bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallization Kinetics of Seeded SBT ( Sr0.7Bi2.4Ta2O9 ) Powders from Sol-Gel Derived Precursors
Authors: Kumar Gopinathan M. A. , Kwak Woo-Chul , Jung Se-Yon , Hwang Seung-Joon , Sung Yun-Mo 
Published: April 2011

AbstractStrontium bismuth tantalate (SBT) having composition of Sr0.7Bi2.4Ta2O9 has been prepared through sol-gel method using their corresponding metal alkoxides as precursors. Seeded SBT powder was prepared by the addition of 5 wt.% of nanometer sized SBT particles to the sol followed by pyrolysis. By applying non-isothermal kinetic analysis to the DTA results, activation energy values for the unseeded and seeded samples were determined. Enhanced crystallization kinetics was observed for the seeded one and the activation energy for the aurivillius phase formation was found to be 318 kJ/mol, while 375 kJ/mol for the unseeded. The Avrami exponent values for the seeded and unseeded were found to be 2.80 and 0.96 respectively.
Pyroelectric Properties of Alanine Doped TGS Single Crystalline Thick Films under Constant Electric Stress
Authors: Pintilie Lucian , Matei Ion , Pintilie Ioana , Alexandru Horia V. , Berbecaru Ciceron 
Published: April 2011

AbstractPyroelectric properties of triglycine sulfate (TGS) thick films, separately doped with L and D alanine were investigated. Internal bias field of about 1 kV/cm, induced by the two dopants, stabilize the polarization in the opposite direction on the ferroelectric axis. Pyroelectric current (under constant stress) was recorded with a computer controlled Keithley 6517 electrometer, crossing up and down the Curie point. A reverse external electric field was applied on doped materials during heating, crossing up the Curie point. It is shown that the pyroelectric coefficient can be increased about four times at room temperature under un optimized DC electric field applied on the pyroelectric wafer.
Direct Nanoscale Observation of Size Effect on Polarization Instability in Pb(Zr,Ti)O3 film capacitors
Authors: Stolichnov Igor , Colla Enrico , Tagantsev Alexander , Hong Seungbum , Cross Jeffrey S. , Tsukada Mineharu 
Published: April 2011

AbstractMapping of polarization distributions in Pb(Zr,Ti)O3 ferroelectric capacitors with sizes down to 0.5 × 0.5 μm has been studied using scanning probe microscope (SPM) with detection of piezoelectric response through the top electrode. A well reproducible anomaly in polarization distribution namely elevated polarization at the edges and inverse polarization in the center has been observed for the FeCaps of several μm size. This polarization pattern is found to be insensitive to the poling voltage polarity and voltage stress prehistory but strongly dependent on the FeCAP size. Specifically, the polarization anomaly tends to disappear as the FeCAP size scales down to the submicron range. Tentative interpretation of this phenomenon in terms of strain-induced phase transitions in combination with depolarization effects is discussed.
Process Induced Modification of the High Frequency Dielectric Behavior of (100) Textured BaxSr1−xTiO3 (x = 0.5 and 0.6) Thin Films
Authors: Majumder S.B. , Jain M. , Martinez A. , Katiyar R.S. , Fachini E.R. , Keuls F.W. Van , Miranda F.A. , Sahoo P.K. , Kulkarni V.N. 
Published: April 2011

AbstractParaelectric BaxSr1−xTiO3 (BST) (x = 0.5 and 0.6) thin films are attractive candidates for the fabrication of various microwave dielectric devices including phase shifters, resonators, filters, oscillators etc. In the present work we have studied the effect of annealing temperature and ambient on the epitaxial quality, surface morphology, dielectric, and phase shifter characteristics of BST thin films deposited on LaAlO3 substrates. The epitaxial quality of the film was markedly improved as the annealing temperature was increased from 1050 to 1100°C. The degree of phase shift increased from 221 to 328° (measured at 14.5 GHz applying a field of 30V/μm) with the improvement of the epitaxial quality of the film. The insertion loss was also increased with the increase in annealing temperature and therefore the effective phase shifter κ factor (defined by the ratio of the degree of phase shift and insertion loss) remained low (∼30°/dB), while annealing these films in N2 ambient significantly reduced the insertion loss, their dielectric breakdown was observed at relatively lower applied voltage as compared to air and oxygen annealed films. The observed electrical behavior was correlated with the composition, chemical state of the constituents and epitaxial quality of the films synthesized under different annealing conditions.
Ferromagnetic and Paramagnetic Semiconductors Based upon GaN, AlGaN, and GaP
Authors: Overberg Mark E. , Thaler Gerald T. , Frazier Rachel M. , Gila Brent P. , Abernathy Cammy R. , Pearton Stephen J. , Theodoropoulou Nikoleta A. , Arnason Stephen B. , Hebard Arthur F. , Park Yun D. 
Published: April 2011

ABSTRACTEpitaxial growth of the ferromagnetic semiconductors GaMnP:C and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP:C films grown with 9.4% Mn are found to be p-type with hysteretic behavior to room temperature. GaMnN films grown at 700 °C with 2.8% Mn show hysteresis at 300 K, while temperature-dependent magnetization measurements indicate that the magnetism may persist to much higher temperatures (> 325 K). Samples of AlGaMnN have also been prepared for the first time that show improved surface morphology compared to GaMnN but which show only paramagnetic behavior.
First-principles Modeling of Co/SrTiO3/Co Magnetic Tunnel Junctions
Authors: Oleinik I.I. , Tsymbal E.Y. , Pettifor D.G. 
Published: April 2011

ABSTRACTThe atomic and electronic structure of Co/SrTiO3/Co (001) magnetic tunnel junctions (MTJs) was investigated by first-principles density-functional theory. We considered different interface terminations and the most stable structure with the TiO2 termination has been identified based on energetics of adhesion. The electronic structure of the TiO2-erminated MTJ shows an exchange coupling between the interface Co and Ti atoms mediated by oxygen. This coupling induces the magnetic moment of 0.25 μB on the interface Ti atom, which is aligned antiparallel to the magnetic moment of the Co layer. We argue that this might cause the inversion of the spin polarization of tunneling across the SrTiO3 barrier that was found in recent experiments.
Kinetic Exchange Vs. Room Temperature Ferromagnetism in Diluted Magnetic Semiconductors
Authors: Blinowski J. , Kacman P. , Dietl T. 
Published: April 2011

ABSTRACTGuided by the internal-reference rule and the known band o sets in - and - diluted magnetic semiconductors, we discuss the feasibility of obtaining p-type conductivity, required for the carrier-induced ferromagnetism, as well as the cases for which the doping by shallow impurities may lead to the ferromagnetism driven by the double exchange. e consider the dependence of kinetic exchange on the p-d hybridization, on the electronic con gurations of the magnetic ions, and on the energies of the charge transfer betw een the valence band of host materials and the magnetic ions. n the case of n-based - compounds, the doping by acceptors is necessary for the hole-induced ferromagnetism. he latter is, how ever, possible without any doping for some of Mn-, Fe- or Co-based - magnetic semiconductors. n nitrides with Fe or Co carrier-induced ferromagnetism with TC > 300 is expected in the presence of acceptor doping.
Successes and Predictions of A Pseudopotential Approach in Anion-Mixed Nitrides
Authors: Bellaiche L. , Al-Yacoub A. , Modine N. A. , Jones E. D. 
Published: April 2011

AbstractThe construction and the parameters of a new-strain dependent empirical pseudopotentials method are described and provided, respectively. This method is shown to reproduce with a very high accuracy some observed unusual properties in various complex anion-mixed nitride alloys. This method is also used to predict and understand anomalous effects that remain to be experimentally discovered in Ga1−yInyAs1−xNx quaternaries and GaAs0.5−xP0.5−xN2x solid solutions.
Space Radiation Effects in Advanced Solar Cell Materials and Devices
Authors: Walters R. J. , Summers G. P. 
Published: April 2011

AbstractAn investigation of the physical mechanisms governing the response of III-V based solar cells to particle irradiation is presented. The effect of particle irradiation on single and multijunction solar cells is studied through current vs. voltage, spectral response, and deep level transient spectroscopy measurements. The basic radiation response mechanisms are identified, and their effects on the solar cell electrical performance are described. In particular, a detailed analysis of multijunction InxGa1-xP/InyGa1-yAs/Ge devices is presented. The MJ cell response is found to be more strongly affected by the internal cell structure than by the In content.
The Influence of Annealing Temperature and Doping on the Red/Near-Infrared Luminescence of Ion Implanted SiO2:nc-Si
Authors: Tetelbaum D. I. , Burdov V. A. , Trushin S. A. , Mikhaylov A. N. , Revin D. G. , Gaponova D. M. 
Published: April 2011

AbstractThe results of an experimental research of the dependence of photoluminescence (PL) intensity in region about 800 nm for silicon nanoinclusions (quantum dots) obtained by Si ion implantation in SiO2 on the dose of Si ions at two temperatures of an annealing ?ann = 1000 and 1100° ? are presented. It is established that in both cases the dependences have the shape of the curves with a maximum. For 1100° ? the maximum is shifted to the lower dose. The influence of an additional ion doping by the phosphorus on intensity of PL is investigated depending on the dose (concentration) of P and the dose of the silicon at ?ann = 1000° ?. It is shown, that in all the investigated region of P doses, the presence of P enhances the PL. The degree of the enhancement increases with the P dose, but the rate of the intensity enhancement goes down. With the growth of Si dose at the constant dose of P, the degree of the enhancement decreases. In an approximation of an effective mass, the energy spectra of a quantum dot are calculated at the presence of one or several P atoms for various their arrangement.
Electronic structure near the band gap of heavily nitrogen doped GaAs and GaP
Authors: Zhang Yong , Fluegel B. , Hanna M. , Duda A. , Mascarenhas A. 
Published: April 2011

AbstractIsoelectronic impurity nitrogen atoms have been found to generate a series of localized states in GaP and GaAs. These states can be either bound (within the band gap) or resonant (above the band gap) when in the dilute doping limit (roughly < 1019 cm−3 for GaP and < 1018 cm−3 for GaAs). With increasing nitrogen doping level, a shift of the absorption edge from the binary band gap has been observed for the so-called GaPN or GaAsN alloy. We discuss the similarity and dissimilarity between the two systems in the following aspects: (1) How does the nitrogen doping perturb the host band structure? (2) How do the nitrogen bound states evolve with increasing nitrogen doping level? (3) What are the dominant contributors to the band edge absorption? And (4) does a universal model exist for GaPN and GaAsN? Other issues that will be discussed are: how does one define the band gap for these materials, and what is the relevance of various theoretical band structure calculations to the experimentally measured parameters.
Enhanced Photoluminescence from Long Wavelength InAs Quantum Dots Embedded in a Graded (In,Ga)As Quantum Well
Authors: Chen L. , Stoleru V. G. , Pal D. , Pan D. , Towe E. 
Published: April 2011

AbstractThree sets of self-organized InAs quantum dots (QDs) embedded in an external InGaAs quantum well samples were grown by solid source molecular beam epitaxy (MBE). By modifying Indium composition profile within quantum well (QW) region, it's found the photoluminescence emission from quantum dots can be greatly enhanced when employing a graded quantum well to surround QDs. This quantum dots in a graded quantum well structure also preserves the long wavelength (1.3 μm) spectrum requirement for the future use in optoelectronics devices.
GaAs Photodetector for X-ray Imaging
Authors: Sun G. C. , Samic H. , Donchev V. , Gautrot S. , Bourgoin J. C. 
Published: April 2011

AbstractWe describe briefly a cheap and non polluting technique to grow epitaxial GaAs layers, several hundred microns thick, in a matter of hour. Detectors consisting of a p+/i/n+ structure have been realised with these layers and we present their characteristics obtained from currentvoltage, capacitance-voltage measurements as well as their response versus the energy and flux of X-rays.
Intersubband Transitions In Ingaas/Inalas Multiple Quantum Wells Grown On Inp Substrate
Authors: Zhou Qiaoying , Manasreh M. O. , Weaver B. D. , Missous M. 
Published: April 2011

AbstractIntersubband transitions in In0.52Ga0.48As/In0.52Al0.48As multiple quantum wells grown on lattice matched InP substrates were investigated using Fourier transform infrared (FTIR) absorption and photoluminescence (FTPL) techniques. The well width was tailored to produce excited states resonant in the conduction band, at the edge of the conduction band, and confined in the quantum wells. Interband transitions were also probed using FTPL and optical absorption techniques. The FTPL spectra show that three interband transitions exist in the quantum well structures with well width larger than 30 Å. The intersubband transitions in this class of quantum wells seem to withstand proton irradiation with doses higher than those used to deplete the intersubband transitions in the GaAs/AlGaAs multiple quantum wells.
Structural Properties and Doping of Zn1-x(Mg,Li)xOMaterials
Authors: Melgarejo R. E. , Tomar M. S. , Hidalgo A. , Katiyar R. S. 
Published: April 2011

AbstractThe possibility of the solid solutions with MgO provides the opportunity in ZnO/ZnMgO quantum well structures. The recent observation that n-type conductivity in ZnO is due to hydrogen doping open the avenue for p-doping to form p-n junction devices in ZnO.. We report on the synthesis and structural properties of Zn (Mg,Li)O. The possibility of p-doping by P has been explored.
New Approach Towards The Deposition of I-III-VI Thin Films
Authors: Afzaal Mohammad , Crouch David , O'Brien Paul , Park Jin-Ho 
Published: April 2011

AbstractThe ternary chalcopyrite semiconductor Cu(In/Ga)(Se/S)2 is currently used as an absorber layer in high efficiency thin film solar cells. In this study, various types of I-III-VI (I = Cu, III = Ga or In, VI = S or Se) thin films (CuGaS2, CuInS2 and CuInSe2) were prepared from a series of organometallic precursors, M[(S/Se)2CNMeR]n (M = Cu, In, Ga; R = alkyl) by aerosol-assisted chemical vapour deposition (AACVD). In contrast to the metal alkyl compounds, MR3 (M = In and Ga; R = alkyl), which are pyrophoric, the precursors are easy to synthesize by one-pot reactions and are air stable. The optimum growth temperature for the preparation of these films on glass substrates using aerosol-assisted chemical vapour deposition (AACVD) was found to be above 400 °C in terms of crystallinity, although deposition does occur at lower temperatures. The films have been characterised using XRPD, SEM and EDS. SEM analyses show all films are microcrystalline. XRPD results show evidence of the crystalline nature of theses films. The results of this comprehensive study are presented and discussed.
Local Vibrational Modes of Carbon-Hydrogen Complexes in Proton Irradiated AlGaN
Authors: Manasreh M. O. , Weaver B. D. 
Published: April 2011

AbstractLocal vibrational modes (LVMs) of carbon-hydrogen (C-H) complexes in proton implanted AlGaN grown on sapphire by metalorganic chemical vapor deposition (MOCVD) were investigated using Fourier transform infrared (FTIR) spectroscopy. The LVMs exhibit five distinctive peaks in the spectral region of 2846∼2963 cm−1, which are due to the symmetric and asymmetric stretching modes of C-Hn (n=1–3). The LVMs intensities in doped AlGaN are increased as irradiation dose is increased in the entire irradiation dose range used without reaching the saturation stage. On the other hand, undoped samples show that LVMs intensity increase then either decreased or saturated as the irradiation dose is increased above 5×1016 cm−2. Proton irradiation causes a drastic increase in the CH3 LVM while electron irradiation causes the opposite effect suggesting strongly that the observed LVMs are truly due to CH complexes.
I-V And C-V Characteristics of nGaAs-nInSb Heterojunctions Obtained by Pulsed Laser Deposition Technique
Authors: Avdjian Karapet E. 
Published: April 2011

AbstractUsing pulsed laser deposition technique, nGaAs-nInSb heterojunctions (HJs) are obtained. Their electrical properties are studied. The Current-Voltage characteristics show that obtained HJs possess rectifying properties. The rectification coefficient depends strongly on the doping level of GaAs substrate. The linear dependence of C−2 (V) curve in Capacitance-Voltage characteristics, as well as the change of photo-response sign with wavelength, indicates that the HJs have abrupt interface, which is, to the best of our knowledge, a novel result for these HJ materials. The full number of interface states arising due to the lattice mismatch is determined which is in agreement with Hall measurements. Current-Voltage characteristics of obtained HJs are analogous to those of metal-semiconductor junction. Based on the obtained results the energy band diagrams of nGaAs-nInSb HJ is constructed taking into account the interface states.
Development of AIIBVI Semiconductors Doped with Cr for IRLaser Application
Authors: Kasiyan V. A. , Shneck R. Z. , Dashevsky Z. M. , Rotman S. R. 
Published: April 2011

AbstractElectrical and optical measurements obtained with CdSe single crystals doped with chromium from a gas source CrSe over a wide temperature range (500–1050 °C) are compared with ZnSe annealed in liquid metal (Zn). These processes are intended to control the concentrations of the impurity and intrinsic defects. The low temperature annealing of CdSe crystals in CrSe atmosphere allows obtaining high electron mobility up to 9000 cm2/Vs at 80 K and demonstrates the low native defect concentration. A high temperature annealing gives rise to increased electron concentration with decreased mobility. Optical absorption measurements show that at the high annealing temperature effective doping with Cr takes place. The impurity absorption beyond the absorption edge is interpreted by the excitation of Cr++ and Cr+ deep levels
Low-Resistance Electrical Contacts to p-Type GaN by Using InxGa1-xN Cap Layers
Authors: Gessmann Th. , Li Y.-L. , Graff J. W. , Schubert E. F. , Sheu J. K. 
Published: April 2011

AbstractA novel type of low-resistance ohmic contacts is demonstrated utilizing polarization-induced electric fields in thin p-type InGaN layers on p-type GaN. An increase of the hole tunneling probability through the barrier and a concomitant significant decrease of the specific contact resistance can be attributed to a reduction of the tunneling barrier width in the InGaN capping layers due to the polarization-induced electric fields. The specific contact resistance of Ni (10 nm) / Au (30 nm) contacts deposited on the InGaN capping layers was determined by the transmission line method. Specific contact resistances of 1.2 × 10-2 Ω cm2 and 6 × 10-3 & cm2 were obtained for capping layer thicknesses of 20 nm and 2 nm, respectively.
High common-emitter current gains obtained by pnp GaN bipolar junction transistors
Authors: Kumakura Kazuhide , Makimoto Toshiki , Kobayashi Naoki 
Published: April 2011

AbstractWe fabricated pnp GaN bipolar junction transistors and investigated their common-emitter and common-base current-voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The base thickness was 0.12 μm and its electron concentration was estimated to be 3 × 1017 cm-3 from the common-emitter current-voltage characteristics and the base conductivity. The common-emitter current-voltage characteristics showed very low leak current. The maximum current gains at room temperature were 50 and 69 from the common-emitter and the common-base current-voltage characteristics, respectively.
Low Resistance Non-Transparent ohmic Pt-contacts on p-GaN
Authors: Weimar Andreas , Bader Stefan , Brüderl Georg , Kümmler Volker 
Published: April 2011

AbstractThe metal – p-GaN junction for low resistance ohmic contacts is still a challenge to be applied in GaN-based opto electronics as well as in power and high frequency devices. Currently, we try to improve the performance of our blue laser diodes. In order to decrease heat generation during device operation it is necessary to ensure as small contact resistances as possible.In this work, we achieved a specific contact resistance value of RC = 1.8 ± 1.7. 10-5 Ωcm2 for Pt-contacts on MOVPE-grown p-GaN. The Pt-layers were deposited by e-beam and thermally assisted vacuum evaporation after a standard cleaning process. For evaluation of Rc we used optimised circular TLM test patterns defined by photolithography. Best contacts were formed by annealing in Nitrogen athmosphere at 500°C.We also investigated the dependence of the contact resistance on the Mg doping concentration. Therefore p-GaN layers with different Mg-concentrations were grown on SiC-substrates and Pt-contacts were processed. For those samples, we investigated the Mg-concentrations, verified by secondary ion mass spectroscopy (SIMS), the hole concentrations and mobilities in dependence of C(Mg), which we obtained from HALL-measurements, and the contact and sheet resistances, measured by circular TLM measurements.The experiments showed that the optimum Mg-concentration for low contact resistances is higher than 2 1019 cm-3 which was found to provide a maximum hole concentration near 7 1017 cm-3. The influence of self-compensation in p-GaN in bulk and near interfaces will be discussed.
X-ray Photoemission Determination of the Surface Fermi Level Motion and Pinning on n- and p-GaN during the Formation of Au, Ni, and Ti Metal Contacts
Authors: Rickert Kimberly A. , Kim Jong Kyu , Lee Jong-Lam , Himpsel Franz J. , Ellis Arthur B. , Kuech T. F. 
Published: April 2011

AbstractSynchrotron radiation-based x-ray photoemission spectroscopy was used to study the Fermi level position within the band gap for thin metal overlayers of Au, Ni, and Ti on n-GaN and p-GaN. The Fermi level position was determined with the measured Fermi edge of the metal on the sample in order to correct for the presence of non-equilibrium effects. There are two different behaviors observed for the three metals studied. For Au and Ti, the surface Fermi positions on n-GaN and p-GaN are roughly 0.5 eV apart within the band gap. For Ni, the n-GaN and p-GaN have a Schottky barrier that forms at the same place at the gap.
Structural Properties of GaN films grown by Molecular Beam Epitaxy on vicinal SiC(0001)
Authors: Lee C. D. , Feenstra R. M. , Shigiltchoff O. , Devatya R. P. , Choyke W. J. 
Published: April 2011

AbstractGallium nitride films are grown by plasma-assisted molecular beam epitaxy (MBE) on vicinal 6H-SiC(0001) substrates with [1 1 00] and [11 2 0] miscut directions. The hydrogen-etched substrates display straight, or chevron shaped steps respectively, and the same morphology is observed on the GaN films. X-ray rocking curves display substantially reduced width for films on the vicinal substrates compared to singular substrates, for the same Ga/N flux ratio used during growth.