bluuebunny/crossref_metadata_2025 huggingface dataset:
Existence of ground state of an electron in the BDF approximation
Authors: Sok Jérémy
Published: April 2014

The Bogoliubov–Dirac–Fock (BDF) model allows us to describe relativistic electrons interacting with the Dirac sea. It can be seen as a mean-field approximation of Quantum Electrodynamics (QED) where photons are neglected.

This paper treats the case of an electron together with the Dirac sea in the absence of any external field. Such a system is described by its one-body density matrix, an infinite rank, self-adjoint operator.

The parameters of the model are the coupling constant α > 0 and the ultraviolet cut-off Λ > 0: we consider the subspace of squared integrable functions made of the functions whose Fourier transform vanishes outside the ball B(0, Λ). We prove the existence of minimizers of the BDF energy under the charge constraint of one electron and no external field provided that α, Λ-1 and α log(Λ) are sufficiently small. The interpretation is the following: in this regime the electron creates a polarization in the Dirac vacuum which allows it to bind.

We then study the non-relativistic limit of such a system in which the speed of light tends to infinity (or equivalently α tends to zero) with αlog(Λ) fixed: after rescaling and translation the electronic solution tends to a Choquard–Pekar ground state.
An image encryption algorithm based on 3D cellular automata and chaotic maps
Authors: Del Rey A. Martín , Sánchez G. Rodríguez
Published: April 2014

A novel encryption algorithm to cipher digital images is presented in this work. The digital image is rendering into a three-dimensional (3D) lattice and the protocol consists of two phases: the confusion phase where 24 chaotic Cat maps are applied and the diffusion phase where a 3D cellular automata is evolved. The encryption method is shown to be secure against the most important cryptanalytic attacks.
Multifractal detrended cross-correlation between the Chinese domestic and international gold markets based on DCCA and DMCA methods
Authors: Cao Guangxi , Han Yan , Chen Yuemeng , Yang Chunxia
Published: May 2014

Based on the daily price data of Shanghai and London gold spot markets, we applied detrended cross-correlation analysis (DCCA) and detrended moving average cross-correlation analysis (DMCA) methods to quantify power-law cross-correlation between domestic and international gold markets. Results show that the cross-correlations between the Chinese domestic and international gold spot markets are multifractal. Furthermore, forward DMCA and backward DMCA seems to outperform DCCA and centered DMCA for short-range gold series, which confirms the comparison results of short-range artificial data in L. Y. He and S. P. Chen [Physica A 390 (2011) 3806–3814]. Finally, we analyzed the local multifractal characteristics of the cross-correlation between Chinese domestic and international gold markets. We show that multifractal characteristics of the cross-correlation between the Chinese domestic and international gold markets are time-varying and that multifractal characteristics were strengthened by the financial crisis in 2007–2008.
Normal bands of commutative cancellative semigroups revisited
Authors: Petrich Mario
Published: May 2014

A semigroup S is of the type in the class of the title if S has a congruence ρ such that S/ρ is a normal band (i.e. satisfies the identities x2= x and axya = ayxa) and all ρ-classes are commutative cancellative semigroups. We consider semigroups S with such a congruence first for completely regular semigroups, then characterize the general case in several ways, including some special cases. When S is an order in a normal band of abelian groups Q, we study the restrictions of Green's relations on Q to S. The paper concludes with the discussion of a free semigroup in the title on two generators.
Determinacy in L(ℝ, μ)
Authors: Trang Nam
Published: April 2014

Assume V = L(ℝ, μ) ⊨ ZF + DC + Θ > ω2 + μ is a normal fine measure on 𝒫ω1(ℝ). We analyze what sets of reals are determined and in fact show that L(ℝ, μ) ⊨ AD . This arguably gives the most optimal characterization of AD in L(ℝ, μ). As a consequence of this analysis, we obtain the equiconsistency of the theories: "ZFC + there are ω2 Woodin cardinals" and "ZF + DC + Θ > ω2 + there is a normal fine measure on 𝒫ω1(ℝ)".
PERFORMANCE COMPARISON OF p–n JUNCTION DIODES USING ZINC OXIDE AND COPPER PHTHALOCYANINE HYBRID NANOCOMPOSITES AND BILAYER HETEROSTRUCTURES
Authors: PADMA N. , GHOSH MANORANJAN , SEN SHASHWATI , TEWARI R.
Published: April 2014

Nanocomposites of n-type Zinc Oxide ( ZnO ) and p-type copper phthalocyanine ( CuPc ) were synthesized using solution route and the electrical properties of heterojunctions of ZnO and CuPc in the nanocomposite film was studied. For comparison, electrical properties of bilayer heterojunction devices using ZnO nanostructure drop cast film and thermally evaporated CuPc were also studied. Rectification ratio (RR) of about 28 and 5.5 was obtained at 4 V for devices with nanocomposite film and bilayer heterojunctions indicating improved formation of p–n junction characteristics for nanocomposite films. Values of ideality factor, barrier height at the p–n junction interface and series resistance were estimated using different methods like semilog plots, Cheung and Norde's methods. Ideality factor estimated from semilog plots and Cheung's methods were found to be higher than unity indicating deviation from ideal diode behavior. Barrier height estimated from different methods was about 0.7 eV. Series resistance measured using Cheung and Norde's methods were found to be about 92 KΩ and 21 KΩ, respectively. Bilayer heterojunction devices exhibited much higher series resistance, ideality factor and barrier height as estimated using all the above-mentioned methods as compared to the devices with nanocomposite film. The above results indicate intimate mixing and improved interface between ZnO and CuPc in the in situ synthesized nanocomposite film thereby offering improved p–n junction characteristics.
A COST-EFFECTIVE MAGNETIC PHOTOCATALYST PALYGORSKITE–TiO2–FexOy WITH EXCELLENT PERFORMANCE FOR DYE PHOTODEGRADATION UNDER VISIBLE LIGHT
Authors: ZHANG JIAHUI , ZHANG LILI , HUANG JIN , ZHOU SHOUYONG , CHEN HAIQUN , ZHANG WEIGUANG , WANG XIN
Published: April 2014

Palygorskite (denoted as Pal) was used as an economical carrier of hybrid photocatalyst TiO 2– Fe x O yvia an in situ depositing technique (marked as Pal– TiO 2– Fe x O y). The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), brunner-emmet-teller (BET) measurements, X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectra measurements. Results showed that TiO 2– Fe x O y composite particles with average size of about 10 nm were loaded onto the Pal fibers' surface. Fe x O y acted not only as magnetic source but also took part in the formation of TiO 2– Fe x O y heterojunction structure, which resulted in the obvious absorption in visible light region for the obtained Pal– TiO 2– Fe x O y composite photocatalyst. The obtained Pal– TiO 2– Fe x O y shows excellent photocatalytic activity toward photodegradation of Methyl orange (MO) under visible light irradiation and the degradation ratio reached 94% within 180 min. Moreover, Pal– TiO 2– Fe x O y could be readily recovered from the reaction solution by the magnet. Possible mechanism for the enhancement was also proposed.
Advanced optical microscopy methods for in vivo imaging of sub-cellular structures in thick biological tissues
Authors: Chen Nanguang , Rehman Shakil , Sheppard Colin J. R.
Published: May 2014

Optical microscopy has become an indispensable tool for visualizing sub-cellular structures and biological processes. However, scattering in biological tissues is a major obstacle that prevents high-resolution images from being obtained from deep regions of tissue. We review common techniques, such as multiphoton microscopy (MPM) and optical coherence microscopy (OCM), for diffraction limited imaging beyond an imaging depth of 0.5 mm. Novel implementations have been emerging in recent years giving higher imaging speed, deeper penetration, and better image quality. Focal modulation microscopy (FMM) is a novel method that combines confocal spatial filtering with focal modulation to reject out-of-focus background. FMM has demonstrated an imaging depth comparable to those of MPM and OCM, near-real-time image acquisition, and the capability for multiple contrast mechanisms.
(Invited) MIEC Materials for Membrane Applications: Enhancing the Oxygen Transport
Authors: Ivers-Tiffée Ellen , Niedrig Christian , Wagner Stefan F.
Published: May 2014

Mixed ionic-electronic conducting (MIEC) materials are of great interest for a variety of high-temperature applications, such as dense ceramic oxygen transport membranes (OTMs) for gas separation. Several MIEC perovskite oxides, e.g., Ba0.5Sr0.5Co0.8Fe0.2O3-δ, La0.58Sr0.4Co0.2Fe0.8O3-δ, or La0.6Sr0.4CoO3-δ exhibit excellent oxygen-ionic and electronic transport properties and are, hence, promising candidates for high-permeation OTMs. It is essential, though, to determine their chemical stability and electrochemical transport properties (D
δ and k
δ) over a broad range of oxygen partial pressure pO2 first. This can both be achieved in a custom-made zirconia “oxygen pump” setup. Surface oxygen exchange (k
δ) becomes rate-determining for oxygen permeation of high-performing thin OTMs. Further increase of oxygen flux requires an enhancement of surface exchange. This can be achieved by modifying the OTM surfaces with a porous functional layer. With the help of a 3D FEM OTM model the interplay of transport parameters and functional-layer microstructure (thickness, porosity, particle sizes) can be readily assessed.
(Invited) Tuning Dielectric Properties of Epitaxial Lanthanide Oxides on Silicon
Authors: Osten H. Joerg , Schwendt Dominik , Chaudhuri Ayan Roy , Fissel Andreas , Shekhter Pini , Eizenberg Moshe
Published: May 2014

The dielectric properties of thin crystalline oxides grown on silicon are sensitive to small variations in structure and symmetry. Here, we report about different investigations on strain-induced effects on dielectric properties. First, we report on the dependence of the dielectric constant on layer thickness for epitaxial Gd2O3 on Si(111). The K-value strongly decreases with increasing layer thickness and reaches the bulk value at around 8 nm. Controlling the oxide composition in ternary (Gd1-xNdx)2O3 thin films enables us to tune the lattice mismatch to silicon, and thus the strain-induced variation in the dielectric constants. We show that solely tetragonal distortion of the cubic lattice is not sufficient to explain the huge enhancement in K-values; more severe strain induced structural phase deformations take place. Further, dielectric properties of epitaxial oxide thin films have been found to improve significantly by incorporation of suitable dopants. We observe substantial reduction of the leakage current density in nitrogen-doped Gd2O3 layers indicating that nitrogen doping can be an effective route to eliminate the adverse effects of the oxygen vacancy induced defects in the oxide layers.
(Invited) Electrical Characterization of Defects in Al2O3
Authors: Schmid Alexander , Kersten Friederike , Rentrop Solveig , Abendroth Barbara , Meyer Dirk Carl , Heitmann Johannes
Published: May 2014

The dielectric properties of atomic layer deposited pure Al2O3 and Si doped Al2O3 thin films were characterized by various measurement techniques. By the use of capacitance voltage and conductance measurements charged defects within the oxide and at the silicon interface were detected. It was shown that the passivation quality of Al2O3 is strongly related to the density of fixed oxide charges Qf and the interface trap density Dit. The fixed charge density could be adjusted from -6.2∙1012 cm-2 for samples annealed at 500°C to +2.1∙1012 cm-2 for as deposited Si doped layers. Additionally current voltage characteristics were performed in a temperature range from 25°C to 125°C. The leakage current was found to increase with higher temperature. A barrier height of 0.4 eV was extracted from the data by assuming a Pool-Frenkel mechanism.
(Invited) Interface Engineering Routes for a Future CMOS Ge-Based Technology
Authors: Mitrovic Ivona Z. , Althobaiti Mohammed , Weerakkody Ayendra Don , Sedghi Naser , Hall Stephen , Dhanak Vinod R. , Mather Sean , Chalker Paul R. , Tsoutsou Dimitra , Dimoulas Athanasios , Henkel Christoph , Litta Eugenio Dentoni , Hellström Per-Erik , Östling Mikael
Published: May 2014

We present an overview study of two germanium interface engineering routes, firstly a germanate formation via La2O3 and Y2O3, and secondly a barrier layer approach using Al2O3 and Tm2O3. The interfacial composition, uniformity, thickness, band gap, crystallinity, absorption features and valence band offset are determined using X-ray photoelectron spectroscopy, ultra violet variable angle spectroscopic ellipsometry, and high resolution transmission electron microscopy. The correlation of these results with electrical characterization data make a case for Ge interface engineering with rare-earth inclusion as a viable route to achieve high performance Ge CMOS.
(Invited) High κ/InGaAs for Ultimate CMOS – Interfacial Passivation, Low Ohmic Contacts, and Device Performance
Authors: Chang W. H. , Lin T. D. , Liao Min-Han , Pi T. W. , Kwo J. Raynien , Hong Minghwei
Published: May 2014

In-situ atomic layer deposited (ALD)-HfO2 has been used to passivate In0.53Ga0.47As. Atom-to-atom interactions for the interfacial electronic/ chemical characteristics of in-situ ALD-HfO2 on pristine molecular beam epitaxy (MBE) grown In0.53Ga0.47As surface have been studied using synchrotron-radiation photoemission (SRPES). ALD-HfO2/ In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) have exhibited excellent capacitance-voltage (C-V) characteristics. The interfacial trap density spectra in absence of mid-gap peaks were attained. Moreover, 1μm-gate-length self-aligned inversion-channel In0.53Ga0.47As MOS field-effect-transistors (MOSFETs) using in-situ ALD-HfO2 as the gate dielectric have achieved record-high maximum drain current (I
D) of 1.5 mA/μm and peak transconductance (G
m) of 0.84 mS/μm. Moreover, low contact resistivity (ρc) of 6.7×10-9 Ω-cm2 by inserting a 0.6 nm ZnO dielectric layer between titanium metal and InGaAs (with Si doping concentration of 1.5×1019 cm-3) has been demonstrated; this contact structure was employed in the source/drain on the implant-free In0.53Ga0.47As quantum-well MOSFETs to obtain peak G
m of 1.25 mS/μm and low source/drain resistance of 190 Ω-μm.
(Invited) Frequency Dispersion and Band Alignments in ZrO2/n-GaAs MOS Capacitor
Authors: Konda R B , White C , Thomas D , Yang Q , Sahu D , Pradhan Aswini K
Published: May 2014

The interfacial characteristics and band alignments of high-k ZrO2 on n-GaAs have been investigated by experimentally and density functional theory. We have demonstrated that the frequency dispersion due to interface traps in capacitance-voltage characteristics of ZrO2/GaAs interface was significantly reduced through self-cleaning by trimethylalumina. The experimental valence band offset of 2.10 eV from X-ray photoelectron spectroscopy is found to be lower than that of the calculated value of 3.02 eV. The calculated conduction band offset is 1.21 eV compared to the experimental value of 1.38 eV confirms significant reduction of interface traps due to the Fermi-level pinning minimizing the band misalignment.
(Invited) Understanding of Growth Kinetics of Thermal Oxides on 4H-SiC (0001) for Control of MOS Characteristics
Authors: Kita Koji , Kikuchi Richard Heihachiro , Hirai Hirohisa
Published: May 2014

Control of thermal oxidation conditions is inevitable to achieve a high-quality MOS interface on SiC substrates. We investigated the kinetics and thermodynamics of 4H-SiC oxidation for nanometer-thick SiO2/SiC system, to find out thermodynamically preferred conditions for a smooth elimination of carbon byproduct from the interface. A linear regime of thermal oxidation of 4H-SiC (0001) was clearly observed with a high activation energy corresponding to direct CO ejection from the interface. Based on our understanding of oxidation kinetics, we found that nearly-ideal MOS characteristics with reduced interface state density ~1011 cm-2eV-1 or less, were achievable on 4H-SiC (0001) only by dry oxidation processes.
Light Wavelength Effects on Charge Trapping and Detrapping of AlOx Embedded ZrHfO High-K Stack
Authors: Liu Xi , Kuo Yue , Zhang Shumao , Yuan Tao
Published: May 2014

The ZrHfO/AlOx/ZrHfO high-k gate dielectric memory capacitors on the p-type Si wafer have been fabricated using the one pumpdown sputtering process followed by rapid thermal annealing. The memory functions were mainly based on holes trapping at the AlOx site and AlOx/ZrHfO interface layer. The hole generation, transfer and storage in the dielectric structure was influenced by light exposure, e.g., the device retained fewer holes with the increase of the wavelength of the light. Under the light exposure, the leakage current decreased in the negative voltage range but increased in the large positive voltage range. The light exposure effect is important for practical applications of the device.
(Invited) High-k Dielectrics and High Work Function Metals for Hybrid Floating Gate NAND Flash Applications
Authors: Lisoni Judit G. , Breuil Laurent , Blomme Pieter , De Stefano Francesca , Afanas'ev Valeri V. , Van den bosch Geert , Van Houdt Jan
Published: May 2014

In this paper we will discuss the key materials issues involved in the successful fabrication of hybrid floating gate (HFG) devices, a solution to scale NAND flash below 20 nm node. In HFG a Si metal stack replaces the standard poly-Si FG. The metal is required to have a high work function (WF) in order to control the leakage through the inter-gate dielectric (IGD); a high k-value of the IGD is essential to increase the coupling factor of the memory cell. Our reference stack uses TiN(WF 4.7 eV) and Al2O3(k~9) IGD annealed at 1000 °C. The metal candidates are Ta1-xAlxNy (WF>4.9eV) and Ru (WF>4.7eV). The high-k IGD of choice are Hf1-xAlxOy, GdxHf1-xOy, GdxSc1-xOy and Sc1-xAl1-xOy. We will show that optimal memory performance is strongly linked to the IGD crystallinity and the thermal stability (inter-diffusion) of the metal-IGD system. The optimal material combination is found to be HfAlO(k~19)/TiN annealed at 800 °C.
(Invited) Photoelectron Spectroscopic Study on High-k Dielectrics Based Nanoionics-Type ReRAM Structure under Bias Operation
Authors: Nagata Takahiro , Yamashita Yoshiyuki , Yoshikawa Hideki , Kobayashi Keisuke , Chikyow Toyohiro
Published: May 2014

We have demonstrated resistance switching using HfO2 film with a Cu top electrode for nonvolatile memory applications, and revealed the Cu diffusion into the HfO2 layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO2/Pt structure by performing current-voltage measurements. The current step from a high resistive state to a low resistive state was of the order of 103-104 Ω, which provided a sufficient on/off ratio for use as a switching device. The filament formation process was investigated by employing hard x-ray photoelectron spectroscopy under bias operation. The application of a bias to the structure reduced the Cu2O state at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2, providing evidence of Cu2O reduction and Cu diffusion into the HfO2 layer. These results also provide evidence that the resistance switching of the Cu/HfO2/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.
(Invited) Octadecylphosphonic Acid Self-Assembled Monolayers in Low Voltage Electrowetting-on-Dielectric Systems
Authors: Mibus Marcel , Hu Xiaoyu , Knospe Carl , Reed Michael L. , Zangari Giovanni
Published: May 2014

Octadecylphosphonic acid reacts with oxidized aluminum surfaces to form a self-assembled monolayer film. The effectiveness of the monolayers are examined for use in an electrowetting-on-dielectric application using anodized aluminum as the substrate. We report growth of the monolayers by monitoring contact angle and SEM imaging. Electrowetting is characterized in static and dynamic configuration, giving advancing, receding, and contact hysteresis. The films greatly reduce the voltage requirement for drop movement, but the high hysteresis currently limits the effectiveness at low voltage operation.
(Invited) Fabrication and Dielectric Properties of BaTiO3 Thin Films on Polycrystalline Ni Foils
Authors: Du Hui , Liang Weizheng , Gao Min , Zhang Y. , Chen C. L. , Lin Yuan
Published: May 2014

The BaTiO3 (BTO) thin films were deposited on polycrystalline Ni foils using a chemical solution approach, polymer-assisted deposition. We show that the interface between the BTO film and the Ni foil plays a critical role in determining the dielectric and ferroelectric properties of this flexible assembly. A pretreatment process of nickel foils with hydrogen peroxide (H2O2) solution has been conducted to form thin nickel oxide layers on the surfaces for the growth of BTO films. A rapid thermal post-annealing in oxygen would also strongly affect the electric properties of the as-prepared thin films. The growth dynamics was systematically studied to optimize the single phase BTO films with good dielectric and ferroelectric properties.
Ultrathin (8-14 nm) Conformal SiN for sub-20 nm Copper/Low-k Interconnects
Authors: Nguyen Son van , Priyadarshini Deepika , Shobha Hosadurga k , Haigh Thomas J , Hu Chao-kun , Cohen Stephan A , Liniger Eric , Shaw Thomas M , Adams Edward D , Burnham Jay , Madan Anita , Klymko Nancy R , Parks Christopher , Yang Daewon , Molis Steven E , Lin Y , Bonilla Griselda , Grill Alfred , Edelstein Daniel , Canaperi Donald F , Xia Li-Qun , Reiter Steven , Balseanu Mihaela , Shek Mei-Yee
Published: May 2014

A multilayer SiN barrier film with high breakdown field and low leakage current is developed for Cu low-k interconnects and is compared with the SiCNH barrier film used in previous technology nodes. Ultrathin SiN barrier cap films also provide high conformality and fill recessions in Cu lines as observed after CMP. The conformal ultrathin (8-14 nm) multilayer SiN cap is robust with higher breakdown field, lower leakage and forms a good oxidation barrier. The electromigration activation energy for a SiN cap layer of 10-12 nm dielectric thickness is about 0.9 eV.
Formation of Large Grain Ge Single Crystal on Insulating Substrate by Liquid-Solid Coexisting Annealing of a-Ge(Sn)
Authors: Matsumura Ryo , Kai Yuki , Chikita Hironori , Sadoh Taizoh , Miyao Masanobu
Published: May 2014

To realize next generation thin-film-transistors (TFTs), seedless rapid-melting growth of Ge on insulator is investigated. By rapid-thermal annealing (RTA) of amorphous GeSn (a-GeSn) layers on insulating substrates at a temperature between the solidification point and the melting point, GeSn layers melt incompletely, which generates a limited number of solid nuclei as residue. Once cooling starts, liquid-phase epitaxial growth occurs from these nuclei, which results in growth of large-grain crystals. Since segregation coefficient of Sn in Ge is very small (~0.02), almost all Sn atoms segregate at edges of the grown regions. As a result, almost Sn-free (≤1%) large Ge crystal grains are achieved on insulating substrates by a self-organizing process.
(Invited) Material Engineering for 7nm FinFETs
Authors: Moroz Victor , Huang Joanne , Choi Munkang , Smith Lee
Published: May 2014

Design rules and several candidate channel materials are explored for the 7nm technology node. FinFET transistor architecture is chosen, and the analysis is performed using 3D modeling tools, including ballistic transport, Schrodinger-driven quantization, and band-to-band tunneling leakage. The comparative analysis of Si, SiGe, Ge, GaAs, InGaAs, and InAs channel materials points to InGaAs with more than 80% Ga content as the best candidate for low power applications at 7nm design rules.
(Invited) Effect of SOI Substrate on CMOS Devices Reliability
Authors: Federspiel Xavier , Arfaoui Wafa , Angot Damien , Monsieur Frederic , Rafik Mustapha , Mora Pascal , Cacho Florian , Roy David , Huard Vincent
Published: May 2014

In this paper we will review the mains consequences of the integration of buried oxide on CMOS device reliability, since the presence of BOx under CMOS devices has already been largely referred in the literature as being responsible for parasitic self-polarization, or unwanted joule heating with negative impact on device reliability. First the reliability of BOx itself will be reviewed, BOx interface defect generation will be analyzed, then the used of body bias polarization on transistor degradation mechanisms (time dependent breakdown tddb, negative bias temp instability NBTI, hot carrier injection HCI) will be presented with a special focus on hci reliability and its dependence on body bias polarization
(Invited) 2.5D Advanced System-in-Package: Processes, Materials & Integration Aspects
Authors: Shenoy Ravindra V , Lai Kwan-Yu , Gusev Evgeni
Published: May 2014

Semiconductor scaling is expected to face several disruptive challenges in the next several years. These challenges need to be especially resolved within constraints of mobile platform of low cost and small form factor. 2.5D advanced system-in-package with low cost interposers would be valuable in addressing these challenges. Some examples of glass interposer have been used to discuss processes, materials and integration aspects of 2.5D advanced system-in-package.
(Invited) Growth and Characterization of High Power AlInN/GaN HEMTs
Authors: Chyi Jen-Inn , Lee Geng-Yen , Tu Po-Tsung , Yeh Nien-Tze
Published: May 2014

In this work, growth of AlInN and its application to AlInN/GaN metal-oxide-semiconductor high electron mobility transistors are investigated. It is found that a GaN cap on AlInN layer improves the transistor’s off-state breakdown voltage (VB) and on-state resistance (Ron).
(Invited) Development of 4 Inch and 6 Inch GaN-on-Si for High-Voltage Operation
Authors: Lo C.-F. , Laboutin O. , Cao Y. , O'Connor K. , Hill D. , Johnson W.
Published: May 2014

4 inch and 6 inch GaN-on-silicon (GOS) epitaxial wafers have been developed to enable large-volume, low-cost manufacturing technology for GaN power electronics. In an effort to reduce the buffer leakage and improve the buffer blocking voltage as well as the device off-state breakdown voltage, carbon-doped buffer epilayers and total nitride epitaxy thickness were investigated. Low normalized buffer leakage of around 3 × 10-9 A/mm and low normalized three-terminal subthreshold leakage of around 2 × 10-7 A/mm with on/off ratio of ~106 were obtained from both 4 and 6 inch GOS HEMT wafers. A three-terminal off-state breakdown voltage of 1.2 kV was achieved on a GOS HEMT with 10 μm GD spacing to confirm a strong potential for high power applications.
(Invited) Impurity Co-doping of Gallium Nitride Materials for Enhanced Light Emission
Authors: Zavada John M
Published: May 2014

Impurity doping of silicon and other semiconductor materials has been an active research area for more than 20 years. There have been two main thrusts of this work, erbium doping to provide infrared light emission in silicon for telecommunications, and doping with other rare earths for full color displays and solid state lighting. Major advances in both of these areas have been achieved through metal-organic chemical vapor deposition synthesis of rare earth doped GaN thin films. However, the low emission efficiency in prototype devices has prevented commercial applications. Recent advances concerning co-doping GaN films with a rare earth and an impurity element are addressed. Experimental data showing enhanced light emission through co-doping of the GaN films are presented. Theoretical simulations of europium and silicon atoms in the GaN lattice are described. These results indicate that significant light emission can be achieved via co-doping of GaN.
(Invited) Carrier Dynamics and Photon Management for Improvement in Quantum Efficiencies of GaN-Based Visible Light-Emitting Diodes
Authors: Ryou Jae-Hyun , Kim Jeomoh , Choi Suk , Kim Hee Jin , Lochner Zachary , Ji Mi-Hee , Satter Md. Mahbub , Detchprohm Theeradetch , Yoder P. Douglas , Dupuis Russell D , Asadirad Mojtaba , Liu Jianping , Kim Jin Soo , Fischer Alec , Juday Reid , Ponce Fernando , Kwon Min-Ki , Yuan Dajun , Guo Rui , Das Suman
Published: May 2014

Data and analysis are presented employing several new methods to address carrier dynamics and photon management issues in order to improve internal quantum efficiency and light-extraction efficiency of GaN-based light-emitting diodes. For the carrier dynamics, studied are the effects of a newly-developed InAlN electron blocking layer and a p-InGaN:Mg layer on electron blocking and hole transport through multiple-quantum well active region. Also, a new technique of direct surface patterning is demonstrated using three-beam interference laser ablation for efficient photon management.
(Invited) Planar Field Effect Transistor Biosensors: Toward Single Molecular Detection and Clinical Applications
Authors: Wang Yuji , Sondergaard Patricia Casal , Theiss Andy , Lee Stephen C. , Lu Wu
Published: May 2014

In this research, a recessed gate AlGaN/GaN heterojunction field effect transistor (HFET) is demonstrated for biodetection sensitivity improvement. The measurements are performed on a zero-bias gate configuration to eliminate the noise and electrochemical activities from the gate electrode. A detection limit in terms of the concentration is demonstrated at 16 aM on a gate-recessed AlGaN/GaN bioHFET for streptavidin (SA) detection. The reduction of low frequency noise contributes to the signal to noise ratio (SNR) improvement. The recessed AlGaN/GaN bioHFETs have also been characterized in direct detection of biomarkers in physiological fluids at low concentrations for early-stage transplant rejection diagnostics. The electrical measurement results from recessed AlGaN/GaN bioHFETs are consistent with the patients’ clinical behavior.
Investigation of Traps in AlGaN/GaN HEMTs by Sub-Bandgap Optical Pumping under DC and Gate-Lag Measurement
Authors: Kang Tsung-Sheng , Cheney David , Gila Brent P , Ren Fan , Pearton Stephen J.
Published: May 2014

We investigated the traps affecting 2DEG density in AlGaN/GaN HEMTs by sub-bandgap optical pump. Based on the fact that the band bending can alter due to the variation in the density of trapped charge at heterostructure, new transition is proposed to explain the phenomenon. The density change in the trapped charges before and after semi-on state stress at VDS=20V and VGS=-2V with the ambient temperature of 80℃ can also be estimated.
(Invited) AlGaN/GaN HEMT Reliability and Trap Detection Using Optical Pumping
Authors: Cheney David
Published: May 2014

Changes in the drain current that correspond to charge trap energies in the band-gap of AlGaN/GaN High Electron Mobility Transistors (HEMTs) were measured when illuminated by below band-gap light. The energy of the applied wavelength of light affects the trapping and de-trapping of carriers within the band-gap, providing an indicator of trap densities. These changes were compared on HEMTs with gate lengths of 0.14 & 0.17 µm, before and after electrically stressing under on-state (VG = 0 V), off-state (VG =-5 V), and typical operating conditions (VG = -2V) indicating a change in trap density as a result of electrical stressing. Changes in trap densities were minimal after both off-state and on-state stressing but significant trap creation in the range EC¬-0.4-0.6 eV were observed in HEMTs exhibiting gradual degradation during stressing. Energy levels corresponding to these values in the literature have been suggested to correlate GaN and NGa substitutional defects, as well as GaI interstitials.
Silicon Nitride Thickness Dependent Electrical Properties of InAlN/GaN Heterostructures
Authors: Singh Sarab Preet , Liu Yi , Kyaw Lwin Min , Ngoo Yi Jie , Bera Milan Kumar , Dolmanan Surani Bin , Tripathy Sudhiranjan , Chor Eng Fong
Published: May 2014

We have investigated the effects of silicon nitride layer thickness on the passivation of InAlN/GaN-on-Si high electron mobility transistors (HEMTs). It is found that the charge density in the two dimensional electron gas (2DEG) at the InAlN/GaN interface increases with increasing SiN
x
passivation layer thickness and saturates at an optimal thickness of ~ 100 nm. A systematic red shift in the photoluminescence (PL) peak position of the GaN channel is observed due to the enhancement in 2DEG carrier density related to SiN
x
layer thickness. Such passivated InAlN/GaN-on-Si HEMTs show increase in the saturation drain current, maximum extrinsic transconductance and negative threshold voltage shifts. A maximum increase of the drain current from 0.64 to 0.92 A/mm, and the peak extrinsic transconductance from 0.165 to 0.206 S/mm are observed for a SiN
x
thickness of 100 nm and higherWe have investigated the effects of silicon nitride layer thickness on the passivation of InAlN/GaN-on-Si high electron mobility transistors (HEMTs). It is found that the charge density in the two dimensional electron gas (2DEG) at the InAlN/GaN interface increases with increasing SiN
x
passivation layer thickness and saturates at an optimal thickness of ~ 100 nm. A systematic red shift in the photoluminescence (PL) peak position of the GaN channel is observed due to the enhancement in 2DEG carrier density related to SiN
x
layer thickness. Such passivated InAlN/GaN-on-Si HEMTs show increase in the saturation drain current, maximum extrinsic transconductance and negative threshold voltage shifts. A maximum increase of the drain current from 0.64 to 0.92 A/mm, and the peak extrinsic transconductance from 0.165 to 0.206 S/mm are observed for a SiN
x
thickness of 100 nm and higher
(Invited) Enhancing the Deep Ultraviolet Performance of 4H-SiC Based Photodiodes
Authors: Sampath Anand V , Chen Yaojia , Rodak Lee Ellen , Zhou Quigui , Campbell Joe C , Shen Hongshen , Wraback Michael
Published: May 2014

In this paper we report on two new approaches for increasing the the deep ultraviolet response (l < 260 nm) of 4H-SiC photodiodes by employing p-n- SiC- metal or p-n- SiC – n- AlxGa1-xN structures. The p-n- SiC- metal diodes, employing a transparent window metal, have a nearly flat response between 200-270 nm with peak external quantum efficiency (EQE) of 45%. A peak QE of 76% is observed for the p-n- SiC – n- AlxGa1-xN diodes at 242 nm. The significant enhancement in short wavelength response observed in both diodes is attributed to preferential absorption of deep ultraviolet photons within the depletion region of these structures as compared to that in the top doped layer of a p-i-n SiC photodiode, and the more efficient collection of photo-generated carriers through drift despite the presence of surface/interface states.
(Invited) Spatially Resolved Study of the EQE Droop in InGaN QW LEDs: Interplay of Point Defects, Extended Defects, and Carrier Localization
Authors: Lin Yue , Zhang Yong , Liu Zhiqiang , Wei Tongbo , Chen Zhong
Published: May 2014

We offer a concise overview for the mechanisms on the external quantum efficiency (EQE) droop in InGaN QW LEDs. We believe that non-radiative recombination due to extended defects and the deficiency in the electron blocking layer are most likely two primary mechanisms responsible for the droop. We perform spatially resolved electroluminescence (EL) measurements with varying injection current on an InGaN QW LED. The analyses of the EL mapping data reveal a correlation between carrier delocalization and EQE droop. In addition, we observe that at very low current, there is virtually no correlation between the local EL intensity and peak energy, reflecting very low carrier mobility; whereas with increasing current, an anti-correlation between the intensity and energy is eventually established, indicating substantial changes in the carrier mobility and diffusion length with increasing current. The results suggest the material inhomogeneity occur in different scales.
Analysis of InGaN/GaN Multiple Quantum Well Heterostructures by Means of Photoconductivity Measurements
Authors: Krause John Robert , Stokes E. B. , Deguzman Panfilo C , Mizuyama Yosuke , Kolli Rajesh
Published: May 2014

A method for the characterization of multiple quantum well (MQW) light emitting diodes(LEDs) is investigated. This method involves taking the I-V curve of the LED while it is irradiated with photons near the absorption edge of the quantum wells within the device under test. A number of features are observed on the I-V curve corresponding to spatial variations within the LED heterostructure. The physical origin of these features and their utility in analysis of the internal structure are discussed.
Ohmic Contact Properties Depending on AlGaN Layer Thickness for AlGaN/GaN High Electron Mobility Transistor Structures
Authors: Takei Yusuke , Okamoto Mari , Saito Wataru , Tsutsui Kazuo , Kakushima Kuniyuki , Wakabayashi Hitoshi , Kataoka Yoshinori , Iwai Hiroshi
Published: May 2014

Mo/Al/Ti or TiN/TiSi2 ohmic contacts were fabricated on AlGaN/GaN HEMT structures having various thicknesses of AlGaN layers. Optimum thicknesses depending on annealing temperature were found, which should be correlated with the contact formation mechanism.
Fabrication and Performance of InAlN/GaN-on-Si MOSHEMTs with LaAlO3 Gate Dielectric Using Gate-First CMOS Compatible Process at Low Thermal Budget
Authors: Bera Milan Kumar , Liu Yi , Kyaw Lwin Min , Ngoo Yi Jie , Singh Sarab Preet , Chor Eng Fong
Published: May 2014

A gate-first CMOS compatible process at low thermal budget to fabricate InAlN/GaN-on-Si MOSHEMTs is reported. This is made possible by a good quality LaAlO3 gate dielectric (k ~ 21.8) and Hf/Al/Ta ohmic contacts that require low annealing temperature. The reverse leakage current of the W/LaAlO3 gate stack remains low (< 3´10-7 mA/mm at -10 V) upon ohmic contact annealing at 600 oC. The fabricated LaAlO3 gate dielectric MOSHEMTs demonstrate a reasonable DC performance (Idsat ~ 510 mA/mm, Gmax ~ 44 mS/mm) for a 1 μm gate length device.
(Invited) Study of Carrier Localization, Carrier Transportation and Carrier Recombination Processes in Blue-Emitting InGaN/GaN MQWs
Authors: Li Cheng , Stokes E. B. , Armour Eric A
Published: May 2014

Carrier localization, transportation and recombination in blue-emitting InGaN/GaN multiple quantum wells were analyzed using temperature-dependent photoluminescence spectroscopy, confocal laser scanning microscopy and time-resolved photoluminescence (TRPL). The temperature-dependent shift of PL intensity was fitted with Arrhenius equation and explained using two non-radiative channels, which are related with thermal activation of carriers from different confining potentials. The S-shaped shift of PL peak energy and inverse-S-shaped shift of PL full width at half maximum were explained with carrier localization and carrier transportation. The TRPL spectra taken at several different places from bright region to dark region in the confocal microscopic image showed that the fast decay lifetime τ1 increases with decreasing PL intensity, indicating a higher carrier transportation rate at bright region, while the slow decay lifetime τ2 decreases with decreasing PL intensity, indicating a higher probability of non-radiative recombination at dark region.
(Invited) Surface Modification of Wide Band-Gaped Anode of Dye-Sensitized Solar Cells by Ionic Liquid Molecules
Authors: Wu Wei-Lin , Chen Yijia J , Lin Ivan J. B. , Lin Ken , Huang Sheng-Fu
Published: May 2014

In this study, we report that the surface treatment of the wide band-gaped anode of titanium oxide by ionic liquid molecules accounts for at least part of the solar cell efficiency enhancement of the dye-sensitized solar cells. We found that the imidazole-derived molecules act as barrier for electron-hole premature recombination between photoelectrons transported on the conduction band of anode and the holes in the electrolyte on the anode/electrolyte interface. The significant efficiency enhancement is not necessarily due to increased dye adsorption on anodes, because we can manage a reduced dye adsorption condition while the solar cell still provides enhanced efficiency.
Bandgap Engineering of ZnO by Alloying with MgO
Authors: Liriano J. , Misra Pankaj , Sahoo Satyaprakash , Katiyar Ram S.
Published: May 2014

We report the synthesis and characterization of Mg doped ZnO thin films prepared by pulsed laser deposition method. From the X-ray diffraction studies it was found that the films are nearly epitaxial in nature without any phase segregation up to 25% of Mg doping. The independent measurements from UV-visible and photoluminescence studies confirmed that with increase in Mg concentration the band gap of Zn1-x-MgxO thin film increases systematically. Interestingly with increase in Mg content, the intensity of the peak related to band to band transition decreased drastically where as an opposite trend was observed for the intensity of defect related peak in the photoluminescence spectra. This has been attributed to dominant non-radiative process.
Impact of Annealing on Contact Formation and Stability of IGZO TFTs
Authors: Mudgal Tarun , Walsh Nathaniel , Manley Robert G. , Hirschman Karl D
Published: May 2014

Annealing processes were investigated on Indium-Gallium-Zinc-Oxide (IGZO) thin-film transistors (TFTs). Molybdenum and aluminum were used as contact metals which defined the working source/drain electrodes. Annealing was performed either pre-metal or post-metal deposition, in various gas ambients including air, oxygen, nitrogen, forming gas (5% H2 in N2) and vacuum. Pre-metal annealing in air ambient resulted in similar I-V characteristics on Mo-contact and Al-contact devices. A post-metal anneal for Mo-contact devices resulted in higher on-state current and steeper subthreshold slope, whereas the Al-contact devices experienced severe degradation suggesting the formation of an AlOx interface layer. A post-metal anneal at 400 °C in N2 followed by an air ambient ramp-down yielded Mo-contact devices with SS ~ 200 mV/dec, channel mobility µsat
~ 8.5 cm2/V∙s, and improved stability over other anneal conditions.
(Invited) Point Defect Characterization of Group-III Nitrides by Using Monoenergetic Positron Beams
Authors: Uedono Akira , Ishibashi Shoji , Oshima Nagayasu , Suzuki Ryoichi , Sumiya Masatomo
Published: May 2014

Positron annihilation is a powerful technique for evaluating point defects in semiconductors. Using this technique, one can detect vacancy-type defects in subsurface regions with high-sensitivity. We have used monoenergetic positron beams to probe native vacancies in InGaN grown on sapphire and GaN substrates by metalorganic vapor phase epitaxy. It was found that vacancy-type defects were introduced with increasing InN composition, and the major defect species was identified as complexes between a cation vacancy and a nitrogen vacancy. The concentration of the defects was found to be suppressed by Mg doping, suggesting that Mg is an excellent suppressor of cation vacancies in InGaN. The crystal quality of the InGaN films was greatly improved using the GaN substrate, but point defects, especially vacancy-type defects were found to present in the film.
(Invited) Rare Earth Luminescence in Nanostructured Amorphous Silicon Alloys
Authors: Tessler Leandro R.
Published: May 2014

Rare Earth (RE) doped amorphous silicon alloys can be prepared by reactive RF sputtering from a Si target partially covered with metallic or oxide RE platelets using appropriate reactive atmospheres. We have studied Er3+, Nd3+, Eu3+ and Tb3+ in a-Si:H, a-SiOx:H and a-SiNx:H. Annealing optimizes the photoluminescence and can induce the formation of Si nanocrystals. The RE act as nucleation centers. The RE ions present intense photoluminescence at room temperature. EXAFS measurements reveal a highly non-centrosymetric lattice site for Er in a-SiOx:H. This partially breaks the selection rule that forbids intra-4f transitions. The RE present two luminescence lifetimes, the fast component determined by the host and the slow component associated to the local symmetry ofthe ions. The amorphous and nanostructured hosts increase the cross section for RE excitation by a few orders of magnitude, making the materials practical for applications as phosphors and active amplifiers.
(Invited) Photon Management Using Si Nanocrystals and Er3+ Ions: Generation of Hot Carries upon Absorption of Low-Energy Photons
Authors: de Jong Elinore M.L.D. , Saeed Saba , Gregorkiewicz Tom
Published: May 2014

The most important limitation for efficiency of photovoltaic energy conversion appears due to the striking mismatch between the broad-band character of the solar radiation and the discrete operation mode of solar devices. Large losses appear at both edges of the solar spectrum. In particular the low-energy photons are commonly not absorbed and escape conversion. Here we discuss how this can be resolved by spectral conversion, making use of active layers of Si nanocrystals in an SiO2 matrix. As a possible solution, we consider generation of hot carriers upon sequential intraband absorption of two or more low-energy photons and present experimental data in support of this. Configurations are proposed in which the efficient spectral conversion could be achieved and their feasibilities are discussed. We also discuss the fast emission from Er3+ ions, purposefully introduced into the active layer, which can be used to trace successful generation of hot carriers, and in that way serve to evaluate specific excitation schemes.
Tb3+ Luminescence in a-SiNx:H
Authors: Bosco Giacomo Ferreira , Tessler Leandro R.
Published: May 2014

Terbium doped hydrogenated amorphous silicon nitride was prepared by reactive RF-sputtering from a silicon target partially covered either with Tb4O7 or metallic Tb platelets in a Ar+N2+H2 atmosphere. When the samples have a high enough bandgap they present characteristic Tb3+ luminescence. The luminescence intensity depends on the annealing temperature. For a given smaple, the luminescence intensity under non-resonant excitation is 10 to 20 times smaller than under resonant excitation of Tb3+. The luminescence intensity under resonant excitation slightly increases with temperature, while under non-resonant excitation it decreases with temperature.. These results are interpreted as due to very effective intra-4f radiative recombination processes in Tb3+ in a-SiNx:H. However, the excitation transfer from the matrix is inefficient or our samples are not yet fully optimized for it.
(Invited) Knitted Electrochemical Capacitors Via Natural Fiber Welded Electrode Yarns
Authors: Durkin David P. , Jost Kristy , Brown E. Kathryn , Haverhals Luke M. , Dion Genevieve , Gogotsi Yury , De Long Hugh C. , Trulove Paul C.
Published: May 2014

This report presents a novel ionic liquid-based method for fabricating flexible double layer supercapacitor electrodes utilizing natural substrates. It investigates the performance of these yarns knitted as fabrics and with other cellulose-based fibers welded with carbon particles. Scanning electron microscopy, mechanical properties testing, conductivity and other electrochemical testing are performed to characterize both individual yarns and knitted devices.
(Invited) Terahertz CMOS Electronics for Future Mobile Applications
Authors: Fujishima Minoru
Published: May 2014

Terahertz (THz) frequency range has been studied to realize attractive applications such as non-invasive sensing and ultrahigh-speed wireless communications. Although THz electronics were conventionally studied with compound semiconductors, recent miniaturized CMOS integrated circuits enable the operating frequency at THz. It is noted that, however, in order to commercialize terahertz application with CMOS circuits, it is necessary to solve technical challenges, and also to consider inevitable needs requiring CMOS circuit. We believe that the CMOS circuit will open up a future portable system with low power consumption even in the terahertz frequency range. To realize it, low power and high speed operation is simultaneously required. In this paper, how to balance the high-speed operation and low power consumption in a CMOS circuit is discussed, and low-power high-speed wireless communication in THz will be demonstrated.