bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model Based Corona Charge - Kelvin Probe Characterization of Patterned Structures
Authors: Marinskiy Dmitriy , Lagowski Jacek 
Published: February 2020

Corona – Kelvin characterization of semiconductor materials is now a common technique that is used as a non-contact replacement of contact CV measurements [1,2]. Traditionally it is applied to planar structures such as an oxide – semiconductor structure or similar. Deposition of corona charge ΔQCORONA causes a change in surface voltage, ΔV = ΔVSB + ΔVD, which includes voltage drop across the semiconductor space charge layer, ΔVSB, and across the dielectric layer, ΔVD. The differential capacitance is calculated as C = ΔQCORONA/ΔV. The incremental charging-measuring cycle gives the non contact CV characteristic and also charge-voltage characteristic, QV, where Q = ΣΔQ, and V = ΣΔV.
In this work we applied the Kelvin-corona method to a patterned structure, which represents a grid of 2 or more locally adjacent elements having different properties (Figure 1). Elements of the structure can constitute a planar structure (Figure 1A) or a non-planar three dimensional structure (Figure 1B). In both cases, the elements of the structure have dimensions smaller than the size of the Kelvin probe, such that at least one cycle of the pattern structure is within the Kelvin probe diameter.
A model based analysis of corona charge – Kelvin probe data (QV data) was developed which is based on the geometrical dimensions, electrical parameters of elements of the patterned structure, and response of each element to corona charging. The effective voltage measured by the Kelvin probe follows: Veff=Σ(aiVi)/Σ(ai), where ai is the area of an element i, and Vi is the voltage in the area ai. The surface voltage for each element of the structure depends on electrical properties of the structure, Vi=f(φMS, CD, QD, DIT), and responds to corona charging according to its electrical properties.
Examples of experimental and simulated data will be presented for a type 1B structure. The simulated data allow quantification of electrical parameters of each element of the structure such as interface properties at the SiO2 / silicon interface, including the interface trap density, DIT, and the flat band voltage, VFB.
The results are of importance for the rapid characterization of 3D structures, such as STI, FinFET, etc. where the electrical properties vary between elements of the structure. The model based QV method enables extraction of electrical parameters that are different for the elements of the structure.
References.

K. Schroder, Meas. Sci. Technol., 12, R16 (2001).

Wilson, D. Marinskiy, A. Byelyayev, J. D’Amico, A. Findlay, L. Jastrzebski, and J. Lagowski, ECS Trans., 3(3), 3 (2006).

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(Invited) Enhanced Light Output Power from Eu-Doped GaN Narrow-Band Red Light-Emitting Diodes By Actively Controlling Photon Fields
Authors: Fujiwara Yasufumi , Inaba Tomohiro , Shiomi Keishi , Tatebayashi Jun 
Published: February 2020

While InGaN/GaN blue and green light-emitting diodes (LEDs) are commercially available, the search for an efficient red LED based on GaN is ongoing. This is essential for the monolithic integration of the three primary colors and the development of nitride-based small-size, full-color, high-resolution displays. We have succeeded in the realization of a red LED using Eu-doped GaN (GaN:Eu) grown by organometallic vapor phase epitaxy [1]. Making use of the intra-4f shell transitions of Eu3+ ions, our LED features an ultra-narrow linewidth of less than 1 nm at room temperature, and unprecedented thermal stability of 1 pm/K. By gradual optimization of the Eu excitation mechanism, we have increased the light output power above 1 mW at 20 mA [2].
One of limiting factors for enhanced light output power is the relatively long radiative lifetime of the Eu emission in GaN:Eu (∼300 µs). According to the Fermi’s golden rule, modifying the spontaneous emission rate of Eu ions can be achieved by increasing the photonic density of states (PDOS) at the frequency of spontaneous emission, as already demonstrated with a planar Fabry-Perot cavity. We have boosted the output power by actively manipulating radiative recombination probability at the atomic level of the Eu ions, which can be achieved through control of their photon fields in micro- and nano-cavities. In a GaN:Eu layer embedded in a microcavity consisting of an AlGaN/GaN distributed Bragg reflector (DBR) and a Ag reflecting mirror, a 21-fold increase of the Eu emission intensity was obtained under optical pumping at room temperature [3]. Furthermore, in a preliminary LED with a microcavity consisting of ZrO2/SiO2 and AlInN/GaN DBRs, the output power was enhanced by 5 times [4]. In this talk, current status of the red LED and strategies for further enhancement of the light output power are reviewed.

A. Nishikawa, T. Kawasaki, N. Furukawa, Y. Terai, Y. Fujiwara, Appl. Phys. Exp. 2, 071004 (2009).

B. Mitchell, V. Dierolf, T. Gregorkiewicz, and Y. Fujiwara, submitted to J. Appl. Phys.

T. Inaba, D. Lee, R. Wakamatsu, T. Kojima, B. Mitchell, A. Capretti, T. Gregorkiewicz, A. Koizumi, Y. Fujiwara, AIP Adv. 6, 045105 (2016).

T. Inaba, K. Shiomi, J. Tatebayashi, and Y. Fujiwara, in preparation.
(Invited) Thick, Low-Doped Homoepitaxial Ga2O3 for Power Electronics Applications
Authors: Tadjer Marko J , Koehler Andrew D , Mahadik Nadeemullah A , Glaser Evan , Freitas Jaime A. , Feigelson Boris , Wheeler Virginia D. , Hobart Karl D. , Kub Francis J , Kuramata Akito 
Published: February 2020

Monoclinic β-Ga2O3 has attracted significant attention as a high power electronics material based on its ultra-wide energy gap (4.9 eV), high theoretical critical field (8 MV/cm), as well as the commercially availability of inexpensive substrates grown from the melt. In order to achieve breakdown field consistent with the theoretical expectations, however, very high quality epitaxial films with very low doping and defect density will be required. Wong et al. have reported a β-Ga2O3 MOSFET with carrier concentration below 4x1014 cm-3, which is the lowest reported value for epitaxial β-Ga2O3 to date [1]. This talk will discuss the structural and electronic properties for thick homoepitaxial β-Ga2O3 with doping as low as 8x1012 cm-3, corresponding to breakdown voltage in excess of 2.38 kV (3.18 MV/cm), measured without field termination for vertical measurements or edge effects correction in the case of lateral devices. Our results show that current β-Ga2O3 halide vapor phase epitaxial technology can produce epilayers with breakdown field approaching the theoretical value of GaN. In addition, we will discuss the annealing of bulk and epitaxial β-Ga2O3 films in O2 atmosphere as a potential pathway to reduce carrier concentration and possibly improve the breakdown voltage of Ga2O3 Schottky diodes. We show that annealing Ga2O3 in O2 will reduce ND-NA by about an order of magnitude, similar to earlier observations by Kuramata et al. [2]. Furthermore, we will present our approach for overcoming the polaron-induced suppression of room-temperature p-type conductivity in Ga2O3, causing holes to preferentially self-trap instead of being available as free carriers [3]. We show that natural p-type semiconducting oxides such as NiO can be integrated with β-Ga2O3 to form a rectifying heterojunction as a fundamental building block for any viable Ga2O3 power device. Finally, we will discuss the low thermal conductivity of Ga2O3 and present our preliminary thermal management simulations and experimental results.
[1] A. Kuramata, et al., Jpn. Jour. Appl. Phys. 55, 1202A2 (2016).
[2] M.H. Wong, et al., Appl. Phys. Express 10, 041101 (2017).
[3] J.B. Varley, et al., Phys. Rev. B 85, 081109(R) (2012).
Electrical and Material Properties Analysis of 5kV 4H-SiC Schottky Barrier Diodes
Authors: Keum Juyeon , Na Moonkyong , Kang In Ho , Bahng Wook , Koo Bonheun 
Published: February 2020

Silicon carbide is an attractive material for next-generation power devices, it has wide band gap and high thermal conductivity. SiC power devices can operate at higher temperatures and voltages compared to silicon devices. But, electrical characteristics of the SiC power devices can be deteriorated by SiC defects. The killer defects such as micropipes and stacking faults have been reduced through the development of SiC growth technique. But still the threading dislocations (TDs) and basal plane dislocations (BPDs) lowered the breakdown voltage and increased the leakage current during device operation [1].
In this study, we fabricated the 5 kV 4H-SiC Schottky barrier diode (SBD) to study the effect of SiC defect on electrical properties of SiC SBDs. The thickness of epitaxial layer was 50 um and the doping concentration is 1E15 cm-3. The device was fabricated with various length of junction termination extension (JTE). Ion implantation was performed to form p surge (Al, 500 °C, 5E19 cm-3) and JTE (B, 500 °C, 2E18 cm-3) regions. Activation annealing was performed at 1700 °C for 60 m. 100 and 30-nm-thick Ni were deposited as the cathode and front-side ohmic metal respectively, and then annealed at 950 °C for 90 s in RTA system. Finally, 100-nm-thick Ni was sputtered on front-side as a Schottky contact metal. We investigated the forward, reverse characteristics, and reverse breakdown voltage of the fabricated 4H-SiC SBDs. The diode characteristics, ideality factor (IF) and Schottky barrier height (SBH) were obtained from the forward electrical characteristics, about the 1.23 and 1.3 eV, respectively. The relative highly ideality factor may be due to rough surface of thick epitaxial layer. The breakdown voltage was obtained above 5 kV with JTE length longer than 60 um. During reverse characteristics the electrically weak points were observed using electroluminescence (EL). The EL spot was mainly aroused from electrically leaky points, it mostly observed at the edge of JTE. Some EL spots were observed inside the JTE or active region. The defects of the fabricated 4H-SiC 5 kV SBDs were analyzed using non-destructive analysis method, X-ray topography (XRT) and electron beam induced current (EBIC). We tried to determine the correlation between the electrical characteristics of the device and the crystal defects in the device.
[1] H. Fujiwara, H. Naruoka, M. Konishi, K. Hamada, T. Katsuno, T. Ishikawa, Y. Watanabe, and T. Endo, Appl. Phys. Lett. 100, 242102 (2012).

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(Invited) Electrochemistry of Transition Metal Oxide Based Mountable Electrochromic Devices
Authors: Deb Biswapriya , Ganesh Gayathri PT , Surendran Sajitha 
Published: February 2020

Although electrochromic (EC) “smart” windows are recently making inroads into consumer applications, any large-scale usage needs further maturity in balancing their cost, processability and usability. A flexible and mountable EC device that can be refitted with a normal glass pane has potential to expand the market for existing buildings, by eliminating the requirement of replacing the entire window. Any EC based tunable windows have several functional components such as active/counter electrodes, conducting back panel and electrolyte. One must adopt a viable low temperature based fabrication process for the transition metal oxide (TMO) films with sufficient cycling stability for the intended application. At the same time, a mechanically robust semi-solid/solid polymer electrolyte (SPE) with adequate thermochemical range must be developed for operational safety. In this work, we demonstrate the use of ultraviolet (UV, 365 nm) photoannealing process for TMOs specially optimized to support flexible ECD operations [Figure-1]. This inexpensive and facile process step enabled us to manipulate nanoscale transport properties to extract preferred functionalities. A significant network densification is observed as photo-decomposition of bridging ligands facilitated direct interactions of surface dipoles in those films that produced ~57% improvement in the optical density (OD) [1]. The free-standing SPEs was designed by dispersing Li-salts into polymer matrix followed by thermochemical crosslinking of the host [2,3]. The assembled ECDs were investigated using electrochemical and spectroelectrochemical techniques to identify the sources of device degradations. A typical device fabricated with optimized components showed remarkably high OD (~0.65) and coloration efficiency (CE) ~122 cm2/C at 600 nm.

Keywords: Electrochromic devices, photo-annealing, polymer electrolyte, mountable foils
[1] Gayathri P.T.G., Sajitha S., Vijitha I., Shaiju S.S., and Biswapriya Deb “Tuning of Physical and Electrochemical Properties of Nanocrystalline Tungsten Oxide through Ultraviolet Photoactivation”, Under Revision (2017)
[2] Gayathri P.T.G., Remya R., Biswapriya Deb, “A pragmatic approach to methyl methacrylate based solid polymer electrolyte processing: A case study for electrochromism”, Sol. Energ. Mat. Sol. Cells 140 17–24 2015
[3] Gayathri P.T.G. and Biswapriya Deb “Designing an All-Solid-State Tungsten Oxide Based Electrochromic Switch with a Superior Cycling Efficiency” Adv. Mater. Interfaces 2017, 1700124
Figure-1: TMO based flexible ECD fabrication; optimization of components through electrochemistry and spectroelectrochemistry studies.

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Fabrication of High Power, Low-Pt Catalyst Coated Membranes
Authors: Garsany Yannick , Swider-Lyons Karen 
Published: February 2020

Fabrication of High Power, Low-Pt Catalyst Coated Membranes
Yannick Garsany1 and Karen Swider-Lyons2

1 EXCET INC, Springfield, VA

2 U.S Naval Research Laboratory, Washington, DC
In the endeavor to create fuel cells capable of generating high power at low platinum loadings, it is crucial that educational and research laboratories have practical, cost-effective ways to make custom membrane electrode assemblies (MEAs). This talk will describe a reliable and reproducible laboratory-scale fabrication protocol based on ultrasonic spray deposition of standard Pt/carbon electrocatalyst directly onto a perfluorosulfonic acid membrane to produce 10 cm2 catalyst coated membranes (CCMs). The CCMs are then transformed into MEAs by compressing them between commercial gas diffusion media (GDM). We present the scientific rationale and electrochemical and microscopy data to reveal how post-deposition processing of the CCM/MEA and assembly conditions affect the performance of single cell fuel cells. Improper post-deposition processing leads to damage of the pore structure of the catalyst layer and/or GDM, diminishing the overall fuel cell performance. Fuel cells that are not assembled properly, either due to under- or over-compression, have high ohmic resistance or damage to the GDM pore structure, both of which negatively affect the PEMFC performance, despite no structural changes in the CCM. Equipped with the understanding of how to reproducibly fabricate standard Pt/Carbon CCMs/MEAs, we have adapted these protocols and tools to produce CCMs/MEAs with a PtCo/C electrocatalyst, short side-chain ionomers, and woven GDM that produce the high power and low Pt loadings desired for advanced fuel cells (Figure 1).
Design and Optimization of PEMFC Electrode for Direct Roll-to-Roll Coating Process
Authors: Kim Jung Ho 
Published: February 2020

The mass production of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction in the materials cost. The most costly component of a PEMFC is the membrane electrode assembly (MEA), which contains the precious metal catalyst, platinum. Methods to reduce the associated coats include synthesizing new materials and minimizing platinum loading through advanced manufacturing. The MEAs are generally manufactured by decal transfer method. The decal transfer method necessitates coating wider catalyst layer to adress alignment tolerance stack up and membrane shrinkage issue at lamination. More recently, inkjet printing and low production processing lines have been investgated. The costs of existing processes are too high and not scalable and the film quality can be too low for long life. In order to support large scale manufacturing. alternative methode for MEA fabrication are imperative. Available fabrication techniques, such as direct coating by solution, vapor, or spraying are limited by slow production rate, excessive cost and waste, lack of discrete control and the need for solvent of additives to obtain more uniform coating.
The development a roll-to-roll manufacturing technique to fabricate MEAs by direct coating electrode in discrete patches onto polymer electrolyte membrane (PEM), through implementation of an advance slot-die coating approach. Direct coating is an enabling manufacturing technique that allows for several key advantages and cost reduction including, enhanced fabrication speeds; reduced yield loss potential; increased precious metal catalyst utilization and membrane utilization and elimination of release film cost (which may not be a trivial consumable cost), among others. However, the electrode for direct coating quite limitation about PEM, catalysts, ionomer and solvent system.
In this work, we focus on the design and optimization on the interfacial structures between direct coating electrode and PEMs and their impact on the fuel cell performance. Our approach includes preparation and characterization of direct coating electrode using variuos electrode components.
Figure. (a) Procedure of direct roll-to-roll coating process, and (b) catalysts coated membrane.

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(Invited) Mechanistic Insights into Highly Active Metal Phthalocyanine Catalysts for Electrochemical Carbon Dioxide Reduction
Authors: Manthiram Karthish 
Published: February 2020

Electrochemical reduction of carbon dioxide to produce fuels and feedstocks may represent one possible strategy for utilizing carbon dioxide that would otherwise contribute towards global warming. The use of electrical potential for making and breaking chemical bonds can allow for reductions in the temperature and pressure needed to drive reactions, enabling modular conversion of point sources of carbon dioxide. We are interested in organometallic macrocycles which can catalyze the conversion of carbon dioxide to syngas, a key chemical intermediate than can be converted into diverse hydrocarbons, alcohols, acids, and esters.
In our work, we have developed metal phthalocyanine catalysts anchored on modified carbon supports, which exhibit high turnover frequencies for reducing carbon dioxide to carbon monoxide. Our supported catalyst alleviates transport limitations that have complicated prior studies, enabling mechanistic studies that provide a molecular-level picture of how metal phthalocyanines drive the desired proton/electron transfers needed to reduce carbon dioxide. Our results indicate how the reaction can be tuned from an electron transfer mechanism to a proton-coupled electron transfer mechanism, with increased rates for the latter. We have also identified regimes in which the catalyst can operate at high ionic strength, minimizing losses due to ionic resistance.
Our results highlight the interplay of kinetics and transport in the widely observed behavior of metal phthalocyanines, as well as potential strategies for mitigating transport limitations. This may inspire concerted molecular level design of metal phthalocyanine catalysts with engineering of transport in reactors. These studies may enable design of catalysts with current densities needed for scalable electrolyzers.
Effective Strategies for Reducing Carbon Monoxide into Liquid Fuels By Copper Catalysts
Authors: Wang Lei , Nitopi Stephanie Anne , Orazov Marat , Morales-Guio Carlos , Hahn Christopher , Jaramillo Thomas F 
Published: February 2020

Understanding the surface reactivity of CO, a key intermediate during electrochemical CO2 reduction, is crucial for the development of catalysts that selectively target desired products for this reaction. In this study, a custom-designed electrochemical flow cell is utilized to investigate planar polycrystalline copper as an electrocatalyst for CO reduction under alkaline conditions. We observed a large positive shift in the overpotential for C-C coupled products under CO reduction conditions compared to CO2 reduction by using the same cell. By investigating the effects of CO partial pressure and electrolyte pH, the aforementioned large potential shift was identified as a pH effect, demonstrating that alkaline conditions can be used to increase the energy efficiency of CO and CO2 reduction to C-C coupled products. Common trends in selectivity were uncovered which indicate both the production of oxygenates and the growth of longer carbon chains are favored at lower overpotentials. These selectivity trends are generalized by comparing to current state of the art rough Cu catalysts, that are able to achieve high oxygenate selectivity by operating at the same geometric current density at lower overpotentials. Combined, these findings outline key design principles for CO and CO2 electrolyzers that are able to produce valuable liquid-phase products with high energy efficiency.
To evaluate these strategies, we carried out electrochemical CO reduction under alkaline conditions on a new high surface area Cu-based catalyst to operate at low overpotentials. With the Cu nanomaterials that were developed in our work, CO is reduced into multi-carbon oxygenates with almost 100% Faraday efficiency at a potential of only –0.23 V versus the reversible hydrogen electrode. Therefore, we conclude that the competing hydrogen evolution reaction can be supressed by successfully engineering the catalyst and electrochemical conditions. A maximum Faraday efficiency of 60% is obtained for ethanol at only –0.33V vs. RHE, demonstrating the high selectivity of this catalyst for liquid fuels at low overpotentials. Thus, this work successfully implements the design principles for pursuing liquid products that were learned from the work on polycrystalline Cu, demonstrating that there are energy-efficient sustainable pathways for the sequential conversion of CO2 to liquid fuels.