bluuebunny/crossref_metadata_2025 huggingface dataset:
All-Solid-State Lithium-Oxygen Batteries Based on Duplex Li+-Selective Solid Membranes
Authors: Choi Youngbin , Moon Jiwoong , Lee Jong-Won
Published: December 2020

With the increase in electric vehicles, rechargeable Li-O2 batteries (LOBs) are attracting considerable attention, as their theoretical energy density is several times higher than that of current Li-ion batteries. To date, ether-based organic liquid electrolytes have been commonly used for LOBs, but unfortunately, they are unstable against superoxide radicals generated during LOB operation. In this respect, other candidates based on sulfones, sulfoxides, and ionic liquids have been explored as alternative electrolytes for LOBs. A truly stable electrolyte is yet to be demonstrated, however. The use of solid-state, Li+-selective conducting membranes (LSSMs) in LOBs may provide an effective approach to address the problems associated with the oragnic electrolytes. Furthermore, an LSSM with relatively high mechanical robustness can retain the dendrite growth on the Li metal anode during repeated discharge-charge cycling and can protect the Li metal anode from parasitic reactions with the impurity species diffusing from the cathode. Herein, we propose an all-solid-state LOB design based on a duplex-LSSM structure. A Li1+x+y
Al
x
Ti2-x
Si
y
P3-y
O12 (LATP)-based LSSM with a duplex (dense/porous) structure is prepared via a tape-casting process combined with co-sintering. A porous LATP layer is then deposited with carbon nanotubes (CNTs) serving as the cathode, and a thin polymeric interlayer is placed between the LSSM and metallic Li to prevent the possible side reactions of Li with LATP. The electrochemical performance of the constructed all-solid-state LOBs is characterized in terms of capacity, rate-capability, and cycling stability under various operating conditions, and the efficacy of the LSSM-based LOB design is discussed.
3D-Structured Metal Oxide/Sulfur Composites for High Performance Lithium-Sulfur Batteries
Authors: Choi Sinho , Kim Tae-Hee
Published: December 2020

The lithium-sulfur (Li-S) system is one of the promising rechargeable battery systems for energy storages and electrification of vehicles due to a high theoretical capacity and energy density, as well as the low cost and availability of non-toxic sulfur. However, polysulfide dissolution is the main limitation to the stability of the Li-S system. Here, we tackle this challenge by synthesizing 3D-structured graphene and porous silica materials with a pomegranate-like architecture through a simple chemical reactions, which is subsequently loaded with sulfur to form a 3D-graphene-sulfur composite (denoted as S@G composite). Furthermore, a thin layer (~100 nm) of tungsten oxide (WO3) on the S@G composite dramatically improves the cycling performance of the Li-S system with an initial capacity of 1425 mAh/g and approximately 95% capacity retention after 500 cycles. The porous silica/sulfur composite cathodes exhibit excellent electrochemical performances including a high specific capacity of 1450 mAh g-1, a reversible capacity of 82.9 % after 100 cycles at a rate of C/2 (1 C = 1672 mA g-1) and an extended cyclability over 300 cycles at 1 C-rate. Through the analysis and the theoretical calculation, results provide a novel material and approach to enhance the electrochemical performance of rechargeable Li-S batteries and sheds light on developing high-performance energy storage devices for a variety of applications.
(Invited) Vertical Gate All Around GeSn/Ge Heterostructure Transistors
Authors: Liu Mingshan , Hartmann Jean-Michel , Grützmacher Detlev , Buca Dan , Zhao Qing-Tai
Published: December 2020

In this paper we present our recent research on vertical GeSn/Ge heterojunction gate all around (GAA) nanowire pMOSFETs. The vertical nanowires were fabricated with a diameter as small as 20 nm. Our experimental results demonstrate that scaling of the nanowire diameter improves the device performance in terms of subthreshold swing, drain induced barrier lowering (DIBL) and Ion/Ioff ratio due to the better gate controllability. However, one of the big challenges for vertical nanowire transistors is the nanowire top contact resistance. Due to the very small contact area the nanowire contact resistance dominates the series source/drain resistance. The contact resistance can be lowered by optimized NiGeSn and NiGe contacts. Compared to vertical Ge homojunction nanowire GAA FETs, the utilization of GeSn as source can significantly lower the source/drain resistance. The band engineering of GeSn/Ge heterojunction for device improvement will be discussed in the paper.
Potassium-Ion (De)Intercalation Mechanism of Honeycomb Layered Oxides Such As K2Ni2TeO6
Authors: Masese Titus , Kanyolo Godwill , Rizell Josef , Yoshii Kazuki , Senoh Hiroshi
Published: December 2020

Rechargeable potassium-ion batteries are appealing candidates for next-generation energy storage devices not only owing to their projected low-cost but also to the high voltage that can be attained.[1-3] Honeycomb layered oxide cathode materials show high voltage and facilitate reversible potassium-ion extraction and insertion (K+ (de)intercalation) at decent capacities. This makes them promising cathode candidates that can be matched to suitable anode materials to design a high-voltage (high-energy density) battery.[4-6] It is crucial to investigate the reaction mechanism of electrode materials in order to understand the structural changes accompanying reversible (de)intercalation of the large K+ that lead to unique staircase-like voltage profiles. Honeycomb layered oxides such as K2Ni2TeO6 facilitate reversible K+ (de)intercalation at high voltages with staircase-like profiles. In this presentation, we will highlight the reaction mechanism of K2Ni2TeO6, based mainly on X-ray diffraction studies.

Acknowledgement

This work was conducted under the support of Japan Prize Foundation, National Institute of Advanced Industrial Science and Technology (AIST) and the Japan Society for the Promotion of Science (JSPS KAKENHI Grant Numbers 19K15685).

References

T. Hosaka, K. Kubota, A. S. Hameed and S. Komaba, Chem. Rev. (2020). https://doi.org/10.1021/acs.chemrev.9b00463

T. Masese, K. Yoshii, Y. Yamaguchi, T. Okumura, Z.-D. Huang, M. Kato, K. Kubota, J. Furutani, Y. Orikasa, H. Senoh, H. Sakaebe and M. Shikano, Nat. Commun., 9, 3823 (2018).

K. Yoshii, T. Masese, M. Kato, K. Kubota, H. Senoh and M. Shikano, ChemElectroChem, 6, 3901 (2019).

T. Masese, K. Yoshii, M. Kato, K. Kubota, Z.-D. Huang, H. Senoh and M. Shikano, Chem. Commun., 55, 985 (2019).

G. M. Kanyolo and T. Masese, chemRxiv,11961123 (2020). https://doi.org/10.26434/chemrxiv.11961123.v1 submitted

G. M. Kanyolo, T. Masese, J. Rizell et al., Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant Insights. arXiv, 2003.03555 [cond-mat.mtrl-sci] (2020). https://arxiv.org/abs/2003.03555 submitted
Sulfated Zirconia Superacid for Improvement of Lithium Metal Batteries with Carbonate Electrolytes
Authors: Woo Sang-Gil , Hwang Eun-Kyoung , Jeong Goojin , Lee Je-Nam , Yu Ji-Sang
Published: December 2020

Although the promise with regard to the energy density has promoted research on lithium (Li) metal batteries (LMBs) because of high theoretical specific capacity (3860 mAh g-1) and the low redox potential (-3.040 vs standard hydrogen electrode), avoiding uncontrolled dendrite growth and resulting increasing of interfacial resistance request a formidable challenge in reversible and sustainable cycling of LMBs.

Here, we introduce coating of sulfated zirconia (S-ZrO2) onto a separator to induce homogeneous growth of Li by achieving high Li ion transference number. Sulfated zirconia synthesized by sol-gel method has high specific surface area and exhibits extremely high acidity, such as several orders of magnitude higher acidity than that of pure sulfuric acid. The extraordinary acidity of S-ZrO2 showed a dense Li plated layer with rounded morphology of individual Li deposits and improved cyclability resulting.
LiFePO4 synthesis Using Refined Li3PO4 from Wastewater in Li-Ion Battery Recycling Process
Authors: Lee Jongkwan , Heo Kookjin , Kim Min-Young , Im Dae-yeong , Gil Woo-ram , Park Won-seok , Lim Jinsub
Published: December 2020

Increased demand for lithium resources has led to increased Li costs and supply problems and increased the importance of lithium ion battery (LIB) recycling. In this study, lithium phosphate from LIB recycling wastewater was refined in a simple process using deionized water (DI). The morphologies and compositions associated with purifying Li3PO4 were investigated using X-ray diffraction, field emission-scanning electron microscopy, simultaneous thermogravimetric-differential thermal analysis, differential scanning calorimetry, pH measurement, inductively coupled plasma optical emission spectroscopy, and carbon and sulfur determinators. Simple refining with DI can increase Li3PO4 purity from 94.601% to 98.867%. LiFePO4 (LFP) was then synthesized using the purified Li3PO4; its morphology was studied and its electrochemical performance evaluated by constant current charge/discharge testing and cyclic voltammetry. The LFP cathode fabricated from purified Li3PO4 exhibited improved electrochemical properties, particularly in terms of initial capacity and cycling stability.
Research of Li-Mg Alloy Electrode for All Solid States Battery
Authors: Kim Sangwoo , Kim DongEung
Published: December 2020

All solid state Li metal battery is regarded as the promising next-generation energy storage device due to the high theoretical energy density and safety. However, the practical application of ASS Li-metal batteries is still limited owing to the cycle stability of both the cathode and lithium metal anode. In particular, the instability in the bulk and at the surface of the lithium anode during cycling becomes a huge obstacle for the practical application of ASS Li-metal batteries, based on the consideration of improving the stability in the bulk and at the surface of the lithium anode.

Our experimental results reveal that the robust passivation layer is formed on the surface of the Li-Mg alloy anode, which is helpful to reduce side reactions, and enable the smooth surface morphology of anode during cycling.

Meanwhile, the mixed electron and Li-ion conducting matrix of the Li-poor Li-Mg alloy as a porous skeleton structure can also be formed after delithiation, which can guarantee the structural integrity of the anode in the bulk during Li stripping and plating step. Therefore, the Li-rich Li-Mg alloy is demonstrated to be a very promising anode material for ASS Li-metal battery.
Gravimetric Measurement of Lithium-Air Battery Cell during Discharge/Charge
Authors: Nomura Akihiro , Mizuki Emiko , Ito Kimihiko , Kubo Yoshimi
Published: December 2020

Lithium-air battery (LAB) is expected to have an extremely high energy density, 5-10 times higher than that of the current lithium-ion batteries. To extend the cycle life of LAB, the oxygen reduction/evolution reactions (ORR/OER) at the cathode must be close to the ideal 2Li+ + O2 + 2e- ↔ Li2O2. So far, these reactions have been quantitatively analyzed using pressure cells and/or differential electrochemical mass spectrometry (DEMS). However these methods are not suitable for long-term measurements such as long-term discharge/charge or cycle tests. We have developed a high-precision weight measurement system that automatically measures the weight of a coin cell during the discharge/charge process. Performing zero correction each time enables long-term monitoring of the cell weight with accuracy of the balance used. Cell weight measurement also provides a more accurate quantitative analysis of the oxygen consumed and the gases evolved than DEMS.

Figure 1(a) shows the galvanostatic discharge/charge profile of a LAB cell under pure oxygen atmosphere. The cell was comprised with a carbon nanotube (CNT) sheet cathode (16 mm in diameter) and a Li metal anode filled with 1M LiTFSI/TEGDME electrolyte. Figure 1(b) presents the amount of cell weight change, which synchronously responded to the discharge/charge profile. The cell weight exhibited -5.63 mg/h weight loss during the first 50 h rest. This corresponds to slow evaporation of the electrolyte solvent and was subtracted as a background in the following analysis. The following 50 h discharge brought linear weight gain by ORR at the cathode equivalent of 1.955 (±0.005) e-/O2, which was slightly lower than the ideal number of 2 for two electron reduction. If we simply assume one-electron and two-electron reactions, this indicates that 4.5% of oxygen inhaled remained one electron reduction while the rest underwent two electron reduction. Then the cell experienced a linear weight loss at 2.109 (±0.006) e-/O2 during the first 30 h of charge, which corresponded to 94.8% weight of ideal oxygen evolution. The weight loss was gradually accelerated near the end of charge, which is attributed to the evolution of CO2 detected by the DEMS. Although the cell weight change gives a complementary profile of the DEMS, it provides a simple way to monitor the discharge/charge reactions of the LAB cells with high accuracy. Long-term cell weight changes under multiple discharge/charge cycles will also be discussed.

Figure 1
Development and Scaling of Lithium Metal Anode Based Batteries
Authors: Henslee Brian E , Zalar Frank
Published: December 2020

The importance of batteries for energy storage is ever present and growing for consumer electronics and electric vehicles. Current Li-ion rechargeable battery solutions are pushing limits for improvement of energy density and present significant safety challenges upon impact damage. New lithium-based cell technologies offer the potential for step-change increase in capacity, energy, and run-time. Next generation cell and battery designs must address not only capacity and weight but also impact and safety challenges. Integrating new materials addressing battery safety with next generation cell chemistry and design will address these critical dual needs. Cornerstone Research Group, Inc. has been developing advanced cells and batteries using high specific capacity materials including lithium metal anodes combined with sulfur and oxide based cathodes to address these challenges. Apart from development of these next generation chemistries additional issues related to scaling devices from coin full pouch cells has also been underway. This talk will discuss development of these cells from bench to scaled storage devices.
(Invited) Electrochemical Investigation of Hard Carbon Electrodes for Sodium-Ion Batteries Using a Coaxial Ring Reference Electrode
Authors: Park Juyeon , Meddings Nina , Raccichini Rinaldo , Rosser Tim , Olson Jarred Zipley , Hinds Gareth
Published: December 2020

Sodium-ion batteries (NIBs) are an attractive alternative to lithium-ion batteries (LIBs) because of the natural abundance of sodium resources [1]. Owing to their similar working principles to LIBs, NIBs also offer the advantage of utilizing the same manufacturing protocols and methodology as LIBs, and as such minimal additional capital costs are required for existing LIB manufacturers to switch to NIB technology.

Since the sodium storage mechanism of hard carbon (HC) was demonstrated by Stevens and Dahn in 2000 [2], it has become the state-of-the-art anode material for NIBs due to its good cycling stability, low working potentials, small voltage hysteresis and relatively low cost. However, the storage mechanism for high performance is not fully understood due to the complexity of the HC structure. The prevalent problem of under-estimated capacity of HC in half-cell tests indicates that this conventional test method requires improvement. Furthermore, half-cell studies are generally carried out in two-electrode configuration, where the counter electrode (CE) acts also as reference electrode (RE). This provides reliable results only if the passage of current does not significantly perturb the potential of the CE [3].

In this study, we present an in-depth investigation of the electrochemical behavior of a range of HC-based working electrodes (WE) in three-electrode half-cell configuration, with a pure Na metal CE and a concentric Na metal coaxial ring RE. The use of a separate RE allows simultaneous data acquisition for both WE and CE, during galvanostatic cycling and electrochemical impedance spectroscopy measurements.

Using this approach, the electrochemical performance, including cycling stability, rate capability and electrochemical impedance, is measured in a reliable manner to assess the capacity and cyclability of HC. In addition, the effect of four different types of electrolyte solution on the electrochemical behavior is analysed and discussed to inform electrolyte selection from a full-cell perspective (Figure 1).

Reference
s
:

[1] C. Vaalma, D. Buchholz, M. Weil, S. Passerini, Nat. Rev. Mat., 3 (2018) 18013.

[2] J. R Dahn, D. A. Stevens, J. Electrochem. Soc., 4 (2000) 147.

[3] R. Raccichini, M. Amores, G. Hinds, Batteries., 5 (2019) 12.

Figure 1
(Invited) Electrodeposition for Die-to-Wafer Very High-Density Interconnect
Authors: Inoue Fumihiro
Published: December 2020

Due to an increasing demand for high performance electronics, e.g. mobile, wearable, artificial intelligence for self-driving, heterogeneous 3D integration chips are highly desired since the integration scheme can be significantly outperforming a 2D integration chip.

There are several 3D stacking integration methods to connect different components, such as wafer to wafer (W2W) bonding and die to wafer (D2W) bonding. W2W hybrid bonding offers a massive connection in a bonding, which decrease the processing cost in particular for small chips. However, there is a limitation that the die must be equal size for the pair wafer. Furthermore, no Known Good Die (KGD) selection is possible in W2W bonding, which can give a negative impact on stacking yield. On the other hand, D2W is able to handle different die sizes, which allow great flexibility in 3D integration. In addition, the capability to select the KGD ensures the yield.

The most commonly used interconnection technique for D2W is solder base thermal compression bonding (TCB). However, there are several challenges in the stacking to achieve below 10 μm pitch. In addition, there is a certain limitation for scaling down below 5 μm of the bump pitches. In order to overcome the issue, implementation of hybrid Cu-Cu bonding technology is desired.

In this presentation, the alternative scheme for solder base thermal compression bonding will be introduced, which enables us to achieve below 10 μm pitch by TCB. In particular, the challenge and solution regarding electrodeposition will be discussed. In addition, our integration approach for hybrid Cu-Cu D2W bonding will also be introduced.
(Invited) Technology of Gallium Nitride Crystal Growth - Challenges and Perspectives
Authors: Iwinska Malgorzata
Published: December 2020

It is well known that gallium nitride (GaN) is the basic material for fabricating optoelectronic devices as Light Emitting Diodes (LEDs) and Laser Diodes (LDs). GaN is also an attractive choice for electronic high-frequency and high-power devices. This is due to its wide band gap, high electron velocity, high breakdown ﬁeld strength and high thermal conductivity. Most of the mentioned GaN-based devices are built on foreign substrates (sapphire, silicon, or silicon carbide). For many years, there was no mass production of native substrates. This happened because GaN crystal growth is quite a challenging process. The compound melts congruently at high temperature and extremely high nitrogen pressure (>6 GPa). Thus, today, it is impossible to grow GaN from the melt. The crystals should be obtained by other techniques requiring lower pressure and temperature. Crystallization from gas phase, solution, or any combination thereof must be included. For more than three decades, crystallization of bulk GaN has remained a big challenge for the nitride community. Work on developing bulk GaN has mainly been motivated by the LD market. All commercially available LD epi-structures are built on GaN wafers. Today, however, not only the LDs, but also the electronic industry and the demand for vertical high power transistors and diodes seem to be the driving force for crystallizing bulk GaN. Thus, GaN substrates of relatively high quality have recently become available. Today, GaN is crystallized by three main methods: i/ sodium flux (Na-flux); ii/ halide vapor phase epitaxy (HVPE); and iii/ basic or acidic ammonothermal growth. Perspectives of all the mentioned above technologies will be presented in this lecture. Special attention will be paid to the basic ammonothermal method and HVPE. It will be shown that growth from the vapor phase needs a new philosophy. The crystallization processes on foreign seeds (sapphire and gallium arsenide) reached their maximum possibilities. Despite many tricks during crystal growth runs the structural quality as well as yield of the obtained GaN crystals and wafers are very low and cannot be improved. The only way is GaN-on-GaN crystallization. Recently, significant progress has been presented in the basic ammonothermal method. High structural quality crystals of lateral size larger than 2 inches and thickness exceeding 6 mm were obtained in one crystal growth process. Use of ammonothermally grown GaN as seed for HVPE will be presented. All challenges and difficulties to grow bulk GaN from the vapor phase will be demonstrated. Scenarios for the further development of bulk GaN crystallization will be shown. Important parameters of GaN substrates for epitaxy of optoelectronic and electronic device structures will be discussed. A new way of better controlling the electrical properties of GaN crystals and wafers will be proposed.
The Structural Evolution of Dot-Core GaN Substrates with Annealing Under Growth-Like Conditions
Authors: Liao Michael Evan , Huynh Kenny , Wang Yekan , Allerman Andrew A. , Goorsky Mark S.
Published: December 2020

The structural evolution before and after annealing of c-plane dot-core GaN substrates under growth-like conditions was studied using monochromatic X-ray topography. The anneal was performed at 1050 °C for 10 hours in a MOCVD growth chamber under conditions optimized for the growth of GaN drift layers but without the group-III alkyl. This replicates the thermal environment the substrates experiences during the growth of > 2 kV PN diodes. In the current literature, fundamental understanding of the defect structure of dot-core GaN substrates – and its direct impact on device performance – is limited. X-ray topography provides a nondestructive method for studying the structural nature of defects which can then be used to understand the impact of defects on device performance. The measurements were performed at the 1-BM beamline of the Advanced Photon Source, Argonne National Laboratory using an X-ray energy of 8.05 keV to measure the (1124) GaN reflection to generate single exposure images (images exposed at a specific ω angular position along the X-ray rocking curve) as well as rocked images (a composite image exposed at many positions along the rocking curve). The step size for the rocked images was 0.008°. The rocked images showed butterfly-shaped diffraction lines centered at each core – indicative of localized distortions due to a high density of defects aggregated at each core. Furthermore, the single exposure images revealed that in the regions between the cores, the lattice is less misoriented than at the cores. The defects present at the cores induce severe lattice tilt emanating radially from the cores, which suggests that these relatively high tilt regions (cores) would be detrimental to device performance. Before annealing, it was observed that adjacent low tilt regions were tilted with respect to each other. The radius of (lattice) curvature of the substrate before annealing was 17 ± 1 m, which indicates that globally throughout the entire substrate there was a high amount of lattice tilt misorientation. After annealing, the substrate flattens – the radius of curvature increased to 27 ± 2 m and an increase in diffracted area between adjacent “low tilt” areas also increased, which is evidence of both local and global structural reconfiguration of the lattice towards a smaller degree of misorientation due to the anneal.

Figure 1
Rapid Non-Destructive Wafer Detection and Tracking of Defects in Bulk and Epitaxially Grown Gallium Nitride
Authors: Elhadj Selim
Published: December 2020

Defects in bulk semiconductor crystals are especially damaging to devices, producing catastrophic electrical and optical failures or even limiting lifetime performance and reliability, while driving materials growth costs. New methods for rapid and non-destructive characterization of materials are needed to help overcome limitations in fabrication throughput and application reliability of wide-bandgap power electronics substrates, especially in the development of emerging bulk Gallium Nitride (GaN). Rapid materials characterization methods will help inform the fabrication process parameters impact on materials defects formation, while speeding-up materials development and, ultimately, the deployment of low defect commercially viable and reliable bulk GaN substrates. Here we present an approach for multi-modal defect non-destructive imaging of device-relevant GaN defects with high resolution and high sensitivity. The scanning GaN defects detection system is based on laser pump-and-probe photoluminescence and photothermal measurements that are compared to diode device reliability data from accelerated lifetime testing. We determine that defects detected at optical frequencies reliably predict lifetime performance issues of power electronic devices operating at near DC frequencies[1, 2]. Bulk and epi grown GaN wafer imaging data and test platform device data are correlated to help validate the proposed multi-modal defect detection approach for the reliable detection of defects relevant to the performance of GaN power electronic devices.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office, FY18/FY19 Lab Call.

J. H. Yoo, A. Lange, J. Chesser, S. Falabella, and S. Elhadj, "A Survey of Transparent Conducting Films and Optoelectrical Materials for High Optical Power Applications," Physica Status Solidi a-Applications and Materials Science 216, (2019).

J.-H. Yoo, S. Rafique, A. Lange, H. Zhao, and S. Elhadj, "Lifetime laser damage performance of β-Ga2O3 for high power applications," APL Materials 6, 036105 (2018).

Figure 1
Synchrotron X-ray Topography Characterization of Commercial GaN Substrates for Power Electronic Applications
Authors: Liu Yafei , Hu Shanshan , Peng Hongyu , Ailihumaer Tuerxun , Raghothamachar Balaji , Dudley Michael
Published: December 2020

As one of the most important wide bandgap semiconductors, Gallium Nitride (GaN) has many applications in power electronic devices such as inverters and switches, as well as optoelectronic devices like light emitting diodes.[1] However, high-quality bulk GaN growth is still limited by the availability of growth techniques. Two most popular growth method for GaN are hydride vapor phase epitaxy (HVPE) [2, 3] and ammonothermal [4, 5] method. HVPE method uses foreign substrates, such as sapphire, gallium arsenide or silicon carbide, which gives a large dislocation density due to significant lattice mismatch and difference in coefficients of thermal expansion. However, in ammonothermal method, native seeds were used to minimize the effects of lattice mismatch and a retrograde direction of GaN transport inside the growth system was utilized to exclude most of the contamination and undesirable phases. So, ammonothermal method gives a much better quality.

In this study, GaN substrates of both HVPE (Figure 1) and ammonothermal (Figure 2) methods have been characterized by synchrotron monochromatic beam X-ray topography (SMBXT)[6]. The distribution of threading screw/mixed dislocations (TSDs/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) is characterized. Ray tracing simulations are adopted to confirm the types of dislocations. The comparison of defect distribution between HVPE and ammonothermal samples has been conducted by both SWBXT and High-resolution X-ray Diffraction (HRXRD).

References

[1] S.J. Pearton, J.C. Zolper, R.J. Shul, F. Ren, Journal of Applied Physics 86 (1999) 1-78.

[2] H.P. Maruska, J. Tietjen, Applied Physics Letters 15 (1969) 327-329.

[3] K. Fujito, S. Kubo, H. Nagaoka, T. Mochizuki, H. Namita, S. Nagao, Journal of Crystal Growth 311 (2009) 3011-3014.

[4] R. Dwiliński, R. Doradziński, J. Garczyński, L. Sierzputowski, A. Puchalski, Y. Kanbara, K. Yagi, H. Minakuchi, H. Hayashi, Journal of Crystal Growth 310 (2008) 3911-3916.

[5] T. Hashimoto, F. Wu, J.S. Speck, S. Nakamura, Journal of Crystal Growth 310 (2008) 3907-3910.

[6] B. Raghothamachar, M. Dudley, G. Dhanaraj, X-Ray Topography Techniques for Defect Characterization of Crystals, in: G. Dhanaraj, K. Byrappa, V. Prasad, M. Dudley (Eds.), Springer handbook of crystal growth, Springer Science & Business Media, 2010, p. 1425.

Figure 1
(Invited) Moderate Temperature Mg Diffusion Doping of GaN
Authors: Voss Lars F. , Frye Clint D. , Allen Noah A. , Harrison Sarah E. , Kweon Kyoung , Varley Joel Basile , Lordi Vincenzo , Nikolic Rebecca , Anderson Travis J. , Hite Jennifer K.
Published: December 2020

Ex-situ p-type doping of GaN has been a long-standing challenge and prevented adoption of numerous devices. While regrowth of p-GaN on etched surfaces and ion implantation have made progress, technical challenges remain. Diffusion of Mg into GaN has received considerably less attention, primarily due to the extremely low diffusivity of Mg in GaN as well as the instability of GaN at the temperatures required (typically >1000oC), as well as its propensity to form compensating defects. Here, we report on a new technique for diffusion doping of GaN with Mg at relevant temperatures (under 1000oC). This approach uses a bi-layer structure, with a solid Mg source in contact with the GaN combined with a metal capping layer. Using this approach, we have measured significant diffusion of Mg into GaN by Secondary Ion Mass Spectrometry at temperatures as low as 800oC and time on the order of minutes (Figure 1) with concentrations exceeding 1019 cm-3 and Mg extending >100 nm into the GaN film. Room temperature Hall effect measurements confirm p-type conductivity under a limited set of diffusion conditions. In other cases, compensation of the diffused Mg by formation of defects during diffusion resulted in highly resistive layers. Photo-Hall measurements using sub-band gap light of different wavelengths was used to excite both holes and electrons, depending on the wavelength. Samples with higher measured Mg concentration show correspondingly increased hole density under illumination with 2 eV light. These results strongly imply the diffusion of Mg through Ga sites, but with corresponding formation of compensating defects as the material becomes more p-type. Density functional theory (DFT) calculations on the diffusivity of Mg through various pathways as well as the formation energies of various compensating defects suggest a path towards achieving higher Mg concentrations with high free hole concentrations.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, LLNL-ABS-810935. This support does not constitute an express or implied endorsement on the part of the Government. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, PNDIODES program monitored by Dr. Isik Kizilyalli.

Figure 1: Mg profiles after diffusion at 800oC for 5 minutes

Figure 1
Characterization of Dislocations in 4H-SiC Single Crystals at the Initial Growth Stage by Synchrotron X-ray Topography
Authors: Ailihumaer Tuerxun , Peng Hongyu , Liu Yafei , Raghothamachar Balaji , Dudley Michael
Published: December 2020

In recent years, 4H-SiC has become a widely acknowledged material applied in high power electronics. 4H-SiC-based devices are able to operate at high voltage, high current and high temperature due to its superior physical properties. However, they have yet to reached to the requirements for mass production, due to the fact of SiC’s relatively inferior crystal quality. Over the past few decades, the effect of various dislocations existing in the crystals such as threading screw/mixed dislocations (TSD/TMDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) has been studied and revealed to be main source for degrading the reliability of SiC power devices[1-2]. Recently, studies on the early stages of physical vapor transport (PVT) growth of SiC have been reported by several groups regarding to the investigation of the step morphology and lattice plane bending [3-5]. However, dislocation propagation behavior and their formation mechanism at the early growth stages are yet to be studied in detail.

This paper describes the investigation of dislocation behavior during the early stages of PVT-grown 6-inch 4H-SiC crystals by synchrotron monochromatic beam x-ray topography (SMBXT) technique. Ray tracing simulation was applied to simulate the dislocation images. Our studies show that most of the TSDs/TMDs are replicated into the newly grown crystal while most TEDs are generated by either nucleation in pairs at the seed/crystal interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown layer are of screw type with 1/3[11-20] and this has been verified by comparison with ray tracing simulated images. TEDs with the same and opposite sign of Burgers vector are found to be deflected on to same basal plane by the overgrowth of macro-steps and start to glide in the same and opposite directions respectively. TMDs deflected on to the basal plane by macro-steps get dissociated into c and a components, with the a segment undergoing glide to form V-shaped configurations.

[1] St.G. Muller, J.J. Sumakeris, M.F. Brady, R.C. Glass, H.M. Hobgood, J.R. Jenny, R. Leonard, D.P. Malta, M.J. Paisley, A.R. Powell, V.F. Tsvetkov, S.T. Allen, M.K. Das, J.W. Palmour, and C.H. Carter. Jr., Eur. Phys. J. Appl. Phys. 27, 29 (2004).

[2] R. Singh and M. Pecht, IEEE Ind Electron M 2, 19 (2008).

[3] E.K. Sanchez, J.Q. Lin, M.De. Graef, M. Skowronski, W.M. Vetter, M. Dudley, J. Appl. Phys. 91 (3) (2002) 1143.

[4] C. Ohshige, T. Takahashi, N. Ohtani, M. Katsuno, T. Fujimoto, S. Sato, H. Tsuge, T. Yano, H. Matsuhata, M. Kitabatake, J. Cryst. Growth 1-6, 408 (2014).

[5] N. Ohtani, C. Ohshige, M. Katsuno, T. Fujimoto, S. Sato, H. Tsuge, W. Ohashi, T. Yano, H. Matsuhata, M. Kitabatake, J. Cryst. Growth 9-15, 386 (2014).

Figure 1
The Energy Band Alignment at the Heterointerface between Nanostructured TiO2 Layer and Au22(SG)18 Clusters for Metal Cluster-Sensitized Solar Cells
Authors: Omelianovych Oleksii , Larina Liudmila L. , Lee Dongil , Park Eunhee , Lee Gilhwan , Choi Ho Suk
Published: December 2020

This study is the first to quantify energy band alignments at the nanostructured TiO2/Au22(SG)18 cluster interface using X-ray photoelectron spectroscopy. The d-band of Au clusters has shown a band-like character and occupied states at the Fermi level were not detected. The results provide evidence of the existence of a finite optical energy gap in the Au22(SG)18 clusters and their molecular-like nature. The pinning position of the Fermi energy level at the interface was determined to be 2.8 and 1.3 eV higher than the top of the TiO2 VB and HOMO level of Au clusters, respectively. The diffuse reflectance and absorption analysis quantified 3.2 eV bandgap of TiO2 layer and 2.2 eV energy gap between HOMO and LUMO levels of Au clusters. Thus, a cliff-like offset of 0.5 eV between the LUMO level and the TiO2 conduction band was determined. The cliff-like offset of 0.5 eV provides room for further improving the efficiency of the MCSSC by lowering LUMO level through changing cluster size. The offset of 0.5 eV between a HOMO level and the 3I-/I-3 redox level yields the remarkable loss-in-potential, which implicates the possibility of further increasing the open-circuit voltage by properly replacing the redox couple in the MCSSCs.

Figure 1
(Invited) Atomic Layer Deposition of Charge Transport Layers for Highly Efficient and Stable Perovskite Photovoltaics
Authors: Shin Hyunjung
Published: December 2020

Atomic layer deposition (ALD) is now being recognized as a powerful, general tool for modifying the surfaces of nanomaterials in applications for many renewable energy conversion devices. ALD techniques are now utilizing in charge transporting layers for solar cells. CH3NH3PbI3 with perovskite crystal structure has attracted considerable interest for high power conversion efficiency (PCE, now certified 25.2 %). ALD chemistry for TiO2, NiO, SnO2, and ZnO are well known and the process requires relatively low deposition temperature as low as ~ 100 °C, which is applicable to deposit onto the halide perovskite layer. In this presentation, highly efficient perovskite solar cells having a long-term stability that adapts uniform and dense inorganic charge transport layers grown by ALD are reported. The devices showed excellent water-resistant properties and long-term stability at 85 °C under illumination.

Figure 1
The Effect of Particle Size and Thickness on Nanocrystalline TiO2 Films on Dye-Sensitized Solar Cells for Indoor Application
Authors: Yoo Kicheon , Kang Hyeong Cheol , Lee Jae-Joon
Published: December 2020

Dye-sensitized solar cell has a unique property such as transparent, colorful characteristics and good performance under low/diffused light intensities, compared to other type of solar cells. Here, we have investigated effects of TiO2 particle size(14, 22, 50nm) and the thickness(2 to 20 μm) on nanocrystalline TiO2 films on photovoltaic performance in dye-sensitized solar cell under 1 sun, compact fluorescent lamp (CFL) and light-emitting diode (LED 3200K, 5000K) at 200 to 1000 lux. Further, the DSSCs fabricated using a TiO2 (22nm) film of 13.73 μm thickness at 1sun condition exhibited the best photovoltaic performance with highest power conversion efficiency (7.22%). However, the DSSC efficiency essentially follows the same trend with TiO2 film thickness, exhibiting the maximum efficiency value of 13.26 % for the 16.72 μm thickness of TiO2 (50nm) film at LED 3200K (1000 lux).
Real Impacts of Ligand-Capped Nanocrystals in Perovskite Solar Cells
Authors: Gong Oh Yeong , Kim Youngsik , Kim Dong Hoe , Han Gill Sang , Jeong Sohee , Jung Hyun Suk
Published: December 2020

Perovskite solar cells (PSCs) has been reached the certified power conversion efficiency (PCE) of 25.2 % in 2019. They are having received large attention because of their superior optoelectronic properties (such as high charge carrier mobility, tunable bandgap, high absorption coefficient) and even the cost-effective process.

In the latest fabrication process for high-efficiency PSCs, surface-defect engineering of perovskite film has attracted tremendous attention. Because, the control of surface-defects can play a critical role in grain boundaries of perovskite, and interfaces between perovskite and charge transport layer, leading to PSCs with further improved photovoltaic (PV) performance and long-term stability. There are many exertion for reducing surface-defects state densities of perovskite film by applying an additional passivation layer, for instance cross-linked molecules and two-dimensional (2D) materials (2D-perovskite, graphene, and MoS2) at surface of perovskite film.

Most recently, perovskite nanocrystals (NCs) are being investigated as an additional layer for high-efficiency PSCs owing to anticipation of their multifunctional properties including high light-harvesting properties, efficient charge transport by carrier cascade effect, and surface passivation effect. However, it seems to remain under question whether these functions are related to the light-harvesting, suitable band alignment, and surface passivation for PSCs, due to ligand capped NCs.

In this study, we investigated that the functions of NCs layer in PSCs with various NCs capped same ligand. To confirm the effects of NC layer in PSCs, we fabricated n-i-p planar devices, which follow FTO/c-TiO2/Perovskite/NC layer/Spiro-OMeTAD/Au structure with three kinds of NCs (CsPbBr3, CsPbI3, and InP). All these NCs have different electrical and optical properties, but nevertheless the devices with each NC layer showed similarly improved PV performance.

In analysis results of each function of the NC layer, there were no light-harvesting effects by all NCs layer due to high absorption coefficient and sufficient thickness of perovskite film. In addition, NC layer could not work as a carrier cascade layer at the interface between the perovskite film and hole transport layer due to poor electrical properties of capping ligand. Finally, the NC layer affected only on the surface passivation of perovskite film, and furthermore we found that Oleylamine (OLA) ligand of the NCs was a major cause of the surface passivation effect. We believe that the optimization of the surface passivation effect of fatty amine ligands can further improve the PV performance of PSCs.
Fabrication of Oriented FTO Film Grown By Spray Pyrolysis
Authors: Yoshino Kenji , Kamimizutaru Koki , Narita Yuki , Minemoto Takashi , Iikubo Satoshi , Shen Qing , Hayase Shuzi
Published: December 2020

SnO2 behaves like an n-type semiconductor with a wide energy gap (~ 3.8 eV) and has a tetragonal structure which is similar to the rutile structure. Of the various potential dopants for SnO2, fluorine is preferred because F-doped SnO2 (FTO) films show high transparency and good conductivity. The spray pyrolysis method is the most convenient method because of its simple and inexpensive experimental arrangement and the ease with which doping materials can be added. However, there are few reports on the growth and detailed analysis of FTO films deposited by spray pyrolysis.

In previous work1, transparent conducting oxide films of non-doped SnO2 and FTO were deposited on glass substrates at 500 °C by spray pyrolysis in order to determine the effect of spray solution concentration and substrate temperature. The films were all polycrystalline with tetragonal crystal structures. The best electro-optic properties were achieved with a fluorine doping concentration of 17 mol%. These conditions resulted in a film with an average optical transmittance of 82%, a resistivity of 4.0 × 10-4 Ωcm, a carrier concentration of 4.7 × 1020 cm-3 and a mobility of 34 cm2 (V s)-1.

In this work, oriented SnO2 and FTO films were deposited on glass substrates by spray pyrolysis. The (110) or (200) orientation film could be obtained by means of the Sn solution concentration. Furthermore, low surface roughness could be also obtained by means of the sample thickness. Oriented FTO film with low surface roughness could be obtained by controlling two methods such as the Sn solution concentration and thickness.

1 M. Oshima, M and K. Yoshino, J. Electron. Mater. 2010, 39, 819-822.
Highly Efficient Anti-Reflection Film for Solar Cells
Authors: Lee Jung-hwa , Cho Jun-hee , Baek Seunghun , Ko Doo-Hyun
Published: December 2020

When light transmits into the solar cell, reflection occurs at the interface between air and an absorptive medium lowers solar cell efficiency. In this study, we present micro-dome structured anti-reflection (AR) films fabricated via simple imprinting technique. The functionality of the film in photovoltaic devices is evaluated, revealing reduced reflection caused by gradient refractive index effect and omnidirectional antireflection behavior, which lead to enhance the photovoltaic performance under both outdoor and indoor lighting. In addition, the AR film does not require any manipulation of solar cells as using a simple strategy of attaching the film on the surface, and its hydrophobic property affords self-cleaning effect, which should be beneficial for building integrated photovoltaics. Combined with these properties, our detachable AR films provide a practical guideline to boost solar cell performance.
TCAD Simulation of a 3D NAND Memory Utilizing In-Ga-Zn-Oxide: "3D OS NAND" with 4 V Drive, High Endurance and Density
Authors: Kunitake Hitoshi , Kimura Hajime , Tsuda Kazuki , Godo Hiromichi , Murakawa Tsutomu , Sawai Hiromi , Baba Haruyuki , Sasagawa Shinya , Ikeda Takayuki , Yamazaki Shunpei
Published: December 2020

Memory-centric computing has been actively researched for AI application. To achieve this, there are growing demands on memories for high density and high endurance. To demonstrate the application, a variety of emerging memory technologies have been proposed; however, they still have difficulties in achieving a density comparable to NAND flash and in improving endurance.

CAAC-IGZO, with a wide bandgap and a heavy hole effective mass, can be applied to a field-effect transistor that is characterized by its extremely-low off-leakage current. Use of CAAC-IGZO FET in non-display fields has been reported in recent years, and 3D NAND utilizing CAAC-IGZO FET has been researched. However, the reported memory cell architecture involves through-dielectric charge trapping in MONOS structures, and has low endurance in the same way as conventional Si-based NAND flash.

In view of the above, we propose a 3D OS NAND memory, a vertically-stackable 2Tr-1C memory having CAAC-IGZO FETs. Potentially, this memory not only enjoys main features of NAND flash such as high density and non-volatility, but also achieves a DRAM-like endurance. In this study, we evaluated our novel memory architecture with TCAD Sentaurus produced by Synopsys.

The cross section, circuit diagram, and 3D overall structure of the memory cell are shown in Fig. 1(a), Fig. 1(b), and Fig. 1(c), respectively. The 3D OS NAND has a memory cell architecture in which a pair of vertically-positioned transistors on the A-A' plane is connected in series to another pair in the Z-axis direction. Taking advantage of extremely-low off-leakage current of CAAC-IGZO FET, the memory cell is composed of only a switching CAAC-IGZO FET and a MIM capacitor. The timing chart of a string of four memory cells connected in the Z-axis direction is shown in Fig. 1(d). Write operation is performed by sequentially lowering the voltage of WG from the bottom with respect to the Z-axis direction, and read operation is performed by lowering the voltage of CG of the memory cell being read. The retention properties of memory cells to which a checker pattern is written are shown in Fig. 1(e). The device simulation indicates a possibility that a memory cell composed of only an CAAC-IGZO FET and a MIM capacitor achieves a retention time of 109 sec or longer.

In this paper, we propose a novel memory architecture with CAAC-IGZO FET by discussing the overview of 3D OS NAND and its write and read performance.

Fig. 1(a) Cross section of 3D OS NAND memory cell, (b) circuit diagram of 3D OS NAND memory cell, (c) 3D structure of 3D OS NAND, (d) timing chart of 3D OS NAND, and (d) retention properties of 3D OS NAND

Figure 1