bluuebunny/crossref_metadata_2025 huggingface dataset:
Narrow-Gap Nonlinear Optical Materials
Authors: Youngdale E. R. , Hoffman C. A. , Meyer J. R. , Bartoli F. J. , Han J. W. , Cook J. W. , Schetzina J. F. , Martinez A.
Published: March 2011

We report an experimental study of the nonlinear optical properties of HgTe-CdTe superlattices grown by MBE and Pb1−x,SnxSe grown by hot wall epitaxy. Nondegenerate four-wave mixing has been employed to measure third-order nonlinear susceptibilities at 10.6 µm as a function of temperature, laser intensity, and difference frequency. The nonlinearity is believed to be due to modulation of the free carrier temperature and density by the optical beams. The HgTe-CdTe results are compared to theoretical calculations based on free carrier contributions to the susceptibility, and the agreement with experiment is quite good. In 1-µm-thick Pb1−xSnxSe layers, multiple internal reflections of the light within the sample is found to enhance the nonlinear signal by an order of magnitude.
Recent Developments in II-VI Diluted Magnetic Semiconductors
Authors: Samarth N. , Furdyna J. K.
Published: March 2011

Much of the work in diluted magnetic semiconductors (DMS) in past years has focused on the alloys such as Cd1−xMnxTe. Recently, there has been an increasing accent on DMS alloys containing the transition metal ions Fe2+ and Co2+. We review here the properties of these new materials and compare them with the alloys. We also examine the novel opportunities afforded by the molecular beam epitaxy of epilayers and heterostructures containing the “metastable” zinc-blende phase of Cd1−xMnxSe.
Photoluminescence Studies of Diluted Magnetic Semiconductors Under Hydrostatic Pressure: Cd1−xMnxTe
Authors: Prakash Maneesha , Chandrasekhar Meera , Chandrasekhar H.R. , Miotkowski I. , Ramdas A.K.
Published: March 2011

We present a photoluminescence study of the excitons and electron-to-acceptor (e-°) transitions in Cd1−xMnxTe (x = 0.05 and 0.15) under hydrostatic pressure at 15K. We investigate the changing magnetic and Coulombic binding energies of the e-° transition under pressure. We find that the e-° binding energy increases with pressure for x = 0.15 where the magnetic term due to the acceptor bound magnetic polaron is large, while it decreases for x = 0.05. We also obtain the pressure coefficients of the excitonic and acceptor related transitions.
Observation of Mn2+ Triplet Clusters and Non-Nearest-Neighbor Exchange Effect in (Cd,Mn)Te
Authors: Wang Xiaomei , Heiman D. , Foner S. , Becla P.
Published: March 2011

Dilute magnetic semiconductors (DMS), such as Cd1−xMnxTe, are excellent hosts for the study of disordered magnetic systems. In these diluted random alloys, neighboring magnetic ions form clusters through short range spin exchange interactions. A number of experiments [1-8] have been devoted to the investigation of the nearest-neighbor (NN) coupled magnetic ion pairs, by measuring the quantized total spin in a field. In (Cd,Mn)Te, the obtained NN exchange constant J1 is -6.1K[7,8]. However, to understand full range of magnetic and optical phenomena in DMS, it is important to explore the behavior of clusters larger than pairs and interactions beyond NN.
In-Situ Studies of Semimagnetic Heterojunction Parameters
Authors: Yu Xiaohua , Troullier N. , Raisanen A. , Haugstad G. , Franciosi A.
Published: March 2011

We have conducted a systematic study of Ge-Cd1−xMnxTe heterostructures prepared in situ by deposition of polycrystalline Ge onto atomically clean Cd1−xMnx (110) surfaces. We examined by means of high resolution synchrotron radiation photoemission the valence band offset δEv as a function of the substrate composition x (x=0, 0.35, and 0.60) and bandgap Eg (Eg = 1.47, 1.93, and 2.13 eV). We find δEv=0.84±0.10eV in all cases, and no dependence of δEv on the substrate bandgap within experimental uncertainty. This finding indicates that within the range of validity of the transitivity rule, Cd1−xMnx-Cd1−yMny heterojunctions may actually follow the common anion rule.
Pulsed Laser Evaporation and Epitaxy Growth of Cd1−xMnxTe
Authors: Zheng X.L. , Huber C.A. , Becla P. , Shih M. , Heiman D.
Published: March 2011

Epitaxial layers of Cd1−xMnxTe have been grown on CdTe (100) substrates by evaporating a target with a 1.06 µm pulsed laser. The high - quality materials were characterized by photoluminescence spectroscopy (PL) and energy dispersive analysis of x-ray (EDAX). We find that the incorporation of the Mn in the epitaxial layer is about two - thirds of the concentration in the target. A comparison is made to the epitaxial layers grown on CdTe (111) and GaAs (100) substrates.
Photoluminescence of ZnSe Epilayers on GaAs Under Hydrostatic Pressure
Authors: Tuchman Judah A. , Sui Zhifeng , Herman Irving P. , Gunshor R. L. , Kolodziejski L. A. , Cammack D. A. , Shone M.
Published: March 2011

The near bandgap photoluminescence of ZnSe epilayers grown on GaAs substrates is measured for pressures up to ∼25 kbar using a diamond anvil cell at T = 9 K. The bandgap changes with pressure, dE/dp, for pseudomorphic and nonpseudomorphic films are obtained, and are compared with results for bulk crystalline ZnSe.
Preparation and Characterisation of (ZnTe)x(CdSe)1−x Single Crystals
Authors: Rani V.K. Madhu Smitha , Vijayalakshmi R.P. , Reddy D. Raja , Reddy B.K.
Published: March 2011

The titlematerial is one of the least studied among the II-VI alloy systems. So far it has not been possible to prepare ZnTe in n-type and CdSe in p-type with appreciable conductivities. Moreover ZnTe crystallises in zincblende whereas CdSe crystallises in wurtzite structure. Because of the varied nature of the end compounds, an attempt has been made to prepare single crystals of (ZnTe)x(CdSe)1−x in the entire range of ‘x’. The alloy material in the entire range Xof composition in the single crystalline form was grown by a modified Piper-Plich method. The grown crystals of this alloy system have been subjected to chemical analysis. DTA and DTG studies carried out on these alloys did not show any phasec transitions. However two exothermic peaks associated with increase in mass were noticed. This has been attributed to oxidation effects of Se/Te or Cd/Zn. XRD data though showed some regularity near end compositions there is still some ambiguity for the middle compositions. Energy gap obtained from reflection spectra and also photocurrent spectral response showed bowing. However, there is a marked different feature at one of the end regions. The growth and the results of all the above mentioned investigations are presented and discussed in this paper.
Deep Level Luminescence Measurements of MBE CdTe Growth Quality and Processing
Authors: Shaw J. L. , Brillson L. J. , Sivananthan S. , Faurie J. P.
Published: March 2011

We used photoluminescence spectroscopy to monitor CdTe in-situ during surface processing in order to optimize the surface electronic quality. Spectra of optimally-prepared (100) films grown by molecular beam epitaxy reveal low intensity emission from deep states relative to typical bulk-grown material.
Solubility of Impurities and Defect Impurity Interaction In II-VI Semiconductors
Authors: Marfaing Y.
Published: March 2011

A description of incorporation and solubility limit of substitutional impurities is made using the alloy CdxHgloxTe as a model of analysis and a source of experimental data.

Then non-equilibrium incorporation of impurities under light excitation is considered. A model of photo assisted doping is presented which accounts for the high doping efficiency reported for the donor indium in photoassisted grown CdTe.
Study of Transcrystallization in Polymer Composites
Authors: Hsiao Benjamin S. , Eric J. H.
Published: March 2011

Transcrystallization of semicrystalline polymers, such as PEEK, PEKK and PPS, in high performance composites has been investigated. It is found that PPDT aramid fiber and pitch-based carbon fiber induce a transcrystalline interphase in all three polymers, whereas in PAN-based carbon fiber and glass fiber systems, transcrystallization occurs only under specific circumstances. Epitaxy is used to explain the surface-induced transcrystalline interphase in the first case. In the latter case, transcrystallization is probably not due to epitaxy, but may be attributed to the thermal conductivity mismatch. Plasma treatment on the fiber surface showed a negligible effect on inducing transcrystallization, implying that surface-free energy was not important. A microdebonding test was adopted to evaluate the interfacial strength between the fiber and matrix. Our preliminary results did not reveal any effect on the fiber/matrix interfacial strength of transcrystallinity.
Effect of Ambient Atmosphere on Thin Film Reaction of Si3N4 with Ti
Authors: Desu Seshu B. , Taylor J. Ashley
Published: March 2011

The reaction of sputtered deposited Ti films of 100 nm thick with low pressure chemical vapor deposited Si3N4 films (300 nm thick) was studied in N2 or Ar, in a rapid thermal annealer. Reactions are followed using x-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. In argon, the Si3N4 and Ti reaction at low temperatures led to the product formation of two layer structure (TiN/Ti5Si3), with some contaminant oxygen and nitrogen released from the reaction uniformly dissolved throughout the remaining unreacted Ti. At higher temperatures, a three layer structure, TiN/TixSiy/TiN, on unreacted Si3N4 was developed. With increasing temperature the value of x and y decreased from 5 to 0 and 3 to 1, respectively. Reactions in N2 ambient, irrespective of temperature, always produced the three layer structure, but the thickness of TixSiy layer was much smaller than that produced in argon ambient for the corresponding temperatures. The reaction mechanism can be explained in terms of relative diffusion coefficients and the stability of the interfaces.
Stability and Reactions at Composite Interfaces of Titanium Aluminides with Potential Fiber Materials
Authors: Dekock J. A. , Chang Y. A. , Zhang M.-X. , Chen O. Y.
Published: March 2011

The Ti-Al-O and Ti-Al-B phase diagrams at 1100°C were estimated using thermodynamic data available in the literature assuming no ternary phases in either of the systems. Diffusion experiments consisting of a matrix of titanium aluminide with 2 at% Ta m contact with both Al2O3 and TiB2 were carded out at 1100° C for up to 192 hours.
The Effect of Temperature on the Chemistry and Morphology of the Interphase in an SCS6/Ti-6AI-4V Metal Matrix composite.
Authors: Jonesa C. , Kielya C. J. , Wang S. S.
Published: March 2011

The changes in chemistry and morphology within the interphase region of an SCS6/Ti-6A1-4V metal matrix composite upon exposure to varying heat treatments have been studied. It is thought that changes such as the formation of small TiC particles at one interface, and the narrowing of a protective pyrocarbon layer at another, induce fracture to occur at different places within the interphase upon heating. Evidence for a phase change on heat treatment of a TixSiy(C) layer to the more thermodynamically stable silicide phase,Ti5 Si3, is also presented.
The Effect of Fiber Coatings on Interfacial Shear Strength and the Mechanical Behavior of Ceramic Composites
Authors: Lowden Richard A. , More Karren L.
Published: March 2011

Thin coatings deposited on ceramic fibers prior to densification employing chemical vapor infiltration techniques have been used to limit fiber-matrix bonding. This has resulted in improvements in strength and toughness at room and elevated temperatures in Nicalon® fiber-reinforced/SiC matrix composites. The properties of the fiber-matrix interface in fiber-reinforced ceramic composites have been examined utilizing an indentation method in which a standard microhardness indentor is used to push on fibers embedded in the ceramic matrix. Compositions and microstructures at the interface have been characterized employing analytical electton microscopy. Correlations between interfacial phenomena and observed mechanical behavior have been made.
Tailored Interphases in Fibre Reinforced Polymers
Authors: Piggott Michael R.
Published: March 2011

The use of fibre coatings to enhance adhesion between fibres and polymers normally means that, in the fibre composite, some residue of the coating is present at the fibre-matrix interface. This constitutes the interphase. The mechanical properties of this material may be measured using simple fibre pull out tests. These tests have the advantage of revealing the interphase failure mode (i.e. brittle or ductile) as well as providing such data as work of fracture, yield stress, interfacial pressure and the coefficient of friction for post-debonding slip. Results obtained so far indicate some ductility and yielding with thermoplastic interphases, although final failure is brittle. Thermoset interphases appear to be universally brittle, with small works of fracture (10-200 Jm−2 ). The change in Young's modulus across the interphase may be a factor influencing brittle fracture, the biggest change giving the most brittle interphase.The ideal interphase should probably have a modulus intermediate between that of the fibre and the polymer, together with moderate yield stress, to give the composites adequate shear strength and good impact resistance through promotion of fibre pull outs.
Interfacial Interactions in Silica Reinforced Silicones
Authors: Aranguren Mirta I. , Macosko Christopher W. , Thakkar Bima , Tirrell Matthew
Published: March 2011

The study of the type and strength of the filler-polymer linkages is of great importance in understanding the reinforcement of elastomers. Silicone rubbers are weak elastomers and the addition of reinforcing fillers is essential in order to obtain useful, strong materials. The best reinforcing filler for these elastomers are fumed silicas. These fillers, like reinforcing carbon blacks, have very complex structures. Both have fractal characteristics, small particles fused together forming open aggregates that can cluster by physical forces. Silicas have sometimes more complex structures than carbon blacks, but have a better understood surface chemistry. Interactions between polydimethylsiloxanes and silica surfaces have been studied using heat of adsorption measurements of mostly low molecular weight analogs or inferring the strength of the adsorption by the shift of particular peaks in the infrared spectrum [1]. Here we will present a new technique that measures directly the strength of the adsorption of the polymer segments onto glass and between themselves. It also allows for comparison of the strength of such bonds with the strength of a polymer entanglement “link”.
Interfacial Effects of Plasma Treatment on Fiber Pull-Out
Authors: Gaur Umesh , Davidson Theodore
Published: March 2011

Surface modification of organic reinforcement fibers by exposure to certain plasmas appears to have considerable potential as a means for improving the performance of composites. Such treatments can change fiber surface properties, leaving the core of the fiber virtually unaffected so that the mechanical properties of the fibers remain unaltered. Previous studies [1–5] have shown that plasma treatment of polymeric fibers can modify surface energetics and that the acid/base characteristics of a fiber surface can be altered by exposure to plasmas of acidic or basic gases. Although several publications [6,7] have reported that the mechanical properties of composites reinforced with plasma-treated fibers are enhanced, there has been no direct evidence to show the impact of fiber surface plasma treatment on interfacial shear strength.
The Effects of Fiber Surface Treatments by a Cold Plasma in Carbon Fiber/Bismaleinide Composites
Authors: Chang Tao C. , Jang B. Z.
Published: March 2011

The effects of plasma treatments on the physical and chemical characteristics of carbon fiber surface and on the mechanical properties of carbon fiber/bismaleimide (BMI) resin composites were investigated. Scanning tunneling microscopy (STM), scanning electron microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and wettability measurements were applied for fiber surface characterization. Oxygen plasmas were found to be effective in enhancing the interfacial adhesion between carbon fiber and BMI matrix. Possible mechanisms of interfacial adhesion promotion were suggested and discussed.
Interphase Behavior in Cyclic Fatigue of Monofilament Composites
Authors: Schadler Linda S. , Figueroa Juan C. , Laird Campbell
Published: March 2011

Macroscopic properties of fiber reinforced composites are dependent on the micromechanics of the filament-matrix interphase. We present here some preliminary results of our studies aimed at understanding the behavior of the interphase when the composite is subjected to cyclic tensile loading. We have used carbon/polycarbonate mono-filament composites as a model system for studying the effects of loading direction (axial and transverse), frequency, and amplitude. The interphase was varied by etching the filament surface. Damage was characterized by fiber matrix debonding, reduction in interphase stress transfer efficiency, and changes in the locus of failure as determined by SEM fractography.
Plasticity During Fracture of the Au/Al2O3 Interface
Authors: Reimanis Ivar E.
Published: March 2011

Au/Al2 O3 interfaces are created by bonding highly textured Au films (25 pm thick) to single crystal A12 O3. Mechanical tests are done under the optical microscope to examine the effect of plastic deformation on the energy of fracture of the interface. Fracture occurs at the interface and is accompanied by plastic deformation in the Au. The relatively large value for the fracture energy measured (50-70J/m2) is attributed to the plastic deformation in the Au. It is also observed that fracture occurs subcritically due to stress corrosion at fracture energies from 10-20J/m2. Topographic features on the fracture surfaces are characterized and discussed briefly.
A Critical Evaluation of the Use of the Microbond Method for Determination of Composite Interfacial Properties
Authors: Haaksma Rebecca A. , Cehelnik Marilyn J.
Published: March 2011

The microbond method has been applied with increased frequency to characterize interfacial adhesion in fiber reinforced composites. Nevertheless, a number of serious questions remain regarding the interpretation of experimental data. This paper addresses material and experimental variables in the microbond test procedure including the cure behavior of thermoset test specimens, matrix heterogeneity, locus of failure in test specimens and load application techniques. The theoretical basis for the method is examined by viewing experimental results in terms of existing theoretical interpretations of interfacial failure. Conclusions are presented regarding the limitations and the potential of the microbond method for determining fiber/matrix adhesive bond strength.
Transmission Electron Microscopy Studies of Silicon Nitride / Silicon Carbide Interfaces
Authors: Kleebe H. J. , Corbin N. , Willkens C. , Rühle M.
Published: March 2011

Microstructural investigations of HIP'ed silicon nitride reinforced with silicon carbide whiskers were performed using a 400 kV high resolution analytical transmission electron microscope. Two different whisker sources as well as uncoated and carbon coated whiskers were evaluated for their effectiveness in improving mechanical properties.

This paper focuses on microstructural and microchemical analysis of interface and grain boundary regions within the composites. Combined HREM and AEM investigations reveal that variations in fracture toughness are mainly influenced by the microstructural and chemical development of the interface. Fracture toughness can be related to the surface chemistry of the reinforcements.
Fibre-Matrix Reaction Zones in Model Silicon Carbide-Titanium Aluminide Metal-Matrix Composites
Authors: Baker D. R. , Doorbar P. J. , Loretto M. H.
Published: March 2011

The reactions between coated SiC continuous fibres and TiAl, Ti3A1, or Ti3A1 + β matrices, have been investigated using optical metallography, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), with chemical information obtained by energy dispersive x-ray analysis (EDX) and electron energy loss spectroscopy (EELS).

Similar sequences of phases were found in all the composites; carbides based on TiC and TixAIC (x=2,3) and titanium silicides based on Ti5Si3 forming in narrow bands outside of the complex carbides. The occurrence of individual phases can be related to published phase diagram information. However, the sequences in which the reaction products occur within the reaction zones cannot be fully rationalised from the present results.
The Study of the Dislocation Structure and Energy of NiO-Pt Interfaces
Authors: Shieu F.-S. , Sass S. L.
Published: March 2011

The dislocation structure of Pt-(001)NiO interfaces was studied using electron microscopy and electron diffraction techniques. Specimens were produced by hot pressing polycrystalline Pt films on to thin NiO single crystals, and bulk Pt single crystals on to bulk NiO single crystals. The polycrystalline Pt specimens were used to determine the favored orientation relationships between the NiO and Pt, while the bulk NiO-Pt specimens were used to study the detailed structure of the interface. Three categories of orientation relationships were identified: exact epitaxy with (001)Pt ║ (001)NiO, [110]Pt ║ [110]NiO; small rotations away from exact epitaxy about the common [001] direction; high index planes of Pt parallel to (001) of NiO. Theoretical calculations of the expected dislocation structures of interfaces with the first two orientation relationships were made using a Bollmann-type analysis. The experimental observations and theoretical predictions were shown to be in good agreement. The energies of the interfaces having the first two orientation relationships were shown to be similar which is believed to be the reason why they both occur.
Growth of Monocrystalline Cosi2 on Cosi2 Seeds in (100)Si
Authors: Maex Karen
Published: March 2011

Growth of monocrystalline CoSi2 on top of (100) Si has been obtained by silicidation of deposited Co films on Si/CoSi2/Si heterostructures formed by ion implantation. The layers are of excellent crystalline quality and the CoSi2/Si interface is atomically flat. The required implanted dose can be reduced, since epitaxial silicidation is possible starting from aligned CoSi2 precipitates in the Si.
Temperature Dependent Current-Voltage Characteristics of TiSi2/n+/p-Si Shallow Junctions
Authors: Shah Bhupen , Ravindra N.M.
Published: March 2011

Modelling of temperature dependent current-voltage characteristics of TiSi2/n+/p-Si shallow junctions has been presented here. The formation of shallow pn junctions, by ion implantation of As+ through Ti films evaporated on p-Si substrates has been performed in these experiments. The temperature dependent factors such as band gap narrowing, intrinsic carrier concentration, mobilities and diffusivities are considered in the model.
Properties of Ohmic Contacts to Heterojunction Transistors
Authors: Harrison H. Barry
Published: March 2011

The electrical and physical properties of the contact between the active channel of high electron mobility transistors (HEMT’s) and the source or drain contacts play an important role in determining the transistor characteristics. This paper considers electrical models that may be applied to the various techniques now available to form these Interconnections. Results of electrical (and some physical) studies with regard to these systems are then discussed and compared where possible with predictions made using the electrical models. The comparisons show that the electrical models provide a useful base to identify the important parameters in these interconnections.
Simulation of Metallization Formation Processes on Si
Authors: Tokarev V. V. , Likholet A. N. , Zon B. N.
Published: March 2011

The processes occuring in thin films, in particular such as silicide formation processes, are rather difficult to control using analytical measurements. Such processes are widely used for the formation of metallization layers and usually require the precise control of film thickness, atomic composition, atomic distribution profiles, phase composition and electric resistance 1. The absence of model concepts of the process of silicide formation hinders the wide use of such processes and makes them labour-consuming ones due to the large number of control measurements.
Controlled Modifications in the Electrical Properties of Metal/GaAs Junctions
Authors: Eizenberg M.
Published: March 2011

Controlled modifications in the electrical properties of metal/GaAs junctions were obtaind by a few different approaches. The first approach is based on modifications induced by solid state reactions occurring between the metal and GaAs substrate, resulting in compound formation and component redistribution. The characteristics of such contacts can further be modified when the contact metal is alloyed with another metal or with a dopant. The second approach is based on modifying the doping level of the near surface region of the GaAs. Here an enhancement of the barrier height was obtained by heavily counter doping the top GaAs region by recoil implantation of Mg from a Mg thin film irradiated by As− ions. The correlations between the electrical properties of the junctions and the physical processes taking place using the above mentioned approaches are discussed.
Rbs Analysis of Intermixing in Annealed Samples of Pt/Ti/Iii-V Semiconductors
Authors: Savin W. , Weir B. E. , Katz A. , Chu S. N. G. , Nakahara S. , Harris D. W.
Published: March 2011

Low resistance Pt/Ti nonalloy contacts to GaAs, GaP, In As, InGaAs, and In Alas have been studied using Rutherford Backscattering. The samples were studied by comparing an as deposited structure to samples annealed at temperatures between 300°C and 600°C for 30 s. For all samples intermixing of the Pt and Ti was observed to start at 350°C. The Ti/HI-V semiconductor interface mixing was strongest for As when it was present, but In and Ga also strongly intermixed for anneals of 4S0°C and above.
Thermally Stable, Low Resistance Indium-Based Ohmic Contacts to n and p-Type GaAs
Authors: Murakami Masanori , Hallali P.-E. , Price W. H. , Norcott M. , Lustig N. , Kim H.-J. , Wright S. L. , LaTulipe D.
Published: March 2011

Recently, thermally stable, low resistance In-based ohmic contacts to n-type GaAs have been developed in our laboratories by depositing a small amount of In with refractory metals in a conventional evaporator, followed by rapid thermal annealing. By correlating the interfacial microstructure to the electrical properties, InxGa1-xAs phases grown epitaxially on the GaAs were found to be essential for reduction of the contact resistance (Rc). This low resistance was believed to be due to separation of the high barrier (φb) at the metal/GaAs contact into two low barriers at the metal/InxGa1-xAs and InxGa1-xAs/GaAs interfaces. In this paper the effects of the In concentration (x) in the InxGa1-xAs phases and addition of dopants to the contact metal are presented. High In concentration is desirable to reduce the φb at the metal/InxGa1-xAs interface. Such contacts were prepared by sputter-depositing InAs with other contact elements, but the low Rc values were not obtained. The reason was explained to be due to an increase in the φb at the InxGa1-xAs/GaAs interface due to the formation of misfit dislocations. However, addition of a small amount of Si to the contact metals reduced significantly the Rc value. This contact demonstrated excellent thermal stability: no deterioration was observed at 400°C for more than 100 hrs. In addition, the use of this Ni(Si)InW contact metal allowed us to fabricate the low resistance ohmic contacts by one-step (simultaneous) annealing for “implant-activation” and “ohmic contact formation”, which simplifies significantly GaAs device fabrication process steps. For p-type ohmic contacts, low resistance contacts were fabricated by depositing the same NilnW contact material to p-type GaAs. This contact was also thermally stable during subsequent annealing at 400°C. Within our knowledge this is believed to be the first demonstration of low resistance, thermally stable ohmic contact fabrication using the same materials for both n and p-type GaAs.
Mn–In–Co, Mn–Pt and Mn–In–Pt Based Contacts to p–GaAs
Authors: Kalkur T. S. , Lu Y. C. , Rowe M.
Published: March 2011

Mn–In–Co, Mn–In–Pt and Mn–Pt metallizations are used to form ohmic contact on Be-implanted rapid thermally annealed GaAs. The rapid thermal alloying of contact metallizations are performed in A.G. Associates Heat pulse system in nitrogen atmosphere in the temperature range of 350°C to 800°C for 5 seconds. The contacts were found to be ohmic at an annealing temperature of 450°C. The In–Mn–Co metallization showed higher minimum contact resistivity (5 × 10−4 ohm.cm2 ) than In–Mn–Pt metallization (1.5 × 10−5 ohm.cm2 ) for an annealing temperature of 700°C and time 5 seconds. The surface morphologies of In–Mn–Pt metallizations were smooth even after alloying at 700°C for 5 seconds. The Auger analysis shows outdiffusion of Ga and As into the contact metallization and negligible indiffusion of In and Mn into GaAs.
Alloying behavior of the Ni/In/Ni/n-GaAs Ohmic Contact
Authors: Jan Chia-Hong , Swenson Doug , Austin Chang Y.
Published: March 2011

The interactions between Ni and Ni/In/Ni thin-films and GaAs were studied by SEM, SAM and AES. The presence of a molten phase was observed for both contacts after annealing at 820°C for 3 minutes. This behavior was rationalized in terms of the presence of a ternary eutectic reaction in the gallium-nickel-arsenic system. DTA confirmed the existence of the reaction:

at 810°C. In the case of Ni/In/Ni, melting was thought to occur because of the segregation of indium metal to the contact surface and the subsequent melting of the nearly ternary interfacial region. Upon further cooling the formation of NiGa, NiAs, InxGa1−xAs and an unspecified compound Ni-In was believed to occur. The contact was shown to be either sintered or alloyed, depending upon processing conditions.
Investigation of Thin Pd-Ge Layer Formation Using Synchrotron Vacuum Ultraviolet Photoemission Spectroscopy
Authors: Meissner P. L. , Bravman J. C. , Kendelewicz T. , Miyano K. , Spicer W. E. , Woicik J. C. , Bouldin C.
Published: March 2011

The formation of Pd-Ge layers was studied as a function of deposition and annealing using synchrotron Ultraviolet Photoemission Spectroscopy (UPS). Pd depositions ranging in thickness from 0.5 monolayers (ML) to 44 ML were examined in-situ on Ge (111) cleaved in ultra-high vacuum. The primary reaction components appear to be Pd2Ge and PdGe. Comparison of bulk and surface sensitive Ge 3d core levels for even the highest coverages indicates that Ge segregates to the surface at room temperature. Such low temperature segregation suggests that Ge can diffuse via a rapid diffusion mechanism.
Taper Etchable Neon-Sputtered Molybdenum Film
Authors: Kato Kinya , Wada Tsutomu
Published: March 2011

Taper etchable molybdenum (Mo) films are successfully obtained by neon (Ne) sputter deposition. Mo films several hundred nanometer thick are deposited using an RF planar magnetron sputtering system. After photolithography, the Ne-sputtered Mo films are etched with a hydrogen peroxide solution. Films deposited in low pressure Ne show an excellent tapered edge with a taper angle of less than 45°, which can eliminate the step-coverage problem. However, higher-pressure Ne-sputtered films and films sputtered in argon (Ar) show steep edge profiles .

Ne-sputtered Mo films show a drastic change in characteristics depending on the gas pressure. The internal stress is strongly compressive for lower pressures and becomes tensile for higher pressures. According to RHEED patterns, lower pressure sputtered film shows a <110> orientation including a halo which indicates the existence of an amorphous-phase, but higher pressure sputtered films show clear <111> orientations. TEM observations confirm the structural change. Higher pressure Ne-sputtered film and Ar-sputtered film show columnar structures, but low-pressure Ne-sputtered film shows the disordered structure.

Taper etchability of the low-pressure Ne-sputtered Mo films is considered to be due to the structural change, especially the included amorphous-phase.
Role of Interface-States in the Reverse Bias Aging of Gaas Schottky Barriers
Authors: Christianson K. A.
Published: March 2011

Forward bias capacitance has been used to examine the Au/W/GaAs and Au/Pt/Ti/GaAs Schottky barriers present in power microwave MESFET devices to see if interface-state generation plays any role in the previously reported reverse bias barrier height aging process. If a constant carrier capture cross-section is assumed, forward bias capacitance has shown that for samples strongly susceptible to aging (i.e. the Au/W/GaAs samples in this study) interface-state generation is taking place during the aging process. The validity of the constant capture cross section assumption has been tested by examining the I-V properties. For those samples whose reverse I-V properties were not dominated by thermionic-field emission, similar increases in interface-state densities were evaluated from the I-V characteristics for the degraded samples.
Thermal Stability of a1-pt Thin Films/Gaas for Self-Aligning Gate Contacts
Authors: Wilk G. D. , Blanpain B. , Olowolafe J. O. , Mayer J. W. , Zheng L. R.
Published: March 2011

Several compositions of Al-Pt thin films have been co-evaporated on GaAs substrates to study the stability of the alloys at high-temperature anneals. The Al concentration in the alloys ranges from 45 at.% to 70 at.%, and we show that the films meet thermal stability requirements imposed by GaAs self-aligning gate technology for compositions between AlPt and Al2Pt.
Electrical Properties and Schottky Barriers of Metal-Semiconductor Interfaces
Authors: Aboelfotoh M.O.
Published: March 2011

The electrical properties of metal/Si(100) and metal/Ge(100) interfaces formed by the deposition of metal on both n-type and p-type Si(100) and Ge(100) have been studied in the temperature range 77-295 K with the use of current- and capacitance-voltage techniques. Compound formation is found to have very little or no effect on the Schottky-barrier height and its temperature dependence. For silicon, the barrier height and its temperature dependence are found to be affected by the metal. For germanium, on the other hand, the barrier height and its temperature dependence are unaffected by the metal. The temperature dependence of the Si and Ge barrier heights is found to deviate from the predictions of recent models of Schottky-barrier formation based on the suggestion of Fermi-level pinning in the center of the semiconductor indirect band gap.
Requirements of Electrical Contacts to Photovoltaic Solar Cells
Authors: Gessert T.A. , Coutts T.J.
Published: March 2011

The importance of contacts to photovoltaic solar cells is often underrated mainly because the required values of specific contact resistance and metal resistivity are often thought to be relatively modest compared with those associated with very large scale integration (VLSI) applications. However, due to the adverse environmental conditions experienced by solar cells, and since many of the more efficient cells are economically advantageous only when operated under solar concentration, the requirements for solar cell contacts are sometimes more severe. For example, at one-sun operation, the upper limit in specific contact resistance is usually taken to be 10−2 Ω-cm2. However, at several hundred suns, this value should be reduced to less than 10−4 Ω-cm2. Additionally, since grid line fabrication often relies on economical plating processes, porosity and contamination issues can be expected to cause reliability and stability problems once the device is fabricated. It is shown that, in practice, these metal resistivity issues can be much more important than issues relating to specific contact resistance and that the problem is similar to that of providing stable, low resistance interconnects in VLSI. This paper is concerned with the design and fabrication of collector grids on the front of the solar cells and, although the discussion is fairly general, it will center on the particular material indium phosphide. This III-V material is currently of great importance for space application because of its resistance to the damaging radiation experienced in space.
Pd-Ge-Au Ohmic Contacts to GaAs: Reliability and Failure Analysis.
Authors: Kazior T. E. , Hieslmair H. , Brooks R. C.
Published: March 2011

We report on experiments that were performed to evaluate the temperature stability and long term reliability of non-alloyed Pd-Ge-Au ohmic contacts on N-type GaAs. Low resistance contacts (≈1×10−6Ωcm2) were obtained for samples that were sintered in a conventional furnace or flash sintered in a graphite susceptor. Elevated temperature storage (≈4000 hours at 280°C) showed improved contact stability when compared to Ni-AuGe-Ni-Au control samples. Gateless MESFETs subjected to bias temperature stress measurements (Ids ≈300-350mA/mm, 2000–4000 hours at 200°C) showed no significant change in device current. This result is in contrast to devices with Ni-AuGe-Ni-Au ohmic contacts which exhibited a 6–27% decrease in current under the same test conditions. Failure analysis reveals significant electromigration and Au diffusion in the drain fingers of devices with Ni-AuGe-Ni-Au contacts. In contrast, devices with Pd-Ge-Au contacts show no electromigration or Au diffusion in the GaAs.
On the Ohmic Contact Formation Mechanism in the Au/Te/N-GaAs System
Authors: Wuyts K. , Langouche G. , Vanderstraeten H. , Silverans R.E. , Van Hove M. , Van Rossum M. , Münder H. , Lüth H.
Published: March 2011

Alloyed Au/Te/n–GaAs ohmic contacts, with contact resistivities comparable to those of the AuGe device standard, have been developed and studied by Mässbauer spectroscopy, Raman scattering and X-Ray Diffraction. The formation of Au-doped Ga2Te3 crystallites, grown epitaxially on a defectively GaAs surface was observed. No evidence for the formation of an n++–GaAs surface layer could be derived. The interpretation of all experimental results leads to a description of the ohmic conduction mechanism based on a resonant tunneling process assisted by defect/impurity related deep levels through low barrier metal/Te/(Au)Ga2Te3/GaAs interfaces
The Effects of Ion Beam Mixing on Rapid Thermal Annealed Ohmic Contacts to N-GaAs
Authors: Kazmi Seemi , Kruzelecky Roman V. , Thompson David A.
Published: March 2011

Ni/Ge/Au and Ni/Ge/Pd contacts have been made on 1018 cm-3 n-type GaAs. The contacts were subjected to ion beam mixing through the metallization using 70-130 keV Se+ ions and subsequently subjected to rapid thermal annealing (RTA). These are compared with unimplanted contacts produced by RTA techniques on the same substrate. The specific contact resistance ,pc, has been measured for the two systems. In addition, the contacts have been studied using Auger depth profiling and SEM studies have been used to determine surface morphology. Values of pc ∽ 10-6 -10-7 ohm-cm2 have been measured. It is observed that ion beam mixing or the addition of a Ti overlayer (to the Ni/Ge/Au) improves the contact morphology.
Ni-Ge Intermixing on GaAs Produced by Temperature Standardized Rapid Thermal Annealing
Authors: Brooks Michael B. , Sigmon Thomas W.
Published: March 2011

A new Rapid Thermal Annealing technique has been developed which uses very small samples of low melting elements and eutectic alloys to standardize temperature measurements. Temperatures of thin films during anneal are shown to lie within −3°C to +13°C of nominal for measured short anneal times using a special sample geometry. Results of annealing Ge/Ni/GaAs and Au/Ge/Ni/GaAs at 200°C and 250°C are presented. Rutherford backscattering is used to analyze the films and the resulting channeling spectra show that Ge consumption follows parabolic kinetics, with an activation energy estimate of ≈ 0.7eV. The data is consistent with a controlling process of fast Ni diffusion through grain boundaries at these low temperatures. We expect that a Ni2Ge phase is being formed preferentially, along with a NixGaAs phase at the GaAs/Ni interface. In this contact metal system Au interacts only minimally for the times and temperatures studied. Our results agree with those of previous workers who studied Ni diffusion during NixGaAs phase formation at comparable temperatures.
Au-Ge-Ni-Ti Ohmic Contacts on Gallium Arsenide
Authors: Alexander K. B. , Stobbs W. M.
Published: March 2011

The influence of titanium additions on the microstructure of Au-Ge-Ni ohmic contacts on gallium arsenide has been evaluated. Sequentially deposited layers of Ge, Au and Ni were topped with a titanium layer. The titanium formed a native titanium oxide on the upper surface of the contact which helped to maintain a continuous film during the anneal. Both the as-deposited and the annealed microstructures were studied with the use of electron microscopy techniques. In order to examine thoroughly the various phases which form in the annealed contact, unique specimen preparation procedures were used to fabricate a single plan-view specimen in which it was possible to examine the microstructure at various depths.
Correlation Between the Interfacial Nonuniformity and the Specific Contact Resistance of Ohmic Contacts to Gaas
Authors: Tuy T. Q. , Mojzes I. , Tuyen V. V. , Cseh I.
Published: March 2011

Considering the effect of the simultaneous presence and interaction of the different phases at the contact, a modification of the model presented by Wu and coworkers (Solid-St. Electron. 29 (1986) 489] for explanation of ohmic contact resistance of n-GaAs was developed. The modified model combines the existence of the mixed phase structure of AuGeNi/n-GaAs contact with assumptions proposed by Wu et al. that the specific contact resistance Rc contains two parts Rcl and Rc2, where Rc1 is the specific contact resistance of the alloyed and underlaying doped contact region, and Rc2, is that of the high-low junction between the heavily doped contact region and the bulk semiconductor. The Rc1 depends strongly on the apparent barrier height and the effective impurity concentration formed by doping from the contact alloys during annealing. In the present paper a new theoretical model for Rc1 is proposed and compared with the experimental results.
Interfacial Microstructure and Carrier Conduction Process in Pt/Ti Ohmic Contact to P-In0.53Ga0.47As Formed by Rapid Thermal Processing
Authors: Chu S.N.G. , Katz A. , Boone T. , Thomas P.M. , Riggs V.G. , Dautremont-Smith W.C. , Johnson W.D.
Published: March 2011

The strong dependence of electrical properties of Pt/Ti ohmic contact to p–In0.53Ga0.47 As (Zn: 5 × 1018 cm−3) on the interfacial microstructure formed by rapid thermal processing (RTP) were intensively studied by transmission electron microscopy, Auger Spectroscopy, and transmission line model (TLM) measurements. The rapid decrease of the specific contact resistance with an increase in RTP temperature was correlated with the development of an interfacial reaction zone. Significant interdiffusion of Ti, In and As across the interface occurred at temperature above, 350°C for a 30 second of RTP. A minimum specific contact resistance (3.4 × 10−6 Ω-cm2) was achieved at RTP temperature of 450°C. The corresponding interfacial microstructure revealed a complicated solid state reaction zone with InAs as one of the major interfacial compounds. The low contact resistance is attributed to the carrier conduction through the InAs regions. This is also consistent with the results of Pt/Ti contact experiments to p-type InAs, InP and GaAs binary surfaces, where the lowest contact resistance was achieved on InAs (3.0 × 10−7 Ω-cm2at Zn: 5 × 1018 cm−3). The temperature dependence of specific contact resistance of as-deposited Pt/Ti contact to InGaAs agrees very well with the thermionic emission dominated carrier transport mechanism with an effective barrier height, φb, of 0.13V. The rapid decrease in the contact resistance as well as its reduced temperature dependence after RTP treatment at elevated temperatures suggesting a partial conversion of thermionic emission dominated contact area to field emission dominated regions. A phenomenological theory of multiple parrallel carrier conduction processes was proposed to analyse the temperature dependence of specific contact resistance for contacts with complicated interfacial microstructure. It was found that, for low resistance contacts, majority of the carriers conducted through only a fraction of the contact area via a tunneling mechanism.
Submicron Pseudomorphic Hemt’S Using Non-Alloyed Ohmic Contacts with Contrast Enhancement.
Authors: Jansen Ph. , De Raedt W. , Van Hove M. , Jonckheere R. , Pereira R. , Van Rossum M.
Published: March 2011

We report for the first time the realization of submicron pseudomorphic Al.15, Ga.85As-In.20Ga.80As HEMT’s with non-alloyed Pd/Ge ohmic coi tacts. Best results of contact resistance were obtained at a sintering temperature of 340°C with values as low as 0.057 Ωmm. Enhanced contrast, needed for accurate alignment of the gate by electron-beam lithography, was obtained by using Pd/Ge/Ti/Pd and Pd/Ge/Ti/Pt metal sequences. These contacts exhibited even lower contact resistances than the standard Pd/Ge contacts. Although Pd/Ge/Ti/Pd exhibits good morphology, reaction is witnessed at the edges, reducing the accuracy of alignment.

Processed enhancement mode devices exhibit maximum transconductances in excess of 520 mS/mm and currents of 300 mA/mm for 0.3 micron gatelength. This study shows that the contact resistance is no longer a restriction for obtaining very high transconductances in high performance devices.
Role of in-Situ Rapid Isothermal Processing (Rip) in the Metallization and Passivation of Indium Phosphide Devices
Authors: Singh R. , Thakur R. P. S. , Katz A. , Nelson A. J.
Published: March 2011

As compared to a stand alone rapid isothermal annealing unit, the integration of deposition system and rapid isothermal processing unit is very attractive for the next generation of micro, opto and cryoelectronics. We have used in-situ rapid isothermal processor for in-situ rapid isothermal chemical cleaning of InP, solid phase epitaxial growth of II-A fluorides, and in-situ metallization of InP capacitors. As compared to ex-situ annealed films, SrF2 films deposited on InP by in-situ rapid isothermal processed films show less thermal stress and lower thermal hysteresis for the identical thermal budget. Similarly, as compared to ex-situ annealing, in-situ cleaning of InP before metallization followed by in-situ annealing results into improved high frequency capacitance-voltage (C-V) characteristics of Al-SrF2-InP capacitors.
Anti-Reflection Coatings (Arc) for use with Aluminum Metallizations on GaAs ICs
Authors: Brady Michael F. , Helms Aubrey L.
Published: March 2011

The need for an Anti-Reflection Coating (ARC) on aluminum metallizations is well known. A new class of materials based on tungsten-silicide and tungsten-silicon-nitride has been developed Tor use as an ARC. It has been shown that the reflectivity (relative to aluminum = 100%) can be decreased to −55% for the tungsten-silicide material and to −6% for the tungsten-silicon-nitride materials. These materials are easily etched in fluorine containing plasmas and are not as sensitive to thickness uniformity issues as dyed resists or amorphous silicon ARC materials. The option of leaving these ARC materials on the aluminum lines may lead to an increase in the electromigration resistance. The dependence of the reflectivity on nitrogen content has been investigated. Additionally, the reflectivity reducing properties have been studied on a variety of substrates such as aluminum, gold, tungsten, tantalum, and silicon.