bluuebunny/crossref_metadata_2025_split huggingface dataset:
Piezoelectric Quantization in GaInN thin Films and Multiple Quantum Well Structures
Authors: Wetzel Christian , Takeuchi Tetsuya , Amano Hiroshi , Akasaki Isamu 
Published: April 2011

ABSTRACTDetails of the electronic bandstructure in pseudomorphic Gal-xInxN/GaN single heterostructures (0 < x < 0.22) are studied. In photocarrier modulated reflectance strong modulation of the density of states (Franz-Keldysh oscillations) is found due to a piezoelectric field of about 0.6 MV/cm in the strained layer. No excitons are expected to form in the presence of this field. Studying the composition dependence we determine a piezoelectric coefficient ∂|P|/∂εzz = 0.46 C/m2 and extrapolate a spontaneous polarization in GaN |Peq| = 3.9 mC/m2. Photoreflection indicates the presence of localized tail states 50 – 100 meV below the bandgap which are well explained by the Franz-Keldysh effect involving k non-conserving transitions in the large electric field. Luminescence is found to originate in these electric field induced states. The derived bandgap energies can be approximated by an interpolation yielding bowing parameters b = 2.6 eV (photoreflection) and b = 3.2 eV (luminescence) for pseudomorphic films with 0.07 ≤ x ≤ 0. 22. These findings may affect interpretation of device performance.
Semiconducting Molybdenum Pyrochlores for high Temperature Applications
Authors: Ponnambalam V. , Varadaraju U. V. 
Published: April 2011

ABSTRACTThe solid solutions (Y1-xYbx)2Mo2O7 were prepared and the systematic changes in the electrical resistivity (ρ=l/σ), thermopower (S) and power factor (S2σ) have been studied in the temperature range 300–900 K. The lattice parameters ‘a’ and ‘c’ are smaller for higher Yb3+ content phases due to smaller Yb3+ radius and a small tetragonality is observed for all the phases. Semiconducting behaviour is seen for all compositions with systematic increase in activation energy with increasing Yb content. All compositions show negative thermopower indicating electrons are the majority charge carriers in the temperature range of measurements. The calculated power factor values S2σ increase with increasing temperature in the low temperature region and a maximum power factor of ∼0.76×10−7 Wcm−1K−2 is observed at 650K.
CVD Diamond as Dielectric Material for Capacitor Applications
Authors: Heidger S. , Fries-Carr S. , Weimer J. , Jordan B. , Wu R. 
Published: April 2011

ABSTRACTDiamond films synthesized using Microwave Plasma Chemical Vapor Deposition (MWCVD) were evaluated for use as dielectric material for high power and high temperature capacitors. The effect that the deposition parameters and annealing have on the frequency and temperature stability of the electronic properties was investigated. Dielectric constants ranging between 8.0 and 4.2 and resistivities between 1× 108 ohm-cm and 5×1014 ohm-cm were obtained. Diamond produced using less than 6.6% methane had very stable dielectric constants over the frequency range of 100 Hz to IMHz, and the loss tangent was less than 0.01. Adding oxygen to the precursor gas increased the dielectric constant and lowered the loss tangent of CVD diamond, but the resistivity was also lowered. As the temperature increased to 300°C, the dielectric constant and loss tangent increased. However, when diamond was annealed to 700°C, there was less than a 5% change in the dielectric constant from 23°C to 300°C.
Optical Characteristics Of Mocvd-Grown Ingan/Gan Multiple Quantum Wells Investigated By Excitation Energy Dependent Pl And Ple Spectroscopy
Authors: Cho Yong-Hoon , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P. 
Published: April 2011

ABSTRACTWe have systematically studied the optical properties of InGaN/GaN multiple quantum wells (MQWs) at 10 K under different excitation conditions using photoluminescence (PL) and PL excitation (PLE) spectroscopy. The MQWs were grown on 1.8-μm-thick GaN on c-plane sapphire films by metal-organic chemical vapor deposition. Structures consist of 12 MQWs with 3-nm-thick In0.2Ga0.8N wells, 4.5-nm-thick GaN barriers, and a 100-nm-thick A10.07Ga0.93N capping layer. We found that the PL emission consists of a strong main peak at 2.80 eV and a much weaker and broader secondary peak at ˜ 2.25 eV. We observed that both the peak position and the spectral width of the main peak vary with the excitation energy. The PL peak blueshifts and narrows when the excitation energies are varied from 3.81 eV (above the bandgap of the AlGaN capping layer) to 2.99 eV (below the bandgap of the GaN barrier layers). The intensity ratio of the main peak to the secondary peak also varied with excitation energy. The PLE studies, combined with the excitation dependent PL emission studies, reveal that the two observed emission peaks originate from different layers of the MQWs. In addition, we found that the InGaN-related spontaneous emission processes are strongly affected by different carrier generation conditions with further complications associated with compositional fluctuations and possible carrier localization. The differences in the observed emission processes under varying excitation conditions can be explained by considering the transfer of carriers between the different layers of the MQW structures.
Thermally Stable Schottky Contacts TO n-GaN
Authors: Venugopalan H. S. , Mohney S. E. 
Published: April 2011

ABSTRACTThe barrier heights of Ni/Ga/Ni and Re Schottky contacts to n-GaN were investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The elemental Ni contacts were also investigated for comparison. The Ni/Ga/Ni and Re diodes were stable on short term annealing up to 700 °C. It was also shown that the Ni/Ga/Ni (84 at% Ni, 16 at% Ga) diodes were more stable than Ni diodes. This work provides the first demonstration of Schottky diodes to n-GaN that are stable upon annealing at 700 °C.
Calculation of Unstable Mixing Region In Wurtzite InGaN
Authors: Takayama Toru , Ueda Tetsuzo , Ishida Masahiro , Yuri Masaaki , Itoh Kunio , Baba Takaaki , Harris James S. 
Published: April 2011

ABSTRACTThe InGaN ternary system, which is useful for blue and green light emitting or laser diodes, is studied with respect to an unstable mixing region in the phase field. The unstable region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The interaction parameters of InGaN obtained by our analysis for the wurtzite and zinc-blende structures are 7.81 kcal/mol and 6.63 kcal/mol, respectively. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN and zinc-blende InGaN are found to be 1967 K and 1668 K, respectively. This suggests that, at a typical growth temperature of 800°C, a wide unstable mixing region exists in both wurtzite and zinc-blende structures. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.
Examination of the Silicon – Silicon Carbide Interface by Ultraviolet Photoemission Spectroscopy
Authors: Koitzscht C. , O'Brient M. , Johri D. , Stoltzt A. , Nemanicht R. 
Published: April 2011

ABSTRACTPhotoemission spectroscopy (UPS) was used to investigate the interface properties of deposited silicon on hexagonal 6H-silicon carbide. SiC cleaned in Si flux from a molecular beam epitaxy (MBE) system was used for this study. All processes were accomplished in an ultra high vacuum integrated system that allowed all cleaning, deposition, and analysis to be completed without exposure to ambient atmosphere. Thicknesses of sub- to multiple monolayers were deposited and the valence band structure was investigated. The valence band maximum (VBM) was observed to shift for Si depositions greater than 1 monolayer. The VBM offset was determined to be 2.4eV for a layer of 60Å Si on SiC. Furthermore, the prominent surface state feature of the silicon carbide (0001)si surface is reduced after Si deposition. The results are discussed in terms of the electronic properties of the Si – SiC interface.
Site-Selective Photoluminescence Spectroscopy of Er-Implanted Wurtzite Gan Under Various Annealing Conditions
Authors: Kim S. , Rhee S. J. , Li X. , Coleman J. J. , Bishop S. G. 
Published: April 2011

ABSTRACTThe ˜1540 nm 4I13/2 → 4I15/2 emissions of Er3+ in Er-implanted GaN annealed at temperatures in the 400 to 1000 °C range were investigated to gain a better understanding of the formation and dissociation processes of the various Er3+ sites and the recovery of damage caused by the implantation with increasing annealing temperature (TA). The monotonic increase in the intensity of the broad defect photoluminescence (PL) bands with increasing TA proves that these are stable radiative recombination centers introduced by the implantation and annealing process. These centers cannot be attributed to implantation-induced damage that is removed by postimplantation annealing. Selective wavelength pumping of PL spectra at 6 K reveals the existence of at least nine different Er3+ sites in this Er-implanted semiconductor. Most of these Er3+ PL centers are attributed to complexes of Er atoms with defects and impurities which are thermally activated at different TA. Only one of the nine observed Er3+ PL centers can be pumped by direct 4f absorption and this indicates that it is the highest concentration Er3+ center and it represents most of the optically active Er3+ in the implanted sample. The fact that this Er3+ center cannot be strongly pumped by above-gap light or broad band below-gap absorption indicates that it is an isolated center, i.e. not complexed with defects or impurities. This 4f-pumped PL spectrum appears at annealing temperatures as low as 400°C, and although its intensity increases monotonically with increasing TA, the wavelengths and linewidths of its characteristic peaks are unaltered. The observation of this high quality Er3+ PL spectrum at low annealing temperatures illustrates that the crystalline structure of GaN is not rendered amorphous by the ion implantation. The increase of the PL intensities of the various Er3+ sites with increasing TA is due to the removal of competing nonradiative channels with annealing.
In Situ Characterization of Ain Films Grown on Silicon by MOCVD
Authors: Serra A. D. , Richardson H. H. 
Published: April 2011

ABSTRACTFilms of AIN were grown on Si under vacuum pressure at 900°C and examined ex situ with infrared reflectance spectroscopy and microscopy, scanning electron microscopy, x-ray diffraction and rutherford backscattering spectroscopy. Collection of IR emission spectra for in situ characterization was successful and used to identify growth parameters during film growth.
Doping of GaN by Ion Implantation: Does it Work?
Authors: Suvkhanov A. , Hunn J. , Wu W. , Thomson D. , Price K. , Parikh N. , Irene E. , Davis R. F. , Krasnobaev L. 
Published: April 2011

ABSTRACTEpitaxially grown GaN by metal organic chemical vapor deposition (MOCVD) on SiC were implanted with 100 keV Si+ (for n-type) and 80 keV Mg+ (for p-type) with various fluences from 1×1012 to 7×1015 ions/cm2 at liquid nitrogen temperature (LT), room temperature (RT), and 700 °C (HT). High temperature (1200 °C and 1500 °C) annealing was carried out after capping the GaN with epitaxial AIN by MOCVD to study damage recovery. Samples were capped by a layer of AIN in order to protect the GaN surface during annealing. Effects of implant temperature, damage and dopant activation are critically studied to evaluate a role of ion implantation in doping of GaN. The damage was studied by Rutherford Backscattering/Channeling, spectroscopic ellipsometry and photoluminescence. Results show dependence of radiation damage level on temperature of the substrate during implantation: implantations at elevated temperatures up to 550 °C decrease the lattice disorder; “hot implants” above 550 °C can not be useful in doping of GaN due to nitrogen loss from the surface. SE measurements have indicated very high sensitivity to the implantation damage. PL measurements at LT of 80 keV Mg+ (5×1014 cm-2) implanted and annealed GaN showed two peaks : one ∼100 meV and another ∼140 meV away from the band edge.
Relaxation Of Non-Equilibrium Hydrogen Distributions In a-Si:H
Authors: Adriaenssens Guy J. , Zhiang Qing 
Published: April 2011

ABSTRACTIt is shown that a reduction of the three-level energy diagram proposed by Van de Walle (Phys. Rev. B 53, 11292, 1996) to describe the relaxation of non-equilibrium hydrogen distributions, to just the interstitial transport level and a distribution of traps, allows an essentially equivalent formulation of the hydrogen relaxation kinetics. The modified formulation offers the possibility of accounting for dispersive diffusion while preserving the essential multiple retrapping aspect of the original proposal.
Concentration of Hydrogen in Titanium Measured by Neutron Incoherent Scattering
Authors: Chen-Mayer H. H. , Mildner D. F. R. , Lamaze G. P. , Lindstrom R. M. , Paul R. L. , Kvardakov V. V. , Richards W. J. 
Published: April 2011

ABSTRACTMass fractions of hydrogen in titanium matrices have been measured using neutron incoherent scattering (NIS) and compared with results from prompt gamma activation analysis (PGAA). Qualitatively, NIS is a more efficient technique than PGAA which involves neutron absorption, and the former may be suitable for on-line analysis. However, for NIS the scattering contribution comes from both the hydrogen and the matrix, whereas prompt gamma emission has minimal matrix effect. To isolate the signal due to hydrogen scattering, a set of polypropylene films is used to simulate the increasing amount of hydrogen, and the scattered intensity is monitored. From this response, an unknown amount of the hydrogen can be deduced empirically. We have further attempted a first principle calculation of the intensity of the scattered signal from the experimental systems, and have obtained good agreement between calculation and the measurements. The study can be used as a reference for future applications of the scattering method to other hydrogen-in-metal systems.
Hydrogen Cycling-induced Phase Segregation in AB 5-Type Intermietallics
Authors: Mordkovich V. Z. 
Published: April 2011

ABSTRACTA study of hydrogen cycling-induced phase segregation in AB5-type intermetallics is presented. Influence of temperature for the alloy compositions Yni4AI, LaNi5, Ce0.5La0.5Ni5 and Ce0.7La0.3Ni5 is shown. Morphology of the nanostructured particles formed is studied and discussed.
Hydrogen-Enhanced SCC of 304 Austenitic Stainless Steel in MgCl2
Authors: Gao K. W. , Qiao L-J. , Luo J. L. 
Published: April 2011

ABSTRACTSCC of 304 stainless steel(ss) in boiling MgCl2at 416K was performed to investigated the effect of hydrogen during test. Results showed that the existence of hydrogen enhanced the susceptibility of SCC of 304ss. The fractography of specimen charged with hydrogen contained more intergranular than that of uncharged ones, and for the both specimens charged or uncharged with hydrogen, SCC initiated and propagated along { 111 } plane.
Hydrogen On Semiconductor Surfaces
Authors: Schaefer J. A. , Balster T. , Polyakov V. , Rossow U. , Sloboshanin S. , Starke U. , Tautz F. S. 
Published: April 2011

ABSTRACTWe review structural and electronic aspects of the reaction of hydrogen with semiconductor surfaces. Among others, we address the Si(100), GexSi1-x(100), GaAs(100), InP(100), SiC(100), SiC(0001) and SiC(0001) surfaces. It is demonstrated that high resolution electron energy loss spectroscopy (HREELS) in conjunction with a number of other surface sensitive techniques like low energy electron diffraction (LEED) and photoelectron spectroscopy (XPS/UPS) can yield important information about the surface atomic structure, the effects of hydrogen passivation and etching and on electronic properties of the surfaces.
Formation of Hydrogen-Related Traps in Electron-Irradiated N-type Silicon by Wet Chemical Etching
Authors: Tokuda Yutaka , Shimada Hitoshi 
Published: April 2011

ABSTRACTInteraction of hydrogen atoms and vacancy-related defects in 10 MeV electron-irradiated n-type silicon has been studied by deep-level transient spectroscopy. Hydrogen has been incorporated into electron-irradiated n-type silicon by wet chemical etching. The reduction of the concentration of the vacancy-oxygen pair and divacancy occurs by the incorporation of hydrogen, while the formation of the NHI electron trap (Ec – 0.31 eV) is observed. Further decrease of the concentration of the vacancy-oxygen pair and further increase of the concentration of the NH1 trap are observed upon subsequent below-band-gap light illumination. It is suggested that the trap NHI is tentatively ascribed to the vacancy-oxygen pair which is partly saturated with hydrogen.
Dose-Dependent “Activation Energy” For Blistering Phenomenon In Hydrogen-Implanted Silicon
Authors: Bedell S. W. , Lanford W. A. 
Published: April 2011

ABSTRACTSilicon samples were implanted with 100 keV hydrogen at doses ranging from 4.9 to 9.9 × 1016 H/cm2. The samples were then annealed in an argon atmosphere using a special furnace mounted on a microscope stage. The time required to observe the onset of Si blistering was then measured as a function of temperature for the various hydrogen doses. An Arrhenius plot of the time-temperature data was made and an “activation energy” was calculated for each dose. The measured activation energies range from 2.6 to 1.1 eV corresponding to 4.9 to 9.9 × 1016 H/cm2, respectively. A qualitative explanation of the dose dependence is given in terms of a stressinduced lowering of the Si-Si bond energy. The hydrogen distribution as a function of annealing temperature was monitored using the 1H(15N,αγ)12C nuclear reaction. The results from the hydrogen profiling indicate that the hydrogen profile flattens at 500°C and concentrates at 550 °C.
Hydrogen Structures in Heavily Hydrogenated Crystalline and Amorphous Silicon
Authors: Jackson W. B. , Franz A. , Chabal Y. , Weldon M. K. , Jin H.-C. , Abelson J. R. 
Published: April 2011

ABSTRACTThe hydrogen binding energy distribution and IR spectra of hydrogen platelets in c-Si have been measured and compared to H in other forms of silicon including hydrogenated polycrystalline and amorphous Si. The binding distribution for platelet containing samples, determined using H evolution, exhibits two peaks: a bulk peak at 1.8–1.9 eV below the transport barrier, and a second possibly surface related peak 1.8–1.9 eV below the surface evolution barrier. The bulk peak grows at 250C and is consistent with calculated energies for platelet structures. The same two evolution peaks are found in hydrogenated polycrystalline Si and amorphous silicon. The IR spectra for heavily hydrogenated c-Si are dominated by the stretching modes at 2076 and 2128 cm-1. Most surprisingly there appears to be a strong mode at 856 cm-1 which is associated with a deformation mode of SiH3. Even more surprising, this SiH3 856 cm-1 mode remains until 550 C indicating that the SiH3 containing structures are rather stable.
Crystallographic Texture and Phase Formation in Blanket TifriN/AICu Films
Authors: DeHaven P. W. , Clevenger L. A. , Schnabe R. F. , Weber S. J. , Iggulden R. C. , Rodbell K. P. 
Published: April 2011

ABSTRACTInterconnection metallization uses film stacks, often composed of thin (<10 nm) Ti, TiN, or Ti/TiN underlayer(s) with a thick (200–1000 nm) Al-alloy film deposited on top. The texture or preferred orientation in such film stacks has important implications for both processing and reliability. Earlier studies' have demonstrated the importance of the underlayers on Al texture; however, to date no systematic work has been done on the effect of processing conditions on underlayer texture. This study examines the effect of deposition parameters on the underlayer texture development as well as the effect of this underlayer texture on subsequently deposited Al-alloy films. Fiber plots were obtained for Ti <002> and <101> and Al <111> reflections for a series of 20 nm Ti/ 10 nm TiN/400 nm AlCu films using both a conventional Siemens D500 diffractometer with a pole figure attachment and a Siemens HI-STAR Area Detector system using Cu radiation from a rotating anode source. Because of overlap between the Al <111> and Ti <101> reflections, the Al was removed with a subtractive etch. In this way both the Al and underlayer film textures could be quantified. It was found that the Ti and Al-alloy film textures vary depending on the deposition temperature, deposition method and final film thickness. For example, an increase in the substrate temperature from 300° to 500°C caused the Ti film texture to change from <002> to <101>. Additionally, switching the TiN deposition process from physical vapor deposition (PVD) sputtering to chemical vapor deposition (CVD) in a Ti/TiN/AlCu film stack caused a degradation in the AlCu <111 > texture.
Imaging Spatial Variations in Resistance Along Interconnects
Authors: Wen Qingzhe , Clarke David R. 
Published: April 2011

ABSTRACTA non-destructive, non-contact method is described for imaging resistance variations along electrical conductors such as interconnects. In its basic implementation, an intensity modulated laser beam is scanned over the circuit carrying a d.c. current and the voltage induced in the circuit at the modulation frequency is used to vary the intensity of a synchronously scanned display. Resistance variations, such as caused by defects, produce variations in the image thereby identifying their spatial location. The voltage signal depends on a number of parameters including the temperature coefficient of resistivity of the conductor, the power of the incident laser, the absorption coefficient of the conductor and the rate of thermal diffusion to the surroundings. One advantage of the method is that it is possible to produce images of conductors below the surface. Whilst there is a degradation in contrast when imaging sub-surface features, it is still possible to identify and distinguish, for instance, tungsten vias and aluminum interconnects passivated by several microns of dielectric, as well as electromigration-induced damage. Under certain circumstances, other features in the immediate vicinity of the conductors, such as remanent photoresist and decohered interfaces, can also be imaged.
Improved Thermal Stability of Ultrathin CoSi2 Layers by Oxygen Annealing
Authors: Tung R. T. , Ohmi S. 
Published: April 2011

ABSTRACTThe thermal stability of thin CoSi2 layers is demonstrated to improve with the use of oxygen-containing annealing ambients. Layer agglomeration in epitaxial and polycrystalline CoSi2 layers grown on single crystal Si and polycrystalline CoSi2 layers grown on α-Si was retarded by oxygen annealing. A thin SiO2 layer grown during oxygen anneals which curbs surface diffusion and reduces the rates of kinetic processes is thought to be the primary reason for the improvement in CoSi2 thermal stability.