bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Affecting the Electrochemical Performance of Graphene like Graphite
Authors: Taninaka Junichi , Maruyama Shunya , Hashiguchi Katsuki , Matsuo Yoshiaki , Muramatsu Yasuji , Cheng Qian , Okamoto Yasuharu , Tamura Noriyuki , Murakami Tomoo
Published: February 2020

Lithium-ion batteries with high energy density, compact size and good cycling performance are attracting much attention for the use of portable electronic devices, electric vehicles and energy storage devices. Graphite is mainly used for the anode materials of them, however, further improvements are needed in terms of both power and energy densities. It has been reported that graphene-based anode materials show high power density and capacity exceeding 1000 mAh/g. However, graphene is known to suffer from a large irreversible capacity due to its intrinsically large surface area. Recently, we have introduced a novel graphene like graphite (GLG) with low surface area and similar interlayer spacing to that of graphite, which was prepared from the thermal reduction of graphite oxide (GO). It showed the capacity of 600 mAh/g, high rate capability and higher coulombic efficiency. In this study, we have prepared GLG samples with various structural parameters and investigated their electrochemical performance in detail.

GO was prepared from natural graphite using modified Brodie’s method. The as-prepared GO was dispersed in 0.1M NH3 aq at various concentrations (0.2-3.0 mg/ml), then the dispersions were spray-dried at 100 or 150℃. The resulting GO samples were heated at 700 – 1000°C under vacuum and GLG with different structural parameters were obtained. The constant current charge-discharge measurement was performed using a two-electrode cell with lithium metal and 1M LiClO4-EC+DMC (1:1) as counter electrode and electrolyte, respectively.

The interlayer spacing, Lc, La and oxygen contents of the resulting GLG samples were 0.336 –0.353 nm, 7.1 – 57 nm, 7.8 -23 nm and 1.0 – 5.1 %, respectively. Based on these parameters and the shape of discharge curves of them, we have concluded that the oxygen content in them is more directly related to their capacity.
(Invited) Direct Band Gap Germanium
Authors: Elbaz Anas , El Kurdi Moustafa , Prost Mathias , Ghrib Abdelhamid , Sauvage Sébastien , Checoury Xavier , Aniel Frederic , Zerounian Nicolas , Picardi Gennaro , Ossikovski Razvigor , Beaudoin Gregoire , Sagnes Isabelle , Boeuf Frédéric , Boucaud Philippe
Published: February 2020

Germanium is an indirect band gap material. This property is a significant disadvantage to realize an efficient laser emitter with this material. This feature can nonetheless be circumvented by strain engineering of the band structure. It is well known that tensile strain can reduce the energy difference between the conduction band valleys and ultimately lead to a band inversion. With a direct band gap material, one should expect to obtain optical gain with a significantly reduced threshold as compared to unstrained or weakly-strained Ge. Consequently, the integration of a group IV emitter on a silicon chip could become more realistic. In this presentation, we will show that direct band gap germanium can be obtained by transferring tensile strain with nitride stressor layers. We have experimentally determined when the cross-over from indirect to direct band gap occurs using temperature-dependent photoluminescence measurements. This cross-over was found to occur for a biaxial tensile strain of 1.67%, the theoretical values varying between 1.5 and 2% in the literature. We will show that this level of strain transfer is compatible with the fabrication of optical micro-resonators with germanium microdisks. Tensile-strained germanium microdisks with circular Bragg reflectors have been successfully fabricated. They exhibit high quality factors for the quasi-radial modes. These types of structures are ideal candidates to realize microlasers with pure germanium. We will discuss the latest progress in this direction.
(Invited) SiOxNy Back-End Integration Technologies for Heterogeneously Integrated Si Platform
Authors: Nishi Hidetaka , Tsuchizawa Tai , Kakitsuka Takaaki , Hasebe Koichi , Takeda Koji , Hiraki Tatsuro , Fujii Takuro , Yamamoto Tsuyoshi , Matsuo Shinji
Published: February 2020

Network traffic is continuously increasing, and the global IP traffic reaches 2 zettabytes in 2019 [1]. Photonic integrated circuits on Si-based substrates are highly demanded for coping with increasing telecommunication network traffic and energy consumption in low-cost ways. Particularly, Si and Ge provide modulators and photodetectors in telecom wavelength with a full monolithic way on SOI substrates. In addition, InP provides lightsources based on low-temperature direct-bonding technique. To connect these dynamic and active devices, we propose back-end photonic wiring by using SiOxNy-based waveguides. In this paper, I review recent progress of our work.

First, I briefly review our early work; Si-Ge-SiOx integration technology and application to the WDM receiver. To increase integration density, recently, we also have developed a silicon-nitride (SiN) waveguide[1]. SiN has moderately high refractive index and provides moderately small passive devices with tolerance for nonlinear effects. We confirmed 1-dB/cm propagation loss for 1.3-, 1.5-, and 1.6-um wavelength range and applied to a compact and low-loss 16-ch. arrayed-waveguide grating (AWG) filter with 200GHz spacing. In addition, for lightsource integration, a InP-wire waveguide was successfully integrated with the SiOx waveguide via a spot-size converter (SSC) on SiO2/Si substrates[2]. The fabricated InP waveguide provides 5.2-dB/cm propagation loss and connected to the SiOx waveguide with a 0.7-dB loss and less than -50-dB reflectance. The InP waveguide can be used as output waveguide for the membrane laser, which utilizes strong optical confinement within the active area to obtain high modulation efficiency and low power consumption[3, 4]. With introducing distributed-reflector (DR) laser structure, the membrane laser exhibits low threshold current of 0.6 mA, output power of 0.7 mW, and 25.8-Gbit/s NRZ direct modulation with 132-fJ/bit energy consumption. In addition, the output InP wire waveguide is successfully integrated with the SiOxwaveguide, which exhibits fiber coupling loss of 2.7 dB and low reflectance at the chip facet to obtain sufficient optical output power and stable single-mode operation.

[1] K. Okazaki et al., Proc. GFP 2014, Vancouver, paper WP43.

[2] H. Nishi et al., IEEE Photonics Journal, vol. 7, pp. 4900308, 2015.

[3] S. Matuso et al., J. Lightwave Technol., vol. 33, pp. 1217, 2015.

[4] H. Nishi et al., Proc. ECOC 2015, Valencia, paper We.2.5.3.
(Invited) Development of SiGeSn Technique Towards Mid-Infrared Devices in Silicon Photonics
Authors: Du Wei , Al-Kabi S. , Ghetmiri Seyed , Tran Huong , Pham Thach , Alharthi Bader , Mosleh Aboozar , Margetis Joe , Tolle John , Naseem Hameed A , Mortazavi Mansour , Sun Greg , Soref Richard , Li B , Yu Shui-Qing
Published: February 2020

GeSn/SiGeSn techniques are of great interest in the area of Si photonics due to: 1) the industry scalable growth; 2) compatible with current Si complementary metal-oxide semiconductor (CMOS) process; 3) capability of monolithic integration on Si; 4) the identified group-IV based direct bandgap materials; and 5) the tunable bandgap allowing the optoelectronic devices operation features broad wavelength coverage in near- and mid-infrared ranges. In the past a few years, the GeSn/SiGeSn material growth, the materials and devices characteristics have been comprehensively studied. Plenty of promising results are reported.

In this work, the following aspects regarding GeSn/SiGeSn techniques are investigated: 1) low-defect material growth technique via Ultra High Vacuum Chemical Vapor Deposition (UHVCVD) system; 2) advanced material and optical characterizations of GeSn/SiGeSn thin films, Ge/GeSn/Ge double heterostructure (DHS), and GeSn/SiGeSn quantum well samples; 3) demonstration of GeSn-based optoelectronic devices including photodetectors and emitters.
Laterial Growth of High Quality GeSn Layers on Si Using Tin As Catalysts
Authors: Li Chuanbo , Yu Kai , Cheng Buwen
Published: February 2020

GeSn is an important Si based semiconductor material. In 2015 it has been reported that a Si-based optical pumping lasing achieved from a direct-band-gap GeSn alloy. The introduce of Sn into GeSn alloy also induce a high-efficiency optical detection in the full-band communication at low concentration of Sn (approximately 3%). Moreover, GeSn alloy has higher carrier mobility than Ge. It has attracted lots of attention in recent years. However, due to the low solid solubility of Sn in Ge, easy segregation of Sn and large lattice mismatch, the growth of GeSn on Si is still a challenge. Some research groups recently realized high-quality GeSn alloy film by molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), but the dislocation density is still high than 107cm-2. Here we report a new way to grow the defect-free GeSn alloy strips on Si substrates with the assistance of Sn. We realize the lateral growth of GeSn alloy strips on Si(111) by Sn self-catalyzed method. The GeSn materials are grown in a custom-designed MBE system with a base pressure of 5 × 10−8 Pa. The growth mechanism and the impact factors on the materials are studied. It is found that different depositions and annealing times of Sn are performed to observe the impact on morphology of the materials. Sn has an important impact on morphology of the GeSn materials. It is indicated that enough depositions and annealing times of Sn to match to the deposition of Ge will contribute to the growth of GeSn alloy strip. GeSn alloy strips show a good quality by the TEM micrographs and the SAED patterns. No dislocation is found in the grown material. The controlled growth of GeSn strips are also studied on pattered substrate. The results in this study will help us obtain the better GeSn materials for device applications.

Figure 1
High Sn-Content GeSn on Insulator Grown By Rapid Melting Growth
Authors: Liu Zhi , Li Chuanbo , Xue Chunlai , Cheng Buwen
Published: February 2020

GeSn is an attractive semiconductor for group IV photonics and microelectronics due to its special energy band structure and the compatibility with complementary metal oxide semiconductor (CMOS) processes. Unfortunately, epitaxial growth of GeSn is a difficult work. Recently, non-equilibrium grown GeSn at low temperature is an effective technology to grow high Sn-content GeSn on Ge or Si substrate by suppress segregation of Sn. However, because of the larger lattice of GeSn than Ge and Si, high crystal quality, high Sn-content, and strain relaxation are paradox in GeSn film grown on Ge or Si substrate. It is a great challenge to grow tensile strained defect-free high Sn-content GeSn. In this work, tensile strained defect-free high Sn-content GeSn on insulator (GSOI) was laterally grown on an insulator using rapid melting growth. The gradient of Sn-content was created along the GeSn stripes by growing process. The Sn-content distribution is in good agreement with calculated results from the Scheil equation. The Sn-contents at the end of GSOI are depend on the length of the GSOI stripes. The highest Sn-content of the GSOI is increase to 14%, which is high enough to transform the GeSn to a direct bandgap material. No dislocation or stacking fault was observed in TEM image, which indicated the high-crystal quality of the GSOI. Metal-semiconductor-metal photodetectors and P-channel MOSFETs were fabricated on this GSOIs. The optical and electrical characteristics of the GSOIs were studied.
(Invited) Challenges and Solutions in Metrology for Complex, Confined Systems
Authors: Vandervorst Wilfried
Published: February 2020

Probing composition, doping , strain and defectivity in confined heterostructures (fins, nanowires, etc) represents a challenge in terms of 3D-spatial resolution, sensitivity as well as in localization and heterogeneity. We will discuss progress and limitations of two approaches. The first approach is linked to methods such as Atomprobe tomography or SPM imaging which provide ultra-high resolution inherently. Unfortunately when reducing the analysed volume to the atomic scale, signal intensity becomes very low limiting the achievable sensitivity. Moreover their application (for instance Atomprobe tomography on embedded FIN, STM on trenches embedded in STI) becomes very complex and prone to many distorting artifacts which one needs to overcome. Speed of the analysis and time to data becomes then another limitation.  In the opposite approach one abandons the idea of achieving the resolution to probe inside one single device but rather exploits broad beams (>1-20 mm)  to investigate an ensemble of many, small identical structures.  In cases like self-focusing SIMS, the physics of cluster ion formation is exploited to confine the information to the very small regions of interest whereby the averaging over many features enhances the signal substantially and enables good sensitivity. Examples demonstrate composition analysis in trenches as narrow as 20 nm. The spatial selectivity even allows to determine the composition of two mixed phases (i.e. InGaAs and InAlAs). Similarly strain and composition can be measured with (Edge-enhanced) Raman in similar trenches, as the confined volume provides a 100x increase in sensitivity. Channeling RBS on ensemble structures has been exploited to probe the early stages of III-V in narrow trenches. The important relevance of this approach is that it provides the opportunity to study the material as it grows in such a confined volume which frequently is very different from blanket experiments while all conventional (broad) methods can still be used.
(Invited) SiGe and III-V Materials and Devices: New HEMT and LED Elements in 0.18-Micron CMOS Process and Design
Authors: Fitzgerald Eugene A , Lee K.E. , Yoon Soon-Fatt , Chua S.J. , Tan Chuan Seng , Ng G.I. , Zhou X. , Gong Xiao , Chang J.S. , Peh L.S. , Boon C.C. , Antoniadis D.a. , Yadav Sachin , Nguyen X.S. , Kohen D.a. , Kumar Annie , Zhang Li , Lee Kwang Hong , Liu Z.H. , Chain S.B. , Ge T , Choi P.
Published: February 2020

The incorporation of new materials into CMOS scaling has become a necessity. Our previous work in SiGe and III-V integration shows promise in allowing further materials integration for increased transistor density. However, a principal concern is that investment returns by further increasing transistor density will likely be negative for all but possibly one or two corporations, and may be negative for all. Moore’s Law metrics for the benefits of incorporating III-V and other materials monolithically into silicon CMOS are not sufficient to determine innovative value for CMOS+X combinations. Such an environment that cannot use traditional metrics is a challenge for all organizations participating in the previous paradigm. Despite these challenging times, we list the likely characteristics of a new innovation path, and describe our efforts to follow it through research into ‘white space’ integrated circuits employing new materials and devices. Initially, we are designing novel integrated circuits, materials and processes incorporating GaN HEMTs, GaN and AlInGaP LEDs, and InGaAs HEMTs monolithically into existing silicon CMOS foundry processes. Both heteroepitaxy and wafer bonding are used in the process flow, and SiGe or Ge buffer layers are used in many processes. A modular process flow is incorporated so that the new devices can be modeled and incorporated into the design kit for a foundry process, allowing us to leverage much of the existing silicon design and manufacturing infrastructure. Our initial focus is on the demonstration of wafer-level integration of III-V devices with foundry 0.18 -micron CMOS devices on 200 mm wafers, and we report on the progress made in materials, device and circuit design towards this goal.
Investigation on Passivation Mechanism of Ge Surface By GeOx
Authors: Zhang Jie , Wang Xiaolei , Zhang Jing , Wei Shuhua , Wang Wenwu
Published: February 2020

The passivation machenism of Ge surface by germanium suboxide GeO­x is investigated. The interface state density (Dit) measured from low temperature conduction method is found to decrease with increasing the GeOx thickness (0.26-1.06 nm). The X-ray photoelectron spectroscopy (XPS) is employed to demonstrate the interfacial structure of GeOx/Ge with different GeOx thicknesses. And the XPS results show that Ge3+ oxide component is responsible to the decrease of the Dit due to the effective passivation of Ge dangling bonds. Therefore, the formation of Ge3+ component is the dominant key to achieve low Dit for Ge gate stacks. Our work confirms that the same physical mechanism determines the Ge surface passivation by the GeOx regardless of the oxidation methods to grow the GeOx interfacial layer. As a result, to explore a growth process that can realize sufficient Ge3+ component in the GeOx interlayer as thin as possible is important to achieve both equivalent oxide thickness scaling and superior interfacial property simultaneously. This conclusion is helpful to engineer the optimization of the Ge gate stacks.

Figure 1
On the Challenges of SiGe HBTs in Advanced BiCMOS Technology Toward Half THz fMAX
Authors: Liu Qizhi , Jain Vibhor , Camillo-Castillo Renata A , Pekarik John J , Adkisson James W. , Joseph Alvin , Harame David L.
Published: February 2020

Advanced BiCMOS technology is a cost-effective candidate for wide-range of applications, including Radar (automotive radars, high-speed industrial sensors), high-speed wireless and wireline communication, high-speed instrumentation, and mmWave THz imaging and sensing that require high performance SiGe HBTs with high cut-off frequencies fT and high maximum frequencies fMAX.

Development of SiGe HBTs in BiCMOS technology with both high fT and fMAX faces significant challenges. Vertical scaling is employed to increase fT in advanced SiGe HBTs including reduction in base and collector thickness or by increasing the collector doping. All these approaches reduce the carrier transit times, but result in an increase in the base resistance and the collector-base capacitance, which degrade fMAX. To overcome these limits, lateral scaling is necessary to reduce the base resistance and the collector-base capacitance. Reduction in emitter width reduces the intrinsic base resistance and Ccb, self-aligned emitter-base integration schemes reduce the extrinsic base link resistance, and raised extrinsic base helps with lower Rb and Ccb. In short, these scaling rules and approaches would need to reduce both base resistance and collector-base capacitance simultaneously for improved fMAX and fT

In this paper, results from two experimental studies are presented in a 90nm SiGe BiCMOS technology. Compared with the baseline, one experiment shows more reduction in collector-base capacitance, while the other shows more reduction in base resistance. Both experiments achieved 300GHz fT and met or exceeded the 360GHz fMAX goal of the technology.

In addition to straight vertical and lateral scaling, a series of experiments employing other process techniques and structure innovation have also been studied and are reviewed in this paper, including millisecond anneal techniques, low temperature silicide and low temperature contact processes, and secondary trench isolation, achieving fT around 300GHz and fMAX toward half THz.
Very High-Resolution Mobility, Resistaivity and Activation for High-Mobility Materials
Authors: Joshi Abhijeet
Published: February 2020

Advanced high-mobility material based devices require knowledge of carrier concentration, mobility and resistivity profiles as well as the effects of strain. Active Layer Parametrics, Inc.’s ALPro system represents a technique to directly measure these parameters as well as the effects of strain from high dopant concentrations in high mobility materials like SiGe, Ge, and III-V high-mobility materials.

Current standard electrical metrology techniques such as Scannning Spreading Resistance Microscopy (SSRM) cannot provide complete mobility and activation data on these high-mobility materials. Furthermore resolutions currently achieved by the ALPro System (>0.5nm in Si, SiGe and Ge) cannot be achieved by SSRM or Spreading Resistance Profiling (SRP). Sample preparation of relatively fragile high-mobilty materials like Ge and GaAs is difficult to standardize, is known to have resulted in widely varying resistivity data values. The continual making and breaking of contacts in both SSRM and SRP, though reasonlably well-understood for Silicon, has not been adequately understood in the case of Ge requiring modeling to account for bandgap changes due to applied pressure that vary with probe dimensions and properties.

The ALPro System overcomes all the above deficiencies while providing a high-resolution, high-throughput system that may be safely deployed in a fabrication environment.

This paper discusses some of the data extracted using the ALPro System for high and low-doped Gematerials.
Role of High-k Interlayer in ZrO2/High-k/ZrO2 Insulating Multilayer on Electrical Properties for DRAM Capacitor
Authors: Onaya Takashi , Nabatame Toshihide , Sawada Tomomi , Kurishima Kazunori , Sawamoto Naomi , Ohi Akihiko , Chikyow Toyohiro , Ogura Atsushi
Published: February 2020

For < 25 nm DRAM capacitors, large cell capacitance (20 fF/cell), low leakage current density (J ≤ 1.6×10-7 A/cm2) at the operation voltage (0.6 V), maximum process temperature < 650 oC and conformal films on a three-dimensional structure (pedestal structure) with a large aspect ratio over 30 are required. Recently, the ZrO2/Al2O3/ZrO2 (ZAZ) multilayer was widely used as insulator of DRAM.[1] Al2O3 has advantages of large band gap and amorphous structure, and disadvantage of low k-value. However, it is still not clear how amorphous structure and band gap of interlayer affect to leakage current property. Here, we pay attention to (Ta/Nb)Ox (TN) because of its high k-value (~29), amorphous structure and low band gap (4.3 eV).[2] In this paper, we studied role of various interlayer between ZrO2 layers on leakage current property for DRAM capacitors with TiN electrode.

We fabricated four TiN capacitors with ZrO2/ZrO2 (ZZ), ZAZ, ZrO2/(Ta/Nb)Ox/ZrO2 (ZTNZ), and ZrO2/(Ta/Nb)Ox-Al2O3/ZrO2 (ZTNAZ) multilayer by atomic layer deposition (ALD) and post-deposition annealing (PDA) processes. The ZrO2, Al2O3, and TN layers were deposited by ALD using (C5H5)Zr[N(CH3)2]3, Al(CH3)3, and (Ta/Nb = 1/1)(NtAm)(NMe2)3 precursor, respectively, and H2O gas. The TNA nano-laminate layers were fabricated by alternately depositing every 1 cycle using TN and Al2O3. After multilayer fabrication, PDA was performed at 600 °C. Finally, TiN top electrode was fabricated by photo-litho. process.

Fig. 1 shows relationship between CET and J at 0.6 V for all capacitors. The J values of the ZTNAZ and ZAZ capacitors decrease significantly by 10-7 ~ 10-8 A/cm2 order of magnitude while ZTNZ exhibits large J of ~ 10-5 A/cm2. Moreover, the J value of the ZTNAZ (CET = 1.2 nm) is lower than that of the ZAZ (CET = 1.3 nm). AFM images and RMS roughness of ZZ (CET = 1.1 nm), ZTNZ (CET = 1.2 nm), ZAZ (CET = 1.3 nm), and ZTNAZ (CET = 1.2 nm) are shown in Fig. 2. The RMS roughness of all samples exhibit almost the same value of around 1 nm. Based on these experimental data, we found that the leakage current property of capacitor is influenced by band gap width (conduction band offset of TiN) rather than amorphous structure. We conclude that the TNA is one of candidate material as interlayer for future DRAM. A part of this research is supported by CREST, JST.

[1] D. Martin et al., J. Appl. Phys. 113, 194103 (2013).

[2] T. Nabatame et al., J. Vac. Sci. Technol. A 33, 01A118 (2015).

Figure 1
(Invited) The Effect of Germanium/Silicon Interface on Germanium Photonics
Authors: Kim Daeik , Bao Shuyu , Tan Chuan Seng , Nam Ju Hyung , Saraswat K. C. , Nam Donguk
Published: February 2020

Obtaining a high-quality germanium layer on silicon has recently garnered much attention for photonic-integrated circuits. Epitaxial growth of germanium on silicon has made significant progress toward suppressing the propagation of threading dislocations that are inevitably created at the germanium/silicon interface due to a large lattice mismatch. Recently, there have been numerous reports on successful demonstration of high-performance MOSFETs fabricated on this improved germanium layer. However, unlike MOSFETs in which charge carriers are transported primarily at the defect-free top interface, the performance of optical devices may be significantly hampered by the defects at the germanium/silicon interface.

In this talk, I will present our research works on the effect of the germanium/silicon interface on germanium-based optical devices. We demonstrate methods to improve structural and optical properties of germanium by effectively reducing the defective interface. By using various characterization techniques including TEM, time-resolved photoluminescence and Raman spectroscopy, we show that the minority carrier lifetime and internal quantum efficiency can be significantly improved. We also show improved performances from devices integrated on our germanium platform.
(Electronics and Photonics Division Award) Physics of Wide Band Gap Semiconductor Devices
Authors: Shur Michael
Published: February 2020

Silicon carbide and nitride based devices have found important commercial applications in both optical and electronic devices. AlGaN deep ultraviolet Light Emitting Diodes (LEDs) are now used for water purification, sterilization, and prolonging food storage. Silicon carbide and gallium nitride based transistors compete with silicon for high power applications and with III-V based transistors for RF applications. The device physics of all these devices is determined by the wurtzite (hexagonal) symmetry leading to strong spontaneous and piezoelectric polarization and by a large polar optical phonon energy, which is the consequence of the strong bonding and small atomic masses of carbon and nitrogen. In AlGaN/GaN and AlGaInN/InGaN devices, the differences in the polarization at the heterointerfaces induce two-dimensional (2D) electron or hole gases at the interfaces (polarization doping) with the electron sheet concentrations up to 10 to 20 times higher than those for more conventional field effect transistors (reaching over 4.5x1013 cm-2 for AlGaN/GaN High Electron Mobility Transistors (HEMTs)). In deep UV LEDs, the polarization induced 2D hole gas is used for improved p-type contacts. A high 2D electron concentration in the III-N HEMT channels enables superior switching characteristics but makes parasitic series resistances and capacitances to be very important. The high current carrying capability and a very high breakdown voltage lead to high power densities and make the issues of heat dissipation to be a priority. The thermal conductivity of SiC (490 W/m K at room temperature) is larger than that for copper (385 W/m K) making it to be an excellent choice as a substrate for power devices. For AlGaN/GaN HEMTs, the research started from using sapphire substrates, but silicon substrates have become a commercial technology. SiC, diamond, or AlN bulk or template substrates could have significant advantages over silicon. The substrates also affect the dislocation and point defect densities in the device channel and strain induced during growth and caused by a strong piezoelectric effect. Such strain is a crucial factor affecting the device reliability (linked to the transient and permanent detects induced under the voltage stress). The large bandgap suppresses the subthreshold leakage making the surface leakage to be one of the dominant leakage mechanisms. Ballistic, overshoot, and electron runaway effects play a dominant role in short channel wide band gap devices now competing for applications in the terahertz (far infrared) range.

Figure 1
(Invited) Periodically Oriented Gallium Nitride for Frequency Conversion
Authors: Hite Jennifer K , Freitas Jaime A. , Mastro Michael A , Vurgaftman Igor , Meyer Jerry R. , Brown Christopher G. , Leach Jacob , Udwary Kevin , Bowman Steven R. , Eddy Charles R. , Kub Francis J
Published: February 2020

Gallium nitride is a semiconductor widely used in both optical and electronic devices. The polarity of GaN (+/- c-direction) influences many properties of the resultant material, including chemical reactivity and electric field in these ‘spontaneously polarized’ materials. By engineering inversion layers, we have demonstrated control of GaN polarity on both polar faces of GaN. By employing a selective growth method to deposit the IL, the lateral polarity of the GaN can be alternated, thus enabling structures referred to as periodically oriented (PO) GaN. We have shown such structures on both N-polar and Ga-polar native substrates by changing the IL material.

On N-polar substrates, we demonstrated that optimization of the MOCVD growth rates resulted in sharp, vertical interfaces and smooth surfaces. This work has moved the technology substantially closer to practical non-linear optic emitters by using HVPE to extend the PO GaN templates on N-polar substrates to total thicknesses of up to 500 μm, while faithfully maintaining the pattern of alternating polarity. Additionally, cross-sectional cathode-luminescence (CL) imaging of such an extension shows that the large initial dislocation densities occurring in the original inversion layers greatly decreased after about 25 μm of regrowth. The results of phase matching experiments with these structures will be presented, with discussion on fabrication issues.

These methods of GaN polarity inversion offer the promise of engineered materials with custom lateral and vertical polarity variations for applications in novel electronic and optoelectronic devices, a subset of which are expected to be suitable for non-linear optics.
Nizo/Ag/Nizo Multilayer Films for Transparent Conducting Electrodes of Polymer Dispersed Liquid Crystal-Based Smart Windows
Authors: Kim Eun Mi , Kim Nam Ho , Kim Young Baek , Heo Gi-Seok
Published: February 2020

Smart window refers to electrically switchable glass in which the light transmission properties change when voltage is applied. For a polymer dispersed liquid crystal (PDLC)-based smart window, a polymer emulsion composed of a polymer and a liquid crystal is fabricated between two sheets of transparent conductor, which serve as electrodes, coated on glass. Multilayer transparent electrodes were prepared by using RF/DC magnetron sputtering system on glass substrates. The sandwich type multilayer structure consisted of NiInZnO/Ag/NiInZnO. The optical and electrical properties of the multilayer structures were investigated with respect to the thickness of each NiInZnO/Ag/NiInZnO layer. Transparent conductive films with a sheet resistance of 9.8 Ω/□ and an average transmittance of 90% at 550nm were obtained. The surface roughness (RRMS) of the obtained NiInZnO/Ag/NiInZnO multilayer films was below 1 nm. Overall, the properties of the NiInZnO/Ag/NiInZnO multilayer films were comparable or superior to those of other multilayers such as InSnO (ITO)/Ag/ITO and InZnO (IZO)/Ag/IZO. The deposited NiInZnO/Ag/NiInZnO multilayer films were used in the fabrication of PDLC-based smart windows. The NiInZnO/Ag/NiInZnO multilayer-based smart window exhibited a lower operating voltage and a higher cutoff rate of infrared light than ITO-based smart window. However, they showed a lower PDLC-ON transmittance than ITO-based smart window.
Effect of Flow Field Configuration on Oxygen Transport Resistances in Proton Exchange Membrane Fuel Cell Cathode
Authors: Karani Jash , Shrivastava Udit N , Tajiri Kazuya
Published: February 2020

Land-channel geometry is necessary for proton exchange membrane fuel cells to transport electron and at the same time to transport reactants/products. However, this configuration causes the difference in transport distance between the flow channel to the catalyst layer, and results in the non-uniform distribution of various factors, such as species concentration, current generation, and rate of degradation. In order to investigate the distributions of various parameters in the land-channel direction, a small-scale segmented cell with about 300-micron resolution was developed by the authors’ group, and successfully measured the current and high-frequency resistance distribution in the land-channel direction. Distribution of oxygen transport resistance from the flow channel to the catalyst layer was also measured using limiting current technique.

The oxygen transport mechanism is completely different in the conventional flow field and in the interdigitated flow field. In the conventional flow field, the oxygen transport is mostly driven by the duffusion due to the concentration gradient. In the interdigitated flow field, on the other hand, the convective flow through gas diffusion layer (GDL) makes the diffusion distance shorter than the conventional flow field case, and therefore the lower oxygen transport resistance is expected.

In this study the oxygen transport resistance distribution in land-channel direction is measured in two different flow field configurations, that is, conventional flow field and interdigitated flow field. The comparison of the results from these two flow fields reveals the impact of the convective transport through GDL on the oxygen transport resistance and on the distribution.
Advanced Characterization of Electrocatalyst Interfaces
Authors: Shao Yuyan , Luo Langli , Cheng Yingwen , Engelhard Mark H , Liu Jun , Wang Chongmin
Published: February 2020

In PEM fuel cells, electrocatalyst interfaces including Pt-C, Pt-ionomer, C-ionomer interfaces, play a critical role for both performance and durability.1-3 Pt-C interface influences the stability and activity of Pt dramatically; electrocatalyst/ionomer interfaces4 in fuel cell catalyst layers determine the electrochemical surface area (ECSA), local transport, and structural stability of catalyst layer. Delineating the structure evolution of the interfaces in response to PEM fuel cell operating environment will provide the science foundation for new electrocatalyst/catalyst layer design therefore improve the performance and durability of PEM fuel cells.

We have developed an aberration corrected environmental transmission electron microscopy (ETEM), which allows unprecedented spatial and temporal resolution in the relevant gas environment, such as O2, H2, H2O, CO, CH4, and CO2. With customized intelligent gas delivery system, the gas environment relevant to PEM fuel cell anode and cathode (H2/H2O, O2/H2O) can be simulated and precisely controlled through the residual gas analyzer (RGA). The ETEM opens new avenue to study the dynamic changes of electrocatalyst interfaces.

In order to study the surface chemistry of catalysts under different environment, a specially-designed pre-treatment system is integrated into X-ray photoelectron spectroscopy (XPS), which allows us to move catalysts seamlessly between the pre-treatment system and XPS chamber so that surface contamination from external environment will be eliminated.

In this talk, we will present our recent progress on identifying both structure and surface chemistry evolution and their correlation in electrocatalysts under PEM fuel cell relevant environment through the combination of ETEM and XPS capabilities.

1. Y. Y. Shao, G. P. Yin and Y. Z. Gao, J. Power Sources, 2007, 171, 558-566.

2. S. Park, Y. Y. Shao, H. Y. Wan, V. V. Viswanathan, S. A. Towne, P. C. Rieke, J. Liu and Y. Wang, J. Phys. Chem. C, 2011, 115, 22633-22639.

3. R. Kou, Y. Y. Shao, D. H. Mei, Z. M. Nie, D. H. Wang, C. M. Wang, V. V. Viswanathan, S. Park, I. A. Aksay, Y. H. Lin, Y. Wang and J. Liu, J. Am. Chem. Soc., 2011, 133, 2541-2547.

4. A. Z. Weber and A. Kusoglu, J. Mater. Chem. A, 2014, 2, 17207-17211.
Cobalt Phosphide Based Nanostructures as Bifunctional Electrocatalysts for Low Temperature Alkaline Water Splitting
Authors: Lambert Timothy N. , Vigil Julian A. , Christensen Ben
Published: February 2020

Hydrogen is regarded as a valuable high energy density, zero-emission fuel for the future, with the potential to reduce or eliminate fossil fuels. H2 also has potential as an energy carrier or storage molecule: i.e. being generated, stored, and consumed to bridge the gap of high and low production cycles of renewable energy sources, such as solar cells and wind turbines. Because molecular hydrogen is not naturally available, the complications of generation, storage and transportation must be addressed. On Earth, hydrogen (H) mainly occurs in combination with oxygen, i.e. in water. One possible technology option for clean H2 generation is low temperature water electrolysis, with the two half-reactions being the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). These reactions, particularly the OER, are mechanistically complex and dependent on the surface energy of multiple intermediate species, leading to high overpotentials and low efficiency. Precious metal-based catalyst materials are ultimately not viable, due to rarity and cost, and typically provide high catalytic activity for the OER or HER, but not both. More effective catalysts with the ability to catalyze both the OER and HER (i.e. OER/HER bi-functional behavior) could improve current electrolyzers and enable future technologies. Thus, there is a desire to design electrocatalysts based on earth- abundant, low-cost materials for overall water splitting.

In this talk we will present on the synthesis and electrochemical characterization cobalt phosphide-based materials. CoP-based electrocatalysts in both thin film and nanoparticle form have been prepared from their respective Co3O4 spinel precursors using phosphine gas, generated in situ from the thermal decomposition of sodium hypophosphite. These electrocatalysts were found to have performance comparable to that of the commercial precious metal benchmarks when examined in alkaline electrolyte. For example, ΔE(OER–HER) values were calculated by adding the overpotentials at which j
geo = 10 mA cm-2 and j
geo = -10 mA cm-2were attained for the OER and HER, respectively, to the thermodynamic OER–HER potential difference of 1.23 V. Values of ΔE(OER–HER) = 1.77 V for cobalt phosphide catalysts are within 70 mV of the idealized water electrolysis with 20% Ir/C (anode):20% Pt/C (cathode) where ΔE(OER–HER) = 1.70 V. Various aspects of this work will be presented.

This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Hydrogen Evolution Reaction on Pt/RuO2-TiO2 Electrocatalyst in Alkaline Media
Authors: He Cheng , Wang Guanxiong , Parrondo Javier , Ramani Vijay K
Published: February 2020

Hydrogen is poised to be a key energy carrier in a sustainable energy economy (1). Among the different approaches to produce hydrogen, water electrolysis has received special attention due to its unique advantages including reactant availability, safety, stable output and product purity (2). Alkaline water electrolysis offers additional advantages, including the possibility of using stainless steel flow fields and endplates (with the subsequent reduction in costs) and the possibility of using cheaper non-platinum-group-metal electrocatalysts for the oxygen evolution reaction. However, the slow kinetics for the hydrogen evolution reaction (HER) in alkaline media is currently a key drawback.

In this work we evaluated a mixed-metal-oxide composed of titanium dioxide and ruthenium dioxide as a support for Pt and measured the catalytic activity of this supported electrocatalys for the HER. The mixed-metal-oxide (TiO2-RuO2, RTO) was synthesized using a wet chemical synthesis procedure, and the Pt/RTO was synthesized by reduction of Pt precursor onto the support using an impregnation-reduction method. These materials were characterized by XRD, TEM and BET. The activity of Pt/RTO towards HER the was compared with a benchmark Pt/C catalyst (46%Pt; Tanaka, K. K.). Rotating disk electrode (RDE) measurements showed Pt/RTO outperforming (under all the conditions) the benchmark catalyst (Pt/C). The specific exchange current density for Pt/RTO was 2.51mA/cm2
Pt (295 K, 1600rpm, H2-saturated 0.1M KOH), more than five times that of Pt/C. The catalysts were also evaluated in a solid-state water electrolyzer operated with ultrapure water at 50°C, wherein MEAs were prepared with IrO2 as a common anode electrocatalyst. The MEAs fabricated with Pt/RTO as the cathode catalyst outperformed the benchmark catalyst by 0.1-0.2 V across relevant current densities (see Figure 1).

1. M. S. Dresselhaus and I. L. Thomas, Nature, 414, 332 (2001).

2. H. Yin, S. Zhao, K. Zhao, A. Muqsit, H. Tang, L. Chang, H. Zhao, Y. Gao and Z. Tang, Nat Commun, 6, 6430 (2015).

Figure 1
Hydrogen Fuel Cells for Unmanned Undersea Vehicle Propulsion
Authors: Swider-Lyons Karen , Deitz Daniel
Published: February 2020

Hydrogen fuel cells materials and systems have attracted billions of dollars of government and commercial research such that they are now reliable and cost effective enough to be commercialized as the power source for automobile propulsion and for materials handling. Also known as polymer electrolyte membrane fuel cells (PEMFCs), hydrogen fuel cells are attractive because they convert high-energy hydrogen fuel and oxygen (typically from air) efficiently to electricity and water through electrochemical processes, and produce relatively little heat and noise. They also respond rapidly to changes in load. The result is that they can have higher specific energy and energy density than battery systems for certain applications. One such application for commercial automotive hydrogen fuel cells is for large unmanned undersea vehicles (UUVs). This paper will describe an Office of Naval Research effort by the U. S. Naval Research Laboratory, Naval Surface Warfare Center Carderock Division, University of Hawaii, and General Motors (GM) to integrate an automotive fuel cell from GM into an unmanned undersea vehicle. The advantages and challenges with taking commercial fuel cell technology and adapting it to undersea use will be discussed.
(Invited) Development of a Hydrogen Energy System as a Grid Frequency Management Tool
Authors: Ewan Mitch , Rocheleau Richard , Swider-Lyons Karen , Devlin Peter , Virji Maheboob B.V. , Randolf Guenter
Published: February 2020

In Hawaii, very high penetration levels of intermittent renewable energy sources such as wind and solar are causing challenges in regulation of grid frequency, and as the percentage of these intermittent resources increases can result in their curtailment. It has been postulated that, similar to a battery, the optimized use of an electrolyzer as a variable load may help regulate grid frequency and increase the penetration of renewable energy resources on the grid. The use of an electrolyzer in this way could provide an “ancillary service” to the grid that can be assigned a monetary value. This monetary value can be used to offset the cost of hydrogen production. The hydrogen in turn can be used in high value applications such as a transportation fuel. The Hawai‘i Natural Energy Institute (HNEI) is conducting research to assess the technical potential and economic value of using an electrolyzer-based hydrogen production and storage system as a demand response tool for grid management.   A 65 kg/day hydrogen energy system (H2ES) consisting of a PEM electrolyzer, 35 bar buffer tank, 450 bar compressor, and associated chiller systems, has been purchased and installed at the Hawaii Natural Energy Laboratory Hawaii Authority (NELHA) to demonstrate long-term durability of the electrolyzer under cyclic operation required for frequency regulation on an island grid system. A secondary objective is to supply hydrogen for three fuel-cell buses to be operated at Hawai‘i Volcanoes National Park (HAVO) and by the County of Hawai‘i Mass Transit Authority. The hydrogen will be transported from the production site by tube trailers to the HAVO dispensing site. A second dispensing site is located at the NELHA production site.     

A comprehensive test plan has been developed to characterize the performance and the durability of the electrolyzer under dynamic load conditions and initial testing was conducted at Powertech Labs in Vancouver Canada. A main objective of the test plan is to determine the operating envelope and dynamic limits of the electrolyzer and the overall H2ES.  A long-term study shall evaluate the H2ES performance under a load profile developed from a fast acting Battery Energy Storage System (BESS) that is currently in use as a grid management tool on the Big Island grid.  These tests shall demonstrate whether the electrolyzer has the capability to effectively mitigate the impacts of intermittent solar and wind power on the grid, while continuously generating 90-80% of its designed hydrogen productioncapacity.

The presentation will describe the H2ES configuration, plans for operation in the field, and results of initial tests to determine the dynamic response of the eletrolyzer and overall system
Cobalt Alloyed Catalyst Combined with Carbide and Carbon As Efficient Oxygen Evolution Reaction Catalysts for Alkaline Water Electrolysis
Authors: Kim MinJoong , Song DongHoon , Oh SeKwon , Cho EunAe
Published: February 2020

Increasing demand for clean energy have triggered researches on alternative energy sources and devices to reduce use of fossil fuel. Hydrogen has been considered as one of the most promising energy source for future due to its high energy density and no air pollutant emission. Splitting water into hydrogen and oxygen is an environmentally friendly method for producing hydrogen gas. This technology can store excess electric energy in the form of chemical bonds of hydrogen, which can resolve an issue about surplus electric power of present renewable energy systems caused by irregular energy source such as airflow and sunlight.

Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, especially OER has much higher overpotential than HER. Therefore, recently major efforts have been devoted to exploring active catalysts for the OER in water electrolysis cell.

Among many kinds of candidate materials for OER catalyst, cobalt (Co) and various Co based materials, including nanostructured Co3O4, CoSe2, Co based perovskites, CoP, CoB and Co/N-doped carbon, have drawn much attention for use in the alkaline water electrolysis system. These Co based catalysts have high OER activity in alkaline media comparable with precious metal based catalysts, such as IrO2 and RuO2. However, previous studies has focused mainly on the exploring desirable composites for low OER overpotential without careful mechanistic study. OER mechanism on Co based catalysts and descriptors for designing more efficient catalysts have been unclear yet.

Herein, we tried to modify the electronic structure of Co through the strain effect. The strain effect modifies the adsorption energy of gaseous or ionic species for OER on Co surface that can be an effective way to design an active electrocatalyst. For making a strain in the Co lattice, we alloyed Co with other transition metals, such as iron (Fe), manganese (Mn), nickel (Ni), and combined with carbide and carbon through a facile solution based process. Graphitic carbon-nitride (g-C3N4) was used as a carbon source. Synthesized alloyed catalyst exhibited higher activity and durability for OER compared with Co and ruthenium dioxide (RuO2) catalysts in alkaline media (0.1 and 1 M KOH). And, the catalysts with tensile strain have much enhanced OER activity than compressive strained one.