bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
(Invited) Modified SAB Methods for Hybrid and All-Cu Bonding for 3D Integration below 200ºC
Authors: Suga Tadatomo , Otsuka Kanji 
Published: February 2024

Two methods of Surface Activated Bonding (SAB) will be proposed to enable low-temperature hybrid bonding for 3D integration.
A modified one involves surface activation processes using Ar fast-atom-beam bombardment with simultaneous co-sputtering of Si nano-adhesion layer, followed by sequential plasma irradiation with N2 radicals. These processes combine hydrophilic treatment and bonding in a low-vacuum chamber. The Si nano-adhesion layer and the sequential plasma treatment appear to enhance hydrophilicity, which enables low-temperature bonding of both Si oxides and Cu pads as hybrid bonding. Bonding in a low-vacuum environment helps to avoid void generation caused by air entrainment.
The other one is the standard SAB. But we will connect two device wafers not in a hybrid bonding but in all-Cu bonding. A small insulation layer surrounds the area around the Cu electrode on the wafers, while the rest is covered with Cu solid layers. These solid layers constitute the ground layer, power layer, or their paired layers and may contribute to heat dissipation when connected to thermal vias. The two wafers are connected only by bonding on the Cu electrodes and solid layers. The insulating parts around the Cu electrodes do not necessarily have to be bonded, and the gaps may be kept in a vacuum. Of course, the bonded surfaces need to be flattened, and a new division and layout design of the solid electrode will be required.
Cu-Cu direct bonding is possible at room temperature by applying the standard SAB directly. Of course, this requires bonding in an ultra-high vacuum condition, which inevitably reduces the throughput. However, room temperature bonding is overwhelmingly advantageous for bonding different types of devices and wafers. It is expected to become a powerful tool for 3D heterogeneous integration of devices in the future.

Figure 1
(Second Best Paper Award) Preferred Grain Orientation to Enhance Interdiffusion at Room Temperature in Atomic Diffusion Bonding: A Fundamental Study Using Ni and Cu Films
Authors: Kikuchi Shun , Goto Fuki , Shimatsu Takehito , Uomoto Miyuki 
Published: February 2024

Atomic diffusion bonding (ADB) of wafers using thin metal films is a promising process to achieve room-temperature wafer bonding [1,2]. During ADB processing, the bonding performance is enhanced by crystal lattice rearrangement, which occurs when two film surfaces mutually contact at room temperature. It is reasonable to infer that the degree of the interdiffusion of the two films at the bonded interface, including crystal lattice rearrangement, depends on the surface roughness and crystallographic grain orientation of the metal films used for bonding. For this study, after Ni film and Cu film were bonded using ADB, the interdiffusion at the bonded Ni/Cu film interface was examined quantitatively using values of saturation magnetization M
s. We assessed the effects of crystallographic preferred grain orientation on the interdiffusion thickness at the bonded interface.
The Ni film thickness was fixed at 20 nm, but the Cu film thickness was varied from 5 nm to 300 nm. For both films, Ta underlayer films were used. Surface roughness S
a, as estimated using AFM of Ni(20 nm) film, was 0.25 nm. The value of S
a for Cu films increased from 0.21 nm to 0.85 nm as the Cu film thickness was increased from 5 nm to 300 nm. XRD findings revealed that both Ni and Cu films showed the (111) preferred grain orientation, but the orientation was degraded at Cu thicknesses of less than 50 nm. Figure 1 presents a STEM cross-section image of bonded Ni(20 nm)/Cu(50 nm) films as an example: no vacancy was observed at the bonded interface. Figure 2 presents values of the interdiffusion thickness T
ID for bonded films as a function of the Cu film thickness. T
IDshowed a maximum of 6.5 nm for a 50-nm-thick Cu film. S
a decreased as the Cu thickness decreased from 50 nm. However, T
ID decreased remarkably. Results suggest that deterioration of the (111) preferred grain orientation of Cu films with reduction of film thickness degraded the interdiffusion at the Ni/Cu bonded interface.
To support this assumption, Ti underlayers were used underneath Ni(20 nm) and Cu(10, 20 nm) films to enhance the degree of the (111) preferred grain orientation of these films. Results indicate that T
ID at the Ni(20 nm)/Cu(10 nm) bonded interface was enhanced to 5.4 nm, which was one order greater than that of the bonded films with Ta underlayers, indicating that enhanced bonding performance of ADB can be achieved with low surface roughness and a high degree of (111) preferred grain orientation. This enhancement is expected to be obtained also via ADB processing using other metal films having an fcc crystal structure, such as Au, Ag, and Al.

T. Shimatsu and M. Uomoto, J. Vac. Sci. Technol., B 28, 706 (2010).

T. Shimatsu and M. Uomoto, ECS Trans., 33 (4), 61 (2010).

Figure 1
Atomic Diffusion Bonding in Air Using Oxide Films
Authors: Shimatsu Takehito , Uomoto Miyuki , Fukunaga Hitomi , Makita Hiroyuki , Suzuki Yudai , Kozuka Yuhei , Muraoka Arina , Saito Takayuki 
Published: February 2024

Atomic diffusion bonding (ADB) of wafers is a promising process to achieve room-temperature wafer bonding [1]. For ADB processing, thin films are fabricated on two flat wafer surfaces using sputter deposition, with subsequent bonding of the two films on the wafers in vacuum. In addition to thin metal films [1], both oxide [2] and nitride [3] thin films are useful for bonding.
For this study, after demonstrating ADB “in air” using oxide films, we compared the resultant bonding performance to that obtained using ADB “in vacuum” with the oxide films. Table 1 presents the surface free energy values at the bonded interface γ for quartz glass wafers bonded using 5-nm-thick Y2O3 film on each side. Using ADB in vacuum, great bonding strength was achieved for as-bonded wafers: the blade could not be inserted between the wafers. Using ADB in air, γ for as-bonded wafers was small, only 0.25 J/m2, but low-temperature annealing at 150 °C enhanced γ to 1.6 J/m2. At 200 °C, γ becomes greater than 2 J/m2. The annealing was conducted in air using a hot plate. Figure 2 portrays STEM cross-section images of Y2O3(5 nm)/Y2O3(5 nm) films (A) bonded in vacuum (as-bonded) and (B) bonded in air (annealed at 150 °C). The bonded interface is not visible in image (A). However, a slightly low-density bonded interface is partially visible in image (B). The difference of the bonded interface structure is consistent with that of γ presented in Table 1.
Various oxide films such as TiO2, ITO, SiO2, and WO3 are useful for ADB in air, as is true also for ADB in vacuum, although post-bonded annealing at a low temperature of 150 °C is necessary for ADB in air to achieve γ greater than 1 J/m2. The bonding process of ADB in air is more convenient to execute than that in vacuum. Moreover, any mirror-polished wafer can be bonded using ADB in air, as is true also using ADB in vacuum. It is likely that H2O gas in air can adsorb on the fresh surface of oxide films efficiently and that well-hydrophilic films surfaces can be obtained easily when the deposited oxide films are removed from the vacuum chambers; in fact, low-temperature annealing at 150 °C enhanced γ remarkably. ADB in air using oxide films is useful for some applications if post-bonded annealing at low temperatures is acceptable for bonding processes.

T. Shimatsu and M. Uomoto, ECS Trans., 33 (4), 61 (2010).

T. Shimatsu, H. Yoshida, M. Uomoto, T. Saito, T. Moriwaki, N. Kato, Y. Miyamoto, and K. Miyamoto, Proceedings of Seventh LTB-3D 2021. p.51 (2021).

M. Uomoto, H. Yoshida, T. Shimatsu, T. Saito, T. Moriwaki, N. Kato, Y. Miyamoto, and K. Miyamoto, Proceedings of Seventh LTB-3D 2021. p.45 (2021).

Figure 1
Improved Thermal Boundary Conductance in Annealed Direct Wafer Bonded Si-Ge
Authors: Huynh Kenny , Liao Michael Evan , Pfeifer Thomas , Yan Xingxu , Rebhan Bernhard , Floetgen Christoph , Pan Xiaoqing , Hopkins Patrick E , Goorsky Mark S. 
Published: February 2024

The evolution of structural and thermal properties of wafer bonded Si|Ge with annealing is investigated in this study. Theoretical work suggests that the thermal boundary conductance between amorphous Si and Ge provide improved thermal properties as compared to a crystalline Si to Ge interface, and wafer bonded systems provides a fabrication method to experimentally test this theory [1]. EVG® ComBond® equipment was used for bonding under high vacuum (~10-8 mtorr) at room temperature to remove unwanted native surface oxides [2-4]. The bombardment of the surfaces prior to bonding produces an amorphous region at the bonded interface that has been seen in many other bonded systems [5,6]. In the as-bonded sample, high resolution scanning transmission electron microscopy revealed a ~1.2 nm amorphous region at the bonded interface. Subsequent annealing was done in an effort to recrystallize the amorphous interface. Previous work has shown that recrystallization between Si|Si wafer bonded samples occurred when annealed at 450 °C for 12 hours [3]. After annealing at 600 °C for 2 hours, the amorphous interface was observed to decrease to ~0.9 nm. Complete recrystallization is observed when the sample was annealed at 600 °C for 48 hours.
Preliminary thermal results show that the thermal boundary conductance (TBC) of the as bonded sample is 47 ± 5 MW/(m2K). The TBC for the sample annealed at 600 °C for 48 hours is 94 ± 5 MW/(m2K), an improvement by a factor of two compared to the as-bonded interface. These results demonstrate that the TBC can be improved through annealing of the interface and that improvements due to an amorphous-amorphous interface do not dominate the thermal boundary conductance in this system. We consider that the improvements are due to recrystallization of the interface and/or to increased interdiffusion, which has been observed to increase TBC in epitaxially grown Si-Ge interfaces [7].

K. Gordiz, et al., J. Appl. Phys., 121(2), p.025102 (2017)

V. Dragoi, et al., ECS Trans., 86(5), 23 (2018)

C. Flötgen, et al., ECS Trans., 64(5), 103 (2014)

M.E. Liao, et al., ECS Trans., 86(5), 55 (2018)

Y. Xu, et al., Ceramics International, 45, 6552 (2019)

F. Mu, et al., Appl. Surf. Sci., 416, 1007 (2017)

Z. Cheng, et al., Nature communications, 12(1), p.6901 (2021)

Figure 1
(Invited) Wafer Bonding for MEMS Integration and Packaging
Authors: Niklaus Frank , Jo Gaehun , Edinger Pierre , Gylfason Kristinn B. , Bleiker Simon J. 
Published: February 2024

Wafer bonding is a critical manufacturing process for a vast number of experimental and commercial microelectromechanical system (MEMS) devices [1-5]. Wafer bonding is used for both the hermetic sealing of MEMS [3-5], and for integrating MEMS with electronic integrated circuits (IC) [1-2]. In this invited talk we present recent examples of wafer bonding approaches targeted at hermetic sealing of emerging MEMS devices such as silicon photonic MEMS [3, 4]. In these processes, the MEMS are sealed by wafer bonding and transferring individual lids, while at the same time keeping the final total die thickness as thin as possible. Furthermore, we also present examples of wafer bonding techniques targeted at integrating MEMS or nanoelectromechanical systems (NEMS) directly on top of electronic integrated circuits (IC), thereby closely packaging the MEMS devices with the electronic circuits that provide an interface to the outside world [1-2]. Ultimately the presented wafer bonding approaches can contribute to further miniaturization and thickness reduction of the final packaged MEMS components.

REFERENCES

[1] Fischer, A.C., Forsberg, F., Lapisa, M., Bleiker, S.J., Stemme, G., Roxhed, N. and Niklaus, F., 2015. Integrating mems and ics. Microsystems & Nanoengineering, 1(1), pp.1-16.
[2] Lapisa, M., Stemme, G. and Niklaus, F., 2011. Wafer-level heterogeneous integration for MOEMS, MEMS, and NEMS. IEEE Journal of Selected Topics in Quantum Electronics, 17(3), pp.629-644.
[3] Jo, G., Edinger, P., Bleiker, S.J., Wang, X., Takabayashi, A.Y., Sattari, H., Quack, N., Jezzini, M., Lee, J.S., Verheyen, P. and Zand, I., 2022. Wafer-level hermetically sealed silicon photonic MEMS. Photonics Research, 10(2), pp.A14-A21.
[4] Edinger, P., Jo, G., Van Nguyen, C.P., Takabayashi, A.Y., Errando-Herranz, C., Antony, C., Talli, G., Verheyen, P., Khan, U., Bleiker, S.J. and Bogaerts, W., 2023. Vacuum-sealed silicon photonic MEMS tunable ring resonator with an independent control over coupling and phase. Optics Express, 31(4), pp.6540-6551.
[5] Wang, X., Bleiker, S.J., Edinger, P., Errando-Herranz, C., Roxhed, N., Stemme, G., Gylfason, K.B. and Niklaus, F., 2019. Wafer-level vacuum sealing by transfer bonding of silicon caps for small footprint and ultra-thin MEMS packages. Journal of microelectromechanical systems, 28(3), pp.460-471.

Figure 1
(Invited) Near-Field Optics and Its Applications in Nanophotonic Devices: A Review
Authors: Wong Victor , Fanchini Giovanni 
Published: February 2024

In our presentation, we will offer an overview of aperture-type scanning near field optical microscopy (SNOM) – a family of nano-optical imaging techniques derived from scanning probe microscopy which are capable of subwavelength resolution, and the development of three dimensional (3D) SNOM methods undertaken by our group to locally image the distribution of the electromagnetic radiation in the proximity of nanoparticles and nano-objects.[1] We will discuss a few applications in which we took advantage of 3D-SNOM to design specific optical nanosystems for light harvesting device applications. Specific case studies that will be presented include the design of plasmonic thin-film solar cells enhanced by random arrays of copper nanoparticles,[2] and the use of 3D-SNOM for characterizing evanescent waveguides self-assembled from of copper nanoparticles assembled on thin films of graphene.[3] In the final part of our talk, we will we present near-field scanning thermoreflectance imaging (NeSTRI), a new pump-probe technique invented in our group (see Figure 1) in which an aperture-type SNOM is used to contactlessly determine the thermal conductivity of inhomogeneous thin films and low-dimensional systems at the nanoscale for heat-spreading and thermoelectric applications.[4,5] These examples well represent the versatility of SNOM imaging and its potential for designing an even wider family of nano-optical devices.
[1] P Bazylewski, S Ezugwu, G Fanchini, Applied Sciences 7 (2017) 973
[2] S Ezugwu, H Ye, G Fanchini, Nanoscale 7 (2016) 252-260
[3] T Ouyang, A Akbari-Sharbaf, J Park, R Bauld, MG Cottam, G Fanchini, RSC Advances 5 (2015) 98814-98821
[4] S Ezugwu, S Kazemian, DYW Choi, G Fanchini, Nanoscale 9 (2017) 4097-4106
[5] S Kazemian, S Ezugwu, G Fanchini, Proc. SPIE 10926, Quantum Sensing and Nano Electronics and Photonics XVI, 109260L (1 February 2019); doi: 10.1117/12.2509828

Figure 1