bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Atomic Layer Deposition on 1D Nanomaterials for Various Applications
Authors: Zazpe Raul , Sopha Hanna , Thalluri Mouli , Hromadko Ludek , Rodriguez Pereira Jhonatan , Rihova Martina , Macak Jan M.
Published: February 2024

One-dimensional nanomaterials – materials with one dimension outside the nanoscale, further noted as 1D NMs – represent a class of very important nanomaterials with continuously increasing importance. Due to their intrinsic features, unique properties and diversity of functionalities, they count among the most widely studied materials nowadays. While considerable research efforts have been spent to synthesize various 1D NMs (e.g. nanopores, nanotubes or nanofibers), limited efforts have been devoted to surface modification and property tailoring of these materials.

However, it is their surface that comes into direct contact with various media (air, gases, liquids, solids) and influences the reactivity, stability and biocompatibility of these materials. The surface and aspect ratio (defined as their diameter to length ratio) influence the performance of these materials in various applications. Considering these facts, it is more relevant to tailor the surface of these materials and to be able to influence their properties and reactivity at the nanoscale, rather than to deal with tailoring their own bulk material composition.

The focus of this presentation is on the modification of two types of 1D nanomaterials – nanotubes and nanofibers. Numerous techniques can be utilized for this purpose, such as for example wet chemical or physical deposition techniques. However, it is only the Atomic Layer Deposition (ALD) that is capable of really uniform and homogenous coating of these 1D nanomaterials, in particular those of very high-aspect ratio.

The presentation will be mainly focused on modification of TiO2 nanotube layers and various nanofibers of different aspect ratios via ALD.

Experimental details and some very recent application examples in photocatalysis, catalysis, sensors, batteries, nanorobots, etc. [1-11] and structural characterizations of these modified materials will be discussed.

Sopha et al (2017), Appl. Mater. Today, 9, 104.

Sopha et al. (2018), Electrochem. Commun.,97, 91.

Ng et al. (2017), Adv. Mater. Interfaces, 1701146.

Dvorak et al. (2019), Appl. Mater. Today, 14, 1.

Sopha et al. (2019), FlatChem 17, 100130.

Motola et al. (2019), Nanoscale 11, 23126.

Ng et al. (2020), ACS Appl. Mater. Interfaces, 12, 33386.

Motola et al. (2020) ACS Appl. Bio Mater. 3, 6447.

Rihova & M. Knez & J. M. Macak et al. (2021), Nanoscale Adv., 3, 4589

Galstyan, T. Djenizian, J. M. Macak (2022), Appl. Mater. Today, 29, 101613

Villa & M. Pumera & J. M. Macak et al. (2022), Small, 2106612
Stepwise Growth of Crystalline MoS2 in Atomic Layer Deposition
Authors: Cho Ah-Jin , Ryu Seung Ho , Kim Seong Keun
Published: February 2024

Transition metal dichalcogenides (TMDCs) are layered materials in which each layer is weakly bound by van der Waals forces. TMDCs have interesting intrinsic properties, including high mobility and excellent electrostatic controllability, even at monolayer thickness. Hence, they have emerged as promising materials for widespread applications in nanoelectronics, optoelectronics, gas sensors, etc. The aforementioned properties of TMDCs are significantly affected by the structural

quality and crystallinity. Accordingly, scalable techniques have been sought for synthesizing well-crystallized TMDCs.

Atomic layer deposition (ALD) is considered a promising growth technique for transition metal dichalcogenides (TMDCs) because it ensures uniformity and homogeneity of the TMDC grains. However, the poor crystallinity of ALD-grown TMDCs remains a critical challenge. Although crystallinity depends on the growth mechanism, the growth behavior of crystalline TMDCs in ALD is unclear. We investigated the growth behavior of highly crystallized molybdenum disulfide (MoS2) by ALD at 650 oC with an extra pulse of remote H2 plasma. Growth at high temperatures using the activated species aided surface diffusion of the adsorbates. The ALD process facilitates repeated growth and saturation of MoS2, unlike the normal ALD of 3D bulk materials, where the film thickness monotonically increases with the number of ALD cycles. This unique behavior resulted from the evolution of the basal plane without dangling bonds. On the basal plane, MoS2 lateral growth dominates vertical growth, and prolonged incubation is required for nucleation on the basal plane. The grain size is small (up to two monolayers) because of the limited mobility on SiO2, and the grains of the third layer grow to a few hundred nanometers. These findings provide insights into the development of ALD technology for application to high-quality TMDCs.
Solution ALD Processing of Halide Perovskite Thin Films Yields Superior Functional Quality and Stability Than Classical Processing
Authors: Koch Vanessa , Barr Maissa K. S. , Büttner Pascal , Bär Marcus , Brabec Christoph , Bachmann Julien
Published: February 2024

The range of materials accessible by classical ALD is limited by the volatility requirement applied to the precursors. However, solution ALD (sALD) transfers the self-limiting surface reaction principle of ALD into the solution processing realm and allows for the same level of control in the deposition of ionic or molecular solids, such as polymers, metal-organic frameworks, and halide perovskites, which cannot be delivered from the gas phase.

We have developed an sALD procedure for the direct deposition of the prototypical halide perovskite compound, methylammonium triiodoplumbate(IV), (H3CNH3)(PbI3), also referred to as methylammonium lead iodide or MAPI. The process saturates upon dosage variation to a self-limiting growth rate. The material is obtained in crystalline and highly pure, stoichiometric form at room temperature. All analytical techniques confer to indicate the absence of any lead iodide trace. The MAPI layers generated by sALD can be integrated into planar heterojunction stacks and yield functional solar cells.

The direct comparison of films of several thickness values prepared in pairs by sALD and by a state-of-the-art spin-coating method shows that the sALD films always overperform their spin-coated counterparts both in terms of charge carrier lifetimes and in terms of stability towards decomposition under thermal, radiative or vacuum stress.

Thus, experimental atomic-level control of solution-processed semiconductors is accessible for the first time. It can now be applied to the accurate investigation of halide perovskite photophysics and photochemistry fundamentals as they pertain to transport and interface phenomena.
Numerical Simulation of Spatial Atomic Layer Deposition on Moving Substrates with Microgrooves and Porous Structures
Authors: Li Zoushuang , Cao Kun , Shan Bin , Chen Rong
Published: February 2024

The need of ultrathin and highly conformal coatings on large-area microstructure substrates such as photovoltaic cells, flexible displays, and Li-ion battery (LIB) electrodes has driven the development of high-efficient ALD. Spatial ALD is a promising high-throughput technique capable of producing ultrathin films on large substrates, which can reach up to two orders of magnitude faster than temporal ALD. However, spatial ALD is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. Compared to the flat substrate, the diffusion process in the microstructures takes longer, limiting the substrate velocity and the deposition rate. In this work, spatial ALD on moving microgroove substrates and porous LIB electrodes are quantitatively studied through the multiscale modelling method by coupling computational fluid dynamics (CFD) with chemical kinetics. Dynamic mesh method is implemented to simulate the ALD reaction with the in-line movement of the substrate. Results show that the vortices always exist in the micro-gap with microgroove substrates. Besides, the top of the microstructure on the first contact with the precursor is the highest, and the surface coverage at the corner on the other side of the microstructure is the lowest. For porous LIB electrodes with large specific surface area, the film coating depth is limited by both the low precursor diffusion rate and the amount of precursor supply. Increasing the carrier gas flow rate increases the film coating depth by increasing the precursor supply over the same time period. Besides, the gas byproduct of ALD remaining at the electrode bottom can be more effectively removed. Quantitative process optimizations of substrate velocity and precursor concentration for different electrode structures are also carried out. It is found that the electrode gradient design with higher porosity on the top is beneficial for obtaining deeper coating depth and higher precursor utilization compared to the inverse gradient design. The present multiscale modeling work provides a comprehensive understanding and important guidance for the industrial application of the spatial ALD process on microstructure substrates.
Stabilized Positive Electrode Material to Enable High Energy/Power Density Lithium-Ion Batteries
Authors: Ahaliabadeh Zahra , Miikkulainen Ville , Mäntymäki Miia , Kallio Tanja
Published: February 2024

Recently, the large-scale deployment of electric vehicles (EVs) and stationary battery systems has put

forward urgent requests for rechargeable batteries with higher energy/power density and longer

lifespans. As such, next-generation Li-ion batteries (LiBs) are expected to meet these requirements. The

possibility of using Ni-rich high-capacity cathode materials (NMC) can help to achieve that goal, however,

they still suffer from significant capacity fade via several chemical and mechanical degradation modes.

One is crack formation within secondary particles which leads to parasitic reactions that evolve oxygen

and potentially initiate the formation of inactive crystal structures. LiBs mechanical and chemical

degradation mechanisms can be extended by applying protective coatings to the cathode’s surface. Many

studies explore atomic layer deposition (ALD) for this purpose. However, the complementary molecular

layer deposition (MLD) technique might offer the benefit of depositing flexible hybrid coatings that can

accommodate potential volume changes of the electrode during the battery cycling. This study reports

the deposition of novel organic-inorganic films via the ALD-MLD method. Characterization analysis such

as FTIR, XPS, SEM-EDS, and TEM confirmed the film deposition on the surface of the NMC electrode.

Besides, the electrochemical results showed the enhancement of the coated electrode, as evidenced by

providing a longer life with a 93% capacity retention after 150 cycles (3.0-4.4 V vs. Li/Li+), while the

uncoated one retained only 83% of its initial capacity. Moreover, in situ dilatometry showed irreversible

volume change for uncoated NMC while it was mostly reversible for coated ones during the cycling. It

revealed the dilation behavior of the electrode, resulting in crack formation, which is significantly

suppressed for the coated samples. Stable cycling of Ni-rich cathode materials in crucial conditions such

as high voltage windows and elevated temperatures is still extremely challenging. To evaluate this, in situ

dilatometry was performed at elevated temperatures (40 °C and 55 °C) and higher voltage ranges (3.0-4.6

V). The results confirmed that in both conditions, the dilation behavior of the coated sample is still under

control while the capacity is comparable to the uncoated sample. This revealed that the coatings present

good lithium-ion kinetics and reduce electrolyte decomposition. Overall, this work showed the liability of

the ALD-MLD films deposited on NMC electrodes to mitigate the degradation mechanisms and provides

insight into a method that seems promising as a protective and elastic coating for future high-energy

lithium-ion battery cathodes.

Figure 1
Atomic Layer Deposition of LixCoyOz Cathodic Thin Films for Li-Ion Batteries
Authors: Peisert Antoine , Adjeroud Noureddine , Lenoble Damien , Lamblin Guillaume
Published: February 2024

Atomic-Layer Deposition (ALD) is an appealing gas-phase technique for the deposition of thin solid cathodic films for 2D and especially 3D Li-ion microbatteries (Li-ion MBs). ALD relies on surface chemistry reactions and allows the fabrication of ultrathin pinhole free solid films with well controlled thickness, continuity and conformality. It has been shown to successfully cover 3D complex shapes for various applications including Li-ion MBs. Yet, a fairly low amount of work has been published on the realization by ALD of such cathodic active thin films. Typical cathodic materials are at least ternary compounds (including Lithium) which call for supercycles or multilayers approaches to synthesize them by ALD. As reminded for example by Maximov M. et al
1, the use of lithiated precursors complexifies the ALD fabrication due to, among others, Lithium high diffusivity and reactivity. In the case of LiCoO2 ALD synthesis for example, the only reported work to date is the one of Donders et al.
2 where the authors used CoCp2/LiOtBu as Cobalt/Lithium precursors respectively and O2 plasma as the oxidizing agent.

The talk will describe the synthesis and characterizations of the LixCoyOzthin filmspreparedby a thermal ALD approach. It will detail the supercycle methods used as well as some of the investigations performed to explore the chemistry of the deposited films (Raman spectroscopy, X-Ray Photoelectron Spectroscopy, X-Ray Diffraction and Energy Dispersive X-Ray). The electrochemical performances of the films will also be shared and compared with the State of the art.

1 Maximov, M.; Nazarov, D.; Rumyantsev, A.; Koshtyal, Y.; Ezhov, I.; Mitrofanov, I.; Kim, A.; Medvedev, O.; Popovich, A. Atomic Layer Deposition of Lithium–Nickel–Silicon Oxide Cathode Material for Thin-Film Lithium-Ion Batteries. Energies
2020, 13, 2345.

2 Donders, M. E., ArnoldBik, W. M., Knoops, H. C. M., Kessels, W. M. M., & Notten, P. H. L. (2013). Atomic layer deposition of LiCoO2 thin film electrodes for all-solid-state Li-ion micro-batteries. Journal of the Electrochemical Society, 160(5), A3066-A3071.
Precision Interface Engineering of CuNi Alloys by Powder ALD Toward High Thermoelectric Performance
Authors: Bahrami Amin , He Shiyang , Jung Chanwon , Zhang Siyuan , He Ran , Nielsch Kornelius
Published: February 2024

The main bottleneck in obtaining high-performance thermoelectric (TE) materials has been identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, we present a precise interface modification approach based on the powder Atomic Layer Deposition (pALD) technology to enhance the performance of CuNi alloys. Single-layer ZnO and Al2O3 layers have been deposited on the surface of powders, typically in 10-100 cycles, and their effect on the TE performance of bulks has been thoroughly investigated. A standard model is proposed and experimentally confirmed to build the relationship between the ALD oxide cycle numbers and Zn and Al content, which could be easily adapted to other pALD processes. The enhancement of the Seebeck coefficient, caused by the energy filtering effect, compensates the electrical conductivity deterioration due to the low electrical conductivity of oxide layers. Furthermore, the oxide layers may significantly increase the phonon scattering. Therefore, to reduce the resistivity of coating layers, a multiple-layer structure is deposited on the surface of powders by inserting Al2O3 into ZnO is constructed on. The atom probe tomography shows that after pressing, the Al atoms diffused into ZnO and realized the doping effect. Al diffusion has the potential to increase the electrical conductivity and complexity of coating layers. In comparison to pure CuNi, zT increased by 227.6% as a result of the decrease in resistivity and stronger phonon scattering in phase boundaries. The study demonstrates that ALD-based interface modification may be a versatile method for decoupling TE parameters and precisely modifying phase boundaries, which is practical for other thermoelectric materials.
ALD-Based Interface Engineering for Improving Electrical Conductivity of Nanoporous Thermoelectric Materials
Authors: Lee Seunghyeok , Jung Sung-Jin , Park Gwang Min , Baek Seung-Hyub , Kim Heesuk , Kim Jin-Sang , Park Tae Joo , Kim Seong Keun
Published: February 2024

The way to improve the performance of thermoelectric materials is to break the strong correlation between electrical conductivity and thermal conductivity. Combining porous structures with atomic layer deposition (ALD) is a promising strategy to solve this problem. The porous structure introduced into thermoelectric materials effectively lowers the lattice thermal conductivity, greatly increasing performance. However, the formation of nanopores is accompanied by a decrease in electrical conductivity. Here, we create nanoporous Bi0.4Sb1.6Te3 powder formed through selective dissolution from the mixture of KCl and Bi0.4Sb1.6Te3 powder. We propose a strategy to control carrier concentration by ALD of ZnO on nanoporous Bi0.4Sb1.6Te3 powder, thereby improving electrical conductivity and lowering thermal conductivity. Even after spark plasma sintering, ZnO is conformally formed at the nanoporous Bi0.4Sb1.6Te3 grain boundaries. The electrical conductivity increases from 651.72 S/cm to 724.52 S/cm by interfacial reaction of ZnO and Bi0.4Sb1.6Te3. In addition, ZnO inhibits grain growth and creates numerous grain boundaries to lower the lattice thermal conductivity of the porous structure. As a result, the ZT of the nanoporous Bi0.4Sb1.6Te3 deposited with ZnO is increased by 46%. This study demonstrates that ALD is an effective method for improving the conductivity of nanoporous thermoelectric materials.
Oxidative Molecular Layer Deposition of Conductive PEDOT Coatings Onto Polymer Sponges to Form Compressible Porous Electrodes
Authors: Young Matthias J. , Mehregan Mahya , Luebbert Gabe , Brathwaite Katrina G. , Wyatt Quinton K. , Throm Eric , Stalla David
Published: February 2024

The formation of compressible porous sponge electrodes is appealing to overcome liquid phase diffusion in electrochemical applications including energy storage, water desalination, and electrocatalysis. Previous work has employed wet chemical synthesis to deliver conductive materials into porous polymer sponge supports, but these approaches struggle to produce functional electrodes due to (1) poor electrical connectivity of the conductive network and (2) mechanical rigidity of the foam after coating. In this work we employ oxidative molecular layer deposition (oMLD) via sequential gas-phase exposures of 3,4 ethylenedioxythiophene (EDOT) and molybdenum pentachloride (MoCl5) oxidant to coat polyurethane sponges with electrically-conductive and redox-active poly(3,4 ethylenedioxythiophene) (PEDOT) coatings. We analyze the oMLD deposition on compressible polyurethane sponges and modify the reaction conditions to obtain mechanically compressible and electrically conductive sponges. We specifically identify the importance MoCl5 dose time to enhance the conductivity of the sponges and the importance of EDOT purge time to preserve the mechanical properties of the sponges. This approach produces an electrically conductive PEDOT network within the sponge support with minimal impact on the sponge’s mechanical properties, offering advantages over wet-chemical synthesis approaches. The compressible, conductive sponges we generate have the potential to be used as compressible electrodes for water desalination, energy storage, and electrocatalysis.
(Invited) Exploring New ALD Processes for Coinage and Transition Metals through Molecularly Engineered Precursors
Authors: Devi Anjana
Published: February 2024

Atomic layer deposition (ALD) of functional materials has gained significant interest during the recent years and a range of new materials has been introduced into semiconducting manufacturing since ‘materials-limited device scaling’ has replaced the days of ‘happy geometric scaling’. The ability to integrate very thin layers into silicon structures has opened the way for a variety of novel applications which enhances the functionality and flexibility for future nanotechnologies. For ALD, precursors are indispensable and there are continuous efforts to develop new or precursors with improved physico-chemical properties.

From the precursor engineering point of view, the concept is not only to synthesize one or more arbitrary members of a particular family of ligands, rather rationally introduce distinct changes in the ligand sphere in a systematic manner. This approach provides knowledge on the relationship between the molecular structure of the precursors, their thermal characteristics and reactivity. This presentation reveals how key precursor design parameters strongly influence the efficacy of ALD by comparing representative precursors possessing the same metal centre but different ligands or same ligand structure but different metal centres. Representative cases with coinage and transition metals will be illustrated. Alternative approaches to grow metal films and proof-of-concept applications will be demonstrated.
(Invited) Nucleation, Growth and Location Regulation of Heterogeneous Catalysts Synthesized by Atomic Layer Deposition
Authors: Qin Yong
Published: February 2024

For supported catalysts, the particle surface or metal-support interface and its vicinity are the main areas providing active sites. In this regard, surface and interface engineering of heterogeneous catalysts is effective and critical for optimizing their catalytic performances. During the formation of active components, the structural uniformity, stability and location of nucleation sites determine the structural and scale uniformity, stability and environmental consistency of active sites, and ultimately determine their catalytic performance. Therefore, the regulation of nucleation, growth and location of active components is the key to precisely regulate the surface and interface structure and properties of supported catalysts. However, traditional preparation methods (such as impregnation method and precipitation method) have limitations in precise regulation of particle size, location and microstructure of catalysts due to the surface heterogeneity of supports and the high surface energy of nanoparticles, which makes it difficult to reliably reveal the structure-activity relationship of the catalyst. Therefore, the development of advanced fabrication methods is of vital significance to realize the nucleation, growth and location regulation of heterogeneous catalysts at atomic level precision. Atomic layer deposition (ALD) is a powerful scientific tool for catalytic research due to its self-limiting, atom-by-atom growth features. However, there is still a lack of rational knowledge of the nucleation and growth mechanism of catalytic particles prepared by ALD, the microscopic mechanism of interface structure modification, and the catalytic reaction mechanism. This is the topic of this lecture, in which we discuss the latest progress made in our group in precisely regulating the microstructure, size and location of ALD-deposited active components by several effective methods including nucleation site engineering, deposition kinetics engineering and template-assisted ALD method, as well as elucidating the nucleation and growth mechanism of ALD-deposited active components by in-situ and operando XAFS characterization based on our designed and built ALD-XAFS device. Through the above works, the nucleation and growth mechanisms of the deposited species and modification species, the microscopic mechanism of interface structure modification, and the influence of the size effect, the interface effect, and the distance effect on the catalytic performance were clarified. The structure-activity relationship was understood at the atomic/molecular level. These works will provide new ideas and scientific basis for the catalyst design and the performance regulation.
Thermal Atomic Layer Deposition of Silicon Carbonitride: A Density Functional Theory Study
Authors: Chowdhury Tanzia , Choi Ye Rim , Kim Yewon , Kim Hye-Lee , Khumaini Khabib , Hidayat Romel , An Jae Seok , Seok Jang-Hyeon , Park Jung Woo , Lee Won-Jun
Published: February 2024

Silicon carbonitride (SiCN) films have received considerable attention due to their lower dielectric constant and better etch selectivity than silicon nitride (SiN) films [1]. Therefore, SiCN is replacing SiN in a variety of applications, such as dielectric barriers for copper interconnects or sidewall spacers for self-aligned contacts. SiCN films have been mainly prepared by plasma-enhanced chemical vapor deposition (PECVD) or plasma-enhanced atomic layer deposition (PEALD). However, plasma-based deposition techniques suffer from poor film quality and lack of conformability on high-aspect-ratio patterns. Thermal atomic layer deposition at high process temperatures can deposit high-quality thin films with excellent conformality. However, no studies have been published on thermal ALD in SiCN, while there are a few reports on PEALD in SiCN. In this work, we studied the thermal ALD process of SiCN by alternating exposures to a carbon-containing silicon precursor and NH3 and compared it with the thermal ALD of SiN processes using carbon-free precursors. Density functional theory (DFT) calculations were used to model and simulate the continuous ligand exchange reactions between the silicon precursor and the substrate surface. The carbon incorporation in the growing film when using carbon-containing precursors was predicted by DFT, which is in good agreement with the experimental observations.

Acknowledgments This work was supported by Hansol Chemical Co., Ltd.

References [1] C. Jung et al., J. Vac. Sci. Technol. A. 39 (2021).
(Invited) Sequential 3D Integration of Ge Transistors on Si CMOS
Authors: Ostling Mikael , Hellstrom Per-Erik
Published: February 2024

In order to keep the scaling progress going is to go 3D. This paper outlines some technology challenges and solutions to integrate Ge p-type MOSFETs sequentially on Si CMOS. Such a solution addresses the grand challenge to enable increased device density. However, the device itself does not have to scale but at the same time innovative solutions are suggested for low supply voltage operation enabling energy efficient integrated circuits (ICs) that will not be dominated by energy consumption in interconnects.

By stacking the transistors on top of each other, and connect them with inter-tier via, the density of transistors per unit area increases. This approach demands that transistors are fabricated at a lower temperature compared to today’s Si CMOS technology. Therefore, we have focused on Ge based transistors, which has an inherently lower process temperature compared to Si transistors.

In this paper several technological and design breakthroughs towards realizing Ge based sequential 3D circuits will be shown. We will present:

A process to realize thin single crystalline Ge layers on planarized wafers with metal layers in lower tiers.

A gate dielectric stack (Ge/Si/TmSiO/Tm2O3/HfO2/TiN) on Ge that enables adequately low defect densities at the dielectric/Ge interface allowing predictable and reliable Ge transistors

Fully depleted Ge pFET devices fabricated at a low temperature compatible with sequential 3D. The devices exhibits 60% higher mobility compared to reference Si devices.

3D digital circuits with pFETs on top of nFETs can enable area reduction by 30-50% depending on cell type.

3D standard cells with lower parasitic capacitance (~30%) compared to 2D cells, enabling lower dynamic power consumption and more energy efficient integrated circuits.
(Invited) Vertically Stacked Graphene Junction Diodes
Authors: Nagase Masao
Published: February 2024

Graphene is expected to be nanomaterial of the post-silicon era because of its numerous advantageous properties. The single crystal graphene thermally grown on SiC substrate is considered the most promising platform for future electric devices. Large area epitaxial graphene on SiC substrate has been successfully fabricated using high-temperature rapid thermal annealing [1]. In this study, we present vertically stacked graphene junction diodes fabricated using direct bonding technique [2–4].

Figure 1(a) shows the schematic of a stacked graphene junction diode. Two graphene layers on SiC are directly bonded to each other. Gold–coated contact pins are attached to the graphene surface to establish ohmic contact. The graphene samples and contact probes are fixed by acrylic molds. Strong nonlinear current–voltage (I-V) characteristics are observed for this simple device configuration, as shown in Fig. 1(b). In the low bias voltage (Vb) region, the resistance of the graphene diode is approximately 20 GΩ. The current abruptly increases when the bias voltage is increased to approximately 30 V. The two-terminal resistance at a high bias voltage (100 V) is approximately 21 kΩ. The vertically stacked graphene junction exhibits bidirectional thyristor-type characteristics with a high on-off ratio of approximately 106. The Fowler–Nordheim (F-N) tunneling phenomenon is observed in the sub-threshold region. The gap distance estimated from the F-N plot is approximately 6 nm, which can be attributed to the large off resistance. The Coulomb force generated by applying the bias voltage causes the two graphene layers to attract each other, resulting in an electrically conductive state. The junction voltage (Vj) of the device was measured using a four-terminal configuration. As shown in Fig. 1(c), negative resistance is observed in the low-resistance region. The effective internal resistance of the junction diode is reduced to approximately 450 Ω. The off resistance of the diodes is considerably modified by the initial distance between the graphene layers. However, the I-Vj characteristics in the negative resistance region are identical for each device. This result suggests that the cause of the negative resistance phenomena is closely related to the band structure of graphene.

A vertically stacked graphene junction diode with a high on-off ratio was demonstrated. The main component of the diode comprised a pair of single-crystal graphene layers fabricated through direct bonding. The negative resistance of the graphene diode presents new possibilities for the application of functional devices, such as terahertz emitters.

[1] T. Aritsuki, et al., Jpn. J. Appl. Phys. 55 (2016) 06GF03.

[2] J. Du, eta al., Jpn. J. Appl. Phys. 58 (2019) SDDE01.

[3] N. Murakami, et al., Jpn. J. Appl. Phys. 60 (2021) SCCD01.

[4] M. Ohi, et al., Jpn. J. Appl. Phys. 62 (2023) to be published.

Figure 1
(Invited) Optical Biosensors in Photonic Integrated Circuits for Smart System Integration
Authors: Steglich Patrick , Paul Martin , Mai Christian , Lecci Giulia , Weller Michael G. , Mai Andreas
Published: February 2024

Photonic integrated circuits (PIC) are like electronic integrated circuits drivers of communication systems. Moreover, state-of-the-art technologies enable the fabrication of electronic-photonic integrated circuits (ePIC), which allows for example the cointegration of ultra-fast BiCMOS devices with high speed photo detectors. Besides that, this technology provides an attractive platform for biosensors. They open the door for label-free detection of various analytes with high specificity and in real-time. This gives perspective to highly scalable and cost effective technologies for smart system integration of biosensors and electronic readouts to realize a true lab-on-a-chip application.

We present the integration of optical biosensors in a Si-based PIC-technology. This comprises a front-end of line with optical waveguides, an integrated Ge-photodiode and a complete back-end of line consisting of three thin and two thick aluminum metal layers. The optical biosensor is integrated by opening the optical waveguide from the backside of the chip. In particular, we released a Si-based slot waveguide, which provides an enhanced evanescent field to interact with the analyte and hence to increase the sensitivity. The slot waveguide is incorporated in a ring resonator and we analyzed the wafer-level performance using the full width at half maximum, which allows us to assess the optical losses. Thermal sensing in a wide temperature range is investigated. In addition, a simple and cost-effective microfluidic is realized and we show initial results of the surface functionalization. Our work demonstrates the compatibility of a photonic biosensor with a photonic integrated circuit technology without any restriction to the standard FEOL and BEOL processing on the wafer front-side, while it keeps the inherent high sensitivity of evanescent-field sensing and opens a route towards smart system integration.

Figure 1
Silicon-Germanium on Insulator CMP Slurry Designed with Oxidant and Accelerator Heading an Amine Functional Group for Remarkably Enhancing Polishing Rate
Authors: Han Manhyup Han , Kim Eun-Seong , Lee Kyung-Sik , Park Jea-gun
Published: February 2024

High quality single crystal silicon-germanium-on-insulator (SGOI) has a potential to enable the next generation

of photonic and electronic devices. However, to utilize an SGOI structure, a high SiGe-film polishing rate is

necessary (i.e., > 200 nm/min) for polishing the facet crystalline SiGe during the fabrication of SiGe on insulator

through epitaxial growth processes.

In previous studies, amine-based chemicals as SiGe-film polishing rate accelerators have been reported, but

there were limitations in increasing the SiGe-film polishig rate by considering only the chemical reaction of SiGe-

film surface. In this study, for the first time, both oxidant(i.e., H2O2) and accelerator with amine functional groups

(i.e., triethanolamine) were designed, resulting in a surprising increase in the SiGe-film polishing rate of 270

nm/min, as shown Fig. 1a.

The SiGe chemical mechanical planarization (CMP) mechanism was clearly demonstrated by precisely

investigating both chemical properties(i.e., GeO2 spectra intensity via X-ray photoelectron spectroscopy) and

mechanical properties(i.e., electrostatic repulsive force between colloidal silica abrasives and the SiGe-film via

electrophoretic light scattering). The remarkable enhancement of the SiGe-film polishing rate for oxidant and

triethanolamine was the result of (i) minimizing the loss of degree of SiGe surface oxidation, as shown Fig. 2, (ii)

enhancing degree of adsorption of the CMP slurry on the polished SiGe-film surface during CMP, and (iii)

decreasing the electrostatic repulsive force between colloidal silica abrasives and the SiGe-film surface, as shown

Fig 1b. Finally, successful removal of the facets in SiGe on insulator wafers was achieved, securing excellent

surface roughness characteristics. SiGe-film polishing mechanism and the SiGe slurry characteristics will be

presented in detail.

Figure 1
Recent Theoretical Advancement of Boron-Rich Compounds for Applications in High-Density Energy Conversion Devices
Authors: Liu Bin
Published: February 2024

Boron-rich compounds (IBCs) such as boron suboxide (B6O) and boron subphosphide (B12P2) are derived from the α-rhombohedral boron lattice with extreme hardness and unusual electrical properties. These compounds display an extraordinary self-healing ability to repair the lattice defects generated from exposure to high-energy irradiation. This unique ability will enable these boron-rich compounds to be deployed in nuclear battery devices for space or deep-sea exploration applications when coupled with their high hole mobility.

Synthesis and control of the stoichiometry of IBCs are the key technical challenge. For instance, the electrical properties of B6O are susceptible to specific B:O ratios. Thus far, the highest quality B6O crystals were obtained from high-pressure, high-temperature (HP-HT) experiments using mixed boron and boron oxide powders. Nevertheless, a mature synthesis protocol yielding consistent, high-quality B6O crystals has not been established.

In this talk, density functional theory (DFT) was used to understand how the structural, electronic, and thermodynamic stabilities of B6O (and other IBCs) are influenced by the interstitial elements and point defects at the icosahedral sites. Using the hybrid HSE functional, we confirmed that the perfect B6O bulk is a p-type semiconductor with a direct band gap of 2.8 eV. Furthermore, by screening the α-boron compounds systematically, we found that a simple octet rule may offer a consistent explanation for the variations in the computed electronic structures. Then, the thermodynamic calculations based on the DFT method predict that formations of interstitial defects become favorable only at higher temperatures.

To understand the self-healing property, the nudged elastic band (NEB) method was employed to identify the minimum energy pathways for the diffusions of dislocated B and O atoms. The diffusion of icosahedral B atoms has an energy barrier of 0.16 eV, confirming that the boron vacancies can be repaired with little kinetic limitation. Nevertheless, a substantially perturbed lattice requires more complex structural reorganization and thus incurs higher barriers (> 1 eV).

Lastly, reactive molecular dynamics simulations with a frozen core were performed to gain insights into the initial crystal nucleation process using a newly developed ReaxFF force field. For the first time, we can gain a molecular perspective on the formations of the boron icosahedra (B12) motif and the energetic profile. Such knowledge will aid the experimental design of IBC synthesis.
Thermal Atomic Layer Deposition of Gallium Nitride Films Using Tris(dimethylamido)Gallium and Ammonia
Authors: CHOI YeRim , Kim Okhyeon , Heo Jian , Kim Hye-Lee , Lee Won-Jun
Published: February 2024

Gallium nitride (GaN) is a III-V semiconductor material with a wide and direct bandgap, relatively high carrier mobility, and high breakdown voltage. GaN is suitable for applications in optoelectronic devices and power devices, including light-emitting diodes (LEDs) and high electron mobility transistors (HEMTs). Typically, epitaxial GaN layers are grown by metal-organic chemical vapor deposition (MOCVD) at high deposition temperatures. However, low-temperature growth of GaN is necessary for temperature-sensitive devices and substrates. Atomic layer deposition (ALD) is a technique that offers unique advantages, such as low process temperature, excellent conformality, and atomic-level thickness control.

In this study, we investigated the thermal ALD process of GaN at a low temperature of 200°C. Tris(dimethylamido)gallium (TDMAGa) was selected as the Ga precursor because tris(dimethylamido)titanium and tris(dimethylamido)aluminum were successfully adopted in the low-temperature ALD process of TiN and AlN thin films [1]. The growth and properties of ALD GaN films were investigated. ALD GaN films exhibited a self-limiting reaction with a deposition rate of 1.34 Å/cycle at 200°C, with a refractive index of 2.07. The saturation times for TDMAGa and NH3 pulses were 5 s and 30 s, respectively. Deposition at 250°C showed a deposition rate higher than 3 Å/cycle due to the thermal decomposition of TDMAGa. The ALD GaN film deposited at 200°C was amorphous and nitrogen deficient. To improve the crystallinity and composition, the as-deposited GaN films were annealed in an NH3 atmosphere in the deposition chamber without air exposure. The effects of annealing on the crystallinity and composition of the films were investigated.

Acknowledgments This work was supported by Samsung Display Co., Ltd.

References [1] J. Musschoot et al., Microelectron. Eng. 86 (2009). [2] A. I. Abdulagatov et al., Russ. J. Gen. Chem. 88, 1699 (2018).
(Invited) Two-Dimensional Low-Toxicity Absorbers for Efficient and Air-Stable Indoor Photovoltaics
Authors: Vivo Paola
Published: February 2024

The toxicity and bioavailability of lead (Pb) in halide perovskites motivates the search of Pb-free perovskite-inspired materials (PIMs), which would replicate the great optoelectronic properties of the traditional Pb-based counterparts. Among them, pnictohalides employing antimony or bismuth are especially attractive due to their low toxicity and inherent air stability. Their wide bandgaps (⁓2 eV) can broaden the application scenario beyond single-junction solar cells, being specifically suitable for e.g., silicon-perovskite tandems, indoor photovoltaics (IPVs), and photocatalysis.

Despite outstanding indoor power conversion efficiencies up to 60% have been theoretically predicted for PIM-based IPVs, this research is still in a very early stage. In this talk, I will highlight some of our key findings on two-dimensional Sb- and/or Bi- based two-dimensional pnictohalides for sustainable indoor light harvesting. The considerable presence of both intrinsic and surface defects in wide-bandgap PIMs is mostly responsible for the modest indoor power conversion efficiency (PCE(i)) reported so far up to ⁓5% at 1000 lux white LED illumination. I will discuss the effective defect mitigation strategies relying on compositional engineering that we proposed to significantly improve the PCE(i) up to nearly 10% (9.53%). Our extensive characterizations at both material and device level evidence the successful suppression of trap-assisted and interfacial charge recombination as the result of a reduced defect density within the PIM domains and/or at their surface.

The importance of our findings for the energy research community (within and beyond halide perovskite) lies in promoting future compositional design effort to reduce the defects in the next-generation wide-bandgap absorbers for eco-friendly energy generation and consumption.
(Invited) Atomic Layer Deposition as the Enabler for the Meta Stable Semiconductor InN and Its Alloys
Authors: Pedersen Henrik
Published: February 2024

Indium nitride (InN) is highly interesting for high-frequency and high-speed electronics given the remarkably high electron mobility in InN. The development of InN based electronics is hampered by the difficulty in depositing high quality thin films. The InN crystal breaks down to indium metal and nitrogen gas at about 500 °C which limits the deposition temperature, making conventional chemical vapor deposition (CVD) poorly suited for InN. Atomic Layer Deposition (ALD) is a low temperature, time-resolved form of CVD where the precursor gases are pulsed sequentially, separated by inert gas. This renders a deposition chemistry fully controlled by surface chemistry. We hypothesized around 2015 that the surface-controlled deposition of ALD will be beneficial for InN deposition and started our activities on ALD of InN.

I will describe our work on ALD of InN films where we have focused on ALD process development and design of new precursors. We now can show that ALD is an enabling technology for InN based electronics as it is capable of depositing a few nanometers continuous, epitaxial InN films.[1] I will describe our results on epitaxial growth of InN by ALD using our newly invented In precursor [2] and describe why we believe that the key to the success of ALD for InN is the dynamic gas exchange during the deposition.[3] I will also show our atomic scale understanding of the growth chemistry from quantum chemical modelling,[4] and how the results can be extended to InxGa1-xN.[5, 6]

References:

[1] Hsu et al. Direct epitaxial nanometer-thin InN of high structural quality on 4H–SiC by atomic layer deposition. Appl. Phys. Lett.
2020, 117, 093101.

[2] O'Brien et al. In Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Growth of Indium Nitride by Atomic Layer Deposition. Chem. Mater.
2020, 32, 4481.

[3] Hsu et al. On the dynamics in chemical vapor deposition of InN. J. Appl. Phys.
2021, 130, 135302.

[4] Damas et al. Understanding indium nitride thin film growth under ALD conditions by atomic scale modelling: From the bulk to the In-rich layer. Appl. Surf. Sci.
2022, 592, 153290.

[5] Rouf et al. In0.5Ga0.5N layers by atomic layer deposition. J. Mater. Chem. C
2021, 9, 13077.

[6] Hsu et al. Homogeneous high In content InxGa1−x N films by supercycle atomic layer deposition. J. Vac. Sci. Technol. A
2022, 40, 060402.
(Invited) GaN Photoconductive Semiconductor Switches for Efficient High-Voltage Power Conversion Applications
Authors: Koehler Andrew , Foster Geoffrey , Leach Jacob , Udwary Kevin , Splawn Heather , Hobart Karl D. , Anderson Travis J.
Published: February 2024

Gallium nitride (GaN) photoconductive switch (PCSS) technology can revolutionize high-voltage, efficient power-switching capabilities. PCSSs are optically driven, which advantageously isolates sensitive control circuitry from electromagnetic interference (EMI) resulting from rapidly switching high voltages and currents (high dI/dt or dV/dt). Fast switching times and extremely low on-resistances are achievable in PCSSs. The conductive channel region during on-state (under illumination) also serves as the voltage hold-off region in the off-state (dark) and does not require an additional drift layer that limits conventional unipolar device performance. In addition, the on-state resistivity can be further reduced by increasing the driving optical power density. Carbon-doped GaN (GaN:C) can result in extremely low dark currents, high blocking voltages, as well as support very low on-resistances.

Lateral and vertical GaN PCSSs are fabricated. Lateral GaN:C PCSS structures consist of a 4 µm thick GaN:C layer grown by metal organic chemical vapor deposition (MOCVD) on a SiC substrate. Vertical GaN:C PCSS structures consist of a 100 µm thick GaN:C layer grown by hydrive vapor phase epitaxy (HVPE) on a native GaN substrate. Contacts were formed by evaporation of Ti/Au (25 nm /250 nm). The PCSS devices are driven with a 3 W commercial off-the-shelf (COTS) ultraviolet (UV) light emitting diode (LED) with peak output at 365 nm and a 10 nm full width half maximum.

Vertical GaN PCSSs demonstrate exceptional on-state characteristics with an on-state current density of ~150A/cm2
, or an on-state resistivity of 66 mΩ-cm2. The off-state (dark) blocking capability exceeds 1 kV (maximum value tested). The transient switching characteristics of GaN:C PCSS will be characterized, and discussion will be provided relating to device design and optical driving conditions, including GaN:C carbon doping density, GaN:C layer thickness considerations, design for reduced contact resistance, illumination power density, and illumination wavelength.
Exploring the Dielectric Properties of Lanthanide Oxide Thin Films
Authors: DeForest Tinsley Elizabeth , Bhansali Shekhar , Urban Frank K , Dong Dongmei , Lou Lihua , Agarwal Arvind , Pinzon Sofia , Derby Benjamin , Valdez James , Uberuaga Blas , Kreller Cortney R.
Published: February 2024

Lanthanide oxides play a crucial role in various applications, such as solid oxide fuel cells, catalysis, and electronics, and their dielectric properties are essential in determining their performance. Ellipsometry is a powerful technique that can provide high-precision information on the dielectric properties of lanthanide oxides. By determining parameters such as the refractive index, thickness, and extinction coefficient of lanthanide oxides, ellipsometry can aid in the design and optimization of lanthanide oxide-based devices and materials for various applications. Our research group is currently using ellipsometry (supported by other characterization techniques) to investigate the dielectric properties of lanthanide oxide thin films, aiming to obtain information about the optical constants, surface roughness, and thickness of the films. This research aims to provide insights into the fundamental properties of lanthanide oxide thin films. Our findings could contribute to the long-term development of more efficient lanthanide oxide-based materials. We present our current findings and discuss the future direction for continued efforts.