bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Characterization of Metallorganic Chemical Vapor Deposition
Authors: Scarmozzino R. , Cacouris T. , Osgood R.M.
Published: March 2011

In situ measurement of resistance has been used for the realtime monitoring of metallorganic chemical vapor deposition (CVD) growth characteristics. In particular, a novel technique for measuring metallorganic CVD activation energies is presented. The micron scale geometry of the experiment makes it relevant to work in localized laser CVD. The technique has been used to measure the CVD activation energy of dimethylaluminum hydride (DMAlH). In addition, a variant of the technique has been used to study the growth stage of a resistless two-step metallization process (nucleation / selective CVD) employing DMAIH as the source gas in both steps.
Wavelength-Dependent Area Selectivity in Photochemical Vapor Deposition of Aluminum Films
Authors: Hanabusa Mitsugu , Ikeda Masashi
Published: March 2011

Thickness profile of aluminum thin films deposited from dimethylaluminum hydride on silicon substrate changed with wavelengths of light chosen from the wide emission spectra of a deuterium lamp. Under illumination of the VUV around 160 nm deposits were formed preferentially in illuminated regions, while such area selectivity was lost and uniformly thick films were deposited all over the substrate when the UV around 240 nm was used. The observed area selectivity can be interpreted as arising from a wavelength-dependent nucleation mechanism; namely, surface photochemical reactions leading to nucleation are induced only by the VUV, while the UV photons are capable of producing photofragments in gas phase responsible for nucleation.
Selective Rapid Thermal Cvd of Germanium
Authors: Grider D.T. , Özttürk M.C. , Wortman J.J. , Littlejohn M.A. , Zhong Y. , Batchelor D. , Russell P.
Published: March 2011

Selective depositions of germanium thin films have been investigated in a cold-wall, lamp heated rapid thermal processor. Films were deposited at low pressures (1 Torr-8 Torr) using the thermal decomposition of germane. Selectivity was maintained throughout the temperature range investigated, 350°C-600°C. Growth rates as high as 800 Å/min were obtained at 425°C where deposition is controlled by the surface reactions, making germanium compatible with the throughput requirements of single wafer manufacturing. Three dimensional growth was seen at temperatures above 450°C resulting in a rough surface morphology. Smooth films were deposited below 450°C with the films characterized by two dimensional growth. In this work, germanium is considered as a potential material to fabricate MOS transistors with raised source and drain junctions (UPMOS). Kelvin structures were fabricated to study the effect of the intermediate germanium layer between aluminum and silicon on contact resistance. It is shown that contact resistivity is improved by approximately 17% using an Al/p-Ge/p+-Si structure. In this work, it is also shown that titanium germanide formation can be used as a means of reducing the resistivity of the Ge buffer layer.
Direct Writing of Copper Lines from Copper Formate Precursors Using a Nd:Yag-Laser
Authors: MOLLER Heinrich G. , Schuler Siegfried
Published: March 2011

An effective method is described for laser induced additive formation of copper conductor lines on alumina substrates. The direct writing process allows for depositions with speeds of up to 50 mm/s and a resolution of about 10 microns with reliable adhesion of the deposited patterns.
Surface Chemistry of Dimethylaluminum Hydride and Trimethylaluminum on Aluminum
Authors: Strongin Daniel R. , Comita Paul B.
Published: March 2011

The surface chemistry of dimethylaluminum hydride (DMAH) and trimethylaluminum (TMA) on aluminum has been investigated with temperature programmed desorption (TPD), and Auger electron spectroscopy (AES). The TPD spectra of TMA shows a single desorption peak with a peak maximum which shifts from 190 to 200 K for surface coverages of 0.5 and 2.0 monolayers (ML) respectively. DMAH desorbs from an aluminum surface between 198 and 236 K at surface coverages ranging from 0.1 to 4.0 ML. A second DMAH desorption peak is observed at about 200 K (2.0 ML) when the aluminum surface is contaminated with carbonaceous species, resulting from the decomposition of DMAH. Both DMAH and TMA yield methane as a reaction product on the aluminum surface. The surface reactions of DMAH on aluminum also yield TMA as a reaction product.
In Situ Measurement of Pulsed Laser Indxuce Carrier Ceneraticn in Doped Silicon Films
Authors: Saveshimn T. , Hara M. , Usui S.
Published: March 2011

Transient conductance measurements were used to study rapid carrier generation during the laser doping of a silicon film. The movement of the liquid-solid interface was measured and the point of initiation of carrier generation frcn dopant atoms diffused to the molten silicon was determined. It was established that the dopant atais are activated at the nmorent the dopant diffused region solidified. Also, the laser doping technique was used to fabricate polycrystalline silicsn thin film transistors (Poly-Si TFT's) ata processing temperature of 250ºC.
Substrate Heating Effects in Excimer Laser Planarization of Aluminum
Authors: Baseman Robert J. , Andreshak Joseph C.
Published: March 2011

Substantial improvements in excimer laser planarization processes are observed with substrate heating. Cavities, associated with filling of high aspect ratio vias at low substrate temperature, can be eliminated by substrate heating. Damage associated with pulse overlap regions can be temperature sensitive, and is reduced as substrate temperatures areincreased. While required fluences for planarization and sample damage both decrease as the sample temperature increases, the relative insensitivity of the damage threshold generally results in larger process windows at higher temperatures. We also report model calculations of the effect of substrate heating on sample temperature distributions and the durations of the laser driven melts.
Phosphorus Doping into Silicon Using ArF Excimer Laser
Authors: Slaoui Abdelilah , Foulon Francois , Fogarassy Eric , Siffert Paul
Published: March 2011

Chemical doping of single-crystal silicon in a PF5 atmosphere is performed byirradiation with an ArF excimer laser working at 193 nm. We have investigated the dependence of doping parameters such as the number of pulses and PF5 gas pressure on the sheet resistance and the impurity concentration profiles. From these results, it is found that phosphorus atoms are produced by pyrolysis of PF5 molecules adsorbed (chemisorbed at low pressure and physisorbed at pressure higher than 1 Torr) on thesilicon surface. As for the incorporation mechanism, it is shown that the process is external rate limited for doping in PF5 ambient whereas mainly diffusion limitedfor doping using only the chemisorbed layer.
The Interaction of Laser Generated Methyl Radicals with Cd, Te, and CdTe Surfaces
Authors: Zinck J.J. , Olson G.L. , Brewer P.D. , Jensen J.E.
Published: March 2011

The mechanism of the interaction of methyl radicals with Cd, Te, and CdTe surfaces has been studied in ultrahigh vacuum by Auger electron spectroscopy and thermal desorption mass spectrometry. Methyl radicals generated by the laser photodissociation of acetone at 193 nm efficiently etch both Te and Te-rich CdTe surfaces. However, there is no evidencefor reaction of methyl radicals with Cd or stoichiometric CdTe. A temperature dependencein the rate of methyl radical etching of Te-rich CdTe is related to a competition between acetone scavanging of radicals on the surface and reaction of radicals to form volatile metalorganics. Acetone itself has a small but finite reaction probability with Te and Te-rich CdTe surfaces.
Holographic Pattern Etching of Silicon—Carbide by Excimer Laser
Authors: Murahara M. , Yonekawa M. , Shirakawa K.
Published: March 2011

The diffraction grating on SiC mirror was performed by a laser holographic method. In the present method, KrF laser and CIF3 was used for etchant gas. The ClF3 gas has an absorption band in the range between 200 and 400 nm. Therefore, CIF3 gas is effectively decomposed by the XeF, KrF and ArF excimer lasers' radiation. It is found that absorption of Si—C is about 50% in the range of between200 and 400 nm, and that the bonding energy of Si—C is lower than the photon energy of KrF laser beam. The above results indicate the direct decomposition of Si—Cbond. On the other hand, the threshold fluence energy for etching was 800 mJ/cm2 in 249 nm and in 193 nm as high as 7 J/cm2. In these results, the KrF laser is more effective than ArF laser. Then we applied KrF laser to crystalline SiC in an atmosphere of C1F3 gas. The divided two polarized KrF laser beams were interfered on the substrate. And the beams were used to photodissociated CIF3 gas in the proximity of substrate. Fluence of KrF laser beam was 1 J/cm2. The incidential angle of KrF laser beams was 20º and the grating gaps were 7170 Å, etching depth 1000 Å, and etching rate was 5 Å/pulse.
Novel Stacked CMOS Process by Local Overgrowth
Authors: Zingg René P. , Hüfflinger B. , Neudeck G. W.
Published: March 2011

A six mask process that yields stacked CMOS circuits is presented. Transistors that were built in reverse order (i. e. the gate first, the gate dielectric second, and only then the channel region) exhibit comparable parameters as conventional devices. A novel device has been built whose current drive is three times that of FETs built in substrate material. The vertical stacking of complementary MOS transistors made it possible to build an inverter with symmetric switching characteristic within the area of a single transistor.
Laser Induced Surface Chemical Epitaxy of II-VI Materials
Authors: Stinespring Charter D. , Freedman Andrew
Published: March 2011

Studies of the thermal and photon-induced surface chemistry of dimethyl cadmium (DMCd) and dimethyl tellurium (DMTe) on GaAs(100) substrates under ultrahigh vacuum conditions have been performed for substrate temperatures in the range of 123 K to 473 K. Results indicate that extremely efficient conversion of admixtures of DMTe and DMCd to CdTe can be obtained using low power (5 - 10 mJ cm−2) 193 nm laser pulses at substrate temperatures of 123 K. Subsequent annealing at 473 K produces an epitaxial film.
Xps Studies of Chlorine Etching Interactions with GaAs(100)
Authors: Freedman Andrew , Stinespring C.D.
Published: March 2011

GaAs (100) substrates have been chlorinated with both atomic and molecular beams of chlorine under ultra high vacuum conditions. X-ray photoelectron spectra of the resulting samples indicate that at a substrate temperatures of 130 K, Cl atoms efficiently penetrate the GaAs lattice forming Ga and As chloride species. Exposure to Cl atoms at 173 K results in desorption of As, leaving GaClx species behind. Molecular chlorine reacts much less efficiently.
Direct Evidence for the Creation of Micropores in UV-Irradiated Poly(Methyl Methacrylate)
Authors: Moore J. A. , Choi Jin-O
Published: March 2011

Films of PMMA containing azobenzene were prepared by casting from polymer solutions containing the probe or by exposing pre-irradiated films to the vapor of azobenzene. These materials were irradiated at 335 nm and the amount of trans azobenzene which had been photoisomerized was monitored spectrophotometrically. The largest amount of photoisomerization was observed for the pre-irradiated samples which had been penetrated by azobenzene from the vapor, indicating that the created free volume allowed the isomerization to proceed more easily.
Etching of GaAs on AlGaAs in Rie-Mode
Authors: Kaufel Gudrun , Olander Elfriede
Published: March 2011

Using MBE and MOCVD, High Electron Mobility Transistor (HEMT) structures were grown on two-inch GaAs wafers. The vertical structure included three GaAs layers and two thin (3nm) Al0.3Ga0.7 As etch stop layers to control precisely the depth of the etched recess and hence the threshold voltage of the devices.

The structure below the second etch stop layer depends on the particular device to be fabricated, but is irrelevant for the etching process. The selective reactive ion etching of GaAs on AlGaAs is done by a Leybold MPE 3003 Plasma Etcher. The etch gas used is CF2Cl2 for GaAs and Ar for AlGaAs. The pressure lies between 30 µbar and 100 µbar and the self bias voltage between 47 V and 250 V. The standard deviation for enhancement FETs is 12 mV for Vt = +0.13 V and for depletion FETs 18 mV for Vt = -0.48 V.
Uv Laser-Induced Etching of the First-Row Transition Metals
Authors: Tyndall George W.
Published: March 2011

The 248 nm excimer laser-induced etching of Ti, Cr, Fe, Co, Ni, and Cu by Br2 has been studied. The experiment consists of focusing the pulsed UV laser beam at normal incidence onto the surface of a quartz crystal microbalance (QCM) coated with 1μm of polycrystalline metal. Absolute etch rates are determined as a function of the Br2 pressure and the laser fluence. On the basis of the kinetic information, four mechanisms are proposed to explain the etching of these transition metals.
Photochemical Area-Selective Etching of Si And Sio2 Using Synchrotron Radiation
Authors: Takahashi Jun-Ichi , Utsumi Yuichi , Urisu Tsuneo
Published: March 2011

Photochemical etching of Si and SiO2 using synchrotron radiation (SR) is carried out. The etching rate of SiO2 is much higher than those of poly-Si and single crystal Si. The etching rate of poly-Si increases as dopant concentration decreases. These material selectivities are quite different from those for plasma- or laser-excited etching. These new phenomena in SR-stimulated etching can be explained by a reaction model that contains reaction centers that are produced by both core and binding electronic excitation of Si and fluorinated Si in the surface layers. These centers are quenched by majority carriers.
Laser-Based Area-Selective Processing Techniques for High-Density Interconnects
Authors: Liu Y.S. , Cole H. S.
Published: March 2011

This paper reviews several laser-based area-selective processing techniques developed for high-density multichip interconnection applications. Key material and process requirements for the development of a viable laser-direct-write interconnect technique on polyimide are addressed.
Laser Direct Writing of Optical Interconnects in Polyimides and Sio2:TiO2 Coatings
Authors: Hewak D.W. , Jerominek H.
Published: March 2011

Commercially available polyimides and SiO2:TiO2 coatings are experimentally studied for their potential application in optical guided-wave interconnect networks. Optical properties are measured, including transmission spectra, refractive index and loss, with the aim of determining the materials most suited for this application. On the most promising candidates, direct writing of strip waveguides with Ar-ion laser at 514.5 and 457.9 nm was performed. Localized thermal curing by writing with speeds up to 250 microns per second allows the achievement of multimode guiding structures. Light propagation loss measurements reveal that attenuation in strip waveguides is of the same order as in slab structures of the same material, typically 5-10 dB/cm at 633 nm.
Double Crystal X-Ray Diffraction Measurement of a Triclinicly Distorted and Tilted AlxGa1-xAs Unit Cell Produced by Growth on Offcut GaAs Substrates
Authors: Leiberich A. , Levkoff J.
Published: March 2011

Corrections are required for double crystal X-ray diffraction characterization of epitaxial AlxGa1-xAs layers grown on offcut GaAs (100) substrates. Double crystal X-ray diffraction measurements show that the cubic film unit cell defined by Vegard's law is triclinicly distorted and tilted with respect to the substrate unit cell. The distortion and tilt angles oppose each other defining a crystal geometry where the substrate and film <100= axes remain approximately coplanar with the surface normal. This film/substrate crystal geometry leads to formulation of a model describing heteroepitaxy on offcut (100) substrates. When film atoms are bonded to an offcut substrate, the already tetragonaly distorted film unit cell is subjected to additional cell distortions. The magnitude of this additional strain depends on where the film atoms are positioned on a substrate terrace. The first few layers of film atoms establish swain grades across individual substrate terraces. Constrained by the geometry of this interface region and driven by strain relaxation in the net growth direction, subsequent heteroepitaxy forms the measured film/substrate crystal geometry.
Interface Strain and the Valence Band Offset at the Lattice Matched In0.53Ga0.47As/InP (001) Interface
Authors: Hybertsen Mark S.
Published: March 2011

Total energy minimization calculations show that the interface bonds are strained in nominally lattice matched In0.53 Ga0.47As/InP (001) heterostructures, in agreement with recent X-ray measurements. Anion intermixing relieves the interface strain. The calculated valence band offset varies with the interface bond lengths so the minimum energy structure must be used for a given composition. Then the calculated offset is independent of composition and is in good agreement with experiment. A simple model exhibits the qualitative features revealed by these calculations.
Atomic Structure of CaSi2/Si Interfaces
Authors: Walle Chris G. Van De
Published: March 2011

The CaSi2/Si interface is studied with state-of-the-art first-principles calculations. Various models for the interfacial structure are examined, in which the Ca atoms at the interface exhibit 5-, 6-, 7-, or 8-fold coordination. The structures with sevenfold coordination (as in bulk CaSi2) have the lowest energy. However, the sixfold- and eightfold-coordinated structures are only ∼0.1 eV higher in energy. Schottky barrier heights are briefly discussed.
Growth Mode at the Ge/(1102) Sapphire Interface
Authors: Malafsky Geoffrey P.
Published: March 2011

The growth mode of Ge on the (1102) surface of sapphire is explored with X-ray photoelectron spectroscopy. Ge exists in two bonding states at the interface, Ge-Ge and Ge-sapphire. Ge forms islands at submonolayer coverage for deposition temperatures of 25°C and 625°C. The formation of the islands is revealed by the rapid increase in the relative fraction of the Ge-Ge bonding state for Ge coverage less than 1 ML. The shift in the Ge-Ge peak binding energy to the bulk Ge value at less than i ML suggests that the islands are three dimensional for deposition at 625°C.
Xps Analysis of the Sapphire Surface as a Function of High Temperature Vacuum Annealing
Authors: Richmond E.D.
Published: March 2011

For the first time the (1102) surface of sapphire has been investigated by X-ray photoelectron spectroscopy to ascertain chemical changes resulting from annealing in vacuum at 1300° C and 1450° C. As received substrates had a substantial surface C contaminant. For substrates that were chemically cleaned before inserting them into the MBE system no trace of carbon is detected. A residual flourine contaminant results from the cleaning procedure and is desorbed by the vacuum annealing. Spectra of annealed substrates are compared to the unannealed chemically cleaned substrates. The annealed substrates exhibit 0.4 to 0.5 eV shift to higher binding energy of the Al peak and a 0.3 eV shift to higher binding energy of the O peak. In addition, a 2% depletion of oxygen from the surface occurs.
Role of Tip Material in Scanning Tunneling Microscopy
Authors: Chen C. Julian
Published: March 2011

In this paper, we show that atomic resolution in scanning tunneling microscopy (STM) originates from pz or dz2 states on the tip. Consequently, only a limited selection of tip materials can provide atomic resolution: d-band metals, for example, Pt, Ir, Pd, Rh, W, Mo; semiconductors that tend to form p-like dangling bonds, for example, Si.
Theoretical Studies of GaAs on Si
Authors: Northrup John E.
Published: March 2011

The energies of various two-dimensional GaAs on Si films have been calculated using the first principles pseudopotential method and density functional formalism. For GaAs on Si(111), the structures formed by adding a bilayer of GaAs to Si(111)1×1:As are shown to have positive formation energies, even after exchange reactions which eliminate the interface dipole are allowed. For GaAs on Si(100), the dependence of the formation energy of the films on the chemical potentials of the atomic constituents has been calculated. In the limit where μAs=μAs(bulk), and assuming the films have equilibrated with a bulk GaAs reservoir (μGa + μAs = μGaAs (bulk)), the lowest energy film is found to be the Si(100)2×1:As surface. In the opposite limit, μGa=μGa(bulk), the lowest energy film is the Si(100)2×1:(GaAs) surface. A new metastable structure obtained by adding 1/2 monolayer of Ga to Si(100)2×l:As has been studied.
A Weak Beam Imaging Technique for the Characterization of Interfacial Roughness in (InGa)As/GaAs Strained Layer Structures
Authors: Yao J. Y. , Andersson T. G. , Dunlop G. L.
Published: March 2011

A transmission electron microscope weak beam imaging technique has been developed for the characterization of interfacial roughness in lattice strained (InGa)As/GaAs multiple layered structures. In this technique, the heterointerfaces of (100) type strained layers are imaged in an inclined projection with a g311 diffracted reflection at off-Bragg conditions which gives an enhanced contrast from variations in strained layer thickness. A calculation based on the kinematic theory of contrast was made in order to gain a better understanding of the contrast. The calculation suggests that the observed contrast is due to monolayer scale variations in thickness of the strained layers.
Structure of a Near-Coincidence Σ9 Tilt Grain Boundary in Aluminum
Authors: Mills M. J. , Thomas G. J. , Daw M. S. , Cosandey F.
Published: March 2011

A systematic study of the structure of tilt grain boundaries in aluminum has been initiated. High resolution transmission electron microscopy is being used to examine the interface structure of several bicrystals with <110> tilt axes. In this paper, we report the structure determination of a grain boundary close to the Σ9 (221) symmetric orientation. The grain boundary plane, which appears wavy at lower magnification, is actually composed of atomically flat microfacets. Two distinct, symmetric structures with (221) boundary planes have been identified within individual microfacets. These observations have been compared with structures calculated using the Embedded Atom Method. The semi-quantitative comparison between the observed and predicted grain boundary structures is accomplished using multislice image simulations based on the calculated structures. The results of these comparisons and the evaluation of the relative energies of the microfacets are discussed.
A Leed Study of Bismuth Overlayer Formation on InSb(110)
Authors: Guo T. , Wan K. J. , Ford W. K.
Published: March 2011

LEED and Auger electron spectroscopy have been used to studied the interface formation of bismuth on InSb(110). For the first time, well defined superstructures were observed at room temperature on metal/semimetal-III-V semiconductors. A (1×2) phase, at 0.5 ML bismuth coverage, and a (1×3) phase, at 0.4 ML bismuth coverage, appear with different thermal heat cycling. The dynamical origin of these phases is thought to be a repulsive interaction between overlayer chains due to the detailed geometry of the overlayer chain structure and to the overlayer induced strain field within the substrate.
A Mechanism for Solute Segregation to Grain Boundaries
Authors: Youyi Chu , Sanhong Zhan
Published: March 2011

Based an the local equilibrium among vacancies, solute atans and vacancy-solute atom complexes, a mechanism for solute segregation to grain boundaries is suggested for a alloy system with binding energy of complex S≫kT. A set of dynamic equations for grain boundary segregation is ived, which can describe both equilibrium and nonequilibrium segregations, as the effect of the equilibrium segregation is taken into account in the bonndary condition. Theoretical calculation is made by computer for boron segregation at austenite grain boundaries as functions of isothermal holding time, cooling rate and quenching teaperature, which agree well with experimental results.
Simulation and Quantification of High-Resolution Z-Contrast Imaging of Semiconductor Interfaces
Authors: Jesson D. E. , Pennycook S. J. , Chisholm M. F.
Published: March 2011

Incoherent characteristics of Z-contrast STEM images are explained using a Bloch wave approach. To a good approximation, the image is given by the columnar high-angle cross-section multiplied by the s-state intensity at the projected atom sites, convoluted with an appropriate resolution function. Consequently, image interpretation can be performed intuitively and quantitative simulation can be implemented on a small computer. The feasibility of ‘column-by-column’ compositional mapping is discussed.
Simulated Image Maps for Use in Experimental High-Resolution Electron Microscopy
Authors: O'Keefe Michael A. , Dahmen Ulrich , Hetherington Crispin J.D.
Published: March 2011

A “map” of all possible high-resolution images may be simulated for a crystalline specimen in a chosen orientation for any particular transmission electron microscope (HRTEM). These maps are useful during experimental high-resolution electron microscopy and make it possible to locate optimum imaging conditions even for foil thicknesses beyond the weak-phase object limit. Although defects such as grain boundaries are not generally periodic, image maps of perfect crystal can be used to optimize defect contrast during operation of the microscope by reference to the image of the perfect crystal neighboring the defect.
High-Resolution Imaging of Coga/GaAs and Eras/GaAs Interfaces
Authors: Zhu Jane G. , McKeman Stuart , Palmstrøm Chris J. , Carter C. Barry
Published: March 2011

CoGa/GaAs and ErAs/GaAs grown by molecular-beam epitaxy have been studied using high-resolution transmission electron microscopy (HRTEM). The epitactic interfaces have been shown to be abrupt on the atomic scale. Computer simulations of the HRTEM images have been obtained for different interface structures under various specimen and image conditions. Practical problems in the comparison between the simulated and experimental images are discussed.
High-Purity Germanium Crystal Growing
Authors: Hansen W. L. , Haller E.E.
Published: March 2011

The germanium crystals used for the fabrication of nuclear radiation detectors are required to have a purity and crystalline perfection which is unsurpassed by any other solid material. These crystals should not have a net electrically active impurity concentration greater than 10l0cm−3and be essentially free of charge trapping defects.

Such perfect crystals of germanium can be grown only because of the highly favorable chemical and physical properties of this element. However, ten years of laboratory scale and commercial experience has still not made the production of such crystals routine. The origin and control of many impurities and electrically active defect complexes is now fairly well understood but regular production is often interrupted for long periods due to the difficulty of achieving the required high purity or to charge trapping in detectors made from crystals seemingly grown under the required conditions.

The compromises involved in the selection of zone refining and crystal grower parts and ambients is discussed and the difficulty in controlling the purity of key elements in the process is emphasized. The consequences of growing in a hydrogen ambient are discussed in detail and it is shown how complexes of neutral defects produce electrically active centers.
Silicon Radiation Detectors - Materials and Applications
Authors: Walton Jack T. , Haller Eugene E.
Published: March 2011

Silicon nuclear radiation detectors are available today in a large variety of sizes and types. This profusion has been made possible by the ever increasing quality and diameter silicon single crystals, new processing technologies and techniques, and innovative detector design. The salient characteristics of the four basic detector groups, diffused junction, ion implanted, surface barrier, and lithium drift are reviewed along with the silicon crystal requirements. Results of crystal imperfections detected by lithium ion compensation are presented. Processing technologies and techniques are described. Two recent novel position-sensitive detector designs are discussed—one in high-energy particle track reconstruction and the other in x-ray angiography. The unique experimental results obtained with these devices are presented.
Silicon Material Growth for Nuclear Radiation Detectors
Authors: Glasow P. A. , Kolbesen B. O.
Published: March 2011

As a base material for semiconductor devices, silicon is more widely used than any other semiconductor. The physical properties, in particular the bandgap which is significantly larger than that of germanium, makes the material extremely important for electronic devices. The world's total annual production of silicon is at present some 2000 t [1]. Compared with this, the 10 kg/year of silicon that is used for detectors is rather modest. However, since work on semiconductor radiation detectors started 25 years ago, silicon in addition to germanium forms the centre of interest as the basis for production of nuclear radiation spectrometers, mainly as high energy particle detectors, but also as X-ray detectors.
High-Voltage Operation of Surface Barrier Silicon Detectors With a Side Groove
Authors: Ohkawa S. , Husimi K. , Kim C. , Kim Y. , Itoh D.
Published: March 2011

A remarkable characteristic of the surface barrier detector with a side groove cooled down to the nitrogen temperature has been observed. That is an abrupt decrease of the output noise at a definite voltage in increasing the bias voltage slowly. This is caused by a carrier injection from the side surface of the groove near the neck narrowed by the side groove. This excess noise disappears after the depletion layer goes through the neck of the side groove. This is confirmed by the fact that the capacitance of the detector decreases abruptly with the decrease of the noise at the same bias voltage. This detector is capable to be operated at a voltage higher than this voltage with a low noise. The maximum bias voltage applied to the detector is 3000 V.
The Fabrication of Mercuric Iodide Detectors for Use in Wavelength Dispersive X-Ray Analysers and Backscatter Photon Measurements
Authors: Howes John H. , Watling John
Published: March 2011

This paper describes the fabrication of mercuric iodide nuclear radiation detectors suitable for X and gamma ray spectrometry at room temperature. The active area of the detectors studied are between 0.2 and 1.5cm sq and they are up to 0.5mm thick. The method of producing a stable electrical contact to the crystal using sputtered germanium has been studied. The X-ray resolution of a 1.5cm sq. area detector at 32 keV is 2.3 keV FWHM when operated at room temperature in conjunction with a time variant filter amplifier. A factor which is important in the fabrication of the detector is the surface passivation necessary to achieve a useful detector life.

This type of detector has been used on a wavelength dispersive X-ray spectrometer for energy measurements between 10 and 100 keV. The advantages over the scintillation counter, more commonly used, is the improved resolution of the HgI2 detector and its smaller size. The analyser is primarily used for the detection of low levels of heavy metals on particulate filters. The detectors have also been used on an experimental basis for gamma ray backscatter measurements in the medical field.
-Search For a Correlation Between Stoichiometry,TSC Spectra and -NUclear Spectroscopic Capabilities of HCI2.
Authors: Tadjine A. , Gosselin D. , Koebel J.M. , Siffert P.
Published: March 2011

Mercuric iodide is, potentially, an interesting material for room temperature high efficiency gamma or X-ray spectroscopy. However, still several parameters limit the performance of these devices and even the crystal growth is not fully under control today, poor reproductibility being reached.An optimization of growth conditions seems difficult since no parameter of the material could be correlated with the spectrometer's performance. Therefore, the effective progress in recent years was rather limited.

The goal of this paper is to investigate systematically if a correlation can be found between bulk stoichiometry for crystal grown under certain conditions, thermally stimulated current (TSC) measurements and nuclear performance. In this study, two families of crystals could be identified. Best results are obtained for nearly stoichiometric materials, exhibiting a specific TSC spectrum. In particular, the peak appearing at 173 K constitutes a good indication of the detection capabilities of the material, both for spectroscopic resolution and polarization.

The growth conditions have been adjusted to produce in a fully reproducible way high performance devices.
The Characterization of Germanium and Silicon for Nuclear Radiation Detectors.
Authors: Darken L. S.
Published: March 2011

Semiconductor nuclear radiation detectors require deep depletion depths (0.03–3.0 cm) and effective charge collection distances which are several times longer than these depletion depths. These requirements place stringent limitations on the net electrically active impurity concentration, and on the concentration of deep centers which can trap carriers generated by the incident nuclear radiation. This need for extremely pure material distinguishes the interests and efforts of the semiconductor detector community from the rest of the semiconductor community. This paper reviews the characterization of shallow-level, deep-level, neutral, and extended defects in germanium and silicon for nuclear radiation detectors. Photothermal ionization spectroscopy has been used extensively to identify the residual hydrogenic impurities in high-purity (∣NA–ND∣ ≈ 1010–1011 cm−3 ) germanium and silicon. Deep level transient spectroscopy has been effectively used to detect and identify deeper levels in high-purity germanium. Residual neutral defects are not necessarily passive: they may complex to form deep or shallow levels, they may precipitate, or they may act as nucleation sites for precipitation. The properties of extended defects (dislocations, lineage, inclusions, precipitates) and their effects on device performance are fundamentally less well understood, as the origin of the electrical activity of these defects is uncertain. It has been found in numerous instances that chemical interactions among defects are important even in these high-purity semiconductors.
Structural Characterizations of Symmetrically Strained Sim Gen Superlattices
Authors: Bowman R. C. , Adams P. M. , Ahn C. C. , Chang S. J. , Arbet V. , Wang K. L.
Published: March 2011

Molecular beam epitaxy was used to grow Sim Gen superlattices on relaxed Si1-xGex buffer layers which symmetrize the strains between the heteroepitaxial layers. Samples with different superlattïce periodicities and individual layer thickness ratios were prepared. The compositions and defect structures of the GexSi1-x buffers have significant influence on the homogeneity and quality of the overlying superlattices. In particular, greater disorder was found in superlattice structures grown on Si0.5 Ge0.5 buffers than for those grown on buffer layers with significantly higher or lower Ge contents.
Modified Dislocation Structures in GexSi1-x Double Epilayers on (001)Si
Authors: Kvam Eric P.
Published: March 2011

Double epilayers of different compositions of GexSi1-x on (001)Si are observed to have dislocation contents which differ markedly from similar single epilayers. An initial epilayer, grown below its critical thickness, underwent substantial misfit dislocation introduction, while a second epilayer, grown at a composition where edge-type misfit dislocations are normally observed to dominate the morphology, contained mostly 60° type dislocations. It is suggested that dislocation entry into the upper, high mismatch epilayer allows many dislocations to enter the buried, low mismatch epilayer, and that this in turn affects the dislocation morphology in the upper layer through strain relief.
Time, Temperature and Strain Relaxation during Fabrication of Strained Heterostructures
Authors: Tsao J.Y. , Dodson B.W.
Published: March 2011

We present a simple example of the time evolution of temperature, excess stress and strain relaxation during growth and subsequent annealing of strained heterostructures.
Thermal Strain Study of Almost Lattice-Matched Epitaxial InuGa1-uAs1-vP1-v Films on InP(100) Substrates
Authors: Bai G. , Nicolet M-A. , Kim S.-J. , Sobers R.G. , Lee J.W. , Brelvi M. , Thomas P.M. , Wilt D.P.
Published: March 2011

Single layers of ~ 0.5µm thick InuGa1-uAs1-vPv (0.52 < u < 0.63 and 0.03 < v < 0.16) were grown epitaxially on InP(100) substrates by liquid phase epitaxy at ~ 630°C. The compositions of the films were chosen to yield a constant banndgap of ~ 0.8 eV (λ = 1.55 µm) at room temperature. The lattice mismatch at room temperature between the epitaxial film and the substrate varies from - 4 × 10-3 to + 4 × 10-3. The strain in the films was characterized in air by x-ray double crystal diffractometry with a controllable heating stage from 23°C to ~ 700°C. All the samples have an almost coherent interfaces from 23°C to about ~ 330°C with the lattice mismatch accomodated mainly by the tetragonal distortion of the epitaxial films. In this temperature range, the x-ray strain in the growth direction increases linearly with temperature at a rate of (2.0 ± 0.4) × 10-6/°C and the strain state of the films is reversible. Once the samples are heated above ~ 300°C, a significant irreversible deterioration of the epitaxial films sets in.
Rayleigh Acoustic waves in fcc/fcc Metallic Superlattices
Authors: Dutcher John R. , Lee Sukmock , Kim Jeha , Stegeman George I. , Falco Charles M.
Published: March 2011

The Rayleigh acoustic waves of sputter-deposited Cu/Co, Ag/Pd and Cu/Pd sup-erlattice films were studied using Brillouin scattering. All three of these systems are fcc/fcc superlattices. The dependence of the Rayleigh wave velocities for these films on the superlattice modulation wavelength is discussed.
Epitaxial growth of Cu-Ni Single Crystal Alloys and Multilayers by Molecular Beam Epitaxy
Authors: Burns R.P. , Lee Y.H. , Parikh N.R. , Posthill J.B. , Mantini M.J. , Markunas R.J.
Published: March 2011

Epitaxial growth of thin films, alloys, and multilayers from the Cu-Ni system are being explored as a means of fabricating a substrate to lattice match diamond. These single crystal films are superior to commercially available substrate material. Due to the high reactivity of the metal surfaces in atmosphere, all processing must be done under UHV conditions. In vacuo preparation, growth, and analysis of the metals is described.
Model for Epitaxial growth of Cobalt on CU(100)
Authors: Vvedensky Dimitri D. , Clarke Shaun
Published: March 2011

The epitaxial growth kinetics of Co on Cu(100) are investigated with a kinetic solid-on-solid model. Two effects are found to dominate the growth of this system reflecting the difference in surface free energies betweenthe two materials: the difference of diffusion parameters, and the inability of Co to wet Cu(100) at lower temperatures.
Kinetic Barriers to Strain Relaxation in GexSi1-x/Si Epitaxy
Authors: Hull R. , Bean J.C.
Published: March 2011

We discuss the kinetic barriers to misfit dislocation nucleation, propagation and interaction in lattice-mismatched GexSi1-x/Si epitaxy. Experimental real-time observations of the strain relaxation process via in-situ annealing experiments in a transmission electron microscope enable each of these processes to be separately studied. Quantitative parameters defining misfit dislocation processes may be derived; these are found to be highly dependent upon the structure geometry. The approximations involved in extending these measurements to a description of the relaxation process during growth are described in detail.
Growth and Characterization of Epitaxial CoSi2 on Si(001)
Authors: Jimenez J.R. , Hsiung L.M. , Thompson R.D. , Hashimoto Shin , Ramanathan K.V. , Arndt R. , Rajan K. , Iyer S.S. , Schowalter L.J.
Published: March 2011

The structural and electrical properties of epitaxial CoSi2, grown on Si(001) by molecular beam epitaxy, have been investigated. Most growth conditions successful on Si(111) have been found to result in misoriented grains when applied to Si(001). However, single-orientation (001) CoSi2 films, with low resistivities (16 µΩ-cm) and low ion channeling minimum yields (χmin=5%), have been obtained by direct codeposition of Co and Si at ~500°C at Co-rich stoichiometries. Single orientation (001) CoSi2 films have also been obtained by using a template method on epitaxially grown Si buffer layers, but the resistivities of these films have not been as good. A Schottky barrier height of 0.71 eV has been measured for single-orientation CoSi2(001)/Si(001). This is significantly higher than the barrier height of 0.64 eV for CoSi2(111)/Si(111).
Epitaxial Growth of TbSi2 on Si(111)
Authors: Kaatz F.H. , Graham W.R. , Van der Spiegel J.
Published: March 2011

We describe the epitaxial growth of TbSi2. In this study, terbium metal is evaporated onto (111) silicon and annealed to form terbium suicide, where the pressure during all procedures is maintained below 5×10-10 Torn The interdiffusion of terbium with silicon occurs at room temperature as determined by in-situ Auger electron spectroscopy. Low energy electron diffraction shows a sharp pattern of the hexagonal suicide after an 850°C anneal. Rutherford backscattering analysis indicates single-crystal growth with a channeling minimum yield of 7–8% for 120Å thick suicide films annealed to 800–900°C. These metal reacted films have pinholes with an average size of less than 0.5 µm and a fault structure along (220) silicon. Electrical measurements show metallic conduction with a room temperature resistivity of 110 µΩ-cm and evidence of magnetic ordering at 38K.
Solid Phase Epitaxy of GexSi1-x Alloys on [100] Si
Authors: Hong Q. Z. , Revesz P. , Yu A. J. , Mayer J. W. , Poate J. M. , Bean J. C. , Eaglesham D. J.
Published: March 2011

Solid phase epitaxy was studied in the GexSi1-x/[100] Si system in the composition range of 4% to 10% Ge. For strained samples regrowth rates decreased with increasing Ge concentrations, with an activation energy of 2.8 and 3.0 eV for the Ge4Si96 and Ge8Si92 alloys respectively. In contrast, the rates of the strain-relaxed samples increased compared with that of pure Si. The minimum yield of fully regrown samples with Ge concentrations lower than 8% recovered to that of the as-deposited samples. However, the minimum yield of a 3500 Å-thick Ge10Si90 alloy increased to 12 % after recrystallization.
Solid Phase Epitaxy of Si1-xGex on Si Strained Layers
Authors: Robinson B.J. , Chilton B.T. , Ferret P. , Thompson D.A.
Published: March 2011

Single strained layer structures of up to 30 nm of Si1-xGex. on (100) Si and capped with 30-36 nm of Si have been amorphized by implantation with 120 keV As . The amorphized region, extending to a depth of 130 nm, has been regrown by solid phase epitaxy (SPE) at 600°C. Characterization of the regrown structure by Rutherford backscattering/channeling techniques and transmission electron microscopy indicates that for x < 0.18 the SPE process results in the recovery of strain, while for x > 0.18 there is increasing strain relaxation and a deterioration of crystal quality.
Effects of Substrate Misorientation and the Growth Mechanism of Si Doped GaAs Grown on (111)A Substrate by MBE
Authors: Okano Y. , Seto H. , Shigeta M. , Nishine S. , Fujimoto I. , Suzuki T.
Published: March 2011

The MBE growth of Si doped GaAs on slightly misoriented (111)A substrates was examined. The conduction types and the carrier concentrations were greatly affected by the degree of substrate misorientation. In the growth on an exactly (111)A oriented substrate, substantially all Si atoms acted as acceptors. With increase of the degree of misorientation and/or with increase of the flux ratio (JAs4/JGa), the number of donor-site Si atoms increased, that is, the hole concentration first decreased by autocompensation of Si and then the conductivity reversed from p-type to n-type. The photoluminescence of highly compensated (111)A films showed characteristics of donor-acceptor pair recombination. A doping mechanism including preferential decomposition of As4 molecules at the steps was proposed.
Step Profile Fluctuations in Quantum-Well Wire Growth on Vicinal Surfaces
Authors: Hugill K.J. , Shitara T. , Clarke S. , Vvedensky D.D. , Joyce B.A.
Published: March 2011

Molecular-beam epitaxy of quantum-well wires on vicinal surfaces is studied by application of Monte Carlo simulations of a solid-on-solid model. Characterization of simulated quantum-well wires indicates an optimum regime within which the quality of the quantum-well wire is maximized. The model is extended to include observed anisotropies in GaAs growth on vicinal surfaces, and the conclusion is reached that better quality quantum-well wires may be grown on substrates misoriented from the (001) towards [110], rather than [110], due to relative step edge stability on the two misoriented surfaces.
Metalorganic Magnetron Sputter Deposition of In1-xGax on (100)GaAs
Authors: Rousina R. , Webb J.B. , Noad J.P.
Published: March 2011

This work reports for the first time, the epitaxial deposition of ln1-xGaxSb on (100)GaAs by Metalorganic Magnetron Sputtering. High quality films could be deposited on GaAs over the entire compositional range despite the large lattice mismatch between the film and substrate (14.6% for InSb and 7.8% for GaSb). The composition of the layers was found to be directly related to the trimethylgallium and trimethylindium fluxes at constant growth temperature. Growth rates of 1 µm/hr for the GaSb and 3 µm/hr for the InSb were observed.
Energetics and Relaxations of Adatom, Dopant and Vacancy Related Complexes on Normal and Strained GaAs(001) Surface
Authors: Ogale S.B. , Madhukar A. , Viswanathan R.
Published: March 2011

Surface complexes involving Ga and Si adatoms, Si dopant and As vacancies at the GaAs (001) surface are examined for their energetics and associated structural relaxations by employing semi-empirical two- and three-body potential energy functions. The energy minimization is achieved via the simulated annealing Monte carlo procedure. An 8 X 8 X 8 GaAs matrix is used with periodic boundary conditions in the lateral plane. The adatom, dopant or vacancy is added to the system after allowing the top two surface layers to reconstruct into a c (2 × 2) pattern. The suitably chosen neighborhood of the modified site is then allowed to relax to a minimum energy configuration. The complexes are studied for both the unstrained and strained surfaces.
Liquid Phase Electroepitaxial (LPEE) Growth of GaSb and GaInAsSb
Authors: Iyer Shanthi N. , Abul-Fadl Ali , Macrander Albert T. , H.Lewis Jonathan , Collis Ward J. , Sulhoff James W.
Published: March 2011

Liquid phase electroepitaxial technique has been used for the growth of GaSb and GalnAsSb in the composition range corresponding to peak band gap wavelengths of 1.7-2.28μm. The growth rate of these layers were examined as a function of current density. The growth rates of these layers are typically 0.8μm/min. at a current density of 10A/cm2. The quality of the layers was evaluated by x-ray diffraction and room temperature photoluminescence.