bluuebunny/crossref_metadata_2025 huggingface dataset:
Boron-Interstitial Cluster Kinetics: Extraction of Binding Energies from Dedicated Experiments
Authors: Ortiz Christophe J. , Pichler Peter , Häaublein Volker , Mannino Giovanni , Scalese Silvia , Privitera Vittorio , Solmi Sandro , Lerch Wilfried
Published: April 2011

A description of the transient diffusion and activation of boron during post-implantation an- nealing steps is one of the most challenging tasks. In industrially relevant situation, it needs to address diffusion at extrinsic concentrations, the agglomeration of self-interstitials, and the formation of boron-interstitial clusters. This article describes the experimental work performed or used to calibrate model parameters as independently as possible. In particular, the experiments used to extract information about the energetics of boron-interstitial clusters are described.
Free-standing line patterns of nanocrystalline electrodeposits
Authors: Pantleon Karen , Jensen Henrik Myhre , Somers Marcel A.J.
Published: April 2011

Free-standing Cu- and Ni-line patterns with varying line dimensions in the range of a few micrometers were manufactured by means of electrodeposition through a lithographically prepared mask. XRD studies revealed for Cu-lines a pronounced influence of the pattern geometry on crystallographic texture and peak broadening. Information on the strain distribution within individual Cu-lines was obtained from FEM.
Pulsed MOCVD of Cu Seed Layer using a (Hfac)Cu(3,3-Dimethyl-1-Butene) Source Plus H2 Reactant
Authors: Park Jaebum , Yang Heejung , Lee Jaegab
Published: April 2011

Pulsed metalorganic chemical vapor deposition (MOCVD) of conformal copper seed layers, for the electrodeposition Cu films, has been achieved by an alternating supply of a Cu(I) source and H2 reactant at the deposition temperatures of 50 - 100°C. The Cu thickness increased proportionally to the number of cycle, and the growth rate was in the range of 3.5 to 8.2 A /cycle, showing the ability to control the nano-scale thickness. As-deposited films show highly smooth surfaces even for more than 100nm. In addition, about a 90% step coverage was obtained inside trenches, with an aspect ratio greater than 30:1. H2, introduced as a reactant gas, can play an active role in achieving highly conformal coatings, with increased grain sizes.
Supercritical CO2 Treatments for Semiconductor Applications
Authors: Gangopadhyay S. , Lubguban J.A. , Lahlouh B. , Sivaraman G. , Biswas K. , Rajagopalan T. , Biswas N. , Kim H. -C. , Volksen W. , Miller R. D.
Published: April 2011

Supercritical fluids (SF) have been used in a wide variety of applications: in industrial processes, analytical, waste detoxification, etc. Recently, its usefulness extends to the semiconductor industry. Researches have shown that supercritical CO2 (SCCO2) can be used to remove photoresists and significantly reduce the amount of waste from solvents in comparison to conventional stripping techniques. SF will also find its usefulness in cleaning high aspect ratio vias and deep trenches as semiconductor features shrink to submicron levels. We will report here the use of supercritical CO2 treatments in extraction of porogens from a nanohybrid film fabricated via templated-porogen approach. Its use as a medium to repair the damage in porous films from plasma ashing will also be presented. The ability to tune the solvation and diffusion power of SCCO2 and to swell the film matrix make it a good medium for silylation to restore hydrophobicity and functionalize the film.
Adhesion Strength Evaluation of Low-k Interconnect Structures Using a Nanoscratch Method
Authors: Ye Jiping , Ueoka Kenichi , Kojima Nobuo , Shimanuki Junichi , Shimada Miyoko , Ogawa Shinichi
Published: April 2011

A convenient nanoscratch method was combined with atomic force microscope (AFM) and transmission electron microscope (TEM) observations to conduct the first-ever evaluation of the adhesion strength of a complicated microstructure Cu/Ta/TaN/pSiO2/low-k/SiC/pSiO2/Si-substrate with the aim of correlating the fracture strength with the results of chemical mechanical polishing (CMP) tests. Concretely, this evaluation focused on the fact that specimens having a low-k layer pretreated with rare-gas plasma prior to the deposition of the SiO2 layer exhibited low delaminated densities in the Cu CMP process. It was found that a specimen with the rare-gas plasma pretreatment exhibited a higher friction coefficient, a higher critical load and brittle adhesive failure resulting from delamination at the interface between the low-k and SiC layers. A specimen without the rare-gas plasma pretreatment displayed a lower friction coefficient, a lower critical load, and ductile cohesive failure in the low-k layer. Because less plastic deformation was observed in the low-k layer subjected to the rare-gas plasma pretreatment, it is assumed that the pretreatment reinforced the mechanical properties of the low-k layer, making it more resistant to ductile cohesive failure. These results agreed with the CMP test data and indicated that the nanoscratch method makes it possible to predict the ability of complicated Cu/low-k interconnect structures to withstand the CMP process.
Anisotropic Elastic Properties of Low-k Dielectric Materials
Authors: Maznev A.A. , Mazurenko A. , Alper G. , Moore C.J.L. , Gostein M. , Schulberg Michelle T. , Humayun Raashina , Sengupta Archita , Sun Jia-Ning
Published: April 2011

A non-contact optical technique based on laser-generated surface acoustic waves (SAWs) was used to characterize elastic properties of two types of thin (150-1100 nm) low-k films: more traditional non-porous organosilicate glass PECVD films (k=3.0) and novel mesoporous silica films fabricated in supercritical CO2 (k=2.2). The acoustic response of the non-porous samples is well described by a model of an elastically isotropic material with two elastic constants, Young's modulus and Poisson's ratio. Both parameters can be determined by analyzing SAW dispersion curves. However, the isotropic model fails to describe the SAW dispersion in the mesoporous samples. Modifying the model to allow a difference between in-plane and out-of plane properties (i.e., a transversely isotropic material) results in good agreement between the measurements and the model. The in-plane compressional modulus is found to be 2-3 times larger than the out-of plane modulus, possibly due to the anisotropic shape of the pores. Elastic anisotropy should therefore be taken into account in modeling mechanical behavior of low-k materials.
Evaluation of Thin Dielectric-Glue Wafer-Bonding for Three Dimensional Integrated Circuit-Applications
Authors: Kwon Y. , Yu J. , McMahon J.J. , Lu J.-Q. , Cale T.S. , Gutmann R.J.
Published: April 2011

The critical adhesion energy of benzocyclobutene (BCB)-bonded wafers is quantitatively investigated with focus on BCB thickness, material stack and thermal cycling. The critical adhesion energy depends linearly on BCB thickness, increasing from 19 J/m2 to 31 J/m2 as the BCB thickness increases from 0.4 μm to 2.6 μm, when bonding silicon wafers coated with plasma enhanced chemical vapor deposited (PECVD) silicon dioxide (SiO2). In thermal cycling performed with 350 and 400 oC peak temperatures, the significant increase in critical adhesion energy at the interface between BCB and PECVD SiO2 during the first thermal cycle is attributed to relaxation of residual stress in the PECVD SiO2 layer. On the other hand, the critical adhesion energy at the interface between BCB and PECVD silicon nitride (SiNx) decreases due to the increase of residual stress in the PECVD SiNx layer during the first thermal cycle.
Hydrogen in Ultralow Temperature SiO2for Nanocrystalline Silicon Thin Film Transistors
Authors: Kattamis Alex , Cheng I-Chun , Allen Steve , Wagner Sigurd
Published: April 2011

Nanocrystalline silicon is a candidate material for fabricating thin film transistors with high carrier mobilities on plastic substrates. A major issue in the processing of nanocrystalline silicon thin film transistors (nc-Si:H TFTs) at ultralow temperatures is the quality of the SiO2gate dielectric. SiO2deposited at less than 250°C by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD), and not annealed at high temperature after deposition, exhibits high leakage current and voltage shifts when incorporated into TFT's. Secondary ion mass spectrometry (SIMS) measurements show that the hydrogen concentration (NH) in PECVD oxide deposited at 150°C on crystalline silicon (x-Si) is ∼ 0.8 at. %. This is much higher than in thermal oxides on x-Si, which display concentrations of less than 0.003 at. %. The leakage current density for thermal oxides on x-Si at a bias of 10 V is ∼9×10−6A/cm2whereas for 200°C PECVD oxides on nc-Si:H the current is ∼1×10−4A/cm2. As the temperature of the SiO2deposition is reduced to 150°C the current density rises by up to two orders of magnitude more. The H which is suspected to cause the leakage current across the PECVD oxide originates from the nc-Si:H substrate and the SiH4source gas. We analyzed the 300-nm gate oxide in capacitor structures of Al / SiO2/n+nc-Si:H / Cr / glass, Al / SiO2/ n+nc-Si:H / x-Si, and Al / SiO2/ x-Si. Vacuum annealing the nc-Si:H prior to PECVD of the oxide drives H out of the nc-Si:H film and reduces the amount of H incorporated into the oxide that is deposited on top. SiO2film deposition from SiH4and N2O at high He dilution has a still greater effect on lowering NH. The leakage current at a 10 V bias dropped from ∼1×10−4A/cm2to about ∼2×10−6A/cm2using He dilution at 250°C, and the vacuum anneal of the nc-Si:H lowered it by an additional factor of two. Thus we observe that both the nc-Si:H anneal and the SiO2deposition at high He dilution lessen the gate leakage current.
Recent Advances in the Synthesis of Polyfluorenes as Organic Semiconductors
Authors: Brennan David J. , Chen Yu , Feng Shaoguang , Godschalx James P. , Spilman Gary E. , Townsend Paul H. , Kisting Scott R. , Dibbs Mitchell G. , Shaw Jeff M. , Welsh Dean M. , Miklovich Jessica L. , Stutts Debra
Published: April 2011

New poly(fluorene-thiophene) alternating copolymers are described in which either the dioctylfluorene or bithiophene units in poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) are replaced by other fluorene or thiophene-based groups, respectively. Improvements in solubility are realized when the bithiophene unit of F8T2 is replaced by dihexylterthiophene or dihexylpentathiophene units. Melting temperatures are also lowered by 50 – 100°C in these polymers when compared to F8T2. Replacement of the bithiophene unit of F8T2 with a dihexylpentathiophene unit also results in a significant improvement in hysteresis (< 2 V vs. 3.5 – 5 V for F8T2). Initial results are also reported on the thermal cleavage of the C8side groups of F8T2, which yields an insoluble polymeric semiconductor film that continues to exhibit transistor switching characteristics as part of a bottom gate device.
Crystalline Organic Semiconducting Thin Films Cast from a Novel Thermolytic Thiophene Oligomer
Authors: Chang Paul C. , Murphy Amanda R. , Lee Josephine B. , Fréchet Jean M. J. , Subramanian Vivek
Published: April 2011

Here we report on OTFTs made from a novel thermoresponsive thiophene based oligomer. The functionalized oligomer is soluble in common solvents, but loses its solubility upon thermolysis. Devices with channel lengths from 5 to 40 νm were fabricated from solution then subjected to thermolysis at temperatures ranging from 150-250°C. The initially amorphous materials reorganize into highly crystalline films upon thermolysis. Crystallinity was characterized by x-ray diffractometry and atomic force imaging. AFM studies depicted the nucleation of molecular terraces, where the formation and overall height of terraces was observed to be dependent upon the thermolysis temperature and solvent choice. These factors correlated to overall performance. For both dip-cast and spin-cast samples, devices were fabricated at a process temperature of 180°C with mobilities of 0.07 cm2/Vs and on/off ratios > 105. The deves were relatively stable in both air and common solvents, with their mobility degrading only by ∼25% upon immersion in the original casting solvents. The solubility characteristics and process temperatures for these devices may be particularly suitable for solution processing on flexible substrates.
Two causes of source/drain series resistance in bottom-contact pentacene thin-film transistors
Authors: Noda Makoto , Yoneya Nobuhide , Hirai Nobukazu , Kawashima Noriyuki , Nomoto Kazumasa , Wada Masaru , Kasahara Jiro
Published: April 2011

We identified two causes of source/drain (S/D) series resistance (Rs) in bottom-contact (BC) pentancene thin-film transistors (TFTs). One is mixed-phase pentacene grown in the blurred- edge region of Au electrodes and the other is the semi-insulating pentacene region between the Au electrode and the carrier-accumulating layer. A novel Au S/D electrode structure with a self-assembled monolayer (SAM) adhesion layer enables direct injection of carriers into the accumulating layer and markedly reduces Rs for unit gate width (RsW) to 6 Mωμ[.proportional]m. BC TFTs with this electrode structure showed extrinsic field-effect mobility as high as 1.1 cm2/Vs.
Study of Percolation in PMMA / Indium Tin Oxide Composites
Authors: Capozzi Charles J. , Shackelford Sandra , Ou Runqing , Gerhardt Rosario A.
Published: April 2011

Knowledge of percolation in binary composites is critical to the development of new materials with specific electrical and optical properties. This report investigates the detection of percolation in novel two-phase composites consisting of poly(methyl) methacrylate(PMMA) and indium tin oxide (ITO). ITO is a filler of particular interest primarily for possessing optical clarity consistent with PMMA in the visible light range. AC impedance measurements were performed on specimens with varying concentrations of ITO particles to determine the percolation threshold. Percolation was observed when specimens contained 2-3% vol. of nano- sized ITO and 6%-8% vol. of coarse-sized ITO. Thus, the percolation threshold appeared significantly decreased with reduced particle size of the filler. It is speculated that minor agglomerates in the bulk of the specimens may have prevented percolation from occurring at even lower volume fractions of the filler phase.
Nanocrystalline fcc metals: bridging experiments with simulations
Authors: Swygenhoven H. Van , Derlet P. M. , Frøseth A. G. , Petegem S. Van , Budrovic Z. , Hasnaoui A.
Published: April 2011

Atomistic simulations have provided unprecedented insight into the structural and mechanical properties of nanocrystalline materials, highlighting the role of the non-equilibrium grain boundary structure in both inter- and intra-grains deformation processes. One of the most important results is the capability of the nanosized grain boundary to act as a source and sink for dislocations. However the extrapolation of this knowledge to the experimental regime requires a clear understanding of the temporal and spatial scales of the modelling technique and a detailed structural characterisation of the simulated samples. In this contribution some of the synergies that can be develo ped between atomistic simulations and experiments for this research field are briefly discussed by means of some typical examples.
Twin Boundaries and Stacking Faults in Monazite (Monoclinic
LaPO4)
Authors: Hay Randall S.
Published: April 2011

Monazite (LaPO4) was indented at room temperature. Deformation twin
boundaries and stacking faults were characterized by high resolution transmission
electron microscopy. Kinked deformation twins were also characterized and analyzed.
Three types of stacking faults associated with climb-dissociated partial dislocations
were observed. Two were found on twin boundaries, and a third in the lattice.
Formation mechanisms are discussed. The superimposition of stacking faults along twin
boundaries during deformation twinning and the glide of climb-dissociated partial
dislocations allowed by stacking fault migration are discussed. The possible
relationship between the formation mechanisms for these defects and the low-
temperature recrystallization and self-annealing of defects in monazite is
considered.
Quantum-Dot Molecules for Potential Applications in Terahertz Devices
Authors: Stoleru Valeria Gabriela , Towe Elias , Ni Chaoying , Pal Debdas
Published: April 2011

The experimental and theoretical results of the electronic and optical properties of quantum dot artificial molecules (AMs), formed by pairs of electronically coupled quantum dots (QDs), are presented here in order to identify the necessary conditions for the development of new types of terahertz (THz) injection lasers based on intraband carrier transitions. We have performed analytical calculations to obtain the spatial strain distribution in vertically aligned (In, Ga)As QDs grown on (001) GaAs substrates by molecular beam epitaxy. Electronic coupling of the dots, mainly governed by the thickness of the separating barrier between the dot layers, is allowed due to the strain field-assisted self-organization of the dots. The calculated strain field reproduces our cross sectional high-resolution transmission electron microscopy observations very well. We further take into account the microscopic effects of the spatial strain distribution on carrier confinement potentials, and compute the electronic structure of the AM. Our calculations of the peak luminescence energies are in good agreement with our experimental results and those of others. The growth of quantum dot molecules represents a major step in tailoring the electronic and optical properties of the nanostructures.
Virtual Fabrication of Small Ga-As/P and In-As/P Clusters with Pre-Designed Electronic Pattern Structure
Authors: Pozhar Liudmila A. , Yeates Alan T. , Szmulowicz Frank , Mitchel William C.
Published: April 2011

Quantum statistical physics methods [1] relate charge transport properties of small atomic clusters (or small quantum dots, QDs) to their equilibrium electronic energy level spectra. Thus, electronic energy level computations for such systems provide a foundation for realization of a virtual (i.e., fundamental theory- based, computational) approach [2] to synthesis of sub-nanoscale materials with pre-designed charge transport properties. In this publication the Hartee-Fock (HF) electronic energy level spectra of several pre-designed small clusters of Ga, As, In and P atoms are studied and compared to those of the corresponding clusters grown at spatially unrestricted conditions. Influence of clusters' growth conditions on formation and structure of their valence and conduction bands is discussed.
ZnO/GaN Heteroepitaxy
Authors: Jang K. W. , Oh D. C. , Minegishi T. , Suzuki H. , Hanada T. , Makino H. , Cho M. W. , Yao T. , Hong S. K.
Published: April 2011

This paper presents the recent achievements of ZnO/GaN heteroepitaxy. The general controlling method and mechanism for the polarity of heteroepitaxial ZnO and GaN films by interface engineering via Plasma-assisted Molecular beam epitaxy(P-MBE) are introduced in a viewpoint of principle for polarity control. We propose the principle of crystal polarity: Crystal polarity can succeed at the heterointerface when no interface layer is formed, while an interface layer with inversion symmetry is formed, the crystal polarity is inverted at the heterointerfae. The effects of polarity on the interface, surface and bulk structure, and the structural and optical properties of ZnO/GaN epitaxy are also included. The polarity of GaN on ZnO is successfully controlled based on the proposed principle for control of crystal polarity. Additionally, the electronic characteristics such as electron concentration, band-line-up, and C-V characteristics of ZnO/GaN heterointerface are dicussed.
MBE-Grown GaNAsBi Matched to GaAs with 1.3-μm Emission Wavelength
Authors: Yoshimoto Masahiro , Huang Wei , Oe Kunishige
Published: April 2011

GaNyAs1-x-yBix alloy lattice-matched to GaAs has been grown by molecular beam epitaxy (MBE). The lattice-matching of GaNyAs1-x-yBix to GaAs was investigated by X-ray diffraction measurements on a series of GaNyAs1-x-yBix with various GaN molar fractions. GaNyAs1-x-yBix lattice-matched to GaAs was obtained, which was confirmed by its diffraction peak overlapped with the peak of GaAs. Photoluminescence (PL) of 1.3 μm was observed from GaNyAs1-x-yBix epilayer matched to GaAs at room temperature. The temperature coefficient of the PL peak energy in a temperature range 150–300K for GaNyAs1-x-yBix was 1/3 of InGaAsP with a bandgap corresponding to 1.3-μm emission. Both lattice-matching to GaAs and bandgap adjustment to 1.3-μm waveband were achieved for GaNyAs1-x-yBix for the first time. This alloy will lead to the fabrication of laser diodes with an emission of temperature insensitive wavelength.
Application of Low Temperature InP Wafer Bonding Towards Optical Add/Drop Multiplexer Realization
Authors: Arokiaraj J. , Vicknesh S. , Ramam A.
Published: April 2011

A method to bond directly Indium Phosphide to Indium phosphide at low temperatures has been realized. The treatment of wafers in HF and oxygen plasma exposure prior to bonding is helpful in activating the surface of the wafers at room temperature. This surface activation is useful to bond the wafers at room temperature. Further higher temperature (220°C) treatment with pressure, aided in the completion of the wafer bonding process. The interface of the bonded structures revealed a very thin amorphous layer of oxide when examined under high resolution TEM. Cross-sectional micro Raman measurements revealed signatures corresponding to some disordered associated layer at the interface. Current-Voltage characteristics exhibited ohmic conduction across the interface. The wafer bonding method developed would serve as a useful tool for the fabrication of photonic and optoelectronic devices.
Annealing Effects of ZnO Nanorods on DC Inorganic Electroluminescent Device Characteristics
Authors: Sasaki Shinya , Miyashita Hiroshi , Kimpara Takashi , Satoh Tomomasa , Hirate Takashi
Published: April 2011

We fabricated a DC inorganic electroluminescent (EL) device whose structure is ITO electrode / ZnS:Mn / ZnO (Mn) nanorods / p−/p++-Si(111) / Au electrode. ZnO nanorods were grown by chemical vapor deposition method combined with laser ablation. ZnS:Mn and ITO were deposited by electron-beam-deposition. We studied on annealing effects of ZnO nanorods on the electrical and electroluminescent characteristics of this device. The device without annealing showed a low breakdown voltage, and any EL emission could not be observed. On the other hand, the device with annealing showed higher impedance and higher breakdown voltage, and the EL emission from the ZnS:Mn layer was observed. An intense EL emission was observed from a peripheral of ITO electrode. An EL emission from the inside area of ITO electrode was very weak.
Defect structures in undoped and doped ZnO films studied by solid state diffusion
Authors: Ryoken Haruki , Sakaguchi Isao , Ohgaki Takeshi , Ohashi Naoki , Adachi Yutaka , Haneda Hajime
Published: April 2011

Defect structures in ZnO thin films were studied to clarify the mechanism of charge compensation and crystallinity degradation induced by alloying. Regarding the undoped ZnO films, it was indicated that the degree of non-equilibrium behavior in the films deposited by PLD was much less than in the films prepared by the other two methods, i.e., MBE and sputtering, and, moreover, the solid-state diffusion behavior in the PLD-grown undoped ZnO was close to that of bulk ZnO. The heavily Al-doped films and alloy films with high concentrations of MgO exhibited significant non-equilibrium behavior, even for those prepared by PLD. It was indicated that the high concentration of extrinsic elements, e.g., Al and Mg, introduces non-equilibrium defects into ZnO films and those defects are the cause of the crystallinity degradation and thermal instability of the films.
Synthesis of Highly Photoluminescent CdTe Nanocrystals and Their Incorporation into Glass Matrices
Authors: Murase Norio , Li Chunliang
Published: April 2011

Photoluminescence (PL) efficiency of thioglycolic-acid (TGA)-stabilized CdTe nanocrystals in water depends strongly on the amount of TGA upon synthesis. The less the amount, the higher the PL efficiency obtained if the colloid is not precipitated. When the molar ratio of TGA against Cd2+ upon preparation is ca. 1.3, PL efficiency of as-prepared solution becomes the maximum and exceeds 60% in red-emitting region. In this case, the spectral widths of the PL become the minimum. We have encapsulated these highly luminescent nanocrystals into glass matrices by using a sol-gel method. Silane coupling agent having an amino-group is effective to preserve the surface of the nanocrystals. The glass thus prepared is stable and shows PL efficiency as high as 40%.
Dopant Activation in bulk germanium and Germanium-on-Insulator
Authors: Chao Y.-L. , Prussin S. , Woo J. C. S. , Scholz R.
Published: April 2011

High levels of electrical activation of both p- and n-type dopants are realized by pre-amorphization implantation (PAI) in bulk germanium wafers and germanium-on-insulator (GOI) substrates. In bulk germanium, p-type dopant yields an electrical activated concentration of 1.5×1020 /cm3 after a 400°C rapid thermal annealing (RTA), which is one order higher than obtained for samples without PAI. N-type dopants also show comparable improvement as 1×1020 /cm3 after 600°C RTA. Both results are the highest ever being reported and are sufficient for advanced CMOS applications. PAI was also employed in dopant activation for GOI substrates. Carrier concentrations of 6×1020 /cm3 and 5×1019 /cm3 were observed for p- and n-type dopants respectively after identical RTA conditions as for bulk germanium counterparts. Hydrogen incorporated in GOI wafers which were prepared by Smart-Cut™ approach may be responsible for the discrepancy of activated concentrations between bulk germanium and GOI. Nevertheless, PAI shows the promise of dopant activation in germanium and can be readily adopted in current CMOS processes.
New Routes To Metal Chalcogenide Nanostructures.
Authors: Christian Paul , O'Brien Paul
Published: April 2011

There is considerable current interest in the synthesis of metal chalcogenide nanostructured materials1 especially for the manufacture of so called 3rd generation solar cells. The facile, large scale, synthesis of such materials is critical to enabling such technology. The synthesis of these materials, especially those of cadmium, has been widely discussed in the literature. However, whilst routes involving pyrophoric materials give high quality particles and structures2, their inherent reactivity results in complications in handling. Although the use of acetates has already been shown to give good results,3 there are, in general, problems in the synthesis of tellurium containing materials.4

This paper describes a new method providing a general synthesis of metal chalcogenide nanomaterials in a TOP/TOPO reaction system involving easy-to-handle reagents. Results for cadmium will for the basis of the discussion, which will include examples from a wider range of metals. The use of cadmium acetate in TOP and solutions of chalcogenides in TOP in the presence of suitable reducing agents provides an exceptionally reactive system. The system is flexible and may be applied to a wider range of chalcogenide based nanomaterials.
Development of Dual MQW Region LEDs for General Illumination
Authors: Nicol David Brackin , Asghar Ali , Strassburg Martin , Tran My , Pan Ming , Kang Hun , Ferguson Ian T. , Alevi Mustafa , Senawiratne Jayantha , Hums Christoph , Dietz Nikolaus , Hoffmann Axel
Published: April 2011

Dual Multi-Quantum Well (MQW) region light emitting diodes (LEDs) for efficient pumping of multiple phosphors have been grown by Metal Organic Chemical Vapor Deposition (MOCVD), for use in broadband, white solid state light sources. Blue (460 nm) and Violet/UV (∼400–420 nm) emitting MQW regions were incorporated into one device and show recombination mechanisms similar to single MQW region devices. The introduction of a decoupling region successfully separated the electroluminescent emissions, and two distinct emission peaks were observed. These devices can be used to pump a variety of phosphors designed for blue and UV sources, allowing for more design flexibility in color rendering and color temperature attributes of solid state light sources.
Optimization of Growth and Activation of Highly Doped p-type GaN for Tunnel Junctions
Authors: Nicol David B. , Asghar Ali , Tran My , Mehta Dhairya , Ferguson Ian T.
Published: April 2011

Highly doped p-type GaN was grown by MOCVD with a Mg source for use in tunnel junctions for dual wavelength light emitting diodes. Highly doped p-type material (p+) is necessary for creating efficient tunnel junctions that act as buried current spreading layers and provide high quality contacts to p-type GaN. Molar flow ratios and growth temperature were varied to achieve maximum doping concentration. A range of post-growth annealing conditions to activate incorporated Mg was investigated. Secondary Ion Mass Spectrometry (SIMS) and Hall effect were used to measure Mg incorporation and carrier concentration, respectively. The maximum carrier concentration achieved employed a hybrid growth scheme that achieved high carrier concentration and high quality material by alternating layers of high and low growth temperature material. Atmospheric annealing was compared to standard RTA under N2 ambient. Successful GaN tunnel junctions were grown using the hybrid p-type doping scheme developed in this work. I-V measurements were taken on these devices to evaluate the effectiveness of the devices.
Sublimation Growth of Aluminum Nitride-Silicon Carbide Alloy Crystals on SiC (0001) Substrates
Authors: Gu Z. , Edgar J.H. , Payzant E.A. , Meyer H.M. , Walker L.R. , Sarua A. , Kuball M.
Published: April 2011

Thick (up to 1 mm) AlN-SiC alloy crystals were grown on off-axis Si-face 6H-SiC (0001) substrates by the sublimation-recondensation method from a mixture of AlN and SiC powders at 1860–1990 °C in a N2 atmosphere. The color of the crystals changed from clear to dark green with increasing growth temperature. Raman spectroscopy and x-ray diffraction (XRD) confirmed an AlN-SiC alloy was formed with the wurtzite structure and good homogeneity. Three broad peaks were detected in the Raman spectra, with one of those related to an AlN-like and another one to a SiC-like mode, both shifted relative to their usual positions in the binary compounds, and the third broad peak with possible contributions from both AlN and SiC. Scanning Auger microanalysis (SAM) and electron probe microanalysis (EPMA) demonstrated the alloy crystals had an approximate composition of (AlN)0.75(SiC)0.25 with a stoi chiometric ratio of Al:N and Si:C. The substrate mi sorientati on ensured a two-dimensional growth mode confirmed by scanning electron microscopy (SEM).
Excitation Wavelength Dependent Raman Scattering in Low and Highly Degenerate InN Films
Authors: Naik V.M. , Dai H. , Naik R. , Haddad D.B. , Thakur J.S. , Auner G.W. , Lu H. , Schaff W.J.
Published: April 2011

The Raman spectra of low and highly degenerate InN films grown by conventional Molecular Beam Epitaxy (MBE) and Plasma Source Molecular Beam Epitaxy (PSMBE) have been studied using visible (514.5 nm) and near infrared (785 nm) excitation wavelengths. The MBE grown InN films have a low electron carrier concentration, ne < 2.0 × 1019 cm−3, exhibiting an optical bandgap absorption edge of 0.6 to 0.7 eV. On the other hand PSMBE grown InN samples are highly degenerate with ne > 3 × 1020 cm−3 with an observed optical bandgap ranging from 1.5 to 1.9 eV. Raman spectra of low degenerate InN films show sharp E2 and A1(LO) modes whereas spectra of highly degenerate InN films show rather broad features indicating the presence of a large number of structural defects. In the latter samples a resonance enhanced Raman scattering is observed especially with 785 nm excitation energy, where the excitation energy matches the optical energy bandgap. Another interesting observation is that the expected coupled plasmon LO-phonon modes are not detected in these films, rather a phonon mode is observed at the location of the unscreened A1(LO) mode. The observation of unscreened LO-phonon, and the absence of coupled plasmon LO-phonon modes have been attributed to Landau damping of the higher energy mode and coupling of the lower energy mode with the electron-hole pair excitations leading to the emergence of a mode very close to the A1(LO) mode.
Probing the formation of two-dimensional electron gas in AlInGaN/ GaN heterostructures by photoluminescence spectroscopy
Authors: Soh C. B. , Liu W. , Chua S. J. , Tripathy S. , Chi D. Z.
Published: April 2011

Using temperature-dependent photoluminescence (PL), we report a detailed study on the optical transitions in AlyInxGa1−x−yN (0.01≤ × ≤ 0.023, 0.07 ≤ y ≤ 0.14) of variable thickness (20 – 100 nm) grown on GaN by metalorganic chemical vapor deposition (MOCVD). At 100 K, highest electron mobility has been obtained for samples with 40 nm thick AlInGaN epilayer and this is due to the contribution from the two-dimensional electron gas (2DEG) in the confined two dimensional potential well. In literature, such 2DEG phenomenon is not discussed for AlInGaN quaternary alloys. In our samples, we have clearly observed such effects from low-temperature PL spectroscopy for AlInGaN epilayer of thickness ≥ 40 nm. The PL peaks observed due to the interband transitions from 2DEG sub-bands to the valence band are in the range 3.55 – 3.68 eV for the sample with an epilayer thickness of 100 nm. Due to the composition pulling effect in this alloy, there is a higher incorporation of Al towards the surface for thicker AlInGaN epilayer, which generates a stronger piezoelectric field and a deeper triangular potential for electron confinement. This is evident from the observation of higher intensity ratio for 2DEG transition compared to band-edge transitions, I2DEG/IBE in sample with thicker AlInGaN epilayer at higher temperature. The intensity ratio, I2DEG/IBE however decreases subsequently for all the samples with further increase in temperature due to thermal excitation.
High Quality, Low Cost Continuous Poly-GaN Film on Si and Glass Substrates Produced by Spin Coating
Authors: Wu Huaqiang , Bourlinos Athanasios , Giannelis Emmanuel P. , Spencer Michael G.
Published: April 2011

Polycrystalline GaN layers have been produced on generic substrates via spin coating. Based on X-ray diffraction and SEM analyses, the GaN particles appear to be highly oriented on the surface. Strong luminescence from these layers has been demonstrated by cathodoluminescence. The source material was high purity, high quality GaN powder produced in our laboratory. Methyl cellulose was successfully used to disaggregate GaN particles in the dispersion. The colloidal dispersions were spun onto different substrates: Si, sapphire and glass. The dispersant was removed by annealing the sample at 500°C. The layer thickness was controlled by varying the number of spin coatings. Applications for spindeposited GaN layers include the fields of light emitting devices and random lasers.
Comparison of the effect of gate dielectric layer on 2DEG carrier concentration in strained AlGaN/GaN heterostructure
Authors: Wang W. , Derluyn J. , Germain M. , Dewolf I. , Leys M. , Boeykens S. , Degroote S. , Ruythooren W. , Das J. , Schreurs D. , Nauwelaers B. , Borghs G.
Published: April 2011

The effect of surface passivation on undoped AlGaN/GaN heterostructures using SiO2, Al2O3, Ta2O5 and Si3N4 as a function of layer thickness is presented. It is found that all of the oxides caused decreased 2DEG carrier concentration with increasing thickness of the respective oxide layers between the gate and AlGaN layer. On the contrary, the 2DEG carrier concentration increased strongly with increasing Si3N4 layer thickness. An elementary polarization model was used to fit the behavior for all materials and thicknesses leading to quantitative results. The fitting suggests that the effect of the oxides and Si3N4 on the 2DEG carrier concentration can be explained by the differences between them with respect to charge accumulation at the AlGaN/dielectric interface. High temperature in-situ deposited Si3N4 especially shows interesting behavior by bowing measurements as it also adds strain which increases piezoelectric polarization charge in AlGaN layer, so that increases the charge density in the 2DEG.
Molecular beam epitaxy of GaN on lattice-matched ZrB2 substrates using low-temperature GaN and AlN nucleation layers
Authors: Armitage Rob , Nishizono Kazuhiro , Suda Jun , Kimoto Tsunenobu
Published: April 2011

GaN epilayers have been grown by plasma-assisted molecular-beam epitaxy on ZrB2 substrates with close in-plane lattice match. Growth processes utilizing both low-temperature GaN (LT-GaN) and AlN nucleation layers were investigated. The x-ray ω-scan widths for the optimized LT-GaN nucleation process were 400 and 750 arcsec for symmetric and asymmetric reflections, respectively. When using LT-GaN nucleation layers, the chemical incompatibility of ZrB2 results in a high dislocation density despite the in-plane lattice match. The epilayer polarity was N-polar for LT-GaN nucleation layers under all conditions investigated. For AlN nucleation layers, Ga-polar epilayers were obtained under suitable conditions (Al-rich, lower nucleation temperatures) for nominal AlN thickness as low as 1 nm. From RHEED analysis it appears that a psuedomorphic Al wetting layer forms on the ZrB2 surface, and that using AlN as the nucleation layer may offer promise for reducing the epilayer defect density.
SITE MULTIPLICITY OF RARE EARTH IONS IN III-NITRIDES
Authors: O'Donnell K.P. , Katchkanov V. , Wang K. , Martin R.W. , Edwards P.R. , Hourahine B. , Nogales E. , Mosselmans J.F.W. , De Vries B.
Published: April 2011

This presentation reviews recent lattice location studies of rare earth (RE) ions in GaN by electron emission channelling (EC) and X-ray absorption fine structure (XAFS) techniques. These studies agree that RE ions at low concentrations (whether they are incorporated during growth or introduced later by ion implantation) predominantly occupy Ga substitutional sites, as expected from considerations of charge equivalence. We combine this result with some examples of the well-documented richness of optical spectra of GaN:RE3+ to suggest that the luminescence of these materials may be ascribed to a family of rather similar sites, all of which feature the REGa defect.
Light Emission in Aperiodic Thue-Morse Dielectrics
Authors: Dal Negro L. , Yi J. H. , Nguyen V. , Yi Y. , Michel J. , Kimerling L.C.
Published: April 2011

Using Plasma Enhanced Chemical Vapor Deposition (PE-CVD) we fabricated silicon rich, light emitting SiNx/SiO2 Thue-Morse (T-M) multilayer structures in order to investigate the generation and transmission of light in deterministic aperiodic dielectrics. We found that light emission is significantly enhanced at the wavelengths corresponding to T-M resonant states with field enhancement, in agreement with optical transmission data. Emission enhancement effects by almost a factor of 6 with respect to a reference homogeneous SiNx dielectric have been experimentally measured. The unprecedented degree of structural flexibility of T-M systems can provide alternative routes towards the fabrication of optically active multi-wavelength photonic devices.
Photoluminescent coupled multiple microcavity structures made of porous silicon
Authors: Agarwal V. , Soto Urueta J.A. , Miguel Gracia J.
Published: April 2011

In this paper we report the fabrication and experimental characterization of photoluminescent coupled multiple microcavity 1-Dimensional photonic bandgap structures for specific photonic applications. These structures have been prepared on silicon substrate as well as free standing. The comparision with theory gave a good fit showing desired structure formation for more than 184 layered structure. These structures can be useful for a large variety of applications such as silicon lasers.
Anisotropically Nanostructured Silicon: A First-Principle Approach.
Authors: Bonder Yuri , Wang Chumin
Published: April 2011

Optical properties of birefringent porous-silicon layers are studied within the density functional theory. Starting from a (110)-oriented supercell of 32 silicon atoms, columns of atoms in directions [100] and [010] are removed and the dangling bonds are saturated with hydrogen atoms. The results show an in-plane anisotropy in the dielectric function and in the refractive index (n). The difference Δn defined as n[110] -n[001] is compared with experimental data and a good agreement is observed. Also, the possibility in determining the morphology of pores by using polarized lights is analyzed.
Location of Er atoms with respect to Si nanoclusters in luminescent Er and Si co-implanted silicates
Authors: Pellegrino P. , Garrido B. , Arbiol J. , Garcia C. , Lebour Y. , Morante J.R.
Published: April 2011

In this contribution we explore the structural properties of different silicate glasses c o-implanted with Si and Er ions to various doses, and see how they affect the emission properties around 1540 nm. We have used silica, soda-lime and aluminium silicates as substrates. A multiimplantation scheme provided an uniform Si excess (5 or 15%) background to the subsequently implanted Er atoms. Er peak concentration has been varied between 2×1019 cm−3 to 6×1020 cm−3. The structural analysis of the resulting structures have been performed by means of SIMS, XPS, Raman, and EFTEM.

It was found that the best photoluminescence (PL) emission properties are the ones for which a phase separation between the implanted Si and the matrix occurs, even without the formation of nanocrystalline aggregates. Amorphous Si nanoclusters with average size around 3 nm (for high Si content) or below 1nm (for low Si content) have been revealed after the EFTEM analysis. By analysing the layers by EELS and HAADF we have been able to determine the location of Er atoms relative to the Si nanoclusters for the first time to our knowledge. In samples with Er concentration higher than 1020 cm−3, the Er atoms are not randomly dispersed in the matrix. On the contrary, they tend to aggregate, forming large agglomerations mostly in the regions of lower density of Si precipitates. This observation correlates with the appearance of PL quenching at concentrations around 2×1020 cm−3. A suitable tuning of the annealing temperature has been found to drastically reduce this deleterious effect.
Possible Operation of Periodically Layered Nanocrystalline Porous Silicon as an Acoustic Band Crystal Device
Authors: Kiuchi Akira , Gelloz Bernard , Kojima Akira , Koshida Nobuyoshi
Published: April 2011

It is shown that the periodic stacked structures of nanocrystalline porous silicon (nc-PS) layers with controlled densities and elastic properties act as an acoustic band crystal (ABC) device. Supposing that the periodic nc-PS layers are formed by conventional modulated anodization technique to fabricate the multi-layered distributed Brag reflection mirror, the acoustic wave propagation modes are investigated theoretically for various structural parameters. According to the calculation results, a significant acoustic band gaps are generated in the ultrasonic regions due to a big contrast in the elastic constant produced between low-porosity and compact nc-PS layers. The propagation of acoustic wave can be completely suppressed in the characteristic band determined from designed parameters. The present result suggests further possibility of the nc-PS layer as a key component of ABC devices.
Towards a Si/SiGe Quantum Cascade Laser for Terahertz Applications
Authors: Paul D.J. , Lynch S.A. , Townsend P. , Ikonic Z. , Kelsall R.W. , Harrison P. , Liew S.L. , Norris D.J. , Cullis A.G. , Zhang J. , Bain M. , Gamble H.S. , Tribe W.R. , Arnone D.D.
Published: April 2011

While electroluminescence has been demonstrated at terahertz frequencies from Si/SiGe quantum cascade emitters, to date no laser has been achieved due to poor vertical confinement of the optical mode. A method of increasing the vertical confinement of the optical mode for a Si/SiGe quantum cascade laser is demonstrated using silicon-on-silicide technology. Such technology is used with epitaxial growth to demonstrate a strain-symmetrised 600 period Si/SiGe quantum cascade interwell emission and the polarisation is used to demonstrate the optical confinement. Electroluminescence is demonstrated at ∼3 THz (∼100 μm) from an interwell quantum cascade emitter structure. Calculated model overlap and waveguide losses for ridge waveguides are comparable to values from GaAs quantum cascade lasers demonstrated at terahertz frequencies. The effects of high doping levels in Si/SiGe quantum cascade structures is also investigated with impurity emission demonstrated rather than intersubband emission for the highest doping levels used in the cascade active regions.
C, Si and Sn Implantation of CVD Diamond as a means of Enhancing Subsequent Etch Rate
Authors: Leech P. W. , Perova T. , Moore R. A. , Reeves G. K. , Holland A. S. , Ridgway M.
Published: April 2011

Diamond films were implanted with C+, Si+ or Sn+ ions at multiple energies in order to generate a uniform region of implantation-induced disorder. Analysis of the C+ implanted surfaces by micro-Raman spectroscopy has shown only minor increase in the proportion of nondiamond or sp2-bonded carbon at doses of 5 × 1013 - 5 × 1015 ions/cm2. In comparison, an amorphization of the structure was evident after implantation with either Si+ ions at a dose of 5 × 1015 ions/cm2 or with Sn+ ions at >5 × 1014 ions/cm2. At a given implantation dose, the etch rate of the diamond film in a CF4/O2 plasma increased with the mass of the implanted species in the order of C+, Si+ and Sn+. For a given implant species, the etch rate was directly proportional to vacancy concentration as controlled by the dose or the implantation-induced disorder.
Photochemical Moisture Proof Coating on Nonlinear Optical Crystal by ArF Excimer Laser
Authors: Kojima M. , Murahara M.
Published: April 2011

Silicone oil was photo-chemically oxidized to change into SiO2 on the crystal by using an ArF excimer laser; the protective moistureproof film has been developed for a nonlinear optical crystal that is deliquescent.

The nonlinear optical crystals such as CsLiB6O10 (CLBO) and KH2PO4 (KDP) are deliquescent, which causes their surfaces to be cloudy by absorbing moisture in the air. We, therefore, demonstrated the growth of the SiO 2 film directly on the crystal so as to be moistureproof.

Firstly, dimethylsiloxane silicone oil (-O-Si(CH3)2-O-)n was poured on the substrate and coated by a spinner for making the silicone oil thin layer. Then, the ArF excimer laser was vertically irradiated on the sample in oxygen atmosphere. The O atom on the substrate surface was photo-excited by the laser to generate a high active O atom. At the same time, the Si-CH3 bond of the silicone oil was photo-dissociated and the dangling bond of Si was linked with the active O atom to form a SiO 2 film on the crystal surface.

In short, the film formed by the new technology can be used as a protective coating, which has the moisture resistance and the UV permeability, for a nonlinear optical crystal.