bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Phosphorus and Si Self-Diffusion in Extrinsic, Isotopically Controlled Silicon Heterostructures
Authors: Silvestri Hughes H. , Bracht Hartmut A. , Sharp Ian D. , Hansen John , Nylandsted-Larsen Arne , Haller Eugene E.
Published: April 2011

We present experimental results of impurity and self-diffusion in an isotopically controlled silicon heterostructure extrinsically doped with phosphorus. As a consequence of extrinsic doping, the concentration of singly negatively charged native defects is enhanced and the role of these native defect charge states in the simultaneous phosphorus and Si self-diffusion can be determined. Multilayers of isotopically controlled 28Si and natural silicon enable simultaneous analysis of 30Si self-diffusion into the 28Si enriched layers and phosphorus diffusion throughout the multilayer structure. An amorphous 260 nm thick Si cap layer was deposited on top of the Si isotope heterostructure. The phosphorus ions were implanted to a depth such that all the radiation damage resided inside this amorphous cap layer, preventing the generation of excess native defects and enabling the determination of the Si self-diffusion coefficient and the phosphorus diffusivity under equilibrium conditions. These samples were annealed at temperatures between 950 and 1100°C to study the diffusion. Detailed analysis of the diffusion process was performed on the basis of a P diffusion model which involves neutral and positively charged mobile P species and neutral and singly negatively charged self-interstitial.
Current Understanding and Modeling of B Diffusion and Activation Anomalies in Preamorphized Ultra-Shallow Junctions
Authors: Colombeau B. , Smith A.J. , Cowern N.E.B. , Pawlak B.J. , Cristiano F. , Duffy R. , Claverie A. , Ortiz C.J. , Pichler P. , Lampin E. , Zechner C.
Published: April 2011

The formation of ultra-shallow junctions (USJs) for future integrated circuit technologies requires preamorphization and high dose boron doping to achieve high activation levels and abrupt profiles. To achieve the challenging targets set out in the semiconductor roadmap, it is crucial to reach a much better understanding of the basic physical processes taking place during USJ processing. In this paper we review current understanding of dopant-defect interactions during thermal processing of device structures – interactions which are at the heart of the dopant diffusion and activation anomalies seen in USJs. First, we recall the formation and thermal evolution of End of Range (EOR) defects upon annealing of preamorphized implants (PAI). It is shown that various types of extended defect can be formed: clusters, {113} defects and dislocation loops. During annealing, these defects exchange Si interstitial atoms and evolve following an Ostwald ripening mechanism. We review progress in developing models based on these concepts, which can accurately predict EOR defect evolution and interstitial transport between the defect layer and the surface. Based on this physically based defect modelling approach, combined with fully coupled multi-stream modelling of dopant diffusion, one can perform highly predictive simulations of boron diffusion and de/re-activation in Ge-PAI boron USJs. Agreement between simulations and experimental data is found over a wide range of experimental conditions, clearly indicating that the driving mechanism that degrades boron junction depth and activation is the dissolution of the interstitial defect band. Finally, we briefly outline some promising methods, such as co-implants and/or vacancy engineering, for further down-scaling of source-drain resistance and junction depth.
Activation, Diffusion and Defect Analysis of a Spike Anneal Thermal Cycle
Authors: Paul Silke , Lerch Wilfried , Hebras Xavier , Cherkashin Nikolay , Cristiano Fuccio
Published: April 2011

In this paper, the evolution of sheet resistance, junction depth and defects during the whole thermal cycle of a typical spike anneal with a peak temperature of 1050°C was investigated in detail. To this purpose, spike anneals were performed at peak temperatures ranging from 800°C up to 1050°C in temperature steps of 50°C. These experiments were done both on B+ (500 eV, 1.1015 cm−2) and BF2+ (2.2 keV, 1.1015 cm−2) implanted wafers. It is found that for temperatures below 850°C BF2+ implanted wafers exhibit a much better electrical activation, resulting in a lower sheet resistance, than B+ implanted ones, due to the amorphisation process occurring during the BF2+ implant and the subsequent solid phase epitaxial growth. In this low temperature regime, boron clustering takes place very rapidly in B+ implanted wafers, as confirmed by both SIMS and TEM analysis. In particular, “large” clusters, i.e. with diameter above the TEM detection limit (∼2 nm), undergo a classical Ostwald ripening process (increase in size, decrease in density). SRP measurements indicate that boron activation in this low temperature regime is not related to cluster dissolution. On the other hand, after the initial solid phase epitaxial regrowth, BF2+ implanted wafers exhibit a slight increase in sheet resistance, due to boron clustering induced by the dissolution of end of range defects. Finally, it is found that at higher spike anneal temperatures (above 850°C), both B+ and BF2+ implanted wafers exhibit a similar behaviour, with a progressive decrease in sheet resistance due to boron cluster dissolution and dopant diffusion.
The Effect of Photoresist Outgassing on Boron Clustering and Diffusion in Low Energy BF2+ Ion Implantation
Authors: Kopalidis Peter , Kondratenko Serguei
Published: April 2011

During high current ion implantation into photoresist-covered substrates, evolution of gaseous by-products of photoresist breakdown occurs that can affect the dose control of the process as well as diffusion and activation of the implanted dopants in silicon. The dosimetry effects are well understood and accounted for in modern ion implanter design. In this work, we report on the effect of photoresist outgassing on the distribution of boron concentration in silicon during the subsequent annealing process, boron electrical activation and sheet resistance measurements. Experiments were performed on mono- crystalline and pre-amorphized silicon and oxide covered wafers that help elucidate the mechanism of boron accumulation and diffusion. Higher carbon concentration on the wafer surface due to photoresist outgassing results in boron clustering and reduction of transient enhanced diffusion, leading to higher sheet resistance at low anneal temperature. Implantation through a thin oxide layer can be used to reduce carbon surface contamination and minimize the effects on the boron profiles and sheet resistance.
Repair of Porous Methylsilsesquioxane Films using Supercritical Carbon Dioxide
Authors: Xie Bo , Muscat Anthony J.
Published: April 2011

Porous methylsilsesquioxane (p-MSQ) films (JSR LKD 5109) were treated with alkyldimethylmonochlorosilanes having chain lengths of one, four, and eight carbon atoms dissolved in supercritical carbon dioxide at 150-300 atm and 50-60°C to repair oxygen ashing damage. Fourier transform infrared (FTIR) spectroscopy showed that trimethylchlorosilane (TMCS), butyldimethylchlorosilane (BDMCS), and octyldimethylchlorosilane (ODMCS) reacted with silanol groups on the surfaces of the pores producing covalent Si-O-Si bonds. Selfcondensation between alkylsilanols produced a residue on the surface, which was partially removed using a pure scCO2 rinse. The hydrophobicity of the blanket p-MSQ surface was recovered after silylation treatment as shown by contact angles >85°. The initial dielectric constant of 2.4 ± 0.1 increased to 3.5 ± 0.1 after oxygen plasma ashing and was reduced to 2.6 ± 0.1 by TMCS, 2.8 ± 0.1 by BDMCS, and 3.2 by ODMCS.
Ruthenium Sputter Deposition on Organosilicate Glass and on Paralyne: an XPS Study of Interfacial Chemistry, Nucleation and Growth
Authors: Zhao X. , Magtoto N.P. , Kelber J. A.
Published: April 2011

The interactions of sputter-deposited ruthenium with organosilicate glass (OSG) at 300 K have been studied by x-ray photoelectron spectroscopy (XPS) for Ru coverages from ∼ 0.1 monolayer to several monolayers, using in-situ sample transfer between the deposition and analysis chambers. The results indicate Stranski-Krastanov (SK) type growth, with the completion of the first layer of Ru at an average thickness corresponding to 1 monolayer average coverage. Ru(0) is the only electronic state present. XPS core level spectra indicate weak chemical interactions between Ru and the substrate. A less pronounced tendency towards SK growth was observed for Ru deposition on parylene. Deposition of Ru on OSG followed by electroless deposition of Cu resulted in the formation of a shiny copper film that failed the Scotch Tape test. Results indicate failure mainly at the Ru/OSG interface.
Nucleation and Growth Dependence of ALD WNC on Substrate Surface Condition
Authors: Abell Thomas , Schuhmacher Jörg , Travaly Youssef , Maex Karen
Published: April 2011

ALD WNC nucleation and growth was observed strongly affected by different substrate materials and surface chemistries. Nucleation was inhibited on most pristine low k surfaces, which is attributed to low concentrations of chemisorption sites (Si-OH). Plasma treatments were used to alter the surface chemistry to improve nucleation. Surface closure and surface roughness of the WNC layer were found to strongly correlate with starting surface condition. Resistivities of the resulting films were also found dependent on starting surface treatment. But the relationship between W content of the films, surface treatment and resistivity was not fully comprehended.
Preparation and Characterization of Copper Film on Plastic Substrate by ECR-MOCVD Coupled with a DC Bias
Authors: Jeon Bup Ju , Lee Joong Kee
Published: April 2011

Copper films were prepared at room temperature under a Cu(hfac)2-Ar-H2 atmosphere in order toobtain metallized plastics by using ECR-MOCVD (Electron Cyclotron Resonance Metal OrganicChemical Vapor Deposition) coupled with a DC bias system. Structural analysis of the films byECR showed that fine copper grains were embedded in an amorphous plastic matrix with goodadherence. Considering the AES result of the film prepared by ECR-CVD, we construe that thecopper film is chemically bonded with a plastic substrate. The delamination force determined bythe nano-scratch tester® showed in the range from 10 to 20mN.
Cross-Section Nano-Indentation for Rapid Adhesion Evaluation
Authors: Brongersma S. H. , Degryse Dominiek , Souiller Jerome , Vandevelde Bart , Maex K.
Published: April 2011

Cross-section nano-indentation is a technique that consists of cleaving a wafer, indenting behind the stack on the side surface causing delamination, and measuring the delaminated area in an optical microscope. It is shown to be a reliable rapid technique for adhesion evaluation and process optimization of the SiO2/barrier/copper stack.
Fatal Void Size Comparisons in Via-Below and Via-Above Cu Dual-Damascene Interconnects
Authors: Choi Z. -S. , Gan C. L. , Wei F. , Thompson C. V. , Lee J. H. , Pey K. L. , Choi W. K.
Published: April 2011

The median-times-to-failure (t50's) for straight dual-damascene via-terminated copper interconnect structures, tested under the same conditions, depend on whether the vias connect down to underlaying leads (metal 2, M2, or via-below structures) or connect up to overlaying leads (metal 1, M1, or via-above structures). Experimental results for a variety of line lengths, widths, and numbers of vias show higher t50's for M2 structures than for analogous M1 structures. It has been shown that despite this asymmetry in lifetimes, the electromigration drift velocity is the same for these two types of structures, suggesting that fatal void volumes are different in these two cases. A numerical simulation tool based on the Korhonen model has been developed and used to simulate the conditions for void growth and correlate fatal void sizes with lifetimes. These simulations suggest that the average fatal void size for M2 structures is more than twice the size of that of M1 structures. This result supports an earlier suggestion that preferential nucleation at the Cu/Si3N4 interface in both M1 and M2 structures leads to different fatal void sizes, because larger voids are required to span the line thickness in M2 structures while smaller voids below the base of vias can cause failures in M1 structures. However, it is also found that the fatal void sizes corresponding to the shortest-times-to-failure (STTF's) are similar for M1 and M2, suggesting that the voids that lead to the shortest lifetimes occur at or in the vias in both cases, where a void need only span the via to cause failure. Correlation of lifetimes and critical void volumes provides a useful tool for distinguishing failure mechanisms.
Electrical Behavior of Nano-Scaled Interconnects
Authors: Engelhardt M. , Schindler G. , Steinhögl W. , Steinlesberger G. , Traving M.
Published: April 2011

Sub-lithographic copper damascene lines were fabricated to investigate already today the physical phenomena and scaling limits of metallic conductors in the metallization systems of chip generations which are believed to be in production 10 years from now and later. Using standard manufacturing processes and state-of-the-art process tools, including standard lithography tools, narrow copper lines were fabricated at the expense of a relaxed pitch by use of a removable spacer technique. These copper nano interconnects were passivated and subjected to electrical measurements. Our results show that continuous down scaling to increase device performance will result in an unfavorable increase of the electrical resistivity of copper in stateof-the-art metallization schemes. Electrical measurements over a wide range of temperatures down to cryogenic temperatures reveal the limited potential of cooling to reduce resistivity of conductors as lateral dimensions will be shrinked down to the sub-100nm regime. By down scaling of copper diffusion barriers in damascene trenches, barrier functionality was demonstrated after high temperature anneals and excessive bias-temperature stress tests for films meeting or even exceeding end-of-roadmap thickness requirements. An analysis of the temperature dependence of the leakage current measured at very high electric fields applied between neighboring damascene lines suggests the conduction mechanism in the SiO2 used as intermetal dielectric to be Frenkel-Poole type rather than Schottky emission. Electromigration life times of sub-100nm copper lines embedded in oxide were found to be comparable with those obtained for similar structures fabricated with today's feature sizes.
Conducting Polypyrrole-based Field Effect Transistors Fabricated by Spin Coating and Inkjet Printing
Authors: Xue Fengliang , Su Yi , Varahramyan Kody
Published: April 2011

Spin coating and inkjet printing are two major deposition techniques for flexible polymer plastic electronics. This paper presents polymer field effect transistors (FET) fabricated by these two techniques using conducting poylmer polypyrole (PPy) as a semiconductor material. These thin film polymer field effect transistors operate in the depletion mode. The field effect mobilities are calculated to be 0.045 cm2 V−1s−1 and 0.036 cm2 V−1s−1, and transconductances are 0.104 νS and 0.096 νS at saturation region of the I-V curves for the spin coated and the inkjet printed transistors, respectively. The measured turn-off threshold voltage is around 20 V for both the spin coated and inkjet printed PPy FET transistors. The device performance of the spin coated transistors is slightly better than that of the inkjet printed transistors. This is mainly due to high surface roughness of the printed polymer film and printed dot boundaries, leading to low charge carrier mobility in the printed polymer FET transistors.
Fabrication Techniques for the Processing of Adhesiveless ULTEM® Polyetherimide Dielectric Film
Authors: Durocher Kevin M. , Dris Irene , Goodwin Stacey , Abbatiello Nicholas
Published: April 2011

Flexible printed circuits are a technology and product enabler for miniature, high density electronic systems, especially mobile communications and automotive applications. Over the past ten years, flexible printed circuit densities have increased, dramatically, while the area they occupy has decreased. The ever shrinking circuit form factor and increasing I/O and interconnect densities are driving flex circuit configurations from single sided to double sided constructions. In addition, the need for high performance steers circuit construction towards thinner dielectrics. Adhesiveless flex circuit constructions, for example, enable direct metal and lamination bonding without the use of added adhesive materials. Removing adhesive layers, such as epoxies or acrylics allows for a thinner more flexible device with a homogeneous dielectric stack (e.g., all polyimide construction), resulting in superior electrical performance. High resolution flexible circuit processes established using General Electric ULTEM [registered trademark] polyetherimide materials have shown ULTEM resin to have excellent electrical properties including dielectric constant and dissipation factor. Adhesiveless single and double sided flexible circuits have been fabricated and tested for performance (electrical, mechanical, thermal) and reliability (thermal cycling, tear propagation, flexural endurance, and solderability). Critical flex circuit fabrication processes such as metal adhesion, micro-via formation, lamination, photolithography, and module singulation have been evaluated. This paper addresses the key steps for flexible substrate fabrication describing the key advantages and disadvantages of the approach.
Tetrahedra from Aryleneethenylenes – From small Molecules to Luminescent Glasses
Authors: Detert H. , Sadovski O. , Sugiono Erli
Published: April 2011

The fourfold Horner olefination of tetraphenylmethane or –silane with fourp-methyl- phosphonate groups and a variety of aromatic aldehydes with donor groups or extended conjugated systems results in the formation of tetrahedra from four chromophores connected via a central atom. Electronic spectra in solution reveal an electronic interaction between the π-systems. In the solid state, the emission of compounds with a dense packing is nearly identical to the solution spectra, more open structures show significant red shifts. The emission of scaffolds with 1-styrylpyrene chromophores is nearly completely quenched. Most of these tetrahedra are thermally stable up to 420°C. Depending on the diameter of the scaffold, glass transitions occur between 99°C and 169°C.
Polymer Electrodes for Flexible Organic Light-Emitting Devices
Authors: Kim Woohong , Palilis Leonidas C. , Mäkinen Antti J. , Kim Heungsoo , Uchida Manabu , Kafafi Zakya H.
Published: April 2011

We report a high luminance and low operating voltage molecular organic light-emitting diode (MOLED) using a conducting polymer hole-injecting electrode (anode) on a plastic substrate. A dramatic improvement in the rectification ratio is observed upon the insertion of a buffer layer between the conducting polymer anode and the organic hole-transporting layer (HTL). Micro-shorts leading to a leakage current caused by the non-uniformity of the polymer film are greatly reduced. Atomic force microscope (AFM) images show a much smoother surface of the polymer anode/buffer layer relative to that of the bare polymer film. A slight increase (0.3eV ± 0.2eV) in the work function of the polymer anode upon the addition of the buffer layer is also measured. A simple method of patterning the conducting polymer electrode on various substrates including plastics is also reported. This approach conveniently provides finely patterned conducting polymer films with νm resolution while maintaining their intrinsic electrical and optical properties such as the surface sheet resistance and the optical transmittance.
Light Sensitive Polymer Thin Film Transistors Based on BAS-PPE
Authors: Xu Yifan , Berger Paul R. , Wilson James N. , Bunz Uwe H.F.
Published: April 2011

The photoresponse of polymer field effect transistors (PFETs) based on the 2,5- bis(dibutylaminostyryl)-1,4-phenylene-b-alkyne-b-1,4-bis(2-ethylhexyl)benzene terpolymer (BAS-PPE) is investigated. BAS-PPE is a photoluminescent conducting polymer with a bandgap of 2.25 eV. The BAS-PPE PFETs were fabricated using an open coplanar configuration and light is illuminated onto the top side of the PFETs. A sweep of VDS demonstrates that IDS saturation is suppressed during illumination, which suggests that pinch-off can not be reached since the injection of photo-generated carriers continues unabated. Also, with incident light, the channel can not be turned off, even at high positive gate biases, due to the accumulation of photo- generated carriers. A sweep of VDS also shows that BAS-PPE can act as a p-type polymer and favors hole injection and transport.
Effect of strain and growth morphology on the evolution of the domain structure of ferromagnetic manganites
Authors: Miller Holly , Higgins J. S. , Mukovskii Y. , Greene R. L. , Biswas Amlan
Published: April 2011

The effect of strain on the surface magnetism of the manganite La0.7Sr0.3MnO3 has been studied as a function of temperature, using magnetic force microscopy. The non- uniform strain distribution in the film leads to a two-phase coexistence between ferromagnetic and non-ferromagnetic phases. This leads to a reduction of the surface curie temperature and the formation of ferromagnetic islands. Methods of controlling this behavior in order to fabricate arrays of magnetic nanodots are discussed.
The Definition of Multiple Bandgaps in Quantum-Dot Material by Intermixing
Authors: Catrina Bryce A. , Marsh John H. , Yanson Dan A. , Kowalski Olek P. , Kim Shin-Sung
Published: April 2011

We present the recent progress in the intermixing of InGaAs/GaAs quantum dot (QD) material. Quantum dot intermixing (QDI) allows the tuning of the energy bandgap in selected areas of the wafer or optoelectronic device, thus modifying its emission or absorption properties, in much the same way as in quantum well (QW) material. QDI has recently received increasing interest, as it combines bandgap engineering with the predicted advantages that quantum dots offer, such as low temperature-sensitivity of threshold current, high modulation frequency and low chirp.

We have applied the dielectric-cap-based techniques that were originally developed for QW structures, to the intermixing of InGaAs/GaAs/AlGaAs QD material with an emission wavelength of 1280 nm. Intermixing was achieved by sputtering a QDI-enhancing cap in some areas, and a QDI-suppressing cap in other areas, followed by a high-temperature anneal cycle. Extremely large bandgap blue-shifts of up to 280 nm have been obtained with an anneal temperature of 800 °C. The shifts were inferred from the photoluminescence (PL) spectra measured at 77 K under red-laser excitation.

To be of use in many applications, QDI must be able to provide a multiplicity of bandgaps on a single substrate. Multiple bandgaps can be created by varying the thickness of the QDI-enhancing cap, repeating the anneal cycle several times, or varying the coverage density of QDI-enhancing features over that of QDI-suppressing ones. The latter approach, termed selective intermixing in selected areas (SISA), involves the deposition of QDI-enhancing patterns of various area fill factors, which, upon annealing, will cause different degrees of intermixing in the underlying regions.

To demonstrate the SISA process in the QD material, we defined patterns containing lines and squares of various sizes (3 - 100 μm) and area fill factors (5% - 95%). The wafer was then annealed at 725 °C for 1 minute. As expected, the observed bandgap shifts were commensurate with the fill factor, with a 5% coverage providing a minimum shift (0 - 10 nm) and ∼40% a maximum one (∼ 120 nm). At fill factors above 40%, the shifts appeared to saturate and even decrease slightly. The effect of the feature size and shape was not very pronounced, with smaller features generating somewhat larger shifts. This may be due to the fabrication-related size bias that will have the strongest effect on the fill factor of smaller features. The PL spectra measured from patterns of large-size features (20 μm or more) often had a lopsided shape and broader peak width, which may be attributed to the limited spatial resolution of the measurement probe.
Electrical and dielectric behavior of Pb(Mg1/4Ni1/4W1/2)O3 ceramics
Authors: Júnior Adolfo Franco
Published: April 2011

In this study full dense polycrystalline samples of Pb(Mg1/4Ni1/4W1/2)O3 have been sintered by solid-state reaction. X-ray data showed the formation of a single-phase new compound with unit cell parameters a = 9.8045 (25) Å, b = 13.1280(25) Å and c = 14.4207 (25) Å. Scanning electron microscopy (SEM) was used to evaluate the microstructures of sintered specimens. Dielectric constant and loss as function of frequency were investigated.
Preparation of Ultraviolet Light Emitting ZnO Nanoparticles Via a Novel Synthesis Route
Authors: Li Yuntao , Yang Richard D. , Tripathy S. , Sue H.-J. , Miyatake N. , Nishimura R.
Published: April 2011

A new synthesis methodology is utilized to prepare ZnO nanoparticles with a narrow size distribution between 2 to 4 nm. The particle growth is found to be reaction time dependent. The dry powders of ZnO nanoparticles show a strong blue-shifted near-band-edge ultraviolet emission, and the size and size distribution of the particles did not exhibit noticeable change during solvent evaporation. Raman spectra show ZnO E22 (TO) phonon mode and other vibration modes that are attributed to the bound acetate group. The CO stretching mode in the Raman spectra is red-shifted to 1401 cm-1, indicating a strong adsorption of the acetate ligands onto ZnO surfaces.
Compositional Ordering in InxGa1-xN and its influence on optical properties
Authors: Liliental-Weber Z. , Zakharov D. N. , Yu K. M. , Wu J. , Li S. X. , Ager J.W. , Walukiewicz W. , Haller E.E. , Lu H. , Schaff W. J.
Published: April 2011

InxGa1-x N layers grown with compositions with the predicted miscibility gap have been studied using Transmission Electron Microscopy (TEM), x-ray diffraction and optical measurements (photoluminescence and absorption). The samples (0.34 < × < 0.8) were deposited by Molecular Beam Epitaxy at 800°C using 200 nm AlN buffer layer grown directly on sapphire substrates. Another sample with × = 0.34 was grown on a GaN buffer layer. Dislocation densities in the InGaN layers were typically in the mid-1010 cm−2 to1011 cm−2 range. Edge dislocations were the most prevalent. For In concentration × = 0.5 compositional ordering is observed leading to extra diffraction spots in electron and x-ray diffraction. The ordering was not observed for the sample with x=0.34 grown on GaN. Based on TEM measurements the estimated period of ordering Δ was about Δ = 45 Å for × = 0.5 and Δ = 65Å for × = 0.78. The sample with × = 0.5 had the highest dislocation density. In addition to the presence of threading dislocations two types of domain boundaries on (0001) and (0110) planes were also observed in this sample. This sample has a broader photoluminescence (PL) that is redshifted compared to the absorption edge (“Stokes shift”).
Ammonothermal growth of GaN utilizing negative temperature dependence of solubility in basic ammonia
Authors: Hashimoto Tadao , Fujito Kenji , Wu Feng , Haskell Benjamin A. , Fini Paul T. , Speck James S. , Nakamura Shuji
Published: April 2011

Ammonothermal growth of GaN was studied to determine its eventual utility for mass production of GaN bulk crystals. Dissolution of GaN in supercritical ammonia with 1 M NaNH2 was investigated through a weight loss method. The time dependence of the weight loss was examined at 500°C and 525°C. Since the weight loss did not reach saturation as a function of time, the solubility limit was not realized. However, experiments demonstrate that GaN has a negative temperature dependence of solubility in supercritical ammonobasic solutions. Based on this result, GaN was grown via fluid transport from metallic Ga to a free-standing GaN single crystal seed by placing the seed crystal in a higher temperature zone and the nutrient in a lower temperature zone. GaN films with thickness of 5 μm (Ga face) and 4 μm (N face) were simultaneously grown on the seed in three days. The surface morphology, optical property, and defect density were found to be different for films on Ga face and N face.
Strain-Induced Effects on the Resonant Tunnelling of Holes in Zinc-Blende AlyGa1-yN/AlxGa1-xN/AlyGa1-yN Heterostructures
Authors: Meguenni C. , Zitouni K. , Mokdad N. , Kadri A.
Published: April 2011

We present a multi-band effective mass kP study of built-in strain induced effects on the resonant tunnelling of holes in Zinc-Blende AlyGa1-yN/AlxGa1-xN/AlyGa1-yN Double Barrier Resonant Tunnelling Heterostructures with 0 ≤ × ≤ 0.15 and 0.2 ≤ y ≤ 0.3. We show the influence of the SH split-off band on the resonant tunnelling of light (LH) and heavy (HH) holes through the strain-induced mixing of valence subband states. This valence subbands coupling is shown to result in a broadening of the resonance peaks in SL, LS hole transmission curves and a smearing out of the corresponding resonance peaks in the tunnel current. This effect is shown to decrease with increasing biaxial compression (decreasing x) and is minimum at x=0 in an Al.20Ga.80N/GaN/Al.20Ga.80N heterostructure.
Oxygen related shallow acceptor in GaN
Authors: Monemar B. , Paskov P. P. , Tuomisto F. , Saarinen K. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I. , Kimura S.
Published: April 2011

We report on deliberate O doping of GaN epitaxial layers during MOCVD growth, using H2O and CO2 as precursors. The photoluminescence spectra show a dominant 3.27 eV emission at 2 K known to be a donor-acceptor pair (DAP) transition. In our samples the intensity of this DAP spectrum correlates with the commonly observed 3.466 eV acceptor bound exciton (ABE) peak, suggesting these spectra are related to the same acceptor. The general correlation of these acceptor spectra with O concentration (as established with SIMS data) suggest that the acceptor is O-related, most likely a VGa-O complex. The concentration was measured with positron annihilation spectroscopy and found to be in the 1016 cm−3 -1017 cm−3 range in different samples. Considering previous results the identity of this residual acceptor is suggested to be a VGa-O-H complex. Previous suggestions that this acceptor is related to Mg, Si or C are discussed and found to be less likely.
Cathodoluminescence of Praseodymium doped AlN, GaN and turbo static BN.
Authors: Maqbool Muhammad , Richardson H. H. , Kordesch M. E.
Published: April 2011

Praseodymium (Pr) doped aluminum nitride (AlN), gallium nitride (GaN) and boron nitride (BN) thin films deposited on Si (111) substrate are studied with cathodoluminescence. AlN:Pr and GaN:Pr films are deposited at 77 K and room temperature respectively while BN:Pr films at 750 K by reactive sputtering, using 100–200 Watts RF power, 5–10 mTorr nitrogen. Metal targets of Al and B with Pr and a liquid target of Ga with solid Pr are used. The dominant peaks observed in the visible range result from 3P0 → 3H4, 3P1→ 3H5, and 3P0 → 3F2 transitions in AlN:Pr, 3P0 → 3H4, 3P0 → 3H6, and 3P0 → 3F2 transitions in GaN:Pr and from 3P0 → 3H4, 3P1→ 3H5, 3P0 → 3H6, and 3P0 → 3F2 transitions in BN:Pr. Additional peaks are observed from AlN:Pr at 335 nm and 385 nm from 1S0 → 1D2 and 1S0 → 1I6 which are not observed in GaN:Pr and BN:Pr films.
Preparation of the atomically straight step-edge Si (111) substrates as templates for nanostructure formation
Authors: Yoshida Shunji , Sekiguchi Takeharu , Itoh Kohei M.
Published: April 2011

We report on the experimental discovery that the distribution of kinks along steps on vicinal Si(111) surfaces depends on the direction of the dc current passed along the steps for resistive annealing. The as-cleaned Si(111) surface miscut ∼1° towards [112] has a small (<3°) unavoidable azimuthal deviation, which produces a number of kinks along the step-edges. When the azimuthal misorientation is from [112] towards [110] [110], dc current flowing in the direction [110] [110] climbing up the kinks straightens the step-edges as opposed to the current flowing in the opposite [110] [110]direction. During annealing around 800°C, the dc current in the direction climbing up the kinks straightens the steps. The up-climbing current direction transports and concentrates the kinks in a region outside the template area, leaving a kink-free atomic step-edge region as an ideal template for a variety of nanostructure formations. The straight step edges produced in this manner have uniform atomic configuration known as U(2, 0).
Pump-probe experiments on Er coupled Si-nanocrystals rib-loaded waveguides
Authors: Daldosso N. , Navarro-Urrios D. , Melchiorri M. , Pavesi L. , Gourbilleau F. , Carrada M. , Rizk R. , García C. , Pellegrino P. , Garrido B. , Cognolato L.
Published: April 2011

Pump and probe experiments have been performed on Er-doped rib-loaded waveguides containing Si nanoclusters grown by reactive magnetron sputtering. An Er3+ absorption cross-section of about 5×10−21 cm2 has been found at 1534 nm by insertion losses measurements. Transmission measurements at 1310 nm under optical pumping (488 nm) shows a decreasing of the signal because of confined carrier absorption of the Si nanoclusters. Amplification experiments at 1535 nm evidence two pump power regimes: losses due to confined carrier absorption in the Si nanoclusters at low pump powers and signal amplification at high pump powers. For strong optical pumping, signal enhancement of about 1.2 dB/cm was observed.
Threshold Voltage Shift in Hetero-nanocystal Floating Gate Flash Memory
Authors: Zhu Yan , Zhao Dengtao , Li Ruigang , Liu Jianlin
Published: April 2011

The threshold voltage shift of a p-channel Ge/Si hetero-nanocrystal floating gate memory device was investigated both numerically and phenomenologically. The numerical investigations, by solving 2-D Poisson-Boltzmann equation, show that the presence of the Ge on Si dot tremendously prolongs the retention time, reflected by the time decay behavior of the threshold voltage shift. The increase of the thickness of either Si or Ge dot will reduce the threshold voltage shift. The shift strongly depends on the dot density. Nevertheless, only a weak relation between the threshold voltage shift and the tunneling oxide thickness was found. A circuit model was then introduced to interpret the behavior of threshold voltage shift, which agrees well with the results of the numerical method.
Structural characterization and Coulomb blockade of a-SiNx/ nanocrystalline Si /a-SiNx asymmetric double-barrier structures
Authors: Wu L. C. , Dai M. , Huang X. F. , Han P. G. , Yu L. W. , Zou H. C. , Li W. , Chen K. J.
Published: April 2011

We have fabricated a series of a-SiNx/nc-Si/a-SiNx double-barrier structural samples by plasma-enhanced chemical vapor deposition (PECVD) and subsequent thermal annealing technique. The micro-structural properties of the samples were studied by using Raman scattering spectroscopy, planar and cross-section transmission electron microscopy (TEM). The electrical properties of the samples were investigated by frequency dependence of capacitance voltage (C-V) measurements. Charging effect in the nc-Si was exhibited through the hysteresis phenomena of the C-V curve and explained by F-N tunneling. For the thicker SiNx barrier layer samples, Coulomb blockade effect was observed in C-V curve for the sample with thinner SiNx barrier layer, in which two capacitance peaks appeared, and explained by direct tunneling of electrons into the nc-Si through the tunneling SiNx layers. From the interval between the two peaks, the Coulomb charging energy of nc-Si dot was estimated.
Recent Results on the Road to a SiGe Quantum Cascade Laser
Authors: Borak Alex , Tsujino Soichiro , Falub Claudiu , Scheinert Maxi , Diehl Laurent , Müller Elizabeth , Sigg Hans , Grützmacher Detlev , Gennser Ulf , Sagnes Isabelle , Blunier Stefan , Fromherz Thomas , Campidelli Yves , Kermarrec Oliver , Bensahel Daniel , Faist Jerome
Published: April 2011

The primary challenges in implementing a Si based quantum cascade laser are discussed. Intersubband absorption measurements were carried out on a series of modulation doped multiquantum well structures. The spectra were compared to the predictions of a 6 band k.p model, which confirmed the excellent accuracy of the model, and its ability to predict the bandstructures of more complicated cascade structures. A detailed structural analysis demonstrated excellent growth quality, with an interface roughness of < 0.4 nm. Electroluminescence measurements on cascade structures with doped contacts, processed as finger structures and waveguides of various sizes, enabled a quantitative analysis of the active region performance. The upper state lifetime τnr was ∼ 100 fs, leading to a total active region optical gain of ∼ 2 cm−1, a factor of ∼ 10 lower than the estimated total losses due to free carrier absorption. The total emitted power and the linewidth of the intersubband emission saturate above ∼ 6.5 kA/cm2, probably due to misalignment of the injector levels at high biases. The effect of leak currents and interspersed light hole states on the intersubband emission are considered.
The Emission of Terahertz Radiation from Doped Silicon Devices
Authors: Pengcheng Lv , Kolodzey James , Thomas Troeger R. , Kim Sangcheol , Ray S.K.
Published: April 2011

Recent interest in biological imaging, remote sensing, and biochemical spectroscopy has made nanoscale Terahertz (THz) emitters based on semiconductors become extremely attractive. THz lasers with good performance (emitting over 1 milliWatt CW at 10 K) have been fabricated from the group III-V compounds by molecular beam epitaxy, but such devices are complex with over 500 quantum wells and barriers and are incompatible with low cost Si processing. Similar devices from the SiGe system have had difficulties because the strain limits the total number of active layers, and have produced relatively poor performance (peak powers near 5 nW), even using strain symmetric active regions on virtual substrates of relaxed SiGe buffers. We report here on the characteristics of a new type of THz emitting device with higher powers (above 0.1 milliWatt) based on radiative impurity transitions in doped silicon, which can be simply fabricated without Ge alloying.

The THz emitters were fabricated from both p-type and n-type doped silicon wafers with typical resistivities of 5 Ω-cm, using conventional photolithography and metal contact lift off. Samples were electrically pulsed and the electroluminescence was measured by Fourier Transform Infrared spectrometry. At 4.2 K, the emission spectra showed several peaks centered around 8.1 THz for the boron doped device, 7 to 13 THz for the gallium doped device, and 6.6 THz for the phosphorus doped device. The electroluminescence was attributed to radiative transitions from excited p-like to s-like hydrogenic dopant states, with emission energies in remarkable agreement with the known dopant absorption levels. Current-voltage measurement suggested an excitation mechanism based on impact ionization of neutral dopants by hot carriers. The net quantum efficiency (emitted photons per injected electron) was estimated to be up to 2 × 10-3. The temperature dependence will be reported with operation above 30 K.
Complex Diameter Modulations in Silicon Carbide Nanowire Growth
Authors: Kohno Hideo , Yoshida Hideto
Published: April 2011

Silicon carbide nanowires were grown via a self-organized process. Some of the nanowires showed complex diameter fluctuations. The fluctuation was studied from the viewpoints of random walk and fractal. Power spectrum analysis of a fluctuation revealed that the fluctuation was not periodic and that the spectrum was colored. The distribution of increments had a fat tail which was not Gaussian but obeyed power law. Thus the diameter fluctuation was interpreted as a Lévy Flight. In addition, the fluctuation also showed multiaffine scaling.
Silicon Nanowires: Doping Dependent N- and P- Channel Fet Behavior
Authors: Byon Kumhyo , Fischer John E. , Adu Kofi W. , Eklund Peter. C.
Published: April 2011

The electrical transport properties of field effect transistor (FET) devices made of silicon nanowires (SiNWs) synthesized by pulsed laser vaporization (PLV) were studied. From as-grown PLV-SiNW FET, we found p-channel FET behavior with low conductance. To improve conductance, spin on glass (SOG) and vapor doping were used to dope phosphorus and indium into SiNW, respectively. From doping after synthesis, we could successfully make both n- and p-channel FET devices.
X-Ray Studies of Near-Frictionless Carbon Films.
Authors: Mehta Nikhil J , Roy Sujoy , Johnson Jacqueline Anne , Woodford John , Zinovev Alexander , Islam Zahirul , Erdemir Ali , Sinha Sunil , Fenske George , Prorok Barton
Published: April 2011

Carbon-based coatings exhibit many attractive properties that make them good candidates for a wide range of engineering applications. Tribological studies of the films have revealed a close correlation between the chemistry of the hydrocarbon source gases and the coefficients of friction and wear rates of the diamond-like carbon films. Those films grown in source gases with higher hydrogen-to-carbon ratios had much lower coefficients of friction and wear rates than did films derived from source gases with lower hydrogen-to-carbon ratios. The mechanism for this low friction is as yet not properly understood. Ongoing structural characterization of the films at Argonne National Laboratory is gradually revealing this mechanism. Recent studies have included x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS) and x-ray reflectivity (XRR). XPS showed ∼10% oxygen at the surface, which was largely removed after a 1 minute sputter; NEXAFS showed a high sp2:sp3 ratio implying a highly graphitic material; and XRR has given a comprehensive depth profile, with three layers of increasing density as the substrate was approached. The paper discusses the results and correlation with previous friction measurements.
Structural, Mechanical and Tribological Properties of TiN and CrN Films Deposited by Reactive Pulsed Laser Deposition
Authors: Phani A. R. , Krzanowski J. E.
Published: April 2011

Nitride thin films have potential applications in different areas of silicon device technology, namely as diffusion barrier in metallization schemes, rectifying and ohmic contacts, and gate electrodes in field effect transistors. In the present investigation, TiN and CrN films have been deposited by reactive pulsed laser deposition technique using Ti and Cr targets at 10mTorr background pressure of N2. Si (100) and AISI 440C steel substrates were used for the present study. Films were deposited at different temperatures in the range of 200°C to 600°C. The deposited films exhibited densely packed grain, with smooth and uniform structures. X-ray Photoelectron Spectroscopy (XPS) analysis of the films showed and 50% Ti and 40% of N in TiN films, 45% of Cr and 45% of N in CrN films deposited on Si (111), with the balance mostly oxygen, indicating near stoichiometric composition of the deposited nitride thin films. Hardness of the films changed from 22 GPa at 200°C to 30 GPa at 600°C for TiN, whereas for CrN we obtained 26 GPa at 200°C to 31 GPa at 600°C. The residual stress in the films showed a change from compressive stress at 200°C to tensile stress at 600°C in both the cases. Friction coefficient of the films were measured by pin-on-disk technique for all films, up to the tested limit of 10, 000 cycles at 1 N load and found to be very high (≥ 1) in both cases.
Tribological Aspects of AlN-TiN Thin Composite Films
Authors: Waters C. , Young G. , Yarmolenko S. , Wang X. , Sankar J.
Published: April 2011

Physical properties, and the friction and wear are important issues in small-scale applications, it is therefore essential that the materials used have good micromechanical and tribological properties. The adhesion, fracture toughness and wear properties of AlN-TiN thin composite films is being investigated in this study. The multilayered structures are generated using Pulsed Laser Deposition (PLD). The durability and functionality of thin films is subject to the adhesion between the coating and the underlying substrate in addition to it's resistance to cracking. The magnitude of the critical load during a scratch test is related to the adhesion of the substrate to the coating. In this test a Berkovich indenter is used for measurements and is drawn across the surface of a coating under an increasing load. The magnitude of the critical load will be studied for various films from a monolayer TiN film to different AlN-TiN films and those relative results compared to their facture toughness and their wear properties. Despite the adhesion, the critical load depends on several other parameters including the friction coefficient. The critical characteristic load is shown to depend on the number of layers and the relative AlN-TiN thickness. The fracture toughness showed a weak dependence on the layer characteristics.
Synthesis and Characterization of Carbon Nitride Thin Film with Evidence of Nanodomes
Authors: Chowdhury S. , Laugier M. T.
Published: April 2011

We have reported the synthesis of carbon nitride thin films with evidence of formation of carbon nanodomes over a range of substrate temperature from 50 °C to 550 °C. An RF magnetron sputtering system was used for depositing carbon nitride films. The size of the nanodomes can be controlled by deposition temperature and increases from 40–80 nm at room temperature to 200–400 nm at high temperature (550 °C). Microstructural characterization was performed by AFM. Electrical characterization shows that these films have conductive behaviour with a resistivity depending on the size of the nanodomes. Resistivity values of 20 mΩ-cm were found for nanodomes of size 40–80 nm falling to 6 m?-cm for nanodomes of size 200–400 nm. Nanoindentation results show that the hardness and Young's modulus of these films are in the range from 9–22 GPa and 100–168 GPa respectively and these values decrease as the size of the nanodomes increases. GXRD results confirm that a crystalline graphitic carbon nitride structure has formed.
Matrix Assisted Pulsed Laser Evaporation of Dexamethasone Thin Films
Authors: Patz Timothy M. , Doraiswamy Anand , Narayan Roger J. , Menegazzo Nicola , Kranz Christine , Mizakoff Boris , Zhong Yinghui , Bellamkonda Ravi , Modi Rohit , Chrisey Douglas B.
Published: April 2011

We have demonstrated deposition of dexamethasone thin films via matrix assisted pulsed laser evaporation (MAPLE). Infrared analysis revealed that dexamethasone thin films deposited by MAPLE and by drop casting had a similar absorbance spectra. AFM imaging of the MAPLE-deposited dexamethasone thin film revealed 2–10 μm punctuate ring-like structures. Deposited dexamethasone was tested for positive bioactivity by treating primary microglia cells with lipopolysacchride and measuring nitric oxide (NO) production. The successful deposition of dexamethasone thin films can be used on neural implants to prevent tissue injury and inflammatory response.