bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation of Hydrogen Dilution Profiling to Material Structure and Device Performance of Hydrogenated Nanocrystalline Silicon Solar Cells
Authors: Yan Baojie , Yue Guozhen , Yan Yanfa , Jiang Chun-Sheng , Teplin Charles W. , Yang Jeffrey , Guha Subhendu 
Published: April 2011

ABSTRACTWe present a systematic study on the correlation of hydrogen dilution profiles to structural properties materials and solar cell performance in nc-Si:H solar cells. We deposited nc-Si:H single-junction solar cells using a modified very high frequency (VHF) glow discharge technique on stainless steel substrates with various profiles of hydrogen dilution in the gas mixture during deposition. The material properties were characterized using Raman spectroscopy, X-TEM, AFM, and C-AFM. The solar cell performance correlates well with the material structures. Three major conclusions are made based on the characterization results. First, the optimized nc-Si:H material does not show an incubation layer, indicating that the seeding layer is well optimized and works as per design. Second, the nanocrystalline evolution is well controlled by hydrogen dilution profiling in which the hydrogen dilution ratio is dynamically reduced during the intrinsic layer deposition. Third, the best nc-Si:H single-junction solar cell was made using a proper hydrogen dilution profile, which caused a nanocrystalline distribution close to uniform throughout the thickness, but with a slightly inverse nanocrystalline evolution. We have used the optimized hydrogen dilution profiling and improved the nc-Si:H solar cell performance significantly. As a result, we have achieved an initial active-area cell efficiency of 9.2% with a nc-Si:H single-junction structure, and 15.4% with an a-Si:H/a-SiGe:H/nc-Si:H triple-junction solar cell structure.
Polysilazane Precursor Used for Formation of Oxidized Insulator
Authors: Urabe Yuji , Sameshima Toshiyuki 
Published: April 2011

ABSTRACTWe report on SiO2 film formation using Polysilazane precursor treated with remote oxygen plasma and high-pressure H2O vapor heating. Polysilazane precursor films with a thickness of 130 nm were formed on silicon substrates by spin coating method. They were annealed at 350°C in remote oxygen plasma at a pressure of 2.0×10−2 Pa and a 13.56×106 Hz radio frequency power of 300 W for 3h followed by 1.3×106-Pa-H2O vapor heating at 260°C for 3 h. Polysilazane precursor films were entirely oxidized by high-pressure H2O vapor heat treatment, and the density of Si-N bonding and Si-H bonding in Polysilazane precursor films were effectively dissociated by the combination of high-pressure H2O vapor heat treatment with remote oxygen plasma treatment. While MOS(Metal-Oxide-semiconductor) capacitors fabricated only by high-pressure H2O vapor heat treatment had a high specific dielectric constant of 6.1, a fixed oxide charge density of 1.3×1012 cm−2 and a density of interface trap of 5.4×1011 cm−2eV−1, the remote oxygen plasma treatment followed by high-pressure H2O vapor heat treatment allowed us to reduce them to 4.1 and 1.6×1011 cm−2, 4.2×1010 cm−2eV−1, respectively.
Electronic Properties Of Nanocrystalline Silicon Deposited With Different Crystallite Fractions And Growth Rates
Authors: Hugger Peter G. , Cohen J. David , Yan Baojie , Yue Guozhen , Xu Xixiang , Yang Jeffrey , Guha Subhendu 
Published: April 2011

ABSTRACTJunction capacitance measurements were used to characterize the properties of nanocrystalline silicon (nc-Si:H) solar cells. These methods included drive-level capacitance profiling (DLCP) to obtain spatially-resolved defect densities, as well as transient photocapacitance (TPC) and transient photocurrent (TPI) spectra to reveal optically responsive states in the band-gap, and to estimate minority carrier behavior before and after lightsoaking. Crystalline volume fractions were estimated using Raman spectroscopy. Previously we had identified at least two types of distinct behaviors in such nc-Si:H materials that depended on the crystalline volume fraction. Here, in one case, we report results indicating that both types of behavior can occur in a single sample, possibly indicating that the structural properties of that sample have evolved during growth.
In-Situ Transmission Electron Microscopy Investigation of Aluminum Induced Crystallization of Amorphous Silicon
Authors: Kishore Ram , Sharma Renu , Hata Satoshi , Kuwano Noriyuki , Tomokiyo Yoshitsuga , Naseem Hameed , Brown W D 
Published: April 2011

ABSTRACTThe interaction of amorphous silicon and aluminum films to achieve polycrystalline silicon has been investigated using transmission electron microscope equipped with in-situ heating holder. Carbon coated nickel grids were used for TEM studies. An ultra high vacuum cluster tool was used for the deposition of a ∼50nm a-Si films and a vacuum deposition system was used to deposit a ∼50nm Al films on a-Si film. The microstructural features and electron diffraction in the plain view mode were observed with increase in temperature starting from room temperature to 275 °C. The specimen was loaded inside TEM heating holder. The temperature was measured and kept constant for 5 minutes during which the microstructure at fixed magnification of X63K was recorded and the electron diffraction pattern of the same area was also recorded. The temperature was then increase and fixed at desired value and microstructure and EDP were again recorded. The temperatures used in this experiment were 30, 100, 150, 200, 225, 275°C. A sequential change in microstructural features and electron diffraction pattern due to interfacial diffusion of boundary between Al and amorphous Si was investigated. Evolution of polycrystalline silicon with randomly oriented grains as a result of a-Si and Al interaction was revealed. After the in-situ heating experiment the specimen was subjected to high resolution TEM and EDS investigations after removing the excess Al. The EDS analysis of the crystallized specimen was performed to locate the Al distribution in the crystallized silicon. These studies show that the Al induced crystallization process can be used to prepare polycrystalline as well as nanocrystalline silicon by controlling the in-situ annealing parameters. The investigations are very useful as the nanocrystalline silicon is being investigated for its use in developing high efficiency silicon solar structures.
Physically Based Compact Model for Segmented a-Si:H n-i-p Photodiodes
Authors: Chang Jeff Hsin , Tredwell Timothy , Heiler Gregory , Vygranenko Yuri , Striakhilev Denis , Kim Kyung Ho , Nathan Arokia 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon (a–Si:H) n–i–p photodiodes are used as pixel sensor elements in large-area flat-panel detectors for medical imaging diagnostics. Accurate model of the sensor plays an imperative role in determining the performances of the detector systems as well as ascertaining design issues prior to production. This work presents the formulation of a compact model for segmented a–Si:H n–i–p photodiodes suitable for circuit-level simulation. The underlining equations of the model are based on device physics where the parameters are extracted from pertinent measurement results of previously fabricated a–Si:H n–i–p photodiodes. Furthermore, the implemented model allows photoresponse simulation with the addition of an external current source. Results of the simulation demonstrated excellent matching with measurement data for different photodiode sizes at various temperatures. The model is implemented in Verilog-A and simulated under Cadence Virtuoso design environment using device geometry and extracted parameters as inputs. The model formulation and parameter extraction process, as well as measurements and simulation results are presented.
Self-aligned Amorphous Silicon Thin Film Transistors with Mobility above 1 cm2V−1s−1fabricated at 300°C on Clear Plastic Substrates
Authors: Cherenack Kunigunde H , Kattamis Alex Z , Hekmatshoar Bahman , Sturm James C , Wagner Sigurd 
Published: April 2011

ABSTRACTWe have developed a fabrication process for amorphous-silicon thin-film transistors (a-Si:H TFTs) on free-standing clear plastic substrates at temperatures up to 300°C. The 300°C fabrication process is made possible by using a unique clear plastic substrate that has a very low coefficient of thermal expansion (CTE < 10ppm/°C) and a glass transition temperature higher than 300°C. Our TFTs have a conventional inverted-staggered gate back-channel passivated geometry, which we designed to achieve two goals: accurate overlay alignment and a high effective mobility. A requirement that becomes particularly difficult to meet in the making of TFT backplanes on plastic foil at 300°C is minimizing overlay misalignment. Even though we use a substrate that has a relatively low CTE, accurately aligning the TFTs on the free-standing, 70-micrometer thick substrate is challenging. To deal with this immediate challenge, and to continue developing processes for free-standing web substrates, we are introducing techniques for self-alignment to our TFT fabrication process. We have self-aligned the channel to the gate by exposing through the clear plastic substrate. To raise the effective mobility of our TFTs we reduced the series resistance by decreasing the thickness of the amorphous silicon layer between the source-drain contacts and the accumulation layer in the channel. The back-channel passivated structure allows us to decrease the thickness of the a-Si:H active layer down to around 20nm. These changes have enabled us to raise the effective field effect mobility on clear plastic to values above 1 cm2V−1s−1
Morphic Architectures: Atomic-Level Limits
Authors: Cavin Ralph , Zhirnov Victor 
Published: April 2011

ABSTRACTIn this paper, we consider a thought problem intended to force consideration of fundamental limits for energy sources, sensors, computing elements, and communication systems as fundamental system dimensions are reduced to the few micron regime. Design of integrated systems at this level are shown to literally require the allocation of atoms for the various functions. We argue that although there are no fabrication technologies for systems on this scale and the tradeoffs between system functions are extreme, systems on this scale might be feasible; given end-of ITRS technologies.
Logic Devices with Spin Wave Buses - an Approach to Scalable Magneto-Electric Circuitry
Authors: Khitun Alexander , Bao Mingqiang , Wu Yina , Kim Ji-Young , Hong Augustin , Jacob Ajey P , Galatsis Kosmas , Wang Kang L 
Published: April 2011

ABSTRACTWe analyze spin wave-based logic circuits as a possible route to building reconfigurable magnetic circuits compatible with conventional electron-based devices. A distinctive feature of the spin wave logic circuits is that a bit of information is encoded into the phase of the spin wave. It makes possible to transmit information as a magnetization signal through magnetic waveguides without the use of an electric current. By exploiting sin wave superposition, a set of logic gates such as AND, OR, and Majority gate can be realized in one circuit. We present experimental data illustrating the performance of a three-terminal micrometer scale spin wave-based logic device fabricated on a silicon platform. The device operates in the GHz frequency range and at room temperature. The output power modulation is achieved via the control of the relative phases of two input spin wave signals. The obtained data shows the possibility of using spin waves for achieving logic functionality. The scalability of the spin wave-based logic devices is defined by the wavelength of the spin wave, which depends on the magnetic material and waveguide geometry. Potentially, a multifunctional spin wave logic gate can be scaled down to 0.1μm2. Another potential advantage of the spin wave-based logic circuitry is the ability to implement logic gates with fewer elements as compared to CMOS-based circuits in achieving same functionality. The shortcomings and disadvantages of the spin wave-based devices are also discussed.
Studies of c-Axis Threading Screw Dislocations in Hexagonal SiC
Authors: Chen Yi , Huang Xianrong , Zhang Ning , Dhanaraj Govindhan , Sanchez Edward , MacMillan Michael F. , Dudley Michael 
Published: April 2011

ABSTRACTIn our study, closed-core threading screw dislocations and micropipes were studied using synchrotron x-ray topography of various geometries. The Burgers vector magnitude of TSDs can be quantitatively determined from their dimensions in back-reflection x-ray topography, based on ray-tracing simulation and this has been verified by the images of elementary TSDs. Dislocation senses of closed-core threading screw dislocations and micropipes can be revealed by grazing-incidence x-ray topography. The threading screw dislocations can be converted into Frank partial dislocations on the basal planes and this has been confirmed by transmission synchrotron x-ray topography.
Observation of Asymmetric Wafer Bending for 3C-SiC Thin Films Grown on Misoriented Silicon Substrates
Authors: Zielinski Marcin , Portail Marc , Chassagne Thierry , Kret Slawomir , Nemoz Maud , Cordier Yvon 
Published: April 2011

ABSTRACTWe present an experimental study of asymmetric wafer deformation for 3C-SiC layers grown on deliberately misorientated silicon substrates. An asymmetric curvature has been observed both on (100) and (111) oriented layers. In this work we focus on the (100) oriented samples. The curvature of the wafers is studied as a function of wafer thickness and offcut angle. We look for the correlations between the observed asymmetric strain relaxation and the layer morphology and microstructure. We claim that different defect pattern, measured along [110] and [1-10] direction can be at the origin of almost complete relaxation of mismatch strain along the offcut direction.
Epitaxial Growth on 2&#176; Off-axis 4H SiC Substrates with Addition of HCl
Authors: Zhang Jie , Sunkari Swapna , Mazzola Janice , Tyrrell Becky , Stewart Gray , Stahlbush R , Caldwell J , Klein P , Mazzola Michael , Casady Janna 
Published: April 2011

ABSTRACTEpitaxial growth on 3-in, 2° off-axis 4H SiC substrates has been conducted in a horizontal hot-wall CVD reactor with HCl addition. The thickness of the epiwafers ranges from 3&#61549;m to 11 &#61549;m and the growth rate is 7 − 7.5 &#61549;m/h. Although a rougher surface and a higher triangular defect density is observed using the standard process for 4° growth, an improved process has resulted in reduced triangular defect density down to around 4 cm−2and a smoother surface with the roughness of 1.1 nm for a 3.7 &#61549;m thick epiwafer. Most interestingly, the basal plane dislocation density in the 2° off-axis epiwafers has been reduced to "negligible" levels, as confirmed by both the non-destructive UVPL mapping technique and the molten KOH etching on 2° epiwafers with thickness of around 10 &#61549;m.
Simultaneous Formation of n- and p-Type Ohmic Contacts to 4H-SiC Using the Binary Ni/Al System
Authors: Ito Kazuhiro , Onishi Toshitake , Takeda Hidehisa , Tsukimoto Susumu , Konno Mitsuru , Suzuki Yuya , Murakami Masanori 
Published: April 2011

ABSTRACTFabrication procedure for silicon carbide power metal oxide semiconductor field effect transistors can be improved through simultaneous formation of ohmic contacts on both the n-source and p-well regions. We have succeeded in the simultaneous formation of Ni/Al ohmic contacts to n- and p-type SiC after annealing at 1000°C for 5 mins in an ultra-high vacuum. Ohmic contacts to n-type SiC were found when Al-layer thickness was less than about 5 nm while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with Al-layer thicknesses in the range of 5 to 6 nm exhibited ohmic behavior to both n- and p-type SiC, with specific contact resistances of 1.8 × 10−4 Ωcm2 and 1.2 × 10−2 Ωcm2 for n- and p-type SiC, respectively. An about 100 nm-thick contact layer was uniformly formed on the SiC substrate and polycrystalline δ-Ni2Si(Al) grains were formed at the contact/SiC interface. The distribution in values for the Al/Ni ratio in the δ-Ni2Si(Al) grains which exhibited ohmic behavior to both n- and p-type SiC was the largest. The smallest average δ-Ni2Si(Al) grain size was also observed in these contacts. Thus, the large distribution in the Al/Ni ratios and a fine microstructure were found to be characteristic of the ohmic contacts to both n- and p-type SiC.
Influence of Shockley Stacking Fault Expansion and Contraction on the Electrical Behavior of 4H-SiC DMOSFETs and MPS diodes
Authors: Caldwell Joshua David , Stahlbush Robert E , Imhoff Eugene A. , Glembocki Orest J. , Hobart Karl D. , Tadjer Marko J. , Zhang Qingchun , Das Mrinal , Agarwal Anant 
Published: April 2011

ABSTRACTThe forward voltage drop (Vf) increase observed in 4H-SiC bipolar devices such as pin diodes due to recombination-induced Shockley stacking fault (SSF) creation and expansion has been widely discussed in the literature. It was long believed that the deleterious affect of these defects was limited to bipolar devices. However, it was recently reported that forward biasing of the body diode of a 10kV 4H-SiC DMOSFET led to similar Vf increases in the body diode I-V curve as well as a corresponding degradation in the majority carrier conduction characteristics as well and this degradation was believed to be due to the creation and expansion of SSFs during the body diode forward biasing. Here we report measurements comparing the influence of similar stressing, along with annealing and current-induced recovery experiments in DMOSFETs and merged pin-Schottky diodes with the previously reported results of these experiments in 4H-SiC pin diodes. The results of these experiments provide sufficient support that the observed degradation in the majority carrier conduction characteristics is the result of SSF expansion.
Strengths and Limitations of the Vacancy Engineering Approach for the Control of Dopant Diffusion and Activation in Silicon
Authors: Claverie Alain , Cristiano Fuccio , Gavelle Mathieu , Sévérac Fabrice , Cayrel Frédéric , Alquier Daniel , Lerch Wilfried , Paul Silke , Rubin Leonard , Raineri Vito , Giannazzo Filippo , Jaouen Hervé , Pakfar Ardechir , Halimaoui Aomar , Armand Claude , Cherkashim Nikolay , Marcelot Olivier 
Published: April 2011

ABSTRACTThe fabrication of highly doped and ultra-shallow junctions in silicon is a very challenging problem for the materials scientist. The activation levels which are targeted are well beyond the solubility limit of current dopants in Si and, ideally, they should not diffuse during the activation annealing. In practice, the situation is even worse and when boron is implanted into silicon excess Si interstitial atoms are generated which enhance boron diffusion and favor the formation of Boron-Silicon Interstitials Clusters (BICs). An elegant approach to overcome these difficulties is to enrich the Si layers where boron will be implanted with vacancies before or during the activation annealing. Spectacular results have been recently brought to the community showing both a significant control over dopant diffusion and an increased activation of boron in such layers. In general, the enrichment of the Si layers with vacancies is obtained by Si+ implantation at high energy. We have recently developed an alternative approach in which the vacancies are injected from populations of empty voids undergoing Ostwald ripening during annealing. While different, the effects are also spectacular. The goal of this work is to establish a fair evaluation of these different approaches under technologically relevant conditions. The application domains of both techniques are discussed and future directions for their development/improvement are indicated.
A Comparison of Intrinsic Point Defect Properties in Si and Ge
Authors: Vanhellemont Jan , Spiewak Piotr , Sueoka Koji , Simoen Eddy , Romandic Igor 
Published: April 2011

ABSTRACTIntrinsic point defects determine to a large extent the semiconductor crystal quality both mechanically and electrically not only during crystal growth or when tuning polished wafer properties by thermal treatments, but also and not the least during device processing. Point defects play e.g. a crucial role in dopant diffusion and activation, in gettering processes and in extended lattice defect formation.Available experimental data and results of numerical calculation of the formation energy and diffusivity of the intrinsic point defects in Si and Ge are compared and discussed. Intrinsic point defect clustering is illustrated by defect formation during Czochralski crystal growth.
Theoretical Model of Crystal Nucleation in PCM Nano-Glasses
Authors: Karpov V. G. , Kryukov Y. A. , Mitra M. , Karpov I. V. 
Published: April 2011

ABSTRACTWe propose a theoretical analysis of crystal nucleation in disordered nano-glass structure of chalcogenide phase change memory. Statistical fluctuations of microscopic structure parameters translate into statistical distribution of nucleation times determining the transition from the highly resistive (glassy) to the low resistive (crystalline) state. This distribution is shown to be log-normal with the peak time exponentially dependent on field strength, temperature, cell area and material parameters.
Sb bonding in GeSbTe compounds by NMR Measurements
Authors: Bobela David , Taylor P. Craig 
Published: April 2011

ABSTRACTWe have measured the 121Sb NMR spectra, which are highly sensitive to the electric field gradients at the nuclear site, for crystalline Sb2Te3, Ge1Sb2Te4, Ge2Sb2Te4, and Ge2Sb2Te5. Estimates of the coupling constants, which are a measure of the field gradient, based on these spectra compare well with compounds containing Sb sites that are approximately 6-fold coordinated. The coupling constants of amorphous phase counterparts are roughly an order of magnitude larger and compare favorably with compounds where the Sb sites are 3-fold coordinated. We argue that the difference in the coupling constants arises primarily from a change in the local coordination, as opposed to the slight differences in the Sb-Te bond lengths and bond angles. The NMR data agree best with a structural model of amorphous phase based upon the “8-N” rule.
THERMAL EXPANSION OF PHASE-CHANGE RANDOM ACCESS MEMORY CELLS
Authors: Li Jianming , Shi L.P. , Yang H.X. , Lim K.G. , Miao X.S. , Lee H.K. , Chong T.C. 
Published: April 2011

ABSTRACTThree-dimensional finite element method (FEM) is used to solve the thermal strain-stress fields of phase-change random access memory (PCRAM) cells. Simulation results show that thermal stress concentrates at the interfaces between electrodes and phase change layer and it is significantly larger than that within the phase change layer. It has been found that the peak thermal stress is linearly related to the voltage of electrical pulse in the reset process but once amorphous state is produced in the cell, a nonlinear relationship between thermal stress and electrical power exists. This paper reported the change of thermal stress during set process. It was found that the stress decreases significantly due to the amorphous active region during set processes.