bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTQuantum 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

ABSTRACTThis 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

ABSTRACTGaNyAs1-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

AbstractA 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

ABSTRACTWe 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

ABSTRACTDefect 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

ABSTRACTPhotoluminescence (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

ABSTRACTHigh 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

ABSTRACTThere 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.4This 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

ABSTRACTDual 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

ABSTRACTHighly 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

ABSTRACTThick (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

ABSTRACTThe 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

ABSTRACTUsing 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

ABSTRACTPolycrystalline 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

ABSTRACTThe 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

ABSTRACTGaN 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

ABSTRACTThis 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

ABSTRACTUsing 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

ABSTRACTIn 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

ABSTRACTOptical 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.