bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence and In/Ga Intermixture in InAs/InGaAs DWELL Structures
Authors: Vivas Hernandez A. , Guerrero Moreno I.J. , Velázquez Lozada E.
Published: April 2011

The photoluminescence (PL) and photoluminescence temperature dependences have been studied in InAs quantum dots (QDs) embedded in the In0.15Ga1–0.15As/GaAs quantum wells (QWs) with QDs grown at different temperatures (470–535 °C). Ground state (GS) related QD PL peaks shift into the red side with increasing QD growth temperature to 510 °C and the blue shift is observed when the temperature increased to 535 °C. The temperature dependences of GS PL peak positions were fitted on the base of Varshni relation and the fitting parameters were compared with the bulk InAs and the In0.21Ga0.79As allow. This comparison has revealed that for QDs grown at 490–510 °C the PL fitting parameters are the same as for the bulk InAs crystal. The DWELL structures with QDs grown at other temperatures have fitting parameters different from the bulk InAs. Last fact testifies that in these structures the Ga/In inter-diffusion between QDs and a QW has been realized. This Ga/In intermixture can be stimulated not only by the high temperature (535 °C), but by the essential elastic stress as well in the DWELL structure with lower QD densities.
Surface Functionalization of Polylactic Film with N-vinylcaprolactam using Photoinduction Process
Authors: Gutiérrez-Villarreal Mario H. , Guzmán-Moreno J. Gustavo
Published: April 2011

A versatile and non destructive technique for a chemical modification by grafting N-vinylcaprolactam (VCL) monomer on the polylactic (PLA) film surface is described. The film substrate is treated with a VCL solution, hexane and benzophenone (BP), the latest promotes the photo initiation. Grafting percentage is derived by a gravimetric method and the success in grafting is evaluated by contact angle technique, UV and ATR-FTIR analysis. The influence of the photoinitiator concentration is evaluated by the polymerization rate (Cp), grafting percentage (Cg) and grafting efficiency (Eg). The modified surface shows higher level of humectation or hydrophilicity, confirming successful surface functionalization of the polylactic acid film.
Metal-Graphite Couples Synthesized by Means of Mechanical Milling
Authors: Estrada-Guel I. , Carreño-Gallardo C. , Pérez-Bustamante R. , Herrera-Ramírez J. M. , Martínez-Sánchez R.
Published: April 2011

The aim of this work is the characterization of some graphite-metal couples prepared by mechanical milling (MM). The morphological and microstructural changes during MM of graphite processed with metallic powders of Cu, Ni and Ag (10 and 15 at. %) are studied. Milling is performed in a high-energy ball mill under an inert atmosphere during 1, 4 and 8 hours. The process is also repeated with a pure graphite sample in order to compare the role of metal type and concentration on the morphological characteristics of milled samples. The results show that increasing the concentration of metal particles accelerates the milling process as a result of faster work hardening and particle fracture. The results of X-ray diffraction analysis show that some crystallographic characteristics of the milled couples change as a function of milling time and metal addition. Also, SEM-EDS studies show an important effect of milling time on metal particle distribution in the prepared graphite couples.
Wear Properties of an In-Situ Processed TiC-Reinforced Bronze
Authors: Sanchez R. , Lopez H. F
Published: April 2011

In this work, an Al-bronze alloy is reinforced with TiC through reaction of the alloy melt with methane gas. The resultant alloy is then centrifugally cast in cylindrical molds. It is found that the surface at the inner diameter of the cast contained in-situ produced TiC as well as Fe-rich inclusions. Metallographic observations using optical and scanning electron microscopy confirmed the presence of TiC particles (30 % volume), alpha and beta grains including iron precipitates. Cylindrical pins are machined from the inner surface and tested under various conditions in a three pin on disk Falex machine. Pins are tested under a constant load of 2.86 MPa and friction and wear rates are determined from measurements of weight losses versus wear lengths. It is found that under the applied load the reinforced material exhibits high friction and relatively low wear when compared with the unreinforced material. Apparently, under these conditions the TiC particles become abrasive particles thus contributing to wear of the steel counter-face through three body abrasive wear.
Nanoceria Coatings and Their Role on the High Temperature Stability of 316L Stainless Steels
Authors: Mendoza-Del-Angel H. , Lopez H. F
Published: April 2011

In this work, a method is considered to produce uniform nanoceria surface coatings on 316L stainless steel such as dipping. Coated steels using the aforementioned method are exposed to high temperature 800–1000°C and their oxidation behavior is investigated. It is found that the nanoceria particles in the implemented coatings exhibit some growth during high temperature exposure. In addition, thermogravimetric determinations of oxidation resistance in coated and bare samples at 900°C clearly indicates that the nanoceria coated stainless steels exhibits a two fold reduction in mass gain when compared with bare ones. Optical and scanning electron microscopy are employed to characterize the developed oxide scale morphologies. It is found that in areas are nanoceria is not uniformly coated, Fe-rich oxide islands develop, whereas in coated regions the scale is Cr and Ce rich indicating that the scale is probably a Ce doped Cr oxide.
Manufacturing of Hybrid Composites and Novel Methods to Synthesize Carbon Nanoparticles
Authors: Fals Andres E. , Quintero Julio , Hernández F. C. Robles
Published: April 2011

In following are presented the characterization results of nanostructured hybrid composites using alumina matrix reinforced with nanostructured particles of Ni, Ti and soot. The soot used in this work is the byproduct from the synthesis of Carbon Nanotubes (CNT) or fullerene and contains traces (>1wt%) of either CNT or fullerene. Ni and Ti are used in this work for their inherent catalytic ability for heterogeneous nucleation of carbon nanostructures (nanotubes, fullerenes). The hybrid composites are produced by a combination of methods including mechanical milling, sonication, and Spark Plasma Sintering (SPS). Mechanical milling is conducted in high energy mills, the milled and as manufactured powders are sonicated to assure their dispersion, homogeneity and promote percolation of the components during sintering. Mechanical milling and SPS have positive effects to promote the synthesis of different carbon nanoparticles. For instance, it is observed that mechanical milling of fullerene soot sponsors the synthesis of nanostructured diamond particles and using SPS can be synthesized diamond too and fullerene. Although, it is important to notice that SPS conditions are critical to the amount and type of synthesized particles. The use of CNT soot sponsors porosity, hence lower density resulting in an ideal material for membrane and porous media applications. The results of characterization (X-Ray diffraction, electron microscopy (scanning and transmission)) and the mechanical properties (Vickers microhardness) are discussed accordingly.
Surface Coating TiO2 on Sepiolite Fibers and Application in Paper-making Waste Water Treatment
Authors: Guo Yajie , Wang Yuran , Wang Guangjian , Liu Zhengwang , Yang Zhengxing , Wang Fei
Published: April 2011

The purpose of this paper was to describe a method of preparing Fe-TiO2 supported on sepiolite fibers with sol-gel method and to discuss the feasibility of photocatalytic degradation of paper-making waste water with chemical oxygen depletion (CODcr) (Potassium dichromate method) as evaluation criterion of catalytic activity. As-fabricated catalysts consisted of TiO2 particles impregnated with iron and dispersed on the sepiolite fibers (S.F.s). The novel Fe-TiO2-sepiolite was characterized by specific surface area and pore size distribution measurements, scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and Fourier transform Infrared spectrometer (FT-IR) etc. The effects of parameters such as the amount of Ti/sepiolite fibers, initial pH, H2O2, Fe-doped, concentration of waste water, etc. were studied in detail. The results indicated that the presence of sepiolite in the support preparation and its role as a matrix over which TiO2 particles were dispersed seem to play an important effect in the migration process of oxygen species through the support vacancies. On the basis of these properties, the most promising carriers to be used in a waste water treatment process were selected.
Synthesis and Catalytic Activity of Ni/Ce-MCM-41 Mesoporous Catalysts for Hydrogen Production
Authors: Wang J. A. , Guevara J. C. , Chen L.F. , Salmones J. , Valenzuela M. A. , Salas P. , Cao F. H. , Yu G. X.
Published: April 2011

Ce-containing MCM-41 mesoporous materials with large surface area and ordered pore structure system have been possible to be synthesized through a surfactant-assisted approach. The textural properties and structural regularity of the materials varied with the Si/Ce molar ratio. It is found that the band at 970 cm-1 in the FTIR spectrum of the Ce-MCM-41 mesoporous materials might be used as an indicator of the formation of the Ce-O-Si bond and its intensity as a measure of a degree of cerium ion substitution in the framework of Si-MCM-41. When Ni was loaded on the Ce-MCM-41 support, the Ni/Ce-MCM-41 catalysts show high catalytic activity which has strong temperature dependence. The methane conversion over these catalysts reached 60-75 % with a 100 % selectivity towards hydrogen.
New Route for the Tetraphenylfuran Synthesis Using a Superacid Sulfonic Clay (SASC) as Catalyst
Authors: Cea Carlos Damián , Labastida Eloy Vázquez , S Manuel Salmon , Valle Sergio O. Flores
Published: April 2011

The transformation of benzoin to tetraphenylfuran catalyzed with a superacid sulfonic clay under different reaction conditions was investigated. Three products with different yields were produced under a nitrogen stream and four products were obtained under an air atmosphere.
The study of DNA nanofibers
Authors: Singh Mahi R.
Published: April 2011

We study the acousto-optic effect on the polaritonic properties of DNA nanofibers which are fabricated by embedding a DNA wire into a polaritonic material. This is a new research area and can be called nanobiopolaritonics. Polaritonic materials have energy gaps in their dispersion relation due to the coupling between optical photons and photons. The bound states of DNA wire are calculated using transfer matrix method. It is found that some of the bound states of the DNA wire lie within the band gap of the polaritonic material. These states do not decay into the polaritonic material since there are not states available for decay process to occur. This means DNA nanofibers has an extremely high Q factor. We have also studied the acousto-optic effect on the photon absorption in DNA nanofibers doped with ensemble of quantum dots. The quantum dots interact with the DNA wire via electron bound polaritons interaction. We have discovered a switching mechanism in DNA nanofibers. When the resonance energy of the quantum dots lies near bound polaritons states, the system becomes transmitting for frequency of a probe field due to the strong electron bound polaritons interaction. This is can be assigned as ‘ON’ of the switch. However, when the strain field is applied the DNA fiber can now absorb the probe beam. This is can be assigned as ‘OFF’ of the switch.
Direct Heteroepitaxial Growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) Substrates by MBE
Authors: Lyon T. J. de , Johnson S. M. , Cockrum C. A. , Wu O. K. , Roth J. A.
Published: April 2011

Epitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0–8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x ray FWHM as low as 55 arcseconds and average etch pit densities of 5 × 106 cm−2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.
Crystallographic and Metallurgical Characterization of Radiation Detector Grade Cadmium Telluride Materials
Authors: Johnson C.J. , Eissler E.E. , Cameron S.E. , Kong Y. , Fan S. , Jovanovic S. , Lynn K.G.
Published: April 2011

Radiation detector grade CdTe crystals are characterized by several crystallographic and metallurgical techniques including infrared microscopy, dislocation etch pitting and X-ray diffraction. Results are presented for 50 detectors fabricated from an ingot produced by the high pressure Bridgman method. Data on the temperature dependence of leakage current and pulse height analysis are presented, along with measurements of room temperature charge transport properties. Attempts to relate crystal structure to detector performance will be discussed.
Performance Characteristics of CDTE Gamma-Ray Spectrometers
Authors: Squillante Michael R. , Cole Herbert , Waer Peter , Entine Gerald
Published: April 2011

The use of cadmium telluride (CdTe) semiconductor nuclear detectors is continuing to expand into new areas because of their unique properties which include room temperature operation and high detection efficiency. In addition, they remain the material of choice in many critical applications such as nuclear medicine and power plant monitoring because of their reputation for reliability and long term stability1. CdTe is by far the most developed of the compound semiconductors used in nuclear detector applications and it offers a number of significant benefits to researchers, clinicians and engineers who have special requirements relating to size, sensitivity and operating temperature.

Recently, there have been improvements in the growth of the crystalline material and in the fabrication procedures which have resulted in better performance and in the ability to produce arrays. This article describes the physical and electronic properties of CdTe nuclear detectors, discusses how the crystal growth and device fabrication procedures can affect these properties, and compares the performance to CdZnTe detectors.
Thermal Stability of Ir-Silicide/SiGe Layers Grown in a Dual Electron Gun Chamber at Ultra-High Vacuum (Extended Abstract)
Authors: Chung C. K. , Hwang J.
Published: April 2011

Heteroepitaxial Ir-silicide/SiGe layers on the top of p-Si(100) have been achieved at a substrate temperature of 450 °C. The co-deposited Ir-silicide layer was determined to be Ir3Si4 with four types of epitaxial modes. Thermal stability of the film was examined by using Auger electron spectroscopy and X-ray diffractometer. The Ir3Si4/SiGe layers were stable as annealed at 550 °C for 20 sec in a rapid thermal annealing furnace, while interdiffusion between Ir3Si4 and SiGe occurs at a temperature of 750 deg;C or higher for 20 sec. The traditional guard-ring fabrication process should be performed before epitaxial films deposition due to this thermal instability.
Influence of Oxygen on the Iridium Silicide Formation by Rapid Thermal Annealing
Authors: Fernandez M. , Rodriguez T. , Almendra A. , Jimenez-Leube J. , Wolters H.
Published: April 2011

Iridium silicide formation by rapid thermal annealing (RTA) in an Ar atmosphere or under vacuum has been investigated. The evolution of the silicide front and the identification of the phases were monitored by Auger Electron Spectroscopy (AES) and Rutherford Backscattering Spectrometry (RBS). Oxygen was incorporated during the RTA process in an Ar atmosphere. The oxygen effect is to slow down the silicide formation and eventually to stop it. In all the cases, the oxygen piled-up at the iridium-iridium silicide interface. No distinguishable phase was formed by RTA in an Ar atmosphere. No oxygen contarsi'nation was detected when the RTA was performed under a vacuum lower than 2×10−5 Torr. In this case Ir1Si1 and Ir1Si1.75 phases were formed.
The Staebler-Wronski Effect and the Thermal Equilibration of Defect and Carrier Concentrations
Authors: Dawson R.M.A. , Fortmann C.M. , Li Y.M. , Wronski C.R.
Published: April 2011

Light induced degradation of intrinsic Amorphous silicon (a-Si:H) is investigated as a function of temperature. Previous work described an equilibrium framework for the high temperature behavior of dangling bonds defects (DB) 11]; and the temperature dependence of the annealed state photo, σPH, and dark, σD, conductivities of a series of intrinsic a-Si:H Materials deposited over a range of substrate temperatures, 200°C < Ts < 380°C [2]. These results are extended to the light degraded state where elevated temperatures provide for equilibration of the free carrier and DB concentrations. For the equilibrium, light degraded state, both σD and σPH, decrease compared to the annealed state while the ratio, σD/σPH remains unchanged. Relationships between the ratio [DB+]/[DB] and the Fermi level are derived from the equilibrium framework.
Recovery Process for Light-Soaked A-Si:H
Authors: Zhang Qing , Takashima Hideki , Zhou Jiang-Huai , Kumeda Minoru , Shimizu Tatsuo
Published: April 2011

We have found that a broad distribution of the annealing activation energies is necessary to interpret the annealing behavior for the density of metastable defects created by 77K light soaking, while a narrow distribution is sufficient for describing the annealing behavior for the density of those created by RT light soaking. We have also found that the recovery of the degraded photoconductivity is easier than the annealing of the photocreated defects for both 77K and RT light soaking and that, at a given defect density, 77K light soaking degrades the photoconductivity more than RT light soaking. Our results suggest that the photocreated defects with a smaller annealing activation energy are more effective recombination centers than those with a larger annealing activation energy.
The Mobility Lifetime Product of Electrons as a Function of Temperature and Electron Concentrations in a-Si:H
Authors: Nishida Shinichi , Fritzsche Hellmut
Published: April 2011

The photo-field effect has been measured between 4.2K and 300K using an a-Si thin film transistor. The data are fit self-consistently taking full account of changes in space charge, photo carrier drift, diffusion and recombination. Gap state density and capture cross sections are fitting parameters. Evidence for tunnel recombination is found. Electron localization radius was found to be 13Å.
Thermal Modulated Esr For The Study Of Defects In a-SiC:H Films
Authors: Demichelis F. , Giorgis F. , Pirri C. F. , Tresso E. , Ravera L. , Rigato V.
Published: April 2011

In this work we present Thermal Modulation Electron Spin Resonance Measurements performed on a-SiC:H films prepared by Plasma Enhanced Chemical Vapour Deposition with energy gap in the range 1.8–2.5 eV. The results have been compared with previously obtained photothermal and photoconductive ones and have been interpreted by means of a defect distribution which takes into account both silicon based and carbon based defects.
Thermal CVD of Amorphous Germanium Films From 2, 5-Bis (Tert.-Butyl) -2, 5-Diaza-l-Germa-Cyclopentane Organometallic Precursor
Authors: Glatz F. , prokop J. , Vepřek S. , Klingan F.R. , Herrmann W.A.
Published: April 2011

A novel organometallic germylene precursor has been synthesized and used for the deposition of amorphous germanium by thermal OM CVD at temperatures below 300°C. The films are of high purity with an oxygen content below the present detection limit of about < 1018 cm−3. Preliminary results on the electronic properties are reported.
Silicon Oxycarbide Microcrystalline Layers Produced by Spatial Separation Techniques
Authors: Martins R. , Ferreira I. , Fortunato E. , Vieira M.
Published: April 2011

Silicon oxycarbide microcrystalline layers, n- and p-doped, highly conductive and highly transparent have been produced using a Two Consecutive Decomposition and Deposition Chamber (TCDDC) system. The films exhibit suitable properties for optoelectronic applications where wide band gap materials with required conductivity and stability are needed. In this paper we present the role of partial oxygen pressure (po2) in controlling the composition, structure and transport properties (conductivity, σd and optical gap, Eop) of silicon oxycarbide microcrystalline layers.
Effects of Top Insulator Overlap on the Stability in Hydrogenated Amorphous Silicon Thin Film Transistors
Authors: Choi H.S. , Kim Y.S. , Lee S.K. , Yoon J.K. , Park W.S. , Han Andm. K.
Published: April 2011

The effects of top-insulator on the instability problems of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) have been studied. In a-Si:H TFT with top-insulator (E/S type), charge trapping into the both of top-insulator and gate insulator has been shown under the bias stress.

In order to investigate the charge trapping effects of top-insulator, we proposed a new method of Measurement. By this Method, we observed that trapped charges in top-insulator increased drain currents for positive gate bias stress, and this increment of drain currents was more serious with increasing the ratio of source/drain overlap length to channel length. It has founded that the instability problems of a-Si:H TFTs was attributed to the effects of top-insulator as well as that of gate insulator.
Determination of the Defect Redistribution and Charge Injection Contributions to the a-Si:H Thin-Film Transistor Instability
Authors: Carluccio R. , Pecora A. , Massimiani D. , Fortunato G.
Published: April 2011

The effects of bias-stressing n- and p-channel thin-film transistors, employing thermal silicon dioxide as gate insulator, have been analysed by using different techniques, including field-effect, space-charge photomodulation and photo-induced discharge. Photo-induced discharge experiments have pointed out as parasitic resistance effects can be present in p-channel devices. In order to reduce this problem, thin active layer p-channel devices have been fabricated and, combining these results to those relative to the n-channel transistors, we deduced a predominance of charge injection at low and moderate stress-biases while at high-stress biases modifications in the density of states take place.
Planarization Ability of Chemical Mechanical Planarization (Cmp) Processes
Authors: Stell Matt , Jairath Rahul , Desai Mukesh , Tolles Robert
Published: April 2011

Methods for determining planarization ability of CMP were explored. Options included film thickness measurements of the dielectric over metal and field, TIR measurements using profilometry, and a combination of the two. The attempt to observe the in situ change in the topography was addressed in two distinct experimental approaches. The first approach involved processing wafers for predetermined intervals. The other approach processed different wafers for different amounts of time. The effects of down force and platen rpm on planarization ability were studied using the first approach. Results indicate that planarization is more efficient at higher down forces and higher platen rpm. Slurry property effects were examined using the second method. The planarization ability appears to suffer at elevated pH values. This is attributed to both the enhanced solubility of the silica particles and the dielectric itself.
Effectiveness of Nitride Diffusion Barriers in a Self-Encapsulated Copper-Based Metallization.
Authors: Adams D. , Spreitzer R.L. , Russell S.W. , Theodore N.D. , Alford T.L. , Mayer J.W.
Published: April 2011

Cu(Ti 27 at. %) and Cu(Cr 26 at. %) codeposited on silicon dioxide substrates were annealed in a flowing NH3 ambient at 400 - 600°C for 30 min. The Ti segregates to both the surface to form a TiN(O) layer and to the alloy/SiO2 interface to form a Ti-oxide/Ti-silicide bilayer. The Cr seems to migrate only to the free surface to form a CrNx layer. A 45 nm - thick Al film was deposited after nitridation, whereupon a second anneal was performed to evaluate these nitride layers as diffusion barriers. It was found that the Ti-nitride was stable up to 500°C as compared to Cr-nitride at 600°C.
Coherent TiN Diffusion Barriers for Sub-0.5 μm Planarized AL Technology
Authors: Ngan Ken , Mosely Rod , Xu Zheng , Raaijmakers Ivo
Published: April 2011

This paper describes in situ post deposition treatment technologies to fortify the coherent PVD TiN barrier so that it will withstand the high temperature (> 450°C) Al deposition or flow process for sub-0.5 μm planarized Al technology. The coherent PVD TiN barriers were sputtered under 3 different pressure conditions and subsequently heat treated for fortification. Such heat treated, fortified PVD TiN barriers exhibit low reactivity with Al, which is illustrated by the minimal sheet resistance increase in TiN/Al thin film stacks during the heat treatment. Furthermore, optical and SEM inspection on the silicon surface show no pitting.

Leakage current of less than 50 pA has been obtained on 10K-contact chains of sub-0.5 (μm devices using a vacuum integrated coherent Ti/fortified PVD TiN/planarized Al process. This development has led to a completely vacuum integrated sub-0.5 μm PVD Al plug fill process.
The In-Based Metal Ohmic Contacts to n-GaAs
Authors: Ding Sun-An , Fan Tiwen , Xu Zhenjia , Hsu C. C.
Published: April 2011

Electrical, structural and reaction characteristics of In-based ohmic contacts to n-GaAs was studied. Attempts were made to form a low band gap interfacial phase of InGaAs to reduce the barrier height at the metal/semiconductor junction and thus yielding a low resistance, high reliability contacts. The contacts were fabricated by e-beam sputtering Ni, NiIn and Ge targets on VPE grown n+-GaAs film (∼1μm, 2xl018 cm-3) in UHV as the structure of Ni(200Å)/NiIn ( 100Å)/Ge(40Å)/n+-GaAs/SI-GaAs, followed by rapid thermal annealing at various temperatures (500-900 °C). The lowest specific contact resistivity (pc) of (1.5±0.5)xl0-6 Qcm2 measured by transmission line method (TLM) was obtained after annealing at 700 °C for 10s. Auger sputtering depth profile and transmission electron microscopy (TEM) were used to analysis the interfacial microstructure. By correlating the interfacial microstructure to the electronical properties, InxGa1-xAs phases with large fractional 'area grown epitaxilly on the GaAs were found to be essential for reduction of the contact resistance.
Electrical Properties of AuZnCr Multilayer Metallizations to InP
Authors: clausen Thomas , leistiko Otto
Published: April 2011

The electrical properties of a Au/Cr/(Au)/Zn/Au (50/25/(50)/100/2 nm) multilayer metallization to n- and p-type InP have been investigated. The results consistently show that it is possible to modulate the effective Schottky barrier height of the metal-semiconductor contact over a large range of values extending from ∼0 eV for contacts to p-type InP to values close to the bandgap of the InP (∼1.3 eV) for contacts to n-type InP. The limiting factor in the developement of the highest quality metal-semiconductor diodes to n-type InP with very high Schottky barrier heights is found to be diffusion of Au elements at high annealing temperatures above 500°C, as determined from I-V, C-V and DLTS plots.
The Reliability of Multilevel Metallization on InGaAs/GaAs Layers
Authors: Chang Edward Y. , Chen J.S. , Wu J.W. , Lin K.C.
Published: April 2011

Non-alloyed ohmic contacts using Ti/Pt/Au and Ni/Ge/Au on InGaAs/GaAs layers grown by Molecular Beam Epitaxy (MBE) have been investigated. The n-type InGaAs film has a doping concentration higher than 1X1019 cm-3. Specific contact resistance below 2X10-7 Ωcm2 could be easily achieved with Ti/Pt/Au. Due to the layer intermixing and outdiffusion of In and Ga, the specific contact resistance and sheet resistance increase after thermal treatment. When Ni/Ge/Au is used as the contact metal, the outdiffusion of In and Ga atoms is more severe than that of Ti/Pt/Au. After annealing at 450°C for two minutes, the Au4In formed and the characteristics of the contact became worse. All the phenomena illustrated above have been observed and investigated by Transmission Line Model, X-ray diffraction, Auger Electron Spectroscopy and Secondary Ion Mass Spectrum. As far as the thermal stability is concerned, it is convinced that Ti/Pt/Au is the best one of these two non-alloyed ohmic contact studied.
Characterization of Tungsten Nucleation Layers Deposited Using Various Sih4 and Wf6 Flows
Authors: Rana V.V.S. , Eizenberg M. , Ghanayem S. , Roberts J. , Sinha A.K.
Published: April 2011

Chemical vapor deposition (CVD) of tungsten nucleation films is typically done using silane (SiH4) reduction of tungsten hexafluoride (WF6). For SiH4/WF6 flow ratios of ≤ 1, pure tungsten of bulk density and resistivity is deposited. Upon increasing the ratio to 2, nearly 40 at.% Si is incorporated in tungsten films. At a ratio of 3, hexagonal WSi2 is deposited, and at ratios of > 6 WSi2 along with silicon is deposited. A maximum in deposition rate is obtained for WSi2 at the ratio of 3, and the deposition rate drops as more silicon is being deposited. The step coverage of films drops dramatically as one moves away from pure W films. The deposition of these films takes place without any incubation time.
Multi-Technique Characterization of WSix films
Authors: Baumann S.M. , Hitzman C.J. , Ivanov I.C. , Craig AY. , Lindley P.M.
Published: April 2011

WSix films are used extensively for contact, interconnect, and, in some cases, diffusion and Schottky barriers in semiconductor devices1. The electrical and barrier properties of these films are affected by a variety of factors, such as film stoichiometry, morphology, impurities, etc. This paper will address the capabilities and limitations of a variety of techniques which are frequently used to characterize WSix films. Techniques which were studied include: Dynamic and Static Secondary Ion Mass Spectrometry (SIMS), Rutherford Backscattering Spectrometry and Elastic Recoil Detection (RBS/ERD), Auger Electron Spectroscopy (AES), Field Emission Scanning Electron Microscopy (FE-SEM), Total Reflection X-ray Fluorescence (TXRF), Atomic Force Microscopy (AFM), and X-Ray Photoelectron Spectroscopy (XPS). Film characteristics which were studied included surface morphology; grain structure; film stoichiometry; surface and interface oxide thickness and composition; and surface, bulk, and interface impurity concentrations including metallic, atmospheric, and dopant impurities. Cross correlation between the techniques was performed whenever possible in order to compare the relative accuracy of the techniques as well.
Investigation and Characterization of Thin Mocvd Copper Films From Pyrazolylborato - Copper (I) Complexes
Authors: Plappert E.-C. , Dahmen K.-H. , Van Den Bergh H. , Stumm T. , Hauert R.
Published: April 2011

Thin copper layers were prepared via MOCVD from volatile pyrazolylborato - copper (I) complexes.

Experiments involved chemical vapour deposition in a low pressure reactor between 150 - 350°C in H2/N2/He mixtures were carried out.

Substrate temperature, source temperature and gas composition were varied to obtain the optimum growth rate.

The copper layers were characterized by optical microscopy and scanning electron microscopy, XRD, and WDX. The metallic nature of the deposited films was proved by a four - point - probe measurement of the electrical resistivity.

A selective deposition on metal seeded surface sites was observed on Au, Al, Pt and W vs. Si02- Antiselective deposition was achieved on Pd seeded samples.
InGaN/AlGaN Double-Heterostructure Blue Leds
Authors: Nakamura Shuji
Published: April 2011

High-brightness InGaN/AlGaN double-heterostructure (DH) blue-light-emitting diodes (LEDs) with a luminous intensity of 1.2 cd were fabricated successfully for the first time. As an active layer, a Zn-doped InGaN layer was used. The peak wavelength and the full width at half-maximum of the electroluminescence were 450 nm and 70 nm, respectively. The forward voltage was as low as 3.6V at 20 mA.
Oxidation and ion Damage of Diamond by Reactive Ion Etching
Authors: Beerling T. E. , Helms C. R.
Published: April 2011

Oxygen is a commonly used etchant of carbon materials, including diamond. In this work, we examine the effects of oxygen ion bombardment to diamond surfaces, as might be encountered in a reactive ion etching (RIE) process. Surfaces were characterized using Electron Energy Loss Spectroscopy (EELS) and Auger Electron Spectroscopy (AES). EELS was used to determine the presence of non-diamond carbon at the surface which may form due to ion damage. AES was used to determine the presence of oxygen on the diamond surface from oxygen ion bombardment. The effect of ambient molecular oxygen present during inert ion bombardment is also addressed. EELS was also used to determine the state of diamond surfaces that were bombarded with hydrogen ions, as might be used in the removal of adsorbed oxygen.
Growth of Single Crystal Copper Films on Diamond Using Fcc-Iron Seed Layers
Authors: Pappas D. P. , Harris V. G. , Hoff H. A. , Watena G. L. , Glesener J. W.
Published: April 2011

Copper films were grown on a single crystal diamond substrate using an iron seed layer. The effect of the crystalline structure of the iron seed on the Cu films was studied with extended x-ray absorption fine structure (EXAFS) and scanning electron microscopy (SEM). The EXAFS study shows that the 10 Å Fe seed layer is in an fee structure, and has collapsed into a bec structure by the time 20 Å of Fe has been deposited. In the SEM pictures it is observed that subsequent layers of Cu grow as continuous films for thin fcc-Fe seeds, and grow in an island mode for the thick, bcc-Fe seeds.
Effect of Oxygen on the Textured Diamond Growth over Nickel Substrates
Authors: Ramesham R. , Rose M. F. , Askew R. F. , Bozack M.
Published: April 2011

Microwave plasma has been used to grow diamond films using CH4 and H2 over nickel substrates. Nucleation of the diamond has been achieved by manual scratching and ultrasonic agitation of the substrates. The substrate was left in the H 2 microwave plasma to remove any oxide film present prior to the diamond growth. According to SEM the morphology of the grown films was (100) textured over the entire surface. Our interest is to study the effect of O2 on the growth rate and the morphology of as-deposited diamond films. Infact, O2 has a tendency to preferentially etch the diamond (etch rate: 111 > 110 >100). Injection of O2 into the reaction mixture could enhance the 100 texture further. Raman analysis confirms the deposited films as diamond. Effect of O2 on the nature of the films and the characterization of as-deposited films is described.
Initial Stages of Growth of Thin Films of III-V Nitrides and Silicon Carbide Polytypes by Molecular Beam Epitaxy
Authors: Davis Robert F. , Ailey K. S. , Kern R. S. , Kester D. J. , Sitar Z. , Smith L. , Tanaka S. , Wang C.
Published: April 2011

The morphology and interface chemistry occurring during the initial deposition of BN, AlN and GaN films via metal evaporation and N2 decomposition under UHV conditions have been determined. FTIR spectroscopy and TEM revealed the consecutive deposition of an initial 20Å layer of a-BN, 20–60Å of oriented h-BN, and a final layer of polycrystalline c-BN. This sequence is attributed primarily to increasing intrinsic compressive stress in the films. XPS analysis revealed the growth of GaN on sapphire to occur via the Stranski-Krastanov mode; growth on SiC showed characteristics of three-dimensional growth. AlN grew layer-by-layer on both substrates. Vicinal 6H-SiC(0001) substrate surfaces contain closely spaced, single bilayer steps. During deposition of Si and C at 1050°C, 6H layers initially form and step bunching occurs. The latter phenomenon results in more widely spaced steps, the nucleation of 3C-SiC both on the new terraces and at the larger steps and formation of double position boundaries. The C/Si ratio in the gaseous reactants also affects the occurrence of these three phenomena.
Acceptor Binding Energy And Band Lineup Of III-V Nitride Alloys And Mocvd Growth Of GaN On GaAs - Or GaP-Coated Si
Authors: Ueta Yoshihiro , Sakai Shiro , Kamiya Yasushi , Sato Hisao
Published: April 2011

The acceptor binding energy is calculated to find out the best acceptor impurity in InN, GaN and AlN. Be is predicted to be the shallowest acceptor and the next are Mg and Zn. Group IV elements such as C or Si are very deep. Band lineup is calculated to be ΔEc : ΔEv = 2.1 eV : 0.76 eV = 0.73 : 0.27 = 2.8 : 1 for GaN/AlN and ΔEc : ΔEv = 0.88 eV : 0.66 eV = 0.57 : 0.43 = 1.3 : 1 for GaN/InN. GaN is grown on GaAs and GaP-coated Si substrate by MOCVD. GaAs intermediate layer gives better GaN compared to GaP intermediate layer. It is suggested that the lower bulk modulus of GaAs than that of GaP gives this difference.
Surface Preparation of Single Crystal C(001) Substrates for Homoepitaxial Diamond Growth
Authors: Humphreys T. P. , Posthill J. B. , Malta D. P. , Thomas R. E. , Rudder R. A. , Hudson G. C. , Markunas R. J.
Published: April 2011

ABSRACT

A novel substrate preparation procedure which can be employed to remove the original surface from as-received C(001) natural diamond substrates has been developed. A description of the various substrate processing steps which includes, low-energy ion implantation of C and O, high-temperature annealing, electrochemical etching and surface plasmas treatments is presented. Also demonstrated is the growth of topographically excellent homoepitaxial films by rf-plasma-enhanced chemical vapor deposition using water/ethanol mixtures on C(001) substrates.
Raman and Photoluminescence Studies of Undoped and Magnesium-Doped Gan Films on Sapphire
Authors: Freitas Jaime A. , Asif Khan M.
Published: April 2011

Room temperature Raman scattering measurements performed on undoped GaN films indicate that high crystalline quality wurtzite material has been deposited on the basal plane of sapphire. Photoluminescence study of these films show that thicker films (t > 4μm) are homogeneous along the growth direction. The PL spectra of Mg-doped films are dominated by an intense emission band around 3.1 eV associated with recombination processes involving donor-acceptor pairs.
Redistribution of Hydrogen in Gan, Ain, and Inn
Authors: Zavada J. M. , Wilson R. G. , Pearton S. J. , Abernathy C. R.
Published: April 2011

Hydrogen incorporation during gas-phase growth of III-V nitrides is thought to play an important role in determining the apparent doping efficiency, due to unintentional passivation of dopants. Hydrogen implantation can also be used for electrical and optical isolation of neighboring devices, as in other lll-V materials such as GaAs. We have implanted2H at 40 keV to doses of 5 × 1015cm-2at room temperature into epitaxial layers of GaN, AIN and InN grown by MOMBE on GaAs substrates, and measured the ion ranges and hydrogen redistribution upon subsequent furnace annealing. The hydrogen profiles remain unchanged for annealing temperatures up to 800–900°C for GaN and AIN, and 600° for InN. Samples were also deuterated from an ECR plasma at 250 or 400°C for 30 min, producing2H incorporation depths of ≤ 1 μ in GaN. With annealing, there is no significant hydrogen redistribution observed at temperatures up 800°C. Hydrogen concentrations remain in the range ∼ 1019cm-3under these conditions. At 900°C considerable hydrogen outdiffusion to the surface occurs. The thermal stability of hydrogen in these III-V nitride films indicates the need for post-growth annealing at high temperatures to achieve appreciable doping efficiencies.
Free Carrier Absorption in N-Type 6H-SiC
Authors: Engelbrecht F. , Helbig R.
Published: April 2011

Free carrier absorption (FCA) in n-type 6H-SiC doped with nitrogen has been studied in the energy range 50–250 cm-1 using samples of different free carrier concentrations ranging from 2.0–1016cm-3 to 7.0–1017cm-3. The index of wave number dependence of FCA p varies between -1.4 and -0.55 depending on free carrier concentration and electron mobility. The experimental results are in good agreement with the classical expression for the FCA coefficient. Quantum mechanical expressions for the FCA coefficient do not reproduce the measured p values. It is supposed that this is due to fact that the requirement for the application of perturbation theory ΩT ≫ 1 is not fulfilled. We investigated the anisotropy of FCA with respect to the c-axis and find a strong difference between ∝ ┴ and ∝∥.
Comparison of Surface Cleaning Processes for Diamond C(001)
Authors: Baumann Peter K. , Humphreys T. P. , Nemanich R. J.
Published: April 2011

Two wet chemical cleaning processes (a conventional chromic acid clean and an electrochemical etch) and a H-plasma exposure have been employed to clean natural type lib semiconducting diamond C(001) wafers. The effects of these processes on the diamond surface have been assessed and compared. As evidenced by Auger electron spectroscopy (AES), an oxygen free surface could be obtained following annealing to 900°C for the electrochemical process compared to 1050°C for the chromic acid etch. In addition, the technique of Atomic Force Microscopy (AFM) demonstrated the presence of oriented pits on the surface of samples electrochemically etched for long times at high currents. Furthermore, heteroepitaxial Cu films have been grown on the diamond substrates cleaned by a process as described above. By means of Ultraviolet Photoemission Spectroscopy (UPS) a Schottky barrier height of ΦB≊ 1.0 eV was measured. Furthermore, the presence a negative electron affinity (NEA) has been determined.
Characterization of Defects in N-Type 6H-SiC Single Crystals by Optical Admittance Spectroscopy
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: April 2011

Optical admittance spectroscopy is a technique for measuring the conductance and capacitance of a junction under illumination as a function of the wavelength of the light and the frequency of the measuring AC signal. This technique has been applied to characterize deep defect levels in 6H-SiC:N. Nitrogen is a donor atom in 6H-SiC which substitutes for carbon in three inequivalent sites (h, k1, k2). giving rise to n-type conduction. Deep defect levels attributable to transition metal impurities have also been identified in 6H-SiC:N. We have examined persistent photoconductance in this material by optical admittance spectroscopy.
The Effect of Phosphine Pressure on the Band Gap of Ga0.5In0.5P
Authors: Kurtz Sarah R. , Arent D. J. , Bertness K. A. , Olson J. M.
Published: April 2011

The band gap of Ga0.51n0.5P is studied as a function of phosphine pressure, B-type substrate misorientation, growth rate, and growth temperature, with emphasis placed on the effect of the phosphine pressure. Over most of the parameter space explored (high temperatures, large substrate misorientations, and low growth rates), the band gap increases with decreasing phosphine. This increase is proposed to be caused by lower phosphorus coverage of the surface, resulting in a different surface structure that doesn't promote ordering. The implications of this effect on the observed variations of band gap with growth temperature, substrate misorientation, and growth rate are discussed. For regions of parameter space in which the ordering appears to be kinetically limited by surface diffusion, the band gap increases slightly with phosphine pressure, consistent with observations that increased group-V pressure decreases the group-III surface diffusion length.
Study of GaInP/GaAs/GaInP Double Heterostructures Grown by MOCVD with Photoreflectance and Photoluminescence
Authors: Kuan H. , Shei S.C. , Tzou W.J. , Su Y. K.
Published: April 2011

The GaInP-GaAs single quantum well structures grown by metal-organic chemical vapor deposition (MOCVD) were investigated by photoreflectance (PR) and photoluminescence (PL) spectroscopies. The built-in electric field in the GaAs close to the top surface was evaluated using the observed Franz-Keldysh oscillations. The fundamental energy gaps and broadening parameters were also determined. The full width at half maximum (FWHM) of the GaInP PL peak is 11 meV
New Technology and Developments in Compound Semiconductor Vertical RDR-MOCVD Growth Systems
Authors: McKee M. , Tompa G.S. , Zawadzki P.A. , Thompson A. , Gurary A. , Beckham C. , Schumaker N.E. , Moy K.
Published: April 2011

Compound semiconductors are at the heart of todays advanced digital and optoelectronic devices. As device production levels increase, so too does the need for high throughput deposition systems. The vertical rotating disk reactor (RDR) has been scaled to dimensions allowing metal organic chemical vapor deposition (MOCVD) on multiple substrates located on a 300 mm diameter platter. This symetric large area reactor affords easy access over a wide range of angles for optical monitoring and control of the growth process. The RDR can be numerically modeled in a straightforward manner, and we have derived scaling rules allowing the prediction of optimum process conditions for larger reactor sizes. The material results give excellent agreement with the modeling, demonstrating GaAs/AlAs structures with <±0.9% thickness uniformities on up to 17-50mm or 4-100mm GaAs substrates. Process issues related to reactor scaling are reviewed. With high reactant efficiencies and short cycle times between growths, through the use of a vacuum loadlock, the costs per wafer are found to be dramatically less than in alternative process reactors. The high reactant utilization, in combination with a dedicated and highly efficient exhaust scrubbing system, minimizes the systems environmental impact.
Chemical Beam Epitaxy (CBE) and Laser-Enhanced CBE of GaAs Using Tris-Dimethylaminoarsenic
Authors: Dong H. K. , Li N. Y. , Tu C. W. , Geva M. , Mitchel W. C.
Published: April 2011

In this paper, we report chemical beam epitaxy (CBE) of GaAs, and for the first time, Arion laser-assisted CBE using triethylgallium (TEGa) and tris-dimethylaminoarsenic (TDMAAs), a safer alternative to arsine. Samples grown at substrate temperatures above 490° C show n-type conduction, while those grown at lower temperatures show p-type conduction. An unintentional doping concentration of n∼lx1016 cm-3 with an electron mobility of 5200 cm2/V.s at 300 K and 16000 cm2/V.s at 77 K have been achieved. These are the best results reported for GaAs grown with TDMAAs. Laser-assisted CBE of GaAs is studied in the substrate temperature range of 240-550°C. There are two different substrate-temperature regions for laser-enhanced growth, 265 to 340°C and 340 to 440°C, which are believed to be caused by different TEGa decomposition mechanisms. The laser-assisted growth with TDMAAs, compared to AS4 or AsH3, shows a wider range of growth enhancement at low substrate temperatures.
A Second-Harmonic Generation Study of GaAs-Oxide Removal Using a Hydrogen Plasma
Authors: Kimura Takahiro , Yamada Chikashi
Published: April 2011

We observed a second-harmonic generation (SHG) in reflection from a GaAs (100) surface during an oxide removal process using a pulsed hydrogen plasma. We found that the P-polarized SH intensity under P-polarized excitation decreased in the [011] azimuth of incidence and increased in the [011] azimuth of incidence during hydrogen plasma irradiation. The input polarization angle dependence of the P-polarized SH intensity before and after oxide removal was fitted to a model which includes both the surface and bulk SHG contributions. We estimated the thickness of the removed oxide based on the bulk SHG contribution change.