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At least 865 records · Page 48

Formation of nickel germanide on SiO{sub 2}-capped n-Ge to lower its Schottky barrier height

In this Letter, NiGe/SiO{sub 2}/n-Ge ohmic contacts were demonstrated with Ge, rather than Ni, diffusion through the ion-implanted SiO{sub 2} films to form NiGe. The equivalent Schottky barrier height reduced from 0.58 eV for NiGe/n-Ge to ohmic contact. The anomalous diffusion behavior and accumulation of Ge in the SiO{sub 2} near the NiGe/SiO{sub 2} interface can be explained by vacancy-enhanced Ge diffusion. It is proposed that the presence of vacancies and Ge atoms embedded in the SiO{sub 2} layer play a significant role in the current enhancement by generation of multiple levels in the SiO{sub 2} band gap.

36 MATERIALS SCIENCE↗

Statistical investigations on nitrogen-vacancy center creation

Quantum information technologies require networks of interacting defect bits. Color centers, especially the nitrogen vacancy (NV{sup −}) center in diamond, represent one promising avenue, toward the realisation of such devices. The most successful technique for creating NV{sup −} in diamond is ion implantation followed by annealing. Previous experiments have shown that shallow nitrogen implantation (<10 keV) results in NV{sup −} centers with a yield of 0.01%–0.1%. We investigate the influence of channeling effects during shallow implantation and statistical diffusion of vacancies using molecular dynamics and Monte Carlo simulation techniques. Energy barriers for the diffusion process were calculated using density functional theory. Our simulations show that 25% of the implanted nitrogens form a NV center, which is in good agreement with our experimental findings.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Low dimension structures and devices for new generation photonic technology

Low dimensional structures and devices are the key technological building blocks for new generation of electronic and photonic technology. Such structures and devices show novel properties and can be integrated into systems for wide applications in many areas, including medical, biological and military and advancement of science. In this invited talk, I will present the main results achieved in our competitive research program which aims to explore the application of the mesoscopic structures in light source, manipulation and imaging and integrate them into advanced systems. In the light source aspect, we have for the first time developed graphene mode-locked lasers which are in the process of commercialization. Nanocrystal Si embedded in dielectrics was formed by ion implantation and subsequent annealing. Si light emitting devices with external quantum efficiency of about 2.9×10{sup −3}% for visible emission were demonstrated at room temperature and the color of emitted light can be tuned electrically from violet to white by varying the injected current. In light manipulation, loss compensation of surface plasmon polaritons (SPPs) using quantum well (QW) gain media was studied theoretically and demonstrated experimentally. The SPP propagation length was effectively elongated several times through electrical pumping. One and two microring resonators based on silicon on insulator and III-V semiconductors technologies have been successfully fabricated and they can be used as filter and switch in the photonic circuit. In imaging, both SPP and low dimension structures are investigated and resolution far beyond diffraction limit in visible range has been realized. The integration of the components in the three aspects into complicated systems is on the way.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

In situ growth and coalescence of He-filled bi-dimensional defects in Si by H supply

In this work, ion implantations with in situ transmission electron microscopy observations followed by different rates of temperature ramp were performed in (001)-Si to follow the evolution of He-plates under the influence of hydrogen. The JANNUS and MIAMI facilities were used to study the first stages of growth as well as the interactions between co-planar plates. Results showed that under a limited amount of H, the growth of He-plates resulting from a subcritical stress-corrosion mechanism can be fully described by the kinetic model of Johnson-Mehl-Avrami-Kolmogorov with effective activation energy of 0.9 eV. Elastic calculations showed that the sudden and non-isotropic coalescence of close He-plates occurs when the out-of-plane tensile stress between them is close to the yield strength of silicon. After hydrogen absorption, surface minimization of final structure occurs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Alternative process for thin layer etching: Application to nitride spacer etching stopping on silicon germanium

Silicon nitride spacer etching realization is considered today as one of the most challenging of the etch process for the new devices realization. For this step, the atomic etch precision to stop on silicon or silicon germanium with a perfect anisotropy (no foot formation) is required. The situation is that none of the current plasma technologies can meet all these requirements. To overcome these issues and meet the highly complex requirements imposed by device fabrication processes, we recently proposed an alternative etching process to the current plasma etch chemistries. This process is based on thin film modification by light ions implantation followed by a selective removal of the modified layer with respect to the non-modified material. In this Letter, we demonstrate the benefit of this alternative etch method in term of film damage control (silicon germanium recess obtained is less than 6 A), anisotropy (no foot formation), and its compatibility with other integration steps like epitaxial. The etch mechanisms of this approach are also addressed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Transport of hydrogen in metals with occupancy dependent trap energies

Common diffusion trapping models for modeling hydrogen transport in metals are limited to traps with single de-trapping energies and a saturation occupancy of one. While they are successful in predicting typical mono isotopic ion implantation and thermal degassing experiments, they fail at describing recent experiments on isotope exchange at low temperatures. This paper presents a new modified diffusion trapping model with fill level dependent de-trapping energies that can also explain these new isotope exchange experiments. Density function theory (DFT) calculations predict that even mono vacancies can store between 6 and 12 H atoms with de-trapping energies that depend on the fill level of the mono vacancy. The new fill level dependent diffusion trapping model allows to test these DFT results by bridging the gap in length and time scale between DFT calculations and experiment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Modeling the dark current histogram induced by gold contamination in complementary-metal-oxide-semiconductor image sensors

We propose a model for dark current induced by metallic contamination in a CMOS image sensor. Based on Shockley-Read-Hall kinetics, the expression of dark current proposed accounts for the electric field enhanced emission factor due to the Poole-Frenkel barrier lowering and phonon-assisted tunneling mechanisms. To that aim, we considered the distribution of the electric field magnitude and metal atoms in the depth of the pixel. Poisson statistics were used to estimate the random distribution of metal atoms in each pixel for a given contamination dose. Then, we performed a Monte-Carlo-based simulation for each pixel to set the number of metal atoms the pixel contained and the enhancement factor each atom underwent, and obtained a histogram of the number of pixels versus dark current for the full sensor. Excellent agreement with the dark current histogram measured on an ion-implanted gold-contaminated imager has been achieved, in particular, for the description of the distribution tails due to the pixel regions in which the contaminant atoms undergo a large electric field. The agreement remains very good when increasing the temperature by 15 °C. We demonstrated that the amplification of the dark current generated for the typical electric fields encountered in the CMOS image sensors, which depends on the nature of the metal contaminant, may become very large at high electric field. The electron and hole emissions and the resulting enhancement factor are described as a function of the trap characteristics, electric field, and temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Parametric interactions in presence of different size colloids in semiconductor quantum plasmas

Present work is an attempt to investigate the effect of different size colloids on parametric interaction in semiconductor quantum plasma. Inclusion of quantum effect is being done in this analysis through quantum correction term in classical hydrodynamic model of homogeneous semiconductor plasma. The effect is associated with purely quantum origin using quantum Bohm potential and quantum statistics. Colloidal size and quantum correction term modify the parametric dispersion characteristics of ion implanted semiconductor plasma medium. It is found that quantum effect on colloids is inversely proportional to their size. Moreover critical size of implanted colloids for the effective quantum correction is determined which is found to be equal to the lattice spacing of the crystal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Gate length and temperature dependence of negative differential transconductance in silicon quantum well metal-oxide-semiconductor field-effect transistors

Introducing quantum transport into silicon transistors in a manner compatible with industrial fabrication has the potential to transform the performance horizons of large scale integrated silicon devices and circuits. Explicit quantum transport as evidenced by negative differential transconductances (NDTCs) has been observed in a set of quantum well (QW) transistors fabricated using industrial silicon complementary metal-oxide-semiconductor processing. Detailed gate length and temperature dependence characteristics of the NDTCs in these devices have been measured. The QW potential was formed via lateral ion implantation doping on a commercial 45 nm technology node process line, and measurements of the transfer characteristics show NDTCs up to room temperature. Gate length dependence of NDTCs shows a correlation of the interface channel length with the number of NDTCs formed as well as with the gate voltage (V{sub G}) spacing between NDTCs. The V{sub G} spacing between multiple NDTCs suggests a quasi-parabolic QW potential profile. The temperature dependence is consistent with partial freeze-out of carrier concentration against a degenerately doped background.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Incorporation of dopant impurities into a silicon oxynitride matrix containing silicon nanocrystals

Dopant impurities, such as gallium (Ga), indium (In), and phosphorus (P), were incorporated into silicon-rich silicon oxynitride (SRSON) thin films by the ion implantation technique. To form silicon nanoparticles, the implanted layers were thermally annealed at temperatures up to 1100 °C for 60 min. This thermal treatment generates a phase separation of the silicon nanoparticles from the SRSON matrix in the presence of the dopant atoms. We report on the position of the dopant species within the host matrix and relative to the silicon nanoparticles, as well as on the effect of the dopants on the crystalline structure and the size of the Si nanoparticles. The energy-filtered transmission electron microscopy technique is thoroughly used to identify the chemical species. The distribution of the dopant elements within the SRSON compound is determined using Rutherford backscattering spectroscopy. Energy dispersive X-ray mapping coupled with spectral imaging of silicon plasmons was performed to spatially localize at the nanoscale the dopant impurities and the silicon nanoparticles in the SRSON films. Three different behaviors were observed according to the implanted dopant type (Ga, In, or P). The In-doped SRSON layers clearly showed separated nanoparticles based on indium, InOx, or silicon. In contrast, in the P-doped SRSON layers, Si and P are completely miscible. A high concentration of P atoms was found within the Si nanoparticles. Lastly, in Ga-doped SRSON the Ga atoms formed large nanoparticles close to the SRSON surface, while the Si nanoparticles were localized in the bulk of the SRSON layer. In this work, we shed light on the mechanisms responsible for these three different behaviors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

All-optical lithography process for contacting nanometer precision donor devices

In this article, we describe an all-optical lithography process that can make electrical contact to nanometer-precision donor devices fabricated in silicon using scanning tunneling microscopy (STM). This is accomplished by implementing a cleaning procedure in the STM that allows the integration of metal alignment marks and ion-implanted contacts at the wafer level. Low-temperature transport measurements of a patterned device establish the viability of the process.

36 MATERIALS SCIENCE↗

How carbon vacancies can affect the properties of group IV color centers in diamond: A study of thermodynamics and kinetics

Recently, there has been much interest in using Group IV elements from the periodic table to fabricate and study XV color centers in diamond, where X=Si, Ge, Sn, or Pb and V is a carbon vacancy. These Group IV color centers have a number of interesting spin and optical properties, which could potentially make them better candidates than NV− centers for important applications in quantum computing and quantum information processing. Unfortunately, the very same ion implantation process that is required to create these XV color centers in diamond necessarily also produces many carbon vacancies (VC), which can form complexes with these color centers (VC−XV) that can dramatically affect the properties of the isolated XV color centers. The main focus of this work is to use density-functional theory to study the thermodynamics and kinetics of the formation of these VC−XV complexes and to suggest experimental ways to impede this process such as varying the Fermi level of the host diamond material through chemical doping or applying an external electrical bias. We also include a discussion of how the simple presence of many VC can negatively impact the spin coherence times (T2) of Group IV color centers through the presence of acoustic phonons.

Kuate Defo, Rodrick↗

Non-dilute helium-related defect interactions in the near-surface region of plasma-exposed tungsten

We report a systematic energetic analysis of helium-related defect interactions that mediate helium (He) segregation on surfaces of plasma-exposed tungsten at different levels of He ion implantation. We focus on high He fluences that increase the He content in the plasma-exposed material well beyond the dilute limit of He concentration and employ atomic configurations generated by large-scale molecular dynamics simulations of He-implanted tungsten. We perform systematic molecular statics computations of cluster– defect interaction energetics in the highly defect-rich near-surface region of plasma-exposed tungsten for small mobile helium clusters as a function of the cluster distance from the surface. In this region, mobile clusters are also subjected to the stress fields generated by defects such as helium bubbles and other clusters, which govern cluster–defect interactions in addition to the cluster–surface interaction. Based on systematic investigation of individual cluster–defect interactions, we develop a mathematical framework to describe the interaction energy landscapes consisting of elastic interaction potential perturbations to finite-width square-well potentials, where the potential well accounts for cluster trapping by the defect at close range and subsequent coalescence and the perturbation potential is parameterized according to elastic inclusion theory. Superposition of all the relevant interaction potentials provides a comprehensive description of the interaction energy landscape that would be experienced by a small mobile cluster along its migration path toward the plasma-exposed surface at high He fluence. Such descriptions are particularly important for developing atomistically-informed, hierarchical multi-scale models of helium cluster dynamics in plasma-facing materials.

36 MATERIALS SCIENCE↗

Electronic and optical characterization of bulk single crystals of cubic boron nitride (cBN)

Cubic boron nitride (cBN) is a relatively less studied wide bandgap semiconductor despite its many promising mechanical, thermal, and electronic properties. We report on the electronic, structural, and optical characterization of commercial cBN crystal platelets. Temperature dependent transport measurements revealed the charge limited diode behavior of the cBN crystals. The equilibrium Fermi level was determined to be 0.47 eV below the conduction band, and the electron conduction was identified as n-type. Unirradiated dark and amber colored cBN crystals displayed broad photoluminescence emission peaks centered around different wavelengths. RC series zero phonon line defect emission peaks were observed at room temperature from the electron beam irradiated and oxygen ion implanted cBN crystals, making this material a promising candidate for high power microwave devices, next generation power electronics, and future quantum sensing applications.

36 MATERIALS SCIENCE↗