bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Metal/Carbon Multilayers by Raman Spectroscopy
Authors: Allred David D. , Wang Qi , Gonzalez-Hernandez Jesus 
Published: March 2011

AbstractLaser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the Raman spectra is due to a-C. The a-C spectra consists of a broad peak at about 1560 cm-1 (G-peak) and a shoulder at about 1400 cm-1 (D-peak). This can be deconvoluted with Gaussian line shapes to yield two peaks (one at about 1560 to 1570 cm-1 and the other at about 1380 to 1420 cm-1). Among the W/C multilayer samples peak positions and relative magnitudes changed little with carbon thickness over the range of 1 to 12 nm. Significant differences are, however, seen as the identity of the metal component is altered or, especially, as the preparations are varied. For example, the intensity ratio of the D-peak to G-peak was much larger for multilayer samples prepared under conditions of good plasma confinement.
Modulation Spectroscopy of Layered Structures
Authors: Glembocki O.J. 
Published: March 2011

AbstractModulation spectroscopies, such as electroreflectance and photoreflectance have become popular as room temperature probes of layered structures. Because of their derivative nature, one observes sharp optical features related to critical points in the dielectric function of the material under study. This allows us to obtain information such as alloy concentration, carrier density, well widths of quantum wells and thicknesses of the constituent layers in superlattices. In this paper, we will review the application of modulation spectroscopy to the study of optical and electronic properties of layered structures.
Photoluminescence Excitation Spectroscopy of Strained Ingaas/GaAs Quantum Wells
Authors: Koteles Emil S. , Owens D. , Elman B. , Melman P. , Bertolet D. , May Lau Kei 
Published: March 2011

AbstractPhotoluminescence excitation spectroscopy of exciton transitions has been utilized to obtain information about light-holes in strained InGaAs/GaAs single quantum wells. By monitoring their behavior with respect to that of heavy-holes, it was shown possible to ascertain whether or not the quantum wells were pseudomorphic (lattice matched but strained) or relaxed and, if strained, the magnitude of strain present. Thus the indium composition of the single QW layers was deduced. This method is advantageous since it is nondestructive, requires no special sample preparation, is accurate and can readily be extended to monitoring strain in QWs subjected to various processing steps associated with device fabrication.
Misfit Dislocation Nucleation and Interactions at GexSi1-x/Si Interfaces
Authors: Perovic D.D. , Weatherly G.C. , Houghton D.C. 
Published: March 2011

AbstractIn the study of elastic strain relaxation in semiconductor heterostructures, a number of misfit dislocation generation mechanisms have been suggested to account for the high interfacial dislocation density observed in these almost defect-free crystals. Several MBE-grown GexSi1-x/Si heterostructures, both in the as-grown and annealed condition have been studied using transmission electron microscopy. The results indicate that some of the popular theories of dislocation generation are less important or not applicable based on both theoretical and experimental considerations. Specifically, it will be shown that: (i) heterogeneous sources play a dominant role in the nucleation mechanisms, (ii) the strain relaxation behaviour during MBE growth may be different from that observed in metastable structures annealed after growth and (iii) the Hagen-S trunk multiplication mechanism is inoperative under most conditions in this system.
Optical Characterization of GaAsP Strained Layers Grown on (111)-Oriented GaP
Authors: Pistol M.-E. , Gerling M. , Gustafsson A. , Paulsson G. , Samuelson L. , Titze H. 
Published: March 2011

AbstractStrained layers of indirect GaAsP have been grown on the (111)B-oriented surface of GaP by Metal-Organic Vapour Phase Epitaxy (MOVPE). These layers have been characterized by low-temperature photoluminescence (PL), electroreflectance (ER), secondary-ion mass spectroscopy (SIMS), and wavelength resolved imaging cathodoluminescence (CL). We have been able to follow the transition energies of the lowest X conduction band edge, as well as the higher Γ band edge of the strained layers, as a function of composition up to an As-concentration of 38 %. The experimental values of the transition energies are compared with predictions made from calculations based on deformation potential theory. CL allows us to directly observe the onset of dislocation formation, i. e. the critical thickness. The appearance and properties of the dislocation network revealed by CL are very different from those of the corresponding network when the strained layers are grown on (001)-oriented surfaces.
Characterization of an Asymmetric Triangular Multiple Quantum Well, by Variable Angle Spectroscopic Ellipsometry
Authors: Herzinger Craig M. , Snyder Paul G. , Woollam John A. , Evans Keith , Stutz C.E. , Jones R. , Merkel K.G. , Reynolds D.C. 
Published: March 2011

AbstractVariable angle spectroscopic ellipsometry (VASE) was used to characterize a 20 period GaAs/Al(x)Ga(1-x)As multiple quantum well structure, grown by molecular beam epitaxy. The barriers were nominally 200 Å Al(.25)Ga(.75)As, and the well regions were grown to approximate a linearly graded composition, from x=0 to x=0.25, with total well width 200 Å. VASE data in the E1, E1,+Δ1. region were analyzed using four different models. It was founcЃ that the dielectric function of the cap GaAs layer was shifted to higher energy with respect to the bulk GaAs dielectric function.
Materials and Device Characteristics of Pseudomorphic AlGaAs-InGaAs-GaAs and AlInAs-InGaAs-InP High Electron Mobility Transistors
Authors: Ballingall J.M. , Ho Pin , Tessmer G J. , Martin P.A. , Yu T.H. , Chao P.C. , Smith P.M. , Duh K.H.G. 
Published: March 2011

AbstractHigh electron mobility transistors (HEMTs) with single quantum well active layers composed of pseudomorphic IπGaAs grown on GaAs and InP are establishing new standards of performance for microwave and millimeter wave applications. This is due to recent progress in the molecular beam epitaxial growth of strained InGaAs heterostructures coupled with developments in short gate length (sub%0.2 µm) device fabrication technology. This paper reviews this progress and the current state-of-the-art for materials and devices.
The Kinetics of Si1-xGex/Si Relaxation using Large Area Dislocation Imaging Techniques
Authors: Houghton D.C. , Timbrell P.Y. , Baribeau J.-M. 
Published: March 2011

AbstractAnnealing experiments in the 450-1000 °C temperature range on various MBE grown Si1-xGex/(100)Si heterostructures have revealed an abrupt thermally activated transition from coherently strained to partially relaxed microstructures. Misfit dislocations at densities 1 to 104 cm-2 have been monitored using Nomarski interference microscopy of defect etched surfaces and charge collection microscopy (EBIC) of Si1-xGex/Si heterojunctions in the scanning electron microscope. The kinetics of misfit relaxation by dislocation glide can be characterized by a relaxation temperature which for 30 minute furnace anneals was ~500 °C for an uncapped Si0.83Ge0.17 stramed layer, and ~600 °C for a similar buried strained layer typical of heterojunction bipolar transistor geometries. Rapid thermal anneals (5s) delayed the onset of relaxation to higher temperatures (~ 200 °C increase) and allowed misfit dislocation velocities to be determined for the temperature range 500-900 °C. The activation energy for dislocation glide was found to be 2.2±0.1eV for a Si0.9Ge0.1/Si strained layer superlattice, 1.6±0.2eV for a Si capped Si0.88Ge0.12 layer and 1.6±0.2eV for a Si0.83Ge0.17 uncapped strained layer.
Strain-Controlled High Mobility in Modulation Doped Si0.5Ge0.5/Ge/Si1-xGex Hetero-Structures
Authors: Miyao Masanobu , Murakami Eiichi , Etoh Hiroyuki , Nakagawa Kiyokazu 
Published: March 2011

AbstractFormation and characterization of a new hetero -structure of modulation doped p-Si0.5Ge0.5/Ge/Si1-xGex are comprehensively studied. In the MBE growth, thick Si1-xGex buffer layers are grown incommensurately at high temperature (520°C), and thin Si0.5Ge0.5/Ge layers are grown commensurately at low temperature (≦450°C). The strain field in the Ge channel layers can be precisely controlled by changing the Si composition (1-X) in the Si 1 -xGex buffer layers. As a result, a large energy discontinuity in the valence band (0.17 eV) is realized at the hetero -interface of p-Si0.5Ge0.5/Ge. This enables a high mobility of two -dimensional hole gas (4500 cm2/Vs) at 77 K.
Plastic Flow in Si/Ge Quantum Well Structures
Authors: Twigg M. E. , Godbey D. J. 
Published: March 2011

AbstractPlastic flow is driven by excess stress, which can be calculated from lattice strain and dislocation line tension. In order to better understand and model plastic flow, we have derived an expression for the dislocation line tension in thin film structures for double kink (dislocation dipole) extension of a threading dislocation. From these calculations, we conclude that the presence of a free surface (i.e. the vacuum/solid interface) significantly reduces the line tension for an extended double kink. For the specific case of a 50nm thick Si0.7 Ge0.3 layer capped with lum of silicon, we find that the line tension is approximately 30% less than the estimate of an analogous model that neglects the influence of a free surface. Therefore, in order to obtain an accurate estimate of the excess stress for a double kink, one must allow for the influence of a free surface.
A Comparative Study of Gas Chemistry in Methane/Hydrogen and Acetylene/Hydrogen Gas Mixtures During Hot-Filament Vapor Deposition of Diamond
Authors: Wu Ching-Hsong , Tamor M. A. , Potter T. J. , Kaiser E. W. 
Published: March 2011

ABSTRACTThe technology of low pressure chemical vapor deposition (CVD) of polycrystalline diamond films has advanced substantially in recent years [1–3]. However, fundamental understanding of the chemistry and physics occurring in this CVD process is still lagging. Although the key role that H atoms play in diamond CVD has long been recognized [4–6], the identity of the gaseous diamond precursors and the mechanism by which diamond is formed are still unclear. Only recently has interest in these critical issues grown. For example, theoretical predictions and quantum mechanical calculations of gas-solid reaction paths involving CH3 and CH3+ [7] or C2H2 [8] have been reported, and the thermodynamic analyses of diamond CVD processes have been examined [9,10]. In addition, experimental results and chemical models [11–16] have been presented in attempts to support specific species as the essential precursors of diamond growth. Nevertheless, no consensus has been reached concerning the growth species and mechanism in CVD diamond processes.
Deposition of Diamond Films by Scanning Oxy-Acetylene Flame
Authors: Tzeng Yonhua , Phillips Richard , Tin Chin C. , Chen Y. , Srivinyunon T. , Cutshaw Calvin 
Published: March 2011

ABSTRACTDiamond films have been deposited on silicon wafers by scanning an oxyacetylene flame against water-cooled silicon substrates. High quality diamond films about 20 um thick can be achieved by scanning the flame at a speed of about 0.2 mm per minute. The as-deposited films exhibit high electrical resistivity exceeding 1014Ωcm. Current voltage measurement shows the trap-dominated current conduction characteristics similar to that for dehydrogenated diamond films deposited by methane/hydrogen plasmas.
Growth of Device-Quality Homoepitaxial Diamond Thin Films
Authors: Geis M. W. 
Published: March 2011

ABSTRACTDiamond has an electric-field breakdown 20 times that of Si and GaAs, and a saturated velocity twice that of Si. This results in a predicted cut off frequency for high-power diamond transistors 40 times that of similar devices made of Si or GaAs. Boron is the only known impurity that can be used to lightly dope diamond. This p-type dopant has an activation energy of 0.3 to 0.4 eV, which results in high-resistivity material that is undesirable for devices. However, heavily boron doped diamond has a very small activation energy and a low resistivity and is of device quality. Transistors can be designed that use only undoped and heavily doped diamond. One of the steps in a device fabrication sequence is homoepitaxial diamond growth. Lightly and heavily doped homoepitaxial diamond films were characterized by scanning and transmission electron microscopy, x-ray diffraction, measurements of resistivity as a function of temperature, and secondary ion mass spectroscopy. It was found that under appropriate growth conditions these films are of device quality.
Characterization of Hollow-Cathode DC Discharge Growth of Diamond: Rotational Vibronic Emission In A CH4-H2 Discharge
Authors: Chu H. N. , Lefkow A. R. , Hartog E. A. Den , Jacobs J. , Sandstrom P. , Anderson L. W. , Lagally M. G. , Lawler J. E. 
Published: March 2011

ABSTRACTExperiments to study the temperature in the discharge produced using a dc spiral hollow cathode with CH4-H2 as the feed gas have been carried out during the rowth of diamond. Optical emission from the R branch of the 3d1 Σ v-O-2p Σ v-O rotational vibronic band are used to determine a rotational temperature. Limitations of this method are discussed.
Laser Assisted Techniques for Diamond and Diamondlike Thin Films
Authors: Rengan A. , Biunno N. , Narayan J. , Moyer P. 
Published: March 2011

ABSTRACTWe have deposited diamond-shaped particles using a non equilibrium process of laser ablation from a solid graphite target in a hydrogen discharge. The nucleation on the heated silicon surface occurs in small regions of ∼ 0.1 to 0.5 mm covering a small fraction of the surface. The faceting of the crystals observed are mainly octahedral [111] faces. The results of using an eximer laser to ablate a graphite target are described. SEM micrographs show octahedral faceting. Micro Raman spectroscopy on the crystalline features exhibit two bands at 1348 and at ∼ 1600 cm−1. The peak position and large FWHM suggests the existence of disordered sp3 bonding or short range order existing in the film. Another possibility is the existence of a stress state in the crystal due to the non equilibrium nature and the high rate of growth of the crystals. We have also irradiated HFCVD grown diamond film with a XeCl UV- eximer laser. The results indicated that sp2 bonded graphitic and amorphous component are selectively ablated, enhancing the sp3 hybrid bonds in the film.
Epitaxial Growth of Diamond and Diamond Devices
Authors: Fujimori Naoji , Imai Takahiro , Nakahata Hideaki , Shiomi Hiromu , Nishibayashi Yoshiki 
Published: March 2011

ABSTRACTFor the practical application of diamond semiconductor devices, the manufacture of planar-type devices is important. Homoepitaxial growth of diamonds would be a useful technique for making semiconducting diamond films. Homo-epitaxial growth of diamonds is achieved by microwave plasma CVD. The properties of epitaxial diamond films depend on the deposition condition and the substrate orientation. Boron doping was easily carried out by this method and boron doped films were determined to be ptype semiconductors. Properties of boron doped epitaxial films were found to be similar to those of natural IIb diamond. The Schottky junction on boron doped epitaxial films was obtained by the deposition of tungsten and aluminum. The Schottky properties of this combination were affected by the surface roughness of the epitaxial films. A field effect transistor and a light emitting device were successfully fabricated using boron doped epitaxial films and Schottky junctions.
Optical Characterisation of Nickel in Diamond
Authors: Nazaré Maria Helena , Neves Aj , Davies Gordon 
Published: March 2011

ABSTRACTOptical absorption and luminescence with zero-phonon lines at 1.401 and 1.404 eV is shown to contain fine structure induced by the isotopes of natural Ni. Uniaxial stress and magnetic field perturbations establish that the optical center has trigonal symmetry. A relationship is estimated between the concentration of Ni in these optical centers and the strength of the optical absorption.
Infrared Characterization of the Hydrogen Environments in Diamond Thin Films
Authors: LeGrice Y. M. , Buehler E. C. , Nemanich R. J. , Glass J. T. , Kobashi K. , Jansen F. , Machonkin M. A. , Tsai C. C. 
Published: March 2011

ABSTRACTCVD diamond films prepared under varying conditions have been investigated with IR and Raman spectroscopy. Raman spectroscopy was used to characterize the crystal structure, and ir absorption was used to determine the H bonding environments. The growth temperatures were varied in one series, while the CH4/H2 ratio was varied in another. The IR absorption of all the samples showed a weak broad band extending from approximately 2800 to 2970 cm−1 which was attributed to H bonded to sp3 C sites. There was no evidence of ir absorption at 3000 to 3200 cm−1 which would indicate H bonded to sp2 or sp1 C sites. For both series, the Raman measurements showed progression from diamond-like films to diamond films. The ir absorption showed a general trend of less H with more well ordered diamond structures. No sharp transition of the H incorporation vs the growth parameters was observed.
In-Situ Characterization of Thin Polycrystalline Diamond Film Quality by Thermal Wave and Raman Techniques
Authors: Pryor R. W. , Kuo P. K. , Wei L. , Thomas R. L. , Talley P. L. 
Published: March 2011

ABSTRACTIn this paper, the thermal wave technique and microfocus Raman spectroscopy are used to measure the relative quality of thin diamond films deposited on silicon. The thermal wave technique uses a modulated heating laser beam, normal to the diamond film surface, to initiate a thermal wave which propagates into the film, the substrate, and the overlying gas(ses). The accompanying modulated gas density is then interrogated by a second (probe) laser beam. The probe beam is deflected by the corresponding periodic changes in the gradient of the refractive index of the gas. The measured probe beam deflection versus offset position is fitted, using a theoretical solution of the three-dimensional thermal diffusion equation for the gas/film/substrate system. The physically important fitting parameter is the thermal diffusivity of the diamond film. Thermal conductivities derived from our diffusivity measurements using this method compare well to previous measurements on similarly prepared films by other methods. Our measured values for the thermal conductivity of the highest-quality polycrystalline diamond films are of the order of 12 W/cm-K. Our measured values of thermal conductivity for diamond films range between this value and the thermal conductivity of graphite. We have also made measurements on bulk diamond using the thermal wave technique, and we obtain a thermal conductivity of 21 W/cm-K, in excellent agreement with values found in the literature. A multi-scan, microfocus ratio of “graphitic” material to diamond material for a relative assessment of film quality.
The Electronic and Optical Properties of Diamond; Do they Favour Device Applications?
Authors: Collins Alan T. 
Published: March 2011

ABSTRACTThe electronic and optical properties of diamond are reviewed, with particular emphasis on current research into the production of semiconducting devices. Although many of the properties of diamond seem, at first sight, to be ideally suited to the development of high power microwave and optoelectronic devices, there are also a number of obstacles to be overcome before diamond may be successfully exploited for device applications.
Cyclic-Cluster Mindo/3 Computations of The Lattice Constant and Band Structure of Boron Nitride, Diamond and Silicon Carbide
Authors: Snyder Lawrence C. , Edwards Arthur H. , Deak Peter 
Published: March 2011

ABSTRACTWe have employed a 32 atom cyclic-cluster and the Modified Intermediate Neglect of Differential Overlap (MINDO/3) method to compute the lattice constant, band structure, heat of formation and other properties of cubic boron nitride, diamond and silicon nitride. The computational scheme we have employed will permit studies of defects in these materials.
Electrical Characterization of Metal Contacts on Diamond Thin Films
Authors: Narducci Dario , Cuomo Jerome J. , Guarnieri C. Richard , Whitehair Stanley J. 
Published: March 2011

ABSTRACTPolycrystalline boron-doped diamond thin films were prepared by microwave-enhanced plasma-assisted chemical vapor deposition. Ti, V, Ta, Nb, Al, Mo and W contacts were prepared by physical vapor deposition and their behavior was studied as a function of the annealing temperature, atmosphere and duration. For Ti contacts, short heat treatments (less than 60 minutes) at 500 °C under argon atmosphere were found to make ohmic contacts for applied voltages up to 50 V. Longer annealing times, more reactive atmospheres, and higher temperatures degraded the contact characteristics. In order to obtain a more complete picture of the interface structure, the capacitance-voltage characteristics and the impedance spectra of the systems were measured between 10 K and 1000 K. The interface contribution to the overall dielectric behavior of the system shows much shallower depletion widths in Ti-diamond (ohmic) contacts than with the non-linear Nb and Ta contacts. The higher values of the contact resistance and the shallower depletion width with Ti can be explained in terms of formation of a thin carbide-like region at the metalsemiconductor interface. The space-charge region width as well as the distribution of localized states in the band gap were also determined. The effect of the microstructure on the electrical properties of the systems is discussed in comparison with the behavior of metal-contacts on single-crystal diamonds.
Properties of CVD Diamond/Metal Interface
Authors: Mori Yusuke , Kawarada Hiroshi , Hiraki Akio 
Published: March 2011

ABSTRACTElectric properties of the interface between metal and semiconducting CVD diamond formed by microwave plasma chemical vapour deposition (CVD) have been investigated. Much better rectifying property due to Schottky barrier has been obtained in the films formed with CO(5%)/H2 compared with CH4(0.5%)/H2. A high breakdown voltage (200 V) and a high rectification ratio (105) have been observed at the evaporated Al/diamond interfaces formed with CO(5%)/H2. In the point contact interfaces, where the metal-carbon reaction is not expected at room temperature, the rectifying and ohmic property depends on the electronegativity of metals.
A Diamond Silicon Heterojunction Diode
Authors: Ellison C. L. , Cohen R. M. , Hoggins J. T. 
Published: March 2011

ABSTRACTThin diamond films were grown on low resistivity p-type Si wafers by microwave plasma assisted chemical vapor deposition. Using gold contacts, diode-like behavior was observed and forward bias current densities in excess of 5 A/cm2 were obtained. Reverse bias current densities were as low as 5 mA/cm2. Photocurrent was measured when photon energies larger than the Si bandgap were used to illuminate the heterojunction. The same photocurrent spectrum was measured even when the illumination spot was moved several centimeters away from the metal-diamond contact. Photovoltage. photocurrent and hot probe measurements have been used to infer the energy band diagram of the diamond-Si p-p heterojunction.