bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Atomic Layer Deposition of (Semi)Conductive Oxides for Photovoltaics and Mo(o)Re
Authors: Macco Bart 
Published: December 2024

(Semi)conductive oxides are a peculiar class of materials that combine optical transparency and (tunable) electrical conductivity, and are typically composed of combinations of In, Zn, Sn or Ga. These materials play a profound role in solar cells, but are also more and mo(o)re considered in memory, logic, photonics and sensing. When they are highly (degenerately) doped, these materials can act as transparent conductive window layers (e.g. in solar cells), and are often referred to as Transparent Conductive Oxides (TCOs). Conversely, for lowly-doped (non-degenerate) semiconductive oxides, the Fermi level is susceptible to external influences. The electrical conductivity can then be modulated, for example by gating in a transistor or gas exposure in a sensor. Often amorphous alloys such as InGaZnO are used, and the more common term is hence amorphous oxide semiconductors (AOS).
Especially since the early 2000s, many ALD processes for doped and compound (semi)conductive metal oxides have been developed. The interest in ALD for preparing these oxides can most likely be attributed to the distinct merits of ALD, such as low-temperature processing, excellent uniformity and conformality, and accurate control over the doping level and composition. Moreover, as device dimensions shrink the need for high-quality ultrathin materials becomes ever more important. These merits of ALD stem directly from the self-limiting nature of the surface chemistry that drives the ALD growth. On the other hand, the strong role that surface chemistry has in the growth mechanism brings in many intricacies, and detailed understanding of these aspects has been vital for the development of high-quality doped and compound oxides by ALD. Examples of growth effects that can occur during ALD of compound oxides include growth delays, clustering of dopants and interruption of grain growth by doping. Such effects often need to be accounted for or mitigated, while on the other hand there are also clear cases where such growth effects can be leveraged to achieve enhanced or new functionality.
Recently, we have reviewed these aspects, focusing on how such underlying ALD mechanisms relate to the resulting performance of the (semi)conductive oxide.[1] In this contribution, we apply these learnings to the application side, specifically looking at silicon and perovskite (tandem) solar cells and back end of line-compatible transistors for nanoelectronics. While these application areas are seemingly distinct, many learnings and parallels can be drawn from an ALD point of view. Topics that will be covered include (1) isotropic doping vs. nanolaminates, (2) advanced ALD (super)cycles, (3) soft deposition, (4) crystallinity control, (5) ultrathin films and more. We will highlight these aspects through case studies, drawing from our own recent work as well as examples from the field.
[1] B. Macco, W.M.M. Kessels, Atomic layer deposition of conductive and semiconductive oxides, Appl. Phys. Rev. 9 (2022) 041313.

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(Invited) Surface Analysis of GaN by Cyclic Etching Process for ALE of III-V Materials
Authors: Sekine Makoto 
Published: December 2024

In the fabrication of next-generation power electronic devices based on the III-V materials i.e. gallium nitride (GaN), AlGaN, etc., atomic layer etching (ALE) with the cyclic process of ion irradiation and Cl adsorption steps has been attracted for the reduction of plasma induced damages and the precise definition of etch depth. For controlling the GaN ALE, we investigated the surface layer of GaN at each Ar ion and Cl radical reaction step using a beam experiments with in situ X-ray photoelectron spectroscopy (XPS).[1,2]
Samples were GaN films on a sapphire substrate by Hydride Vapor Phase Epitaxy (HVPE) method. Native oxide on GaN surface was removed by wet cleaning (5% HF) and Ar ion sputtering before the beam experiments. The wet cleaned surface was exposed to Cl radicals generated in Cl2 gas plasma. Then, Ar ions were irradiated with the accelerating voltage of 100 V or 200 V.
The one cycle consisted of these Cl radical exposure and Ar ion irradiation. To stabilize the GaN surface, five cyclic processes were carried out. The GaN surface at each step was analyzed by angle-resolved XPS with the take-off-angles (TOA) of 20, 30, 40, 60, and 90 degrees with respect to the wafer surface. The depth profiles were analyzed by the maximum entropy method.
In the GaN cycle process by Cl adsorption and Ar ion irradiation, the reaction in the Cl adsorption step is saturated at the order of 1019 cm−2. The reaction in the Ar ion irradiation step was saturated by Ar ion irradiation of the order of 1016 cm−2, and the formation of Ga dangling bonds occurred with the etching of Ga chloride and the desorption of N atoms. Increasing the Ar ion energy increased the amount of Ga dangling bonds formation and the subsequent increase of Cl adsorbed amount by the radical irradiation. At the same time, higher the Ar ion energy, higher the required doses of Cl and Ar ions to saturate the reaction in each step.
The Cl adsorption behavior was depended on the depth profile of the Ga dangling bonds and varied with Ar ion energy. At 47.6 eV, which is below the energy of GaN ALE window, the Ga chloride could not be desorbed, but ions in this energy break Ga-N bonds and desorb N atoms. At 86.8 eV, which is the energy band of the ALE window of GaN, Ga chloride and N atoms can be desorbed, and it was confirmed that the Cl adsorption behavior depends on the ion energy. From these results, it is considered that the Cl adsorption depth and etching depth continue to change even in the energy band of the ALE window.
Consequently, to achieve a higher Synergy and precise etching of GaN, tuninng of ion energy beside the ALE window should be necessary.
Acknowledgement
The author thanks Drs. Masaki Hasegawa, Takayoshi Tsutsumi, Kenji Ishikawa, Masaru Hori, Hiroki Kondo, Shouhei Nakamura, Atsushi Tanide, Souichi Nadahara, Osamu Oda, Jia He for their discussions and providing the data.
[1] T. Takeuchi et al., J. Phys. D: Appl. Phys. 46, 102001 (2013).
[2] Y. Zhang et al., J. Vac. Sci. Technol. A 35, 060606 (2017).
Molecular Dynamics Simulation of Bubble Formation in Confined Water in Si/SiO2 Nanochannels
Authors: Taghavi Nasrabadi Amir , Nishikido Shuuichi , Simms Ihsan , Nakamori Mitsunori 
Published: December 2024

Megasonic-based techniques are employed in the etching and cleaning processes in the semiconductor industry since they are gentler than other cleaning techniques and less apt to cause damage. In these processes, sound waves, at a frequency of 1 MHz or higher, are sent into etching or cleaning fluid, which could result in the formation of bubbles inside the fluid, revealing features and producing patterns. The formation and collapse of bubbles in nano-scale features is of interest in the semiconductor industry due to the potential effects on etching performance and surface roughness. Our understanding is still limited, however, because of the dimensions involved. Typically, the bubble size is too small, and the duration of bubble formation/collapse is too short, to allow easy study of the characteristics of bubble formation or collapse through experimental methods. Molecular dynamics (MD) simulation is a powerful tool to simulate such a phenomenon, which can facilitate understanding of bubble behavior in a confined space, and in the vicinity of the surface.
In this work we use MD simulations to simulate bubble formation in confined water in silicone (Si) and silicon dioxide (SiO2) nanochannels. Our focus of study is to identify the mechanism type for bubble formation in these nanofeatures, and determine how the surface characteristics, including the wettability, influence bubble formation. Figures 1a and 1b show the simulation results of bubble formation in confined water in the Si and SiO2 nanochannels, respectively. Our results show that the bubble forms on the hydrophobic Si surface, indicating a heterogeneous bubble formation, while for the hydrophilic SiO2 surface, the bubble tends to form away from the surface and in the bulk of the liquid, indicating a homogeneous bubble formation. In a hybrid situation where both the hydrophobic Si and hydrophilic SiO2 surfaces are present (Figure 1c), heterogenous bubble formation is dominant and the bubble forms on the Si surface. Our work provides insights into the mechanism of bubble formation in the confined water in nanofeatures and how surface wettability affects it.
(Invited) Ultra-thin Oxide TFTs and Related Instabilities
Authors: Kim Junghwan , Song Minju , Kim Soohyun , Shin Hyoseon , Yeom Jiho 
Published: December 2024

Keywords: Amorphous oxide semiconductors, Ultra-thin oxide TFTs, NBTS, PBTS
Recently, amorphous oxide semiconductors have attracted much attention for BEOL-compatible electronics such as next-generation memory applications (e.g. 2T0C). For practical use of oxide TFTs in BEOL-compatible electronics, ultra-thin channel thickness is essential. However, we have recently discovered that the well-known reliability issues such as negative bias temperature stress (NBTS) and positive bias temperature stress (PBTS) become more serious in ultra-thin oxide TFTs. In this respect, we investigated on how channel thickness relates with the instabilities in this study. As seen in Fig.1, PBTS instability becomes worse with the decrease in channel thickness. It is discovered that back-channel trap states are critical to PBTS instabilities, and such a back-channel effect appears more seriously when the channel thickness decreases. More details including experimental evidence and TCAD simulation results will be discussed at the conference.

Figure 1. Comparison of positive bias temperature stress (PBTS) test results of IGZO TFTs with different channel thickness (7, 15, 20, 30, 40, 60 nm).

References:

Shiah, Yu-Shien, Kihyung Sim, Yuhao Shi, Katsumi Abe, Shigenori Ueda, Masato Sasase, Junghwan Kim, and Hideo Hosono. "Mobility–stability trade-off in oxide thin-film transistors." Nature Electronics 4, no. 11 (2021): 800-807.

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(Invited) Emerging Two-Dimensional Materials for Device Applications
Authors: Lou Jun 
Published: December 2024

Two-dimensional (2D) materials, such as Graphene, h-BN and MoS2, are promising candidates in a number of advanced device applications, owing to their exceptional electrical, optical and mechanical properties. Scalable growth of high quality 2D materials is crucial for their adoption in technological applications the same way the arrival of high-quality silicon single crystals was to the semiconductor industry. While CVD growth of wafer-scale monolayer graphene and TMDs has been demonstrated, considerable challenges still remain. In this talk, we first report a CVD method to grow fluorine rich 2D polymer (2DP-F) on varies substrates for low-k dielectrics in 2D TMDs based devices. Using precursors with low vaporize temperature, a uniform and ultra-flat 2DP-F film with controlled thickness can be deposited on silicon oxide wafer, glass, sapphire and mica substrates. Dielectric properties and relevant mechanical properties were carefully characterized. These 2DP-F films were then used as the substrate for transition metal dichalcogenides (TMDs) based devices, and significant improvements in device performances were found, possibly owing to the ultra-smooth and dangling bond free surface of 2DP-F that can significantly reduce the interfacial scattering of carriers.
Next, we show that atomically thin Cs3Bi2I9, an all-inorganic lead-free perovskite derivative with strong optical activity can be successfully synthesized by vapor growth method. Reducing the dimensionality of such perovskites could utilize the materials’ advantages for solid-state information devices like valleytronics. By breaking the inversion symmetry, 2D Cs3Bi2I9 flakes with odd-layer number exhibited persistent, optically addressable valley polarization. This study potentially opens generalizable CVD method for growing a broad range of 2D perovskites towards cost-effective and energy-efficient integrated device applications. Finally, we report a two-step vapor phase growth process for the creation of high-quality vdW heterostructures based on perovskites and TMDCs, such as 2D Cs3Bi2I9/MoSe2, with a large lattice mismatch. Supported by experimental and theoretical investigations, we discover that the Cs3Bi2I9/MoSe2 vdW heterostructure possesses hybrid band alignments consisting of type-I and type-II heterojunctions because of the existence of defect energy levels in Cs3Bi2I9. More importantly, we demonstrate that the type-II heterojunction in the Cs3Bi2I9/MoSe2 vdW heterostructure not only shows a higher interlayer exciton density, but also exhibits a longer interlayer exciton lifetime than traditional 2D TMDCs based type-II heterostructures. Such vdW heterostructures provide promising platforms for exploring novel physics and cutting-edge optoelectronics and valleytronics applications.
A New Patterning Method of SnO2-Based Transparent Conductive Oxide Films By Two-Step Wet Processes Using Reduction in Gluconic Acid Aqueous Solution
Authors: Ogawa Daisuke , Namiki Hiromasa , Miyashita Yuito , Isoda Kazutaka 
Published: December 2024

In order to realize a sustainable, recycling-oriented society, it is intrinsically important to develop new technologies to substitute rare elements with elements abundant in resoueces, to save energy, to introduce renewable energy, or recyce the devices.
Transparent conductive oxide (TCO) films are essential materials for transparent electrodes in clean energy production sources (solar cells) and energy-saving devices (liquid crystal displays, light-emitting diodes, etc.). Indium tin oxide (ITO) is currently the most widely used TCO film. However, ITO is mainly composed of indium, a rare-earth. From the perspective of the SDGs, there is a strong need to promote the use of alternative materials to ITO, that are mainly composed of elements abundant in resources and can also be recycled.
Tin dioxide (SnO2) is a TCO film in practical use during more than half a century. It is mainly composed of tin (Sn), which is abundant in resources, and has excellent weatherability and chemical resistance. It is used in solar cells, heater glass to prevent fogging, and viewing windows of analyzers. If SnO2 can replace ITO, it will have a very large impact on the realization of a recycling society.
TCO films are generally patterned when used as transparent electrodes. ITO films can be easily patterned by wet processes using commercially available etchants the photoresist masks fabricated by photolithography. In contrast, SnO2 films are quite difficult to pattern by wet processes due to its high chemical resistance. SnO2 films are mainly patterned by dry processes, such as laser processing or sandblasting. However the former is expensive in cost, and the latter may cause substrates to break after shipping. If SnO2-based TCO films can be patterning by wet process, it will directly lead to improved throughput, cost reduction, and lower product defect rate, and will be a step forward toward the major goal of replacing ITO.
We developed a new patterning method of SnO2-based TCO films by two-step wet processes. In the first step, the SnO2 was reduced to metallic Sn by applying voltage in gluconic acid aqueous solution (Figure 1). The reduction to Sn was confirmed by X-ray diffraction measurements. Cross-sectional observation by a scanning electron microscope (SEM) revealed that reduction proceeds from the surface of the SnO2 film toward the inside.
In the second step, Sn was removed by acid, base, or electrolysis. The complete removal of the SnO2 film was confirmed by SEM and energy-dispersive X-ray spectroscopy. In addition, transmittance and reflectance of the glass substrate after removal of SnO2 film were measured.
It was found that patterning SnO2-based TCO films in the micrometer order scale is possible by combining the developed two-step method with the photoresist masks fabricated by photolithography.

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(Invited) Improving Resilience of Wide Bandgap Electronics
Authors: Rasel Md Abu Jafar , Al-Mamun Nahid , Haque Amanul , Wolfe Douglas , Ren Fan , Pearton Stephen J 
Published: December 2024

Wide-bandgap electronics operate at much higher voltages and frequencies compared to silicon counterparts. They are more resilient as well, being able to withstand much higher electrical field and temperature. However, a gap remains between their potential and measured performance and reliability. This gap is typically sought to be closed by perfecting materials synthesis and device fabrication processes.
In this presentation, we offer a different perspective by focusing on the residual defects and stresses that are localized in these devices. Typically, average values of such stresses are not high enough to draw attention. However, the core contribution of this research is to highlight that the localized values can be deceptively high to impact the device properties even though their global average could be negligible. We study SiC, Ga2O3 diodes and AlGaN/GaN high electron mobility transistors (HEMTs) to show that mechanical confinements lead to enhanced radiation vulnerability and accelerated ageing degradation. The reverse is also true; removal of the confined stresses leads to enhanced performance. We will present some extreme examples where we rejuvenate the degraded devices to demonstrate the resilience achieved from the ability to control defects and microstructures. Rejuvenation is achieved through a unique room temperature, ultrafast processing technique that requires only the electrodes, hence it can be performed in-operando. We exploit high resolution techniques such as transmission electron microscopy (TEM) and micro-Raman spectroscopy to spatially resolve the stress field in GaN HEMTs to demonstrate the localization effects on degradation.
Stacking Fault Analysis for the Early-Stages of PVT Growth of 4H-SiC Crystals
Authors: Hu Shanshan , Chen Zeyu , Cheng Qianyu , Raghothamachar Balaji , Dudley Michael 
Published: December 2024

With wide band gap, high thermal conductivity, and high breakdown field, silicon carbide, typically 4H-SiC, has steadily become the material of choice for next generation high-power electronic devices[1]. However, the presence of defects especially dislocations and stacking faults (SFs), such as threading screw dislocations (TSDs), threading edge dislocations (TEDs), threading mixed dislocations (TMDs), basal plane dislocations (BPDs), Frank dislocations, Shockley SFs and Frank SFs, are hindering the widespread application of 4H-SiC device due to their harmful effects on the reliability of high-performance SiC power devices[2]. In particular, SFs are particularly deleterious as they degrade the blocking and on-state conduction performance and/or reliability of devices[3].
A recent approach to lowering defect densities is to closely examine the early-stages of crystal growth when many defects are nucleated. Recently, we have reported on the expansion of Shockley stacking faults in the facet region during the early growth stage[4]. Continuing these early-stage studies, we seek to better understand the effects of various growth parameters on resulting defect structures, especially stacking fault formations. Multiple short duration growths have been carried out under varying conditions of nucleation temperature, thermal gradients, and N incorporation. In this study, three types of Frank type or Frank+Shockley stacking faults are observed distributed across the growth surface: Type A, stacking faults bounded by 2 opposite sign Frank type dislocations; Type B, stacking faults bounded by a pair of same sign Frank-type dislocations. As higher partial pressures of N2 are deployed, the occurrence of the Type B stacking fault is found to be suppressed (Figure 1); Type C, stacking faults regions shown as “carrot” defects on the as-grown surface of crystal (Figure 2). The formation mechanisms of these stacking fault formation will be suggested. The implications of these observations to achieve better control of the PVT growth process and resultant defect reduction will be discussed.

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Photosensitive Adhesive Bonding between Laser Diode and Optical Nonreciprocal Device
Authors: Yokoi Hideki , Ikeda Hiroki 
Published: December 2024

INTRODUCTION
In optical communication systems, optical nonreciprocal devices such as optical isolators or optical circulators are indispensable for protecting active photonic devices from unwanted reflected light. In the near-infrared region, magnetic garnet crystals are necessary components of optical nonreciprocal devices because of their transparency and large magneto-optic coefficient. Active photonic devices consist of III-V compound semiconductors. Therefore, a novel integrating technology must be developed for integration of a semiconductor laser diode and an optical isolator employing magnetic garnet crystals. In this paper, the authors report on an integrating technique between a laser diode and an optical isolator by means of photosensitive adhesive bonding.
DEVICE STRUCTURE
Figure 1 shows a laser diode integrated with an interferometric optical isolator by photosensitive adhesive bonding. The optical isolator employing a nonreciprocal phase shift has a magneto-optic waveguide with a (CeY)3Fe5O12 (Ce:YIG) layer. The nonreciprocal phase shift occurs in TM modes that travel in magneto-optic waveguides in which magnetization is aligned transverse to the light propagation direction in the film plane. An optical interferometer is comprised of two multimode interference couplers, nonreciprocal phase shifters in two arms and a reciprocal phase shifter in one of the arms. The reciprocal phase shift is obtained by an optical path difference between the two arms. An external magnetic field is applied to two arms in the interferometer in order to achieve a push-pull nonreciprocal phase shift.
The magneto-optic waveguide includes the magnetic garnet layer as either a guiding layer or a cladding layer. When the refractive index of the strip is less than that of Ce:YIG, the magneto-optic waveguide has a Ce:YIG guiding layer. On the other hand, when the refractive index of the strip is more than that of Ce:YIG, the magneto-optic waveguide has a Ce:YIG cladding layer.
The coupling efficiency from an active layer of the laser diode to a guiding layer of the optical isolator was calculated by use of beam propagation method.
Photosensitive adhesive bonding between III-V compound semiconductors and magnetic garnet crystals was studied. The adhesive bonding of two planar substrates was successfully achieved with the heat treatment at 160°C. The adhesive bonding between a planar substrate and a nonplanar one with rib structures was also successful.
ACKNOWLEDGMENT
This work was partially supported by the SIT Research Center for Green Electronics.

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