bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation of Continuous Nanometer PtSi Thin Film on Si by Pulsed Laser Deposition (PLD)
Authors: Li Meicheng , Chen Xuekang , Wang Jing , Yang Jianping , Lei Zhanxu , Wu Gan , Zhao Liancheng 
Published: April 2011

ABSTRACTMetal-based silicides on silicon substrates are a widely used material system for infrared detection. PtSi/p-Si infrared Schottky barrier detectors (IRSBD) have become one of the most successful photoemisive infrared detectors. Till now, most of the efforts have been focused on the design of two dimensional PtSi-SBD arrays for the infrared (IR) camera. In this paper, we discussed the formation conditions of PtSi. Qualities are compared for PtSi films prepared at different conditions including different annealing sequences, annealing time, film thickness, and annealing ambient using pulsed laser deposition on various temperature substrates. Film structures and compositions, phase's formation using different processes are analyzed. By studying the kinetics of PtSi formation during various annealing processing, preferable preparing conditions are proposed to form the continuous PtSi ultra-thin film on Si substrate by PLD.
Effect of Copper-Induced Recrystallization on the Piezoresistivity of Germanium Films
Authors: Khakifirooz A. , Mohajerzadeh S. S. , Haji S. , Soleimani E. Asl 
Published: April 2011

ABSTRACTEffect of copper-induced recrystallization on the piezoresistivity of germanium films is reported. SEM and XRD are used to study the crystalline structure of the films, while RBS, PIXE, and EDX are utilized to investigate their composition. Significant grain growth is observed in Ge films, upon annealing a Cu/Ge bilayer at 400°C for 30 minutes. Also a dominant orientation of Ge(111) is observable when amorphous precursor films are used. Hall measurements and cantilever beam bending show a considerable increase in hole mobility and longitudinal gauge factor, respectively
Formation of Self-Assembled Nanometer-Scale InP Islands on Silicon Substrates
Authors: Bakin A.S. , Piester D. , Wehmann H.-H. , Ivanov A.A. , Schlachetzki A. , Becker K.D. 
Published: April 2011

ABSTRACTThree-dimensional islands of InP have been reproducibly grown in the Stranski-Krastanow growth mode on Si (001) and (111) by using metal-organic vapor phase epitaxy in order to obtain nanometer-scale quantum dots. Atomic-force microscopy was used to determine the morphology of the samples and to evaluate the dimensions of the islands. Formation of three-dimensional islands with densities as high as 2.5×1010 cm−2 and small sizes have been observed. The evolution of island morphology is explained in terms of strain-relaxing mechanisms at the first stages of InP/Si heteroepitaxy.
X-ray Photoelectron Spectroscopy Evaluation on Surface Chemical States of GaN, InGaN and AlGaN Heteroepitaxial Thin Films Grown on Sapphire by MOCVD
Authors: Li K. , Wee A.T.S. , Lin J. , Feng Z. C. , Chua S.J. 
Published: April 2011

ABSTRACTThe surface chemical states of MOCVD grown GaN, AlGaN and InGaN, and the influence of different dopants have been studied with x-ray photoelectron spectroscopy (XPS). The results show that for most of the samples the N 1s peak can be fitted with a dominant GaN peak at the binding energy of 397.2 ± 0.2 eV and a small N-H peak at the binding energy of 398.5 ± 0.2 eV, while Ga 3d can be deconvoluted into three peaks, i.e., elemental Ga at 18.5 ± 0.1 eV, GaN at 19.7 ± 0.1 eV, and Ga2O3 at 20.4 ± 0.1 eV. Si-doping appears to have small influence on the surface chemical states of GaN. Compared with Si-doping, the influence of Mg-doping appears -to be larger. In addition to a change in the component intensities, Mg-doping also causes the N ls and Ga 3d peaks to broaden. The ternary AlxGa1−xN (x ∼ 0.025) sample shows aluminum surface segregation, while the undoped InxGa1−xN(x ∼0.12) shows indium surface deficiency
New Tools to Control Morphology of Self-Organized Quantum Dot Nanostructures
Authors: Shchukina V.A. , Ledentsova N.N. , Ustinov V.M. , Musikhin Yu.G. , Volovik V.B. , Schliwa A. , Stier O. , Heitz R. , Bimberg D. 
Published: April 2011

ABSTRACTWe consider several approaches to control morphology of self-organized quantum dot (QD) nanostructures. (i) We study effects of temperature and of temperature ramping on formation of QD arrays. The theory of equilibrium distribution of island volumes is developed predicting an entropy-driven decrease of island volume at higher temperatures. Experiments on InAs/GaAs(001) obtained both at submonolayer deposition and in Stranski-Krastanow (SK) growth mode reveal the decrease of island volume with temperature increase that agrees with the thermodynamic picture of island formation. (ii) We show a reversibility of temperature-driven changes in island volume, shape, and density for SK InAs/GaAs(001) islands and a new possibility to control QDs. (iii) We consider an advanced way of formation of complex QD structures. For multisheet arrays of strained islands a transition between correlation and anticorrelation driven by the spacer thickness is predicted theoretically and confirmed experimentally. (iv) The overgrowth of InAs/GaAs islands by an InGa(Al)As alloy leads to alloy phase separation in the capping layer and an effective increase of both the lateral size and the height of the QDs. These complex growth approaches enable us to tune efficiently electronic spectra of the QD systems.
The Effect of Magnesium Oxide Buffer on the Epitaxial Growth of Zinc Oxide on Sapphire
Authors: Chen Y.F. , Ko H.J. , Hong S.K. , Hanada T. , Yao T. , Segawa Y. 
Published: April 2011

ABSTRACTZnO single crystal thin film is grown on Al2O3(0001) substrate by plasma-assisted molecular beam epitaxy employing a thin MgO buffer layer. Using reflection high-energy electron diffraction (RHEED), we investigated the surface morphology evolution during the buffer and ZnO growth. We found that a few nanometers thick MgO layer deposited on Al2O3(0001) substrate strongly influences the subsequent growth of ZnO by promoting lateral epitaxial growth, which eventually leads to an atomically flat surface. As a result, (3×3) surface reconstruction of ZnO is observed and RHEED intensity oscillations are recorded. Structural investigations indicate that MgO with rock-salt crystallographic structure forms on the Al2O3(0001) surface as a template between the substrate and ZnO epilayer. Above that, the ZnO epilayer grows with little strain. The mosaicity in the ZnO film is suppressed by more than two orders as indicated by both symmetric and asymmetric X-ray rocking curves. The twin defect with a 30° in-plane crystal orientation difference is completely eliminated. Free exciton emissions at 3.3774 eV (XA) and 3.383 eV (XB) are observed in photoluminescence at 4.2 K further indicating the high quality of the resulting ZnO epilayers.
Kinetic Roughening of Multilayer Ag/Ag(100) Films: Complex Temperature-Dependence in a Simple System
Authors: Stoldt C.R. , Caspersen K.J. , Bartelt M.C. , Jenks C.J. , Evans J.W. , Thiel P.A. 
Published: April 2011

ABSTRACTMetal(100) homoepitaxial systems constitute perhaps the simplest class of systems in which to study thin film growth. Yet, our Variable-Temperature Scanning Tunneling Microscopy (VTSTM) analysis of Ag/Ag(100) homoepitaxy reveals that the variation of roughness with temperature is extraordinarily complex. As the deposition temperature is reduced from 300K to 50K, the roughness of 25 monolayer films first increases, then decreases, and then increases again. Furthermore, a transition from mound formation to self-affine (semi-fractal) growth occurs at around 135K. We postulate that the following the atomistic mechanisms underly this behavior: the existence of a small step-edge barrier inhibiting diffusive downward transport; “downward funneling” of atoms deposited at step edges and microprotrusions towards lower four-fold hollow adsorption sites; and statistically significant deviations from “complete” downward funneling at lower temperatures, where deposited atoms instead become trapped on the sides of (the more prevalent) small steep microprotrusions. To support these postulates, we employ kinetic Monte Carlo simulations to show that atomistic (lattice-gas) models for epitaxial growth, which incorporate these mechanisms, reproduce the experimental data quantitatively.
Microscopical Study of the Structural Evolution of Sol-Gel Derived Buffer Layers for the Integration of YBCO on Biaxially Textured Nickel
Authors: Dobberstein H. , Schwartz R. W. , Clem P. G. , Carroll D. L. , Czerw R. 
Published: April 2011

ABSTRACTEpitaxial buffer layers of Ho2O3 on biaxially textured nickel were fabricated using a chelate (acetic acid) solution route as an alternative to the 2-methoxyethanol solution approach, which has demonstrated good texturing characteristics. Plan-view SEM studies of the films as a function of heat treatment temperature have shown that the holmium oxide film pyrolyzes into an open structure with a high level of interconnected porosity before densification, without significant film shrinkage in the thickness direction. Consolidation of the film started around 900°C along the backbone of the open structure and sintering to a dense film of uniform small crystallites (∼25 nm) was observed at higher temperature. The as-received nickel tapes displayed significant surface damage with a roughness on the order of 1000 Å. Electron backscattering analysis suggests that only 65% of the nickel grains were aligned along the (100) axis within 5°. Finally, STM studies of the nickel substrate have shown that small nickel oxide crystallites were formed on the surface when the substrate is in contact with air.
Control of Variants in Heteroepitaxy by Substrate Miscut
Authors: Flynn C P , Bonham S M , Eades J A , Ondrejcek M , Swiech W , Zhou G L 
Published: April 2011

ABSTRACTThis paper discusses variants that occur in heteroepitaxy when the substrate possesses symmetries that are absent from the epilayer. Variants are enumerated in terms of 2-D symmetries of the substrate and epilayer, as they exist terminated at their interface. In this formulation, all possible cases can be presented in a single table. The role of miscut in controlling otherwise equal variants proportions is discussed with a view to eliminating unwanted variants and thereby improving the translational invariance of the materials. We summarize an experimental study of a (3m) symmetry epilayer growing on a (2mm) substrate, specifically Cu3Au (111) grown by molecular beam epitaxy on Nb (110), for which the two variants predicted from symmetry are stacking twins. Miscuts of about 1° along the indicated azimuth are sufficient to eliminate all except ∼ 0.1% of the less favored variant. This has interesting consequences in the context of the theory. A detailed understanding of the mechanisms for this example requires information about nanostructures that develop on the miscut Nb (011) surface. State-of-the-art information about novel substrate nanostructures, derived from scanning probe and low energy electron microscopies, is presented, and the prospects for a predictive science of variant control in heteroepitaxial growth are assessed.
AlGaN-Based Microwave Transmit and Receive Modules
Authors: Zolper John C. 
Published: April 2011

ABSTRACTAlGaN High Electron Mobility Transistors (HEMTs) have made great progress for solid state power amplifiers with the demonstration of an X-band power density up to 9.8 W/mm. This high power density is the result of the high current and voltage capability of this material system. Recently, it has also been shown that these devices can achieve low microwave added noise figures (NF = 0.6 dB at 10 GHz) while maintaining a large breakdown voltage (>60 V) and hence a large dynamic range. These results imply that AlGaN HEMTs can be used to perform the active transmit and receive functions in more robust, higher dynamic range modules. In this paper, the progress in AlGaN microwave HEMTs is reviewed and the issues related to AlGaN transmit and receive (T/R) modules are described.
A comparative study of AlGaN- and GaN-based lasing structures for near- and deep-UV applications
Authors: Bidnyk Sergiy , Lam Jack B. , Gainer Gordon G. , Little Brian D. , Kwon Yong-Hwan , Song Jin-Joo , Bulman Gary E. , Kong Hua-Shuang 
Published: April 2011

ABSTRACTWe report a comprehensive study on the optical properties of GaN- and AlGaN-based lasing structures at high-levels of optical excitation (carrier densities of 1017−1020 cm−3) and identify critical issues necessary for the development of near- and deep-UV light emitting devices. We successfully achieved room temperature stimulated emission (SE) with emission wavelengths ranging from 351 nm to 373 nm in a variety of samples. Through an analysis of the temperature-dependent lasing characteristics, combined with absorption and time-resolved photoluminescence measurements, we estimated the carrier density required to achieve the SE threshold in GaN epilayers. We found that in AlGaN epilayers, the onset of SE (∼1019 cm−3) occurs at carrier densities one order of magnitude higher than in thick GaN epilayers, indicating that an electron-hole plasma is the dominant gain mechanism over the entire temperature range studied (10 K to 300 K). A remarkably low lasing threshold was observed in GaN/AlGaN heterostructures over the temperature range of 10 K to 300 K. Our experimental results indicate that GaN/AlGaN heterostructures could be used to efficiently generate laser emission with wavelengths shorter than 373 nm. The implications of this study on the development of UV laser diodes is discussed.
Lateral polarity heterostructures by overgrowth of patterned AlxGa1-xN nucleation layers
Authors: Dimitrov R. , Tilak V. , Murphy M. , Schaff W.J. , Eastman L.F. , Lima A.P. , Miskysa C. , Ambacher O. , Stutzmann M. 
Published: April 2011

ABSTRACTIn this study thin AlxGa1−xN nucleation layers on sapphire were patterned and overgrown by plasma-induced molecular beam epitaxy (PIMBE) and metalorganic chemical vapor deposition (MOCVD) to obtain adjacent regions of GaN and AlGaN/GaN heterostructures with different polarities. The role of polarity on the structural and electrical properties of epitaxial layers and AlGaN/GaN heterostructures was investigated for samples grown on patterned AlN or GaN nucleation layers. Epitaxial GaN and AlGaN/GaN heterostructures grown on Al-face AlN or N- face GaN nucleation layers were found to be Ga-face or N-face, respectively, independent of the technique used for the overgrowth.
Cathodoluminescence of Lateral Epitaxial Overgrowth GaN: Dependencies on Excitation Conditions
Authors: Cargill G. S. , Campo Eva , Yue Lanping , Ramer J. , Schurman M. , Ferguson I. T. 
Published: April 2011

ABSTRACTWe have found that near-band-edge cathodoluminescence (CL) emission decreases with time for some nominally undoped GaN samples. The rate of intensity decrease depends on the incident beam current. It also depends on the size of the area being scanned, which is determined by the magnification used, although the electron beam voltage and current are held constant and similar regions of GaN are being examined. Faster decrease with time occurs with higher beam currents and higher magnifications. The reduced luminescence efficiency persists over at least 24 hour beam-off periods. The dependence of CL intensity on beam current and on scanned area may be a result of different levels of local charging, and structural modifications caused by this charging, for different beam current and magnification settings.
Photoconductivity Recombination Kinetics in GaN films
Authors: Misra M. , Moustakas T.D. 
Published: April 2011

ABSTRACTPhotoconductive detectors were fabricated on autodoped n-GaN films, with resistivity varying from 10 Ohm-cm to 107Ohm-cm, by molecular beam epitaxy. The mobility-lifetime product, determined from the measurement of photoconductive gain, was found to decrease monotonically from 10−2 cm2/V to 10−7 cm2/V as the dark resistivity was increased. This variation in the ντ products is attributed to changes in photocarrier lifetimes. In order to understand the recombination mechanisms responsible for this photoconductive behavior, the dependence of photoconductivity on excitation intensity (δμσ fλ) was investigated. The exponent λ was found to vary from 0.5 to 1.0, as the dark resistivity of the films increased. These results indicate the presence of exponential band tails extending from the conduction band edge. Furthermore, the dependence of photoconductivity on dark resistivity indicates that the photoconductive response is governed primarily by the location of the dark fermi level. A model accounting for these observations is presented.
Formation and Characterization of Oxides on GaN surfaces
Authors: Mistele D. , Rotter T. , Fedler F. , Klausing H. , Semchinova O.K. , Stemmer J. , Aderhold J. , Graul J. 
Published: April 2011

ABSTRACTWe characterized oxides formed directly on n-GaN surfaces. The methods used for oxide layer formation were both photoanodic oxidation and thermal oxidation. The photoanodic oxidation took place in aqueous solutions of potassium hydroxide with pH values lower than 13. Homogenous oxide films were obtained in the voltage range from -0.6 V to 0.4 V vs the saturated calomel electrode (SCE). The characterization of the oxide layers was performed primarily by Auger electron spectroscopy (AES). First the surface chemistry was determined, proving that Ga-oxide is formed with an attributed stoichiometry of Ga2O3. Secondly, depth profiling shows the oxide thickness to be dependent on the photoanodic voltage and oxidation time. Complementary X-ray diffraction (XRD) studies suggest an amorphous state of the formed layers. Annealing GaN in O2-atmospheres above 900°C also lead to surfaces fully covered with gallium oxide. We found that N-polar surfaces oxidize faster than Ga-polar surfaces, which is in agreement to the theoretical work of Zywietz et al [1]. Furthermore, we report on the electrical properties of the anodized oxide layers by analyzing MOS structures.
Monte Carlo Based Calculation of Transport Parameters for Wide Band Gap Device Simulation
Authors: Bellotti E. , Farahmand M. , Nilsson H.-E , Brennan K. F. , Ruden P. P. 
Published: April 2011

ABSTRACTWe present Monte Carlo based calculations of transport parameters useful in the simulation of III-nitride and SiC based devices. The calculations are performed using a full band ensemble Monte Carlo model that includes numerical formulations of the phonon scattering rates and impact ionization transition rates. Calculations are made for the wurtzite and zincblende phases of GaN, the wurtzite phase of InN, and the 3C (cubic) and 4H phases of SiC. The basic transport parameters determined are saturation drift velocity, and the ionization coefficients as a function of applied electric field. Results from the various materials are finally compared.
Design of AlGaN/GaN Heterojunction Bipolar Transistor Structures
Authors: Zhang Yumin , Cai Cheng , Paul P. 
Published: April 2011

ABSTRACTThe potential of III-nitride materials for the fabrication of bipolar transistors is investigated theoretically. Several different pseudomorphic AlGaN/GaN n-p-n heterojunction bipolar transistor structures are examined through calculations of their band profiles and majority carrier distributions in equilibrium. Spontaneous and piezoelectric polarization charges are utilized to create large hole sheet carrier densities in the base layer, thus minimizing the base spreading resistance. At the same time, a large accelerating field in the base can help reduce the base transit times of the electrons and, hence, increase the current gains of these devices. The effect of strain due to substrate mismatch is also investigated.
Thermal Modeling of III-nitride Heterostructure Field Effect Transistors
Authors: Li T. , Ruden P.P. , Albrecht J.D. , Ancona M.G. , Anholt R. 
Published: April 2011

ABSTRACTThe output characteristics of AlGaN/GaN semiconductor heterostructure field effect transistors are strongly dependent on the ambient temperature of the channel region due to relatively large variations in the electron drift velocity with temperature. A model to simulate the heat flow in AlGaN/GaN HFETs on sapphire and SiC substrates is presented. The non- linearity of the problem arising from the temperature dependencies of the III-nitride and substrate thermal conductivities is examined through the technique of self-consistent boundary conditions. It is found that the use of the linearizing Kirchhoff transformation is a good approximation for these systems. Alternative approaches of heatsinking the devices from the top of the wafer are explored also.
Ohmic Contact Formation Mechanism of Pd-based Contact to p-GaN
Authors: Kim Dae-Woo , Bae Joon Cheol , Kim Woo Jin , Baik Hong Koo , Kim Chong Cook , Je Jung Ho , Hong Chang Hee 
Published: April 2011

ABSTRACTWe have investigated surface treatment effect on the interfacial reaction of Pd/p-GaN interface and also room temperature ohmic contact formation mechanism of Pd-based ohmic contact. In order to examine room temperature ohmic behavior, various metal contact systems were deposited and current-voltage measurements were carried out. In spite of large theoretical Schottky barrier height between Pd and p-GaN, Pd-based contact showed perfect ohmic characteristic even before annealing. According to the results of synchrotron X-ray radiation, the closed-packed atomic planes (111) of the Pd film were quite well ordered in surface normal direction as well as in the in-plane direction. The effective Schottky barrier height of Au/Pd/Mg/Pd/p-GaN was 0.47eV, which was estimated by Norde method. This discrepancy between theoretical barrier height and the measured one might be due to the epitaxial growth of Pd contact metal and so the room-temperature ohmic characteristic of Pd-based ohmic contact was related strongly to the in-plane epitaxial quality of metal on p-GaN.
Reactive Ion Etching of CVD Diamond in CF4/O2, O2 and O2/Ar Plasmas
Authors: Leech Patrick W. , Reeves Geoffrey K. , Holland Anthony S. 
Published: April 2011

ABSTRACTThe reactive ion etching of diamond in O2, CF4/O2, CHF3/O2, O2/Ar) discharges has been examined as a function of bias voltage, flow rate and composition of the gas mixtures. Etching in O2 and O2/Ar plasmas (with flow ratio of O2/Ar >25% ) was characterised by a high etch rate (∼35 nm/min) and an increase in surface roughness with rising bias voltage. The CF4/O2 plasmas also produced a high etch rate (∼50 nm/min) but with only minor dependence of roughness on bias voltage. In comparison, the O2/Ar (with O2/Ar flow ratio <25%) and CHF3/O2 plasmas resulted in a low etch rate (7-10 nm/min). The high and low rate regimes were identified as ion- enhanced chemical etching and physical sputtering respectively. Etching in the O2/Ar plasmas has been attributed to a combination of the two processes dependent on the O2 content.
A Study of Pt/AlN/6H-SiC MIS Structures for Device Applications
Authors: Thompson Margarita P. , Auner Gregory W. , Huang Changhe , Hilfiker James N. 
Published: April 2011

ABSTRACTAlN films with thicknesses from 53 to 79 nm were deposited on 6H-SiC substrates via Plasma Source Molecular Beam Epitaxy (PSMBE). The influence of deposition temperature on the growth mode and film roughness was assessed. The optical constants of the films in the range 0.73-8.75 eV were determined using spectroscopic ellipsometry. Pt/AlN/6H-SiC MIS structures were created and current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed at room temperature and at 250°C. Most of the MIS structures showed rectifying I-V characteristics regardless of growth temperature. A 120-nm-thick AlN film was deposited at 500°C. MIS structures created on this film showed a very low leakage current densities of 6×10−8 A/cm2. The dielectric constant of the film was estimated at approximately 9. The relation between film structure and electrical properties of the films is discussed.