bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low-Field Electron Emission Properties from Intrinsic and S-Incorporated Nanocrystalline Carbon Thin Films Grown by Hot- Filament CVD
Authors: Gupta S. , Weiner B. R. , Weiss B. L. , Morell G. , Johnson Kenyetta , Oritz Oscar O. 
Published: April 2011

AbstractResults are reported on the electron field emission properties of intrinsic and S- incorporated nanocrystalline carbon (n-C:S) thin films grown on molybdenum substrates by hotfilament CVD technique from methane-hydrogen (CH4/H2) and hydrogen sulphide-hydrogen (H2S/H2) gas pre mixtures respectively. The field emission properties for the S-incorporated films were investigated as a function of substrate temperature (TS). Lowest turn-on field was observed at 4.5 V/μm for one of the sample, which was grown at 900 °C, demonstrating the effect of sulfur addition. The S-incorporation also causes microstructural and structural changes, as characterized with ex situ techniques such as SEM, AFM and Raman spectroscopy (RS). Sassisted films show smoother surfaces and finer-grained than those grown without it. The electron field emission properties of S-assisted films is also compared to the film grown without it (intrinsic) at a particular deposition temperature and the turn-on field was found to be almost half for the S-assisted film than for the non S-assisted film. The influence of growth temperature was also conducted and an inverse correlation was found with the turn-on field (Ec). These studies were performed in order attempt to “tailor-the-material” as a viable cold cathode material by introducing the defecTS and altering the electronic structure.
A Memory Device Utilizing Resonant Tunneling in Nanocrystalline Silicon Superlattices
Authors: Montès Laurent , Grom Galina F. , Krishnan Rishi , Fauchet Philippe M. , Tsybeskov Leonid , White Bruce E. 
Published: April 2011

AbstractA quantum structure based on Si/SiO2 and fabricated using standard Si technology has strong potential for applications in non-volatile and scaled dynamic memories. Among standard requirements, such as long retention time and endurance, a structure utilizing resonant tunneling offers lower bias operation and faster write/read cycle. In addition, degradation effects associated with Fowlher-Nordheim (FN) hot electron tunneling can be avoided. Superlattices of nanometer size layers of silicon and silicon dioxide were obtained by sputtering. The size of the silicon nanocrystallites (nc-Si) is fixed by the thickness of the silicon layer which limits the size dispersion. A detailed analysis of the storage of charges in the dots, as a function of the nanocrystals size, is investigated using capacitance methods. Constant voltage and constant capacitance techniques are used to monitor the discharge of the structure. Room temperature non-volatile memory with retention times as long as months is evidenced.
Optical and Structural Characterization of Nanocrystalline Silicon Superlattices: Toward Nanoscale Silicon Metrology
Authors: Zollner Stefan , Konkar Atul , Liu Ran , Yapa Himansu , Dryer Patricia F. , Neeley Victoria A. , Xie Qianghua , Grom Galina F. , Zhu Qingyuan , Krishnan Rishikesh , Fauchet Philippe M. , Tsybeskov Leonid V. 
Published: April 2011

AbstractShort-period superlattices consisting of nanocrystalline Si wells and amorphous SiO2 barriers were analyzed using various structural (transmission electron microscopy, atomic force microscopy, and x-ray diffraction) and optical (Raman scattering and spectroscopic ellipsometry) characterization techniques. We observe parallel layers containing polycrystalline Si wells, primarily with <111> orientation, and an interesting surface morphology due to sputtering damage. Raman spectra show a redshift and broadening due to finite-size effects. The ellipsometry data can be described using the effective medium approximation (since the superlattice period is much shorter than the wavelength of the optical excitation) or a superlattice approach based on the Fresnel equations with a polycrystalline Si dielectric function.
AlGaN p-i-n Photodiode Arrays for Solar-Blind Applications
Authors: Lamarre P. , Hairston A. , Tobin S. , Wong K. K. , Taylor M. F. , Sood A. K. , Reine M. B. , Schurman M. J. , Ferguson I. T. , Singh R. , Eddy C. R. 
Published: April 2011

ABSTRACTThis paper presents UV imaging results for a 256×256 AlGaN Focal Plane Array that uses a back-illuminated AlGaN heterostructure p-i-n photodiode array, with 30×30 μm2 unit cells, operating at zero bias voltage, with a narrow-band UV response between 310 and 325 nm. The 256×256 array was fabricated from a multilayer AlGaN film grown by MOCVD on a sapphire substrate. The UV response operability (>0.4×average) was 94.8%, and the UV response uniformity (σ/μ) was 16.8%. Data are also presented for back-illuminated AlGaN p-i-n photodiodes from other films with cutoff wavelengths ranging between 301 and 364 nm. Data for variable-area diagnostic arrays of p-i-n AlGaN photodiodes with a GaN absorber (cutoff=364 nm) show: (1) high external quantum efficiency (50% at V=0 and 62% at V=-9 V); (2) the dark current is proportional to junction area, not perimeter; (3) the forward and reverse currents are uniform (σ/μ=50% for forty 30×30 μm2 diodes at V=−40 V); (4) the reverse-bias dark current data versus temperature and bias voltage can be fit very well by a hopping conduction model; and (5) capacitance versus voltage data are consistent with nearly full depletion of the unintentionally-doped 0.4 μm thick GaN absorber layer and imply a donor concentration of 3-4×1016 cm−3.
AlGaN/InGaN Heterostructure Field Effect Transistors Grown on Sapphire by Metal-Organic Chemical Vapor Deposition
Authors: Chuo Chang-Cheng , Kan Chia-Min , Chyi Jen-Inn , Nee Tzer-En , Lee Chia-Ming , Peng Chin-Kun 
Published: April 2011

ABSTRACTAlGaN/InGaN heterostructure field effect transistors were grown on sapphire by metalorganic chemical vapor deposition. Transmission electron microscopy shows that there are no additional dislocations induced by inserting the InGaN channel while a variation of strain field across the channel is observed. The transistors exhibit good pinch-off characteristics with a threshold voltage of about −2.9 V and a saturation current density of 0.55 A/mm. At room temperature, a peak transconductance of 132 (mS/mm) was obtained for a 1.0 μm-device. Current gain cutoff frequency fT of 9.4 GHz and maximum oscillation frequency fmax of 28.2 GHz were measured for the 1.0 μm-device. As the temperature is increased to 300 °C, the transconductance decreases to 50 mS/mm accompanied by a reduction of saturation current density of 0.24 A/mm due to the enhanced carrier scattering, gate leakage, and drain-source resistance.
High-Frequency Capacitance-Voltage Characteristics of Pecvd-Grown SiO2 Mis Structure on GaN and GaN/AL0.4Ga0.6N/GaN Heterostructure
Authors: Chen P. , Zhou Y.G. , Bu H.M. , Li W.P. , Chen Z.Z. , Shen B. , Zhang R. , Zheng Y.D. 
Published: April 2011

ABSTRACTMetal-insulator-semiconductor structures are fabricated by depositing SiO2 films on an MOCVD-grown n-type GaN epitaxial layer and a GaN/Al0.4Ga0.6N/GaN double heterojunction. The SiO2 films are grown by plasma-enhanced chemical vapor deposition. High-frequency C-V characteristics show the agreement of the measured C-V curve of SiO2/n-GaN with an ideal curve in deep depletion and the very small hysteresis, which indicates that the interface traps concentration in the sample is low. However, for SiO2/GaN/Al0.4Ga0.6N/GaN, the measured C-V curves show a notable flat-band shift of about 9.2 V and a typical polarization hysteresis window. These show the influence of the polarization charges in this structure. The capacitance on SiO2/GaN/Al0.4Ga0.6N/GaN reaches a minimum value under around –5V bias. The saturation at a minimum value of the C-V curve indicates the presence of holes accumulation in the MIS structure. These results imply that the piezoelectric effect in GaN/Al0.4Ga0.6N/GaN play an important role for the formation of the p-channel.
Preliminary Characterization of GaN MBE Epitaxial Layers Grown on Nanoporous 6H-SiC Substrates
Authors: Wolan J. T. , Gopalkrishna A. , Saddow S. E. , Mynbaeu M. , Morkoç H. , Reshchikov M. , Yun F. , Dmitriev V. , Wood C.E.C. 
Published: April 2011

ABSTRACTWe report on the growth and quality of plasma enhanced molecular beam epitaxy (PEMBE) of an n-GaN layer grown on a 6H-SiC substrate, which was prepared to be half nanoporous. A layer of nanoporous SiC was fabricated on a half section of n-type, on-axis (0001)Si face 41 mm commercial wafer by surface anodization. Following H-plasma surface cleaning and in-situ thermal annealing, a 0.7µm thick silicon doped GaN film was deposited at a growth rate of 0.35µm/hr. Substrate temperature during GaN growth was 709oC with a chamber pressure of 1.9 × 10−5Torr. Results of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) characterization suggest improved chemical quality of the film grown on the nanoporous section. Photoluminescence (PL) data indicate greatly reduced nonradiative recombination in the epi layer grown on the nanoporous as compared to the control surface.
Impact of the Growth Polar Direction on the Optical Properties of Gan Films Grown by Metalorganic Vapor Phase Epitaxy
Authors: Setoguchi A. , Yoshimura K. , Sumiya M. , Uedono A. , Chichibu S. F. 
Published: April 2011

ABSTRACTThe growth polar direction during metalorganic chemical vapor phase epitaxy of wurtzite GaN films was shown to affect the optical properties in terms of impurity and vacancy-type defect incorporation during the growth. The GaN film grown towards the Ga- face (0001) (+c polarity) exhibited clear excitonic features in its optical absorption and luminescence spectra up to room temperature. Conversely, the film with the N-face (000-1) (-c polarity) exhibited a broad emission band, which is located in the broadened absorption tail. The Stokes shift remained even at 300 K. The difference between the two was explained in terms of the presence of impurity-induced band tail states in –c GaN due to increased impurity density and enhanced incorporation of large volume vacancy-type defects, which were confirmed by secondary ion mass spectrometry [Sumiya et al., Appl. Phys. Lett. 76, 2098 (2000)] and monoenergetic slow positron annihilation technique.
In Segregation Effects on Optical and Doping Properties of InAlGaN Quaternary for UV Emitting Devices
Authors: Hirayama Hideki , Kinoshita Atsuhiro , Yamanaka Takuya , Hirata Akira , Aoyagi Yoshinobu 
Published: April 2011

ABSTRACTWe demonstrate room temperature intense ultraviolet (UV) emission wavelength ranging 300- 340 nm from InxAlyGa1-x-yN quaternary alloys grown by metal-organic vapor-phase-epitaxy (MOVPE). We found that the UV emission is drastically enhanced by introducing several percent of In into AlGaN. We fabricated single quantum well (SQW) consisting of InxAlyGa1-x-yN quaternary well and barrier, and clearly observed In segregation of sub-micron size from a cathode luminescence (CL) images. The intensity of 320nm-band emission from InAlGaN/InAlGaN QWs were as strong as those of 410nm-band emission from InGaN based QWs, at room temperature. The temperature dependence of photoluminescence (PL) emission for InAlGaN based QWs were much improved in comparison with GaN or AlGaN based QWs. We also grew Mg-doped InxAlyGa1-x-yN quaternary, and obtained hole concentration of 3×1017cm−3 by Hall measurement for high Al content (more than 50%) InxAlyGa1-x-yN quaternary.
Simulation of Stress Generation during GaN Lateral Epitaxial Overgrowth
Authors: Feng Zhaohua , Lovell Edward G. , Engelstad Roxann L. , Kuech Thomas F. , Babcock Susan E. 
Published: April 2011

ABSTRACTTo facilitate an understanding of defect production in gallium nitride during lateral epitaxial overgrowth, computer models have been developed to simulate the complete mechanical stress and strain fields. The virtual process included the deposition of a GaN seed layer on a sapphire substrate followed by a silicon dioxide stencil mask through which, and over which, the GaN product layer evolved and then cooled down to room temperature. Lattice mismatch and thermal strain were continuously assessed. Shear stresses on different crystallographic planes were analyzed to predict dislocation generation.
Step Flow Surface Morphology in Plasma Assisted Molecular Beam Epitaxy Grown GaN
Authors: Kusakabe Kazuhide , Kikuchi Akihiko , Kishino Katsumi 
Published: April 2011

ABSTRACTThe surface morphologies of homoepitaxial GaN films grown by molecular beam epitaxy (MBE) on metalorganic chemical vapor deposition (MOCVD) grown GaN template layers were investigated, using atomic force microscopy (AFM). Typical surface morphology of MBE-grown films on MOCVD-templates was dominated by spiral hillocks due to the high density of dislocations having a screw character and large driving force of MBE growth. Introduction of the AlN multiple interlayer (AlN -MIL) into MBE-GaN layers suppressed the formation of spiral hillocks. It was attributed to obstructing the dislocation propagation by AlN-MIL. Migration enhanced epitaxy (MEE) growth of GaN also reduced the density and tightness of spiral hillocks. This observation was attributed to that MEE growth technique decreased the driving force of growth.
A Study on the Growth of Cubic GaN Films Using an AlGaAs Buffer Layer Grown on GaAs (100) by Plasma-Assisted Molecular Beam Epitaxy
Authors: Kimura Ryuhei , Takahashi Kiyoshi , Grahn H. T. 
Published: April 2011

ABSTRACTAn investigation of the growth mechanism for RF-plasma assisted molecular beam epitaxy of cubic GaN films using a nitrided AlGaAs buffer layer was carried out by in-situ reflection high energy electron diffraction (RHEED) and high resolution X-ray diffraction (HRXRD). It was found that hexagonal GaN nuclei grow on (1, 1, 1) facets during nitridation of the AlGaAs buffer layer, but a highly pure, cubic-phase GaN epilayer was grown on the nitrided AlGaAs buffer layer.
Approaches For Reduction Of The Defect Density In Group III Nitride Based Heterostructures
Authors: Zheleva T. S. , Karoui F. , Kirchner K. , Derenge M. , Jones K. A. , Vispute R. D. , Venkatesan T. 
Published: April 2011

ABSTRACTLateral epitaxial overgrowth (LEO), pendeo-epitaxy (PE), and solid-phase epitaxial recrystallization (SPER) are discussed as three approaches for reducing the defect density in group III nitride based heterostructures. Studies of the LEO GaN and PE GaN revealed, that a major factor for the defect reduction in the laterally overgrown regions is the change of the dominant growth direction - from vertical in the window regions to lateral in the regions over the mask or over the trenches, and the related threading dislocations lines redistribution. The mechanisms of defect reduction in LEO GaN and PE GaN are similar, although they arise through different process routes, and are related to the free-standing (PE) or quasi-free-standing (LEO) growth of GaN, and the associated stress redistribution. The stress distributions in the LEO and PE GaN heterostructures are calculated and compared with finite element modeling. Another approach for reduction of the defects is the SPER process and the related thermal activation for dislocation reactions and grain boundary mobility and migration. This approach is shown in the example of annealed AlN films.
Characterization of the Mechanism of Activation for Visible Luminescence in Tb-Doped Crystalline and Amorphous AlN Thin Films
Authors: Spalding C. M. , Caldwell M. L. , Martin A. L. , Dimitrova V. I. , Kordesch M. E. , Richardson H. H. , Patten P. G. Van 
Published: April 2011

ABSTRACTHigh-temperature treatments are necessary for luminescence ‘activation’ of sputterdeposited, RE-doped, III-nitride phosphor materials. We report an investigation of the activation process in crystalline and amorphous Tb-doped AlN films. These films were characterized before and after thermal activation at temperatures up to 1000° C by cathodoluminescence (CL), static and time-resolved photoluminescence (PL), and secondary ion mass spectrometry (SIMS). The results suggest that the absence of luminescence in unactivated and in old activated samples is due to rapid quenching of the RE excited state. Furthermore, the quenching in the activated, aged samples appears to be due to sorption of ambient water vapor. Energy transfer to a harmonic of the O-H vibration is a likely quenching pathway in these samples. Unfortunately, this water-related quenching mechanism is implausible as a candidate in freshly-made, unactivated samples since water is excluded from the growth chamber.
Unusual Surface Undulations Observed in Ge/Si(100) Multilayers
Authors: Pai Woei Wu , Peng Y. H. , Chung W. F. , Wang S. Y. , Chen K. N. , Cheng H. H. 
Published: April 2011

AbstractMultilayer Ge/Si quantum wells grown on Si(100) at lower temperatures (300 C for Ge and 435 C for Si) exhibit unexpected large surface undulations. These groove-like features along <110> directions are correlated to the underlying dislocation networks. Studies on the dependence of surface roughness versus Ge spacer thickness exclude kinetic limitation as the cause of the observed troughs. Further comparison of the surfaces for multilayer and single-layer samples indicates a combination of the multilayer structure and the inhomogeneous surface strain field greatly enhances the undulations.
Epitaxial growth of (001) and (111) Ni films on MgO substrates
Authors: Lukaszew Rosa Alejandra , Stoica Vladimir , Uher Ctirad , Clarke Roy 
Published: April 2011

AbstractMetal-ceramic interfaces are important in applications as diverse as magnetic storage media and supported catalysts. It is very important to understand how the crystallography and microstructure of metallic films deposited onto ceramic substrates depend on growth and/or annealing conditions so that their physical properties (e.g. magnetic, electronic, etc.) can be tailored for specific applications. To this end, we have studied the epitaxial growth and annealing of (001) and (111) Ni films MBE grown on MgO substrates, where we have observed the evolution of the surface using correlated in- situ RHEED (reflection high-energy-electron diffraction) and STM (scanning tunneling microscopy) measurements.
Studies of Silicon Oxynitride Films Produced by Radio-Frequency Plasma Assisted Electron Cyclotron Resonance
Authors: Brewer J.D. , Raveh A. , Irene E.A. 
Published: April 2011

AbstractSingle crystal silicon wafers were treated by direct oxynitridation using electron cyclotron resonance (ECR) and radio-frequency (rf) plasma with separate N2 and O2 gas sources. Fabricated layers were characterized by ex situ spectroscopic ellipsometry (SE), Auger electron spectroscopy (AES), and atomic force microscopy (AFM).The thickness and nitride/oxide ratio of silicon oxynitride layers were found to be dependent on the main process variables, namely gas pressure, bias voltage, and N2/O2 flow rate ratio. It was also observed that ECR/rf plasma is more efficient for the formation of layers with higher nitrogen content at relatively low pressure (≤ 200 mTorr) and bias voltage (−40 V) when compared to that of rf plasma alone. SE modeling provided good fitting to experimental data, while AES and AFM analyses supported SE results. The effects of fabrication conditions on the thickness and composition of the layers will be presented.
Growth Front Roughening of Room Temperature Deposited Oligomer Thin Films
Authors: Tsamouras D. , Palasantzas G. , De Hosson J. Th. M. , Hadziioannou G. 
Published: April 2011

AbstractGrowth front scaling aspects are investigated for PPV-type oligomer thin films vapor- deposited onto silicon substrates at room temperature. For film thickness d~15-300 nm, commonly used in optoelectronic devices, correlation function measurement by atomic force microscopy yields roughness exponents in the range H=0.45±0.04, and an rms roughness amplitude which evolves with film thickness as a power law σ∝ dβ with β=0.28±0.05. The non-Gaussian height distribution and the measured scaling exponents (H and β) suggest a roughening mechanism close to that described by the Kardar-Parisi-Zhang scenario.
Investigation of GaN epilayers growth mechanisms using in-situ reflectance in MOCVD
Authors: Moret Matthieu , Briot Olivier , Ruffenach-Clur Sandra , Aulombard Roger-Louis 
Published: April 2011

AbstractGaN is a wide gap semiconductor which is now used to produce blue and green light emitting diodes, blue laser diodes and which has numerous other potential applications, like high frequency HEMT transistors, UV sensors, etc. A complicated two step process, using a low temperature buffer layer, subsequently annealed and followed by the deposition of the monocrystalline semiconductor was developed, and due to the excellent results obtained following this method, a rush towards applications resulted. There is now a need to investigate in more detail the growth mechanisms, and the influence of the growth parameters, in order to ensure a better reproducibility of the results. In this paper, we report an investigation of the growth mechanisms and the influence of the growth parameters using in-situ reflectance experiments. The reflectance measurements allow us to follow the growth rates, and the changes in the surface morphology (transitions between islands growth and 2D growth). Additional exsitu measurements (AFM ) were performed at different stages of the growth process to ensure additional information. As a result, we demonstrate that the recrystallization of the low temperature buffer layer is a critical step, which is drastically influenced by the composition of the annealing atmosphere (amount of ammonia present in the gas phase), while the deposition temperature and buffer thickness have a moderate effect. We will discuss here the growth mechanisms which may be involved to explain such a behavior.
Investigation of The Oxidation Behaviour of A TiAlCrYN Pvd Hard Coating
Authors: Lembke Mirkka I. , Titchmarsh John M. , Lewis D. Brian , Münz W.-Dieter 
Published: April 2011

AbstractFor dry high speed cutting the oxidation resistance of the protective hard coating of the cutting tool surface is very important. Therefore the effects of heat treatment on a TiAlN based hard coating deposited by the combined cathodic arc unbalanced magnetron sputtering technique have been studied using cross sectional transmission electron microscopy (XTEM) and energy dispersive X-ray analysis (EDX). The combination of these analytical techniques revealed the diffusion paths and preferences in diffusion of various coating and substrate elements in a physical vapour deposited (PVD) type coating after heat treatment. The structure comprises a ~2 µm thick TiAlCrYN coating on top of a 0.25 µm thick TiAlCrN base layer deposited on a stainless steel substrate. In the as-deposited sample Y was distributed in a fine layered structure (1.7 nm) throughout the coating. The coating was heat treated at temperatures between 600 °C and 900 °C in air for 10 hrs duration. With increasing temperature the microstructure changed gradually from interrupted columnar growth to a fully columnar structure at 900 °C as observed with XTEM. EDX analysis after heat treatment at 700 °C showed the presence of substrate elements Fe and Cr mainly at column boundaries in the base layer. In contrast no evidence of substrate elements could be observed in the TiAlCrYN coating, thus showing a sharp change in elemental composition concerning Cr and Fe between base layer and coating. This indicates that Y segregation in the TiAlCrYN coating along column boundaries inhibited column boundary diffusion of the substrate elements Cr and Fe. Energy dispersive X-ray distribution maps recorded after 800 °C annealing showed distinct segregation of Y along the column boundaries. The substrate elements, Fe and Cr, were observed through the coating along column boundaries up to 0.95 µm from the base layer/coating interface. After heat treatment at 900 °C the substrate elements had diffused from the substrate/coating interface to the coating surface. Y out-diffused, too and was concentrated adjacent to TiO2 crystals in the oxide layer.