bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Monolithic Integration of III-V Semiconductors by Selective Area Growth on Si(001) Substrate: Epitaxy Challenges & Applications
Authors: Merckling Clement , Jiang Sijia , Liu Ziyang , Waldron Niamh , Boccardi G , Rooyackers R , Wang Zhechao , Tian Bin , Pantouvaki Marianna , Collaert Nadine , Van Campenhout Joris , Heyns Marc , Van Thourhout Dries , Vandervorst Wilfried , Thean Aaron 
Published: February 2020

Driven by fabrication cost reduction and device performance improvement, the Silicon semiconductor industry continues its never-ending pursuit of new approaches for fabricating integrated circuits. Monolithic integration of III-V semiconductors epitaxially grown on Si substrate have been attracting much attention as building blocks for next-generation electronics and photonics due to their potential intrinsic properties.
Direct heteroepitaxy of III-V compound semiconductors on Si has traditionally represented a formidable challenge, due to the extensive lattice mismatch of 8% between the Si substrate and high mobility III-V compounds, such as In0.53Ga0.47As/InP heterostructure. The defect confinement technique has recently attracted great interest due to the possibility of obtaining high quality III-V based active layers on Si. Using this approach we integrate III-V materials monolithically on Si through the epitaxial growth of III-V materials into a pre-patterned structure by Selective Area Metal-Organic Vapor Phase Epitaxy.
We report here on the growth of InP on STI patterned Si wafers using the defect confinement technique while focusing on scaled trench widths (W < 50 nm). We demonstrate the impact of the crystalline alignment of the InP layer with the underlying substrate by exploring as starting geometry at the bottom in between the STI either a rounded etch pit covered with a Ge buffer layer versus a crystalline <111> V-groove structure in Si. We show the large impact of the main layer growth temperature and the growth pressure on the trench filling, the growth uniformity and the crystal quality which we could correlate with changes in resistivity and the presence of impurity diffusion in the III-V layer. Moreover, we derived a fundamental understanding and theoretical modeling of the growth mechanisms in STI trenches and the determining role of the nucleation layer. This lead to a strong enhancement of the crystalline quality and growth uniformity of the InP semiconductor.
As a conclusion, this study of III-V selective area growth brings some elements for the optimization of the heteroepitaxy of III-V compounds on (001) oriented Si substrates. The demonstration of a clear reduction in defect density along the trench orientation is original and obviously confirm the potential of this heterogeneous integration option for high mobility logic devices, and photonic applications on a common Si platform.
Influence of Annealing Condition on TSV Pumping and Microstructure Evolution
Authors: Jing Xiangmeng , Lee Ui-Hyoung , Xu Cheng , Niu Zhongcai , Song Chongshen , Zhang Wenqi , Bae Jong-yong , Won Jaihyung 
Published: February 2020

Stacking of ICs using three-dimensional (3D) integration technology helps in significantly reducing wiring lengths, interconnection latency, and power dissipation while enhancing performance. Through silicon vias (TSVs) are regarded as a key enabling technology for 3D IC integration which assists in the realization of highly miniaturized and complex next-generation systems. Due to the thermal expansion (CTE) mismatch between copper and silicon, the copper in silicon vias tends to pump up as a result of thermal-mechanical stress during the post fabrication processes and/or during the lifetime of chip usage. One way to minimize or get rid of copper pumping is through heat treatment, for instance annealing or aging. The TSV wafers could be annealed right after copper plating process, or after chemical mechanical polish (CMP) process, or both. The residual stress might be thoroughly released by repeating annealing and CMP processes several times, however, the cost for fabricating the TSVs is increasing drastically, which is mainly attributed to the use of expensive CMP. To lower down the cost and minimize the CMP steps is one of the concerns from industry. In this paper, we report the thermal mechanical assessment of Cu pumping treated at different annealing conditions. moreover, the impact of different integration approaches on the TSV pumping behavior is also investigated. The finite element analysis method, ANSYS, is used to model and simulate the copper pumping at different temperatures, as shown in Fig.1. The pumping is measured by optical profiler, BRUKER ContourGT-X3, as shown in Fig.2. It has been found out that the copper grain size increases with annealing temperature, which is potentially contributed to larger protrusion. The preliminary results show that the annealing after copper plating process affects the microstructure evolution and pumping of TSVs.

Figure 1
On the Origin of the Gate Oxide Failure Evaluated by Raman Spectroscopy
Authors: Yokogawa Ryo , Tomita Motohiro , Mizukoshi Toshikazu , Hirano Takehiro , Kusano Kenichiro , Sasaki Katsuhiro , Ogura Atsushi 
Published: February 2020

1. Background and purpose

In the miniaturization of the large-scale integrated-circuit (LSI), gate oxide thinning is one of the most important techniques for the performance improvement. However, the ultimately thinned gate oxide causes in the failure with high leakage current. Thus, the evaluation and control of the gate oxide integrity is indispensable in the present LSI technology. In this study, we evaluated the origin of the gate oxide failure by Raman spectroscopy in conjunction with optical beam induced resistance change (OBIRCH) analysis.

2. Experiments

Metal-oxide-semiconductor (MOS) capacitors were used as the samples. The 2.8 nm thick gate oxinitrid insulator film and the poly-Si gate electrode layer were formed on a P type Si substrate. The poly-Si layer was deposited at 620 oC with the SiH4 flow rate of 150 or 350 sccm. The gate oxide integrity was evaluated by the test element group (TEG) measurements. The failure was observed only for the 150 sccm SiH4 flow. The current-voltage (I-V) characteristics were shown in Fig. 1. The positions with high leakage current were specified by OBIRCH, and evaluated by Raman spectroscopy. One-dimensional measurements were performed for the Raman spectroscopy by using a quasi-line excitation source at the same time. Excitation laser was Nd:YAG laser (wavelength: 532 nm), and the focal length of the spectrometer was 2,000 mm. The length of the quasi-line laser was approximately 100 μm. We investigated the origin of the gate oxide failure by Raman Spectroscopy obtained at the leakage position determined by OBIRCH.

3. Result
s
and
Discussion

Figure 2 shows the light emission image obtained by OBIRCH at the MOS capacitor with gate oxide failure fabricated with 150 sccm SiH4 flow. We confirmed that there are two defect points in the MOS capacitor. Figure 3 shows the Raman intensity distribution across the leakage position in the sample. The higher Raman intensity than the surroundings was confirmed at the failure position. Figure 4 shows the distribution of the Raman shift and the full width at half maximum (FWHM) across the failure position. As shown in Fig. 4, we verified that the Raman peaks at the defect positions shifted toward the lower wave number compared with the other positions. It can be considered that the gate oxide failure was induced by the high tensile strain in the poly-Si layer, probably due to the lack of the SiH4 supply during the deposition. Furthermore, FWHM of Raman spectra were not different comparing with the other position. Thus, there is no difference in the crystallinity and the grain size of the poly-Si. In conclusion, we have evaluated the gate oxide failure with leakage current by Raman spectroscopy and found that the origin was high tensile strain in the gate poly-Si.

References

[1] M. Yamano et al., Jpn. J. Appl. Phys. 53(2014)
[2] M. Takei et al., Jpn. J. Appl. Phys. 51(2012)

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(Invited) Thermal Limitations in Wide Bandgap (WBG) Semiconductor Power Switching Devices
Authors: Shenai Krishna 
Published: February 2020

Power switching devices made using wide bandgap (WBG) semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) have the potential to make transformative impact on electrical energy generation, transmission, distribution and conditioning [1]. Although SiC power diodes and power MOSFETs are commercially available for voltage ratings up to 1,700 volts, a careful review of the published data suggests that reliability of WBG power devices may be severely compromised compared to identically rated silicon power devices. For example, dv/dt, avalanche, and safe-operating area (SOA) of SiC power diodes and MOSFETs are inferior to silicon power devices with identical ratings. This paper will present a simple physics-based thermal analysis of the power handling capability of WBG power devices and explain the possible causes of lower reliability ratings.
[1] K. Shenai et al, “Current status and emerging trends in wide bandgap (WBG) semiconductor power devices,” ECS J. Solid State Sci. and Tech.
2(8), N3055-N3063, Jul. 2013.
ALD NiO Thin Films As a Hole Transport-Electron Blocking Layer Material for Photo-Detector and Solar Cell Devices
Authors: Nam Wook Jun , Gray Zachary , Stayancho John , Plotnikov Victor , Kwon Dohyoung , Waggoner Shawn , Shenai-Khatkhate Deodatta V , Pickering Michael , Okano Terumi , Compaan Alvin , Fonash Stephen J 
Published: February 2020

A thin layer of a wide bandgap material disposed between an electrode and an absorber material in a photo-detector or solar cell can play important transport and optical roles in enhancing device performance. When the energy band edges of the materials are properly aligned, the thin layer can control the flow of photo-generated carriers preferentially: i.e., it can permit the transport of one type of carrier while blocking the other type.1 Further such wide band gap materials can affect light trapping.2 NiO is a p-type conductive oxide, and has, due to its band edge positions, a high potential as a hole transport-electron blocking layer (HT-EBL) material. Due to its wide bandgap, it is also a transparent material. Both the potential transport and the optical roles of wide bandgap thin film materials in opto-electronic devices require the ability to precisely control film deposition thickness and conformality. In the case of HT-EBL candidate materials, atomic layer deposited (ALD) NiO has proven to have the material properties and excellent deposition control potential needed for hole transport and electron blocking optical layers. Because of this ALD NiO has become a subject of research in many research groups.3-6

In this report, we demonstrated the usefulness of ALD NiO thin films as HT-EBL/optical material by using it in very thin CdTe solar cells with a superstrate configuration. The CdTe cells were fabricated on a soda-lime glass substrate, and configured with layers of 200nm of SnO2:F/ 50 nm CdS/ 500nm CdTe/4nm Cu and 20nm Au. In test samples, a 3nm thick ALD NiO layer was deposited on the CdTe layer before the Cu/Au deposition. The resulting test and control cells were characterized under AM 1.5G (100mW/cm2) spectrum. The results of the device performance are summarized in Table 1. As may be noted, the CdTe cells with the ALD NiO layer on the anode showed better Voc and FF, and resulted in 15% higher power conversion efficiency (PCE) than that of the control cells. The enhancement of the Voc and FF were ascribed to the enhanced control of the photo-generated carriers. It remains to be determined if the reduction of. Jsc in the test samples is due to optically non-optimized NiO thickness and therefore reflection loss at the back contact or to non-optimized hole collection at the back contact.

References

S. J. Fonash, Solar cell device physics, 2nd ed., Elsevier, (2010).

S. J. Fonash, Introduction to light trapping in solar cell and photo-detector devices, Elsevier, (2014).

S. Lattante, Electronics, 3, 132, (2014).

E. Thimsen, et., al., J. Phys. Chem. C., 116(32), 16830, (2012).

T. S. Yang, et., al., J. Vac. Sci. Technol. A., 23(4), 1238, (2005).

H. L. Lu, et., al., J. Crystal Growth, 310, 5464, (2008).

Figure 1
(Invited) Benchmarking and Protocol Development for Data Comparison Between Laboratories
Authors: Bender Guido , Kocha Shyam S 
Published: February 2020

Comparison of the performance and durability of fuel cell materials and components across laboratories is a challenging undertaking that requires attention to detail with respect to test hardware, protocols, operating conditions and instrument calibration. NREL has fuel cell capabilities ranging from materials to component and systems research. At the materials level, research is being conducted on novel electrocatalyst synthesis methods. These materials are screened in rotating disk electrodes for ORR activity and cyclic durability and compared to statistically reproducible benchmark values for commercial Pt/C using test protocols specifically developed for this purpose. At the component level, research includes studying the effects of contaminants that originate from stack and balance of plant materials. To enable a comparison between the data of the laboratories participating in these studies a significant effort was made to benchmark test stations to achieve identical results for identical tests and operating conditions.
This presentation will focus on the challenges encountered and solutions found when developing test protocols for benchmarking electrocatalyst performance via RDE experiments. It will also cover strategies for comparing and reporting on single cell performance with and without contaminants across collaborating industry, university institutions and national labs.
The Effect of Blockages in a PEM Electrolyzers Flow-Field on Performance and Temperature Distribution
Authors: Fritz David L , Carmo Marcelo , Müller Martin , Stolten Detlef 
Published: February 2020

The ever growing demand for renewable energies is currently focused primarily on wind and solar energy. The technologies that capture these renewable energies have developed greatly in the past few decades with an ever increasing installed capacity all around the world. This capacity is however limited by grid demand and intermittency of the source1. In order to fully utilize the installed capacity of sustainable and renewable energy harnessed in wind and solar farms the energy collected at off-peak hours needs to be stored. By coupling a water electrolyzer to the wind and solar power farms the normally unutilized wind and solar energy can then be stored as hydrogen2. Hydrogen has a distinct advantage over other storage methods such as batteries, compressed air or pumped water as it can be stored and then employed into a variety of applications. The stored hydrogen could be used to fuel transportation, process chemicals, produce fertilizers and regenerate electricity1. Hydrogen also shares the ability to be produced, stored and distributed locally or centralized making it a versatile solution that can be brought very quickly into real, already existing commercial markets1.
The major hurdles facing PEM electrolysis before it can truly and competitively enter commercial markets, is the cost of production and the operational cost of the system. The production costs have been a major focus of research since 2010, and a 41% reduction in cost has been shown at the stack level alone in the past 5 years3. The reduction of operational costs and increase in life expectancy and performance of the stacks also plays a critical role in the overall cost of hydrogen production. Some external factors such as poor water supply quality, hot spots from areas of high contact resistance or uneven loading of the catalyst layer, or even blockages in the flow-fields may limit a PEM electrolysis systems lifetime as well as its performance.
In this article the effect of a blockage, as well as multiple blockages in a parallel flow channel were investigated using a segmented cell capable of reading temperature and current distribution over the entire active area of the test cell. A blockage in the flow-field could arise in an electrolysis cell through a large variety of sources, broken pieces of sealing material, poor water quality, large particles from corroded supply tubing and errors made during assembly. This could cause increases in mass transport losses and increased degradation rates on the rest of the cell. The cells operating parameters were also varied to explore and determine how to mitigate the effects a flow blockage has on cell performance.

Figure 1
(Invited) Electrosynthesis of Fuels Directly from CO2
Authors: Co Anne C. , Billy Joshua , Muhlenkamp Katheriine 
Published: February 2020

Introduction

Carbon dioxide (CO2) is a readily available industrial byproduct that can be used to produce useful chemical compounds. Electrochemical reduction is a highly effective method for converting CO2 to CO, organic acids, low molecular weight hydrocarbons and alcohols. Product distribution from the reduction of CO2 is highly dependent on the composition and preparation of the catalysts and reduction potential, as such, multiple reduction pathways are observed depending on the catalysts material and the preparation methods.
Copper-based catalysts have been found to produce higher molecular weight hydrocarbons, such as ethylene, methanol and ethanol. Here we demonstrate a high surface area Cu catalysts that has a preferential selectivity towards the formation of C2 and C3 species. This paper will also discuss our attempts to understand the mechanistic pathway using in-situ vibrational spectroscopy under reaction conditions.

Experimental

A copper/aluminum alloy was used as the starting material for producing a high surface area copper catalyst. The aluminum was removed through an etching procedure in strong base. The resulting nanoporous copper was crushed and mixed with Nafion, a binding agent, then casted over a copper foil substrate. Carbon dioxide electroreduction was performed by placing the catalyst in a specially designed flow cell. A bubbler in the cell was used to deliver CO2 to saturate the electrolyte, 0.1 M KHCO3, at a rate of 10 mL/min. The catalyst acts as the working electrode in this electrochemical cell. The product distribution from the electroreduction process was collected at a series of potentials. Gaseous products were identified and quantified using gas chromatography coupled with both mass spectrometry and a thermal conductivity detector. Liquid products were analyzed using nuclear magnetic resonance.
The surface morphology and composition of the catalyst was characterized using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The SEM images show a rough surface that retains a porous structure before and after experiments. XPS studies incorporated depth profiling, and show that ruthenium from the surface of the material migrates to the bulk after electrolysis.
Nitrogen-Doped Hierarchical Mesoporous/Macroporous Carbon (H-C) Prepared from the Combined Silica Templates with Different Size for Oxygen Reduction
Authors: Wu Mingjie , Shi Jingjing , Wang Qiang , Qiao Jinli , Liu Yuyu 
Published: February 2020

The doped mesoporous carbon as the cathotdic electrode materials for oxygen reduction reaction (ORR) have drawn great attention due to the high specific surface area and porous structure, which can facilitate the accessible part of active sites and the transport properties of ORR-relevant species.1,2 For obtaining the specified morphology and predetermined microstructure, the mesoporous carbon were usually synthesized using a sacrificial support method (SSM), during which the excess amount of hydrofluoric acid (HF) have to be added to vacate the silica and other metal-containing precursors.2,3 The waste liquid generated in the process of centrifugal brings a lot of damage for the environment. Therefore, try to develop and/or find a green and effective method for the preparation of mesoporous/microporous carbon materical is no doubt an urgent issue.
Here, by combining a simple two-step graphitization of the impregnated carbon with sodium hydroxide (NaOH), a green and efficient procedure has been demonstrated for the synthesis of nitrogen-doped hierarchical mesoporous/microporous carbon material using poly(ethyleneimine) (PEI) and ferrous sulfate (FeSO4 7H2O) as precursors. The obtained doped mesoporous carbon shows very high catalytic activity toward oxygen reduction reaction (ORR). Additionally, the suction filtration can be adopted rather than centrifuge and, 50% more yield of cathotdic electrode material can be obtained. Therefore we can completely use sodium hydroxide instead of hydrofluoric acid to vacate the silica, which is very green and environmentally friendly.
Electrode Kinetics of the Ni Porous Electrode for Hydrogen Production in the Molten Carbonate Electrolysis Cell (MCEC)
Authors: Hu Lan , Lindbergh Göran , Lagergren Carina 
Published: February 2020

There is a growing interest in electrolysis cell technology for producing hydrogen that is today considered as an important fuel in the future systems. Electrolysis in molten carbonate salts at high temperature is a promising method for hydrogen- and/or syngas (H2+CO2) production. Due to the favorable thermodynamic and kinetic conditions, high-temperature electrolysis will gain higher overall efficiency and require lower applied voltage when compared to low-temperature electrolysis. Electrolysis in molten carbonates has been investigated by some authors mainly by converting CO2into CO [1-3]. In our previous study, the feasibility of running the molten carbonate fuel cell reversibly with conventional state-of-the-art cell components is evidenced [4]. However, the Ni hydrogen electrode shows slightly higher polarization losses in water electrolysis than in hydrogen oxidation. For the development of molten carbonate electrolysis cells it is important to figure out the activity of the Ni electrode for water electrolysis in molten carbonates.
In the present study the kinetics and reaction mechanism of hydrogen production in the Ni porous electrode in a molten carbonate electrolysis cell is investigated. For this purpose the electrochemical reaction orders of hydrogen, carbon dioxide and water were determined on basis of the steady-state polarization data. Within the temperature range of 600-650 °C the electrochemical reaction order of hydrogen is not constant; the value was found to be 0.49-0.44 at lower H2 concentration, while increasing to 0.79-0.94 when containing 25-50% H2, i.e. not strongly depending on the temperature. On the other hand the partial pressure dependence of CO2 exhibits a larger influence by temperature increasing from 0.62 to 0.86 when the temperature rose from 600 to 650 °C. The reversed water-gas shift reaction has little or almost no impact on the electrochemical reaction order of hydrogen and carbon dioxide. The electrochemical reaction order of water shows two cases as does hydrogen. At lower water concentration, 10-30%, the reaction order is in the range of 0.47-0.67 while it increases to 0.83-1.07 with 30-50% water at 600-650 °C. When taking the shift equilibrium into account, the reaction order of water is constant and the value is approaching to that of higher water content. The activation energy of the Ni porous electrode for hydrogen production is in the range of 55-100 kJ·mol-1, which indicates that the Ni electrode is under mixed-control.
Reference
[1] W.H.A. Peelen, K. Hemmes, and J. H. W. De Wit, Electrochim. Acta, 43, 763 (1997).
[2] V. Kaplan, E. Wachtel, K. Gartsman, Y. Feldman, and I. Lubomirsky, J. Electrochem. Soc., 157, B552 (2010).
[3] D. Chery, V. Albin, V. Lair, and M. Cassir, Int. J. Hydrogen Energy, 39, 12330 (2014).
[4] L. Hu, I. Rexed, G. Lindbergh, and C. Lagergen, Int. J. Hydrogen Energy, 39, 12323 (2014).