bluuebunny/crossref_metadata_2025_split huggingface dataset:
InGaAs/InGaAsP Quantum-Well Engineering for Multiple Regrowth MOVPE Process
Authors: Lohe Hans-Jeorg , Gini Emilio , Scollo Riccardo , Robin Franck , Jaeckel Heinz 
Published: April 2011

ABSTRACTFor the heterogeneous integration of several layer structures for absorber, gain and passive waveguide sections in a monolithically-integrated mode locked laser diode, the bandgap of the absorber section has to be matched to the emission wavelength of the gain section. Because of the use of a multiple regrowth process for optical butt-coupling, the first grown multiple quantum-well gain material undergoes a quantum-well intermixing process, resulting in a blue shift of the emitting optical wavelength. Experimental results show, that the blue shift is dependent on the process details and cannot be investigated by simple thermal cycling of unprocessed quantum well-structures. With the introduction of an effective quantum-well width computed from the emission wavelength we found a linear relationship between the effective quantum well width shrinkage and the cumulated regrowth heating time of 8.3Å/h at a growth temperature of 630°C. Therefore knowing the cumulated regrowth time for a laser fabrication, we could successfully design the initial quantum well thickness that yields the targeted emitting wavelength and excellent matching to the absorber bandedge.
Nano-patterned Growth of Ge Quantum Dots for Infrared Detector Applications
Authors: Chen Christopher , Cha Dongho , Lee Joo-young , Kim Hyung-jun , Liu Fei , Tong Song , Wang Kang L. , Wang Jia-Yu , Russell Thomas P. 
Published: April 2011

ABSTRACTQuantum dot infrared photodetectors (QDIPs) have been studied widely for normal-incidence infrared detection. The 3D confinement provided by quantum dots allows for the elimination of gratings that are typically required for normal-incidence detection in quantum well infrared photodetectors (QWIPs). Furthermore, the growth of Ge dots on Si substrates offers the potential for integration with existing CMOS platforms. To date, however, Ge QDIPs have typically been grown epitaxially by Stranski-Krastonov growth – producing pancake-like dots with base dimensions of 50-100 nm, heights of 7-10 nm, and an aerial dot density of 109–1010 cm−2. Such dots have poor lateral confinement, causing them to have non-ideal normal-incidence absorption characteristics, similar to quantum wells. In this work, we demonstrate infrared absorption in Ge dots with base dimensions of approximately 15 nm. These dots are epitaxially grown on pre-patterned Si substrates, with an aerial dot density of approximately 1011 cm−2. The substrates are prepared by using diblock copolymers to create a nano-pattern on the substrate surface which is transferred to the substrate by dry etching. The size of this pattern determines the base dimensions of the Ge dots. After growth, these dots are then tested for their infrared absorption properties using Fourier Transform Infrared (FTIR) Spectroscopy. The normal-incidence absorption of the dots can be studied with FTIR by varying the polarization angle of the infrared light. We present FTIR absorption spectra for samples grown with various conditions (e.g., different dot doping levels, numbers of layers, and dot base dimensions) and investigate the effects of different growth conditions on infrared absorption properties. We also report on the normal-incidence absorption characteristics of these dots by presenting absorption spectra for various polarization angles of infrared light.
A Novel InSb Photodiode Infrared Sensor Operating at Room Temperature
Authors: Ueno Koichiro , Camargo Edson Gomes , Kawakami Yoshifumi , Moriyasu Yoshitaka , Nagase Kazuhiro , Kuze Naohiro 
Published: April 2011

ABSTRACTA microchip-sized InSb photodiode based infrared sensor (InSb PDS) that operates at room temperature was developed. The InSb PDS consists of 700 photodiodes connected in series and consumes no power, because it works in photovoltaic mode to output an open-circuit voltage. The InSb PDS has a typical responsivity of 1,900 V/W and an output noise of 0.15 μV/Hz1/2. A detectivity of 2.8×108 cmHz1/2/W was obtained at 300 K. The InSb PDS has performance high enough for applications such as mobile electronic equipment, personal computers, and consumer electronics
Effect of Substrate Variation on Electrical and Magnetic Properties of Mn Doped ZnO of Dilute Magnetic Semiconductors
Authors: Manchiraju Srikanth , Mundada Govind , Kehl Ted , Vera Craig , Patel Rishi , Kahol Pawan , Ghosh Kartik 
Published: April 2011

ABSTRACTIn this paper, the effect of substrate on the domain structure growth and electrical and magnetic properties of epitaxial Mn-doped Zn0.8Mn0.15O (ZnMnO) thin films has been investigated. Epitaxial thin films of ZnMnO dilute magnetic semiconductors (DMS) were grown on various substrates such as single crystal sapphire, single crystal silicon, and quartz substrates using Pulsed Laser Deposition (PLD) technique . Structural, surface, magnetic, and optical properties have been observed on these films using X-Ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Raman spectroscopy. X-Ray Diffraction shows that films are highly epitaxial and c-axis oriented with some induced strain. AFM images show that film surface is smooth with RMS roughness of the order of 1-2 nm over 5*5sq.micron. Magnetic characteristic properties such as carrier concentration, mobility, and temperature dependent resistivity were also investigated. Carrier concentration decreases and mobility increases for both the films on silicon and quartz substrates when compared to film on sapphire.
Improved Photoconductivity of ZnO by Ion Beam Bombardment
Authors: Wellenius I. P. , Dhawan Anuj , Muth J. F. , Guardala Noel A. , Price Jack L. 
Published: April 2011

ABSTRACTIn this study, single crystal ZnO films are grown by pulsed laser deposition and ion beam processing is used alter the resistivity of the films. A 3He ion beam was chosen with a specific energy to transmutate oxygen into nitrogen. Analytical ion beam techniques were used to monitor the transmutation process, and changes in film characteristics were monitored by making resistance, photoconductivity and luminescence measurements before and after ion beam processing. The amount of nitrogen produced by this method was estimated to be ∼ 1014 cm−3, and was too low to be observable as a p-type dopant due to compensation by the naturally n-type material. However, the ion beam processed films improved dramatically in resistivity, defect luminescence was reduced and photoconductivity increases consistent with the improvements with resistivity were observed. These improvements were attributed to ion beam annealing of the crystal resulting in a reduction of point defects. In some films, blistering of the surface occurred and was attributed to the formation of gas bubbles which causes delamination of the film from the substrate.
Changes in Optical Properties of GaAsN During Annealing
Authors: Liu Ting , Chandril Sandeep , Schires Eric D. , Wu Nianqiang , Chen Xinqi , Korakakis Dimitris , Myers Thomas H. 
Published: April 2011

ABSTRACTGaAs1−xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 °C a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples.
In-Situ Investigation of Surface Stoichiometry During InGaN and GaN Growth by Plasma-Assisted Molecular Beam Epitaxy Using RHEED-TRAXS
Authors: Tompkins Randy Preston , VanMil Brenda L. , Lee Kyoungnae , Schires Eric D. , Chye Yewhee , Lederman David , Myers Thomas H. 
Published: April 2011

AbstractReflection high-energy electron diffraction total-reflection-angle x-ray spectroscopy (RHEED-TRAXS) uses high-energy electrons from RHEED to excite x-ray fluorescence. Monitoring characteristic x-rays of selected elements thus allows study of surface coverage of materials. In this study, surface coverage of Ga and In during growth of GaN and InGaN was probed using this technique. Evolution of the surface layer of Ga on GaN during growth and deposition of Ga on static GaN at room temperature were studied. RHEED-TRAXS measurements were performed during growth of InGaN by measuring the ratio of the In Lα to Ga Kα intensity. A significant surface coverage of In was observed at all temperatures investigated regardless of actual In incorporation.
Modification of InN Properties by Interactions with Hydrogen and Nitrogen
Authors: Losurdo Maria , Giangregorio Maria Michela , Bruno Giovanni , Kim Tong-Ho , Wu Pae , Choi Soojeong , Morse Mike , Brown April , Masia Francesco , Polimeni Antonio , Capizzi Mario 
Published: April 2011

AbstractThe interaction of InN epitaxial films grown by r.f. plasma assisted molecular beam epitaxy with atomic hydrogen and nitrogen, produced by remote r.f. H2 and N2 plasmas, is investigated. InN strongly reacts with both atomic hydrogen and nitrogen yielding depletion of nitrogen and concurrent formation of In clusters. The impact of hydrogen treatments on the optical properties of InN is assessed using photoluminescence (PL). It is found that hydrogen suppresses the intense PL band peaked at approximately 0.7eV for the as-grown InN epitaxial layers, and results in the appearance of a new PL band whose peak energy and intensity increase with H-dose. The effect of exposure to atomic hydrogen and nitrogen on electrical properties of InN is investigated using Hall effect measurements. Atomic force microscopy is also used for studying the morphological changes of InN upon interaction with atomic hydrogen and nitrogen.
Growth, processing and characterization of GaN/AlGaN/SiC vertical n-p diodes
Authors: Boeykens Steven , Leys Maarten , Germain Marianne , Poortmans Jef , Van Daele Benny , Van Tendeloo Staf , Belmans Ronnie , Borghs Gustaaf 
Published: April 2011

AbstractApplication of SiC substrates instead of the most commonly used sapphire for the heteroepitaxial growth of III-Nitrides offers advantages as better lattice matching, higher thermal conductivity, and electrical conductivity. This namely offers interesting perspectives for the development of vertical III-Nitride devices for switching purposes. For example, an AlGaN/SiC heterojunction could improve the performance of SiC bipolar transistors. In this work, n-type GaN layers have been grown by MOVPE on p-type 4H-SiC substrates using Si doped Al0.08Ga0.92N or Al0.3Ga0.7N nucleation layers. They have been characterized with temperature dependent current-voltage (I-V-T), capacitance-voltage (C-V) techniques and transmission electron microscopy (TEM).
Fabrication and electrical characteristics of Ti/Al ohmic contact to Si+ implanted GaN
Authors: Ito Nobuyuki , Suzuki Akira , Kawamura Mitsunori , Nomoto Kazuki , Kasai Takeshi , Mishima Tomoyoshi , Inada Taroh , Nakamura Tohru , Satoh Masataka 
Published: April 2011

AbstractTi/Al ohmic contact with an extremely low specific contact resistance has been formed by the deposition of Ti and Al films on Si+ lanted GaN. The ohmic contact formed by annealing at 600 o C of Ti film with a thickness of 50 nm and Al film with a thickness of 200 nm reveals the good smooth surface and uniform structure as compare to those of contacts formed above 700 °C, which is correlated to whether the Al-Ti alloy is melted during the annealing of ohmic contact or not. The specific contact resistance of 2 × 10-6Ω-cm2 is obtained for Si+ implanted GaN with a dose of 5 × 1013 cm-2. As Si ion dose increases to 5 × 1014 /cm2, the specific contact resistance is reduced to 2 × 10-8 Ω-cm2. It is revealed that the selective doping at high impurity concentration in the surface region by Si+ implantation is useful to reduce the contact resistance for Ti/Al contact to GaN.
Low Temperature Selected Area Re-Growth of Ohmic Contacts for III-N FETs
Authors: Saripalli Yoganand , Zeng Chang , Jin Yawei , Long Joseph P , Grenko Judith A , Dandu Krishnanshu , Johnson Mark A.L , Barlage Doug W 
Published: April 2011

AbstractGaN has a wide band gap energy, high electron mobility, high saturation velocity, and excellent thermal properties making it a promising material for high power and high frequency electronic devices. The development of enhancement mode GaN metal oxide semiconductor (MOS) transistors has been elusive due to the non-availability of a good insulating gate dielectric and the difficulty in forming of ohmic source/drain regions. Ion-implantation of dopants causes severe lattice damage requiring a high temperature post-implant anneal and has not been a successful method to obtain acceptable low-resistance source/drain regions. At the same time, gate dielectrics for most compound semiconductors, in addition to difficulties in minimizing the density of interface states which pin the Fermi level by inducing trap levels in the midgap, are degraded by instabilities as a result of high temperature annealing. The paper presents the development ohmic source/drain contacts for GaN MOSFETs by selected area epitaxial regrowth. Re-growth of GaN on patterned substrates by metal-organic chemical vapor deposition (MOCVD) employs a growth regime to decrease the enhanced growth rates and island formation that result from the diffusion of precursors to the selected area. The enhanced growth rate is 4.5μm/hr compared to 0.5μm/hr of the as-grown GaN on the unpatterned substrate. The enhanced growth rate also results in heavily porous GaN. Selected area growth, device processing, the material and device characterization results will be presented. In particular the selected area growth of doped contacts in the 800°C temperature range leads to superior morphology and contact resistance as compared to similar contacts grown at 1060°C. The contact resistivity of the n+ re-growth region measured was ∼2×10-4 Ω-m and the morphology of the re-grown region was comparable to the as-grown GaN with an RMS roughness ∼1.4nm. The success of fabricating low temperature contacts for GaN enhancement mode MOS transistors is a critical step in fabricating these devices opening new applications.
Plasma-Assisted MOCVD Growth of ZnO Thin Films
Authors: Losurdo Maria , Giangregorio Maria Michela , Capezzuto Pio , Bruno Giovanni , Malandrino Graziella , Blandino Manuela , Fragalà Ignazio 
Published: April 2011

AbstractZnO thin films have been grown by metalorganic chemical vapor deposition (MOCVD) also plasma assisted (PA-MOCVD) on c-axis oriented sapphire (0001) and Si(001) substrates using the alternative Zn(TTA)2·tmed (HTTA=2-thenoyltrifluoroacetone,TMED=N,N,N’,N’-tetramethylethylendiamine) precursor. The structural, morphological and optical properties of ZnO films have been investigated. The results show that the O2 plasma assisted growth results in an improvement of the structure, in smoother morphologies and in a better optical quality with a sharp and intense exciton of ZnO films.
High quality GaN layers grown on slightly miscut sapphire wafers
Authors: Brüeckner Peter , Feneberg Martin , Thonke Klaus , Habel Frank , Scholz Ferdinand 
Published: April 2011

AbstractHVPE grown layers typically show a high density of pyramidal structures on the surface. We found that a slight off-orientation of the substrate totally suppresses the development of these structures. Further we found that a misorientation toward the m-plane of GaN features a smoother surface morphology, compared to an off-orientation towards the a-plane. After the improvement of the surface morphology and other properties of the HVPE grown layers, we studied self-separation processes. Our approaches to remove the thick GaN-layer from the substrate were a low-temperature interlayer and a structured dielectric mask.
Polarized Photoluminescence Study on AlGaN of AlGaN/GaN Heterostructure
Authors: Kitagawa Sachio , kosaka Kenichi , Tuchiya Tadayoshi , Suzuki Akira , Araki Tsutomu , Nanishi Yasushi 
Published: April 2011

AbstractOptical properties of tensile strained AlxGa1-xN films of AlxGa1-xN/GaN heterostructures grown on sapphire were investigated by using polarization-resolved photoluminescence spectroscopy. Emissions from AlxGa1-xN with polarization of E//c and E⊥c were obtained at different peak energies. The energy separation of these emissions with polarization was increased linearly with the increase in Al mole fraction of the strained AlxGa1-xN, indicating that the energy separation was due to biaxial strain in the tensile strained AlxGa1-xN.
Refractive Indices of A-plane GaN Thin Films on R-plane Sapphire
Authors: Cai Ailing , Wellenius Ian Patrick , Gerhold Mike , Muth John , Osinsky Andrei , Xie J. Q. , Dong J. W. 
Published: April 2011

AbstractA-plane GaN grown on r-plane sapphire is a promising material for optoelectronic applications such as laser diodes and LEDs. The absence of a built-in electrostatic field in the nonpolar a-plane GaN-based quantum wells can limit the piezoelectric polarization effect and result in higher emission efficiency. The knowledge of the planar anisotropic nature of nonpolar a-plane GaN is important to understand the growth mechanism of a-plane GaN is fundamental for optoelectronic device design. Two a-plane GaN samples were grown on r-plane sapphire, one being grown on intentionally miscut 4 degrees from r-plane sapphire. The films exhibited different surface morphologies and were characterized using imaging cathodoluminescence and SEM. The ordinary and extraordinary indices of a-plane GaN thin film were obtained using a prism-coupling technique. It was found that one sample the c-axis lay in the plane of the thin film as expected, and in the sample grown on miscut sapphire the c-axis was out of the plane of the film.
High quantum efficiency of photoluminescence in GaN and ZnO
Authors: Reshchikov Michael A. , Gu Xing , Nemeth Bill , Nause Jeff , Morkoç Hadis 
Published: April 2011

AbstractThe quantum efficiency (QE) of photoluminescence (PL) has been estimated in GaN and ZnO samples. A Si-doped GaN layer grown by molecular beam epitaxy (MBE) exhibited the highest QE of about 90% at low temperatures. Recombination via the shallow donor-acceptor pair transitions dominated in this sample. In contrast, a bulk ZnO crystal with the QE of PL of about 85% contained almost no defect- or impurity-related PL signatures besides the emission attributed to free and bound excitons. The sources of radiative and nonradiative recombination in GaN and ZnO are discussed.
Influence of the Annealing Ambient on Structural and Optical Properties of Rare Earth Implanted GaN
Authors: Lorenz Katharina , Nogales E. , Nédélec R. , Penner J. , Vianden R. , Alves E. , Martin R. W. , O`Donnell K. P. 
Published: April 2011

AbstractGaN films were implanted with Er and Eu ions and rapid thermal annealing was performed at 1000, 1100 and 1200 °C in vacuum, in flowing nitrogen gas or a mixture of NH3 and N2. Rutherford backscattering spectrometry in the channeling mode was used to study the evolution of damage introduction and recovery in the Ga sublattice and to monitor the rare earth profiles after annealing. The surface morphology of the samples was analyzed by scanning electron microscopy and the optical properties by room temperature cathodoluminescence (CL). Samples annealed in vacuum and N2 already show the first signs of surface dissociation at 1000 °C. At higher temperature, Ga droplets form at the surface. However, samples annealed in NH3 + N2 exhibit a very good recovery of the lattice along with a smooth surface. These samples also show the strongest CL intensity for the rare earth related emissions in the green (for Er) and red (for Eu). After annealing at 1200 °C in NH3+N2 the Eu implanted sample reveals the channeling qualities of an unimplanted sample and a strong increase of CL intensity is observed.
Characterization of lattice mosaic ofa-plane GaN grown onr-plane sapphire by metalorganic vapor-phase epitaxy
Authors: Kusakabe Kazuhide , Ando Shizutoshi , Ohkawa Kazuhiro 
Published: April 2011

AbstractNonpolara-plane GaN films were grown on r-plane sapphire substrates by atmospheric metalorganic vapor-phase epitaxy. The as-grown layers were studied by high-resolution x-ray diffraction. Thea-plane GaN lattice mosaic is orientation dependent as determined by x-ray rocking curve (XRC) measurements. The tilt mosaic measured with the c-axis within the scattering plane (c-mosaic) was greater than the mosaic measured with the m-axis within the scattering plane (m-mosaic). The mosaic along both azimuths decreased and thec-mosaic/m-mosaic ratio was increased with increase of growth temperature from 1050 °C to 1080 °C. The morphological transition was correlated to change in thea-plane GaN tilt mosaic measured by XRC.
Energy Use and Greenhouse Gas Emissions in the Life Cycle of CdTe Photovoltaics
Authors: Fthenakis Vasilis , Kim Hyung Chul 
Published: April 2011

AbstractThe life cycle of the thin film CdTe PV modules in the U.S. have been investigated based on materials and energy inventories for a commercial 25 MW/yr production plant. The energy payback times (EPBT) of these modules are 0.75 years and the GHG emissions are 18 gCO2-eq/kWh for average U.S. solar irradiation conditions. Adding the impact of an optimized ground-level balance of system (BOS), result in a total EPBT of 1.2 years and total life-cycle GHG emissions of 24 gCO2-eq/kWh.
Suggested Strategies for the Ecotoxicology Testing of New Nanomaterials
Authors: Stone Vicki , Fernandes Teresa , Ford Alex , Christofi Nick 
Published: April 2011

AbstractNanotechnology is a rapidly expanding and advancing field of research that has already yielded a variety of commercially available products including cosmetics, suntan lotions, paints, self cleaning windows and stain resistant clothing. The Royal Society and the Royal Academy of Engineering in their recent report ‘Nanotechnology and nanoscience: opportunities and uncertainties’ (http://www.nanotec.org.uk/finalReport.htm) concluded that nanotechnology is likely to have ‘huge potential’. While this report indicated that ‘many applications of nanotechnology pose no new health or safety risks’, it also recognised that the health, safety and environmental hazards of nanoparticles (diameter less than 100nm) and nanotubes requires investigation. A significant body of data exists regarding the toxicological effects of nanoparticles (also termed ultrafine particles) in mammalian systems, particularly with respect to the lungs and cardiovascular system. Such studies suggest that smaller particles, with a larger surface area per unit mass, are more potent at inducing oxidative stress and inflammation leading to adverse health effects. However, very few papers have been published regarding the effects of nanoparticles on other phyla such as micro-organisms, invertebrates and vertebrates from terrestrial and aquatic habitats. Since nanoparticles from both domestic and industrial products will be released into the environment, eg. wastewater, it is essential to investigate the impact on such species and the ecosystem. This presentation will aim to discuss how existing knowledge regarding the mammalian toxicology of nanoparticles could be used to generate an effective, efficient and focused strategy for testing the ecotoxicolgy of nanoparticles.