bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoluminescence and Photoluminescence Excitation Spectroscopy of In Situ Er-Doped and Er-Implanted GaN Films Grown by Hydride Vapor Phase Epitaxy
Authors: Kim S. , Li X. , Coleman J. J. , Zhang R. , Hansen D. M. , Kuech T. F. , Bishop S. G. 
Published: April 2011

AbstractPhotoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been carried out at 6K on the 1540 nm 4I13/2 ← 4I15/2 emission of Er3+ in in situ Er-doped and Er-implanted GaN grown by hydride vapor phase epitaxy (HVPE). The PL and PLE of these two different Er-doped HVPE-grown GaN films are compared with Er-implanted GaN grown by metal organic chemical vapor deposition (MOCVD).In the in situ Er-doped HVPE-grown GaN, the lineshape of the broad PLE absorption bands and the broad PL bands is similar to that in Er-doped glass. The PL spectra of this in situ Er-doped sample are independent of excitation wavelength, unlike the PL of the Er-implanted GaN. These PL spectra are quite different from the site-selective PL spectra observed in the Er-implanted GaN, indicating that the seven different Er sites existing in the Er-implanted MOCVD-grown GaN are not observed in the in situ Er-doped HVPE-grown GaN. Four of the seven different Er3+ sites observed in the Er-implanted MOCVD-grown GaN annealed at 900°C under a flow of N2 are present in the Er-implanted HVPE-grown GaN annealed at 800°C in an NH 3/H2 atmosphere.
GaN Growth by Remote Plasma MOCVD: Chemistry and Kinetics by Real Time Ellipsometry
Authors: Losurdo M. , Capezzuto P. , Bruno G. 
Published: April 2011

AbstractCubic and hexagonal GaN layers have been grown on GaAs (001) and α-Al2O3 (0001) substrates, respectively, by remote plasma metalorganic chemical vapor deposition (RPMOCVD). In situ spectroscopic ellipsometry is used to monitor in real time the chemistry and kinetics of the GaN growth. The subtrate/GaN interface formation is highlighted and the effect of the substrate plasma nitridation on the initial growth stage is discussed.
Characterization of Be-Implanted GaN Annealed at High Temperatures
Authors: Ronning C. , Linthicum K.J. , Carlson E.P. , Hartlieb P.J. , Thomson D.B. , Gehrke T. , Davis R.F. 
Published: April 2011

AbstractSingle crystalline (0001) gallium nitride layers were implanted with beryllium and subsequently annealed within the range of 300-1100°C for 10-60 minutes under a flux of atomic nitrogen obtained using a rf plasma source. The nitrogen flux protected the GaN surface from decomposition in vacuum at high temperatures. SIMS measurements revealed that no long range diffusion of the implanted Be occurred at 900 or 1100°C. XRD spectra showed defect-related peaks in the as-implanted samples; these peaks disappeared upon annealing at 900°C and higher for 10 minutes. Photoluminescence (PL) measurements showed one new line at 3.35 eV which provided strong evidence for the presence of optically active Be acceptors.
Thermal Residual Stress Modeling in Ain and GaN Multi Layer Samples
Authors: Wang Kai , Reeber Robert R. 
Published: April 2011

AbstractThermal residual stresses can detrimentally affect the electronic and optical properties of epitaxial films thereby shortening device lifetime. Based on our earlier work on thermal expansion of nitrides, we provide a finite element modeling analysis of the residual stress distribution of multilayered GaN and AlN on 6H-SiC. The effects of thickness and growth temperatures are considered in the analysis.
Gallium Nitride Growth Using Diethylgallium Chloride as an Alternative Gallium Source
Authors: Zhang Ling , Zhang Rong , Boleslawski Marek P. , Kuech T.F. 
Published: April 2011

AbstractMetal organic vapor phase epitaxy (MOVPE) of GaN has been carried out using diethyl gallium chloride (DEGaCI) and ammonia. The growth rate and efficiency of the DEGaCl-based growth decreases with increasing temperature when compared to trimethyl gallium (TMG)-based growth under similar conditions. Both low temperature buffer and the high temperature GaN layers were grown using the DEGaCI-NH3 precursor combination on the basal plane of sapphire and compared to similar structures grown using TMG and NH3. DEGaCl-based growth reveals an improved growth behavior under identical growth conditions to the conventional TMGa and ammonia growth. X-ray, Hall, and atomic force microscopy (AFM) measurements have been carried out on these samples providing a direct comparison of materials properties associated with these growth precursors. For the DEGaCl-based growth, the x-ray rocking curve line width, using the (0002) reflection, is as low as 300 arcsec on a 2.5-micron thick film. A RMS surface roughness of ∼0.5nm measured over a 10x10 micron area.
Behavior of W and WSix Contact Metallization on n- and p- Type GaN
Authors: Cao X. A. , Ren F. , Lothian J. R. , Pearton S. J. , Abernathy C. R. , Zolper J. C. , Cole M. W. , Zeitouny A. , Eizenberg M. , Shul R. J. 
Published: April 2011

AbstractSputter-deposited W-based contacts on p-GaN (NA∼1018cm-3) display non-ohmic behavior independent of annealing temperature when measured at 25°C. The transition to ohmic behavior occurs above ∼250°C as more of the acceptors become ionized. The optimum annealing temperature is ∼700°C under these conditions. These contacts are much more thermally stable than the conventional Ni/Au metallization, which shows a severely degraded morphology even at 700°C. W-based contacts may be ohmic as-deposited on very heavily doped n-GaN, and the specific contact resistance improves with annealing up to ∼900°C.
Characterization of Flicker Noise in GaN Based Modfets at Low Drain Bias
Authors: Hol W.Y. , Fong W.K. , Suryal C. , Tong K.Y. , Kim W. , Botcharev A. , Morkoc H. 
Published: April 2011

AbstractWe report systematic characterizations of flicker noise in GaN based MODFETs. Flicker noise was measured across the channel of the devices from room temperature to 130 K. The voltage noise power spectra, Sv(f) were found to be proportional to l/f, where γ depends on the device temperature as well as the gate bias. Study of Sv(f) as a function of the biasing condition was conducted in detail and was found to vary as VD2/(VG-VT)β where β changes with temperature from about 2.1 at room temperature to about 0.9 at 130K. Analyses of the data showed that the noise originated from thermal activation of carriers to localized states in the channel area. The data suggested that the trapping and detrapping of carriers did not lead to fluctuations in the carrier concentration as postulated in the McWhorter's model. However, more work is needed to determine if surface mobility fluctuations played key role in the l/f noise.
Symmetry of Electrons and Holes in Lightly Photo-Excited InGaN LEDs
Authors: Kennedy T.A. , Glaser E.R. , Carlos W.E. , Ruden P.P. , Nakamura Shuji 
Published: April 2011

AbstractThe symmetry of the recombining electrons and holes in lightly photo-excited InGaN LEDs revealed through ODMR is related to the physical structure, band structure and defects present. Calculations of the electron-g within the k•p formalism give the average shift from the free-electron value for GaN but are not fully reconciled with the anisotropy. This theory is also extended to InGaN alloys for both pseudomorphic and relaxed layers. The average shift is close to the experimental values for the green LED. The strongly reduced hole anisotropies seen experimentally are explained by a recently published theory for acceptors in GaN.
Fabrication of Smooth GaN-Based Laser Facets
Authors: Stocker D. A. , Schubert E. F. , Boutros K. S. , Redwing J. M. 
Published: April 2011

AbstractA method is presented for fabricating fully wet-etched InGaN/GaN laser cavities using photoenhanced electrochemical wet etching followed by crystallographic wet etching. Crystallographic wet chemical etching of n- and p-type GaN grown on c-plane sapphire is achieved using H3PO4 and various hydroxides, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {1010}, {1011}, {1012}, and {1013}. The vertical {1010} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope (FESEM), indicating a surface roughness less than 5 nm, suitable for laser facets. The etch rate and crystallographic nature for the various etching solutions are independent of conductivity, as shown by seamless etching of a p-GaN/undoped, high-resistivity GaN homojunction.
Group-III Nitride Etch Selectivity in BCl3/Cl2 ICP Plasmas
Authors: Shul R. J. , Zhang L. , Willison C. G. , Han J. , Pearton S. J. , Hong J. , Abernathy C. R. , Lester L. F. 
Published: April 2011

AbstractPatterning the group-III nitrides has been challenging due to their strong bond energies and relatively inert chemical nature as compared to other compound semiconductors. Plasma etch processes have been used almost exclusively to pattern these films. The use of high-density plasma etch systems, including inductively coupled plasmas (ICP), has resulted in relatively high etch rates (often greater than 1.0 μm/min) with anisotropic profiles and smooth etch morphologies. However, the etch mechanism is often dominated by high ion bombardment energies which can minimize etch selectivity. The use of an ICP-generated BCl3/Cl2 plasma has yielded a highly versatile GaN etch process with rates ranging from 100 to 8000 Å/min making this plasma chemistry a prime candidate for optimization of etch selectivity. In this study, we will report ICP etch rates and selectivities for GaN, AIN, and InN as a function of BCl3/C12 flow ratios, cathode rf-power, and ICP-source power. GaN:InN and GaN:AIN etch selectivities were typically less than 7:1 and showed the strongest dependence on flow ratio. This trend may be attributed to faster GaN etch rates observed at higher concentrations of atomic Cl which was monitored using optical emission spectroscopy (OES).
Cross-Sectional and Plan-View Observation of Cracks Introduced in Si at the Ductile-Brittle Transition Temperature
Authors: Suprijadi  , Saka H. 
Published: April 2011

AbstractMode I cracks introduced in Si at the ductile-brittle transition temperature (DBTT) have been examined extensively using transmission electron microscopy. Cross-sectional as well as plane-view specimens suitable for the observation were prepared using a focused ion beam technique. Many small dislocation loops nucleate at the fracture surface of a mode I crack during the propagation at DBTT.
Unstable Stacking Fault Free Energies in Silicon through Empirical Modeling
Authors: De Koning M. , Antonelli A. , Bazant Martin Z. , Kaxiras Efthimios , Justo J.F. 
Published: April 2011

AbstractThe temperature dependence of unstable stacking fault free energies on glide and shuffle {111} planes in silicon is investigated using a finite temperature molecular dynamics approach which includes a full treatment of anharmonic vibrational effects. The results are compared to earlier zero temperature ab initio calculations in which finite temperature effects were estimated using a harmonic approximation to transition state theory (TST). The unstable stacking free energies are interpreted within the framework of Rice‘s dislocation nucleation criterium to characterize a possible change from shuffle to glide plane dominance in the context of dislocation nucleation processes at a sharp crack tip. Such a change may be related to the abrupt brittle-ductile transition observed in silicon.
Simulation of Void Growth at High Strain-Rate
Authors: Belak J. , Minich R. 
Published: April 2011

AbstractThe dynamic fracture (spallation) of ductile metals is known to initiate through the nucleation and growth of microscopic voids. Here, we apply atomistic molecular dynamics modeling to the early growth of nanoscale (2nm radius) voids in face centered cubic metals using embedded atom potential models. The voids grow through anisotropic dislocation nucleation and emission into a cuboidal shape in agreement with experiment. The mechanism of this nucleation process is presented. The resulting viscous growth exponent at late times is about three times larger than expected from experiment for microscale voids, suggesting either a length scale dependence or a inadequacy of the molecular dynamics model such as the perfect crystal surrounding the void.
Mechanisms of Intergranular Fracture
Authors: Farkas Diana 
Published: April 2011

AbstractWe present a study of the atomistic mechanisms of crack propagation along grain boundaries in metals and alloys. The failure behavior showing cleavage crack growth and/or crack-tip dislocation emission is demonstrated using atomistic simulations for an embedded-atom model. The simulations follow the quasi-equilibrium growth of a crack as the stress intensity applied increases. Dislocations emitted from crack tips normally blunt the crack and inhibit cleavage, inducing ductile behavior. When the emitted dislocations stay near the crack tip (sessile dislocations), they do blunt the crack but brittle cleavage can occur after the emission of a sufficient number of dislocations. The fracture process occurs as a combination of dislocation emission/micro-cleavage portions that are controlled by the local atomistic structure of the grain boundary. The grain boundary is shown to be a region where dislocation emission is easier, a mechanism that competes with the lower cohesive strength of the boundary region.
Mobility of Non-Planar Screw Dislocations ahead of a Mode III Crack Tip
Authors: Ngan A.H.W. , Zhang H.F. 
Published: April 2011

AbstractThe generalised Peierls-Nabarro model is used to study the transformation of screw dislocation cores from the three-fold, non-planar state to the planar, glissile state ahead of a mode mll crack tip.
Stability and Oxidation Behavior of Ir Thin Film Electrodes on Si and SiO2
Authors: Saenger K.L. , Grill A. , Shaw T.M. , Neumayer D.A. , Lin Chenting , Wang Y.Y. 
Published: April 2011

AbstractThis paper examines factors affecting the oxidation behavior of Ir thin film electrodes and the stability of bilayer Ir/Ir-Ir-O-Si electrodes on silicon substrates. We first examine the morphology and texture of faceted IrO2 extrusions formed on the Ir films during thermal oxidation, and show that an Ir grain-growth anneal in N2 at 650°C for 5 min prior to the oxidation treatment increases both the areal density of IrO2 extrusions and the IrO2<110> x-ray diffraction intensity while decreasing apparent film roughness. We then examine the stability of bilayer lr(100 nm)/Ir(20 nm) films on polycrystalline silicon and show how fairly mild oxygen anneals of the Ir(20 nm)/Si structures can provide an in-situ formed Ir-O-Si barrier that protects the subsequently deposited Ir(100 nm) layer from silicidation reactions during annealing in N2 ambients at 750°C. Transmission electron microscopy indicates that this in-situ formed barrier at the Ir/Si interface has a two layer structure comprising an IrSix underlayer in contact with the silicon substrate and an SiO2 overlayer directly below the remaining Ir.
Simple Electrode-Barrier Structure Using Ir for Integration of PZT-Based High-Density Nonvolatile Memories
Authors: Lee Kwang B. , Tirumala S. , Song Y. , Ryu Sang O. , Desu Seshu B. 
Published: April 2011

AbstractWe have investigated the electrode-barrier properties of Ir for PZT-based nonvolatile memories. Ir layer was rf-sputtered onto a poly-Si coated Si wafer. PZT thin films were deposited on Ir/poly-Si/SiO2/Si by means of sol-gel spin coating. Highly c-axis oriented perovskite PZT thin films were obtained, which might be due to the interface-controlled growth. We found that Ir in itself acted as an oxygen barrier, which was confirmed from the measurement of P-E hysteresis loops with the electrical contact between top-electrode and bottom-poly-Si. Remanent polarization and coercive field of 1rO2/PZT/Ir/poly-Si capacitor were 20 μC/cm2and 30 kV/cm, respectively and the capacitor showed negligible polarization fatigue up to 1011 switching repetitions. However, the leakage current density at the field of larger than 80 kV/cm was high, which was believed to be related to the unknown phase in PZT caused by the reaction of PbO with bottom-Ir. Such high leakage current behavior could be successively improved by the insertion of vacuum-annealed IrOx buffer layer between PZT/Ir. The electrical properties of IrOx/PZT/annealed-IrO2Ir/poly-Si capacitors are also discussed.
Surface Roughness and Growth Texture of (Ba,Sr)TiO3 Thin Films Formed by MOCVD
Authors: Gao Y. , Alluri P. , He S. , Engelhard M. , Lea A.S. , Finder J. , Melnick B. , Hance R. L. 
Published: April 2011

AbstractMetalorganic chemical vapor deposition (MOCVD) has been used to grow (Ba,Sr)TiO3 thin films on Ir/SiO2/Si substrates. β-diketonates of Ba, Sr, and Ti were used as the precursors, and delivered to the reactor via direct-liquid injection. Growth rate and film thickness were monitored by in-situ spectroscopic ellipsometry, and determined after growth. Film growth was studied as a function of film thickness, composition, substrate temperature, and mixture of O2 and N2O with and without microwave plasma enhancement. Dense, mirror-like films were obtained under all conditions except when pure oxygen plasma enhancement was used. Surface roughness of the films appears strongly dependent on film thickness and composition. Film composition and growth temperature determine growth texture of the films. This paper describes these results as well as the correlation between these results and dielectric properties.
Low Temperature Crystallization of SrBi2Ta2O9 Film by Excimer Laser Irradiation
Authors: Seol K.S. , Hiramatsu H. , Ohki Y. , Shin D.-S. , Choi I.-H. , Kim Y-T. 
Published: April 2011

AbstractUsing a KrF or ArF excimer laser as an irradiation photon source, we have succeeded in crystallizing amorphous SrBi2Ta2O9 films at 200-290°C, quite lower temperatures than the conventional crystallization temperature. The crystallization is enhanced when the substrate temperature, irradiation time, or the laser power density is higher.
Studies of Dielectric Properties of Pulsed Laser Deposited (Ba, Sr)TiO3 Films Using LaNiO3 as Conductive Electrode
Authors: Srivastava Anuranjan , Kumar D. , Singh Rajiv K. 
Published: April 2011

AbstractLaNiO3 (LNO) films were used as conductive bottom and top electrodes for the fabrication of (Ba0.5Sr0.5) TiO3 (BST) capacitors on silicon substrates. LNO as well as BST films were grown in-situ using a pulsed laser deposition technique with no subsequent heating or oxygenation treatments. Capacitance and leakage current measurements of BST films were carried out using LNO/BST/LNO/Si structures. Using these measurements, the dielectric constant and leakage current of BST films were found to be ∼250 and ∼10−8 A/cm2, respectively. The results obtained in the present study suggest that LNO is a good contact electrode material for BST films in the fabrication of BST capacitors with good structural and electrical properties.
Electrical Properties of Fully Epitaxial PZT/MgO/Si Stacked Structures for Nonvolatile Future Memory Devices
Authors: Senzaki J. , Ueno T. 
Published: April 2011

AbstractFully epitaxial Pb (Zr,Ti)O3(PZT)/MgO/Si(001) stacked structures, one of the potential components of ferroelectric-gate FETs, have been fabricated and characterized. According to the structural and electrical characterization of MgO/Si structures, epitaxially grown MgO thin films on the Si substrates showed a small leakage current of ∼ 10−8 A/cm2 at the electric field of 1 MV/cm. In the C-V measurements of the as-grown MgO/Si heteroepitaxial interfaces, injection-type hysteresis was observed because of the crystal defects in the MgO film adjacent to the interface. Using oxygen annealing with a temperature of 400 °C, it showed no hysteresis and a lower interface trap density of the order of 1011 cm−2eV−1 could be achieved with no formation of a low dielectric layer at the MgO/Si interface. These results indicate that the epitaxial MgO thin films are applicable as the gate insulators of FETs. After the PZT film was deposited on the MgO/Si structure, the C-V characteristic of the stacked structure showed a ferroelectric hysteresis curve and the low interface trap density of 5 × 1011 cm−2eV−1 A maximum memory window width of 1.2 V could be obtained in the PZT thin film on the Si substrate with a MgO intermediate layer.
Piezoelectric Characterisation of Ferroelectric PZT Thin Films Using an Improved Vibrating Beam Method
Authors: Defay E. , Baboux N. , Malhaire C. , Kleimann P. , Barbier D. 
Published: April 2011

AbstractThis study proposes an improvement of the free vibrating beam method allowing characterization of the d31 coefficients of piezoelectric thin films. Preparation and piezoelectric characterization of PZT thin films are shown. An analytical model of the beam and the thin film is developed. Finite element modeling allows for definition of the validity conditions of the model. A numerical fitting of the model to the experimental values exhibits an excellent overlap. We obtain d31 values from 10 pC/N to 14 pC/N. Advantages of this method are shown compared to the first maximum voltage method.
Electromechanical Properties of Lead-Based Ferroelectric Thin Films
Authors: Kholkin A. L. , Brooks K. G. , Taylor D. V. , Setter N. , Safari A. 
Published: April 2011

AbstractPiezoelectric properties of Pb(Zr,Ti)O3 (PZT) and PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) films are investigated by interferometric technique combined with conventional dielectric and polarization measurements. It is shown that the piezoelectric d33 coefficient of both materials can be expressed based on their polarization and dielectric constant values using an equation for the electrostriction biased by the polarization. The obtained values of electrostriction coefficients are nearly field-independent and significantly smaller than in bulk materials of the same composition. Polarization offset is observed in PZT films subjected to bipolar fatigue, UV illumination and poling at high temperature, and is explained based on the pinning of ferroelectric domains in preferred orientations. The piezoelectric properties of rhombohedral PZT films are found to depend on their texture. The highest piezoelectric coefficient is observed in (100) oriented films, which have smaller polarization as compared to films having (111) preferred orientation. This difference is explained by the different values of electrostriction coefficients in materials with different textures.
Fabrication and Characterization of Pzt Thin-Film on Bulk Micromachined Si Motion Detectors
Authors: Garino T.J. , Tuttle B.A. , Laguna G. , Clem P. 
Published: April 2011

AbstractMotion detectors consisting of Pb(ZrxTi(1−x))O3 (PZT) thin films, between platinum electrodes, on micromachined silicon compound clamped-clamped or cantilever beam structures were fabricated using either hot KOH or High Aspect Ratio Silicon Etching (HARSE) to micromnachine the silicon. The beams were designed such that a thicker region served as a test mass that produced stress at the top of the membrane springs that supported it when the object to which the detector was mounted moved. The PZT film devices were placed on these membranes to generate a charge, or a voltage, in response to the stress through the piezoelectric effect. Issues of integration of the PZT device fabrication process with the two etching processes are discussed. The effects of PZT composition and device geometry on the response of the detectors to motion is reported and discussed.
Fabrication and Characterization of Lithium Tantalate / PZT Composite Thick Film Ultrasonic Transducers
Authors: Chen Y. , Sayer M. , Zou L. , Jen C.-K. 
Published: April 2011

AbstractLithium tantalate (LiTaO3)/PZT ceramic films with thickness above 50 µm have been deposited on stainless steel substrates using a modified sol-gel process. LT powders are dispersed in a PZT sol-gel matrix to form 0-3 ceramic/ceramic composites. The dielectric and impedance response of the LiTaO3/PZT films supported by the substrates has been studied. The pulse echo response of the films as ultrasonic transducers demonstrates a broadband frequency response. The transducers can operate at least up to a temperature of 368°C.