bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Lying Excitations and Local Motions in Na β-Alumina
Authors: Villa Marco , Bjorxstam John L.
Published: March 2011

We present an NMR study of sodium motion and distribution in Na β-alumina below 160K. The 23Na lineshape shows that a rearrangement of sodiums occurs near 100K. Below this “transition”, a fraction of the sodium ions undergo a local motion that is an efficient mechanism for 23Na spin-lattice relaxation in the interval 50÷80K. This motion does not have a major influence upon the 27A1 relaxation. Below 50K the low-lying excitations typical of glasses control the spin-lattice relaxation processes of 27AI and, to a certain extent, 23Na.
Mixed Alkali Effects in δ-Aluminas
Authors: Bjorkstam John L. , Villa Marco , Aldrovaidi Sergio , Corti Maurizio , Frye Jamies S.
Published: March 2011

This paper presents a NMR study of mixed alkali effects in δ-aluminas. It is shown that the BPP theory of relaxation does not describe the NMR results. However, with an elementary analysis of the data, NMR yields information about the cation dynamics which substantially agrees with the diffusion measurements.
Microscopic Study of Metal Hydrides using Electron Spin resonance
Authors: Venturini E. L.
Published: March 2011

Electron spin resonance (ESR) of dilute paramagnetic ions in nonmagnetic metallic hydrides provides microscopic information about the hydrogen ions in the immediate vicinity of the impurity. By comparing ESR spectra for different host metals and several hydrogen/metal ratios, one can determine material properties including host lattice symmetry, phase boundaries and occupation of available sites by hydrogen. Examples are presented of ESR of dilute Er in group IIIB and IVB metal hydrides, demonstrating the sensitivity and versatility of ESR as a spectroscopic technique.
MÖssbauer Effect Investigation of Hydrogen Rich Ternary Hydrides of YFe2 , DyFe2 and ErFe2
Authors: Viccaro P. J. , Niarchos D. , Shenoy G. K. , Dunlap B. D.
Published: March 2011

The hydrogen rich ternary hydride phases of RFe2Hx (R=Y Dy, Er) with x>4 have been investigated using 57Fe, 161Dy and 166Er Mössbauer spectroscopy and bulk magnetization. In all cases, the presence of hydrogen results in a dramatic reduction in the moment on Fe as well as the magnetic transition temperature. The data also imply a simultaneous weakening of the R-Fe magnetic exchange.
Laser-Pulse Melting of Hafnium-Implanted Nickel Studied with Tdpac and Rbs/Channeling Techniques
Authors: Buene L. , Kaufmann E. N. , Mcdonald M. L. , Kothaus J. , Vianden R. , Freitag K. , Draper C. W.
Published: March 2011

The perturbed angular correlation technique has been applied to study the local environment of tantalum in nickel after ion implantation of hafnium and after laser-pulse melting. The magnetic hyperfine interaction at the daughter nucleus tantalum in nickel is used to determine the uniqueness of the tantalum lattice site. Several hafnium concentrations were employed and auxiliary measurements using ion-beam channeling, Rutherford backscattering and Auger electron spectroscopy were performed.
The Electric Field Gradient in Noncubic Metals and Alloys
Authors: Witthuhn W. , De U. , Engel W. , Hoth S. , Keitel R. , Klinger W. , Seeböck R.
Published: March 2011

The electric field gradient (efg) present in noncubic solids causes an energy–splitting of the nuclear levels via the quadrupole hyperfine interaction. During the last few years the perturbed angular correlation method has proved a unique experimental tool for investigating this interaction especially in metals. The basic principles of the method are discussed. Recent experimental results are given for pure metals and highly diluted systems as well as for alloys and intermetallics. The last section deals with theoretical aspects of the temperature dependence of the efg in pure metals.
Magnetic Resonance as a Probe of Anisotropic Conductors
Authors: Clark W. G.
Published: March 2011

A review is given of the wide range of magnetic resonance methods used to study the special properties of quasi onedimensional (1-d) conductors. Specific examples are presented which show how magnetic resonance methods have been exploited (a) to tell if the conduction is 1-d, (b) to locate the conduction electrons on a molecular distance scale, (c) to probe the unusual effects of disorder in 1-d conductors, (d) to study the charge density wave transition, and (e) to verify exotic electrical transport mechanisms, such as charged solitons in trans-(CH)x.
Nmr and Mössbauer Effect Studies on Diluted Heisenberg Ferromagnets and Spin-Glasses: EuxSr1−xS
Authors: Lütgemeier H. , Sauer Ch. , Zinn W.
Published: March 2011

The systematic variations of experimentally determined exchange and hyperfine (h.f.) interactions between Eu2+ ions are compared firstly within the EuX (X=0,S,Se,Te) series of compounds and secondly in the magnetic dilution system EuxSr1−xS. Reasonably relations can be established between the individual nearest and next nearest neighbour exchange interactions (J1,J2 ) and the transferred h.f. interactions (ΔB1 , ΔB2 ), respectively, by considering their variations with the Eu–Eu distances (R1,R2). Using these results, the measured mean hyperfine field, BI(x), and the ferromagnetic saturation h.f. field, B↑↑ (x), of the EuxSr1−xS system can be related reasonably well to the ferro- and paramagnetic phase boundaries, Tc(x) and θ (x), respectively.
Nuclear Spin Relaxation Investigations on the Influence of Impurities and Temperature on the Mean Free Path of Mobile Dislocations in Nacl
Authors: Alsem W. H. M. , Th. J. , De Hosson M. , Tamler H. , HackelÖEr H. J. , Kanert O.
Published: March 2011

Dislocation motion in alkali halide single crystals is strongly impeded by the presence of impurities, apart from obstacles built by the forest dislocations. The mean free path L of stepwise moving dislocations is measured by determination of the spin-lattice relaxation rate 1/T1ρ as a function of the strain rate έ, varying the content of impurities and the temperature. The latter influences the distribution of the point defects and the activation rate of dislocations before obstacles, while the former merely shorten L, thereby raising 1/T1ρ.
μ+e-Hyperfine Interactions in Quartz Crystals
Authors: Brewer J.H. , Fleming D.G. , Spencer D.P.
Published: March 2011

Longitudinal muonium spin relaxation/modulation in zero magnetic field (zf-MSR) has been used to study muonium (μ+e-) atoms in single-crystal α-quartz between 5 K and room temperature. At 6 K, three frequencies are observed, corresponding to a triaxial hyperfine matrix whose principal values are close to those observed for hydrogen atoms frozen into known sites. For intermediate temperatures the Mu atoms “hop” between sites, causing a relaxation whose rate first increases with the hop rate and then decreases due to motional narrowing. Finally, at room temperature, a single-frequency oscillation is observed, corresponding to a uniaxial motionally-averaged hyperfine interaction.
The Motionally Narrowed Nmr Line Shape of Ammonium Selenate,
Authors: Yao Ching , Hallsworth R. , Lowe I. J.
Published: March 2011

The proton free induction decay f(t) of ammonium selenate is measured from temperatures of no apparent effects of lattice motion (−185°C) upon f(t), to substantial motional effects (−145°C) upon f(t). Our measured results are consistent with a classical hindered rotational motion of the ammonium group. The deviation of f(t) from the rigid-lattice fid fo(t) can be expanded in a Taylor series as

From the Δ1f(t) data, a3 and a4 are derived, and they are well fitted by the simple relations

where ν is the jump frequency of the rotational motion, T1r is the rotating-frame spin-lattice relaxation time, and ω1 the strength of the rotating magnetic field in frequency units. α, C3 and C4 are calculable constants of order unity.
Impurity Diffusion by NMR
Authors: Beckett James R. , Pourquié Jean , Ailion David C.
Published: March 2011

ABSTRIACT

We discuss a recently developed technique for studying the diffusion of spins with a small gyromagnetic ratio and apply it to investigate the nature of Ag+diffusion in AgF. We also investigate the potential application of this technique to the observation of diffusing impurities. Experimental studies on Cu:3% Al and (P2O5).8(Li2O).2 glass are described.
Use of a Native Oxide of AlxGa1−xAs in the Fabrication of Integrated Laser/Modulators
Authors: Burton R.S. , Schlesinger T.E.
Published: March 2011

A planar self-aligned process for fabricating integrated lasers and modulators is described. This process employs a native oxide of AlxGa1−xAs to form the waveguide structure and dielectric passivation layer. Wet oxidation of AlxGa1−xAs is being investigated to determine possible processing parameters that result in good quality oxides and a reliable fabrication process. Variations in the mechanical properties were observed with changes in processing parameters.
Many Body Effects in Strained Quantum Well Lasers
Authors: Banerjee S. , Srivastava A. K. , Bandyopadhyay A. , Chand N.
Published: March 2011

Unusually large transverse magnetic component has been observed at energy corresponding to the edge of heavy hole band in the optical emission from unstrained and strained layer single quantum well lasers above threshold condition. The existing model of Fermi sea shake-up is inadequate to explain the enhancement in the TM component beyond lasing threshold. Our results indicate that under lasing conditions the directional properties of the emitting dipole arising from electronic transitions to the heavy hole band is modified such that the dipole moment has equal projections in x, y and z directions.
Fabrication Techniques for GaAs Based HBTS and FETs
Authors: Ren F.
Published: March 2011

Process technologies for self-aligned AlGaAs/GaAs and lnGaP/GaAs heterojunction bipolar transistors (HBTs) as well as dry etching fabrication schemes for submicron AlGaAs/GaAs based field effect transistors (FETs) are presented. Multiple energy F+ and H+ ions were used to isolate the active devices for HBTs. The resistance of test wafers at 200 °C showed no change over periods of 50 days. Highly selective dry and wet etch techniques for InGaP/GaAs and AlGaAs/GaAs material systems were used to uniformly expose junctions. Reliability of the alloyed ohmic contact and feasibility of the non-alloyed ohmic contact metallizations for both p and n type GaAs layers will be discussed. The reproducible gate recess etching is one of the critical steps for AlGaAs/GaAs based FETs. The etching selectivity, damage, pre and post-clean procedure were studied in terms of device performance. A simple low temperature SiNx deposition and an etch-back process with optical stepper were used to demonstrate 0.1 μm Y-shape gate feature.
Magnetron Dry Etching for Photonic Device Fabrication
Authors: Arnot H. E. G. , Zappe H. P. , Epler J. E. , Graf B. , Widmer R. , Lehmann H. W.
Published: March 2011

Magnetron dry etching using SiCl4, combined with a smooth reflowed photoresist masking technique has been used to fabricate GaAs/AlGaAs ridge waveguides. The effect of pressure, flowrate and power on etch rate and sidewall smoothness has been studied. Waveguides fabricated using optimum parameters exhibited optical losses lower than those achievable using wet etching. This process was further used in the fabrication of Fabry Perot ridge lasers, detectors and phase modulators.
Schottky Contacts Formed on Phosphidized InGaAs
Authors: Sugino Takashi , Sakamoto Yoshifumi , Ninomiya Hideaki , Matsuda Koichiro , Shirafuji Junji
Published: March 2011

The surface of InGaAs (In 53 %) lattice-matched to InP has been phosphidized using phosphine plasma. X-ray photoelectron spectroscopy analysis indicates that substitution of phosphorus for arsenic and deposition of phosphorus layer occur due to phosphidization. Formation of indium and arsenic oxides is suppressed at the phosphidized surface of InGaAs, while phosphorus oxide is observed. Tunneling metal-insulator-semiconductor type Schottky contacts are formed on phosphidized InGaAs by evaporating various metals such as Au, Cu, Ti and Al. An effective barrier height as high as 0.7 eV is evaluated from the room temperature current-voltage characteristic for Au/InGaAs Schottky contacts. The true barrier height estimated from the Richardson plot varies depending on the metal work function.
Behavior of Zinc During Formation of Au(Zn) Ohmic Contacts to P-Type GaAs
Authors: Kamińska E. , Piotrowska A. , Mizera E. , Zarecka R. , Adamczewska J. , Dynowska E.
Published: March 2011

The reactions between (100) GaAs and Au, Zn, and Au(Zn) ohmic contact metallization have been investigated by the use of transmission electron microscopy and x-ray diffraction. Emphasis is placed on the particular role of Zn during consecutive stages of the formation of an ohmic contact to p-GaAs. The most significant feature of the interaction of Zn with GaAs is the penetration of Zn atoms into the native oxide, which remains at the surface of GaAs after chemical treatment. Moreover, the presence of Zn in Au-based metallization is found to considerably suppress the thermally induced growth of metallization grains, making the microstructure of the contact virtually intact upon annealing at temperatures up to 460°C.
Low Contact Resistivity Mn/Au/Ti/Pd/Au P-Ohmic Contacts for HBTs
Authors: Vetanen B. , Haynes C. , Prasad S.J. , Beers I. , Park S.
Published: March 2011

Obtaining good p-ohmics to the base layers of AlGaAs/GaAs HBTs have been difficult due to metal spiking and instability of the contacts to subsequent processing temperatures. To avoid spiking, non-alloyed contacts have been traditionally used. In this paper, we present a stable, non-spiking, low contact resistivity alloyed p-ohmic contact to HBT structures.
Current Transport in Low-Resistance Metal-InP Contacts
Authors: Clausen Thomas , Leistiko Otto
Published: March 2011

The limiting transport processes for current flow across metal-semiconductor (MS) ohmic contacts to n- and p-type InP have been investigated for Au-based metallizations containing the doping elements Germanium and Zinc. It has been found that the Schottky barrier is lowered and in some cases vanishes during annealing. The current flow for an optimal ohmic contact is diffusion limited by a Fermi potential difference between the alloyed metallization and the bulk InP. For non-optimal ohmic contacts the current flow is also limited by thermionic emission across a low effective Schottky barrier.
Unexpected Penetration of AuGe/Pt Metal into a Interface Between a Atmospheric Chemical Vapor Deposition Silicon Dioxide Film and GaAs Wafer Surface
Authors: Saito Yasuyuki
Published: March 2011

It was observed that thin metal (catalytic metal: platinum) penetrated into a interface between a chemical vapor deposition (CVD) silicon dioxide film and a Si–implanted electric thermal furnace, on the way to carrying out experiments on alloyed ohmic–metals with Si–implanted electrically conductive n–type GaAs crystal layers in order to obtain stable and uniform ohmic contact electrodes of low specific ohmic contact resistances for metal–semiconductor field–effect–transistor arrays as a observation tool of semi–insulating GaAs–crystal crystallographic uniformity.
Differences of Damage Production in GaAs and InP after MeV and Low Energy Ion Implantation
Authors: Wendler E. , Bachmann T. , Wesch W.
Published: March 2011

Ion implantation induced damage production in GaAs and InP is investigated using Rutherford backscattering spectrometry in combination with channeling techniques and near-edge optical measurements. 200 keV and 1.6 MeV Ar+ ions are implanted at room temperature in GaAs and InP with ion doses varying between 2 × 1012 cm−2 and 3 × 1015 cm−2. Our results show that InP behaves similar for the two implantation energies and no influence of energy loss in electronic processes is found. In GaAs in the region of maximum nuclear energy deposition almost no difference in the damage production occurs for the two implantation energies. But for 1.6 MeV Ar+ implantation within the first 500 nm the defect concentration is very low in comparison to the nuclear energy deposition, which may be the consequence of ionizationinduced defect annealing and/or of the fact that in this depth region the amount of nuclear energy deposition is less than a critical value being necessary for the production of heavily damaged and amorphous zones.
Thermal Equilibrium Concentrations and Effects of Ga Vacancies in n-TYPE GaAs
Authors: Tan Teh Y. , You Homg-Ming , Gösele Ulrich M.
Published: March 2011

We have calculated the thermal equilibrium concentrations of the various Ga vacancy species in GaAs. That of the triply-negatively-charged Ga vacancy, V3Ga has been emphasized, since it dominates Ga self-diffusion and Ga-Al interdiffusion under intrinsic and ndoping conditions, as well as the diffusion of Si donor atoms occupying Ga sites. Under strong n-doping conditions, the thermal equilibrium V3Ga concentration, CeqvGa.3−(n), has been found to exhibit a temperature independence or a negative temperature dependence, in the sense that the CeqvGa.3−(n) value is either unchanged or increases as the temperature is lowered. This is contrary to the normal positive temperature dependence of point defect theerqmal equilibrium concentrations, which decreases as the temperature is lowered. This CeqvGa.3−(n) property provides explanations to a number of outstanding experimental results, either requiring the interpretation thatV3−Ga has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect non-equilibrium phenomena. Furthermore, there exist also a few quantitative data which are in agreement with the presently calculated results.
Energetics of Impurity-Free Vacancy-Mediated Disordering of AlGaAs/GaAs Superlattices
Authors: Olmsted B.L. , Houde-Walter S.N.
Published: March 2011

We report on a systematic study of impurity-free Al-Ga interdiffusion in AlGaAs/GaAs superlattices in sealed ampoules. Three ambients were explored: along the Ga-rich solidus, with no excess Ga or As in the evacuated ampoule, and with excess As less than that required to reach the As-rich solidus limit. In each of the ambients the Arrhenius dependence of the Al-Ga interdiffusion coefficient is represented by a single activation energy throughout the temperature range investigated (700-1050 °C). These results were obtained using four structures with superlattice periods ranging from 90 to 520 Å. Excellent agreement was obtained between the Al-Ga interdiffusion coefficients measured using superlattices on Sidoped and undoped GaAs substrates. With proper normalization to a constant As overpressure, PAs4 = 1 atm, the Ga- and As-rich activation energies are 3.26±0.12 eV and 4.91±0.23 eV, respectively. These activation energies are in the range predicted for Al-Ga interdiffusion mediated by group Ill-vacancy second nearest-neighbor hopping. The increase in energy when going from Ga- to As-rich conditions is attributed to a shift in the Fermi-level position towards the valence band with an increase in the ionized group Ill-vacancy concentration.
Si-Induced AlGaAs/GaAs Superlaitce Disordering Using a Grown-In Impurity Source and the Effects of Annealing Ambient
Authors: Olmsted B.L. , Houde-Walter S.N.
Published: March 2011

We report on a study of the role of defect diffusion from the crystal surface in the disordering of a multiple quantum well structure that was Si-doped during MBE growth. The distribution of native defects was inferred from correlating the results of photoluminescence spectroscopy, secondary ion mass spectrometry, and electrochemical C-V profiling. No significant change was observed between the Al-Ga interdiffusion coefficients of Si-doped and undoped superlattices when annealed with excess Ga. This is attributed to the lack of a source of group III vacancies. Furthermore, only a small fraction of the enhancement predicted for the Si doping was observed when excess As was used instead. The largest Fermi-level enhancement was observed when no excess Ga or As was included in the evacuated ampoule. The results indicate that the crystal surface was the source and sink of the native defects known to mediate the Al-Ga interdiffusion. Furthermore, significant electrical compensation of the donors was observed after both As- and Ga-rich anneals. This is attributed to ionized group III vacancy generation in the former case, and Si atoms moving from group In to V sites in the later.
Investigation of Carbon Incorporation into GaAs by TEGa-AsH3 Based Low Pressure Metalorganic Chemical Vapor Deposition
Authors: Feng M. S. , Chen H. D. , Wu C. H.
Published: March 2011

Heavily Carbon doped GaAs(l×1018−1×1020cm−3 ) grown by low pressure metalorganic chemical vapor deposition(LPMOCVD) using triethylgallium(TEGa), arsine(AsH3) as sources and liquid carbon-tetrachoride(CCI4) as dopant has been investigated. The carrier concentration was verified at various growth temperatures, V/III ratios and CCI4 flow rates. Dopant concentration first increased from 550°C and reached a maxium at 570°C and then decreased monotonously. Carbon incorporation was strongly enhanced when V/III ratio was less than 30 at Tg=590°C or less than 40 at Tg=630°C. Hole concentration increased and then decreased as CCI4 increased. The doping efficiency of epitaxtial layers grown on(100) substrate was higher than that on 2° off toward <110> misoriented substrate. Carbon doped GaAs films had higher Hall mobility than zinc doped GaAs films at high doping level due to less self-compensation. The highest dopant concentration in this system was 2.3×1020cm−3 at Tg=580°C and V/III=10.
Capacitance-Voltage-Method Carrier Concentration Depth Profiles in Liquid-Encapsulated-Czochralski-Technique Grown GaAs Wafers from Near-Stoichiometric and Extremely-Composition Melts
Authors: Saito Yasuyijki , Nishio Jhoji
Published: March 2011

It was observed that carrier concentration depth profiles under 200μm-diameter gold Schottky electrodes of deeply Si-implanted electrically active layers on undoped semi-insulating GaAs wafers depend on melt composition of liquid-glass encapsulation Czochralski technique (LEC) growth, Fourier-transformed infrared (FT-IR) measurement carbon content of LEC growth, and consecutive cooling thermal cycle of LEC growth. In the range of this experiment, for head position of boules and 2.5 × 10exp.12/cm2 Si dosage, peak carrier concentrations of As-rich melt LEC growth (initial: [As]/([As]+[Ga])≃0.526) were comparable to or slightly higher than those of near-stoichiometric melt LEC growth. For tail position and 3 × 10exp.12/cm2 Si dosage, a peak carrier concentration of a father As-rich melt LEC-growth was clearly higher than that of Ga-rich melt LEC-growth. LEC-grown melt composition effect depended on consecutive cooling thermal cycle. For peak carrier concentration dispersion of head position, there was anticorrelation between carbon content of FT-IR measurement and peak carrier concentration dispersion.
Junction Formation in Silicon by Rapid Thermal Annealing
Authors: Fair Richard B.
Published: March 2011

The feasibility of using isothermal RTA in annealing ion implanted layers for forming junctions has been investigated for the past 10 years. While many of the scientific details surrounding defect formation, transient diffusion and dopant activation remain to be clarified, RTA intrinsically is a viable annealing process which is essential for fabricating advanced silicon devices.
Rapid Thermal Processing for Strained-Layer Semiconductor Devices
Authors: Zolper John C. , Myers David R.
Published: March 2011

Strained-layer semiconductors have revolutionized modern heterostructure devices by exploiting the modification of semiconductor band structure associated with the coherent strain of lattice-mismatched heteroepitaxy. The modified band structure improves transport of holes in heterostructures and enhances the operation of semiconductor lasers. Strainedlayer epitaxy also can create materials whose band gaps match wavelengths (e. g. 1.06 μm and 1.32 μm) not attainable in ternary epitaxial systems lattice matched to binary substrates. Other benefits arise from metallurgical effects of modulated strain fields on dislocations.

Lattice mismatched epitaxial layers that exceed the limits of equilibrium thermodynamics will degrade under sufficient thermal processing by converting the as-grown coherent epitaxy into a network of strain-relieving dislocations. After presenting the effects of strain on band structure, we describe the stability criterion for rapid-thermal processing of strained-layer structures and the effects of exceeding the thermodynamic limits. Finally, device results are reviewed for structures that benefit from high temperature processing of strained-layer superlattices.
Fabrication/Characterization of a Pseudomorphic Ga0.1In0.9P/InP MESFET
Authors: Feng M. S. , Hsin Y. M. , Wu C. H.
Published: March 2011

A pseudomorphic Ga0.1In0.9P/InP MESFET grown by low pressure metalorganic chemical vapor deposition(LP-MOCVD) has been fabricated and characterized. The results indicated a transconductance of 66.7 ms/mm and a saturation drain current (Idss) of 55.6 mA have been achieved; furthermore, the Schottky barrier on InGaP as high as 0.67eV can be obtained using Pt2Si as the gate material. For comparison, a conventional InP MESFET with 5μm gate length has also been fabricated on InP epitaxial layer grown by low pressure metalorganic chemical vapor deposition on Fe-doped semi-insulating InP substrate. The transconductance and Idss were found to be 46.7 mS/mm and 43.1 mA at zero gate, respectively, for the depletion mode n-channel MESFET with Au as the gate metal; whereas, for the MESFET using Pt2Si as the gate metal, a transconductance of 40.3 mS/mm and a saturation drain current of 41.1 mA at zero gate bias have been obtained. The results indicated that Ga0.1In0.9P/lnP MESFET has better performance than InP MESFET because of higher energy gap of Ga0.1In0.9P.
Evaluation of Electrical Contact Material Stability on Mercuric Iodide
Authors: Cheng A. Y.
Published: March 2011

Mercuric iodide detectors are leading candidates for room-temperature radiation detection applications. The inherently reactive nature of mercuric iodide limits the number of materials suitable for fabrication of electrical contacts. The theoretical stabilities of elemental contact materials on mercuric iodide were evaluated at 25°C. Additionally, the stabilities of transparent conductive compounds, for photodetector applications, were studied. Calculations were based on Gibbs free energy data, estimates and a series of hypothesized reactions with mercuric iodide. Leading candidate materials were identified and compared to experimental results.
Investigation of Deep Levels In X-Ray Detector Material With Photo Induced Current Transient Spectroscopy (Picts)
Authors: Eiche C , Fiederle M , Weese J , Maier D , Ebling D , Benz K W
Published: March 2011

Deep levels have a great influence on the recombination behavior of the free carriers in semiconductors. For several years PICTS has been used to investigate the deep levels in high resistivity material such as GaAs or CdTe used in detector applications. An important feature of the PICTS measurements is the analysis of the current transients after pulse excitation. We propose using a new method based on Tikhonov regularization. This method was implemented in the program FTIKREG (Fast Tikhonov Regularization) by one of the authors. The superior resolution of the regularization method in comparison to conventional techniques is shown using simulated data. Moreover, the method is applied to investigate deep levels in CdTe:Cl, SI-GaAs and GaAs:Cr samples used for room temperature radiation detectors. A relation between deep level properties and detector performance is proposed.
Electrical Properties of Natural Iia Diamonds Using Photo- and Particle Excitation
Authors: Pan L. S. , Han S. , Kania D. R. , Gan K. K. , Zhao S. , Kagan H. , Kassa R. , Malchow R. , Morrow F. , Palmer W. F. , White C. , Kim S. K. , Sannes F. , Schnetzer S. , Stone R. , Thomson G. B. , Sugimoto Y. , Fry A. , Kanda S. , Olsen S. , Franklin M. , Ager J. W. , Pianetta P.
Published: March 2011

Two complementary techniques are used to study the electrical transport properties related to the use of diamonds as materials for ionizing radiation detectors. Transient photoconductivity using soft x-rays is used to probe the first few microns of the material, while ionizing particle-excited conductivity is used to probe the entire bulk of the material (1 millimeter). Both techniques measure the mean drift distance of free carriers, or the collection distance d. In addition, transient photoconductivity is able to extract the lifetimes and mobilities of the excited carriers. The collection distance measured by the two methods are in agreement, suggesting the material is homogeneous. At an applied field of 10 kV/cm, d is 25 to 30 microns, and, up to a field of 25 kV/cm, d has not saturated. The lifetime varies between 100 and 600 ps, and the mobility varies between 1000 and 4000 cm2/V-s, the range due to natural variations from sample to sample. The primary defects limiting the lifetime are believed to be nitrogen impurities and dislocations.
Diamond Doping by Low Energy Ion Implantation During Growth
Authors: Jamison K.D. , Schmidt H.K. , Eisenmann D. , Hellmer R.P.
Published: March 2011

A novel method of implanting dopant material in diamond using low energy ions during growth is described. In this method, relatively low energy (∼10 KeV) dopant ions are directed through an aperture into a hot filament chemical vapor deposition growth chamber and onto the growing diamond sample. Collisions with the gas molecules in the growth chamber (∼10 Torr of a 99.5% H2 - 0.5% CH4 gas mixture) partially neutralize the ion beam and slow the dopant atoms down to a few hundred electron volts before striking the growing diamond crystal. The residual energy is large enough to embed the dopant atoms a few layers deep in the crystal but not large enough to cause significant lattice damage. Continued doping during growth yields uniformly doped material throughout the implanted region. Results for sodium, rubidium, and phosphorus atom doping are presented with sodium found to be a p-type dopant and phosphorus a deep n-type dopant.
Experimental Results in Picosecond and Subpicosecond Range of IIa Type Diamond Detector in X-UV, Visible and Ir Fields
Authors: Nail M , Gibert Ph. , Miquel J.L. , Cuzin M.
Published: March 2011

Type IIa diamonds present photoconductive properties as well in X-ray detection range, as in near UV, visible, IR light range, in spite of the large bandgap of the material. Experimental results in these four fields, time measurements in picosecond and subpicosecond ranges are presented.
X-Ray Studies of Synthetic Radiation-Counting Diamonds
Authors: Yacoot Andrew , Moore Moreton , Makepeace Anthony
Published: March 2011

Synthetic diamonds with a nitrogen content less than 100ppm may be used as radiation dosimeters in a conduction counting mode, and are especially useful in medical applications. Crystal imperfections, revealed by X-ray diffraction topography, were found to affect counting performance. The best quality diamond gave the highest photocurrent (500nA at 50 V mm−1 and 2.75 Gy min−l). Diamonds containing dislocations had lower photocurrents but had the advantage of shorter settling times (seconds rather than minutes). Placing contacts on two opposite cube {100} faces gave a higher photocurrent than on a pair of octahedral {111} faces. Higher photocurrents were also achieved when the majority of dislocations were perpendicular rather than parallel to the electric field. Some recommendations for selecting synthetic diamonds for dosimeters are given.
New Compound Semiconductor Materials for Nuclear Detectors
Authors: Squillante Michael R. , Zhang John , Zhou Chuxin , Bennett Paul , Moy Larry
Published: March 2011

In many instances, the ability of scientists and engineers to make nuclear radiation measurements is only limited by the properties of available radiation detectors. Because of this, research into new semiconductor materials for radiation detection has been, and continues to be, a very active field. This article reviews recent research on several promising “new” materials.
Variable Angle Spectroscopic Ellipsometry Studies of HgI2
Authors: Yao Huade , Johs Blaine
Published: March 2011

Variable angle spectroscopic ellipsometry (VASE) measurements were employed to study the optical properties of HgI2. The bulk crystal HgI2 surface was subjected to a 10% KI etching prior to the VASE measurements. SE measurements were performed at room temperature, in air with several different angles of incidence. The uniaxial anisotropic nature of the HgI2 crystal was treated in the VASE analysis. Anisotropic dielectric functions of single crystal HgI2, ε||(wo) and ε⊥(ω), for optical electric field vector oriented parallel and perpendicular to the c axis, respectively, were obtained in the range of ∼2.0 - 5.0 eV. Surface aging effects of the HgI2 crystal, after the 10% KI etching, were characterized by VASE.
Physical-Chemical Considerations for Semiconductor Room-Temperature Radiation Detectors
Authors: Schieber M. , Hermon H. , Roth M.
Published: March 2011

Physical properties of large band gap semiconductors such as: HgI2, CdTe, Cd0.8Zn0.2Te, CdSe, Cd0.7Zn0.3Se, GaAs, PbI2 and TlBr are briefly reviewed and discussed in terms of their use as room temperature operating x-ray and gamma ray radiation detectors. It is shown that HgI2 which has the largest drift length for holes, λ=μτE i.e., the product of the mobility μh, life time τh and the electrical field E, is at present the leading material, being followed by the newly developed Cd0.8Zn0.2Te. Chemical defects in HgI2 were enhanced by doping the material with aliphatic, aromatic and oxyhydrocarbons as well as with excess Hg and I2 and the increase in unit cell parameter was studied as a function of the amount of dopant. The value of τ was measured as a function of dopant concentration and it was found that Hg doping causes the most severe trapping defects. Low temperature studies of τh down to 170K allowed the identification of the trapping energy levels and concentration of electrically active defects. Shallow traps of 0.13-0.18 eV stemming from deviation from stoichiometry of H-gI2 were found to be in the ppm level whereas deeper traps of 0.4-0.5 eV stemming from hydrocarbons were found to be in the ppb level. It is concluded that only extensive research on the physical, chemical and structural defects correlated with improved crystal growth and device fabrication methods, would lead, in the future, to improvements in λh also of the other large Eg semiconductor detector materials.
Analysis of Deep Levels in GaAs Detector Diodes Using Impedance Spectroscopy
Authors: Eiche C , Fiederle M , Weese J , Maier D , Ebling D , Ludwig J , Benz K W
Published: March 2011

Impedance or admittance spectroscopy has been shown to be a very convenient tool for the investigation of deep levels in semiconductor junctions. At constant temperature a frequency sweep is performed. After that the impedance signal is analysed by a regularization method based on Tikhonov regularization in order to obtain the thermal relaxation times of the deep levels present in the junction. The high resolution of the regularization method in comparison to conventional techniques is demonstrated using simulated data. The temperature dependence of the thermal relaxation times provides information about the properties of the deep levels such as activation energy or capture cross section. Two donor levels with activation energies dE1 =0.58 eV and dE2 =0.68 eV are observed in our detector diodes. It can be shown that the concentration of level 2 is increased after irradiation.
Experimental Results from γ-irradiated GaAs Crystals Grown with Different Techniques
Authors: Bencivelli W. , Bertolucci E. , Bottigli U. , Cavallini A. , D'Auria S. , Via C. Da , Papa C. Del , Fantacci M.E. , Rosso V. , Stefanini A. , Stefanini G.
Published: March 2011

Gallium Arsenide crystals are among the most efficient detectors of X-rays at room temperature. Different GaAs crystals have been irradiated with photons from radioactive sources, to compare their response in view of a possible application for Digital Radiology. The detectors have been obtained by various manufacturers and with different techniques (LEC and LPE crystals). Experimental results include I-V curves, charge collection efficiency and detection efficiency as a function of bias. A comparison is made with a simulation program.
Defect Reduction in Cd1−xZnxTe Epilayers on GaAs Substrates
Authors: Chadda Saket , Malloy Kevin , Reno John
Published: March 2011

Cd0.91Zn0.09Te/CdTe multilayers of various period thicknesses were inserted into Cd0.955Zn0.045Te bulk alloys grown on (001) GaAs. The net strain of the multilayer on the underlying Cd0.955Zn0.045Te was designed to be zero. X-ray diffraction full width at half maximum (FWHM) was used as a means to optimize the period thickness of the multilayer. Transmission electron microscopy of the optimum period thickness samples demonstrated four orders of magnitude decrease in the threading dislocation density. Mechanism of bending by equi-strained multilayers is discussed.
Direct Heteroepitaxial Growth of ZnTe(100) and CdZnTe(100)/ZnTe(100) on Si(100) Substrates by MBE
Authors: Lyon T. J. de , Johnson S. M. , Cockrum C. A. , Wu O. K. , Roth J. A.
Published: March 2011

Epitaxial films of ZnTe(100) and CdZnTe(100)/ZnTe(100) have been deposited by molecular-beam epitaxy onto Si(100) substrates misoriented from 0-8 degrees towards the [011] direction. The films were characterized with x ray diffraction, photoluminescence spectroscopy, optical microscopy, and stylus profilometry. Through use of ZnTe buffer layers, single crystal CdZnTe(100) films have been demonstrated on both 4° and 8° misoriented Si with structural quality comparable to that obtained with GaAs/Si composite substrates. X ray rocking curves for ZnTe(400) with FWHM less than 300 arcseconds and for CdZnTe(400) with FWHM less than 160 arcseconds have been obtained for as-grown films. The observed surface morphologies are superior to those obtained on GaAs/Si composite substrates. HgCdTe(100) films with x ray FWHM as low as 55 arcseconds and average etch pit densities of 5 x 106 cm−2 have been deposited by liquid phase epitaxy on these MBE CdZnTe/ZnTe/Si substrates.
Study of different Cadmium Telluride Materials doped with V, Zn and Cl grown by vertical Bridgman Furnace and by THM.
Authors: Steer Ch. , Chibani L. , Koebel J.M. , Hage-Ali M. , Siffert P.
Published: March 2011

The properties of Cadmium Telluride are very sensitive to impurities. The growth method has also a strong impact on the material characteristics. Crystals grown by THM have good X-ray detector properties, while normal undoped Bridgman grown crystals do not detect. We have grown pure and doped samples by Bridgman and THM methods. As doping materials we used V, Zn and Cl, also in different combinations. The samples were characterized by several methods, including resistivity, TSC and nuclear detection measurements.
Progress in Cdl-xZnxTe (CZT) Radiation Detectors
Authors: Butler J. F. , Doty F. P. , Apotovsky B. , Friesenhahn S. J. , Lingren C.
Published: March 2011

Results of a program to improve the performance of Cd1-xZnxTe detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature Cdl-xZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at −25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cdl-xZnxTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd1-xZnxTe detector arrays are described, and imaging data for a 32 × 32 monolithic array of 1 mm2 elements on a 42mm × 42mm substrate are presented.
Fast Avalanche Photodiode Detectors for the Superconducting Super Collider
Authors: Vasile Stefan , Gordon Jeffrey S. , Farrell Richard , Squillante Michael R.
Published: March 2011

The tracking of high energy, secondary products in the Superconducting Super Collider (SSC) presents challenging sensitivity and timing requirements for the scintillating fiber converters and the optical radiation detectors planned for use as signal readouts. Silicon Avalanche Photodiodes (APD) are very promising detectors which may ultimately meet these requirements.

We have designed and manufactured 1 mm2APDs, to be operated in Geiger mode as single photon detectors for the SSC. The progress on decreasing the APD response time by platinum doping, device thinning and external avalanche quenching is reported.
Improvements of a-Si:H/CsI(TI) X-RAY Detectors for Radiation Monitoring
Authors: Manfredotti C. , Fizzotti F. , Boero M. , Cannistraci F. , Vittone E. , Torti A. , Turnaturi M.
Published: March 2011

Photosensitive a-Si:H p-i-n diodes, working in photovoltaic mode, have been coupled to CsI(T1) scintillators for dosimetry applications to X-ray monitoring in the energy range from 50 keV up to 15 MeV. A “mesa” approach for p-i-n diodes has been adopted both in order to better define the geometry and to obtain very low dark current. In order to optimize the geometry, a computer program has been created which simulates light generation in the scintillator, the collection by the detector and the photovoltaic current obtained as a function of exposure rate.

Measurements have been carried out in the X-rays energy ranges 50-240 keV, at 6MeV and at 15 MeV. Detectors are linear in response and shows a good sensitivity, with the capability of measuring dose rates as low as 60 mR/h.

The agreement between experimental data and simulation outputs can be considered good.
Point Defects in a Directly-Bonded Wafer, and its Comparison with the Bonded Soi Wafers
Authors: Usami Akira , Kaneko Keisuke , Ito Akira , Ishigami Shun-ichiro , Wada Takao
Published: March 2011

<Directly-bonded wafers were characterized using capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. We also studied silicon on insulator (SOI) wafers with different interfacial oxide thicknesses. In the active layers of the directly bonded wafer, two dominant electron traps (Ec-0.16eV, Ec-0.24eV) were observed at 23 μμμμm from the bonded interface. Both trap densities are almost constant (about 2 × 1011cm−3) at distances larger than about 10 μm. In the substrate, the density of the shallower electron trap increases (about 8 × 1011 cm−3) within about 20 μm from the interface, while the other trap concentration is almost constant and nearly equal to that in the active layers. No trap was observed near the wafer backside. These traps were also observed in the bonded SO1 wafers. Both the trap concentrations depend on the thickness of the bonded interfacial oxide. The shallower trap concentration increases with increasing oxide thickness, and the deeper one decreases.
Evaluation of Silicon Photodiode as X and Gamma-Ray Detector at Room Temperature
Authors: Cimpoca V. , Caragheorgheopol G.H. , Lazarovici D. , Lazarovici C. , Ruscu R.
Published: March 2011

A silicon photodiode 10 sqmm area designed for 0,45 A/W and maximum sensitivity at 900 μm, was tested as X and gamma-ray detector in the 6-122 keV range. The simple structure, good manufacturing and passivating for a NIP photodiode (6 KΩcm,p- type material) gives a yield of 20% from batch with suitable characteristics for low energy X and gamma-ray detection. A cheap nuclear detector for technical measurements results. Evaluation and analysis of parameters in X and gamma detection is made for these silicon structures; they are mounted on TO-8 holders without entrance lenses. The applications proposed namely the composition test of alloys (with known matrix) by X-ray fluorescence analysis and in radiation safety field (absorbed dose survey), ex. in radiological clinics defectoscopic laboratories or in front of video displays.
Analysis of HgI2 And PbI2 Crystals and Detectors by Particle-Induced X-Ray Emission (PIXE) and Ion Backscattering Spectroscopy (IBS)
Authors: Bench G. S. , ANTOLAK A. J. , MORSE D. H. , HEIKKINEN D. W. , PONTAU A. E. , JAMES R. B. , DAVID D. C. , BURGER A. , VAN DEN BERG L.
Published: March 2011

The Ion Micro-Analysis Group (IMAG) in Livermore conducts quantitative trace elemental analysis with PIXE and depth profiling with IBS using an MeV ion microbeam. The system has the capability to produce two-dimensional trace element and IBS images. PIXE analyses have been conducted on HgI2 and PbI2 crystals and detector materials in order to identify and quantify near surface trace contaminants. IBS measurements have been conducted to investigate elemental depth distributions in various materials. The results of measurements on several different samples are reported and a discussion of factors affecting quantitative in vacuo microanalysis of these materials is presented.
In-Situ Temperature Control for Rtp Via Thermal Expansion Measurement
Authors: Peuse Bruce , Rosekrans Allan
Published: March 2011

A new method of temperature control for rapid thermal processing of silicon wafers is presented whereby in-situ wafer temperature is determined by measurement of wafer thermal expansion via an optical micrometer mechanism. The expansion measurement technique and its implementation into a rapid thermal processing system for temperature control are described. Preliminary data show the wafer to wafer temperature repeatability to be 1% (3-σ) using this technique.
In-Situ Temperature Monitoring in Rtp by Acoustical Techniques
Authors: Degertekin F.L. , Pei J. , LEE Y.J. , Khuri-Yakub B.T. , Saraswat K.C.
Published: March 2011

A new technique utilizing the high sensitivity of acoustic wave velocity to temperature is used to measure the wafer temperature in RTP. Acoustic energy is coupled to a Lamb wave mode in the wafer using the quartz support pins already present in most rapid thermal processors. The tips of the pins are sharpened to have point contact with the wafer and acoustic transducers are bonded to the other end to excite and detect acoustic waves. By measuring the pin-to-pin time of flight of Lamb waves, it is possible to monitor the wafer temperature in-situ in the 20 - 1000°C range with ±5°C accuracy. Increasing SNR to 50dB by spring loading the pins and using better electronics, it is possible to improve this figure to ±1°C. Also a modified system with multiple spring loaded pins is constructed and wafer temperature mapping is performed using tomographic reconstruction techniques. The resulting images are in good agreement with thermocouple readings and can be used for temperature control and rapid thermal processor design.
Rapid Thermal Processing: Status, Problems and Options After the First 25 Years
Authors: Roozeboom Fred
Published: March 2011

This paper reviews the current status, problems and options in RTP system and process design. Some commercial systems will be discussed along with some improvements that can still be made in temperature reproducibility, process control and yield. This includes some recent developments in temperature reproducibility by compensated emissivity control.

Uniformity issues regarding temperature and process gas hydrodynamics are highlighted in relation to reactor design. Especially in CVD applications, where radiative heat transfer may not longer dominate convective and conductive heat transfer, modeling and visualization of gas flow patterns are becoming increasingly important. Here, reactor design should be such that a laminar flow regime is reached without turbulence and without chemical memory effects upon switching to other gas compositions. Some flow visualization results are illustrated.

Some new options for micro- and nanocrystallization reactions are presented before we conclude with a technology roadmap to the 1-Gbit era.