bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Beam Irradiated Li4Ti5O12 Electrode for High Rate Lithium Ion Batteries
Authors: Park Yiseul , Park Jung Soo , Baek Seong-Ho , Kim Jae Hyun
Published: February 2020

In this study, we demonstrate that the rate capability of the Li4Ti5O12 (LTO)-based anode in a lithium ion battery can be improved by electron beam (EB) irradiation, without the need for complicated synthesis procedures. In order to achieve this, we investigated the effect of EB irradiation on rate capability by EB irradiation i) of an electrode coated with a LTO, PVDF, and super P slurry mixture and, also, ii) of individual component powders. In the case of the EB-irradiated electrode, the LTO, PVDF, and super P were irradiated together in a single mixture. In contrast, the individually EB-irradiated component powders were mixed with other non-irradiated components, followed by coating of the mixture on Al foil. The EB-irradiated electrode shows an enhanced rate capability, while retaining a discharge capacity of ~80 mAh g-1 at the 20 C-rate. The effect of the EB irradiation on the properties of each component is examined by characterization of the EB-irradiated materials using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, charge-discharge analysis, and electrochemical impedance spectroscopy. As a result, the enhanced rate capability was attributed to the changes in the properties of the LTO and PVDF due to the EB irradiation. The electronic conductivity of LTO was enhanced by Ti3+ formation, while the PVDF mechanical strength and interaction with other components may have been improved by crosslinking, and unsaturated and hydrophilic structure formation under EB irradiation. Because the EB irradiation process is already well established in the industrial process, it could easily be applied to the mass production of LTO-based electrodes with improved charge-discharge properties.
Surface Modification of Manganese-Rich Cathode Materials in Lithium Ion Batteries
Authors: Lee Jieun , Lee Jeongyeon , Hwang Taejin , Noh Hana , Choi Wonchang
Published: February 2020

Introduction

High energy density of Li-ion batteries becomes more and more important for electric vehicle and hybrid electric vehicle. The many researches have been focused on cathode materials to substitute the commercial LiCoO2. Among various cathode materials, Over-lithiated Layered Oxide (OLO), recently investigated, is the layered transition metal oxide having more than unit Li concentration. Because OLO exhibits much higher capacity over 250mAh/g as well as lower cost, high safety and thermal stability [1,2]. So the OLO is considered as attractive candidate for cathode material because of the high capacity, reduced toxicity and low cost. However this material generates gas inevitably during charge/discharge process and exhibits not good cycle performance and poor electrical conductivity compared to other cathodes. As one of the approaches to solve these problems, we introduced surface modification with conducting polymer. Field Emission Scanning Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Various Charge-discharge measurements were also performed to investigate the effect of surface-coating layer.

 

 

 

Experimental

To prepare Samples, modified OLO is made by wet-type coating method. Electrode slurry has been made of 94% of cathode materials, 3% of Denka black, 3% of PVdF. The slurry was casted on the Al foil for current collector and assembled with 2032 coin cell. Field Emission Scanning Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Various Charge-discharge measurements were also performed to investigate the effect of surface-coating layer.

 

 

Results and discussion

Fig. 1 show the discharge profiles of the rate capability for the pristine, 1wt.% PEDOT:PSS coated OLO and 3  wt.%PEDOT:PSS coated OLO electrode between 2 and 4.6 V. Surface-modification of cathode electrodes with conducting polymer leads to the more good rate properties.

Reference

1. M. M. Thackeray, S.-H. Kang, C. S. Johnson, J. T. Vaughey, R. Benedek, S. A. Hackney, J. Mater. Chem. 17, 3053-3272(2007).

2. X. Lie, H. Li, D. Li, M. Ishida, H. Zhou,  J. Power Sources 243, 374-380. (2013).

Figure 1
Monoclinic TiO2 As Active Anode Material for Li-Ion Batteries
Authors: Cech Ondrej , Chladil Ladislav , Kazda Tomá , Kapárek Vít , Cudek Pavel , Vanýsek Petr
Published: February 2020

Chemical and thermal stability are the key bottlenecks of conventional graphite anodes used in the li-ion batteries today. Graphitic materials are the most common anode active materials mostly due to their high specific capacity and relatively low cost. On the other hand, drawbacks like low stability of solid electrolyte interface layer protecting it from spontaneous reaction with electrolyte and the risk of thermal runaway are more and more evident with rising of interest in the electro mobility and EV.

One of the most promising successors in the field of lithium anode active materials is the group of ceramic materials based on titanium oxide. Their thermal and chemical stability is incomparable with graphitic materials – they are almost inert and due to higher operation voltage they do not suffer from irreversible capacity loss as a result of SEI layer formation.

This work deals with structural and electrochemical characterisation of monoclinic TiO2 as anode active materials for lithium-ion batteries.

Soft chemical synthesis was utilized for preparation of monoclinic TiO2 and precursors based on different layered alkali metal titanates were used. Titanates with formula A2TinO2n+1 form variety of layered structures for n between 3 and 6 with alkali metal cations A in the interlayer space. These structures are composed of corrugated layers of TiO6 octaedra which can share edge or corners to form stepped layered structure. The step length for a given composition is determined by the A+ to Ti+ ratio and is in correlation with the ability to form monoclinic TiO2.

Alkali titanate precursors in the form of K2Ti4O9 and Na2Ti3O7 were prepared by high-temerature solid-state reaction and by hydrothermal synthesis respectively. Subsequent ionic exchange of K+ to protons was made and resulting protonated titanate was dehydrated at slightly rised temperature.

The influence of precursor structure and dehydratation temperature on electrochemical properties as anode material for li-ion batteries was investigated by cyclic voltammetry, galvanostatic cycling, electrochemical impedance spectroscopy and rate capability. Physical characterization by XRD, SEM and BET was provided.

Figure 1
A Comparative Study of the Dwt and Wpt for Electrochemical Information Extraction of a LiCoO2 Cell
Authors: Kim Jonghoon
Published: February 2020

In general, an experimental discharging/charging terminal voltage is highly dependent to the pulse current. According to the pulse currents including different magnitude, time interval, and type (discharging/charging), it is possible to get various terminal voltages with non-stationary and transient phenomena. In this work, for elaborate information extraction of electrochemical characteristics from a LiCoO2 cell, the wavelet transform (WT) can be properly considered as a significant role. The WT is a state-of-the-art mathematical approach that decomposes a time domain signal into different frequency groups and provides an effective solution for analyzing the non-stationary signals. Specifically, this work introduces a comparative study of the discrete wavelet transform (DWT) and wavelet packet transform (WPT) for electrochemical feature extraction of a LiCoO2 cell. Both of DWT and WPT have the framework of multi-resolution analysis (MRA) with a vigorous function of both time and frequency localization. Through MRA requiring filtering and down-sampling, the information on the electrochemical characteristics of a LiCoO2 cell can be extracted from the discharging/charging voltage signal (DCVS) over a wide frequency range. Namely, the structure of the WPT is similar with that of the DWT. The main difference in the two techniques is the decomposition ability of high frequency band. In the DWT-based MRA, only the low frequency band is decomposed giving a right recursive binary tree structure, whereas in the WPT-based MRA, the low, as well as the high frequency bands are decomposed giving a balanced binary tree structure. Thus, the WPT can be defined as extension of the DWT. According to the DCVS with and without frequent discharging/charging, one of the two techniques will be finally selected as the optimum solution of electrochemical characteristics analysis. Extracted information can be usefully applied to cell’s discrimination for stable pack configuration, model-based state-of-charge (SOC) and state-of-health (SOH) estimations, etc.
A Study into the Significant Improvement in Performance of Silicon Nanowire Electrodes through the Use of Electrolyte Additives
Authors: Kennedy Tadhg , Ryan Kevin M
Published: February 2020

Si nanowires (NWs) are a promising anode material for next generation lithium-ion batteries due to their large maximum theoretical capacity (3579 mAh/g) when compared with conventional graphitic based materials (372 mAh/g). NWs also provide good electrical conductivity along their length, have a high interfacial area in contact with the electrolyte, have an optimal short diffusion distance for Li-ion transport and can be grown directly from current collectors, eliminating the need for binders and conductive additives. However before Si NWs can be realized as a viable alternative to graphite it is essential that suitable electrolytes are developed that result in a stable SEI layer formation over the initial cycles. Here we present a systematic study of the effect of common LIB electrolyte additives such as FEC and VC on the capacity retention, rate capability and SEI layer composition of binder-free Si NW electrodes. The efficacy of 5 different electrolyte additives in various combinations and used in conjunction with standard carbonate based electrolytes was investigated. We show that small quantities of additives can improve the cycle life and rate capability of the Si NWs significantly when compared with a standard 1M LiPF6 in EC/DEC electrolyte. Using XPS and EIS techniques we elucidate the effect of each additive combination on the composition and electrical properties of the SEI layer and correlate these results with the improved performance. Furthermore, through an ex-situ high-resolution transmission electron microscopy and high-resolution scanning electron microscopy study we show that the additives can also affect a change in morphology of the active material with cycling, with the better performing additives inducing a change from a NW morphology to a stable porous network like structure over initial cycles.
Probing Life Limiting Parasitic Reactions: A Conceptual Model for Long Term Impedance Rise
Authors: Takeuchi Esther S , Marschilok Amy C , Takeuchi Kenneth J
Published: February 2020

The detailed understanding of non-Faradaic parasitic reactions which diminish battery calendar life is essential to the development of effective batteries for use in long life applications.  The dissolution of cathode materials including manganese, cobalt and vanadium oxides in battery systems has been identified as a battery failure mechanism, yet detailed dissolution studies including kinetic analysis are absent from the literature.  The results presented provide a framework for the quantitative and kinetic analyses of the dissolution of cathode materials which will aid the broader community in more fully understanding this battery failure mechanism.

In this study, a series of vanadium oxide and phosphate based cathode materials are studied relative to their dissolution in battery electrolyte.  Kinetic analysis of the results provides a quantitative framework for rationalizing the impact of structure and composition on dissolution.  Further, the result of cathode solubility at the systems level is investigated shedding light on the interaction of the negative electrode with the dissolved transition metal species.  The findings are used to provide a conceptual model for the resultant impedance rise.
Gallium Arsenide As an Alloying Anode for Lithium Ion Batteries
Authors: Hays Kevin Alan , Banek Nathan A , Wagner Michael J
Published: February 2020

Li alloying metals have much greater specific and volumetric energy densities than current state of the art graphite used in commercial Li ion batteries.  However, the extremely large volumetric changes that the metals undergo when alloying with Li lead to the structural degradation of the electrode with consequent poor cycle life.   We are attempting to make stable Li alloying metal electrodes, specifically with gallium arsenide, by akalide reduction on carbon matrices.

Arsenic has been largely ignored as a candidate for Li alloying anode materials despite having the third best gravimetric capacity of the alloying metals and being abundant and inexpensive, on par with the cost of bulk silicon1. Gallium, a lithium alloying metal that melts at 29.8°C, has shown promise because of its self-healing ability at increased temperatures2,  although it suffers from a lower gravimetric capacity than some of its more popular lithium alloying counterparts. 

Here we show the synthesis of Gallium Arsenide by akalide reduction.  It is characterized by powder x-ray diffraction, transmission electron microscopy, thermo-gravimetric analysis, and x-ray fluorescence spectroscopy.  Electrochemical testing of lithium half-cells, cycled from 0.02 to 1.5V versus lithium at a rate of C/10, showed a reversible capacity of 1365 mAh/g with good capacity retention.

(1) Nitta, N.; Yushin, G. Particle & Particle Systems Characterization, 31, 317-336.

(2) Deshpande, R. D.; Li, J. C.; Cheng, Y. T.; Verbrugge, M. W. Journal of the Electrochemical Society, 158, A845-A849.

Figure 1
(Gordon E. Moore Medal for Outstanding Achievement in Solid State Science and Technology) Research on Nano and Giga Electronics – Breakthroughs Along the Path
Authors: Kuo Yue
Published: February 2020

ICs and TFT LCDs are two largest semiconductor industries nowadays. The former is mainly driven by the Moore’s Law in the continuous shrinkage of the nano-size devices for improved speeds and functions. The latter has progressed toward the manufacture of high density devices on the ultra-large glass substrate. However, the most critical devices in both products, i.e., MOSFETs and TFTs, are operated based on the same principle. The success of these technologies is dependent on the thorough understanding and controlling of material properties, fabrication processes, and device physics. In this presentation, I will review some key breakthroughs achieved in my laboratory, such as the generalized material-process-device relationship for the large-area TFT array, the simplest 2-mask TFT process, the plasma radiation damage mechanism, the plasma-based room-temperature copper etch process, the doped metal oxide high-k gate dielectrics, the nanocrystals embedded high-k nonvolatile memories, the solid-state incandescent LEDs, and various new devices. Future developments of the technologies will be discussed.
(Invited) Planar Nanoelectronic Devices and Biosensors Using Two-Dimensional Nanomaterials
Authors: Al-Dirini Feras , Mohammed Mahmood A , Hossain Md Sharafat , Hossain Faruque M , Nirmalathas Ampalavanapillai , Skafidas Efstratios
Published: February 2020

The recent discovery of two-dimensional (2D) nano-materials with unique electronic properties has introduced a new platform for the realization of electronic devices. This work presents an array of nanodevices that can be realized within a single 2D monolayer, reducing the required number of processing steps and enabling extreme miniaturization and CMOS compatibility. By etching graphene down into narrow nanoribbons with controlled widths, graphene can be tuned from semi-metallic to semiconducting. Using this approach we propose a new class of all-graphene planar field effect devices that incorporate metallic as well as semiconducting graphene regions concurrently realized within a single graphene monolayer. Such Metal-Insulator-Semiconductor (MIS) based structures are used to implement different types of planar devices that can achieve rectification, Negative Differential Resistance (NDR) and tunable biosensing. We then investigate the extendibility of the proposed concept to other types of 2D nanomaterials, by implementing the proposed devices using MoS2 and Silicene. We finally present a very promising class of planar all-graphene resonant tunneling devices that exhibit very promising performance and require minimal process steps during fabrication, while still maintaining CMOS compatibility.
Fabricating Si Nanowires with Precisely Controlled Diameter and Spacing
Authors: Li Luping , Fang Ying , Xu Cheng , Zhao Yang , Ziegler Kirk J
Published: February 2020

Due to their unique optical and electronic properties, Si nanowires are the building blocks in various applications, including nanoelectronics, catalysis, and sensors. Nanowires with different diameters, spacing, and length are often required for these functional devices to achieve optimal performance. In this work, we demonstrate the large-scale synthesis of vertically aligned, hexagonally packed Si nanowires with precisely controlled diameter and spacing. Nanosphere lighography and metal-assisated chemical etching are combined to prepare nanowires with diameters between 100 to 500 nm. Nanowire diameters are dictated by the SiO2 nanopheres used for spin-coating, while their spacing is controlled by using different parameters during spin-coating, including spin speed and time.
Oxide-Based Synaptic Transistors for Neuromorphic Systems
Authors: Wan Qing
Published: February 2020

Inspired by the energy-efficient and cognitive computational ability of a biological brain, neuromorphic computing is an attractive computation paradigm that complements the von Neumann architecture. Hardware implementations of synapses, dendrites and spiking neural networks represent a promising computational paradigm for solving complex pattern recognition and sensory processing tasks. Here, artificial electronic synapses and dendrites are proposed based on the oxide-based electrical-double-layer transistors. Strong electrostatic coupling effect and electrochemical doping were observed due to proton migration in the P-doped SiO2 electrolyte films. Protons in the P-doped SiO2 electrolyte and oxide channel conductance were regarded as the neurotransmitter and synaptic weight, respectively. Spike-timing dependent plasticity, short-term plasticity, including paired-pulse facilitation, dynamic filtering was mimicked. Most importantly, dendritic arithmetic and spiking pH sensors with extremely low energy dissipation of 0.5pJ are also demonstrated in a simple artificial synapse with multiple pre-synaptic inputs. Our oxide-based protonic/electronic hybrid artificial synaptic transistors are potential building blocks for brain-inspired computers and neuromorphic systems.

[1] L. Q. Zhu, C. J. Wan, L. Guo, Y. Shi, and Q. Wan*. Nature Communications, 5, 3158, 2014.

[2] C. J. Wan, L. Q. Zhu, J. M. Zhou, Y. Shi, Q. Wan*. Nanoscale. 6, 4491, 2014.

[3] C.J. Wan, L. Q. Zhu, Y. H. Liu, Y. Shi, and Q. Wan*. IEEE Electron Device Letters. 35,  672,  2014.

[4] L.Q. Guo, Q. Wan*, C. J. Wan, L. Q. Zhu, Y. Shi. IEEE Electron Device Letters. 34,1581,  2013.

[5] M.Z. Dai, Q. Wan*. Nano Letters 11, 3987, 2011.
(Invited) Monolithic Integration of III-V As- and P-Based Devices on Si through Direct MBE Growth and Using Lattice Engineered Substrates
Authors: Lubyshev Dmitri , Fastenau Joel , Liu Amy , Wu Ying
Published: February 2020

Mainstream silicon (Si) CMOS technology is finally experiencing limitations of pure Si-based material and process. For digital electronics, to extend Moore’s law, the industry increasingly is investigating alternative materials and technologies to enhance channel transport properties and reduce power dissipation for future generation transistor circuitry. Heterogeneous integration of compound III-V semiconductor devices on Si may realize high performance integrated circuits for analog and digital applications and can incorporate optoelectronic components for high-speed data transfer. Such integration provides the combined advantages of high volume production of Si-based electronic circuitry with superior high-speed performance of III-V components. At IQE, we developed molecular beam epitaxy (MBE) growth processes for the production of high quality III-V based transistor structures monolithically integrated onto CMOS-compatible substrates by direct MBE growth on Si wafers and also by utilization of specialized Si-on-Lattice-Engineered-Substrate (SOLES) substrates.

 Through work with industry partners, IQE has grown InP-based high electron mobility transistor (HEMT) and quantum well field effect transistor (QWFET) structures directly on Si substrates by MBE. Following a high-K gate dielectric fabrication process, QWFET devices demonstrated high transconductance of 1750μS/μm and high drive current of 0.49mA/μm at VDS=0.5V.
[1]
As part of a program funded by the US Defense Advanced Research Projects Agency, IQE developed a direct MBE growth approach of an InP-based heterojunction bipolar transistor (HBT) structure on the SOLES substrates, and together with our collaborators successfully created clusters of high-speed III-V HBT circuitry monolithically integrated side-by-side with Si CMOS on the same wafer.
[2]

            In this paper, we will discuss structural and electronic properties of epitaxial device material, including dislocation filtering in the mismatched metamorphic buffers, and compare performance of devices fabricated on Si with reference material grown on lattice-matched InP substrates.

[1] Radosavljevic, M.; Chu-Kung, B.; Corcoran, S.; Dewey, G.; Hudait, M. K.; Fastenau, J. M.; Kavalieros, J.; Liu, W. K.; Lubyshev,D.; Metz, M.; Millard, K.; Mukherjee, N.; Rachmady, W.; Shah, U.; Chau, R. (2009), IEDM Tech. Dig., p.13.1.

[2] W. K. Liu, D. Lubyshev, J. M. Fastenau, Y. Wu, M. T. Bulsara, E. A. Fitzgerald, M. Urteaga, W. Ha, J. Bergman, B. Brar, W. E. Hoke, J. R. LaRoche, K. J. Herrick, T. E. Kazior, D. Clark, D. Smith, R. F. Thompson, C. Drazek, and N. Daval, J. Crystal Growth, 311, 1979 (2009).
(Invited) Dopant Activation and Deactivation in InGaAs during Sub-Millisecond Thermal Annealing
Authors: Sorg Victoria , Zhang Suki Naifang , Hill Megan , Clancy Paulette , Thompson Michael O.
Published: February 2020

Dopant activation of In0.53Ga0.47As was determined following laser spike annealing (LSA) at temperatures up to 900 oC with dwells from 250 μs to 2000 μs. Temperatures of the InGaAs under LSA were measured using Pt thermistors and calibrated to the known decomposition temperature of a simple polymer. Using spatially resolved probes, temperature dependent activation levels were determined by scanning across a single laser stripe. Raman analysis of the LO phonon peak and the LO phonon-plasmon coupling mode (LOPCM) peak were used to monitor crystal quality and carrier concentrations following anneals of Si+ implanted InGaAs. Compared to furnace annealing, LSA was found to increase active carrier concentration and extend the temperature limit before damage. CAPRES 4-point measurements were similarly used to determine carrier activation as a function of annealing temperature. For a 1014 cm-2 Si implant dose at 20keV, a minimum sheet resistance of 135 Ω/sq was obtained for a 1000 μs dwell at 845oC, with a peak carrier concentration of 7.7x1018 cm-3.

Figure 1
(Invited) Plasma Etching Technology Challenges for Future CMOS Fabrication Based on Microwave ECR Plasma
Authors: Izawa Masaru , Tanaka Motohiro , Yasui Naoki , Morimoto Michikazu
Published: February 2020

As dimensions of semiconductor devices shrink further into the nanometer range, transistor performance is improved not only by scaling and adopting boosting technology, but also by adopting new channel material and structure. It is also required to reduce power consumption for mobile devices. In MOS logic devices, 3D-trasistor (FinFET) was adopted to improve switching property. When fabricating, more accurate and higher aspect ratio patterning is required, e.g. fin width reaches 3.7 nm at the 5nm node, where nanowire FET and Ge/III-V channel materials are other candidates [1]. Thus, required accuracy will reach atomic level in the etching process. To realize nm scale etching, new etching process functions are necessary to suppress wiggling, roughening, and degradation of etched layer. At the same time, reasonable productivity is required for mass production.

To improve etched profiles, we have been investigated and improved microwave ECR plasma etch tool, e.g. installation of time modulation (pulsing of RF bias, discharge, and gas) technologies, accurate power control of wafer RF bias, end-point monitor, and so on. TM bias (wafer RF bias pulsing) technology is already    used in semiconductor fabrication [2]. Lower RF bias power and zero bias condition were effective for extremely high-selective etching.

Microwave ECR plasma tool seems to have good affinity to pulsing discharge because it was designed to avoid the drift of plasma density. By using the pulsing discharge, wiggling was suppressed dramatically in DSA mask etching [3].

  Gas pulsing technology was also investigated for fin etching. Etching progress and sidewall protection steps were changed cyclically without interruption of the discharge. It was found that etched profile (vertical, etch front flatness, and mask selectivity) was improved [4].

  Atomic level precision etching is required in future MOS device fabrication where etched material, etch stop layer, and structure become more complicated. It will be necessary to control lower ion incident energy with vertical direction, lower the gas dissociation to reduce aggressive radical generation and reduce sidewall deposition. We believe multi-pulsing technology (discharge, bias, and gas) and low bias power control at low pressure operation are key technologies to realize atomic level precision etching.

[1]    ITRS 2013.

[2]    T.Ono el al, JJAP. 38, 5292 (1999).

[3]    M. Morimoto et al., SPIE 2014 [9054-18].

[4]    M. Tanaka et al., JSAP Autumn meeting, 19p-S10-7, 2014.
Ag-Fe2O3 Heterostructured Nanoparticles as Photocatalysts under Visible Light Irradiation
Authors: Liu Shiben , Chen Yingjie , Dong Lifeng
Published: February 2020

Due to the synergistic effect between different composites, an increasing number of functional semiconductor-metal hybrid nanomaterials with core-shell or heterostructure geometry has been fabricated and proposed as the preferred form of catalysts. For example, Au@Co3O4 core-shell nanostructures showed higher oxygen evolution reaction activity than a mixture of Au and Co3O4 nanoparticles, or Co3O4 and Au nanoparticles alone. In addition, PbS-Ag heterostructure nanotubes exhibited significantly enhanced photocatalytic activity.

Thanks to the controlled syntheses of semiconductor-metal nanocomposites with desired morphologies, it has been feasible to study the nanostructure tuning capacities. Herein, Ag-Fe2O3 core-shell and heteromer nanocomposites were synthesized by a seed-mediated growth method reported previously, and hollow Fe2O3 nanoparticles were obtained by the transformation of  Ag-Fe2O3 core-shell nanocomposites. Subsequently, the photocatalytic activity of Ag-Fe2O3 core-shell nanocomposites was directly compared with that of Ag-Fe2O3 heteromer and hollow Fe2O3 nanoparticles, respectively. Finally, we could demonstrate experimentally whether the enhanced photocatalytic activity of Ag-Fe2O3 core-shell arise from its wide absorbance range of visible light and favorable charge separation. This investigation would help us to further understand nanostructure tuning capacity of nanocomposites and control their syntheses for a given application.
Invited: Point Defects in Chalcogenide Compound Semiconductors
Authors: Rockett Angus
Published: February 2020

The II-VI chalcogenide semiconductors are used widely in applications ranging from phase change memory materials to photovoltaics.  In some cases, such as phase change materials, defects are relatively unimportant while in optoelectronic devices such as photovoltaics, these defects are critical.  Indeed, this ultimately led to the choice of III-V nitrides over the II-VI compounds for visible light emitters.  This talk focuses on materials primarily used for photovoltaics and photosensors, as this has been the most successful application of the chalcogenides in optoelectronic devices.  When one considers the series of increasingly ionic semiconductors Ge, GaAs, ZnSe, and CuBr, the impact of grain boundaries on device performance continuously decreases, allowing practical devices made from chalcogenide polycrystals.  Remarkably, many devices work better as polycrystals than as single crystals.  This is because valence compensation is increasingly important and point defects are easily created that passivate extended defects.  At the same time, when one considers the sequence ZnSe, CuInSe2, Cu2ZnSnSe4, the increasing complexity of the compounds leads to an ever increasing potential for formation of detrimental point defects and second phases.  Ordering of point defects is common in these materials and can mitigate their effects and lower their formation energy, allowing significant deviation from stoichiometry without loss of performance.  These topics and the experimental evidence related to their activity are reviewed in this talk, primarily focusing on the chalcopyrite materials as examples and photovoltaics as the application.  Selected advanced characterization methods such as scanning microwave microscopy for study of the materials are also noted.
(Invited) Advanced Photon Management in Printed High-Efficiency Multijunction Solar Cells
Authors: Sheng Xing , Rogers John A.
Published: February 2020

High efficiency photovoltaic (PV) cells represent a clean and efficient method to utilize the abundant solar energy in both space and terrestrial applications. Advances in solar cell technology and associated light management systems are the primary determinants of improvements in efficiency. Single junction (SJ) solar cells are already near theoretical efficiency limits defined by thermalization losses and sub-bandgap transparency. Devices that incorporate multiple junctions (i.e. sub-cells) in monolithic stacks, known as multijunction (MJ) cells, provide one of the most attractive routes to ultrahigh efficiency. Over the last decade, increases in the efficiency of MJ cells correspond to nearly 1% (absolute) per year, reaching values that are presently ~44%. Further improvements, however, will require solutions to daunting challenges in achieving lattice-matched or metamorphic epitaxial growth in complex stacks and in maintaining current matched outputs from each of the sub-cells. Here we present materials and strategies to make printed multijunction solar cell structures, to bypass the challenges in conventional multijunction cell design. In the first part, I will talk about printing-based assembly of microscale, quadruple junction, four-terminal solar cells with measured efficiencies of 43.9% at concentrations exceeding 1000 suns, and modules with efficiencies of 36.5%. Secondly, I will introduce an alternative device architecture, which uses low refractive index interface materials for enhanced photon recycling in printed multijunction solar cell stacks. These results establish routes to ultrahigh efficiency cells and modules, with potential to approach thermodynamic efficiency limits and realize large-scale photovoltaic energy production.
(Invited) Radiation Effects in AlGaN/GaN and InAlN/GaN High Electron Mobility Transistors
Authors: Pearton Stephen J. , Hwang Ya-Hsi , Ren Fan
Published: February 2020

GaN-based devices are more radiation hard than their Si and GaAs counterparts due to the high bond strength in III-nitride materials. In this paper we review data on the radiation resistance of GaN-based transistors such as AlGaN/GaN and InAlN/GaN High Electron Mobility Transistors (HEMTs) to different types of ionizing radiation. In this paper, the primary energy levels introduced by different forms of radiation, carrier removal rates and role of existing defects are discussed. The carrier removal rates are a function of initial carrier concentration, dose and dose rate but not of hydrogen concentration in the nitride material grown by Metal Organic Chemical Vapor Deposition. Proton and electron irradiation damage in HEMTs creates positive threshold voltage shifts due to a decrease in the two dimensional electron gas concentration resulting from electron trapping at defect sites, as well as a decrease in carrier mobility and degradation of drain current and transconductance. Neutron irradiation created more extended damage regions and at high doses leads to Fermi level pinning while 60Co γ-ray irradiation leads to much smaller changes in HEMT drain current relative to the other forms of radiation.
(Invited) Simulation of Radiation Effects in AlGaN/GaN HEMTs
Authors: Patrick Erin , Choudhury Mohua , Ren Fan , Pearton Stephen J. , Law Mark E
Published: February 2020

AlGaN/GaN high electron mobility transistors are desirable for space applications because of their relative radiation hardness. Predictive modeling of these devices is therefore desired; however, physics-based models accounting for radiation-induced degradation are incomplete. In this work, we show that a partially ionized impurity scattering mobility model can explain the observed reduction in mobility. Electrostatic changes can be explained by confinement of negative charge near the 2DEG in the GaN buffer layer. Simulation results from FLOODS (a TCAD simulator) demonstrate that partial ionization of donor traps is responsible for this phenomenon. Acceptor traps are ionized near the AlGaN/GaN interface and continue to be ionized deep into the GaN layer, while donor traps do not become ionized until farther into the GaN layer. Compensation of the acceptor traps by the ionized donors in the GaN confine the acceptor traps (negative space charge) to a thin layer near the AlGaN/GaN interface. The simulation results show that near equal concentrations of Gallium vacancies (at Ev+1.0 eV) and Nitrogen vacancies (at Ec-0.1 eV) can account for the performance degradation of HEMTs given 5 MeV proton radiation at a fluence of 2×1014 cm-2. Our results imply that device performance can be accurately simulated by simultaneously accounting for mobility and electrostatic degradation in TCAD solvers using the presented approach.
(Invited) GaN High Power Devices and Their Applications
Authors: Mun Jae-Kyoung , Chang Woojin , Kang Dong Min
Published: February 2020

Wideband gap semiconductors, such as GaN and SiC, are called as next generation compound semiconductor platform. In material aspect, GaN has wideband gap energy(Eg=3.4eV), excellent electron transport properties, including good mobility, and high saturated drift velocity. So, GaN-based HEMT devices are attractive candidates for high-power amplifiers for communication and radar systems, and high power electronic switching devices for high efficient energy conversion systems.[1-5]

We started the R&D of GaN technologies in 2010, and the progress of GaN RF device and power amplifier technologies will be presented today. Especially, I’d like to mention about recent demonstration of GaN power HEMTs developed using the ETRI’s proprietary 4-inch GaN full process for S-band and X-band ship radar systems. We are developing high power GaN devices technologies using two platforms. One is a GaN-on-Si for cost-effective power electronic device solutions and the other a GaN-on-SiC for performance-oriented power amplifier device solutions. But my presentation will be focused on the high power amplifier devices technologies and recent radar demonstration results.

A 200W solid state power amplifier (SSPA) was developed using ETRI’s 100W GaN transistors and mounted it on the S-band ship radar system. We tested and successfully got good radar images. To evaluate our device performance, we made and installed two kinds of high power SSPA modules using ETRI’s and Cree’s commercial GaN HEMTs products, respectively. Using these modules, we performed comparative study on the radar images each other. This is the first demonstration of SSPA ship radar in Korea. Test results were almost same and will be presented in this conference.

References:

1. Millan, J. “Wide band-gap power semiconductor devices”, IET Circuits Devices Syst., Vol.1(5), pp. 372–379(2007).

2. Jae Kyoung Mun, RF Integrated Circuit Technology Workshop 2011, pp. 483-495.

3. Jae Kyoung Mun et. al.,“Current Status of GaN Technologies in ETRI”, AWAD 2012.

4. Jae Kyoung Mun, “Current Status of S-/X-/Ku- Band GaN Transistors in ETRI”, 6th Microwave and Millimeter-Wave Components Workshop for Military Applications(2012)

5. Jae Kyoung Mun et. al.,“Current Status of GaN Power Electronic Device Technologies in ETRI”, ICAE 2013.

6. Youngrak Park et al, ELECTRONICS LETTERS, Vol. 50 No. 16, pp. 1164–1165(2014)
Impact of Microstructure and Defects on Surface Reactivity during Wide Bandgap Semiconductor Epitaxy
Authors: Yanguas-Gil Angel , Zapol Peter
Published: February 2020

A great amount of research on wide bandgap semiconductors is currently focused on point and 1D defects, due to its key role in device performance. It is therefore surprising that the interplay between defects and surface kinetics is relatively unexplored. There is a strong interaction between these two aspects that goes both ways: surface kinetics can promote the formation of surface defects that get subsequently incorporated into the bulk. If we were able to predict the role that surface kinetics has on defect formation, this would allow us to greatly assist process development to achieve a further reduction in the density of defects. Conversely, surface defects and surface morphology affects the reactivity of the surface, and this can lead to intra-wafer variability based on the morphology and defect density at different points of a wafer substate. However, despite this strong correlation, the atomistic aspects of precursor-surface interaction are not well understood.

In this talk we will focus on the impact of surface morphology and defects on the surface reactivity during epitaxy. In a step flow growth mode, the density of step sites will play an important role in the overall reaction probability of the different surface species. We have therefore developed models that explore the interaction between the effective reactor probability (the probability that a precursor molecule reacts with the surface) and both surface morphology and defect concentration. One of our key results is that, under the reaction-limited conditions in which the growth rate is linear with precursor concentration, it is possible to greatly accelerate the determination of the statistical outcome of precursor-surface interaction. We can use this  information to understand where particles are more likely to react locally on the surface and the relative stability of certain surface configuration.  We have used this result to investigate the impact that surface residence time has on the reaction probability as a function of miscut and in the presence of thread screw dislocations, and the role that step roughening can have in promoting surface vacancies that can lead to point defects in the solid.
(Invited) Nitride Photocatalyst to Produce Clean Hydrogen from Water without Extra Bias
Authors: Ohkawa Kazuhiro
Published: February 2020

Nitride semiconductors are attractive materials as clean energy devices. Nitride photocatalysts are possible to produce “clean hydrogen” from water using light energy. The nitride photoelectrode was immersed into a 1-M NaOH electrolyte with a Pt counterelectrode. There is no chemical bias which is caused by different pH solutions. Furthermore there is no extra bias between the nitride photoelectrode and Pt. A Xe lamp with 100 mW/cm2 was used as a light source. The energy conversion efficiency from light energy to H2 chemical energy was calculated using the Gibbs energy of H2 combustion (-237.13 kJ/mol). The energy conversion efficiency for GaN photocatalyst was 1.4%. Continuous hydrogen generation was confirmed for 500 hours.
(Invited) Group-III Nitrides to the Extreme --- from LEDs and Solar Cells to the Transistor
Authors: Bross Adam , Zhao Liang , Elsaesser David , Li Zhongda , Durniak Mark , Detchprohm Theeradetch , Chow Tat-Sing Paul , Wetzel Christian
Published: February 2020

Achieving p-type conduction in GaN has poised the material a power semiconductor on all fronts. Record conversion efficiencies and power densities in LEDs render it a platform of GW installation base. After commercial success as a blue light emitter, the emphasis now rests on the expansion of its capacity as a full spectrum direct emitter --- and absorber. Green and amber LEDs will allow full control of lighting quality and specificity in photochemistry. In early results we find evidence of temperature performance crucially superior to those of the incumbent. Next, we explore the same GaInN/GaN quantum wells as a concentration solar cell converter. While definitely limited to the short wavelength range so far, we find respectably high spectral conversion efficiencies and outstanding temperature stability. Such performance, however, is just early indication of what else lies ahead in terms of power electronics in the form of lateral and vertical transistor. In early results we monolithically integrate LED and transistor.
Hydrothermally Grown Nonpolar a-Plane ZnO and Its Applications
Authors: Kim Jimin , Baik Kwang Hyeon , Jang Soohwan
Published: February 2020

There has been great interest in ZnO as promising alternative light emitting material. It has wide direct bandgap of 3.37 eV and large exciton binding energy of 60 meV. A diverse of growth methods have been developed for ZnO epitaxial layer growth such as laser-assisted plasma enhanced chemical vapor deposition (PECVD), metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydrothermal synthesis. Among them, hydrothermal growth is the cost-effective, environmentally friendly, and low thermal budget requiring process compared to conventional MOCVD. Most of hydrothermally grown ZnOs are in the shapes of nanorod or nanowire along c-axis due to fast growth rate of c-plane.

Commercially available LEDs are based on GaN related material system, which is grown along the polar c-axis of wurtzite crystal structure. In this crystal, there exists spontaneous and piezoelectric polarization inducing internal electric fields which result in spatial separation of electron and hole wave functions. This quantum confined stark effect (QCSE) causes reduction in radiative recombination efficiency under high current injection. As one of solution, extensive efforts on nonpolar a-plane GaN are exerted.

Nonpolar a-plane ZnO with high crystalline quality was successfully grown on a-plane GaN tempelate by simple, low-cost, and mass producible hydrothermal method. Synthesized a-plane ZnO thin film was studied with SEM, TEM, XRD, AFM, and PL analyses. In this presentation, growth of hydrothermal ZnO and its applications will be introduced.
(Invited) Investigations and Improvements of AlInN/GaN HEMTs Grown on Si
Authors: Chyi Jen-Inn , Hsin Yue-Ming , Lee Geng-Yen , Chiu Hsien-Chin
Published: February 2020

GaN-based high electron mobility transistors (HEMTs) have attracted tremendous attention because of its wide bandgap and high power handling capability, which are the two fundamental merits for power electronics applications. Lattice-matched AlInN/GaN heterostructure has been considered a promising alternative to its AlGaN/GaN counterpart due to its stronger spontaneous polarization, which induces higher carrier concentration and therefore reduces channel resistance. In addition, InAlN lattice-matched to GaN would not be subject to the inverse piezoelectric effect that deteriorates device reliability as observed on AlGaN/GaN HEMTs.  While a few excellent device characteristics have been demonstrated over the years, AlInN/GaN HEMTs are in general still more vulnerable than AlGaN/GaN HEMTs. It is desirable to clarify the origin(s) of this problem to expedite the development of high power AlInN/GaN HEMTs and the devices alike. In this talk, we will present our recent works on the growth and electrical characterization of AlInN/GaN HEMTs, including capping layer designs, off-state breakdown mechanisms, dynamic resistance measurements as well as low frequency noise measurements. Solutions to cope with the material issues and process issues will also be addressed.
Effects of Chemical Doping and Defect Density on Electrical and Optical Properties of Graphene As a Transparent and Conductive Electrode
Authors: Oh Sooyeoun , Yang Gwangseok , Jung Younghun , Kim JiHyun
Published: February 2020

Indium tin oxide (ITO) has been commonly used as a transparent and conductive electrode in many applications owing to its outstanding electrical conductivity and transparency. However, ITO still suffers from limited resource, low transmittance at UV and IR region, chemical instability, poor flexibility and complex fabrication process. Recently, graphene is considered as one of the ideal materials for transparent and conductive electrodes because it has intriguing properties such as high conductivity, transmittance at wide wavelength ranges, flexibility and so on. But its high sheet resistance compared to that of ITO needs to be improved. Chemical doping of graphene can be used to reduce its sheet resistance. Similarly, defects in graphene can affect its electrical, optical properties and chemical sensitivity. Therefore, we investigated the effects of chemical doping and defects on graphene.

In our experiments, single layered graphenes grown by chemical vapor deposition method on Cu-foil were used. The details of the results will be presented at the meeting.
Analysis of Patterned Defects on Graphene Using Micro-Raman Spectroscopy and Liquid Crystals
Authors: Yang Gwangseok , Oh Sooyeoun , Kim JiHyun
Published: February 2020

Graphene has been used in various applications such as light-emitting diodes, solar cells, transistors, and chemical sensors because of its intriguing properties. Since defects in graphene can affect its intrinsic properties, defect characterizations in graphene are crucial. Micro-Raman spectroscopy has been considered one of the powerful and non-destructive techniques to analyze fundamental properties of graphene. Since fast characterization of large-area graphene is critical for its commercialization, large-area graphene was analyzed using liquid crystal with polarized optical microscopy at different temperatures.

 Chemical-vapor-deposited graphene was transferred onto pre-patterned SiO2/Si substrate by using conventional wet-transfer method. Defects were intentionally generated by oxygen plasma for various treatment times. The details of our experiments and results will be discussed in the meeting.