carrier concentrations and mobilities were obtained on all Si-implanted samples, and a comparison of the results was made between room temperature and 800°C implantation. Photoluminescence measurements were also performed in an effort to better understand the electrical activation behavior of the Si implants in GaN.
Electron transport in AlN under high electric fields
Authors: Collazo Ramón , Schlesser Raoul , Roskowski Amy , Davis Robert F. , Sitar Z. 
Published: April 2011

AbstractThe energy distribution of electrons transported through an intrinsic AlN film was directly measured as a function of the applied field, and AlN film thickness. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through films thicker than 95 nm and applied field between 200 kV/cm -350 kV/cm occurred as steady-state hot electron transport represented by a Maxwellian energy distribution, with a corresponding carrier temperature. At higher fields (470 kV/cm), intervalley scattering was evidenced by a multi-component energy distribution with a second peak at the energy position of the first satellite valley. Electron transport through films thinner than 95 nm demonstrated velocity overshoot under fields greater than 550 kV/cm. This was evidenced by a symmetric energy distribution centered at an energy above the conduction band minimum. This indicated that the drift component of the electron velocity was on the order of the “thermal” component. A transient length of less than 80 nm was deduced from these observations.
Improvements of Structural and Optical Properties of GaN/Al0.10Ga0.9N Multi-Quantum Wells by Isoelectronic In-doping
Authors: Wang Lianshan , Chua Soo Jin , Sun Wenhong 
Published: April 2011

Absratct:The effects of isoelectronic In-doping were studied on the structural and optical properties of 3-periods and 10-periods of GaN/Al0.10Ga0.90N multi quantum wells (MQWs). The GaN/Al40.10Ga0.90N MQWs were grown on u-GaN/sapphire via metalorganic chemical deposition (MOCVD) at 1050°C in H2 carrier gas. X-ray diffraction (XRD), and micro-Photoluminescence (PL) measurements revealed that In-doping into well layers improves the crystalline and optical properties of MQWs relative to those samples without In-doping. With increasing Trimethylindium (TMIn) flow rates from 4.2 mol/min to 42.6 mol/min, PL peaks from well layers obviously redshifted, due to the improvement of the strain along the interfaces between MQWS, irrespective of 3-periods or 10 periods MQWs. The improvement of the crystal quality was also confirmed by XRD.
Infrared and Ultraviolet Raman Spectra of AlN Thin Films Grown on Si(111)
Authors: Naik V. M. , Haddad D. , Danylyuk Y. V. , Naik R. , Auner G. W. , Rimai L. , Weber W. H. , Uy D. 
Published: April 2011

AbstractInfrared (IR) spectroscopy and ultraviolet near-resonance enhanced Raman scattering have been used as alternative techniques to characterize the AlN films grown on Si(111). Epitaxial AlN films have been prepared by plasma source molecular beam epitaxy (PSMBE) at growth temperatures of 400 and 650 oC. The AlN/Si grown at 650°C shows distinct reflection high-energy electron diffraction (RHEED) patterns with the following epitaxial relations: AlN [0001] ‖ Si [111], and AlN < 011 0 > ‖ Si < 112 >. This is in sharp contrast with the observation of a spotty RHEED pattern for AlN/Si sample grown at 400°C, which appeared the same when viewed along any Si azimuth. Furthermore, the X-ray diffraction (XRD) rocking curve width showed a significant reduction from 5.7ofor sample grown at 400°C to 2° for the one grown at 650°C. The observation of Raman active A1(LO) and E2, and IR active E1(TO) zone center phonons, in both the films, is in accordance with the c-axis orientation of the films. However, the observed phonon mode frequencies and line widths indicate that the AlN samples grown at 400°C have less strain but more disorder compared to the ones grown at 650°C in agreement with RHEED and XRD data.
Light Emission from Quantum-Dot-Like Structures in Cubic GaN/InGaN/GaN Double Heterostructures and Quantum Wells
Authors: Lischka K. 
Published: April 2011

AbstractRecent results of experimental investigations of cubic GaN/InGaN/GaN double heterostructures grown by molecular beam epitaxy are reviewed. Micro-Raman effect, photoluminescence and photoluminescence excitation spectroscopy as well as high-resolution x-ray diffraction measurements reveal clear evidence that the photoluminescence of these double heterostructures is related to In-rich quantum dot-like structures which are embedded within the InGaN layers. Annealing experiments corroborate the assumption that the formation of the In-rich clusters is terminated already during the growth process.
Piezoelectric Field and its Influence on the Pressure Behavior of the Light Emission from InGaN/GaN and GaN/AlGaN Quantum Wells
Authors: Suski T. , Perlin P. , Lepkowski S.P. , Teisseyre H. , Gorczyca I. , Prystawko P. , Leszczynski M. , Grandjean N. , Massies J. , Kitamura T. , Ishida Y. , Chichibu S.F. , Okumura H. 
Published: April 2011

AbstractIn this paper we review studies aiming at elucidation of the mechanisms responsible for anomalously low pressure coefficients of the light emission energy, dEE/dP, observed in quantum structures of InGaN/GaN and GaN/AlGaN. We have established that in hexagonal InGaN/GaN and GaN/AlGaN structures the main mechanism involved is related to the pressure induced increase of the piezoelectric field which determines also the strong red shift of the emission energy with thickness of the quantum well. To reproduce the experimental findings in InGaN/GaN case, it is necessary to take into account the dependence of the piezoelectric constants on the volume-conserving strain. Whereas the experimental results on a decrease of dEE/dP in GaN/AlGaNstructures can be fully accounted for within the linear elasticity theory. In contrast to these findings, dEE/dP magnitude measured in cubic InGaN/GaN quantum structures shows value close to changes of the InGaN bangap with pressure obtained from first principle calculations. The latter result is consistent with the absence of the built-in electric fields in the cubic nitride structures.
Photoluminescence of Excitons in n-Type In0.11Ga0.89N/In0.01Ga0.99N Multiple Quantum Wells
Authors: Monemar B. , Paskov P.P. , Bergman J.P. , Pozina G. , Kamiyama S. , Iwaya M. , Amano H. , Akasaki I. 
Published: April 2011

AbstractIn0.11Ga0.89N/In0.01Ga0.99N multiple quantum wells (MQWs) with heavily Si-doped barriers are shown to be very sensitive to a near surface depletion field. For a sample with 3 QWs, similar to what is often used in LEDs, only the QW most distant from the surface is observed in photoluminescence (PL). The appearance of a second lower energy PL peak below the ordinary QW exciton peak is a proof of a substantial band bending across the MQW structure. A similar effect seems to occur in pn-junctions having an MQW in the depletion region of a highly doped n-side. The strong depletion field is suggested to explain these results. The apparent absence of PL from the QWs closer to the surface (pn-junction) is tentatively ascribed to a loss of hole confinement in the strong depletion field.
Magneto-Spectroscopy of Two-Electron Transitions in Homoepitaxial GaN.
Authors: Wojdak M. , Baranowski J.M. , Wysmolck A. , Pakula K. , Stepnicwski R. , Potemski M. , Grzegory I. , Porowski S. 
Published: April 2011

AbstractTwo-electron transition occurs when the exciton bound to a neutral donor (DBE) recombines and leaves the donor in an excited state. The two-electron energy is therefore lower than that of the DBE peak by the difference in ground and excited state of the neutral donor. In a magnetic field the two-electron satellite splits into several components. These intra-donor excitations have been studied in homoepitaxial GaN up to magnetic fields reaching 23T. For Faraday (B‖c) configuration the two-electron transition splits mainly into 2s, 2p0, 2p+ and 2p- components. The total splitting between 2p+ and 2p- is equal to Landau energy. For Voigt (B???c) configuration in addition to transition to 2s, 2p0, 2p- and 2p+ there are additional lines which origin is discussed. It has been found that for two configurations of magnetic field the separation between 2p+ and 2p- is not exactly equal, what indicates the anisotropy of the electron effective mass. It has been found that m| = 0.205m0 and m??? = 0.225m0.
Measurement of the Effective Piezoelectric Constant of Nitride Thin Films and Heterostructures Using Scanning Force Microscopy
Authors: Rodriguez B. J. , Kim D-J. , Kingon A. I. , Nemanich R. J. 
Published: April 2011

AbstractPiezoelectric properties of wurtzite AlN and GaN/AlN are investigated using scanning force microscopy (SFM). The magnitude of the effective longitudinal piezoelectric constant d33 of AlN and GaN/AlN thin films are measured and reported, and the d33 coefficients of these films are verified using an interferometric technique. Simultaneous imaging of the topography, and of the phase and magnitude of the piezoelectric strain is performed. Using a GaN film with patterned polarities, we demonstrate that polarity can be inferred from the phase image of the piezoelectric strain. We report d33=3±1 pm/V for AlN/SiC and 2 1 pm/V for GaN/AlN/SiC. Films grown by organo-metallic vapor phase epitaxy (OMVPE) on SiC, sputtered AlN films and films grown by molecular beam epitaxy (MBE) are characterized and compared.
Light pulse propagation in three-dimensional photonic crystals
Authors: Kitano H. , Minami F. , Sawada T. , Yamaguchi S. , Ohtaka K. 
Published: April 2011

AbstractThe phase characteristics of transmitted optical pulses in three-dimensional photonic crystals were investigated in the frequency and time domain by using the spectrally resolved cross-correlation technique. The temporal evolution of femtosecond pulses passing through polystyrene colloidal crystals exhibits a large phase distortion near the stop bands. The phase discontinuity around the band gap was observed in the frequency-domain. The phase of the transmitted pulses is found to change by π across the band gap. The dispersion curve estimated from the phase shift shows good correspondence with those calculated from a photonic band calculation. The group velocity significantly slows down near the stop bands. A large change of the group velocity dispersion is also observed near the band edges. These results are in good agreement with the band theory.
Polymer Dispersed Liquid Crystals as Mesoscale 2D and 3D Lattices
Authors: Escuti Michael J. , Crawford Gregory P. 
Published: April 2011

AbstractWe introduce and explore two- and three-dimensional lattices formed in Holographic-Polymer Dispersed Liquid Crystals (H-PDLC) materials, which exhibit an electrically controllable index modulation in multiple dimensions. As electro-optically active holograms, these materials exhibit fast dynamic switching phenomena (~100 microseconds), and are simple to fabricate. While many applications have been proposed for these materials, almost all are based on one-dimensional index modulations in various grating regimes. However, constraints in additional dimensions lead to a much greater sensitivity of the polymer morphology to monomer functionality, exposure irradiance, and grating pitch. In an effort to begin to understand this relationship, two-dimensional triangle lattices were created using two monomeric blends exposed over a range of powers. Final diffraction efficiency (Bragg regime), saturation voltage, and polymer morphology were examined from the resulting triangle lattices. Three- dimensional lattices are discussed and a six-beam holographic method is proposed. Photonic crystal applications are envisioned where the pseudo-bandgap can be electrically controlled.
Thermo-optical switches using coated microsphere resonators
Authors: Tapalian C. , Laine J.-P. , Lane P. A. 
Published: April 2011

AbstractWe report optical switching by a silica microsphere optical resonator coated by a conjugated polymer. Microspheres were fabricated by melting the tip of an optical fiber and coated by dipping in a 1 mg/ml toluene solution of poly(2,5-dioctyloxy-1,4-phenylenevinylene) (DOO-PPV). The resonator properties were characterized by evanescently coupling 1.55 µm light propagating along a stripline-pedestal anti-resonant reflecting optical waveguide into optical whispering gallery modes (WGMs). WGM linewidths less than 2 MHz were measured, corresponding to cavity Q > 108. WGM resonant frequency shifts as large as 3.2 GHz were observed when 405 nm pump light with a power density of ~100 mW/cm2 was incident on the microsphere. The time constant of the observed frequency shifts is approximately 0.165 seconds, leading us to attribute the frequency shift to thermo-optic effects. Such a system should be capable of thermo-optically switching at speeds on the order of 10 kHz.
Toward the Integration of Photonic Crystals with Optical Fiber
Authors: Suzuki Y. , Chen Lu , Kohnke Glenn E. 
Published: April 2011

AbstractWe have developed a novel silicon platform where light from optical fiber is coupled directly into and out of silicon-based photonic crystal structures with over 30dB suppression of transmission from 1400nm to 1700nm and defect energy levels tuned to within 2nm in the bandgap. Insertion losses as low as 3.5dB have been achieved. The optical spectra of our one-dimensional silicon-based photonic crystals can be quantitatively described by a simple model of light incident on a series of dielectric interfaces. The agreement between experiment and simulation and the low insertion losses are promising for the future integration of photonic crystals into optical communications.
Two Dimensional Photonic Crystal Modes and Resonances in Three-dimensional Structures
Authors: Fan Shanhui , Joannopoulos J. D. 
Published: April 2011

AbstractWe present three-dimensional analysis of two-dimensional guided resonances in photonic crystalslab structures. This analysis leads to a new understanding of the complex spectral properties of such systems. Specifically, we calculate the dispersion diagrams, the modal patterns, and transmission and reflection spectra of these resonances. From these calculations, a key observation emerges involving the presence of two temporal pathways for transmission and eflection processes. Using this insight, we introduce a general physical model that explains the essential features of complex spectral properties. Finally, we show that the quality factors of these resonances are strongly influenced by the symmetry of the modes, and the strength ofthe index modulation.
Residual Stress and Microstructure of Electroplated Cu Film on Different Barrier Layers
Authors: Volinsky Alex A. , Hauschildt Meike , Vella Joseph B. , Edwards N.V. , Gregory Rich , Gerberich William W. 
Published: April 2011

ABSTRACTCopper films of different thicknesses between 0.2 and 2 microns were electroplated on adhesion-promoting TiW and Ta barrier layers on <100> single crystal 6-inch silicon wafers. The residual stress was measured after each processing step using a wafer curvature technique employing Stoney's equation. Large gradients in the stress distributions were found across each wafer. Controlled Cu grain growth was achieved by annealing films at 350 C for 3 minutes in high vacuum. Annealing increased the average tensile residual stress by about 200 MPa for all the films, which is in agreement with stress-temperature cycling measurements.After aging for 1 year wafer stress mapping showed that the stress gradients in the copper films were alleviated. No stress discrepancies between the copper on Ta and TiW barrier layers could be found. However, X-ray pole figure analysis showed broad and shifted (111) texture in films on a TiW underlayer, whereas the (111) texture in Cu films on Ta is sharp and centered.
X-Ray Diffraction Analysis and Modeling of Strain Induced Thermal Cycling in a Thin Aluminum (011) Bicrystal Film
Authors: Nowak D. E. , Thomas O. , Baker S. P. , Stach E. A. , Balzuweit K. , Dahmen U. 
Published: April 2011

ABSTRACTHeteroepitaxial films of aluminum bicrystals grown on silicon provide a model system in which to study plasticity in polycrystalline metal thin films. For the bicrystal films, dislocations are confined to move on two different slip plane orientations because of the orientation of the crystals on the substrate. In-situ transmission electron microscopy (TEM) observations during thermal cycling have shown two threshold temperatures for dislocation motion on cooling. A simple model uses the resolved shear stress on the possible slip planes to explain the TEM observations. Mechanisms responsible for the dislocation behavior are studied in-situ during thermal cycling between room temperature and 450°C with x-ray diffraction. The strains are determined using a sin2(Ψ) analysis at each temperature. Direct comparisons are made between the TEM observations, the model and x-ray diffraction results.
Plastic Relaxation in Thin Copper Films
Authors: Shu Jonathan B. , Baker Shefford P. 
Published: April 2011

ABSTRACTWe have studied the isothermal relaxation behavior of 500 nm Cu films with SiNx passivation and barrier layers on Si substrates. Oxygen content in the Cu films was varied by deposition in various oxygen partial pressures in the range 10-10 to 10-4 Torr. The substrate curvature method was used to investigate the thermomechanical behavior of the Cu films. Isothermal relaxation experiments were performed in the temperature range 50-175°C. Comparison with constitutive creep deformation equations shows that the relaxation data in this temperature range are well described by power law behavior. Under certain isothermal conditions related to temperature, stress, and thermal history, anelastic recovery was observed– i.e. while in a tensile stress state and with the temperature held constant, the overall film stress was seen to increase over a relatively short time scale.
Controlled Stress Refractory Metallizations
Authors: Golecki Ilan , Eagan Margaret 
Published: April 2011

ABSTRACTRhodium and iridium are highly electrically conductive refractory metals, which can be used as current-carrying thin-film metallizations. Their chemical inertness further enables their application at relatively high temperatures. However, due to the high elastic modulus of such metals, a residual tensile stress of 300 to 400 MPa is measured in evaporated thin films. We present novel results evidencing complete control over both the magnitude and the sign of the residual stress in such refractory thin films. The metallic layers are deposited by means of ion-beam-enhanced physical vapor deposition and both electrical resistivity and stress are controlled. Controlling the stress in this manner has enabled achieving thicker films and films with near-zero residual stress.
Effects of Pressure on the Vibrational, Structural and Electronic Properties of C60 Powder and Thin Films
Authors: Sharma S. C. , Ha B. , Rhee J. H. , Li Y. , Singh D. , Govinthasamy R. 
Published: April 2011

ABSTRACTWe present results from a study of the vibrational, structural, and electronic properties of C60 powder and thin films. Raman spectroscopy and diamond anvil cell have been used to study pressure dependence of the Raman active modes of C60 powder. The material undergoes structural phase transition between 9 and 15 GPa. Some of the Raman modes soften, while others harden with increasing pressure. Thin films of C60 and La-doped C60 have also been studied by using Raman scattering, x-ray diffraction, x-ray photoelectron spectroscopy and uv photoemission spectroscopy. Whereas the powder and La-doped C60 films exhibit fcc crystalline structure, the C60 film appears disordered. Further, we observe a significant difference in the electronic valence bands of the doped and undoped films.
Nanoindentation Analysis of Viscoelastic Thin Films: Strain Rate and Adhesion Effects
Authors: Palacio Manuel Luis B. , Scherban Tracey , Sun Brad , Xu Jessica , Gerberich William W. 
Published: April 2011

ABSTRACTThe mechanical properties of two viscoelastic thin films were measured, a polyimide and a low-k polymer dielectric. The static modulus and hardness were obtained from nanoindentation experiments using an elastic-plastic unloading model (J. Mater. Res., 13, 421 (1998)). Nanoindentation creep tests were also performed, where a value for the modulus was extracted by fitting the data to an equation based on the three-element standard linear solid model. Aside from being comparable to values reported in the literature, the moduli from creep experiments are at most 1.3 times lower than the static moduli. This decrement can be attributed to the differences in strain rate for the two methods and the effect of adhesive forces.
Stress Hysteresis and Mechanical Characterization of Plasma-Enhanced Chemical Vapor Deposited Dielectrics
Authors: Thurn Jeremy , Cook Robert F. , Kamarajugadda Mallika , Stearns Laura C. 
Published: April 2011

ABSTRACTTwo plasma-enhanced chemical vapor deposited (PECVD) dielectric films pertinent to microelectronic-based applications were examined for thermo-mechanical stability. Both films–silicon nitride and silicon oxy-nitride–showed significant permanent non-equilibrium changes in film stress on thermal cycling and annealing. The linear relationship between stress and temperature changed after the films were annealed at 300°C, representing a structural change in the film resulting in a change in coefficient of thermal expansion and/or biaxial modulus. A double-substrate method was used to deduce both properties before and after the anneal of selected films and the results compared with the modulus deconvoluted from the load-displacement data from small-scale depth-sensing indentation experiments.