bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion Milling and Reactive Ion Etching of III-V Nitrides
Authors: Pearton S. J. , Abernathy C. R. , Ren F. , Lothian J. R. 
Published: April 2011

ABSTRACTDry patterning of GaN, InN, AlN and InGaN grown by MOMBE on GaP, Al2 O3 or GaAs substrates was performed with 100–500 eV Ar+ ions at beam angles of incidence ranging from 0–75° from the normal, or with ECR discharges of BCl3/Ar, CH4/H2 or Cl2/H2. The mill rates normalized to the Ar+ beam current were typically a factor of 2 lower than for GaAs and InP (i.e. maximum values of 300–500 Å·min-1·mA-1·cm-2 at 400eV Ar+ beam energy and 60° angle with respect to the beam normal). The surface morphology of the ion milled nitrides was smooth even at 500 eV Ar+ energy, with no evidence for preferential sputtering of N as determined by AES. The ECR dry etch rates were fastest with elevated temperature Cl2/H2discharges, although both of the other chemistries investigated provide smooth, anisotropie pattern transfer. Since the ion mill rates are slow for single-crystal nitrides and less than the mill rates of common masking materials (SiO2, SiNx, photoresist) it appears this technique is useful only for shallow-mesa applications, and that dry etching methods involving an additional chemical component or ion implantation isolation are more practical alternatives for device patterning.
Characterization of CVD Diamond Films Used for Radiation Detection.
Authors: Foulon F. , Pochet T. , Gheeraert E. , Deneuville A. 
Published: April 2011

ABSTRACTDiamond films produced by microwave plasma enhanced chemical vapor deposition (CVD) technique and used to fabricate radiation detectors have been characterized. The polycrystalline diamond films have a measured resistivity of 1012 Ω.cm and a carrier lifetime of about 530 ps. The carrier mobility - lifetime product depends on the density of photogenerated carriers. The carrier mobility decreases from 160 to 13 cm2/V.s for a carrier density increase from 2 × 1011 cm-3 to 3.7 × 1013 cm-3. The detector response to laser pulses (λ= 355, 532 and 1064 nm), X-ray flux (2.5 – 16 keV) and alpha particles (241Am, 5.49 MeV) has been investigated. The response speed of the detector is in the 100 ps range. X-ray photon flux measurements and alpha particle counting capabilities of the CVD diamond detectors are demonstrated.
Cobalt Silicide OHMIC Contacts to 6H-SiC
Authors: Lundberg Nils , Östling M. 
Published: April 2011

ABSTRACTMaterials and electrical evaluation were performed to determine the characteristics of ohmic contacts to 6H-SiC. Both elemental metal (Co) and suicides (CoSi and CoSi2) were studied following heat treatments at 500 °C and 900 °C for 5 hours and 2 hours, respectively. Materials analysis by Rutherford Backscattering Spectrometry (RBS) and X-ray Diffraction (XRD) monitored the temperature stability of the contacts after the annealings. Current density-voltage measurements at elevated temperatures established the specific contact resistance pc.
Chemical Reaction Mechanisms of Diamond Growth
Authors: Frenklach Michael 
Published: April 2011

ABSTRACTIt is becoming increasingly apparent that future progress in diamond chemical vapor deposition depends on deeper understanding of the underlying mechanism of surface processes. Substantial efforts toward this goal have led to several conclusions on which consensus is beginning to emerge. Among them are the mediating role of hydrogen atoms, generic features of the growth kinetics, thermodynamic stability of reconstructed (100) surfaces, and the insertion reaction of methyl into (100)-(2×l) dimers. Despite these efforts, an overall picture of diamond growth in terms of elementary processes is still lacking. In this paper, the current state of mechanistic understanding is reviewed, emphasizing common themes, and new results are presented. Among the latter are the effect of reaction reversibility on surface morphology, surface migration, and a new mechanism for diamond growth from acetylene.
Dynamics at a Step on the Diamond (111) Surface
Authors: Davidson Brian N. , Pickett Warren E. 
Published: April 2011

ABSTRACTUsing an accurate tight-binding method, we examine the structure and dynamics at a C(lll) step. We find the H vibration frequencies at a step are distinguishable from the flat surface. Removal of H from the surface creates an unstable bulk terminated diamond structure which relaxes to a graphitic layer and pulls away from the bulk. The explanation for these results can be given in terms of the relationship of the band structure to the relaxed geometries. The addition of H stabilizes this surface and reverts it back to sp3 bonding. The addition of CH3 near a step is also discussed. These results are important towards the understanding of possible diamond growth mechanisms that occur at a step.
Diamond Homoepitaxy Kinetics: Growth, Etching, and the Role of Oxygen
Authors: Rawles Robin E. , D'Evelyn Mark P. 
Published: April 2011

ABSTRACTGrowth and etch rates for diamond homoepitaxy have been measured in situ using Fizeau interferometry. Experiments were conducted in a hot-filament reactor using hydrogen, methane, and oxygen feed gases at a reactor pressure of 25 torr. The substrate temperature dependence for growth on diamond(lOO) was studied for 0.5% and 1% CH4 and 0–0.44% O2. Apparent activation energies of 17 and 5 kcal/mol were determined for growth from 0.5% and 1% CH4 in hydrogen, over the ranges of 700 – 1000 °C and 800 – 1050 °C, respectively. When a minimal amount of Oxygen was added to the feedstock, the growth-rate behavior was similar for that with pure methane. With greater amounts of added oxygen, growth rates were higher than those without Oxygen at low temperatures, proceeded through a maximum, and then decreased until etching was observed at high temperatures. Similar behavior was observed for growth from 1% CH4 with and without oxygen. We also measured the temperature dependence for etching of homoepitaxial diamond films in hydrogen with 0–0.1% O2, and observed etch rates of 0.01 – 0.1 microns/hr in the range of 950 – 1150 °C. We propose that oxygen facilitates diamond growth at low temperatures by enhancing the removal of both sp2- and sp3-bonded “errors” and/or by increasing the efficiency of carbon incorporation by roughening the diamond surface, and that these etching processes become dominant at high temperatures.
Diamond Nucleation Studies on Refractory Metals and Nickel
Authors: Wolter S. D. , Stoner B. R. , Yang P. C. , Lui W. , Glass J. T. 
Published: April 2011

ABSTRACTDiamond nucleation has been investigated on a variety of potential heteroepitaxial substrate materials. Previous work in this laboratory has demonstrated heteroepitaxial nucleation on both Si and SiC substrates via bias-enhanced nucleation (BEN). In this study the effects of BEN of diamond on refractory metal substrates is investigated in detail. Initial data suggest a strong correlation between the carbide forming nature of the substrate material and the rate of nucleation during biasing. Our second avenue of research involves low pressure diamond growth on nickel. This material is a promising material due to its close lattice match and recent evidence of epitaxy reported by other researchers. To form heteroepitaxial diamond on nickel a high temperature pretreatment routine has been established and is the basis for this area of research. The relative importance of hydrogen absorption during this routine is explored and correlated to the formation and degree of diamond epitaxy.
Defects and Growth of Diamond Wafers
Authors: Shechtman D. 
Published: April 2011

ABSTRACTCrystallographic defects which form during growth of CVD diamond were studied and their effect on the surface structure of the growing wafer evaluated. The most abundant defects are β=3 twins boundaries whose density is very high at the nucleation side and as low as one twin per 10 /μm at the growth surface. The intersection of these twin boundaries with one another results in a formation of higher order twin boundaries. β=9 as well as β=27 and β=81 boundaries have been analyzed. The surface crystallography of optical quality diamond wafers reveals the role of β=3 twins in promoting fast growth.
Deposition of Diamond using an Electron Cyclotron Resonance Plasma System
Authors: Gilbert Donald R. , Singh Rajiv , Brock Alexander W. , Lee Dong Gu , Doering Patrick 
Published: April 2011

ABSTRACTWe have used an electron cyclotron resonance plasma system to perform chemical vapor deposition experiments on single-crystal, (110) oriented diamond substrates. The depositions were carried out at 0.060 Torr using mixtures of methanol in hydrogen. Substrate temperatures were varied from approximately 620 to 800 °C The film morphology was examined using SEM and microstructural phase determination was attempted using micro-Raman spectroscopy. Based on the results of these experiments, we have determined general trends for the characteristics of films deposited on diamond from the ECR plasma at low pressures and temperatures.
Phase Transformation of Smooth Diamond Films Grown by hot Filament Chemical Vapor Deposition on Positively Biased Silicon Substrates.
Authors: Popovici G. , Chao C. H. , Prelas M. A. , Charlson E. J. , Meese J. M. 
Published: April 2011

ABSTRACTSmooth diamond films have been grown by hot filament chemical vapor deposition under d.c. bias on mirror-polished Si substrates. Films a few micrometers thick were obtained in 30 minutes. Raman spectra showed very broad diamond peaks. X-ray diffraction showed the presence of diamond and also other carbon phase with a line 2.11 Å. With time, the films apparently underwent a phase transformation.
ECR-Assisted Reactive Magnetron Sputtering of InN
Authors: Bryden W. A. , Ecelberger S. A. , Hawley M. E. , Kistenmacher T. J. 
Published: April 2011

ABSTRACTThe growth of high-quality thin films of the Group IIIA nitrides is exceedingly difficult given their propensity for nonstoichiometry and the lack of suitable substrates for either homoepitaxial or heteroepitaxial growth. A novel deposition technique, ultrahigh vacuum electron cyclotron resonance-assisted reactive magnetron sputtering, has been developed for the preparation of Group IIIA nitride thin films. Thus far, thin films of the semiconductor InN have been deposited on AlN-seeded (00.1) sapphire substrates, and the properties (structural, morphology, and electrical transport) of these films studied as a function of growth temperature. Comparison to InN thin films grown by conventional reactive magnetron sputtering shows enhanced Hall mobilities (from about 50 to over 100 cm2/V-sec), a decreased carrier concentration (by about a factor of 2–3), an increased optical bandgap, and an apparent reduction in homogeneous strain that is in part to be due to film relaxation induced by the ECR beam and in part to enhanced nitrogen content and more nearly stoichiometric films.
Deposition And Characterization of CNx Films
Authors: Cui X. T. , Zhang Z. H. , Chen Q. Y. , Romero-Borja F. , Liu J. R. , Zheng Z. S. , Pan D. W. , Wood L. T. , Chu W. K. 
Published: April 2011

ABSTRACTCNx films with x around 1.0 have been made by inverted cylindrical DC magnetron sputtering. RBS, XPS, IR spectroscopy, ERD and SEM were used to characterize the composition and bonding properties of the films, while X-ray diffraction was used for crystal structure determination. XPS data indicated the existence of the tetrahedral C3N4 phase in the CNx films, which was consistent with the C-N single bond suggested by IR spectra. The annealing effect on CNx films will also be discussed.
NMR Spin Lattice Relaxation in NITROGEN-Doped 6H Silicon Carbide
Authors: Stephen Hartman J. , Narayanan Arjun , Wang Youxiang 
Published: April 2011

ABSTRACTNuclear magnetic resonance (NMR) spin lattice relaxation is highly sensitive to the nature, amount, and homogeneity of unpaired-electron-containing impurities in silicon carbide and similar solids, and is a promising tool for the study of dopants and impurities. In nitrogen-doped 6H silicon carbide, 13C and 29Si NMR spin lattice relaxation is highly site-dependent. Not only do carbon sites relax much more rapidly than the corresponding silicon sites, but also there are unprecedented differences in relaxation efficiency among the different carbon (and silicon) sites, consistent with much higher unpaired electron density at the higher-symmetry (Types A and B) sites than at the lowest-symmetry (Type C) site. In contrast, all sites relax at equivalent rates in undoped samples and in commercial abrasive grade material with high levels of impurities, although there are large differences in relaxation efficiency among samples. The change in the nature of the relaxation process, from exponential in high-purity to stretched exponential in lower-purity samples, is apparently related to changes in unpaired-electron mobility.
Electronic Structure of Diamond, Silicon Carbide, and the Group-III Nitrides
Authors: Lambrecht Walter R. L. 
Published: April 2011

ABSTRACTThis paper describes the trends in the electronic structure of diamond, silicon carbide, the group-Ill nitrides and some related materials. The relationships between the electronic band structures in the zincblende and wurtzite structures are adressed. For SiC, the discussion is extended to other poly types. The trends with ionicity and atomic number are explained. The purpose of this discussion is to help identify the similarities and differences between the various classes of wide bandgap semiconductors. The strain effects on the band structure are discussed and calculated elastic constants are given for SiC, GaN and AlN. Spectroscopie probes of the band structure such as pholoemission and UV-refiectivity are discussed for GaN and SiC. Materials with the formula II-IV-2 are proposed to be an interesting complement to the III-N's. In particular, BeCN2 is a direct gap semiconductor with elastic properties close to those of diamond and may also be useful as a bufferlayer for diamond growth.
A Spin Resonance Study of The 2.9 eV Luminescence Centers in Natural and Synthetic Diamond
Authors: Hofmann D. M. , Stadler W. , Meyer B. K. , Pereira L. , Santos L. , Pereira E. 
Published: April 2011

ABSTRACTTime resolved photoluminescence and optically detected magnetic resonance experiments were performed on the 2.985 eV (N3) luminescence band in natural diamond and the 2.964 eV luminescence center in synthetic diamonds. For the N3 luminescence the resonance occurs in the 2E excited state of the center. On the 2.964 eV luminescence a strongly anisotropie resonance signal is observed. The frequency response of the magnetic resonance signals confirms the time resolved photoluminescence measurements.
Native Defects in Wurtzite GaN And AlN
Authors: Boguslawski P. , Briggs E. , White T. A. , Wensell M. G. , Bernholc J. 
Published: April 2011

AbstractThe results of an extensive theoretical study of native defects in GaN and of vacancies in AlN are presented. We have considered cation and anion vacancies, antisites, and intersti-tials. The computations were carried out using quantum molecular dynamics, in supercells containing 72 atoms. Due to the wide gap of nitrides, the formation energies of defects depend strongly on the position of the Fermi level. The N vacancy in GaN introduces a shallow donor level that may be responsible for the n-type character of as-grown GaN.Other defects introduce deep states in the gap, with strongly localized wave functions.
Surface Cleaning, Topography, and Temperature Measurements of Single Crystal Diamond
Authors: D'Evelyn Mark P. , Struck Lisa M. , Rawles Robin E. 
Published: April 2011

ABSTRACTApplication of surface science methods to single crystal diamond surfaces requires the preparation of clean, well-ordered surfaces and accurate measurement of substrate temperature. Cleaning of diamond (100) in H2SO4/HNO3/HClO4 produced several infrared absorption features between 1025 and 1275 cm-1, as observed by infrared multiple-internal-reflection spectroscopy. These modes are assigned to surface hydroxyl and bridge-bonded oxygen. Heating an oxidized surface to ca. 1130 °C caused disappearance of a surface hydroxyl mode centered at 1080 cm-1. We show by atomic force microscopy that an as-polished diamond (100) sample is covered by grooves and ridges several nm in height, implying a modest density of atomic steps. The surface of a diamond that underwent etching via numerous adsorption/desorption experiments in ultrahigh vacuum and was acid cleaned several times was essentially unchanged, indicating a minimal perturbation of the surface topography. The capability of Fizeau interferometry for accurate measurement of single-crystal diamond temperatures is demonstrated.
Materials Aspects of Diamond-Based Electronic Devices
Authors: Zeidler J. R. , Hewett C. A. , Nguyen R. 
Published: April 2011

ABSTRACTAn overview of enabling materials technologies required for fabrication of electronic devices on diamond is presented. Emphasis is placed on electronic doping of diamond by boron ion implantation. Van der Pauw resistivity and Hall Effect measurements were used to determine the net carrier concentration, carrier mobility and resistivity of natural and synthetic diamonds implanted under various conditions. The measured results for a range of implantation conditions and post-annealing temperatures are discussed in the context cf a model developed by J.F. Prins1. The requirements placed on ohmic contacts to diamond, and a process for fabricating ohmic contacts, is discussed briefly. Finally, current-voltage characteristics of a simple MISFET fabricated on ion implanted natural diamond are presented and analyzed. 1J.F. Prins, Physical Review B, 38 (1988) 5576.
Mechanical, Thermal and Flow Dynamics Issues in Compound Semiconductor MOCVD Reactor Design
Authors: Gurary A.I. , Tompa G.S. , Moy K. , Zawadzki P. 
Published: April 2011

ABSTRACTIn recent years Metalorganic Chemical Vapor Deposition (MOCVD) becomes a key epitaxial process for a variety of compound semiconductor devices such as: GaAs/AlGaAs lasers, HEMTs, LEDs, photocathodes, solar cells, and MESFETs; InP/InGaAsP long wavelength lasers and detectors; InP/InGaAs quantum wells and detectors, etc. Development of reliable, high throughput equipment is a major task in the implementation of MOCVD into cost-effective manufacturings. We have used Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) software to model thermal, structural, and flow processes for the scaling of EMCORE vertical, high speed rotating disk reactor (RDR) to large dimensions (four 4″ wafers located on 12″ wafer carrier). Flow modeling was used to determine basic reactor geometry and the relation between process parameters such as total reactant flow, temperature, pressure, and rotation speed. Thermal and structural analysis was used to produce a uniform substrate temperature, avoid reactor overheating and decrease thermal stress. Flow and temperature distribution predicted by the modeling were found to be well correlated with experimental results.
Novel Group V Sources for Use in Mombe
Authors: Abernathy C. R. , Bohling D. A. , Muhr G. T. , Wisk P. W. 
Published: April 2011

ABSTRACTDue to the extreme toxicity, and in the case of Sb stability, of the Group V hydrides, alternative gaseous Group V sources for III-V epitaxy are highly desirable. Trisdimethylaminoarsenic (DMAAs) has proven to be a useful replacement for AsH 3 for growth of GaAs and AlGaAs by MOMBE. This paper will discuss the P and Sb analogs to this compound, namely trisdimethylaminophosphorus (DMAP) and trisdimethylaminoantimony (DMASb). Both sources decompose readily on the growth surface. InP surfaces, for example, can be maintained with either source over a wide range, 375° - 525°C, as can GaAs, 375° - 600°C. Using DMAP, GaP can be grown at rates up to 200Å/min with slightly less carbon contamination than obtained with similar flows of PH3. When trimethylindium (TMI) is introduced, however, the DMAP does not readily decompose thus leaving In droplets on the surface. InP was successfully grown by thermally cracking the DMAP prior to injection to the chamber. The dependence of cracking efficiency and impurity uptake on cracker temperature will also be presented. DMASb was found to produce just the opposite effect, apparently preventing the adsorption of TEG, TIBG, or TMAA on the surface for sufficient time to allow growth to occur.
Dry ETCH Induced Defects and H Passivation of GaAs Surfaces Produced by CH4/H2/Ar Plasmas
Authors: McLane G. F. , Buchwald W.R. 
Published: April 2011

ABSTRACTAn investigation was performed of surface region etch-induced damage of GaAs magnetron reactive ion etched in CH4/H2/Ar gas mixtures for 10% and 20% Ar concentrations. Schottky barrier I-V measurements showed that changes in surface potential (ϕb) upon etching and subsequent annealing can be explained by a combination of H passivation effects and As removal from the surface region. Changes in Schottky barrier ideality factor (n) can be explained by the presence of etch-induced surface region defects such as donor-like As vacancies and deep level recombination centers, both of which are passivated by H. Schottky barrier C-V measurements indicated that H passivation extends about 0.3 μm below the surface. Rapid thermal annealing at 400°C for 30 s was effective in removing most of the H passivation effects.
Temperature Dependence of Carbon Incorporation in AlxGa1-xAs Grown by Metalorganic Chemical Vapor Deposition (MOCVD)
Authors: Forbes D.V. , Coleman J.J. 
Published: April 2011

ABSTRACTThe dependence of carbon concentration on growth temperature and V/HII ratio for high composition AlxGal-xAs (x>0.40) grown by metalorganic chemical vapor deposition using trimethyl sources has been investigated. The carbon concentration exhibits at least two temperature regimes having different trends with temperature. In the region of 600-675°C, the carbon concentration decreases with temperature, while in the range of 700-800°C, the carbon concentration increases with temperature. This dependence was observed in samples grown in two separate reactors. High values of V/III ratio have been found to suppress the low temperature carbon incorporation in AlAs. The results are qualitatively explained in terms of the chemical reactions and surface kinetics that may occur during the growth of GaAs or AlxGal-xAs.
Nitrogen Location on ZnSe Surface During MBE Growth
Authors: Kubo Minoru , Sasai Yoichi , Narusawa Tadasi 
Published: April 2011

ABSTRACTWe first present the nitrogen location on radical nitrogen doped ZnSe-MBE surface studied by ISARS(Ion Scattering And Recoiling Spectrometry). In the recoiling nitrogen measurements of heavy doped ZnSe:N surface, a two-peak structure is observed corresponding to two recoil processes, i.e., direct recoil (DR) and surface recoil(SR). DR events occur due to the singlecollision recoiling from Se site nitrogen. On the other hand, SR events occur due to the nitrogen recoiling scattered by second layers and is highly sensitive to the nitrogen location on ZnSe:N surface during MBE growth. The experimental results and calculation suggest that the optimum doped nitrogen atoms locate in the substitutional Se sites but excess nitrogen atoms locate in the interstitial sites.