bluuebunny/crossref_metadata_2025 huggingface dataset:
Light Induced Changes in the Non-Gaussian Noise Statistics in Doped Hydrogenated Amorphous Silicon
Authors: Fan J. , Kakalios J.
Published: March 2011

The power spectrum of coplanar current fluctuations in n-type doped hydrogenated amorphous silicon (a-Si:H) has been measured before and after metastable defect creation by light soaking. The average magnitude and spectral slope of the 1/f noise are not affected by illumination, however significant changes in the higher order statistics are observed. Associated with the decrease of conductivity upon light soaking (the Staebler-Wronski effect), there is a decrease in the correlation of the noise power which characterize the non-Gaussian noise in the annealed state. These changes in the noise statistics are reversible by annealing. The light-induced changes in the non-Gaussian statistics provide experimental support for models of light induced defect creation which involve long-ranged and many body interactions.
Metastable Phenomena in the Thermally Activated Conductivity of Hydrogenated Amorphous Germanium (a-Ge:H)
Authors: DrÜsedau T. , Pang D. , Sauvain E. , Wickboldt P. , Liu E.Z. , Chen J.H. , Paul W.
Published: March 2011

The activated conductivity of a-Ge:H between room temperature and 460K was investigated using heating and cooling rates in the range between .001 and 0.1 K/s. A splitting of the cooling curves obtained at different rates, which defines the so called equilibrium temperature TE, is observed mainly between 420 and 430K. Taking into consideration that TE depends on the maximum cooling rate, the present results are in good agreement with those reported by Eberhardt et al. The higher cooling rate always leads to the lower conductivity at any temperature below TE. These effects can be rationalized in terms of a reversible shift of the Fermi level towards midgap at higher temperature. Though reversible changes of the mobility cannot be excluded, they cannot account for our set of experimental data. Rather, changes in the density of electronic states within the mobility gap can explain the effects observed.
Proton and Deuteron Double Resonance Studies of Structural Differences Between Amorphous Si and Ge Films
Authors: Chan P.H. , Fedders P.A. , Norberg R.E. , Paul W. , Pang D. , Wickboldt P.
Published: March 2011

Proton and deuteron double resonance methods have been used to study the structure of high quality plasma-deposited a-Si:H,D and a-Ge:H,D films. The micro-structure of the a-Si is dominated by nanovoids with dimension <3 Å while the a-Ge shows many larger microvoids. We have observed new proton HD multiple echoes in the films by using a three pulse sequence double resonance method. The new echoes imply that HD molecules in a-Ge principally are located in large microvoids, which is not the case in high quality a-Si.
Improved Amorphous Silicon Solar Cells Using RPCVD
Authors: Park Kyu Chang , Kim Tae Gon , Kim Sung Ki , Kim Sung Chul , Hwang Myung Hak , Jun Jung Mok , Jang Jin
Published: March 2011

We have studied the depositions of amorphous silicon, silicon carbon alloy, doped microcrystalline silicon in order to apply these films as the component materials for the p-i-n and double stacked solar cells. We have obtained low band gap a-Si:H by decreasing the deposition rate under the proper preparation conditions and highly conductive, thin microcrystalline Si and SiC layers. We have developed a stable a-Si/a-Si double stacked solar cell with a conversion efficiency of ∼ % using narrow band gap a-Si:H as a i-layer of bottom cell.The performance of this cell does not degrade until 100 hrs illumination under 350 mW/cm2.
Defect and Band Gap Engineering of Amorphous Silicon Solar Cells
Authors: Schropp R.E.I. , Ouwens J.Daey , Von Der Linden M.B. , Von Der Werf C.H.M. , Van Der Weg W.F. , Alkemade P.F.A.
Published: March 2011

This paper demonstrates that the incorporation of an unoptimized, wide band gap a-SiC:H layer near the p-type emitter layer in addition to a graded bandgap ”buffer” layer, leads to improved fill factors and open circuit voltages, in spite of the increased number of recombination sites at the p/i heterojunction. The as deposited as a function of a-SiC:H thickness shows an optimum of 10.5 % at a thickness of 10 – 20 Å. We have further improved this type of cell by incorporating a reverse carbon graded p-type layer and have thus achieved efficiencies in excess of 11.0 %. The cells are all amorphous and do not comprise antireflective coatings or enhanced back reflectors. A new defect engineering scheme to accomplish enhanced stabilized efficiencies of amorphous silicon solar cells is also proposed here.
Amorphous Silicon-Carbon Alloys for Solar Cells
Authors: Li Yuan-Min
Published: March 2011

Recent efforts to optimize undoped, glow-discharge hydrogenated amorphous silicon-carbon alloys (a-SiC:H) with 1.9-2.0 eV bandgaps for solar cell applications are reviewed. Hydrogen dilution coupled with relatively low substrate temperatures (below 200 °C) have led to great improvements in the optical and phototransport properties of a-SiC:H films. The issue of alternative carbon feedstocks other than methane (CH4) will be explored. The improved a-SiC:H alloys have resulted in solar cells with high open circuit voltages (V∞ > 1.0 volt) and high fill factors (> 0.7). Further, the a-SiC:H solar cell instability upon prolonged light exposure has been much reduced. Correlation will be made between the properties of bulk undoped a-SiC:H films and the performance of p-i-nsingle junction solar cells using corresponding a-SiC:H thin i-layers.
Improved Electrical Performance of a-Si:H Thin Film Transistors, TFTs with n+ (μc-Si Contact, and Silicon Oxide and Nitride Dual-Layer Dielectrics
Authors: He S.S. , Stephens D.J. , Lucovsky G.
Published: March 2011

We report the use of heavily-doped n-type μc-Si as a source and drain contacts in a-Si:H TFTs. Dual-layer dielectrics comprised of SiO2 and Si3N4 layers are employed, and the back channel regions are passivated to prevent depletion region formation. We have compared the electrical performance of TFTs with n+ a-Si source and drain contacts and n+ μc-Si source and drain contacts, relating some differences in performance to the properties of the source and drain materials. In addition we discuss the fabrication and performance of TFT structures that include B-compensated i-μc-Si channel regions and heavily-doped n+ μc-Si source and drain contacts.
Subthreshold Characteristics and Interface State Density of a-Si:H TFT
Authors: Maeda Keiji , Koyanagi Hiroki , Jinnai Toshihide
Published: March 2011

Inverted-staggered a-Si:H TFT was prepared by successive PECVD of a- SiN1.7:H and a- Si:H layers. Drain current ID vs gate voltage VG characteristics of the TFT were investigated. The gate-voltage swing defined by S=dVG/d(log ID) in the subthreshold region was 1.4 V at room temperature. If the observed S value is attributed to the bulk gap state density, the space- charge layer width is estimated to be about 450 A. This value is too small compared with the a-Si:H layer width of about 3000 A in the TFT, which exhibits good performance. On the other hand, if the S value is attributed to the interface states, a state density of 1.5×l012 (cm2 eV)-1 is necessary. Nearly the same density, (l-2)xl012 (cm2 eV)-1, nearly independent of the energy level, was obtained in oura-SiN1.7:H/c-Si interface by capacitance measurements. Therefore, it is concluded that the interface states are the main origin of the subthreshold characteristics in our a-Si:H TFT.
Electronic Properties of a-SiNx:H Thin Film Diodes
Authors: Shannon J.M. , Sandoe J.N. , French I.D. , Annis A.D.
Published: March 2011

Metal-semiconductor-metal diodes have been fabricated using a range of dilute a - SiNx:H alloys. Current transport in unstressed devices was dominated by thermionic-field emission of electrons through the reverse biassed metal-semiconductor contacts with a tunnelling effective mass ≈0.1me. The barriers to electrons were strongly pinned by bulk states and scaled almost linearly with optical band gap.

Under high current stress, defect states were created below the Fermi level forming a -ve charge that changed the effective barrier height and produced drift in the current voltage characteristic. Unipolar stress measurements showed that this effect was related to hole transport. After prolonged stress the electrical characteristics were dominated by bulk effects due to the high density of metastable defects in the band gap.
Current Transport Modeling in an Amorphous Silicon Antifuse Structure
Authors: Amerasekera Ajith , Kwok S.Ping , Seitchik Jerold
Published: March 2011

We have studied the transport mechanisms in thin film (≈ 2000 Å ) hydrogenated α-Si structures used as programmable antifuses in Field-Programmable-Gate-Arrays (FPGA) The antifuse was simulated using a back-to-back Schottky model for a metal/Si/metal thin film incorporating the thermionic-emission diffusion model for the metal-semiconductor contacts. The model predicts the current transport in the low voltage and high voltage regions. In the intermediate voltage range a linear field dependence of the barrier lowering is observed in the experimental results which leads to higher currents than predicted with the image force barrier lowering in the simulations. An important observation is that carrier multiplication is essential for breakdown which is evidence of impact ionization in α-Si. The permanent breakdown condition is modelled thermally, based on the steady- state solution to the heat equation.
Esr Studies in Amorphous Insulators
Authors: Griscom David L.
Published: March 2011

Some applications of electron spin resonance to the study of amorphous insulators are briefly described. Specific topics addressed include radiation-induced defect centers, redox equilibria, phase separation, photochromics, and ferromagnetic precipitates.
Utility of the MÖssbauer Effect in the Assessment of Chemical Transformations in Unsupported Catalyst Systems as a Function of the Metal Salt
Authors: Good Mary L. , Akbarnejad M. , Patil M. D. , Donner J. T.
Published: March 2011

This paper is presented to illustrate the utility of Fe-57 Mössbauer spectroscopy in the physical and chemical characterization of metallic catalysts as a function of preparation and subsequent treatment. The particular example chosen for investigation is the Ru-Fe bimetallic salt system which has significant potential as an active Fischer-Tropsch catalyst. The interpretation of the resulting Mössbauer parameters provides information on the chemical state of the metals as a function of treatment and initial salt properties and allows certain deductions to be made about particle size and solid state properties.
MÖssbauer Study of Iron and Tin Exchanged into Victorian Brown Coal
Authors: Cashion J.D. , Clark P.E. , Cook P.S. , Larkins F.P. , Marshall M.
Published: March 2011

Mössbauer effect measurements have been taken of iron and tin introduced into brown coal to act as catalysts for hydrogenation. Spectra taken with 119Sn show that after introduction from solution, the tin appears as SnO2. During subsequent hydrogenation in an autoclave, some of the SnO2 is converted to β-tin and SnS. Ion-exchanged iron is shown from 57Fe measurements to occupy at least one site not populated in the native coal. Line broadening in this site and the other two original sites indicate the existence of variations in the local environment.
Nmr Study of Sodium Ion Mobility in a Single Crystal of Na β”-Alumina and Water Effects in Polycrystalline Samples
Authors: Hayes Cecil E. , Ailion David C.
Published: March 2011

We measured the temperature dependence of T1 in a Mg-stabilized single crystal of Na β”-alumina. A comparison with earlier measurements on Li-stabilized polycrystalline samples indicates that, below 500K, the sodium ion kinetics are not directly affected by the stabilizing element. Above 500K our measured T1 shows a dependence on sample composition. Observations of NMR linewidth and signal intensity vs. water content indicate that, at low water concentration (< 2%), all sodium is in contact with water in its conduction plane; at higher water concentrations, the additional water may be forming complexes with some of the sodium.
Nuclear Magnetic Resonance in Alloys
Authors: Bennett L. H.
Published: March 2011

Many papers on NMR in alloys are addressed to NMR specialists rather than to metal or alloy specialists, and talk about the “potential” of NMR for application to alloys. This presentation emphasizes a review of some useful results of NMR experiments in alloys, including applications in diffusion, phase diagrams, magnetic materials, ordering in intermetallic compounds, liquid alloys and amorphous alloys.
Spin Susceptibility of Intercalated Graphite and Doped Polyacetylene
Authors: Kaufer James W. , Ikehata Seiichiro
Published: March 2011

We have examined the electronic susceptibility of intercalated graphite and doped (CH)x using ESR [1]. The dopant in both cases was AsF5. For metallic intercalated graphite and for heavily doped (CH)x, the low frequency Schumacher-Slichter technique was used to determine the density of states at the Fermi energy. In the case of doped (CH)x, susceptibility measurements as a function of temperature allowed separate determination of the Curie and Pauli contributions.
Nuclear Magnetic Resonance Studies of Type II Superconductors
Authors: Fradin F. Y.
Published: March 2011

The results of nuclear magnetic resonance (nmr) experiments on simple type–I superconductors were among the first and most important verifications of the BCS theory of superconductivity. In this paper, the application of nmr techniques to the study of superconducting properties in the more complex type–II superconductors will be reviewed. The discussion will include the effect of material parameters (e.g., degree of long range crystalline order, density of states at the Fermi level, effects of magnetic dopants) on the superconducting properties, including size of the superconducting gap, vortex structure, upper–critical field Hc2, and variations in Tc. Emphasis will be placed on high Tc, high Hc2 materials, i.e., A15 compounds and the ternary Chevrel phases.
The Anomalous Spectral Density Function for Diffusive Motion of Hydrogen in LaNi5H7
Authors: Chang H. , Lowe I. J. , Karlicek R. J.
Published: March 2011

Measurements of T1 (Bo = 0.94T), and T1r as a function of temperature have been carried out on a LaNi5H7 sample at 4 different rotating magnetic field values. The T1 and T1r data are consistent with earlier data by Karlicek and Lowe [3,4], in which an asymmetry in the slopes of the log T1r vs. T−1 plot was found. The new data has been analyzed assuming a spectral density function J(ω,τc) of form J(ω, τc) = A(τc)B(Ω)F(ωτc), with τc = τc∞ exp(Ea/kT). This assumption leads to a spectral density function that fits all our data well, with Ea = 39 KJ/gm-Atom H, and J(ω)∼ Wω−1.35 in the high frequency limit. This Ea agrees well with the Ea obtained from diffusion constant measurements.
Nmr in Liquid Semiconducting Sex Te1-x
Authors: Dupree R. , Kirby D.J. , Gardner J.A.
Published: March 2011

For x > 0.2, liquid SexTel-x alloys are semiconducting near the liquidus and have strongly temperature–dependent magnetic susceptibilities. We have studied the electronic paramagnetic centers by measuring their influence on the nuclear magnetic resonance shift and relaxation times of 77 Se and 125 Te in liquid Se .5Te.5. We find that the electronic centers are highly localized, their average hyperfine contact interaction with 125Te is three times that with 77Se, and the electronic spin correlation time is of order 1 psec at 350°C and decreases with rising T.
Muon Spin Depolarization in Metals with Dilute Magnetic Impurities
Authors: Brown J. A. , Heffner R. H. , Hutson R. L. , Kohn S. , Leon M. , Olsen C. E. , Schillaci M. E. , Dodds S. A. , Estle T. L. , Vanderwater D. A. , Richards P. M. , Mcmasters C. D.
Published: March 2011

Muon diffusion can be studied in metals without nuclear moments by the addition of paramagnetic impurities. We describe the theory and report measurements of muon depolarization in gold and silver doped with gadolinium and erbium. As well as diffusion rates, strength of the magnetic interaction and spin lattice relaxation rate of the paramagnetic ion are inferred from the data.
Dislocation Motion in Metals Investigated by Means of Pulsed Nuclear Magnetic Resonance
Authors: Tamler H. , HackelÖer H. J. , Kanert O. , Alsem W. H. M. , Th. J. , de Hosson M.
Published: March 2011

We report the first use of nuclear magnetic resonance to investigate dislocation motion in metals. The spin-lattice relaxation rate in the rotating frame T 1ρ−1, of 27Al in polycrystalline, ultrapure Aluminium foils has been measured as a function of plastic-deformation rate έ for two different temperatures (77K and 300K). For έ = 0, the relaxation rate is determined by conduction electrons. For a finite deformation rate έ, an additional contribution to the relaxation rate arising from fluctuations in the nuclear quadrupole interaction due to dislocation motion is observed. From the motion-induced part of the relaxation rate the mean jump distance of a mobile dislocation is calculated which is determined by the density of lattice defects acting as obstacles for moving dislocations.
Geometrical Structure of Lattice Defect-Impurity Configurations Determined by TDPAC
Authors: Deicher M. , Echt O. , Recknagel E. , Wichert Th.
Published: March 2011

The perturbed angular correlation technique (TDPAC) was applied to determine the orientation of the electric field gradient tensor induced by lattice defects at the probe 1l1In. The experimental results obtained for self-interstitials, vacancies and defect clusters in Cu, Ag and Au are shown and their microscopic interpretation is discussed.
Investigation of Lattice Defects in Hcp Metals
Authors: Keitel R. , Engel W. , Hoth S. , Klinger W. , Seeböck R. , Witthuhn W.
Published: March 2011

With the perturbed angular correlation and distribution methods we studied the trapping and annealing of lattice defects in the hcp metals Cd and Zn. The defects were produced (i) by proton irradiation, (ii) by quenching, and (iii) by heavy ions recoiling after a nuclear reaction As probe ions we used 111Cd (i,ii) and 67Ge,69 Ge,71 Ge,113 Sn, and116 Sn (iii). The In-impurities in Zn and Cd are trapping centers for vacancies. At low temperatures (100 to 200 K) simple defect configurations are observed. In the in–beam experiments a sharp annealing step due to detrapping of vacancy type defects is found.
Nuclear Magnetic Resonance on Rare-Earith Nuclei in Re-Fe2 Intermetallic Ccmpounds
Authors: Berthier Y. , Devine R.A.B. , Butera R.A.
Published: March 2011

NMR results in RE-Fe2 internmtallic compounds at low temperatures are reported. Using a spin-echo spectrometer in the U.H.F. range, hyperfine field parameters have been measured on 167Er, 163Dy, 169 Tn and 159Tb at 1.4K. These cctnpounds have high Curie temperatures and the magnetic moment of the rare-earth, gJμB is nearly saturated. The value of the iron moment is also known from Mossbauer measurements and accurate data for the hyperfine field at the rare-earth site obtained from NM enables us to extract the internal field due to conduction electrons.
MÖssbauer Study of New Laves Phases Rfe2 Compounds (R = Pr, Nd, Yb)
Authors: Meyer C. , Hartmann-Boutron F. , Gros Y.
Published: March 2011

A summary of the magnetic properties of three Laves Phases compounds RFe2 (R = Pr, Nd, Yb) synthesized under high pressure is presented. Most of the results have been obtained by Mössbauer spectroscopy. Through the 57Fe resonance, the easy directions of magnetization between 4 and 300 K have been determined; the hyperfine field at Fe contains a large anisotropic contribution, only partly due to dipolar effects. From the Yb170 Mössbauer resonance measurements in YbFe2, the exchange field of the iron and the crystalline field, acting on Yb3+, have been derived.
Epr Investigations of Impurities in the Lanthanide Orthophosphates
Authors: Abraham M. M. , Boatner L. A. , Rappaz M.
Published: March 2011

Lanthanide orthophosphates formed from elements in the first half of the 4f transition series are analogs of the monoclinic mineral monazite. The known geologic properties of this mineral make the general class of lanthanide orthophosphate compounds attractive substances for long-term containment and disposal of α-active actinide nuclear wastes. EPR spectroscopy has been used to investigate the structural properties and solid state chemical properties of impurities in these materials and to compare the characteristics of single crystals and polycrystalline bodies.
57Fe and 125Te Mossbauer Study of LiFeCo3TeO8 and LiFeNi3TeO8
Authors: Gerard Andre , Grandjean Fernande , Flebus Carlo
Published: March 2011

57 Fe and 125 Te Mössbauer data on the spinels LiFeNi3TeO8 and LiFeCo3TeO8 are presented. Structural information relating to site occupations by Fe, valency of Fe and Te and magnetic hyperfine fields are obtained from this study.
Quadrupole Hyperfine Interaction and Magnetic Hyperfine Field in Feocl and its Intercalates
Authors: Maeda Y. , Herber R. H.
Published: March 2011

FeOCl is a layered compound belonging to the orthorhombic space group Pmnm (D2h13), with two formula units per unit cell. Adjacent layers in the (010) crystallographic plane, in which chlorine atoms face each other, are held together by van der Waals forces which are readily disrupted by the insertion of appropriate Lewis base molecules. This intercalation of “guest” species causes an expansion in the b-direction, leaving the remainder of the unit cell dimensions unchanged. Among base molecules which are readily intercalated are NH3, pyridine and a wide variety of substituted pyridines, nitrogen containing heterocyclic molecules, phosphines and phosphites. The limiting stoichiometry ranges from 1:3 (“guest” to Fe atom ratio) for small intercalants to 1:6 for large “guest” molecules. Using both powder X-ray diffraction and temperature dependent 57 Fe Mössbauer effect spectroscopy, the lattice dynamics, hyperfine interactions, magnetic ordering temperature and magnetic hyperfine field (at 4.2 K) have been studied for the neat matrix and a number of base intercalates. The magnetic hyperfine field at the iron atom at 4.2 K is 441╪3 KOe, independent of the magnitude of the b-axis expansion. Vzz is negative for neat FeOCl and intercalates in which the “guest” to host ratio is ≤ 1:3, and positive when this ratio is ≥ 1:4.
New Method for the Determination of Diffusion Constants from Partially Narrowed Nmr Lines
Authors: Wolf D.
Published: March 2011

The effect of atomic and molecular motions on the NMR free-induction decay (FID) and lineshape is investigated theoretically in the intermediate temperature range in which the NMR line is only partially narrowed. It is shown that the FID may be decomposed into the weighted sum of a rigid-lattice (background) contribution and an exponentially decaying part containing all the information on the diffusive or reorientational motions in the crystal in terms of the spin-spin relaxation time T2.
A Method for Determining Impurity-Host Force-Constant Ratios
Authors: Kolk Berend
Published: March 2011

One of the parameters of interest in studies on dilute alloys is the ratio of the effective host-host to impurity-host interaction. A method is presented which allows the evaluation of the effective impurity-host force-constant ratio, A′/A, for substitutional, isolated, impurity atoms in a cubic lattice by combining recoilless-fraction data (Mössbauer effect) of the impurity atoms with x-ray– or neutron-diffraction data of the host lattice. With this method, values of A′/A are obtained for dilute 57Fe impurities in various hosts.
Nmr Techniques for Studying Ionic Diffusion in Solids
Authors: Ailion David C.
Published: March 2011

A survey of NMR relaxation time techniques for studying ionic diffusion in solids is presented. Particular emphasis is placed on discussing the kinds of information obtainable from T1, Tlρ, TlD, and TlD' measurements. Applications to the study of local and nonlocal diffusion, diffusion in weakly magnetic systems, and motions between unequal potential wells are described. Relaxation due to fluctuating dipolar, quadrupolar, and chemical shift anisotropy interactions is discussed.
Material Characteristics of InGaAsP/InGaP Lasers
Authors: Yoo Jae S. , Ko Young T. , Park Georgui , Kim Tae I. , Kang Kyung I. , Kim Han S.
Published: March 2011

A study of material and optical characteristics of InGaAsPAnGaP lasers grown on GaAs (100) substrate, Operating at λ = 0.8μm was carried out. The main features of InGaAsPAnGaP lasers over the conventional AlGaAs/aCAs; ones were not only stable epitaxial layer growth due to the aluminum-free material, but also strong resistance to the degradation. The other benefits of InGaAsP/inGaP laser over AlGaAs/GaAs one was the quantum-well structure growth by a simple version of liquid-phase epitaxy (LPE), which might be irnispensable to the high power operation of a semiconductor laser. The separate confinement heterostructure single quantum weil(SCH-SQW) InGaAsP/nGaP lasers were fabricated for the material charaterization of quaternary systen. The local temperature rise at the mirror facet of a InGaAsP/InGaP laser, which is the barometer of a reliable operation, was less than 30°C under even above 500 mW CW operation. We presumably attribute this low local temperatur rise of the quaternary system to the fact that it has thenodynamically stable minor facet. The surface analysis of InGaAsP layer by ESCA showed that the formation of indium oxide would prevent the elemental segragation constituting dangling orbital, which is common to A1GaAs material systems.
Formation of Long Wavelength InP Laser MESAS
Authors: Ren F. , Pearton S. J. , Tseng B. , Lothian J. R. , Constantine C.
Published: March 2011

Narrow (1 μm), deep (3.5 μm) laser mesas have been formed on 2”φ InP wafers using stepper lithography and dry etching techniques for both dielectric and semiconductor patterning. Contrast enhancement techniques produce excellent edge acuity and vertical sidewalls on the initial photoresist lines. Pattern transfer to the underlying SiO2 regrowth mask is achieved by ECR SF6/Ar dry etching at 1 mTorr and –100V, conditions which also retain the verticality of the mesa. The semiconductor is etched using an ECR Cl2/CH4/H2/Ar discharge at 0.3 mTorr and –80V, with the sample held at ∼ 150°C. The etch rate under these conditions is ∼1 μm/min, with a selectivity of ≥10:1 for the semiconductor over the dielectric mask. The smooth etched surface and low degree of damage make this process ideal for epitaxial regrowth. The uniformity of each process step is also acceptable (≤7%). Comparison of the elevated temperature Cl2/CH4/H2/Ar mixture with the more conventional room temperature CH4/H2 plasma chemistry will be given.
Enhancement of the Metal/Si-Doped AlGaAs Schottky Barrier Height by CH4/H2 Reactive Ion Etching
Authors: Pereira R. , Van Hove M. , De Raedt W. , Alay J. , Bender H. , Vandervorst W. , Borghs G. , Van Rossum M.
Published: March 2011

The damage introduced by CH4/H2 reactive ion etching (RIE) on Si-doped AlGaAs layers is studied by X-Ray Photoelectron Spectroscopy (XPS), Auger electron spectrocopy (AES) and electrical measurements on Schottky contacts. The XPS analysis of the surface stoichiometry after RIE exposure shows arsenic depletion and adsorbed carbon as the main characteristics. The carbon spectrum consists of a component due to atmospheric contamination and an additional photoelectron peak at 283 eV, which we correlate with the formation of Ga-C radicals at the AlGaAs surface during RIE. The reaction process at the Au/TiW/Ti/AlGaAs interface after RIE exposure and subsequent thermal annealing is monitored by AES. Also by this technique, carbon was detected at the Ti/AlGaAs interface and no interdiffusion was observed. The electrical behaviour of the contacts is characterized by capacitance-voltage (CV) and current-voltage (IV) measurements. Schottky barrier height, ideality factor and reverse breakdown were determined. The barrier height extracted from CV measurements of the samples exposed to RIE shows increased values (1.1 to 1.4 eV) compared to the reference samples (1.0 to 1.1 eV), depending on the aluminium concentration. The same behaviour was observed in the ideality factor. The results are explained by the formation of a p-n junction below the metal/AlGaAs barrier. Good agreement between experimental and theoretical values is found when the compensation of Si donors was taken into account.
Dual Role of Tin Reaction Barrier in Gold-Based Metallization to GaAs
Authors: Piotrowska A. , Kaminska E. , Guziewicz M. , Kwiatkowski S. , Turos A.
Published: March 2011

The formation of ohmic contacts to p-GaAs based on Au-Zn system comprising a TiN diffusion barrier has been investigated using 2 MeV He+ RBS and the specific contact resistance measurements. It has been proved that TiN films deposited by reactive RF bias magnetron sputtering serves two purposes. First it suppresses the arsenic evaporation and thus confines the reaction between AuZn and GaAs. Second, it prevents intermixing between p-GaAs/Au(Zn) ohmic contact and an overlayer of Au.
Pd/Ge Contacts to n-TYPE InP
Authors: Jian Ping , Ivey Douglas G. , Bruce Robert , Knight Gordon
Published: March 2011

Multilayer metallizations of Pd/Ge/Pd, with different thickness ratios of Ge and Pd, were deposited onto n-type InP by means of electron beam evaporation. The specimens were then annealed in flowing N2 gas at temperatures ranging from 250 to 425°C for various times. Transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDX) and electron diffraction were used to identify the phase changes during reaction. The four point probe method was used for electrical resistance measurements. A Pd-In-P amorphous phase and a Pd2Ge compound formed during deposition. Subsequent annealing resulted in crystallization of the amorphous phase followed by epitaxial growth of Pd2InP(II) on InP at 350°C. At 425°C, Pd2InP(II) with Ge in solution, decomposed producing a contact with a lower specific contact resistance. The lowest contact resistances achieved were ∼10−5 Ωcm2. Further annealing led to more decomposition of InP, including presumably the Ge doped InP surface region, which corresponded to an increase in contact resistance.
The EFfects of Elemental Sequence and Pairing on Interdiffusion and Phase Formation of Al-Ge-Ni Ohmic Contacts for (001) GaAs
Authors: Lampert W. V. , Haas T. W. , Holloway Paul H.
Published: March 2011

The growth sequence of Al, Ge, and Ni metals has been shown to dramatically affect the amount of heat treatment time required to convert the ohmic contact metallization from Schottky to ohmic behavior. Interpretation of interdiffusion and phase formation of the Al-Ge, Al-Ni, or Ni-Ge thin film couples were measured. Auger depth profiles and thin film X-ray diffraction were used to determine interdiffusion and phase formation resulting from various types of thermal processing. The effects of interdiffusion and formation of phases such as Ni-Ga, Ni-As, Ni-Ga-Ge, and Ni-As-Ge from the two element metallizations on GaAs will be used to explain the origin of ohmic behavior for the ternary Al-Ge-Ni contacts to GaAs.
The Low Specific Ohmic Contact Resistivity of Alloyed Ge—LOW—Content Au on Si—Implanted Electrically—Active GaAs Crystal Layers
Authors: Saito Yasuyuki
Published: March 2011

The author did experiments on ohmic contacts between alloyed goldgerumanium (AuGe) thin film systems and Si–implanted n–type GaAs crystal conductive layers on semi–insulating wafers in order to obtain stable ohmic contacts for source–drain electrodes of Si–implanted metal–semiconductor field–effect–transistor arrays as the tools of investigating semi-insulating GaAs crystallographic–characteristics uniformity. Hot–stage–alloyed low–Ge–content (content in charged AuGe wire: < a few wt.%) AuGe/Au films and GaAs crystal n–type Si–implanted layers showed smooth metallic surface morphology (like gold reflection) and low specific ohmic resistivity (≃10exp.−6 Ω/cm2) (by G.S.Marlow and M.B.Mukunda method) at Room temperature on the condition of typical 0.25 X 10exp.13/cm2− 1 X 10exp.13/cm2 Si dosage at 100keV–200keV and 850°C-15 min capless annealing in 2.7 Torr AsH3+Ar atmosphere for S.I GaAs crystal wafers.
An Optimization Study of Thermal Stability of W/GaAs Schottky Gates
Authors: Favoretio Marcio , Swart Jacobus W.
Published: March 2011

This paper presents an experimental study of the physical and electrical characteristics of tungsten (W) thin films versus the deposition parameters of sputtering. A correlation between the W film characteristics and thermal stability of the W/GaAs Schottky diodes is also presented. Good thermal stability was obtained for W gates with low resistivity and α-W phase, deposited at low pressure and low RF power. W films deposited at high pressure presented high resistivity, β-W phase and weak thermal stability. Diodes annealed under As over-pressure ambient presented an enhanced thermal stability of about 100°C.
Fabrication, Performance, and Reliability of InP-Based HBTs
Authors: Stanchina William E. , Metzger Robert A. , Jensen Joseph F. , Hafizi Madjid , Rensch David B.
Published: March 2011

Over the past 10 years, heterojunction bipolar transistors (HBTs) have progressed to where integrated circuit (IC) products are being sold and foundry services are being commercially offered utilizing gallium arsenide (GaAs) based technology. We will discuss, here, an alternative HBT technology based on indium phosphide (InP). While this technology is less mature than its GaAs counterpart, it offers several attractive benefits in comparison with GaAs. These benefits are provided through several key material properties of InP and ternary compound semiconductors, eg. gallium indium arsenide (GaInAs), grown on the InP. We review the status of this npn HBT technology and present performance results which illustrate the benefits of the technology with respect to electronic applications. Finally, we present measured reliability data for this technology which shows outstanding projected lifetimes.
Reliability of Implant-Isolation Regions in Highly-Doped GaAs-Based Structures
Authors: Ren F. , Pearton S. J. , Lothian J. R. , Fullowan T. R. , Abernathy C. R. , Chu S. N. G.
Published: March 2011

Highly-doped n-type (2 × 1019 cm−3) and p-type (7 × 1019 cm−3) GaAs layers were implanted with multiple energy F+ or H+ ions and subsequently annealed at ∼550°C to produce high resistance regions. The resistance of these layers at 200°C was monitored as a function of time and showed no changes for periods of several months. This is in contrast to some previously reported data, which showed complete loss of isolation after a period of several days in proton-implanted n+ GaAs. Here, we show that isolation of heavily-doped near-surface regions by protons requires implantation through cap layers which place the peak of the nuclear stopping profile at the GaAs surface. The application of these results to isolation of thick, multilayer heterostructure devices is discussed and SIMS and TEM data are used to illustrate the redistribution of the implanted ions and the defects they create, respectively.
Differential Reflectance Studies of Structural Changes in GaAs Caused by Ar+ Ion Bombardment
Authors: Ludwig M. H. , Hummel R E.
Published: March 2011

Differential reflection (DR) spectrometry has been used to investigate and characterize the effect of sputter damage of GaAs by Ar+ ions. The DR technique provides the photon-induced critical point interband transition energies which are sensitive to the electron and the crystal structure. The spectral dependence of the normalized difference in reflectivity is obtained by periodically scanning monochromatic light across a pair of GaAs samples. In the present case one part has been damaged by Ar+ ions with energies ranging from 500 to 5000 eV. The other half is the undamaged reference. The DR structure caused by interband transitions and designated as E1 and E1 + δ1 were found to shift in energy with increasing ion beam energy or with sputter damage. Two annealing stages were observed, one at 200°C and the other between 400°C and 450°C. They were attributed to different recovering mechanisms of As Frenkel pairs.
Time Dependent Diffusion of P-Type Dopants in Gallium Arsenide
Authors: Robinson H.G. , Jones K.S. , Deal M.D. , Hu C.J.
Published: March 2011

The diffusion of implanted p-type dopants in GaAs often exhibits transient effects during annealing. This diffusion can greatly affect device performance and must be understood in order to create accurate, physically based process modeling simulation tools for compound semiconductors. The transient diffusion is believed to be related to defects created during implantation, but a direct correlation between implant damage and dopant redistribution has been difficult to establish. Results are presented in this paper of experiments designed to gain insights into the fundamental mechanisms underlying the relationship between defects and diffusion. Many anomalies in previous data are the result of implanting dopants under poorly controlled conditions, particularly implant dose rate and temperature. Special care was taken in this work to ensure that the implants were performed under well controlled conditions. Al was co-implanted with Mg and Be to study the effect of implant damage without affecting the position of the Fermi level. A correlation was found between the initial transient diffusion observed in low dose Be implants and the presence of dislocation loops. This may present a viable method for suppressing diffusion of implanted Be. SIMS profiles of Mg and Al co-implants were anomalous and difficult to interpret. Cap failure, dopant segregation to the surface and/or defects may be responsible for the discrepancies in the data. P-type doping appears to stabilize dislocation loops, probably by increasing the concentration of positively charged Ga interstitials. RBS measurements of implanted Mg indicates a link between damage production, implant dose rate, and diffusion. This result agrees with previous work on damage production in Si implanted GaAs.
Comparison of AlN films grown by RF magnetron sputtering and ion-assisted molecular beam epitaxy
Authors: Chan J. , Fu T. , Cheung N. W. , Ross J. , Newman N. , Rubin M.
Published: March 2011

Crystalline aluminum nitride (AIN) thin films were formed on various substrates by using RF magnetron sputtering of an Al target in a nitrogen plasma and also by ion-assisted molecular beam epitaxy (IAMBE). Basal-oriented AIN/(1 11) Si showed a degradation of crystallinity with increased substrate temperature from 550 to 770 °C, while the crystallinity of AIN/ (0001) A12O3 samples improved from 700 to 850 °C. The optical absorption characteristics of the AIN/(0001) A12O3 films as grown by both deposition methods revealed a decrease in subbandgap absorption with increased substrate temperature.
Utilization of ß-Diketones for Etching and Cleaning of Metal Oxide and Sulfide Thin Films
Authors: Droes Steven R. , Jain A. , Kodas T.T. , Hampden-Smith M.J. , Muenchausen R.
Published: March 2011

We are examining dry processes for wafer cleaning and producing patterned thin films of metal oxides. This research focuses on determining the kinetics and mechanism of the reaction between ß-diketones and selected metal oxides. Preliminary experiments indicated that CuO, MgO, PbO and ZnO all react readily with 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH). Thin films of CuO and MgO were fabricated via pulsed laser deposition, characterized by various analytical techniques such as Rutherford Backscattering Spectrometry and Scanning Electron Microscopy, etched using hfacH, and then further characterized. Etching rates for CuO and MgO were measured in order to develop a mechanistic understanding of the reaction.
The Diffusivity-Mobilitt Ratio Under Strong Magnetic Field in III-V Superlattices with Graded Structures
Authors: Ghatak Kamakhya P. , De Badal
Published: March 2011

In this paper we have studied the Einstein relation for the diffusivity-mobility ratio in III-V superlattices with graded structures under magnetic quantization by formulating a new dispersion law. It is found, taking InAs/GaSb an example that the diffusivity mobility ratio increases in an oscillatory way with increasing carrier degeneracy as a consequence4SdH effect. The Einstein relation in IIIV superlattice is greater than that of the same for the constituent materials. Besides the theoretical results are in agreement with the suggested experimental method of determining the same ratio in degenerate materials having arbitrary dispersion laws.
A structure observation of GaAs micro crystal/Se-terminated GaAlAs interface for the quantum well box structure
Authors: Chikyow Toyohiro , Lijima Michihisa , Koguchi Nobuyuki
Published: March 2011

A selective growth of GaAs micro crystals was demonstrated on a Se-terminated GaAIAs surface by sequential supplies of Ga and As molecules for the quantum well box structure. After the growth, the surface consisted GaAs micro crystals with (111) facets and some Se clusters. The cross sectional investigations by the high resolution electron microscope revealed an epitaxial growth of GaAs micro crystals on the surface and a mixture of Ga2Se3 and A12Se3 layer formation at the interface of GaAs/Se-terminated GaAIAs. The selenidation process seems to be a reaction limited one. The Se cluster segregation could be avoided by selenidation in As molecule atmosphere.
Nitrogen-Atom Bonding at SiO2/Si Interfaces in Metalinsulator-Semiconductor (MIS) Stacked Gates Made by Integration of Plasma Assisted Oxidation-Deposition and Rapid Thermal Processing
Authors: Ma Y. , Yasuda T. , Lucovsky G.
Published: March 2011

SiO2 thin films were deposited by remote PECVD on Si surfaces exposed to species generated in O2/N2 and O2/NH3 plasmas. The surface chemistry was studied by Auger Electron Spectroscopy, AES, and the electrical properties of the SiO2/Si interface by high frequency and quasi-static Capacitance-Voltage, C-V, measurements. The AES results showed that Ccontamination was removed by exposure to both plasma-excited gas mixtures, but that N-atoms were incorporated into the SiO2 film, and Si-N bonds were formed at the SiO2/Si interface. C-V measurements indicated that the Si-N bonding structure, rather than the N-atom concentration, is critical in determining the interface electrical properties. The effects of Rapid Thermal Annealing, RTA, on the electrical properties of these SiO2/Si interfaces were also studied.
Rapid Thermal Annealing for Electrical Activation in the Fabrication of GaAs MESFET
Authors: Choi S.W. , Yang J.W. , Koak B.H. , Cho K.I. , Park H.M.
Published: March 2011

Rapid thermal annealing (RTA) has been employed for the electrical activation of shallow n-channel layer by Si+ implantation in the fabrication of GaAs MESFET. To prevent considerable outdiffusion of gallium and arsenic from GaAs substrate during annealing, encapsulating layers such as SiNx and SiNx/SiO2 are deposited. The SiNx/SiO2 double dielectric encapsulant is shown to be more effective to improve the electrical activation. Depending on RTA temperature between 900 and 950°C, the maximum activation efficiency exhibits 77% at the implanted energy of 70 keV and the dose of 5×1012 cm−2. SIMS analyses show the reduction of the hydrogen contained in the silicon nitride and no outdiffusion of Ga and As during RTA. It also shows the sharp Si-profile after RTA at 950°C, 30 sec. The MESFET fabricated using activaton with RTA provides better transconductance than that with furnace-annealed activation.
A Dual-Function UHV-Compatible Chamber for i) Low-Temperature Plasma-Assisted Oxidation, and ii) High-Temperature Rapid Thermal Processing of Si-Based Dielectric Gate Heterostructures
Authors: Hattiangady S. , Xu X-L , Watkins M.J. , Hornung B. , Misra V. , Lucovsky G. , Wortman J.J.
Published: March 2011

A combination of i) low-temperature, 300-400°C, plasma-assisted oxidation to form the SiO2/Si interfaces, and ii) 800°C rapid thermal chemical vapor deposition, RTCVD, to deposit SiO2 thin films have been used to fabricate gate-oxide heterostructures. This sequence separates SiO2/Si interface formation by the oxidation process from the deposition of the bulk oxide layer by RTCVD. These two processes were performed in situ and sequentially in a single-chamber, ultraclean quartz reactor system. We have studied the chemistry of the interface formation process by Auger electron spectroscopy, AES, and the electrical properties of MOS devices with Al electrodes by C-V techniques.
Fabrication and Low Temperature Transport Studies of Sub-Micron, In-Plane Gated Fets Defined by Low Energy Ion Exposure
Authors: Andrews C.C. , Spencer G.F. , Li F. , Weichold M.H. , Kirk W.P.
Published: March 2011

Nanoscale gated quantum wires in GaAs MODFET material with the conduction channel and gates in the plane of the 2DEG have been fabricated and studied. Electron beam lithography was used for mask definition followed by flood exposure to low energy argon ions (150 eV) for pattern transfer into the 2DEG. Compared to metal top-gate designs the in-plane design simplifies fabrication and reduces device capacitance, promising ultra-fast operation. This method of pattern transfer produced devices having channel-to-gate isolation of 1014 Ω and breakdown fields above 106 V/cm at 4.2 K. In addition to exhibiting standard FET characteristics, including gating to pinchoff, the devices showed significant negative differential resistance (NDR) in the saturation region.
Selective Area Epitaxy for Optoelectronic Devices
Authors: Temkin H. , Hamm R. A. , Feygenson A. , Cotta M. A. , Harriott L. R. , Ritter D. , Wang Y. L.
Published: March 2011

We discuss the characteristics of MOMBE based selective area epitaxy useful in the preparation of optoelectronic devices. Selective area epitaxy, a process in which epitaxy is restricted only to the areas opened in a suitably prepared dielectric mask, offers a powerful method of preparing high performance devices, varying the thickness and composition of the grown layers simply by controlling the width of the open areas and monolithically integrating different device types on common substrates. Lasers, heterostructure bipolar transistors, and optoelectronic integrated circuits based on InGaAs/InP system and relying on selective area epitaxy are described.
Electronic Characterization of Mercuric Iodide Gamma Ray Spectrometers
Authors: Gerrish Vernon M.
Published: March 2011

During the past four years the yield of high-resolution mercuric iodide (HgI2) gamma ray spectrometers produced at EG&G/EM has increased dramatically. Data are presented which demonstrate a strong correlation between starting material and spectrometer performance. Improved spectrometer yields are attributed to the method of HgI2 synthesis and to material purification procedures. Data are also presented which show that spectrometer performance is correlated with hole mobility-lifetime products. In addition, the measurement of Schottky barrier heights on HgI2 spectrometers has been performed using I-V curves and the photoelectric method. Barrier heights near 1.10 eV have been obtained using various contacts and contact deposition methods. These data suggest the pinning of the Fermi level at midgap at the HgI2 surface, probably due to surface states formed prior to contact deposition.
A Study of Dark Currents on Various Modified Surfaces of Mercuric Iodide Single Crystals
Authors: Jayatirtha H. N. , Azoulay M. , George M.A. , Burger A.
Published: March 2011

The surface modifications that occur on °-mercuric iodide surfaces during the fabrication process are crucial for the development of a low noise, high resolution X-ray spectrometer. In this study, we discuss the effects of surface treatments on the dark currents and the results are correlated with surface morphology studies that were carried out by the atomic force microscopy (AFM) technique.