bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pressure Dependence of Optical Transitions in InGaN/GaN Multiple Quantum Wells
Authors: Shan W. , Ager J.W. , Walukiewicz W. , Haller E.E. , McCluskey M.D. , Johnson N.M. , Bour D.P. 
Published: April 2011

AbstractThe effect of hydrostatic pressure on optical transitions in InGaN/GaN multiple quantum wells (MQWs) has been studied. Photoluminescence (PL) and photomodulated transmission (PT) measurements were performed under applied pressure to examine the pressure dependence of optical transitions associated with confined states in MQWs. The PL emission from the MQWs was found to shift linearly to higher energy with applied pressure but exhibit a significantly weaker pressure dependence compared to epilayer samples with similar bandgap energies. Similar pressure coefficients obtained by PT measurements rule out the possibility of PL resulting from deep localized states. We show that the difference in the compressibility of InGaN and of GaN induces a tensile strain in the compressively strained InGaN well layers that partially compensates the applied hydrostatic pressure. This mechanical effect is the primary factor for the smaller pressure dependence of the optical transitions in the InGaN/GaN MQWs. At pressure above 100 kbar, the PL signal in MQWs samples is quenched, indicating that the carriers involved in the radiative recombination processes in the well layers originate primarily from the adjacent GaN layers.
Cubic InGaN Grown by Mocvd
Authors: Li J.B. , Yang Hui , Zheng L.X. , Xu D.P. , Wang Y.T. 
Published: April 2011

AbstractWe report on the growth of high-quality cubic phase InGaN on GaAs by MOCVD. The cubic InGaN layers are grown on cubic GaN buffer layers on GaAs (001) substrates. The surface morphology of the films are mirror-like. The cubic nature of the InGaN films is obtained by X-ray diffraction (XRD) measurements. The InGaN layers show strong photoluminescence (PL) at room temperature. Neither emission peak from wurtzite GaN nor yellow luminescence is observed in our films. The highest In content as determined by XRD is about 17% with an PL emission wavelength of 450 nm. The FWHM of the cubic InGaN PL peak are 153 meV and 216 meV for 427 nm and 450 nm emissions, respectively. It is found that the In compositions determined from XRD are not in agreement with those estimated from PL measurements. The reasons for this disagreement are discussed.
Nitridation of GaAs (001)-2x4 Surface Studied by Auger-Electron Spectroscopy
Authors: Aksenov Igor , Nakada Yoshinobu , Okumura Hajime 
Published: April 2011

AbstractAuger electron spectroscopy (AES) was used to investigate the processes taking place during the initial stages of nitridation of GaAs (001) surface. The analysis of the AES results combined with that of RHEED show that the processes taking place during nitridation greatly differ depending on the nitridation temperature. At low temperatures (≤ 200°C) nitridation is hindered by kinetic restrictions on atomic migration, whereas at high temperatures (≥ 500°C) the process of nitridation takes place simultaneously with the etching of the surface. However, for intermediate temperatures (300°C ∼ 400°C) the results indicate that a complete monolayer of N atoms may be formed on the substrate during the initial stage of nitridation. The post-nitridation annealing of the samples nitrided at the intermediate temperatures results in the formation of a crystalline GaN layer, the line shape of the AES signals from which is identical to that for a GaN reference sample.
Piezoelectric Level Splitting in GaInN/GaN Quantum Wells
Authors: Wetzel C. , Takeuchi T. , Amano H. , Akasaki I. 
Published: April 2011

AbstractIdentification of the electronic band structure in AlInGaN heterostructures is the key issue in high performance light emitter and switching devices. In device-typical GaInN/GaN multiple quantum well samples in a large set of variable composition a clear correspondence of transitions in photo- and electroreflection, as well as photoluminescence is found. The effective band offset across the GaN/GaInN/GaN piezoelectric heterointerface is identified and electric fields from 0.23 - 0.90 MV/cm are directly derived. In the bias voltage dependence a level splitting within the well is observed accompanied by the quantum confined Stark effect. We furthermore find direct correspondence of luminescence bands with reflectance features. This indicates the dominating role of piezoelectric fields in the bandstructure of such typical strained layers.
Epitaxial Growth and Structural Characterization of Single Crystalline ZnGeN2
Authors: Zhu L.D. , Maruska P.H. , Norris P.E. , Yip P.W. , Bouthillette L.O. 
Published: April 2011

AbstractA new nitride semiconductor, single crystalline ZnGeN2 has been successfully grown by MOCVD for the first time. The epitaxial ZnGeN2 is found to be of hexagonal wurtzite lattice without ordering of the zinc and germanium atoms in the pseudomorphic Group III sublattice. Lattice constants of the ZnGeN2 are a = 3.186 ± 0.007 A, c = 5.174 ± 0.012 A, which gives c/a = 1.624.
Homo- and Hetero-Epitaxial Gallium Nitride Grown by Molecular Beam Epitaxy
Authors: Foxon C.T. , Cheng T.S. , Korakakis D. , Novikov S.V. , Campion R.P. , Grzegory I. , Porowski S. , Albrecht M. , Strunk H.P. 
Published: April 2011

AbstractVarious methods have been used to initiate growth by Molecular Beam Epitaxy (MBE) of GaN on sapphire, or other substrates, but there is always a problem with morphology and with a high defect density which results in the formation of a sub-grain boundary structure. We show that by using, homo-epitaxial growth on properly prepared bulk GaN substrates, combined with high temperature growth, we obtain a significant improvement in surface morphology. Growth at sufficiently high temperature leads to a rapid smoothing of the surface and to almost atomically flat surfaces over relatively large areas. Multi-Quantum Well structures grown on such GaN epitaxial films are dislocation free with abrupt interfaces.
Epitaxial Lateral Overgrowth of GaN with Chloride-Based Growth Chemistries in Both Hydride and Metalorganic Vapor Phase Epitaxy
Authors: Zhang R. , Zhang L. , Hansen D.M. , Boleslawski Marek P. , Chen K.L. , Lu D.Q. , Shen B. , Zheng Y.D. , Kuech T.F. 
Published: April 2011

AbstractEpitaxial lateral overgrowth (ELO) of GaN on SiO2-masked (0001) GaN substrates has been investigated by using chloride-based growth chemistries via hydride vapor phase epitaxy (HVPE) and metal organic vapor phase epitaxy (MOVPE). Diethyl gallium chloride, (C2H5)2GaCl, was used in as the MOVPE Ga precursor. The lateral and vertical growth rates as well as the overgrowth morphology of ELO GaN structures are dependent on growth temperature, V/III ratio and the in-plane orientation of the mask opening. A high growth temperature and low V/III ratio increase the lateral growth rate and produce ELO structures with a planar surface to the GaN prisms. High-quality coalesced and planar ELO GaN has been fabricated by both growth chemistries. The use of the diethyl gallium chloride source allows for the benefits of HVPE growth to be realized within the MOVPE growth environment.
GaN P-N Structures Fabricated by Mg ION Implantation
Authors: Kalinina E.V. , Solov'ev V.A. , Zubrilov A.S. , Dmitriev V.A. , Kovarsky A.P. 
Published: April 2011

AbstractIn this paper we report on the first GaN p-n diodes fabricated by Mg ion implantation doping of n-type GaN epitaxial layers. Ion implantation was performed at room temperature. Implantation dose ranged from 1013 to 2 × 1016 cm2. After implantation samples were annealed for 10-15 s at a wide temperature interval from 600°C to 1200°C in flowing N2 to form p-type layers. Secondary ion mass spectroscopy, scanning electron microscopy with electron beam induced current and back scattered electron modes as well as current-voltage and capacitance-voltage measurements were used to study structural and electrical characteristics of the Mg implanted p-n structures.
Minimum Surface Formation Energy for Three-Dimensional Intergranular Fracture
Authors: Holm E. A. , McGovney G. N. 
Published: April 2011

AbstractThe minimum expended energy for fracture is the free energy required to form two new surfaces. For intergranular fracture, the minimum surface formation energy is complicated by the rough fracture surface, with area greater than the specimen cross-section. We utilize network optimization algorithms (max-flow/min-cut) to determine the minimum surface formation energies and surfaces for intergranular fracture in 3D polycrystals. For equiaxed grains and uniform boundary strength, the minimum energy fracture area is independent of grain size and is 45% larger than the specimen cross-section, and intergranular fracture will occur when surface energy is less than 1.6 times the grain boundary energy. The 3D fracture area is larger than projected from 2D systems. In systems with microcracked boundaries, the fracture surface deviates to preferentially include microcracked boundaries, creating interlocking grain configurations. Two-dimensional percolation of microcracks occurs at about 80% microcracked boundaries.
Dislocation Emission from a Thin-Film-Covered Crack
Authors: Zhang Tong-Yi , Qian Cai-Fu , Wang Tianhong , Tong Pin 
Published: April 2011

AbstractThe present work investigates the effects of a passive film formed during stress corrosion cracking on ductile/brittle fracture behavior, considering the interaction of a dislocation with a thin- film-covered crack under an applied remote load. The dislocation emission from the thin-film- covered crack tip is analyzed, on the basis of the two-dimensional Rice-Thomson model, for screw and edge dislocations. The results show that the nominally critical stress intensity factor for dislocation emission is related to the thin film thickness, the properties of the film and the loading conditions. For a given loading mode and a given crack length, there exists a critical value of the film thickness at which the film does not influence the dislocation emission. When the film thickness is smaller than the critical value, a harder thin film makes the dislocation emission easier and a softer film makes the dislocation emission more difficult. The opposite is also true if the film thickness is larger than the critical value.
Growth, Microstructural and Ferroelectric Properties of PZT Films Prepared by Pulsed Laser Deposition Method
Authors: Kumar Ashok , Alam M.R. , Shamsuzzoha M. 
Published: April 2011

AbstractPb(ZrxTi1−xO3 (lead zirconate titanate or PZT) ferroelectric thin film capacitors are of considerable interest for the realization of memory devices such as nonvolatile random access memories (NVRAMs). The PZT capacitors were prepared on platinized silicon Pt/(100)Si using conducting oxide LaxSrl.xCOO (lanthanum strontium cobalt oxide or LSCO) as electrodes. The PZT and LSCO thin films were deposited by the KrF excimer laser ablation technique. The optimum preparation conditions such as oxygen pressure, laser energy influence and substrate temperature were investigated. The PZT and LSCO films grown on Pt/(100)Si are polycrystalline. The crystallographic properties of the films were determined using X-ray diffractometer (XRD) method. The cross-sectional transmission electron microscope showed very smooth interface among different layers of films. The electrical characterizations of the films including hysteresis loop, fatigue, and retention properties were determined by the RT66A Standardized Ferroelectric Test System.
Effect of Stoichiometry on the Ferroelectric Properties of (Pb1−xLax)TiO3 Thin Films
Authors: Lin I-Nan , Lin Cheng-Hsiung , Hsu Yen-Hua , Teng Han-Fang , Cheng Hsiu-Fung 
Published: April 2011

AbstractThe (Pb1−xLax)TiO3, (PLT) thin films possessing good ferroelectric properties were successfully obtained by using metal-organic-decomposition (MOD) process, followed by furnace post-annealing at 600-700°C (60 min) or rapid thermal annealing (RTA) at 600-700°C (60 s). Excess Pb-species incorporated in precursors for compensating for the Pb-loss during MOD process results in pronounced modification on thin film's electrical properties. The leakage current is reduced from JL= 1 × 10−3 A/cm2 to 1 × 10−4 A/cm2 (at 400 kV/cm) and the remanent polarization is increased from Pr= 8.3 µ C/cm2 to 12.6 µC/cm2, when 10 mol% excess-Pb is added. On the other hand, larger La-content in PLT films results in more pronounced Pb-loss and induces larger leakage current, which significantly degrades the ferroelectric properties of the films. The best properties obtained for PLT films prepared by the MOD process are: Pr= 12.6 µC/cm2, Ec = 80 kV/cm and JL= 10−5 A/cm2 (at 400 kV/cm).
Properties and Orientation of Antiferroelectric Lead Zirconate Thin Films Grown by MOCVD
Authors: Chen Nan , Bai G. R. , Auciello O. , Koritala R. E. , Lanagan M. T. 
Published: April 2011

AbstractSingle-phase polycrystalline PbZrO3 (PZ) thin films, 3000-6000 A thick, have been grown by metal-organic chemical vapor deposition (MOCVD) on (111)Pt/Ti/SiO2/Si substrates at ≍525°C. X-ray diffraction analysis indicated that the PZ films grown on (111)Pt/Ti/SiO2/Si (Pt/Tgi/Si) showed preferred pseudocubic (110) orientation. In contrast, PZ films grown on 150 A thick PbTiO3 (PT) template layers exhibited a pseudocubic (100) preferred orientation, and PZ films deposited on TiO2 template layers consisted of randomly oriented grains. The PZ films grown on Pt/Ti/Si with or without templates exhibited dielectric constants of 120-200 and loss tangents of 0.01-0.0. The PZ films with (110) orientation exhibited an electric-field-inducedtransformation from the antiferroelectric phase to the ferroelectric phase with a polarization of ≍34 µC/cm2, and the energy that was stored during switching was 7.1 J/cm3. The field needed to excite the ferroelectric state and that needed to revert to the antiferroelectric state were 50 and 250 kV/cm, respectively. Relationships between the MOCVD processing and the film microstructure and properties are discussed.
Heteroepitaxial Growth of PZT Film on (100)Ir/(100)YSZ/(100)Si Substrate Structure Prepared by Reactive Sputtering
Authors: Horita Susumu , Horii Sadayoshi 
Published: April 2011

AbstractA heteroepitaxial (001)Pb(ZrxTi1−x)O3(PZT) film was grown on the (100)Ir/(100)YSZ/Si structure with a cube-on-cube relationship by using reactive sputtering. The X-ray diffraction patterns of this sample showed that the double domain crystal layer of the (110) IrO2 was formed between the Ir and PZT films. According to reflection high energy electron diffraction observation and X-ray photoelectron spectroscopy measurements, it was found that the initial epitaxial growth of the PZT film occurred on the Ir film. The polarization-electric field hysteresis loop of the 285-nm-thick epitaxial PZT film with the top electrode of IrO2 showed a saturated square shape at the ac amplitude of 3V, and the remanent polarization 2Pr and the coercive field 2Ec were 80 µC/cm 2 and 100 kV/cm, respectively. The 2Pr's were not reduced up to the switching cycles of 5 × 1010 with ± 5V bipolar pulse.
Effect of Annealing Treatment on PZT Thin Fiilm Properties Using Oxygen 18 Depth Profiling Technique
Authors: Ayguavives F. , Ea-Kim B. , Agius B. , Vickridge I. , Kingon A. I. 
Published: April 2011

AbstractLead zirconate titanate (PZT) thin films have been deposited in a reactive argon/oxygen gas mixture from a metallic target of nominal composition Pb1.1(Zr0.4Ti0.6)O3 by rf magnetron sputtering on Si substrates and RuO2/SiO2/Si structures. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements clearly show a correlation between the evolution of characteristic atomic emission line intensities and the thin film composition determined by simultaneous Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA). As a result, the cathode surface state can be monitored by OES to ensure a good compositional transferability from the target to the film and reproducibility of thin film properties for given values of deposition parameters. Electrical properties and crystallization have been optimized with a 90 nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550°C) are fatigue-free and show very low leakage currents (J=2.10−8 A/cm2 at 1 V). The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using 18O as a tracer, to study the oxygen vacancy migration which plays a key role in fatigue, leakage current, and electrical degradation/breakdown in PZT thin films.
Suppression of Size Effects in Ferroelectric Films
Authors: Desu Seshu B. 
Published: April 2011

AbstractIt is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizes conductive oxide electrodes that are ferroelectric in nature the polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3 thin films with stoichiometric composition on SrTiO3 single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppress the size effects.
Antiferroelectric to Paraelectric Phase Transition in Lead Zirconate Thin Films
Authors: Fanning D.M. , Robinson I.K. , Tani T. , Payne D. A. 
Published: April 2011

AbstractLead zirconate, PbZrO3, is antiferroelectric at room temperature and has a first-order phase transition to the paraelectric state at 230°C in bulk crystals. At room temperature, the antiferroelectric Pb displacements along [110] directions produce a superstructure at the (h+¼ k+¼, 1) positions (referenced to pseudo-tetragonal unit cell). The Pb displacements occur perpendicular to the shorter c axis. In this study, the behavior of thin films was compared to the bulk. Films of lead zirconate were deposited onto electroded silicon wafers via the sol gel method. By varying the deposition conditions of the Pt substrate, films with both {111} and {100} preferred orientation were grown. The crystalline film consisted of columnar grains which were not completely aligned with each other, but had a random orientation with respect to the film's perpendicular axis. Measurements of superstructure peak intensities vs. temperature show that the thin films exhibit a much more gradual phase transition to the paraelectric state compared to the bulk. Furthermore, comparison of a and c vs. temperature show this effect, as well as a strain of about 0.5% in c. In the {100} oriented films, we found that the c-axis was oriented perpendicular to the film's surface, meaning they should be classified as (001).
Synchrotron X-Ray Scattering of (Ba0.5Sr0.5)TiO3 Thin Films Epitaxially Grown on MgO(100)
Authors: Kim Sang S. , Je Jung H. 
Published: April 2011

Abstract((Ba0.5Sr 0.5)TiO3 thin films of two different thicknesses (∼ 250 Å and ∼ 1330 Å) epitaxially prepared on MgO(100) using pulsed laser deposition were studied by synchrotron x-ray scattering measurements. The film initially grew on MgO(100) with a cube-on-cube relationship, maintaining it during further growth. As the film grew, the surface of the film became rougher significantly, but the interface between the film and the substrate did not change so much. In the early stage, the film was highly strained in a tetragonal structure with the longer axis parallel to the surface normal direction. As the growth proceeded further, it was mostly relaxed to a cubic structure with the lattice parameter of the bulk value and the mosaic distribution improved significantly in both the in-plane and the out-of-plane directions. The thinner film showed only one domain limited mainly by the film thickness, but the thicker film exhibited three domains along the surface normal direction.
Preparation and Characterization of Bi2VO5.5 Films by MOD Method
Authors: Tokumitsu E , Takahashi Y. , Ishiwara H. 
Published: April 2011

AbstractWe report the preparation and characterization of Bi2VO5.5(BVO) films grown on SrTiO3, Pt/SiO2/Si, and n-Si(100) substrates by the MOD technique. Since a dielectric constant of BVO is much lower than that of PZT or SBT, BVO is one of the promising candidates for metal-ferroelectric-semiconductor field-effect transistors (MFSFETs). It is found by X-ray diffraction (XRD) measurements that highly (001)-oriented BVO films were obtained and that the crystalline quality was improved with increasing the annealing temperature. The full width at half maximum (FWHM) in the X-ray rocking curve measurements for BVO films on SrTiO3, Pt/SiO2/Si, and n-Si(100) substrates are 0.60, 1.00, and 5.10, respectively. Electrical properties were measured with Pt top electrodes and the typical relative dielectric constant determined by the C-V characteristics is 60-80.
Characterization of Pb(ScTa)1−xTixO3 (x<0.3) Thin Films Grown on LaNiO3 Coated Si by MOCVD
Authors: Lin C. H. , Kuo H. C. , Stillman G. E. , Chen Haydn 
Published: April 2011

AbstractHighly (100) textured pseudo-cubic Pb(ScTa)1−xTixO3 (x=0-0.3) (PSTT) thin films were grown by metal-organic chemical vapor deposition (MOCVD) on LaNiO3 (LNO) electrode buffered Si substrates at 650 °C. The microstructure and chemical uniformity were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and nanoprobe X-ray energy dispersive spectroscopy (EDS). The temperature dependence of dielectric properties and P-E behavior were measured. A shift of Curie temperature of these PST-based thin films due to Ti addition was demonstrated, Furthermore, the pyroelectric properties of these thin films were estimated.
Lattice Parameter Change of BaSrTiO3 Films Grown by Pulsed Laser Deposition
Authors: Kim W.J. , Chang W. , Qadri S.B. , Horwitz J.S. , Chrisey D.B. 
Published: April 2011

AbstractSingle phase Bao0.5Sro0.5TiO3 films with three different thicknesses (40, 80, and 160 nm) have been deposited onto MgO substrates by pulsed laser deposition (PLD). The lattice parameters for the thin film have been measured using x-ray diffraction. The deposited films all show a significant tetragonal distortion. The in-plane lattice parameters for all film thickness are always larger than surface normal lattice parameters for as-deposited films. Films (80 and 160 nm) annealed at 900, 1100, and 1200 °C for 6 hours after deposition show reduced tetragonal distortion compared to as-deposited films. Further, tetragonal distortion of annealed films with thicknesses of 80 and 160 nm were reduced with decreasing annealing temperature from 1200 °C to 900 °7, while that with a thickness of 40 nm is increased with decreasing annealing temperature. This result indicates that the stress due to lattice mismatch and thermal expansion difference changes as a function of film thickness.