bluuebunny/crossref_metadata_2025 huggingface dataset:
Liberation of Ion Implanted Ge Nanocrystals from a Silicon Dioxide Matrix via Hydrofluoric Acid Vapor Etching
Authors: Sharp I.D. , Xua Q. , Liao C. Y. , Ager J.W. , Beeman J.W. , Yu K.M. , Zakharov D. , Liliental-Weber Z. , Haller E.E.
Published: June 2019

A method to liberate germanium (Ge) nanocrystals from silicon dioxide (SiO2) thin films by hydrofluoric acid (HF) vapor etching is presented. Multi-energy implantation of mass separated Ge ions into 500-nm-thick wet oxide layers on silicon (Si) substrates followed by thermal annealing produces nanocrystals that are 2 to 8 nm in diameter. Raman spectra exhibit the expected asymmetric line shapes due to the phonon confinement effect, but with a higher peak frequency than predicted. To free the nanocrystals, samples are etched in HF vapor to selectively remove the SiO2 matrix and expose the nanocrystal surfaces. Raman spectra of etched samples display peak frequencies consistent with relief of compressive stress. The liberated nanocrystals show long-term stability under ambient atmospheric conditions. Ge nanocrystals can be removed from etched surfaces using an ultrasonic methanol cleaning procedure. The nanocrystal-containing solution is applied to a TEM grid and the solvent is evaporated. Subsequently obtained electron diffraction patterns confirm that the nanocrystals survive this transfer step. Thus, liberated Ge nanocrystals are expected to be accessible for a wide range of manipulation processes and direct characterization techniques.
SOS Simulation of Sputtered Nanoripples
Authors: Stepanova Maria , Dew Steven K.
Published: June 2019

We report a Monte-Carlo simulation of nanostructures that self-organize on surfaces under oblique ion bombardment. We have developed a quantitative solid-on-solid (SOS) model that describes the surface morphology during ion bombardment and performed the first systematic investigation for Cu bombarded by 1000 eV Ar+ ions at 0°–80° incidence. When the angle of ion incidence exceeds ∼40°, we observe 2–5 nm wide ripples aligned parallel to the ion beam plane in agreement with existing analytic theory. We also detect ripples directed perpendicularly to the ion beam plane, but the conditions under which they arise disagree with the theory. We have investigated the effect of surface relaxation on the morphologies and found two different regimes of ripple evolution depending on the efficiency of relaxation. After ∼100 nm are removed, secondary 10–50 nm wide patterns are formed provided that relaxation is sufficiently high. We compare our simulations with those from other authors and with experiments.
Fabrication of Hologram Coins using Electron Beam Lithography
Authors: Leech Patrick W. , Sexton Brett A. , Marnock Russell J. , Smith Fiona
Published: June 2019

Diffractive grating structures formed by electron beam lithography have been replicated into the surface of silver commemorative coins. The detailed features of the gratings and the depth of relief were accurately transferred from the resist master plate to the surface of the fine silver coins using a Ni shim as a replication tool. This method has produced an optically variable device (OVD) in the surface of the coins which exhibited a strong intensity of first order diffraction over the area of the image (3 × 1.5 cm). A feature of the grating structures formed in the coins were fine-scale protrusions located along the length of the ridges. The presence of these protrusions has been attributed to an adhesive transfer and back-transfer of Ag during the cycle of impact loading of the Ni shim for sequential coins.
Light-Induced Microstructural Ordering: Study Of Lithium-Incorporated Cobalt Oxide Films On Aluminium And Glass Substrate
Authors: Das Mahua , Subbanna G. N. , Shivashankar S.A.
Published: June 2019

Photocrystallization is a phenomenon whereby an amorphous matrix undergoes structural changes to micro- or nano-crystals upon irradiation with photons. Topologically, a crystalline phase embedded in an amorphous matrix is expected to be advantageous over a fully crystalline phase, in applications such the as cathode material in thin film lithium-ion rechargeable batteries. As this particular microstructural feature provides a high surface area and enables smooth contacts, it may be expected to result in fast ion conduction between cathode and electrolyte, while retaining the electrochemical property associated with the specific crystal structure of the material. Amorphous films of lithium- incorporated cobalt oxide were obtained on glass and aluminium substrate using a sol gel spin-coating technique. The photocrystallization and microstructural changes in these films upon irradiation with unpolarised light were investigated using XRD, SEM, and TEM analysis.
Amorphous calcium phosphate nano-powders made from radio frequency (RF) plasma spraying
Authors: Jinling Xu , Kumar Rajendra , Khor K.A. , Cheang P.
Published: June 2019

Predominantly amorphous nano powders of calcium phosphate were produced by radio frequency (RF) plasma and subsequently characterised by SEM, TEM and XRD. Quantitative phase analysis was carried out by the Rietveld method. The starting feedstock was comprised of hydroxyapatite (HA) powders spray dried from a suspension. The input parameters were varied to produce predominantly amorphous calcium phosphate powders. Results showed that as the plate power was increased and the flow rate of feedstock was decreased the as-sprayed powders produced were predominantly amorphous. The average particle size of the powders was about 20-40 nm, depending on process parameters, as confirmed by TEM observation. These powders are thought to have excellent bio-resorbability and are targetted for use in gene and drug delivery technologies. These nano-sized powders are also envisioned to enhance the mechanical properties of bulk products sintered by appropriate techniques.
Direct Observations of Grain Boundary Phenomena during Indentation of Al and Al-Mg Thin Films
Authors: Soer W. A. , De Hosson J. Th. M. , Minor A. M. , Stach E. A. , Morris J. W.
Published: June 2019

The deformation behavior of Al and Al-Mg thin films has been studied with the unique experimental approach of in-situ nanoindentation in a transmission electron microscope. This paper concentrates on the role of solute Mg additions in the transfer of plasticity across grain boundaries. The investigated Al alloys were deposited onto a Si substrate as thin films with a thickness of 200–300 nm and Mg concentrations of 0, 1.1, 1.8, 2.6 and 5.0 wt% Mg. The results show that in the Al-Mg alloys, the solutes effectively pin high-angle grain boundaries, while in pure Al considerable grain boundary motion is observed at room temperature. The mobility of low-angle grain boundaries is however not affected by the presence of Mg. In addition, Mg was observed to affect dislocation dynamics in the matrix.
Effects of α and γ Radiolysis of Water on Alteration of the Spent UO2 Nuclear Fuel Matrix
Authors: Jégou C. , Broudic V. , Poulesquen A. , Bart J. M.
Published: June 2019

An experimental approach was developed to quantify the influence of α and γ radiolysis of water on the dissolution kinetics of the spent UO2 fuel matrix. Two types of experiments were carried out: leaching experiments in deaerated media with UO2 fuel pellets doped with alpha emitters (238Pu), and leaching experiments with UO2 fuel pellets (standard or doped with alpha emitters) submitted to γ irradiation. Leaching experiments on UO2 pellets doped with alpha-emitters in deionized water and in deaerated media showed a correlation between the alpha particle flux at the reaction interface and uranium release in solution. The higher the alpha particle flux at the reaction interface, the higher the uranium release rate (mean rates over 30 days at S/V = 3 m−1: 15-year batch, r = 2.5 mg·m−2d−1; 1500-year batch, r = 0.2 mg·m−2d−1; 40 000-year batch, r = 0.04 mg·m−2d−1). These results, obtained at low flux levels that are realistic on a disposal time scale, supplement existing data describing the effect of doping on UO2 alteration at higher flux levels. Leaching experiments with the 1500-year batch under gamma irradiation allowed us to quantify the impact of a gamma irradiation field on the UO2 release. At 650 Gy·h−1 the effects of alpha irradiation appear to be fully masked since the uranium release is 450 times higher than in the presence of the alpha irradiation field alone. The Chemsimul code was also used to model water radiolysis and uranium release into solution.
Jet-based Photonic Crystals for Terahertz Technology – A Need for Higher Resolution
Authors: Li Jin , Horgan Thomas M. , Gatesman Andrew J. , Giles Robert H. , Karakashian Aram S. , Goodhue William D.
Published: June 2019

Two-dimensional hexagonal photonic crystals of air columns in a wax substrate were fabricated by jet-based methods. By modifying the structure of the photonic crystals (PC), electromagnetic waves can be controlled, enabling the design of novel devices for waveguides, filters, and couplers. The jet-based processing is a solid freeforming method that can fabricate complex 2D or 3D photonic structures quickly and easily as compared to micro-machining and lithographic methods. The resolution of our 3D Systems ThermoJet® solider object printer is 300 × 400 × 600 dpi (XYZ) with the layer thickness of 0.042 mm. The wax used is a thermopolymer build material, similar to production investment casting wax material. The periodicity of the lattice of our 2D PC structures was designed to form bandstop filters in the 0.1–0.3 THz range. Transmission spectra of the structures were measured with a Bruker IFS 66v FT-IR interferometer. Photonic band gaps were observed at 0.17 THz and 0.23 THz along the Γ-M direction for both the TM and TE polarized incident beam for the PC structures with lattice constant of 0.787 mm and 0.586 mm, respectively. The location and width of the bandgaps agree with theoretical calculation based on a block-iterative frequency-domain method for Maxwell's equations in a planewave basis. To the best of our knowledge, this is the first time a jet-based process has been used successfully to fabricate PC structures at these high frequencies. However, the ThermoJet® printer as well as other current available solid freeforming technologies lack the resolution to PC structures operating in the terahertz regime. To extend this technology to terahertz applications, such as terahertz lasers, waveguides, and imaging system, a 10-fold increase in machine resolution is required to produce finer structures. Engineering materials with lower electromagnetic absorption and higher dielectric constants at terahertz frequencies are also critical to developing THz photonic bandgap technology.
Direct-Write Deposition and Laser Processing of Dry Fine powders
Authors: Kumar Pranav , Das Suman
Published: June 2019

We present a concept for multi-material solid freeform fabrication of 2D and layered 3D heterogeneous components. This technique involves direct-write deposition of multiple, patterned powder materials followed by laser processing. The direct-write deposition system features miniature hopper-nozzles for depositing dry powdered materials by gravity or by high frequency vibration-assisted flow onto a movable substrate. A dual wavelength laser processing workstation was used to consolidate the deposited pattern to desired densities. The feasibility of this concept was proved by direct-writing and laser processing various powder material patterns.
Controlled Electrospray for Tissue Engineering Applications
Authors: Paine M.D. , Stark J.P.W
Published: June 2019

The development and status of a novel electrospray system, capable of a variety of applications, including the fabrication of tissue engineered structures is described. The system requirements dictate the following key components: a micro-fabricated silicon electrospray emitter, a mass spectrometer capable of selecting molecules having a charge to mass ratio up to 32, 000 with a resolution of 10, 000, and an integrated ion optics system permitting depositing the selected molecules ‘softly’ onto a target with a spatial resolution of 0.1μm. One critical feature of the system is the overall efficiency of transferring biomolecules from a buffer solution, typically comprising water, acetonitrile and ammonium acetate, into an ion flux. Commercial ES/MS systems are generally designed with simplicity of operation as a design driver, together with the low probability of transmitting spray droplets directly into the quadrupole mass selection system. This has focused attention onto the detailed design and characterization of the electrospray emitter and the environment into which the spray is launched. This has highlighted the need to evaluate in detail, an electrospray operating into a low pressure environment and to improve our understanding of the interaction between voltage and flow rate in the transition from nano-electrospray mode, wherein no positive pressure is applied to the fluid and normal electrospray mode, close to minimum flow rate. Early results of this investigation are presented. There is evidence that at reduced ambient pressure there is a small reduction in spray current, however this is offset by improved transmission of the beam into the first quadrupole stage.
Production of complex nano-structures by electro-hydro-dynamics
Authors: Loscertales Ignacio G. , Barrero A. , Márquez Manuel
Published: June 2019

The use of electro-hydro-dynamic (EHD) forces to generate highly charged coaxial jets of immiscible fluids, with diameters in the micro and nano regime, has unravel itself as a very interesting choice for producing complex nanostructures from a vast variety of precursors, provided they can solidify, polymerize or gel, in times comparable or shorter than the living time of the coaxial nanojet. For time ratios larger than one, the result of the process are micro or nanocapsules, while for time ratios smaller than one coaxial nanofibers are produced. We show examples of both situations, with organic and inorganic precursors. On the other hand, realization of the process in a liquid bath opens the door to production of controlled micro and nanosized complex emulsions.
Grown-in and Radiation-induced Defects in 4H-SiC
Authors: Eberlein T. A. G. , Jones R. , Briddon P. R. , Öberg S.
Published: June 2019

SiC is a material that seems ideal for high-power, high frequency and high temperature electronic devices. It does not suffer from large reverse recovery inefficiencies typical for silicon when switching. In contrast to silicon, SiC is however difficult to dope by diffusion, and instead ion-implantation is used to achieve selective area doping. The drawback of this technique is that irradiating the crystal with dopant atoms creates a great deal of lattice damage including vacancies, interstitials, antisites and impurity-radiation defect complexes. Although many of the point defects can be eliminated through thermal annealing, some however, e.g. the photoluminescence (PL) DI and DLTS Z1/Z2 centers in ·4H-SiC, are stable to high temperatures. In this polytype, DI and the related alphabet lines are the most prominent PL signals. The latter can be seen directly after low energy irradiation while DI usually dominates the PL spectrum of implanted and irradiated SiC after annealing. Not only implantation but also rapid growth of SiC by CVD methods leads to a deterioration in quality with an increase in electrically active grown in defects. Among these, the Z1/Z2 defects are dominant in n-type 4H-SiC, as well as material that has been exposed to radiation. We use first principles density functional calculations to investigate defect models for the above mentioned defects in 4H-SiC and relate their electrical and optical activity to experiments.
Void Formation in Hydrogen Implanted and Subsequently Plasma Hydrogenated and Annealed Czochralski Silicon
Authors: Job R. , Düngen W. , Ma Y. , Huang Y. L. , Horstmann J. T.
Published: June 2019

By μ-Raman spectroscopy the formation of hydrogen related defects (vacancy-hydrogencomplexes, hydrogen saturated silicon dangling bonds, H2 molecules in multi-vacancies andvoids/platelets) has been investigated in H-implanted and subsequently H-plasma exposed andannealed Czochralski (Cz) silicon wafers. Annealing was done either in air or in an ambientcontaining hydrogen (forming gas). The investigations were applied under conditions, which arerelevant for ion-cut processes and layer exfoliation in Cz Si for SOI-wafer fabrication at reducedimplantation doses (as compared to standard procedures like the smart-cut® process).
Modelling the MOS Device Conductance Using an Extended Tunnelling Model and Subsequent Determination of Interface Traps.
Authors: Konofaos N.
Published: June 2019

The contribution of the AC conductance on admittance spectroscopy measurements on Metal-Insulator-Semiconductor (MIS) devices allows the calculation of the interface traps density and the relevant time constant. Two equivalent model approaches can be applied in order to explain the experimental results. One model is the statistical model based on the Shockley- Read-Hall (S-R-H) recombination statistics and the other one is a model based on the quantum tunneling effect. Recent evidence suggest that the tunneling model can be equivalent to the statistical one if a continuum of states is also considered in the modeling, creating an extended tunneling model. In the present paper, a further investigation on the extended model is attempted. Admittance spectroscopy data were collected for various Insulator/Si combinations, such as SrTiO3 and BaTiO3 deposited on Si. Both the S-R-H based and the extended tunneling models were used to analyze the data. The results showed that the extended tunneling can model the conductance of the device successfully and can calculate the interface states density and the traps time constant.
Electrical Transient Based Defect Spectroscopy in Polymeric and Organic Semiconductors
Authors: Mohapatra Y.N. , Varshney V. , Rao V. , Singh Samarendra P. , Samal G.S.
Published: June 2019

The relation between electrically active defects in organic and polymeric semiconductor materials and degradation of devices such as loss of luminance is currently not understood. In this paper, we study defect related charge processes using electrical transients in polymeric and organic diodes. We monitor slow charging and discharging currents as a function of time for both virgin and electrically aged devices. The current transients are analyzed spectroscopically in time domain using a technique called Time Analyzed Transient Spectroscopy, which is similar to DLTS in its implementation. We observe highly stretched exponentials over 3—4 orders of magnitude in time up to thousands of seconds indicating existence of large distribution in time constants in aged PLED devices. We demonstrate ability to distinguish between different mechanisms of charge storage related to defect related processes in typical OLED and PLED.
Towards the Routine Fabrication of P in Si Nanostructures: Understanding P Precursor Molecules on Si(001)
Authors: Schofield Steven R. , Curson Neil J. , Warschkow Oliver , Marks Nigel A. , Wilson Hugh F. , Simmons Michelle Y. , Smith Phillip V. , Radny Marian W. , McKenzie David R.
Published: June 2019

The ability to controllably position individual phosphorus dopant atoms in silicon sur-faces is a critical first step in creating nanoscale electronic devices in silicon, for example a phosphorus in silicon quantum computer. While individual P atom placement in Si(001) has been achieved, the ability to routinely position P atoms in Si for large-scale device fabrication requires a more detailed understanding of the physical and chemical processes leading to P atom incorporation. Here we present an atomic-resolution scanning tunneling microscopy study of the interaction of the P precursor molecule phosphine (PH3) with the Si(001) surface. In particular, we present the direct observation of PH3 dissociation and diffusion on Si(001) at room temperature and show that this dissociation is occasionally complete, leaving a P monomer bound to the surface. Such surface bound P monomers are important because they are the most likely entry point for P atoms to incorporate into the substrate surface at elevated temperature.
Influence of Oxygen Vacancies and Strain on Electronic Reliability of SiO2-x Films
Authors: Suzuki Ken , Ito Yuta , Miura Hideo , Shoji Tetsuo
Published: June 2019

We performed a quantum chemical molecular dynamics analysis for SiO2-x structure under strain to make clear the effect of the strain and intrinsic defects on both electronic and structural characteristics of SiO2-x. The SiO2-x showed a large change of the structure during the simulation. This is mainly because that the Si-O bonds near an oxygen vacancy were broken and a free silicon monoxide molecule was generated in the SiO2-x structure. The magnitude of the band gap of the SiO2-x decreased drastically due to the formation of the free monoxide. In addition, the band gap decreased further under large tensile strain of about 10%. We can conclude therefore, that both the existence of oxygen vacancies and tensile strain in SiO2-x films deteriorate the electronic reliability of the oxide film seriously.
μ-Raman Spectra Analysis of the Evolution of Hydrogen Related Defects and Void Formation in the Silicon Ion-Cut Process
Authors: Düngen W. , Job R. , Ma Y. , Huang Y. L. , Fahrner W. R. , Keller L. O. , Horstmann J. T.
Published: June 2019

Hydrogen implanted, boron doped (100) Czochralski silicon wafers, which were annealed after implantation up to 600 °C, are investigated by μ-Raman spectroscopy (μRS). We have studied the thermal evolution of hydrogen related defects, including vacancy-hydrogen (VnHm) complexes, H-saturated dangling bonds and trapped H2 molecules. Applying temperatures above ∼ 400 °C, the hydrogen related defects and the formation of voids/platelets are distinctly modified. The measured intensity of the local vibration mode (LVM) of H2 molecules trapped in multi-vacancy complexes at a frequency of ∼ 3820 cm-1 decreases while the LVM of H2 in platelets or larger voids (∼ 4150 cm-1) is increasing. This indicates that multi-vacancy complexes coalesce and form larger voids/platelets. Most of the VnHm complexes (∼ 2000 – 2200 cm-1) are dissolved during annealing at 600 °C, where a thin silicon layer exfoliates due to the ion-cut mechanism. However, the Raman modes of the characteristic V2H6 complex, of Si-Hx bonds stemming from H-terminated surfaces and of H2 located in voids/platelets still can be observed after a short time annealing (≤2 min) at 600 °C.
Hydrogen Ion Implantation Caused Defect Structures in Heavily Doped Silicon Substrates
Authors: Li Minhua , Wang Q.
Published: June 2019

The defects caused by hydrogen ion (H+) implantation were studied for heavily arsenic (As), boron (B), and phosphorous (P) doped (100) silicon substrates. At the implantation energy of 170keV, H+ beam generates defect zones in both arsenic and boron doped silicon wafers. The width of implant damage zone in the heavily As-doped silicon increased from 138nm to 415nm when H+ ion implant dose increased from1×1016 ion//cm2 to 5×1016 ion/cm2, respectively. This dependence is however, opposite in the heavily B-doped substrate. The defect zone decreased with increasing H+ ion dose. The second ion mass spectrometry (SIMS) data show that in both heavily As- and P-doped silicon substrates, hydrogen distribution was governed by both H+-dopant pairing reaction and the amount of the crystal damage, whereas it is exclusively determined by pairing reaction in heavily B-doped silicon substrates. The atomic force microscope (AFM) measurement indicated that the rms roughness of the as-exfoliated surface was 18.86nm, 13.06nm, and 6.79nm for P-, As- and B-doped silicon substrates, respectively. An rms roughness improvement of 20nm-170nm was observed when wafers were annealed at 270°C.
Effect of Substrate Orientation on the Growth Rate and Surface Morphology on GaSb Grown by Metal-Organic Vapor Phase Epitaxy
Authors: Yu Jian , Bhat Ishwara B.
Published: June 2019

MOVPE of GaSb grown on (100), (111)A and (111)B GaSb substrates were investigated to study the effect of substrate orientation on the growth rate and surface morphology. Besides growth temperature and V/III ratio, the GaSb growth rate strongly depends on the crystallographic orientation. As the V/III ratio rises, the growth rate on the (111)B oriented substrate decreases, whereas that on the (111)A oriented substrate increases. The surface morphology on different substrates was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). On (111)A substrates, triangular hillocks are the dominant defects, while on (111)B planes, three distinct types of hexagonal hillocks are observed, namely, non-flat top hexagonal structure with spiral growth features (Type I), flat top structure with lateral growth features (Type II), and non-flat top hexagonal structure with multiple islands (Type III). For all types, the basal edges of each hillock are preferentially aligned along <110> directions. A closer look reveals that the top surface of Type II feature consists of many levels of small hexagonal shaped terraces, with each step height in the monolayer range, indicating a step flow growth involved.
Thermal Transformation of Hydrogen Bonds in a-SiC:H Films: Structural and Optical Properties
Authors: Vasin Andrey V. , Kolesnik Sergey P. , Konchits Andrey A. , Lysenko Vladimir S. , Nazarov Alexey N. , Rusavsky Andrey V. , Ashok S.
Published: June 2019

Hydrogenated amorphous silicon carbide (a-SiC:H) films have been deposited using magnetron sputtering technique. Investigation of the effect of the vacuum annealing temperature on photoluminescence properties and paramagnetic defects, and its correlation with structural transformation of a-SiC:H have been performed. Significantly enhanced light emission efficiency after low-temperature vacuum treatment (450 °C) is found due to enhanced passivation of paramagnetic defects associated with carbon-rich chemically disordered structure. Subsequent high-temperature vacuum annealing results in a decrease of luminescent intensity that is associated with increase of carbon related paramagnetic defect states, shown to be the primary nonradiative recombination centres. For the first time silicon-related dangling bonds in a-SiC:H have been detected reliably by electron paramagnetic resonance measurements in annealed samples.
Probing Process-Induced Defects in Si Using Infrared Photoelastic Stress Measurement Technique
Authors: Liu X.H. , Wong S.P. , Peng H.J. , Ke N. , Zhao Shounan
Published: June 2019

The stress depth distribution in the silicon substrate under thin thermal oxide layers has been measured using the photoelastic technique. With the high sensitivity and improved spatial resolution of a newly developed low level birefringence detection system, it is confirmed that the stress distribution deviates significantly from the linear distribution predicted by classical bi-metallic strip theory. The deviation can be attributed to arising from Si self-interstitial injection during the thermal oxidation process. Long term changes in the stress distribution with time have also been observed and the changes can be understood in terms of point defect movements under the stress field in the substrate. Our preliminary results have demonstrated how we can probe microscopic point defect processes in thin film SiO2/Si substrate systems using a macroscopic photoelastic stress measurement technique.
Defect Reduction in Si-based Metal-Semiconductor-Metal Photodetectors with Cryogenic Processed Schottky Contacts
Authors: Li M. , Anderson W. A.
Published: June 2019

Metal-Semiconductor-Metal photodetectors (MSM-PD's) and simple Schottky diodes were fabricated using a low temperature (LT) technique to greatly reduce the device dark current. LT processing for metal deposition increased Schottky barrier height by improving the interface between metal and semiconductor to reduce the leakage current of the device. The structure consists of a 20 Å oxide over the active area to passivate surface states, a thicker oxide under contact pads to reduce dark current and the interdigitated Schottky contacts. A comparison was made for Schottky metal deposited with the substrate at 25 °C or -50 °C (LT). The devices fabricated using the LT process had better I-V characteristics compared to detectors fabricated using the standard room temperature (RT) metal deposition technique. The dark current for the LT film was found to be one to three orders lower in magnitude compared to the film deposited at RT. In one case, for example, the dark current was significantly reduced from 1.69 nA to 4.58 pA at 1.0 V. The active area for the device was determined to be 36 × 50 μm2 with 4 μm electrode width and 4 μm electrode spacing. Additionally, LT-MSM-PD's exhibited an excellent linear relationship between the photo-current and the incident light power. The Schottky barrier height for LT processing was found to be 0.79 eV; however, this value was 0.1 eV more than that of the same contact obtained by RT processing.
Nanoindentation as a Tool for Formation of Thin Film-Based Barrier Structures
Authors: Khlyap H. , Sydorchuk P.
Published: June 2019

A2B6 semiconductors and their solid solutions (ZnSe, ZnTe, CdTe, ZnCdHgTe) are matter of choice for near- and far-infrared optoelectronics. The importance of maximally reduced degree of defectness for these materials is not subjected to discussion. However, preparation of high quality barrier structures based on these compounds by means of MBE, laser technology or liquid phase technique is not always successful due to lattice parameters mismatch. At the same time, good selection of a proper buffer layer may also pose some unavoidable problems. From this point of view the nanoindentation as a tool of defect engineering can be effective for fabrication of surface barrier structures. The first experimental results and numerical simulation of experimental data obtained under investigation of nanoindentation effect on electric characteristics (in particular, current – voltage (I-V) and capacitance – voltage (C-V)) of ZnCdHgTe thin films and ZnCdHgTe/Cd(Zn)Te heterostructures at the room temperature are presented.
High-Rate Deposition Of Rare-Earth Doped Silicate Nanoparticles For Porous & Dense Optical Films
Authors: Horne Craig R. , Mascarel Pierre de , Blume Russell , Jur Jesse , Cohen-Jonathan Cecile , Chapin Michael , Posner Jonathan , Foo Wei Cho , Honeker Christian , Zhu Qing , Chiruvolu Shiv , Mosso Ronald , McGovern William
Published: June 2019

A novel deposition process has been developed for manufacturing of high quality rare-earth doped glass films with complex composition. This process, Laser Reactive Deposition (LRDTM), comprises photothermal laser pyrolysis using an aerosol feedstock coupled with deposition of the resulting nanoparticle product onto Si substrates with our without an underlying glass film. This paper describes this novel process as well as the structure, properties and performance of the Erdoped, multicomponent silicate glass films produced to date with this process.
Visible and Infrared Emission from Er-doped III-N Light Emitting Diodes
Authors: Zavada John M. , Nyein Ei Ei , Hömmerich Uwe , Li J. , Lin J. Y. , Jiang H. X. , Chow P. , Dong Jian-Wei
Published: June 2019

We report on the visible and infrared emission characteristics of Er-doped III-N lightemitting diodes (LEDs). Quantum well-like device structures were grown through a combination of metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) on cplane sapphire substrates. The dual stage growth process was used to take advantage of the high quality of AlGaN layers produced by MOCVD and in situ doping of Er during MBE growth. The multilayer structures were processed into devices and LEDs with different sizes and geometric shapes were produced. Electroluminescence (EL) was observed under either forward or reverse bias conditions. Visible and infrared spectra displayed narrow emission lines representative of the Er3+ system. The temperature dependence of the spectra, which were measured from 100K to 300K, showed a stability in the visible emission intensity but a sharp decrease in the infrared intensity at room temperature. Based on light output vs current measurements, estimates of the excitation cross-section were obtained for visible EL emission.
Nonequilibrium Carrier Dynamics Studied in Er, O-Codoped GaAs by Pump-Probe Reflection Technique
Authors: Fujiwara Yasufumi , Nakamura Kazuhiko , Takemoto Shoichi , Terai Yoshikazu , Suzuki Masato , Koizumi Atsushi , Takeda Yoshikazu , Tonouchi Masayoshi
Published: June 2019

Carrier dynamics in Er,O-codoped GaAs (GaAs:Er,O) have been systematically investigated by means of a pump and probe reflection technique with a mode-locked Ti:sapphire laser. In GaAs:Er,O, it has been found that the codoping produces a single atom configuration (Er-20 configuration) as an Er atom located at the Ga sublattice with two adjacent O atoms together with two As atoms, resulting in extremely strong Er luminescence. Time-resolved reflectivity of GaAs:Er,O exhibited an abrupt increase in amplitude, followed by a steep decrease to negative in less than 1 ps and then a gradual increase in approximately 100 ps. The steep decrease is due to bandgap renormalization. The gradual increase in reflectivity depended strongly on Er concentration, indicating that a trap induced by Er and O codoping plays an important role in dynamics of nonequilibrium carriers in GaAs:Er,O.
Rare Earth Ion Implantation for Silicon Based Light Emission: From Infrared to Ultraviolet
Authors: Skorupa W. , Sun J. M. , Prucnal S. , Rebohle L. , Gebel T. , Nazarov A.N. , Osiyuk I.N. , Dekorsy T. , Helm M.
Published: June 2019

Using ion implantation different rare earth luminescent centers (Gd3+, Tb3+, Eu3+, Ce3+, Tm3+, Er3+) were incorporated into the silicon dioxide layer of a purpose-designed Metal Oxide Silicon (MOS) capacitor with advanced electrical performance, further called a MOS-light emitting device (MOSLED). The silicon dioxide layer did not contain silicon nanoclusters. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The electroluminescence properties were studied with respect to the luminescence spectra, decay time, impact excitation, cross relaxation (Tb3+), and power efficiency. Top values of the efficiency of 0.3 % corresponding to external quantum efficiencies well above the percent range were reached. The electrical properties of these devices such as current-voltage and charge trapping characteristics, were also evaluated. Moreover, we demonstrate photo- and electroluminescence in correlation to charge trapping characteristics for Er-rich MOSLEDs with a varying silicon cluster content. Finally, application aspects to the field of biosensing will be discussed.
Characterization of Er/O-doped Si-LEDs with Low Thermal Quenching
Authors: Karim A. , Ni W.-X. , Elfving A. , Persson P.O.Å. , Hansson G.V.
Published: June 2019

Electroluminescence studies of MBE-grown Er/O-doped Si-diodes at reverse bias have been done. For some devices there is much reduced thermal quenching of the emission at 1.54 νm. There are examples where the temperature dependence is abnormal in that the intensity for a constant current even increases with temperature up to e.g. 80 °C. These devices have been studied with cross-sectional transmission electron microscopy to see the microstructure of the Er/O-doped layers as well as the B-doped SiGe-layers that are used as electron emitters during reverse bias. Although there are defects in the layers there is no evidence for large thick precipitates of SiO2. While reduced thermal quenching often is attributed to having the Er-ions within SiO2 layers, this is not the case for our structures as evidenced by our TEM-studies. The origin of the abnormal temperature dependence is attributed to the two mechanisms of breakdown in the reverse-biased diodes. At low temperature the breakdown current is mainly due to avalanche resulting in low-energy electrons and holes that quenches the intensity by Auger deexcitation of the Er-ions. At higher temperature the breakdown current is mainly phonon-assisted tunneling which results in a more efficient pumping with less de-excitation of the Er-ions. Finally at the highest temperatures the thermal quenching sets in corresponding to an activation energy of 125 meV, which is slightly lower than 150 meV that has been reported in other studies.
Gallium Oxide as a Host for Rare Earth Elements
Authors: Muth J. F. , Gollakota P. , Dhawan A. , Porter H. L. , Saripalli Y. N. , Lunardi L.M.
Published: June 2019

Pulsed Electron Beam Deposition (PEBD) and Pulsed Laser Deposition (PLD) were used to grow Gallium Oxide (Ga2O3) thin films on double sided polished sapphire substrates. At 850°C substrate temperature, smooth single crystal β-Ga2O3 films were obtained, which were confirmed with measurements by AFM of RMS surface roughness of about 1 nm. When characterized under electron beam excitation, the films exhibited different responses. For example: Europium doped films emitted intense red emission from 5D0 to 7Fj transitions while exhibiting weak broad emission from 300 to 500 nm. In contrast, Erbium doped films emitted strong emission from 300 to 500 nm peaked at 360 nm that was attributed to defects in the host matrix. Green emission from the Erbium transitions was observed at 528 and 550 nm. Films with different rare earth compositions varying from 0.1 % to 0.4 % were also prepared.

High quality natural waveguides were formed with the deposited Ga2O3 films on the lower refractive index substrate sapphire. This was confirmed by measuring the refractive index by prism coupling and sharp coupling spectra.
Role of Molecular Structure of Complexing/Chelating Agents in Copper CMP Slurries
Authors: Patri Udaya B. , Pandija S. , Babu S.V.
Published: June 2019

The role of the molecular structure - different functional groups, the length of the carbon chain and the relative positions of different functional groups – of several complexing/chelating agents (acetic acid, glycine, ethylene diamine, succinic acid, alanine and amino butyric acid (ABA)) in controlling copper (Cu) removal rates was investigated. The results are consistent with the known activity of –COOH groups at acidic conditions and that of –NH2 groups in an alkaline environment. In comparison with glycine, it was also observed that an increase in the carbon chain length increased the removal rates at acidic pH values and decreased the removal rates at alkaline pH values. Also, Cu removal rates decreased with an increase in the distance between the –NH2 and –COOH groups in an amino acid at all pH values except at 4.
Effect of Temperature on Defect Generation during Copper Chemical Mechanical Planarization
Authors: Mudhivarthi Subrahmanya , Zantyea Parshuram , Kumara Ashok , Shim Jeung-Yeop
Published: June 2019

Chemical Mechanical Planarization (CMP) is the process of choice for planarization of the constituent layers of the Multi Level Metallization schemes in modern Integrated Circuits. Besides having a lot of advantages, copper CMP process still needs significant process control to eliminate defects such as delamination, microscratches, dishing, erosion etc. In this research, effect of heat generated at the interface on the generation of CMP defects has been investigated. CMP of blanket and patterned samples has been carried out at two conditions of pressure x velocity values with varying slurry temperature. Post CMP metrology is carried out using Atomic force microscopy (AFM) in order to characterize the variation in scratch depth, dishing profile and non-uniformity in step coverage. Pictures of the patterned samples polished at different temperatures are captured using Optical Microscopy (OM) to study the dishing and dissolution of copper lines in greater detail. The primary goal of this study was to gain deeper understanding of the effect of heat generation and rise in temperature at the pad-wafer-slurry interface on CMP induced defectivity.
Abrasive Contribution to CMP Friction
Authors: Evans David R. , Oliver Michael R.
Published: June 2019

Friction in the CMP process is a subject of ongoing interest. The sources of friction can be the viscosity of the slurry between the pad and wafer, as well as the physical contact between the pad asperities and the wafer. The contact between the pad and the wafer can be direct or also through slurry particles trapped between the pad asperity and the wafer. We measure the friction between the wafer and the pad by measuring the CMP table current and subtracting out the background level. This is done for different concentrations of silica abrasive between 0 and 13%, as well as for different pressures and table speeds. Two widely different types of silica particles used in CMP are spherical colloid particles and aggregated fumed particles. We also compare the resultant friction behavior by comparing the results for both types of particles. For different abrasive contributions, the friction measurements are compared to the CMP removal rates. This evaluation is also done with a stationary wafer carrier, so that the observed removal rate at a specific point on the wafer is proportional to the local pressure on the wafer. The wafer carrier used for these tests uses a gimbal design. In this case the pressure at the leading edge of the wafer is larger than that at the trailing edge. From these studies we find that, for gimbaled systems with grooved pads, the friction is primarily caused by pad-asperity contact, and the addition of slurry particles does significantly change the friction interaction in the CMP process. Further, the non-uniformity in friction across the wafer is controlled by the pad surface structure and mechanical design of the CMP tool.
The effect of pad conditioning on planarization characteristics of chemical mechanical polishing (CMP) with ceria slurry
Authors: Yamamoto Yuichi , Kozuki Takaaki , Shibuki Shunichi , Maeda Keiichi , Inoue Yasuaki , Tawara Shinji , Toge Naoki
Published: June 2019

A ceria-based in-situ conditioning process was successfully developed. A new single layered metal bonded conditioner was developed to solve problems encountered in implementing ceria based in-situ conditioning process. The planarity was significantly improved compared with that of conventional Ni-plated in-situ conditioning.
Correlation of Defects on Dielectric Surfaces with Large Particle Counts in Chemical-Mechanical Planarization (CMP) Slurries Using a New Single Particle Optical Sensing (SPOS) Technique
Authors: Remsen Edward E. , Anjur Sriram P. , Boldridge David , Kamiti Mungai , Li Shoutian
Published: June 2019

A dual-sensor single particle optical sensing method (SPOS) is described for the measurement of the large particle count (LPC) in fumed silica polishing slurries. LPC values were expressed on a silica sphere-equivalent diameter scale rather than a polystyrene latex-equivalent size basis. Linear correlations between LPC and scratch counts on SiO2 surface films for wafers polished under clean room and table-top CMP conditions are demonstrated. However, these correlations were obtained for a limited set of model slurries; and further investigation will be needed to assess the general applicability of dual-sensor SPOS for oxide scratch defect prediction in CMP slurries.
A Predictive Model for Controlling Wafer Level Polish Rate Uniformity in Oxide CMP
Authors: Merchant Tushar P. , Borucki Leonard J. , Lawing A. Scott , Banerjee Suman K. , Zabasajja John N.
Published: June 2019

A stress based engineering model has been developed that predicts the removal rate profile across the wafer as a function of the principal and shear stresses on the wafer. The model reproduces the form of the radial variation in polish rate that is seen without back side air for the current set of consumable conditions and the changes in the polish rate profile that occur when back side air pressure is used on an IPEC-472 tool. The model which is GUI based and can be run in the fab, returns the optimum recipe setting to maximize polish rate uniformity based on the current tool performance. Implementing this model in production resulted in a 50% improvement in within wafer uniformity statistics.
A Dishing Model for STI CMP Process
Authors: Chang Shih-Hsiang
Published: June 2019

It is well known that oxide dishing occurring in STI CMP leads to considerable sidewall and edge-parasitic conduction. Thus, a closed-form solution for quantitative prediction of oxide dishing is needed. A contact-mechanics-based approach to describe the steady-state oxide dishing occurring in STI CMP process is presented. The theory is validated through comparison with experimental data in the literature. Once validated, the model is used to quantify the effect of pattern geometry on oxide dishing. It is shown that the predictions of the model agree reasonably well with the experimental results measured in overpolishing time.
On the Relationship of CMP Wafer Nanotopography to Groove-Scale Slurry Transport
Authors: Muldowney Gregory P.
Published: June 2019

Material removal in CMP occurs during intervals of pad-wafer contact separated by intervals of non-contact. One predictable sequence of non-contact intervals for a fixed point on the wafer is the traverse of the pad grooves, during which the wafer surface is renewed with fresh chemistry and heat is conveyed away. It is well understood that good uniformity requires machine kinematics that expose all points on the wafer to the same total contact time, mean slurry concentration, and temperature. Less widely known is that coherent structures tens to hundreds of nanometers high and matching the pitch of the pad groove pattern may be formed on an otherwise planar wafer despite multiple rotary motions. This unexpected phenomena is of interest not only because it manifests the impact of grooves and transport at scales not easily studied, but also because shrinking device architectures will ultimately disqualify even nanoscale departures from planarity. Wafer polish experiments are conducted alternately using circular, Cartesian grid, and spiral groove patterns using specialized pad conditioning and CMP recipes to amplify groove-induced nanotopography. Polish results illustrate sharp patterns in finished wafers (visible to the naked eye) that should not survive dual-axis tool kinematics. Computational 3-D model results are then presented for transient slurry mixing in the pad-wafer gap of a 200-mm polisher using the same groove patterns. A direct correspondence is found between observed wafer nanotopography and predicted groove-scale slurry mixing dynamics. In particular, the surface structures are underpolished areas traceable to intervals of non-contact protracted by depleted polish chemistry that prevails in groove segments when oriented relative to the local pad and wafer motion in a way that suspends transverse mixing in the groove crosssection. The study conclusively defines the features required in a groove pattern and polish recipe to form coherent structures matching the groove pitch. As validation of the theory, a groove pattern expected to form no surface topography is defined, experimentally tested, and shown to perform as predicted. Findings are discussed in the context of next-generation pad grooving and texturing as required for progressively more demanding applications of CMP.