bluuebunny/crossref_metadata_2025_split huggingface dataset:
Piezoelectric Effects in GaN/AlGaN Multiple Quantum Wells Probed by Picosecond Time-Resolved Photoluminescence
Authors: Kim H. S. , Lin Y. , Jiang H. X. , Chow W. W. , Botchkarev A. , Morkoç H. 
Published: April 2011

AbstractPiezoelectric effects in GaN/AlGaN multiple quantum wells (MQWs) have been directly probed by picosecond time-resolved photoluminescence (PL) spectroscopy. The time-resolved PL spectra of the 40 Å well MQWs reveal that the PL transition peak position is in fact blueshifted at early delay times due to the collective effects of quantum confinement of carriers, piezoelectric field, and Coulomb screening. However, the spectral peak position shifts toward lower energies as the delay time increases and becomes redshifted at longer delay times. By comparing experimental and calculation results, we have obtained a low limit of the piezoelectric field strength to be about 560 kV/cm in the 40 Å well GaN/Al0.15Ga0.85N MQWs.
Effects of Surface Preparation on Epitaxial GaN on 6H-SIC Deposited Via Mocvd
Authors: Xie Z. Y. , Wei C. H. , Li L. Y. , Edgar J. H. , Chaudhuri J. , Ignatiev C. 
Published: April 2011

AbstractA comparison was made of 6H-SiC surfaces etched with H2, C2H4/H2, and HCl/H2, and the resulting crystal quality of epitaxial GaN films deposited on these substrates. To remove the many fine scratches and to smooth the rough surfaces typical of commercial SiC substrates, the Si-face 6H-SiC substrates were etched in H2, C2H4/H2, and HCl/H2 at 1450°C. GaN was subsequently deposited on these etched surfaces after first depositing a low temperature GaN buffer layer via metalorganic chemical vapor deposition (MOCVD). The surface morphologies after etching and after GaN deposition were characterized by atomic force microscopy and Normaski differential interference contrast microscopy, while the crystal quality of the GaN films was assessed by double crystal x-ray rocking curves and x-ray topography. 6H-SiC substrate surfaces were improved in terms of the removal of scratches and the reduction of surface roughness, and both surface morphology and crystal quality of the subsequently deposited GaN films were enhanced. However, the dislocation density was not decreased by the surface etching. The best GaN film was produced by etching the substrate in pure H2 for 40 minutes before growth. Recommendations for the optimum substrate treatment are made.
Influence of the First Preparation Steps on the Properties of GaN Layers Grown on 6H-SIC by Mbe
Authors: Lantier R. , Rizzi A. , Guggi D. , Lüth H. , Neubauer B. , Gerthsen D. , Frabboni S. , Colì G. , Cingolani R. 
Published: April 2011

AbstractThe Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550°C on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AIN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations.
Temperature Effect on the Quality of Ain Thin Films
Authors: Thompson Margarita P. , Drews Andrew R. , Huang Changhe , Auner Gregory W. 
Published: April 2011

AbstractAIN thin films were deposited at various substrate temperatures via Plasma Source Molecular Beam Epitaxy. The films were grown on 6H-SiC (0001) substrates. Reflection High Energy Electron Diffraction and Atomic Force Microscopy showed a dramatic change in the surface morphology of the film grown at 640°C. This is attributed to a change in the growth mechanism from pseudomorphic at lower temperatures to three-dimensional at higher than 640°C temperatures. Photoreflectance measurements showed an absorption shift toward 200 nm as the deposition temperature increases which is attributed to the change in the growth mechanism at higher temperatures. X-Ray Diffraction was unable to conclusively determine the AIN (0002) peak due to a significant diffuse intensity from the SiC (0002) peak. A MIS structure was created by depositing Pt contacts on the film grown at 500°C. I-V measurements showed that the Pt/AIN contact is Schottky.
Piezoelectric Field Effect on Optical Properties of GaN/GaInN/AlGaN Quantum Wells
Authors: Im Jin Seo , Kollmer H. , Gfrörer O. , Off J. , Scholz F. , Hangleiter A. 
Published: April 2011

AbstractWe designed and studied two sample groups: first, GaInN/AlGaN/GaN quantum wells with asymmetric barrier structure and secondly, GaInN/GaN quantum wells with asymmetrically doped barriers. Time-resolved measurements on the asymmetric structure reveal an enhanced oscillator strength when the AlGaN barrier is on top of the GaInN quantum well, indicating a better carrier confinement in such a structure. The photoluminescence emission energy of the GaInN/GaN quantum well with doped GaN barriers shifts towards higher energy than that of undoped samples due to screening, but only when the GaN barrier layer below the quantum well is doped. In contrast, the sample where only a GaN cap layer above the quantum well is doped, shows no blue-shift. These results, showing asymmetries in GaInN/GaN quantum wells, provide confirming evidence of the piezoelectric field effect and allow us to determine the sign of the piezoelectric field, which points towards the substrate in a compressively strained quantum well. Furthermore, we performed model calculations of the global band bending and the screening effect, which consistently explain our experimental findings.
Rapid Thermal Processing of Implanted GaN Up to 1500°C
Authors: Cao X. A. , Pearton S. J. , Singh R. K. , Abernathy C. R. , Han J. , Shul R. J. , Rieger D. J. , Zolper J. C. , Wilson R. G. , Fu M. , Sekhar J. A. , Guo H. J. , Pennycook S. J. 
Published: April 2011

AbstractGaN implanted with donor(Si, S, Se, Te) or acceptor (Be, Mg, C) species was annealed at 900-1500°C using AIN encapsulation. No redistribution was measured by SIMS for any of the dopants and effective diffusion coefficients are ≤2×10-13 cm2 s-1 at 1400°C, except Be, which displays damage-enhanced diffusion at 900°C and is immobile once the point defect concentration is removed. Activation efficiency of ∼90% is obtained for Si at 1400°C. TEM of the implanted material shows a strong reduction in lattice disorder at 1400-1500°C compared to previous results at 1100°C. There is minimal interaction of the sputtered AIN with GaN under our conditions, and it is readily removed selectively with KOH.
Photoelectrochemical Etching of InxGal-xN
Authors: Cho Hyun , Donovan S.M. , Abernathy C.R. , Pearton S.J. , Ren F. , Han J. , Shul R.J. 
Published: April 2011

AbstractA comparison of KOH, NaOH and AZ400K solutions for UV photo-assisted etching of undoped and n+ GaN is discussed. The etching is diffusion-limited (Ea < 6kCal-mol-1) under all conditions and is significantly faster with bias applied to the sample during light exposure. No etching of InN was observed, due to the very high n-type background doping (> 1020cm-3) in the material.
Modeling of a GaN Based Static Induction Transistor
Authors: Bunea Gabriela E. , Dunham S.T. , Moustakas T.D. 
Published: April 2011

AbstractStatic induction transistors (SITs) are short channel FET structures which are suitable for high power, high frequency and high temperature applications. GaN has particularly favorable properties for SIT operation. However, such a device has not yet been fabricated. In this paper we report simulation studies on GaN static induction transistors over a range of device structures and operating conditions. The transistor was modeled with coupled drift-diffusion and heat-flow equations. We found that the performance of the device depends sensitively on the thermal boundary conditions, as self-heating effects limit the maximum voltage swing.
Ensemble Monte Carlo Study of Electron Transport in Bulk Indium Nitride
Authors: Bellotti E. , Doshi B. , Brennan K. F. , Ruden P. P. 
Published: April 2011

AbstractEnsemble Monte Carlo calculations of electron transport at high applied electric field strengths in bulk, wurtzite phase InN are presented. The calculations are performed using a full band Monte Carlo simulation that includes a pseudopotential band structure, all of the relevant phonon scattering agents, and numerically derived impact ionization transition rates. The full details of the first five conduction bands, which extend in energy to about 8 eV above the conduction band minimum, are included in the simulation. The electron initiated impact ionization coefficients and quantum yield are calculated using the full band Monte Carlo model. Comparison is made to previous calculations for bulk GaN and ZnS. It is found that owing to the narrower band gap in InN, a lower breakdown field exists than in either GaN or ZnS.
Monte Carlo Simulation of Hall Effect in n-Type GaN
Authors: Albrecht J.D. , Ruden P.P. , Bellotti E. , Brennan K.F. 
Published: April 2011

AbstractResults of Monte Carlo simulations of electron transport for wurtzite phase GaN in crossed, weak electric and magnetic fields are presented. It is found that the Hall factor, τH = μHall/μdrift, decreases monotonically as the temperature increases from 77K to 400K. The low temperature value of the Hall factor increases significantly with increasing doping concentration. The Monte Carlo simulations take into account the electron-lattice interaction through polar optical phonon scattering, deformation potential acoustic phonon scattering (treated as an inelastic process), and piezoelectric acoustic phonon scattering. Impurity scattering due to ionized and neutral donors is also included, with the latter found to be important at low temperature due to the relatively large donor binding energy which implies considerable carrier freeze-out already at liquid nitrogen temperature. The temperature dependences of the electron concentration, drift mobility, and Hall factor are calculated for donor concentrations equal to 5 × 1016 cm-3, 1017 cm-3, and 5 × 1017 cm-3. The Monte Carlo simulations are compared to classical analytical results obtained using the relaxation-time approximation, which is found to be adequate at low temperatures and sufficiently low carrier concentrations so that inelastic scattering effects due to optical phonons and degeneracy effects are negligible. The influence of dislocations on the Hall factor is discussed briefly.
Phonon Dynamics and Lifetimes of AIN and GAN Crystallites
Authors: Bergman Leah , Alexson Dimitri , Nemanich Robert J. , Dutta Mitra , Stroscio Michael A. , Balkas Cengiz , Davis Robert F. 
Published: April 2011

AbstractThe quasi-LO and quasi-TO modes of AIN crystallite were investigated. The analysis indicates that the Raman mode behavior concurs with Loudons’ model of mode-mixing in wurtzite (WZ) structure crystals which is due to the long-range electrostatic field. Phonon-lifetimes of GaN and AIN crystallites were studied via Raman lineshape. It was found that the low energy E2 mode lifetime is about an order of magnitude longer than that of the other modes, and that impurities impact significantly the phonon-lifetimes.
Transport, Growth Mechanisms, and Material Quality in GaN Epitaxial Lateral Overgrowth
Authors: Coltrin Michael E. , Willan Christine C. , Bartram Michael E. , Han Jung , Missert Nancy , Crawford Mary H. , Baca Albert G. 
Published: April 2011

AbstractGrowth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1 μm nucleation zones. Although emission is comprised of both UV (∼365nm) and yellow (∼550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines.
Fabrication of Self-Assembling AlGaN Quantum Dot on AlGaN Surfaces Using Anti-Surfactant
Authors: Hirayama H. , Aoyagi Y , Tanaka S. 
Published: April 2011

AbstractWe report on the first artificial fabrication of self-assembling AlGaN quantum dots (QDs) on AIGaN surfaces using metal organic chemical vapor deposition (MOCVD). The AlGaN QDs are fabricated using a growth mode change from 2-dimensional step-flow growth to 3-dimensional island formation by modifying the AlGaN surface energy with Si anti-surfactant. The average lateral size and the thickness of fabricated AlGaN QDs, as determined by AFM, are approximately 20 nm and 6nm, respectively. The dot density was found to be controlled from 5×1010cm-2 down to 2×109 cm-2 by increasing the dose of Si anti-surfactant. We obtained the photoluminescence (PL) from AlGaN QDs embedded with Al0.38Ga0.62N capping layers. The Al incorporation in AlGaN QDs was controllable within the range of 1-5 %.
Ni/Si-Based Contacts to GaN: Thermally Activated Structural Transformations Leading to Ohmic Behavior
Authors: Kaminska E. , Piotrowska A. , Jasinski J. , Kozubowski J. , Barcz A. , Golaszewska K. , Thomson D.B. , Davis R.F. , Bremser M.D. 
Published: April 2011

AbstractStructural transformations in Ni/Si-based contacts to GaN occurring under heat treatment have been studied using transmission electron microscopy and secondary ion mass spectrometry. Transition from non-ohmic to ohmic behavior correlates with reaction between Ni and Si, and decomposition of the initially formed interfacial Ni:Ga:N layer. Transport of dopant atoms from metallization into GaN testifies in favour of the SPR process of ohmic contact formation
Epitaxial and Conductive RuO2 Thin Films Grown on MgO and LaAlO3 by MOCVD
Authors: Lu P. , He S. , Li F. X. , Jia Q. X. 
Published: April 2011

AbstractConductive RuO2 thin films have been grown epitaxially on (100) MgO and (100) LaAlO3 substrates by metal-organic chemical vapor deposition(MOCVD) at different temperatures. The microstructural properties of the RuO2 films have been studied using x-ray diffraction and scanning electron microscopy. Different growth and microstructure properties were observed for the films deposited on the two substrates. The films on MgO are epitaxial at deposition temperatures as low as 350°C, and consist of two variants with an orientation relationship given by (110) RuO2 /(100) MgO and [001] RuO2//[011]MgO. The films on LaAlO3, on the other hand, are epitaxial only at deposition temperatures of 600°C and above, and contain four variants with an orientation relationship given by (200)RuO2//(100)LaAlO3 and [011] RuO2//[011] LaAlO3. The observed microstructures of epitaxially grown films can be explained based on geometric considerations for the films and substrates.
Dependence of Ferroelectric Properties of SBT Based Capacitors on the Electrode Material
Authors: Tirumala S. , Ryu S. O. , Lee K. B. , Vedula R. , Desu S. B. 
Published: April 2011

AbstractThe effect of various electrode materials on the ferroelectric properties of SrBi2Ta2O9 (SBT) thin films has been investigated for non-volatile memory applications. Two sets of electrode structures, viz., Pt-Ir based and Pt-Rh based, were sputter deposited in-situ on Si substrates. SBT thin films were deposited on these electrodes using a metal-organic solution deposition technique followed by a post-deposition anneal at 750 °C in oxygen. Structural characterization revealed a polycrystalline nature with predominant perovskite phase in SBT thin films. Ferroelectric properties were studied in capacitor mode by depositing top electrodes, where the top electrode material is identical to that of the bottom electrode. Extensive analysis of the ferroelectric properties signify the important role played by the electrode material in establishing the device applicability is reported in this work.
All Epitaxial Babi4Ti4O15 - LaNiO3 Heterostructures
Authors: Satyalakshmi K. M. , Pignolet A. , Alexe M. , Zakharov N. D. , Harnagea C. , Senz S. , Reichelt S. , Hesse D. , Gösele U. 
Published: April 2011

AbstractBismuth-based layer-structured ferroelectric oxides are gaining much attention for ferroelectric thin film applications due to their low fatigue. Epitaxial thin films of these layered ferroelectric oxides grown on epitaxial perovskite-type conducting oxide electrodes such as LaNiO3 are known to further improve the fatigue resistance. In this paper the ferroelectric properties of BaBi4Ti4O15films grown by pulsed laser deposition on epitaxial LaNiO3/SrTiO3(100) and LaNiO3/YSZ/Si(100) substrates are presented. BaBi4Ti4O15thin films with mixed a - and c - orientation exhibit ferroelectric hysteresis loops with a remanent polarization Pr of 2 μC/cm2and a coercive field Ec of about 75 kV/cm. The effect of the deposition parameters on thin film orientation, morphology and the ferroelectric properties of BBiT are discussed.
Chemical Vapor Deposition Technology of (Ba,Sr)TiO3 Thin Films for Gbit-Scale Dynamic Random Access Memories
Authors: Horikawa Tsuyoshi , Tarutani Masayoshi , Kawahara Takaaki , Yamamuka Mikio , Hirano Noriko , Sato Takehiko , Matsuno Shigeru , Shibano Teruo , Uchikawa Fusaoki , Ono Kouichi , Oomori Tatsuo 
Published: April 2011

AbstractThe current status of (Ba,Sr)TiO3 [BST] capacitor technology using a liquid source chemical vapor deposition (CVD) method is reviewed, focusing on the CVD techniques and the physical, electrical and process-integration-related properties of Ru/BST/Ru capacitors. The use of a new titanium metalorganic (MO) source, titanium bis(tert-butoxy) bis(dipivaloylmethanato) [Ti(tertBuO)2 (DPM)2] dissolved in tetrahydrofuran (THF) turned out to enable highly conformal deposition of BST films with a coverage ratio of ∼ 70 % for a trench with an aspect ratio of ∼ 5. Electrical properties of a 24-nm-thick BST film, deposited on a Pt substrate at a low substrate temperature of 480 °C, were also confirmed to be equivalent SiO2 thickness (teq) of ∼ 0.5 nm and leakage current of ∼ 1 ×10-7 A/cm2 at 1 V. As for the Ru/BST/Ru capacitors, no deteriorations of Ru electrode and BST/Ru interface were observed after 750 °C post-annealing experiment, showing good thermal stability of Ru as a practical electrode material. Although current leak through Ru/BST/Ru capacitors slightly increased after the H2 annealing, such degradation in the leakage properties was restored by post-annealing in N2 ambience. Integrated Ru/BST/Ru capacitors with a 30-nm-thick CVD-BST film were fabricated by 0.5 μm ULSI technology, and low leakage current was confirmed for the stacked capacitors. Regarding the reproducibility of BST deposition by the liquid source CVD method, the deviation ratio of ∼ ± 2.3 % in film thickness was obtained for ∼ 100 successive depositions, thickness uniformity across the wafers was ∼ ± 1.1 %. The above results imply the potential applicability of BST capacitor technology using a liquid source CVD method for Gbit-scale DRAMs.
Schottky Barrier Heights of Tantalum Oxide, Barium Strontium Titanate, Lead Zirconate Titanate and Strontium Bismuth Tantalate
Authors: Robertson J , Chen C W 
Published: April 2011

AbstractSchottky barrier heights of various metals on tantalum pentoxide, barium strontium titanate, lead zirconate-titanate and strontium bismuth tantalate have been calculated as a function of metal work function. These oxides have a dimensionless Schottky barrier pinning factor, S, of 0.28 – 0.4 and not close to 1, because S is controlled by the Ti-O type bonds not Sr-O type bonds, as assumed previously. Band offsets on silicon are asymmetric with much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate (BST) are relatively poor barriers to electrons on Si.
In-Situ TEM Study of Domain Propagation in Ferroelectric Barium Titanate, and Its Role in Fatigue
Authors: Krishnan A. , Bisher M.E. , Treacy M.M.J. 
Published: April 2011

AbstractWe have conducted in-situ transmission electron microscopy (TEM) experiments on thinned single crystal barium titanate in order to study the effects of applied electric field, temperature, electron beam irradiation and UV irradiation on domain nucleation and propagation. We observe two basic modes of domain wall motion; (i) a lateral motion which uniformly widens or narrows the total domain width; (ii) a “zipping” motion in which one end of a domain narrows to a point, which then propagates lengthwise, widening (or narrowing) the domain behind it. Both domain creation and destruction can occur by this latter process. When cooling from above Tc, domain growth usually occurs by the “zipping” motion. We believe that both the lateral and “zipping” modes of motion are related. The “zipping” mode tends to occur in the presence of inhomogeneous long-range strain fields, or when trapped charges are present locally. In some instances, the trapped charge is strong enough to show significant image contrast in bright-field. Domain motion, initiated by heat, electric fields or UV irradiation, moves such charges. A model of domain motion is presented which shows how displacement charge can be injected into the ferroelectric, and which may contribute to the fatigue of these materials.
Strain in Epitaxial BaTiO3 Thin Films Prepared by MOCVD
Authors: Chattopadhyay S. , Teren A. , Wessels B.W. 
Published: April 2011

AbstractThe microstrain in epitaxial BaTiO3 thin films has been investigated using x-ray diffraction. The full width half maximum of the (001) diffraction peaks ranged from 0.12 to 0.49 deg. From the analysis of the angular dependence of the diffraction peak broadening, it is concluded that the broadening is due predominantly to strain. The magnitude of the microstrain decreases sharply with increasing film thickness.
MOCVD Process of Ferroelectric Lead Germanate Thin Films and Bottom Electrode Effects
Authors: Zhang Fengyan , Li Tingkai , Nguyen Tue , Hsu Sheng Teng 
Published: April 2011

AbstractPb5Ge3O11 is a new promising candidate for nonvolatile memory such as one-transistor memory applications because of its moderate polarization and relative low dielectric constant. But this material is a low symmetry ferroelectric material and it is said the spontaneous polarization exists only along the c-axis. Furthermore, in the PbO- GeO 2 system, the stability range for the Pb5Ge3O11 phase is very limited and that even a relatively small deviation in composition or in growth temperature could lead to the formation of other lead germanate compounds. Many methods have been used to grow Pb5Ge3O11 film. This is the first time the Pb5Ge3O1 thin film has been successfully grown by advanced MOCVD technique with a liquid delivery system. This paper will discuss the MOCVD process for growing Pb5Ge3O11 thin films on different electrodes (Pt, Ir and Pt/Ir). The properties of these electrodes, the microstructures of the Pb5Ge3O11 thin films on these electrodes and their ferroelectric properties will be discussed. The advanced two-step deposition technique has been used to improve the uniformity of the Pb5Ge3O11 film. Pure c-axis oriented Pb5Ge3O11 thin film and polycrystalline Pb5Ge3O11 thin film with preferred c-axis orientation and some Pb3GeO5 secondary phase have been successfully grown on these electrodes with good ferroelectric properties.