bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Emissions During Indentation Tests
Authors: Weihs T P , Lawrence C W , Derby B , Scruby C B , Pethica J B
Published: March 2011

When a hard tip indents a sample, cracking, delamination and plasticity can all produce acoustic signals in the form of elastic waves. This paper describes how these acoustic emissions (AE) can be monitored using piezoelectric elements and a load-controlled indentation instrument. Signals emitted from thin films and bulk materials are shown and they are correlated with distinct jumps in displacement of the indenter tip. The benefits and difficulties of different methods of monitoring the emissions are also considered.
Relaxation in Sub-Micron Si-1-xGex Strain-Layer Mesas
Authors: Luo Dawei , Howard David J. , Paine David C.
Published: March 2011

Finite element modelling of strain-layer mesa structures shows that edge effects can contribute to the relaxation of in-plane misfit stress. Calculations were performed for a 200 nm thick layer of Si90Ge10 grown epitaxially on an <001> Si substrate which was patterned into 400-nm-high mesas ranging in diameter from 0.6 to 7 μm. These calculations were experimentally investigated using plan-view TEM to study relaxation in patterned and unpatterned material. This composition and film thickness exceeds the critical thickness predicted using simple strain energy considerations. In one experiment, an initially defect-free 200-nm-thick Si90Ge10 layer was annealed at 960°C for 1 hr to create a nearly fully relaxed layer which was then lithographically patterned into an array of sub-micron mesas. The wafer was then annealed for a second time and changes in the character of die pre-existing dislocations were studied.
Stress and Microstructure in Rf-Diode and Dc-Magnetron Sputtered Beryllium Thin Films
Authors: Mutikainen Risto H.
Published: March 2011

The effect of deposition parameters on the properties of sputtered Be films has been studied. The parameters have been optimized to obtain stress free films. Nitrogen pulsing has been used to improve the film microstructure by suppressing the columnar grain growth.
Thermal Degradation of SiGe Interfaces Studied by X-Ray Reflectivity and Diffraction
Authors: Hudson J. M. , Powell A. R. , Bowen D. K. , Wormington M. , Tanner B. K. , Kubiak R. A. , Parker E.H.C.
Published: March 2011

We demonstrate the use of x-ray diffraction to provide accurate compositional information, together with grazing incidence reflectivity to provide information on layer thicknesses and surface and interface roughnesses, on Si/Si1-xGex superlattice structures of less than 200nm total thickness.

The quality of SiGe interfaces has been investigated in superlattices where x varies from 0.1 to 0.5. At low Ge compositions the interfaces are shown to be smooth to a few angstroms. However, as the Ge composition in the SiGe layer approaches 50%, severe roughness is observed at the SiGe to Si interfaces, although the Si to SiGe interfaces remain relatively smooth.

Upon annealing for one hour at 850°C the Ge diffuses outwards from the SiGe layers and can be closely modelled by inclusion of a (2.4±0.3)nm linearly graded layer either side of the SiGe layer into a simulation program. The long range roughness at the SiGe to Si interface is lost upon annealing leaving only a short range roughness of similar size to the Si to SiGe interface roughness.

Reflectivity measurements have been shown to distinguish between interface roughness and interdiffusion for the annealed system.
Nanometer-Scale Modification and Imaging of Polyimide Films by Scanning Force Microscopy
Authors: Unertl W. N. , Jin X.
Published: March 2011

The sharp tip of a scanning force microscope can be used to make controlled modifications of polymer surfaces. In this paper, we describe the properties of micrometer size pits up to 900 Å deep formed on Kapton-H surfaces. The structure at the bottom of the pits appears to be closely related to the degree of crystallinity near the surface. We also use elasticity theory to estimate that the resolution of scanning force microscopy for polymer surfaces is about 160 Å for tips with 400 Å radius. This estimate agrees well with the resolution obtained in images of polyimide surfaces.
Thin Film Adhesion Study in Microelectronic Packaging
Authors: Jeong H. S. , Chu Y. Z. , Freiler M. B. , Durning C. , White R. C.
Published: March 2011

Fracture energy (Ga) of BPDA-PDA polyimide (PI) on modified and unmodified Si surfaces was measured by the “blister” test as a function of final cure temperature. It is proven quantitatively that surface modification prior to thin film deposition enhances adhesion. Metal adhesion to PI was also measured by the same method. Reproducibility of the data was found to be exceptionally good for both cases. The linear elastic model is quite valid for the test of thin film adhesion. Therefore, it is believed that this test is best suited for Ga measurements in the study of thin film adhesion for microelectronic packaging.
Cracking and Adhesion of Ceramic Films
Authors: Atkinson Alan , Guppy Richard M.
Published: March 2011

Brittle films of ceramics on metal substrates become mechanically unstable when a critical thickness is exceeded. Experiments have been carried out to investigate this instability for films under tension and compression. Films of cerium oxide gel under tension were prepared by spin-coating a ceria sol onto stainless steel substrates. Films exceeding a critical thickness failed by through-film cracking. The relationship between crack spacing and film thickness was consistent with partial interfacial delamination accompanying film cracking. Films of nickel oxide under compression were prepared by the oxidation of nickel and NiAl and NiCr alloys. The adhesion of the films to the substrates was measured in a double bending beam configuration and by scratch testing. A critical thickness was observed at which adhesion became very low and which depended on the composition of the metal substrate. The observed behaviour is consistent with a buckling instability in the film. In both types of film the conditions for crack propagation appear to determine instability, but the nature of the failure-initiating defects remains obscure.
The Origin of Anomalous Strain in Thin Sputtered Mo Films on Si(100)
Authors: Tao J. , Adams D. , Yalisove S. M. , Bilello J. C.
Published: March 2011

Stress and structure evolution in thin films of sputtered Mo on Si(100) substrates has been studied, as a function of microstructure, by x-ray diffraction, transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). Double crystal x-ray diffraction topography (DCDT) has been employed to determine film stress as a function of thickness. High compressive stress, about 1000 MPa, is found for the thinnest Mo film. With increasing film thickness a minimal residual stress level is reached. Low incidence angle x-ray diffraction patterns indicated that crystalline Mo is present even in the thinnest films. Line broadening of the Mo(l10) diffraction peak has shown that the grain dimension is comparable to the film thickness over the range studied. Plan view TEM observations of films less than 20nm demonstrated the presence of continuous film with grain dimensions on the order of film thickness, in good agreement with the x-ray results.
Frictional Effects in the Buckling Delamination of a Compressed Thin Film and Implications for Interfacial Fracture
Authors: Stringfellow R. G. , Freund L. B.
Published: March 2011

As a film in residual compression delaminates from a substrate, the post-buckling response of the film tends to drive it into the substrate in the region directly behind the delamination front. We consider the process of frictional interaction between the film and the substrate during the delamination process in order to assess the effect of Coulomb friction on the energy release rate, G, driving the delamination. For the case in which the film and the substrate have identical elastic properties, we derive a singular integral equation to determine the relative sliding displacement of the opposing faces of the interface. Using an analytical model, we find that G decreases by about 35% when the coefficient of interfacial friction is equal to one. Using finite element methods, we then investigate the effects of compliance differences between the film and the substrate. We find that, when the film is more compliant than the substrate, frictional interaction is enhanced and the calculated energy release rate decreases substantially. We conclude that frictional effects can account for a significant portion of the energy dissipation during the delamination process, and thus can play an important role in the observed arrest of spreading delaminations.
Continuous Microindentation and Microscratch Measurements of Metal-Ceramic Adhesive strengths
Authors: Venkataraman S. , Kohlstedt D. L. , Gerberich W. W.
Published: March 2011

To investigate the effect of heat-treatment on the adhesion of Pt thin films to NiO substrates, the strain energy release rate, interfacial fracture toughness and interfacial shear strength were determined from continuous microscratch and continuous microindentation experiments. Samples were prepared by sputtering Pt onto single crystals of NiO, followed by a heat-treatment at temperatures of 300, 500 and 800°C and an oxygen partial pressure of either 0.21 or 10-5 atm. Continuous microscratch tests were performed by driving a conical indenter with either a 1 or 5 μm tip radius simultaneously into and across the Pt film. From the magnitude of the critical load at the point of film delamination and the area of the delaminated piece of the thin film, the strain energy release rate (practical work of adhesion) and interfacial fracture toughness were calculated. The practical work of adhesion and interfacial fracture toughness increased from 0.2 J/m2 and 0.2 MPa√m, respectively, for as-sputtered samples to 4.6 J/m2 and 1 MPa√m for samples heat-treated at 500°C and 10-5 atm. Preliminary analysis of continuous microindentation results for Pt/NiO samples yielded interfacial shear strengths of 270 MPa for as-sputtered samples and 725 MPa for samples heat-treated at 500°C and 10-5 atm. While these values are in good agreement with those determined by other methods for metal-ceramic systems, there are sufficient differences in test method for a single system to require additional analysis of the proposed models.
Improvement of Tribological Properties of Mosa Films by Forming Interlayers and/ or Bombarding with Ions
Authors: Matsui Akihiko , Kagimoto Yoshimi
Published: March 2011

The effects of forming interlayers and/or bombarding with ions on the tribological properties of the sputter-deposited MoS2 films were investigated. The MoS2 films on substrates of Ti-alloy, martensitic stainless steel and high speed tool steel with TIN interlayers were evaluated by ball/disk sliding tests under ultra-high vacuum condition. Furthermore, nitrogen- or sulfer-ion-bombarded MoS2 films tested too. The test results showed correlation between the surface hardness of substrates and the wear life of MoS2 films. The wear life of the ion-bombarded MoS2 films was improved by mixing film/substrate interface.
Effect of High Temperature Stress on Titanium-Tungsten Gold thin Films on Alumina
Authors: Koh Wei H. , Louie W.
Published: March 2011

The adhesion of a sputtered titanium-tungsten gold (Ti-W/Au) thin film on alumina substrates is found to be weakened after being stressed at temperatures above 575°C, due to depletion of the Ti-W base metal. Thin films deposited on substrates having a fine grain structure and as fired surfaces, however, maintained their adherence at temperatures up to 650°C.
Adhesion and Tribological Properties of Ag and Ag/Ti Films on Zro2 Ceramic Substrates After Heat Treatment at 250°C
Authors: Hsieh J. H. , Ajayi O. O. , Erdemir A. , Nichols F. A.
Published: March 2011

Ag and Ag/Ti films were deposited on ZrO2 substrates by ion-beam-assisted deposition. Adhesion of these films was measured before and after heat treatment at 250°C in air. The results show that a graded interface between Ag and Ti was necessary for the Ag films to survive the heat treatment. Reciprocating pin-on-disc tests were performed at 150°C after heat treatment to investigate the relationship between adhesion and tribological properties. The failure of Ag and Ag/Ti (without graded interface) films was also observed during wear tests. However, this Ag film failure did not result in negative effects. All three Ag-coated substrates show better tribological behavior.
Electromigration Resistance and Mechanical Strength: New Perspectives for Interconnect Materials?
Authors: Arzt E. , Kraft O. , Sanchez J. , Bader S. , Nix W. D.
Published: March 2011

A brief review is given of models which propose a correlation between electromigration resistance and the mechanical strength of thin film interconnects. In an attempt to achieve metallurgical strengthening and improved electromigration resistance, aluminum films were implanted with oxygen ions. Preliminary electromigration tests on line arrays patterned from these films resulted in lifetimes comparable to the standard Al films. The lack of improvement is attributed to enhanced hillock/whisker growth during electromigration in the implanted interconnects. This behavior is coincident with a lower compressive strength in similarly treated continuous films at elevated temperatures as measured by the substrate curvature technique.
Strain Dependent Diffusion in the Dry Thermal Oxidation Process of Crystalline Si
Authors: Bjorkman C. H. , Lucovsky G.
Published: March 2011

We have investigated the influence of strain on the rate of thermal oxidation of crystalline Si. This was carried out by performing the oxidation in two steps at 850°C with an intermediate annealing step. It was observed that an anneal at 1050°C increased the oxidation rate 20% compared with an anneal at 850°C. At the same time, the films annealed at higher temperatures exhibited lower levels of strain, as determined by infrared spectroscopy, in the oxide layer grown before the anneal. These results have been interpreted in terms of a strain dependent diffusion model for the thermal oxidation process.
Transport in Compounds Containing a Dispersed Second Phase.
Authors: Bruce Wagner J.
Published: March 2011

The introduction of a dispersion of small (≃ 1μ1m) insulating particles into an ionic conductor results in an increase in the ionic conductivity. This behavior is not in accord with classical theory. A number of different examples such as a dispersion of a metallic conductor in a semiconductor, a dispersion of an insulator in a semicondutor, and a dispersion of a metallic conductor in an ionic conductor all yield unusual transport behaviors when the surface area to volume ratio of the dispersoid is large. Under such conditions, a space charge layer or double layer adjacent to the dispersoid must be considered. Practical applications such as solid electrolytes, electrodes, corrosion systems and geological systems were discussed.
Refractory Materials For High-Temperature Thermoelectric Energy Conversion
Authors: Wood Charles , Emin David
Published: March 2011

Two refractory material systems show promise for efficient energy conversion at high temperatures (>1000 K): the rare-earth chalcogenides and the boron-rich borides. The electronic and thermal transport properties of these two systems are compared and discussed.
Densification of Shock-Treated Aluminum Nitride and Aluminum Oxide
Authors: Beauchamp E. K. , Graham R. A. , Carr M. J.
Published: March 2011

The structures of aluminum nitride and aluminum oxide powders have been modified by explosive shock treatment at pressures from 4 to 27 GPa. Shockinduced dislocations in AlN were apparently responsible for enhancement in hot pressing behavior. In Al2O3 an increase 3 to 4 times in densification rates after shocking resulted-from rapid sintering of aggregates in the powder.
Submicron Particle Sizing by Light Scattering and Sedimentation
Authors: Taylor Jenifer
Published: March 2011

Submicron particle sizing is complex, requiring careful interpretation of distribution data. Information gathered from laboratory use of a sedimentometer and a light scattering system are discussed in terms of strengths and weaknesses.
Transmission Electron Microscopy of Shock-Modified and Annealed Rutile
Authors: Carr M. J. , Graham R. A. , Morosin B. , Venturini E. L.
Published: March 2011

The annealing behavior of shock modified rutile (TiO2) powder was studied by transmission electron microscopy, x-ray line broadening, and electron spin resonance. Specimens were examined in the as-received and as-shocked conditions, and in shocked and annealed conditions after one hour at 475° or 1000°C. The dislocations generated by the shock treatment were found to persist essentially unaltered through the 475°C anneal. Substantial recovery was observed after the 1000°C anneal.
Metallic Microwave Conductivity in Shock-Loaded Rutile
Authors: Venturini E. L. , Graham R. A.
Published: March 2011

Electron spin resonance (ESR) has been used to characterize the paramagnetic defects present in both single crystal and powder rutile (TiO2) subjected to explosiveshock loadingand preserved for post-shock study. The Ti+3defect concentration produced by the shock process is an order of magnitude larger than values reported for vacuumreduced rutile. The ESR lineshape is characteristic of a conducting material, and the estimated microwave resistivity in the shock-loaded powder is more than an order of magnitude lower than the minimum dc value measured in vacuum-reduced rutile. It appears that shock-wave loading leaves the rutile in a defect state not achieved in prior work.
Status, Needs, and Opportunities for Structural Ceramics in Advanced Heat Engines
Authors: Tennery V. J.
Published: March 2011

The potential for using structural ceramic materials in components of advanced heat engines including the gas turbine and adiabatic diesel has recently been demonstrated by results in DOE and DOD engine development programs. Status of these efforts, technical needs for candidate ceramic materials, and research opportunities in new DOE and NASA ceramic technology programs oriented to heat engines are reviewed.
Modification of Point Defects in Quartz for Device Applications
Authors: King J. C. , Koehler D. R.
Published: March 2011

Impurity centers in quartz play a significant role in the behavior of precision crystal resonators subjected to ionizing radiation. The substitutional Al center, charge compensated by Na, Li, H or a hole, is now known to be the primary contributing factor in most radiation-induced effects. Acoustic loss measurements, ESR measurements, optical studies and IR studies of these defects, over extended temperature ranges, have contributed substantially to our understanding of the impurity centers' role. Radiation-induced frequency and acoustic loss changes in quartz crystal resonators are now understood in terms of the evolving character of the defect center in a radiation field. This understanding has prompted material modification efforts such as high temperature electrolysis and doping technologies which permit, for instance, the fabrication of frequency control devices that are little affected by hostile environments.
Displacive Phase Transformation in Vanadium - Substituted Lanthanum Niobate
Authors: Aldred A. T. , Chan S.-K. , Grimsditch M. H. , Nevitt M. V.
Published: March 2011

The displacive transformations in complex oxides of the type LaNb1-xVxO4 has been studied by x-ray diffraction and Raman scattering for 0 < x < 0.3. X-ray diffraction results indicate that the transformation from the tetragonal high temperature structure (C4h6) to the monoclinic low-temperature structure (C2h6) is higher than first order and that the transformation temperature Tc is depressed significantly by V substitution. Raman scattering results show that the force constant between the nearest (Nb, V)O4 tetrahedral units behave uniquely compared to others. It softens at Tc as a function of composition and it also softens as a function of temperature as Tc is approached from above.
Quantitative Depth Profiling Resonance Ionization Mass Spectrometry of III-V Heterostructure Semiconductors
Authors: Emerson A. B. , Downey S. W. , Kopf R. F.
Published: March 2011

Resonance ionization mass spectrometry (RIMS) of neutral atoms sputtered from III-V heterostructure semiconductor materials provides quantitative information about the dopant position near interfaces. The prerequisite for quantitative results is the saturation of the ionization step. The absolute signals are affected by primary ion beam parameters which affect sputter yield, atomization efficiency and quantum state partitioning, but not ionization efficiency. We have found that matrix effects are minimal and use RIMS results to help elucidate dopant migration near interfaces and interpret SIMS matrix effects. Device performance and understanding of materials growth are both aided.
Impact of a Vicinal Growth Surface on AlAs / GaAs Superlattice Layer Thickness Measurements with Double Crystal X-ray Diffraction
Authors: Leiberich A. , Levkoff J. , Robertson A.
Published: March 2011

Microelectronic devices require deposition of sequences of thin epitaxial layers, with individual layer thicknesses in some instances specified to within tolerances of the order of inter-atomic spacings. Double crystal X-ray diffraction provides measurements of superlattice layer thicknesses to a resolution of the order of inter-atomic spacings, provided diffraction line shifts originating from substrate wafer misalignments are accounted for.
Semi-Insulating InP Grown by MOCVD
Authors: Feng M. S. , Wu C. C. , Lin K. C. , Chan S. H. , Chen C. Y.
Published: March 2011

Fe (C5H5)2 and Fe (CO)5 were used as the 3d transition metal dopants in semi-insulating InP epitaxial layer grown by MOCVD. From the bright and dark field images of the TEM analysis, many precipitates were observed. Three extra peaks of the X-ray diffraction were found. The peaks of free-exciton recombination, donor-acceptor transition and the recombination of bound exciton with phonon emission were observed in the short wavelength range. Two Fe related peaks was observed at 0.7079 eV and 0.6897 eV. For a wide range (10–600) of In/Fe mole fraction, the resistivity keeps at high values (about 108 Ω -cm) and appears the highest resistivity of 5 × 108 Ω -cm for 1 μ m layer.
Constant Depth DLTS Measurements on Compound Semiconductors
Authors: Denenberg David , Blew Austin
Published: March 2011

This paper describes a useful measuring technique enabling Deep Level Transient Spectroscopy [DLTS] on compound semi-conductors. We will report on the methodology of DLTS measurements using newly available software for Miller Feedback Profilers. This method has the advantages of using the constant depth capabilities of the profiler. The combination instrument offers flexibility in limited clean room space.
Damage Introduced by Chdamage Introduced by CH4/H2 Reactive Ion Etching in Pseudomorphic AlGaAs/InGaAs MODFETs
Authors: Pereira R. , Van Hove M. , De Raedt W. , Van Hoof C. , Borghs G. , Van Rossum M. , Braspenning R. H. , Eijkemans T. J. , Van Es C. M. , Wolter J. H.
Published: March 2011

The damage introduced by CH4/H2 reactive ion etching (RIE) and its recovery after thermal annealing has been investigated by Hall measurements and low temperature photoluminescence (PL) on pseudomorphic AlGaAs/InGaAs modulation doped structures. After plasma exposure, the PL intensity has significantly decreased and shifted in energy. In order to study the recovery of the damage introduced by the plasma, thermal annealing was done at temperatures between 350 and 500°C. We observed that the luminescence emission is totally recovered after annealing at 450°C. Hall measurements at room temperature (RT) and at 77K showed that the electrical characteristics of these structures can be restored only after thermal annealing at 500°C.

The optimised etching conditions have been applied in a fabrication process for submicron dry gate recessed pseudomorphic delta-doped AlGaAs/InGaAs modulation doped field effect transistors (MODFETs). For a 0.25 mm gatelength device the maximum DC transconductance value was as high as 680 mS/mm. The same value was extracted from measurements at 15 GHz.
CHF3and NH3Additives for Reactive ion Etching of GaAs Using CCl2F2and SICI4
Authors: Din Kuen-Sane , Chi Gou-Chung
Published: March 2011

Two fundamental requirements for RIE are the formation of nearly volatile etch products and sufficiently high physical bombardment to remove all substances on the surface. In this study, the GaAs wafer was in-situ pretreated with NH3or CHF3plasma prior to actual etching process. The main etchants are CCl2F2and SiCl4. By adding these additives to the main etch gases, the resulting etch performance was significantly affected. For instance, DC self-bias of CCl2F2plasma is relatively low and can increase with such gas addition, thus the etching properties related to physical bombardment change too. CHF3improve GaAs etch rate in CCl2F2through increasing concentration of reactive chlorine-containing species. While CHF3enhance etch rate in SiCl4plasma. The as etched samples were examined with X-ray photoelectron spectroscopy. Details of the experimental results will be described.
Formation of Ohmic Contacts to InP by Means of Rapid Thermal Low Pressure (Metalorganic) Chemical Vapor Deposition (RT-LPMOCVD) Technique
Authors: Katz A. , Feingold A. , Pearton S. J. , Nakahara S. , Lane E. , Geva M.
Published: March 2011

The viability of forming an ohmic contact to InGaAs/InP structures by means of a load-locked RT-LP(MO)CVD integrated process, was demonstrated. The wafer was loaded into the reactor chamber and was exposed to a sequence of dry and in-situ processes which led to the formation of an ohmic contact. After an in-situ cleaning of the wafer through a thermal cycle at 500°C under a flow of tertiarybutylphosphine (TBP), which provided the needed free hydrogen for a mild etching of the surface, however with an over pressure of P to eliminate surface degradation, a layer of silicon oxide (SiOx ) was rapid thermal chemical vapor deposited (RT-CVD) onto the InGaAs/InP sample via a rapid thermal cycle (500°C,30 s) in a low pressure O2 and 2% diluted SiH4. Dry etching of 50–150 μm wide contact stripes was carried out using a contact stencil mask by an electron-cyclotron resonance (ECR) dry etching. Subsequently the wafer was reloaded through the load-lock to the main chamber and a TiNx layer were selectively deposited into the via-holes and processed to provide an ohmic contact to the InGaAs/InP substrate. Finally, a blanket deposition of conducting cap layer was realized by means of RT-LP(MO)CVD. This work provides a solid demonstration to the feasibility of the single-wafer-integrated-process (SWIP) as an approach to replace the batch process traditionally used for manufacturing the InP-based optoelectronic devices.
Improvement of Ohmie Contacts on GaAs with In-Situ Cleaning
Authors: Ren F. , Pearton S. J. , Fullowan T. R. , Hobson W. S. , Chu S. N. G. , Emerson A. B.
Published: March 2011

An in-situ argon ion-mill clean step prior to ohmic metal deposition combined with a Mo barrier layer AuGe based ohmic metallization which is compatible with dry-etch process have been demonstrated to improve the uniformity of the contact parameters and reduce the contact resistance. After ion mill cleaning, the native oxide regrowth of MBE grown GaAs and AlGaAs layers in vacuum chamber was also studied to optimize the processing. These oxide layers were identified as the cause of problems in the formation of good ohmic contacts to the GaAs or AlGaAs, the Mo diffraction barrier also reduced the contact resistivity with excellent adesion, smooth morphology, and sharp edge definition.
Investigation of Ge, As, and Au Diffusion in Non-Alloyed Epitaxial Au-Ge Ohmic Contacts to n-GaAs Using Secondary Ion Mass Spectroscopy Backside Sputter Depth-Profiling
Authors: LEE H. S. , Lareau R. T. , Schauer S. N. , Moerkirk R. P. , Jones K. A. , Elagoz S. , Va Vra W. , Clarke R.
Published: March 2011

A SIMS backside sputter depth-profile technique using marker layers is employed to characterize the diffusion profiles of the Ge, As, and Au in the Au-Ge contacts after annealing at 320 C for various times. This technique overcomes difficulties such as ion beam mixing and preferential sputtering and results in high depth resolution measurements since diffusion profiles are measured from low to high concentration. Localized reactions in the form of islands were observed across the surface of the contact after annealing and were composed of Au, Ge, and As, as determined by SIMS imaging and Auger depth profiling. Backside SIMS profiles indicate both Ge and Au diffusion into the GaAs substrate in the isalnd regions. Ohmic behavior was obtained after a 3 hour anneal with a the lowest average specific contact resistivity found to be ∼ 7 × 100−6 Ω- cm2.
Ambipolar Lifetimes in GaAs/AlGaAs Self Electro-Optic Effect Devices
Authors: Swaminathan V. , Freund J. M. , Focht M. W. , Guth G. D. , Przybylek G. J. , Smith L. E. , Leibenguth R. E. , D'Asaro L. A.
Published: March 2011

The forward current-voltage (I-V) characteristics of GaAs/AlGaAs Self Electro-optic Effect Device (SEED) p-i-n diodes were measured. The I-V curves exhibited a diode like behavior with an ideality factor of 2 for voltages in the range 0.5–1.25V. In this region, the diode series resistance varied inverse proportional to the forward current with the constant of proportionality being equal to this voltage drop in the i-region. From an analysis of the experimentally obtained voltage drop, the ambipolar lifetime was determined. For the standard device whose i-region had a multi quantum well structure consisting of 60 periods of 100Å undoped GaAs wells and 65Å undoped Al0.30Ga0.70As barriers, the ambipolar lifetime was found to be 79.6±3 psec for a 30×30 μm2mesa device and 92 ± 4 psec for a 100×100 μm2mesa device. When the barrier width was reduced to 35Å or when the barrier Al composition decreased to 0.2, no significant change in the ambipolar lifetime was measured. Since previous measurements have indicated that decreasing the barrier width or height greatly enhances carrier escape from the wells during the operation of the GaAs/AlGaAs p-i-n diode as a photodetector, it is inferred that the carrier escape and collection times are smaller than ∼ 80–90 psec.
Observation of the Influence of Strain Induced deep Level Defects on the Electroabsorption Characteristics of InGaAs/GaAs (100) Multiple Quantum well Structures and Implications for Light Modulators
Authors: Chen Li , Chen Wei , Rajkumar K. C. , Hu Kezhong , Madhukar A.
Published: March 2011

In a thick strained GaAs/InGaAs MQW we recently reported the unusual observation of the exciton linewidth initially narrowing upon application of a reverse bias, before the usually observed broadening set in with further increase in the bias. The phenomena suggested the existence of a spatially varying electric field in the MQW region arising from a depletion of the net charge density with increasing reverse bias. Here we provide an explanation for the unusual observation arrived at through a systematic examination of the sample behavior using electro-transmission, electro-photoluminescence, capacitancevoltage profiling and transmission electron microscopy. We conclude that shallow levels cannot account for the observation and that the presence of strain induced point defect related deep levels (either n of p type) offers a consistent explanation. This is the first clear manifestation of the influence of deep levels on the free exciton electroabsorption behavior and has practical implications for MQW based electroabsorptive / electrorefractive light modulators.
Comparison of Dislane and Tetraethyltin as Gaseous Dopants for Growth of n-GaAs and O-AlGaAs by MOMBE
Authors: Wisk P. , Abernathy C. R. , Pearton S. J. , Ren F. , Fullowan T. , Lothian J.
Published: March 2011

We have investigated the effect of growth temperature and V/III ratio on dopant incorporation from disilane (Si2H6) and tetraethyltin (TESn) over the temperature range 475°C-525°C during growth of GaAs by metal organic molecular beam epitaxy (MOMBE). Increasing V/III ratio produced only a slight decrease in the dopant concentration while increasing growth temperature resulted in slighdy higher dopant levels. Addition of Al and H to the growth surface via introduction of trimethylamine alane had no apparent effect on dopant incorporation. No significant differences were observed in the incorporation behaviors of Si2H6 and TESn, and both sources yielded comparable base-collector junction behavior when used for growth of heterojunction bipolar transistors (HBTs).
Raman Characterization of AlGaAs Superlattice Channel Waveguide Structure formed by CIB and FIB Implantation
Authors: Choo A. G. , Gupta V. , Jackson H. E. , Boyd J. T. , Steckl A. J. , Chen P. , Weiss B. L. , Burnham R. D.
Published: March 2011

Raman scattering has been used to characterize lattice damage and impurity-induced compositional disordering in AlGaAs superlattice suitable for optical waveguiding. The degree of damage induced by both conventional ion beam (CIB) implantation and focused ion beam (FIB) implantation is studied using a spatial correlation model to interpret the Raman spectra. FIB implantation is found to induce slightly more damage than CIB implantation for doses of 8×1013 cm−2 and 4×1014 cm−2. and significantly more damage with 2×1015 cm2 compared to CIB implantations of the same dose. Suitable FIB implantation and rapid thermal annealing (RTA) conditions which provide compositional mixing were determined using Raman and photoluminescence spectroscopy. Using these conditions, an optical channel waveguide in AlGaAs superlattice formed by FIB-induced compositional intermixing is demonstrated.
Excitation Power Dependence of Photoluminescence in CIB and FIB Implanted Superlattices
Authors: Choo A. G. , Jackson H. E. , Chen P. , Steckl A. J. , Gupta V. , Boyd J. T.
Published: March 2011

Low temperature photoluminescence spectra have been used to characterize conventional ion beam (CIB) and focused ion beam (FIB) implanted superlattices. The excitation dependence of the single scan FIB is found to be significantly different from CIB and multiple scan FIB implantations which are similar. The peak position of the donor-acceptor transition is observed to change to higher energies significantly slower with excitation intensity for the single scan FIB case when compared to the multiple scan FIB and CIB cases. Simple models to describe these effects are briefly discussed.
Determination of Ga Self-Diffusion Coefficient in GaAs
Authors: Tan T. Y. , Yu S. , Gösele U.
Published: March 2011

A quantitative determination of the contributions of the triply-negatively charged Ga vacancies and of the doubly-positively charged Ga self-interstitials to Ga self-diffusion coefficient in GaAs has been carried out. Unde thermal equilibrium and intrinsic conditions, the contribution is characterized by an activation enthalpy of 6 eV for As-rich crystals and of 7.52 eV for Ga-rich crystals, while the contribution is characterized by an activation enthalpy of 4.89 eV for As-rich crystals and of 3.37 eV for Ga-rich crystals.
Mechanism of Cr Diffusion in GaAs
Authors: Yu S. , Tan T. Y. , Gösele U.
Published: March 2011

Diffusion of substitutional Cr atoms (Crs) in GaAs results from the rapid migration of interstitial Cr atoms (Cri) and their subsequent changeover to occupy Ga sites (or vise versa), a typical substitutional-interstitial diffusion (SID) process. There are two possible ways for the Cri-Crs changeover to occur: the kick-out mechanism in which Ga self-interstitials are involved, and the dissociative mechanism in which Ga vacancies are involved. The Crs indiffusion profiles are of characteristic shapes indicating the dominance of the kick-out mechanism, while the Crs outdiffusion profiles are error-function shaped, indicating the dominance of the dissociative mechanism. In this study, an integrated SID mechanism, which takes into account the effects of both the kick-out and dissociative mechanisms, is used to analyze Cr diffusion results. Going beyond just qualitative consistency, the Cr in- and outdiffusion features in GaAs are explained on a quantitative basis. In this model the kick-out mechanism dominates Cr indiffusion while the dissociative mechanism dominates Cr outdiffusion. Parameters used to fit existing experimental results provided quantitative information on the Ga self-interstitial contribution to the Ga self-diffusion coefficient.
Implantation-Induced Voids for Thermally Stable Electrical Isolation in GaAs
Authors: Ko K. Y. , Chen Samuel , Tong S. , Braunstein G.
Published: March 2011

Microscopic voids, formed from the condensation of supersaturated vacancy point defects, were recently discovered in implanted and annealed GaAs. These defects have been shown to suppress carrier concentrations. Since voids are formed only at relatively high temperatures (> 650 °C), the possibility exists that voids can be used for thermally stable implant isolation. In this paper, we report on the formation of highly resistive layers in GaAs, created by Al+ implantation and annealing in the 700–900 °C range. In samples containing voids, their sheet resistivities increased by about six orders of magnitude from the as-grown value. Formation of these thermally stable, high resistivity regions is different from the conventional H or O implant isolation techniques, which use lattice damage to create the isolation characteristics. However, since lattice damage is annealed out between 400–700 °C, this type of isolation becomes ineffective at high processing temperatures. By contrast, voids are stable at high processing temperatures, and potential advantages of using such defects for device isolation in GaAs are pointed out.
A Purely Spectroscopic Technique for Determining Energy Band Offsets in Quantum Wells
Authors: Koteies Emil S.
Published: March 2011

We have developed a novel experimental technique for accurately determining band offsets in semiconductor quantum wells (QW). It is based on the fact that the ground state heavy- hole (HH) band energy is more sensitive to the depth of the valence band well than the light-hole (LH) band energy. Further, it is well known that as a function of the well width, Lz, the energy difference between the LH and HH excitons in a lattice matched, unstrained QW system experiences a maximum. Calculations show that the position, and more importantly, the magnitude of this maximum is a sensitive function of the valence band offset, Qy, which determines the depth of the valence band well. By fitting experimentally measured LH-HH splittings as a function of Lz, an accurate determination of band offsets can be derived. We further reduce the experimental uncertainty by plotting LH-HH as a function of HH energy (which is a function of Lz ) rather than Lz itself, since then all of the relevant parameters can be precisely determined from absorption spectroscopy alone. Using this technique, we have derived the conduction band offsets for several material systems and, where a consensus has developed, have obtained values in good agreement with other determinations.
X-Ray Diffraction Studies of Low Temperature GaAs
Authors: Kowaljki G. , Leszcjynski M. , Kurpiewski A. , Kaminska M. , Suski T. , Weber E. R.
Published: March 2011

GaAs layers grown by molecular beam epitaxy (MBE) at low substrate temperatures (LT GaAs) were studied in a novel purpose designed X-ray experiment. It combines X-ray double crystal rocking curve measurements with some elements usually found in optical setups like light illumination at liquid nitrogen temperatures applied to transfer EL2 type defects into metastable state. Ability to record such transfers with the X-ray experiment as well as large lattice relaxation accompanying this process is presented.
An Investigation on the Lattice Site Location of the Excess Arsenic Atoms in GaAs layers Grown by Low Temperature Molecular Beam Epitaxy
Authors: Yu Kin Man , Liliental-Weber Z.
Published: March 2011

We have measured the excess As atoms present in GaAs layers grown by molecular beam epitaxy at low substrate temperatures using particle induced x-ray emission technique. The amount of excess As atoms in layers grown by MBE at 2000C were found to be ∼4×1020 cm−2. Subsequent annealing of the layers under As overpressure at 600'C did not result in any substantial As loss. However, transmission electron microscopy revealed that As precipitates (2- 5nm in diameter) were present in the annealed layers. The lattice location of the excess As atoms in the as grown layers was investigated by ion channeling methods. Angular scans were performed in the <110> axis of the crystal. Our resutls strongly suggest that a, arge fraction of these excess As atoms are located in an interstitial position close to an As row. These As “intersitials” are located at a site slightly displaced from the tetrahedral site in a diamond cubic lattice. No interstitial As signal is observed in the annealed layers.
Study of Modulation in GaAs Misfets with LT-GaAs as a Gate Insulator
Authors: Yin L.-W. , Ibbetson J. , Hashemi M. M. , Jiang W. , Hu S.-Y. , Gossard A. C. , Mishra U. K.
Published: March 2011

DC characteristics of a GaAs MISFET structure using low-temperature GaAs (LTGaAs) as the gate insulator were investigated. MISFETs with different gate to channel separation (d) were fabricated. The dependence of four important device parameters such as gate-drain breakdown voltage (VBR), channel current at zero gate bias (Idss), transconductance (gm), and gate-drain turn-on voltage (Von) on the gate insulator thickness were analyzed. It was observed that (a) in terms of Idss and gin, the LT-GaAs gate insulator behaves like an undoped regular GaAs layer and (b) in terms of VBR and Von, the LT-GaAs gate insulator behaves as a trap dominated layer.
Electrical Characterization of Low Temperature GaAs Layers, and Observation of the Extremely Large Carrier Concentrations in Undoped Material
Authors: Tadayon Bijan , Fatemi Mohammad , Tadayon Saied , Moore F. , Dietrich Harry
Published: March 2011

We present here the results of a study on the effect of substrate temperature, Ts, on the electrical and physical characteristics of low temperature (LT) molecular beam epitaxy GaAs layers. Hall measurements have been performed on the asgrown samples and on samples annealed at 610 °C and 850 °C. Si implantation into these layers has also been investigated.
Molecular Beam Epitaxy of Low Temperature Grown GaAs Photoconductors
Authors: Dykaar D. R. , Eaglesham D. J. , Keil U. D. , Greene B. I. , Saeta P. N. , Pfeiffer L. N. , Kopf R. F. , Darack S. B. , West K. W.
Published: March 2011

We report on the characterization of Low Temperature (LT) epitaxial growth of GaAs photoconductors. Samples were characterized using electro-optic sampling, transient femtosecond reflectivity, transmission electron microscopy, and pulsed terahertz spectroscopy as a function of growth temperature, As4 flux, doping and anneal conditions. We find the strongest effect on pulsewidth to be the temperature of an ex-situ rapid thermal anneal. In addition we find evidence of a temperature threshold for As precipitation. For more than an order of magnitude change in As precipitate density we find no corresponding change in electrical pulsewidth. Doping to 1017/cm3 also produces no change in the measured electrical response.
InP Layers Grown by Molecular Beam Epitaxy at Low Substrate Temperature
Authors: Xie K. , Wie C. R. , Wicks G. W.
Published: March 2011

InP layers were grown on semi-insulating InP wafer by molecular beam epitaxy (MBE) at low substrate temperatures (<200° C), using solid phosphorus source. We use x-ray diffraction, double crystal x-ray rocking curve, Auger electron spectroscopy, and temperature-dependent Van der Pauw and Hall effect measurements to characterize the as-grown and annealed InP layers. It is found that the InP layer is in poly-crystal state with excess P over 7 at%. The layers became single crystal after annealing above 400°C. The resistivity of the InP layer decreased from 60 Ωcm for an as-grown sample to 0.82 Ωcm after 400°C RTA annealing. The different role of excess P as compared to the role played by excess As in LT-GaAs is discussed based on the P properties.
Growth and Characterization of Low Temperature InP by Gas Source MBE
Authors: Maracas G. N. , Shiralagi K. T. , Puechner R. A. , Yu F. , Choi K. T. , Bow J. S. , Ramamurti R. , Kim M. J. , Carpenter R. W.
Published: March 2011

The introduction of GaAs grown at low MBE growth temperatures has spurred considerable activity in attempts to understand conduction mechanisms and optical properties. In LT GaAs, the formation of microscopic As precipitates dominates the conductivity, producing electronic transport mainly by variable range hopping conduction. The resulting high resistivity and short carrier lifetimes have enabled the use of LT GaAs in FET buffer layers as well as in ultra-fast optical switches. An extension to AlInAs has also been performed and it was seen that variable range hopping is also present in the Asbased ternary.

We report the optical and electronic properties of InP grown at low temperatures in a gas source MBE using dimeric phosphorus produced from cracked phosphine. The conductivity is higher than the equivalent GaAs LT material and does not have the same temperature dependence. The conditions under which growth occurs ie, substrate temperatures, V/ill ratios and annealing is explored. The structural properties, temperature dependence of the conductivity, deep level structure and the photoluminescence properties of the material are also investigated.
Device Applications of Low-Temperature-Grown GaAs
Authors: Smith Frank W.
Published: March 2011

Low-temperature-grown (LTG) GaAs is a unique material that has been used in a variety of device applications to achieve record performance. LTG GaAs used as a buffer layer eliminates sidegating and backgating and in GaAs integrated circuits. Record output power density (1.57 W/mm) and superior microwave-switch performance were demonstrated when LTG GaAs was used at a gate insulator in a metal-insulator-semiconductor field-effect transistor. High-speed (0.5 ps) and high-voltage (1 kV) LTG GaAs photoconductive switches have also been demonstrated. Using the same material, researchers have demonstrated highresponsivity (0.1 A/W), wide-bandwidth (∼ 375 GHz) LTG GaAs photodetectors. Devices incorporating LTG GaAs are currently being optimized for systems applications. LTG GaAs technology can enhance system performance and enable new systems for military and commercial applications in the areas of radar, communications, instrumentation, and highspeed computing.
Transport Modeling and Compensation Mechanism for Semi-Insulating LT-Gaas and InP: Cu
Authors: Xie K. , Wie C. R.
Published: March 2011

The compensation mechanism and transport properties of annealed GaAs grown by molecular beam epitaxy at low substrate temperature (LT-GaAs) and Cu diffused InP are analyzed by using a deep donor band model and a precipitate model. It was found that the compensation in highly resistive LT GaAs can not be explained by the precipitate model alone, and therefore a high donor density had to be considered. In Cu diffused InP, the precipitate model gives a consistent explanation for the observed carrier compensation and mobility data. For both semi-insulating LT-GaAs and fully-compensated, lightly-doped InP:Cu, the neutral impurity scattering was found to be a major carrier scattering mechanism.
Insulating and Breakdown Characteristics of Low Temperature GaAs
Authors: Grubin H. L. , Kreskovsky J. P. , Levy R.
Published: March 2011

The electrical characteristics of an N(LT)N structure are studied through implementation of numerical simulation techniques for the case of donor traps 0.83 ev below the conduction band and acceptor traps 0.3 ev above the valence band. The results show characteristics sensitive to the relative densities of the traps. In particular, high acceptor trap / low donor trap concentrations generally result in low breakdown voltages, whereas high acceptor / high donor concentrations result in higher breakdown voltages.