bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxidation behavior of TiN with a Ti interlayer on stainless steel
Authors: Shiao Ming-Hua , Wang Ching-Chiun , Su Chien-Ying , Shieu Fuh-Sheng 
Published: April 2011

AbstractCharacterization of the TiN coatings oxidized in air at temperatures at 600 and 700°C for 30 min was carried out by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). TiN thin films with a Ti interlayer were prepared by hollow cathode discharge ion plating on AISI 304 stainless steel. Both XRD and TEM results show that the TiN coatings and Ti interlayer have columnar structure with (111) and (0002) preferred orientations, respectively. AFM results show the existence of pinholes on the surface of specimens due to electropolishing process of the steel substrate, and the surface roughness (Ra) changes from 3.5 nm for the as-deposited specimen to 11.6 nm after oxidation at 700°. After oxidation, the TiO2 oxide layer formed on the specimen surface was porous and retained the columnar structure as the original TiN coating. The microstructure of the Ti interlayer gradually changed from columnar to polycrystalline structure due to grain growth. The Auger elemental depth profiling indicated that interdiffusion of the Ti interlayer with steel substrate had occurred during the oxidation process.
Nanopatterning on Reconstructed Ceramic Surfaces
Authors: A Shwetha Shetty , Shenoy Vijay B , Carter C. Barry , Ravishankar N. 
Published: April 2011

AbstractThe use of reconstructed ceramic surfaces as templates for nanopatterning has been demonstrated recently. This technique differs from the surface decoration by Au on stepped surfaces of alkali halides which has been a topic of intense research in the past. Some of the intriguing aspects related to the physical origin of the phenomena have been considered here. Based on heterogeneous nucleation of Pt vapor on wedged alumina surfaces, it has been shown that the valley sites are the preferred sites for nucleation. However, the hill sites are decorated by the particles in the present study pointing out to a different physical origin for the formation of the nanoparticles. The role of electrostatic energy reduction on the formation of such nanopatterns is discussed.
Grain Boundary Properties and Grain Growth: Al Foils, Al Films
Authors: Barmak Katayun , Archibald Wayne E. , Rollett Anthony D. , Ta'asan Shlomo , Kinderlehrer David 
Published: April 2011

AbstractRelative grain boundary energy as a function of misorientation angle has been measured in cube-oriented, i.e., <100> fiber-textured, 120 [.proportional]m-thick Al foil using orientation imaging microscopy and a statistical multiscale method. The energies of low-angle boundaries increase with misorientation angle, in good agreement with the Read-Shockley model. The relative energies of high-angle boundaries exhibit little variation with misorientation. Examination of the grain structure of <111> fiber-textured, 100 nm-thick Al films annealed at 400°C for 0.5-10 h shows 5 and 6 sided grains to be the most frequent, and the fraction of four-sided grains to be significant. The mean number of sides is slightly lower than the expected value of 6 for two- dimensional structures. Of lognormal, gamma and Rayleigh distributions, gamma gives the best fit to the grain size data in the films; however, the difference between gamma and lognormal is small. Grain growth is not self-similar and stagnates after one hour of annealing. The evolution of the grain size distribution with time indicates that the growth stagnation in the films is neither consistent with boundary pinning by grooving nor with conventional treatments of solute drag. Surface, elastic-strain and plastic-strain energy driving forces do not play a significant role in the grain growth and the subsequent stagnation since the films are strongly textured even in the as- deposited state. The steady-state distributions of reduced grain area for two-dimensional, Monte Carlo and partial differential equation based simulations show excellent agreement with each other, even when anisotropic boundary energies are used. However, comparison with experimental distributions reveals a significantly higher population of small grains in the experiments.
Charge coupled cyclotron motion of electrons and holes in InGaAsN epitaxial layers
Authors: Porteanu H. E. , Loginenko O. , Koch F. , Dumitras G. , Geelhaar L. , Riechert H. 
Published: April 2011

ABSTRACTTime resolved cyclotron resonance measurements are used to investigate more in further detail the effective mass of electrons and holes in InGaAsN epitaxial layers. The In and N content in the alloy are adjusted to yield the latticematching of the epilayers (200 nm thick) to GaAs. A continuous increase of the effective mass of electron and an increase of the resonance associated with holes is observed. Through the evolution of the imaginary part of conductivity as a function of the elapsed time we show that this observation is a coupled cyclotron resonance that may have maxima in the real part of conductivity but should not be necessarily correlated with the “increase” of the effective mass.
Structural and Optical Effects of Capping Layer Material and Growth Rate on the Properties of Self-Assembled InAs Quantum Dot Structures
Authors: Agnello Gabriel , Tokranov Vadim , Yakimov Michael , Lamberti Matthew , Zheng Yuegui , Oktyabrsky Serge 
Published: April 2011

ABSTRACTIn order to develop nanoengineering methods to control electronic spectrum of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy, we have utilized atomic force microscopy (AFM), photoluminescence (PL) and TEM methods to investigate the effects of capping layer growth on the physical/chemical properties as well as the optical/electronic performance of QD device structures. Capping layer material choice (or its absence all together) has been found to directly influence QD dimensions (size, height), and subsequently, to affect QD emission wavelength. We report results of QD lateral size and height as well as densities of InAs QDs capped with 2ML (monolayers) of AlAs or GaAs grown at various rates. Our AFM results are complemented by PL measurements, where the optical properties of capped versus non-capped QDs have been explored and direct correspondence between structural differences induced by capping and the electronic/optical properties of QDs is demonstrated. Analysis of the data shows that the results can be explained by two competing surface processes. The first of which is the redistribution of indium between QDs on top of the 2D wetting layer, resulting in the increase of QD size with time. The second effect is the diffusion of indium out of the QDs and onto the top of the capping layer. TEM with multislice image simulation has supported our AFM and PL observations with the demonstration of “indium driven” alloy intermixing in the overlayer as well as significant alloying in the InAs wetting layer.
Electrical Measurement of Recombination Lifetime in Blue Light Emitting Diodes
Authors: Awaah M. A. , Nana R. , Das K. 
Published: April 2011

ABSTRACTA recombination lifetime of approximately 25 ns was extracted from measured reverse recovery storage times in AlGaN/GaN/AlGaN double heterojunction blue light emitting diodes. This experimentally determined lifetime is expected to arise from a combination of radiative and non-radiative processes occurring in the diodes. The non-radiative processes are likely to be due the presence of a high concentration deep-states as identified from the current-voltage and capacitance-voltage measurements. Current-voltage characteristics of these diodes were highly non-ideal as indicated by high values of the ideality factor ranging from 3.0 – 7.0. Logarithmic plots of the forward characteristics indicated a space-charge-limited-current (SCLC) conduction in presence of a high density of “deep-level states” in the active region of the diodes. An analysis of these characteristics yielded an approximate density of these deep-level states as 2 × 1017/cm3. The density of deep-states extracted from capacitance-voltage measurements were in good agreement with that obtained from current-voltage measurements.
Growth and Characterization of ZnO Nanonail
Authors: Seo H. W. , Wang D. , Tzeng Y. , Sathitsuksanoh N. , Tin C. C. , Bozack M. J. , Williams J. R. , Park M. 
Published: April 2011

ABSTRACTZinc oxide (ZnO) is an interesting material for short-wavelength optoelectronics due to its wide band gap. The nanostructures of ZnO are also intriguing since a variety of morphology can be obtained by employing different processing parameters. In our laboratory, ZnO nanonails were successfully synthesized at low temperature using a thermal chemical vapor deposition. The morphology of the sample was studied by using scanning electron microscopy. The shape of the nail head can be controlled from hexagon to quasi-circular shape. X-ray diffraction, Raman scattering, photoluminescence spectroscopy were also performed to analyze the ZnO nanonail. Photoluminescence spectroscopy suggested that the defects in the ZnO nanonail and nanobone are of different nature.
Raman spectroscopy of V and Co doped ZnO ceramics and thin films
Authors: Samanta K. , Awasthi N. , Sundarakannan B. , Bhattacharya P. , Katiyar R. S. 
Published: April 2011

ABSTRACTLattice dynamical and electronic transition changes due to V and Co doped ZnO have been investigated using optical techniques. Vanadium and Co doped ZnO pellets were prepared using conventional ceramic processing route and thin films were fabricated by pulsed laser deposition. Raman spectra of Zn1-xVxO targets showed many additional peaks in the range of 230 to 350 cm-1 and 750 to 900 cm-1. Integrated intensities of these additional modes decreased with increase of temperature as similar to the host ZnO modes, which precludes electronic Raman scattering to be the origin. Raman peaks for stoichiometric Zn3(VO4)2 and Zn2V2O7 compounds also had additional peaks that can be attributed to the secondary phases formed in the compositions of Zn1-xVxO. Raman spectra of Zn1-xCoxO showed no additional modes besides ZnO modes, however, the intensity of the second order peak at 540 cm-1 was increased due to Co doping. Thin films of Zn1-xCoxO exhibited highly c-axis orientation deposited on (001)Al2O3 substrates. The optical absorption of the films showed that the band gap decreased with increase of Co concentrations at room temperature along with the sub bandgap absorptions due to d-d transitions of Co2+.
Longitudinal Modes in InAlGaAs/AlGaAs High-Power Laser Diodes
Authors: Passmore B. S. , Chua Y. C. , Manasreh M. O. , Tomm J. W. 
Published: April 2011

ABSTRACTThe emission from bias voltage driven In0.06Al0.08Ga0.86As/Al0.3Ga0.7As edge-emitting diode lasers with cavity lengths of 0.6 and 0.9 mm was measured at 290 K using a high resolution Fourier-transform infrared spectrometer. The light-current (L-I) characteristic curves showed that a threshold current of ∼ 0.5 and 0.8 A was needed to reach the stimulated emission in laser diodes with cavity lengths of 0.6 and 0.9 mm, respectively. The laser diode longitudinal modes were observed in the stimulated emission spectrum for each of the devices. These spectra enabled us to calculate the refractive index, total loss, and gain of the active region. On the other hand, the cavity length was determined by utilizing the interferogram spectrum, longitudinal modes spacing, and direct measurements of the laser dimensions. A good agreement between the cavity length values obtained from the three methods was achieved.
Ultrashort Pulse Generation with Semiconductor Modelocked Lasers Using Saturable Absorbers Based on Intersubband Transitions in GaN/AlGaN Quantum Wells
Authors: Ahmad Faisal R. , George Paul , Dawlaty Jahan , Rana Fahan , Shaff William J. 
Published: April 2011

ABSTRACTWe present a novel scheme for generating high energy ultrashort pulses in modelocked semiconductor lasers using a fast saturable absorber based upon intersubband transitions (ISBT) in GaN/AlGaN superlattice. The fast electron relaxation time (∼100–300 fs) in this saturable absorber enables the generation of stable sub-100 fs pulses at the communication wavelength (1.55μm) with high pulse energies (5–10 pJ).
Zener tunneling of light in an optical superlattice
Authors: Ghulinyan Mher , Gaburro Zeno , Pavesi Lorenzo , Oton Claudio J. , Toninelli Costanza , Wiersma Diederik S. 
Published: April 2011

ABSTRACTWe report on the observation of resonant Zener tunnelling of light waves in an optical superlattice. The one dimensional (1D) structures are made in free-standing porous silicon and are designed specifically to exhibit two photonic minibands. A controlled optical path gradient has been maintained over the sample thickness which resulted in tilting of photonic minibands and formation of optical Wannier-Stark ladders. At a certain value of optical gradient the two minibands couple within the extension of the structure and a resonant tunnelling channel through the superlattice forms, resulting in a very high transmission peak. Ultrafast time resolved transmission experiments were performed: excitation of the Wannier-Stark states causes the appearance of photonic Bloch oscillations, which are strongly damped when Zener tunneling modes are excited. The observed phenomenon is the optical analogue of resonant Zener tunnelling in an electronic superlattice.
Characterization of Minority-Carrier Hole Transport in Nitride-Based Light-Emitting Diodes with Optical and Electrical Time-Resolved Techniques
Authors: Kaplar R. J. , Kurtz S. R. , Koleske D. D. , Allerman A. A. , Fischer A. J. , Crawford M. H. 
Published: April 2011

ABSTRACTForward-to-reverse bias step-recovery measurements were performed on In.07Ga.93N/GaN and Al.36Ga.64N/Al.46Ga.54N quantum-well (QW) light-emitting diodes grown on sapphire. With the QW sampling the minority-carrier hole density at a single position, distinctive two-phase optical decay curves were observed. Using diffusion equation solutions to self-consistently model both the electrical and optical responses, hole transport parameters τp = 758 ± 44 ns, Lp = 588 ± 45 nm, and μp = 0.18 ± 0.02 cm2/Vs were obtained for GaN. The mobility was thermally activated with an activation energy of 52 meV, suggesting trap-modulated transport. Optical measurements of sub-bandgap peaks exhibited slow responses approaching the bulk lifetime. For Al.46Ga.54N, a longer lifetime of τp = 3.0 μs was observed, and the diffusion length was shorter, Lp ≈ 280 nm. Mobility was an order of magnitude smaller than in GaN, μp ≈ 10−2 cm2/Vs, and was insensitive to temperature, suggesting hole transport through a network of defects.
Optimization of GaN Channel Conductivity in AlGaN/GaN HFET Structures Grown by MOVPE
Authors: Hubbard S.M. , Zhao G. , Pavlidis D. , Cho E. , Sutton W. 
Published: April 2011

ABSTRACTOptimization of GaN channel conductivity in AlGaN/GaN Heterojunction Field Effect Transistor (HFET) structures was performed using High Resistivity (HR) GaN templates grown by Metal-organic Vapor Phase Epitaxy (MOVPE). The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature. Using an annealing temperature of 1033°C, GaN with sheet resistance of 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. X-Ray Diffraction (XRD) and Photoluminescence (PL) analysis show that the high resistance GaN is achieved due to compensating acceptor levels introduced through edge-type threading dislocations. XRD analysis also shows optimization of annealing temperature provided a means to maximize GaN sheet resistance without significantly degrading material quality. AlGaN/GaN HFET layers grown using HR GaN templates gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.
Electrical and Optical Properties of 1 MeV-electron irradiated AlxGa1-xN
Authors: Hogsed Michael R. , Ahoujja Mo , Ryu Mee-Yi , Yeo Yung Kee , Petrosky James C. , Hengehold Robert L. 
Published: April 2011

ABSTRACTThe optical and electrical properties of Si doped GaN and Al0.20Ga0.80N films irradiated with 1 MeV electrons at a fluence of 1×1017 cm−2 are investigated using cathodoluminescence (CL), variable-temperature Hall-effect, and deep level transient spectroscopy (DLTS) measurements. The CL spectra measured at 6 K show peak luminescence intensity of the near band edge decreases, on average, by 50% after electron irradiation, indicating the creation of non-radiative recombination centers which are stable at room temperature. At room temperature, the free carrier concentration decreases significantly in both the GaN and AlGaN samples following the irradiation, and the carrier removal rate depends strongly on the initial carrier concentration. DLTS measurements show three electron traps in the as-grown Al0.20Ga0.80N. Following 1 MeV electron irradiation of the Al0.20Ga0.80N sample, three additional electron traps labeled R2, R3, and R4 are observed. The first two traps appear to correspond to radiation-induced traps reported in GaN while the latter appears to be unique to AlGaN.
Reduction of dislocation density in AlGaN with high AlN molar fraction by using a rugged AlN epilayer
Authors: Ishiga Akira , Onishi Takashi , Liu Yuhuai , Haraguchi Masaya , Kuwano Noriyuki , Shibata Tomohiko , Tanaka Mitsuhiro , Miyake Hideto , Hiramatsu Kazumasa 
Published: April 2011

ABSTRACTA method for making AlGaN with a high AlN molar fraction and low dislocation density is needed for fabricating deep ultraviolet emitters and detectors. In this study, we reduced the dislocation density in AlGaN over a large surface area by using low-pressure MOVPE on a continuously rugged epitaxial AlN substrate. The AlN molar fraction of the AlxGa1-xN was × = 0.51, and atomic steps in the surface were clearly observed with an atomic force microscope (AFM). In addition, the dislocation density was estimated to be 8.8 × 107 cm−2, which is two orders of magnitude lower than that of AlGaN grown on a flat AlN epitaxial layer. Our results indicate that the dislocation density of AlGaN can be greatly reduced by using a rugged AlN epitaxial substrate with continuously inclined facet.
The effect of periodic silane burst on the properties of GaN on Si (111) substrates
Authors: Zang K. Y. , Chua S. J. , Thompson C. V. , Wang L. S. , Tripathy S. , Chow S. Y. 
Published: April 2011

ABSTRACTThe periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper.
Normally-off operation GaN HFET using a thin AlGaN layer for low loss switching devices
Authors: Ikeda Nariaki , Kato Kazuo , Li Jiang , Hataya Kohji , Yoshida Seikoh 
Published: April 2011

ABSTRACTWe report on the novel normally-off GaN-based heterojunction field effect transistors (HFETs) on a Si substrate. The AlGaN/AlN/GaN heterostructure was grown using a metalorganic chemical vapor deposition (MOCVD). The HFET for a normally-off operation was fabricated using a precisely controlled thin-AlGaN layer as an electron supply layer. As a result, the HFET was operated at the condition of the positive gate bias. We also characterized the enlarged gate-width devices. The breakdown voltage of FET was over 300 V. A normally-off operation using GaN based HFETs with a thin-AlGaN/AlN/GaN heterostructure on the silicon substrate were thus confirmed for the first time.
P-type GaN epitaxial layers and AlGaN/GaN heterostructures with high hole concentration and mobility grown by HVPE
Authors: Usikov A. , Kovalenkov O. , Ivantsov V. , Sukhoveev V. , Dmitriev V. , Shmidt N. , Poloskin D. , Petrov V. , Ratnikov V. 
Published: April 2011

ABSTRACTIn this paper we report p-GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg or Zn impurities were used for doping. Layer thickness ranged from 2 to 5 microns. For both impurities, as-grown GaN layers had p-type conductivity. Concentration NA-ND was varied from 1016 to 1018 cm−3. An annealing procedure at 750°C in argon ambient typically increased the concentration NA-ND in 1.5–3.5 times. For Mg doped GaN layers, room temperature hole mobility of 80 cm2V−1s−1 was measured by conventional Van Der Pau Hall effect technique for material having hole concentration of about 1x1018 cm−3. Initial results on highly electrically conducting p-type AlGaN/GaN heterostructures doped with Zn are also reported.
Silicon-based Integrated Optics: Waveguide Technology to Microphotonics
Authors: Janz Siegfried , Bogdanov Alexei , Cheben Pavel , Delâge André , Lamontagne Boris , Picard Marie-Joseé , Xu Dan-Xia , Yap Kuan Pei , Ye Winnie N. 
Published: April 2011

ABSTRACTUsing a waveguide spectrometer chip as an example, we describe how high index contrast waveguides systems such as silicon-on-insulator can be combined with microphotonic design rules to extend the performance of waveguide devices. The challenges arising in the implementation of silicon microphotonic technology are discussed, and recent work addressing the issues of waveguide coupling, polarization sensitivity, waveguide loss and massively parallel data acquisition is reviewed.
Pump-probe experiments on low loss silica waveguides containing Si nanocrystals
Authors: Navarro-Urrios D. , Daldosso N. , Melchiorri M. , Sbrana F. , Pavesi L. , García C. , Garrido B. , Pellegrino P. , Morante J. R. , Scheid E. , Sarrabayrouse G. 
Published: April 2011

ABSTRACTRib-loaded silica waveguides containing Si nanocrystals were grown by quadruple implantation of Si ions into a 2 μm-thick thermally-grown SiO2 layer. The thickness of the resulting flat-profile active region was about 300 nm, with a 9.5% Si excess (determined by X-ray photoelectron spectroscopy). Complete phase separation and nanocrystal formation was assured by annealing at 1100 °C, and studied by means of optical tools such as Raman and luminescence. The rib-loaded structure of the waveguides was fabricated by photolithographic and reactive ion etching processes, with patterned rib widths ranging from 1 to 8 μm. Efficient light propagation was observed when end-fire coupling a probe signal both at 633 nm and 780 nm into the waveguides, with attenuation losses as low as 11 dB/cm. Signal amplification experiments, with pulsed and continuous wave (CW) top pumping, have shown increased signal absorption when the pump power is raised. This couples with the lack of any fast component in the time decay of the amplified spontaneous emissions as measured by ns pulsed pumping Variable Stripe Length (VSL) experiments. These two phenomena are interpreted as due to the lack of stimulated emission in these nanocrystalline systems.