bluuebunny/crossref_metadata_2025 huggingface dataset:
What Happens to Repeatable Low TCE Copper with Annealing
Authors: Kondo Kazuo , Dinh V Quy
Published: December 2020

1. Introduction

Since the Copper resistivity is second lowest next to the Silver, the Copper electrodeposits have been very intensively used in the wiring for the semiconductor and the printed circuit board (PCB). The Copper problem is the thermal coefficient of expansion(TCE). The TCE of Silicon is 2x10-6(1/K) and the TCE of Copper is 18x10-6(1/K). If the composite of the Silicon and the Copper warpage, protrusion or delamination occurs. This discussion is focused on the low TCE Copper with repeatable annealing.

2. Results

1) Figure 1 shows the TCE comparison with our repeatable low TCE Copper and the conventional Copper. X-axis is the expansion length and y-axis is the temperature. For the conventional Copper, the TCE is 18x10-6(1/K) and the expansion length is linear with the temperature. However, for our repeatable low TCE Copper, the TCE is 6x10-6(1/K) and 1/3 of the conventional Copper. The TCE of 6x10-6(1/K) repeats three times. This TCE of 6x10-6(1/K) starts after two times pre-annealing.

2) Also we have run 200 cycles of -40℃ to 200℃ heat cycle test and measured the TCE and the resistivity. These TCE and the resistivity have been measured after 50,100,150 and 200 cycles.

The TCE up to 300℃ for 50, 100 and 150 cycles show constant value and the TCE is lower with 200 cycles. The resistivities of 50,100,150 and 200 cycles become even lower than as deposit of zero cycle.

The repeatable low TCE mechanism will be discussed at the meeting.

Reference

V. Q. Dinh and K. Kondo, ECS J.Solid State Sci. Technol., 6, P566-P569 (2017)

Figure 1
Understanding the Role of Electrochemically Inactive Substituent in Layered Oxide Cathode Materials for Advanced Sodium Ion Batteries
Authors: Yang Junghoon , Bak Seongmin , Teeter Glenn , Han Sang-Don
Published: December 2020

The importance of electrochemical energy storage systems for large-scale application has been growing increasingly over the last decades. Due to high cost, limited source and several technical barriers of the lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) are considered as one of promising candidates for large-scale energy storage systems based on their cost-effective, earth abundant and recyclable characteristics.[1] As promising cathode materials for SIBs, P2-type sodium iron manganese oxide with layered structures (Na
x
Mn
y
Fe1-y
O2, 0.5 < x < 0.8) demonstrates similar high energy density analogous to the LiBs.[2] However, the capacity retention of the cell with layered structure cathode is not optimized especially when it is charged and discharged with wide voltage window to obtain higher capacity. The major reason for this is a phase transition induced by gliding of transition metal slabs, which causes irreversible structural changes gradually during cycling.[3]

To address this phase transition issue, we introduce electrochemically inactive component (e.g., Mg2+) in the material. The introduction of the Mg2+ by substituting with existing transition metal(s) is able to provide improved capacity retention due to their enhanced structural stability. We systematically analyzed the capacity fading trends at high and low voltage regions, where each different transition metal dominantly contributes to the redox reactions, which provides mechanistic understanding of the structural degradation of P2-type NaxMnyFe1-yO2 and the effect of Mg2+ on transition metal redox behaviors. In addtion, by tracing the structural changes in the cathode, we demonstrated that the introduction of Mg2+ effectively abbreviates the unwanted phase transitions. The results can provide the insights of the phase transition mechanism and redox behaviors of layered type cathode materials and the strategies to stabilize the structure by employing electrochemically inactive substituent(s), thus enabling rational design of new cathode materials for the development of next generation SIBs.

[1] M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Adv. Funct. Mater. 23 (2013) 947-958.

[2] C. Delmas, C. Fouassier, P. Hagenuller, Physica B+C 99 (1980) 81-85.

[3] E. Talaie, V. Duffort, H. L. Smith, B. Fultz, L. F. Nazar, Energy Environ. Sci., 5 (2015) 2512.

Acknowledgement

J. Yang and S.-D. Han acknowledge funding support by the Laboratory Directed Research and Development (LDRD) program at National Renewable Energy Laboratory (NREL).

The work done at Brookhaven National Laboratory was supported by Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. DOE, through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704.
A Simulation Study on the Transient Leakage Current Analysis of a GaN Epitaxial Layer
Authors: Nishida Hirofumi , Kataoka Hiroaki , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki
Published: December 2020

GaN epitaxial layers on Si substrate are being used as semiconductors for power devices owing to its wide bandgap, a high breakdown voltage with low on-resistance [1]. Due to the presence of crystal defect both in energy and its depth profile, a transient behavior is commonly observed in the channel current. Some of characterization methods, including deep level transient spectroscopy (DLTS), can extract the energy levels with its depth profile, by adopting a Schottky electrode to the epitaxial layer. Therefore, the extracted profile is limited to the surface of the GaN layers. In this work, we conducted a simulation study to extract the defect density profile from a direct current obtained from a GaN epitaxial layer on Si substrate with an Ohmic contact electrode to the surface. While applying a step voltage to the electrode, the transient current was measured and characterized.

The proposed defect extraction method can be analytically expressed by the change in the depletion capacitance (ΔC) in the epitaxial layer upon a voltage of V applied to the electrode at t=0 as shown in equation (1).

Here, ε, Wo
d , W∞
d

,
q, N
d and N
t are the permittivity, depletion width at t=0, depletion width at steady state, doping density of the GaN layer and the trap density, respectively. The change in the charge accumulated to the electrode (ΔQ) can be written as the equation (2). Therefore, by the integral of the transient current, one can obtain the relationship between V and N
t, which can be transformed into the defect density depth profile of the epitaxial layer.

The simulated model is shown in fig. 1(a), where two GaN layers of each N
d=1016 /cm3 are stacked with in two metal electrodes. The area of the electrode is 0.1 mm2. Defect levels of E3 and E7 with a density of N
t,E3 and N
t,E7 are introduced in the top and bottom GaN layers, respectively. By applying a positive V to the Ohmic top electrode, the depletion width increases from the Schottky bottom electrode, depending on the N
d
. By the presence of E3 and E7, a transient current with a time constant depending on the defect levels is obtained as is shown in fig. 2(b). By obtaining the relationship between the ΔQ and the V, as shown in fig. (2), firstly we can extract the N
d of each layer from the change in the slope. The extract N
d values showed a nice agreement to the values set in the simulations. Also, from the ΔQ itself, we can deduce the N
t of each layer.

In conclusions, we have made a simulation of the transient current response of a stacked GaN layers with different defect levels. From the transient current integral, we can extract the doping density and the defect density of each layer.

References

[1] B. J. Baliga, Semicon. Sci. Tech., 28, 074011 (2013). [2] D.V. Lang, Journal of Applied Physics., 45, 3023 (1974)

Figure 1
2-Dimensional Ga2O3 Based Field Effect Transistor for Hydrogen Sensing Application
Authors: Kim Mankyung , Kim Yukyung , Baik Kwang Hyeon , Jang Soohwan
Published: December 2020

β-phase gallium oxide (β-Ga2O3) has attracted a lot of interest for the applications of high-power electronics, gas sensors, and solar-blind photodetectors. β-Ga2O3 is an alternative semiconducting material for high-power and high-temperature devices due to a large bandgap energy of 4.9 eV and high critical breakdown field (> 8 MV/cm). The Baliga’s figure of merit is 3400, which is 4-10 times higher than those of GaN and SiC. Ga2O3 based devices is expected to be more efficient with reduced size and high level of integration because the theoretical on-state resistance is almost one order magnitude lower than those of GaN and SiC devices at the same breakdown voltage. When compared to GaN and SiC, single crystal Ga2O3 wafers are available at low cost with floating zone and the edge-defined film-fed growth methods. The monoclinic β-Ga2O3 is the most stable form among five different crystal phases of Ga2O3. The large lattice constant of 12.23 Å of β-Ga2O3 along [100] direction enables to achieve the facile cleavage of β-Ga2O3 crystal into 2-dimensional flake though β-Ga2O3 is not a Van der Waals material. The thin channel of Ga2O3 flake is beneficial to the FET (field effect transistor) type gas sensor. In this study, the fabrication of 2-dimensional β-Ga2O3 flake based field effect transistor and its hydrogen sensing characteristics for hydrogen sensor application will be presented.
(Invited) from the Top or through the Edge: What Is the Most Scalable Contact to 2D Semiconductors?
Authors: Franklin Aaron D
Published: December 2020

The most common approach for establishing electrical contacts to 2D semiconductors, such as MoS2, is by fabricating metal contacts on top of the inert crystal surface. From an electron transport perspective, these top-contact interfaces can be awkward, with a van der Waals gap or some difficult-to-control form of interfacial bonding. Pure edge contacts (where the interface between the metal and 2D semiconductor occurs completely along the open bonds of the 2D crystal edge) provide a more natural bonding structure and potentially better carrier transport behavior; however, edge contacts have proven more difficult to realize. In this talk, recent success with establishing clean, pure edge contacts between metals and 2D semiconductors will be discussed, including an approach involving an in situ ion beam within a thin-film deposition system. Evaluation of these edge contacts compared to other approaches will be provided, along with demonstration of how edge-contact scaling affects the performance of 2D transistors compared to top-contact scaling. While there remains much to be learned about these interesting metal-2D edge interfaces, results thus far show significant promise for yielding a more scalable and potentially reproducible contact for 2D-based devices.
Low-Temperature Chemical Sintering Technique for Flexible Dye-Sensitized Solar Cells
Authors: Lung Quang Nhat Dang , Yoo Kicheon , Ko Kwan-Woo , Nath Narayan Chandra Deb , Lee Jae-Joon
Published: December 2020

Chemically sintered, mesoporous TiO2 electrodes were prepared at low-temperature (≤150 °C) using polymeric- binder free TiO2 paste consisting of binary-liquid mixture of 1-octanol and a series of chlorinated hydrocarbons (CHCs), such as carbon tetrachloride (CCl4), tetrachloroethylene (C2Cl4) or chloroform (CHCl3). In this work, CHCs were introduced to lower the boiling point of the mixture and to perform as an active agent for chemical treatment of TiO2 paste. Long chain alcohol 1-octanol increased the viscosity and diminished the surface tension of TiO2 paste to the hydrophobic surface of the substrate, which promoted the paste adhesion. A maximum power conversion efficiencies (PCEs) of c.a. 6.66 and 4.30% (under 1 sun illumination –100 mW cm-2) were obtained for the rigid dye-sensitized solar cells (DSSCs) with fluorine-doped tin oxide (FTO) and the flexible one with indium tin oxide-polyethylene naphthalate (ITO/PEN) substrates, respectively. Under LED daylight illumination, maximum PCEs of 10.10% at 3.39 mW cm-2 and 8.35% at 1.87 mW cm-2
have also achieved for DSSCs prepared on FTO substrate. The improved chemical bonding of particle network and strong adhesion to the substrates facilitated the electron transfer from TiO2 photoelectrodes to charge collectors, which played an important role for the significant enhancement of photocurrent density as well as PCE of DSSCs. The effect of CHCs on TiO2 is found to be a promising strategy to prepare well-connected TiO2 film for other applications.
Exploring the Effect of Double Additives in Mixed 2D/3D Sn-Based Perovskite Solar Cells
Authors: Sandhu Sanjay , Singh Ranbir , Lee Jae-Joon
Published: December 2020

Additive doping improves the tin (Sn)-based perovskite film morphology and ambient stability, however the function of additive in the perovskite film is limited, especially when two or more additives are used. In this study, the effect of double additives such as 2-phenylethylammonium iodide (PEAI) and ethylenediammonium diiodide (EDAI2) on the formamidinium tin iodide (FASnI3) films were explored. The perovskite film with only PEAI has showed several pinholes which is not suitable for ideal large area solar cell. While mixing of the two additives for an optimum concentration of PEAI (8 mol%) and EDAI2 (1 mol%) produced pinhole-free compact perovskite film with superior crystallinity, preferential orientation, low background charge carrier density, reduced trap states, and suppressed non-geminated recombination losses. The reduced dimensionality and favored perovskite layer stacking led to better interlayer coupling and increase charge transfer at interfaces. Consequently, a high-power conversion efficiency (PCE) of 8.47% and an open circuit voltage (V
OC) of 0.634 V were achieved for the perovskite solar cell (PSC) with mixed additive, and the fabricated solar cells exhibits excellent stability for 5 days in ambient conditions.
Towards Tm2+ in Sialon Thin Films Using the Gradient Deposition Method
Authors: Bosco Giacomo , van der Kolk Erik
Published: December 2020

There are different material candidates for efficient industry compatible luminescence solar concentrators to be used in electricity generating glass applications. Among them, divalent thulium (Tm2+) doping has been shown to have a high potential. It has been reported to have 65% absorption of the solar spectral range when in di-halide hosts, while showing no self-absorption and a relatively neutral color [1]. These characteristics are possible because Tm2+ has a strong absorption from the UV up to about 900 nm. This absorption is generated by intense 4f13 → 4f125d1 electronic transitions and a single emission line at 1140 nm, credited to the 2F5/2 → 2F7/2 transition of the 4f13 configuration. However, this specific oxidation state of thulium is rather anomalous: so far it was only stabilized on di-halide crystals. These crystals are very hygroscopic in nature, therefore not sufficiently attractive for scaling up in industry standard thin film growth techniques. Thus, it is necessary to research on the possible extension in the list of materials able to host such a promising optically active element. However, the intrinsic complex nature of the lanthanide’s electronic structure has prevented a detailed understanding of the valence stability of its elements. Therefore, designing industry compatible hosts ensuring that such exotic ion is stable and capable of efficiently emitting NIR light is a challenging task.

In this work, we show the progress made so far towards unraveling the conditions for stabilization of the Tm2+ in industry compatible thin film materials – more specifically, thin film materials of the SiAlON family. I report recent results on Tm doped SiAlON thin films grown by combinatorial magnetron reactive sputtering. The gradient characterization method [2], developed at the TU Delft’s luminescence materials research group, was used in order to relate position dependent film composition – determined by energy dispersive x-ray spectroscopy – with local transmission, photoluminescence emission and excitation data. This singular approach makes it possible to retrieve a wide composition range in a smaller number of different films. These results are discussed upon the valence stability model of lanthanides of Dorenbos [3], and the model of impurity ionization adopted in solid state statistics.

References

[1] O. M. ten Kate, K. W. Krämer, and E. van der Kolk, “Efficient luminescent solar concentrators based on self-absorption free, Tm2+ doped halides,” Sol. Energy Mater. Sol. Cells, vol. 140, pp. 115–120, Sep. 2015.

[2] E. P. J. Merkx and E. van der Kolk, “Method for the Detailed Characterization of Cosputtered Inorganic Luminescent Material Libraries,” ACS Comb. Sci., vol. 20, no. 11, pp. 595–601, Nov. 2018.

[3] P. Dorenbos, “Valence stability of lanthanide ions in inorganic compounds,” Chem. Mater., vol. 17, no. 25, pp. 6452–6456, Dec. 2005.
High Efficiency Solution-Processed Aluminum-Alloyed Chalcopyrite Thin Film Solar Cells
Authors: Septina Wilman , West Thomas , Giovanelli Anne Curtis , Gaillard Nicolas
Published: December 2020

CuInGaSe2 (CIGSe) chalcopyrite is one most efficient materials for light conversion to electricity with a record efficiency surpassing all other thin film photovoltaic technologies, achieving 23.4% efficiency. Record efficiencies of CIGSe are typically achieved using 1.16 eV absorbers even though Shockley-Queisser (SQL) limit predicts an optimum bandgap of around 1.4 eV for a single junction solar cell. In theory, higher efficiencies can be expected from wider gap chalcopyrite, however, all attempts to increase efficiency with wide bandgap Ga-rich CIGSe have led to defective materials. Another alternative to increase the band gap of chalcopyrites is by partial replacement of In with other group-V atoms, such as aluminum (Al). The band gap energy of CuInAlSe2 (CIASe) can be tuned from 1.0 eV (CISe) to 2.7 eV (CASe). In addition, Al is also very appealing to reduce the raw materials' cost since it is much more abundant in the earth’s crust than Ga (Al: 82,000 ppm, Ga: 19 ppm) and significantly cheaper (Al: ~$2/kg, Ga: ~$200/kg).

In an attempt to fabricate high-efficiency CIASe devices, we demonstrated an alternative and low cost method by fabricating bandgap tunable Cu(In,Al)(S,Se)2 (CIASSe) utilizing molecular ink consisted of Cu, In, Al, and sulfur containing salts dissolved in methanol. In this study, Cu-In-Al-S containing ink was spin coated into a molybdenum substrate and followed by selenization at high temperature to form selenium-rich CIASSe. We are able to achieve a device with maximum efficiency of 11.6% using CIASSe having relatively low-content of Al (Al/(Al+In)~0.1), significantly higher efficiency than CISSe (no Al) fabricated with the same process (8.3%-efficient). To our understanding, this study is the first demonstration of a relatively high-efficiency Aluminum-alloyed chalcopyrite solar cells through solution-based process. Details of the fabrication process and materials characterization will be discussed.
Welcome Remarks - H02: Photovoltaics for the 21st Century 16: New Materials and Processes
Authors: Hamada Hiroki
Published: December 2020

Welcome to H02: Photovoltaics for the 21st Century 16: New Materials and Processes! Take a moment to listen to welcome remarks from the lead organizer, Hiroki Hamada.
(Invited) Highly Reliable Metal Oxide Thin Film Transistors for Flexible Devices
Authors: Uraoka Yukiharu , Corsino Dianne , Bermundo Juan Paolo , Fujii Mami N. , Uenuma Mutsunori
Published: December 2020

Amorphous oxide semiconductors (AOS), such as amorphous InZnO (IZO), have been widely explored as channel material for thin-film transistors (TFTs) due to its high mobility (μ) and excellent uniformity.Its solution processability allows for application to cheap and flexible electronics. To achieve cheaper manufacturing cost and large-area production, successful integration of solution-based layers is necessary. In fact, other popular solution-based conductive films, such as carbon nanotubes and polymeric materials have been previously used as electrodes. However, their conductivity is generally lower and their integration requires complex processes. Meanwhile, AOS show promising optoeletronic properties as well as good contact with oxide channels. In this work, solution-based IZO semiconductor was functionalized for electrode applications using photo-assisted treatments, namely UV and excimer laser irradiation, and was employed in an all-solution oxide TFT fabrication.

IZO functionalization was achieved through either UV (λ=254 nm) irradiation for 15 to 60 mins or with additional excimer laser (λ=248 nm) irradiation in vacuum, air, or N2 at a fluence from 100 to 140 mJ cm-2. The results of X-ray photoelectron spectroscopy O 1s analysis suggests oxygen vacancy generation which effectively increases the carrier concentration in the irradiated IZO film. Moreover, IZO was crystallized from the amorphous as-deposited film after irradiation as obtained from X-ray diffraction and scanning transmission electron microscopy analyses. The laser-induced heating likely caused the IZO crystallization which provided the enhanced charge transport in the oxide film. Finally, the metal-oxide functionalization was employed in an all-solution processed oxide TFT fabrication using IZO for the channel and the electrodes, and fluorinated polysiloxane for the gate insulator. The self-aligned TFT structure that was employed, enabled the selective functionalization of the IZO gate, source, and drain electrodes. The metal oxide functionalization using UV and excimer laser irradiation yielded oxide TFTs with excellent transfer characteristics and good stability even after three months of storage in air. The all-solution processed fabrication demonstrated in this work is relevant for high throughput fabrication such as roll-to-roll processing.
(Invited) Heterojunction Channel Engineering for in-Ga-Zn-O Thin-Film Transistors
Authors: Furuta Mamoru , Koretomo Daichi , Magari Yusaku
Published: December 2020

Heterojunction channel engineering approach is presented as a means of enhancing the performance and reliability of In–Ga–Zn–O thin-film transistors (IGZO TFTs). A bottom-gate IGZO TFT with the heterojunction channel was formed by depositing an In-rich IGZO on a typical composition of IGZO111. A potential well of 0.4 eV was expected to form for electrons at the heterojunction interface. Field effect mobilities (μFE) of the TFTs were 12 cm2/Vs and 23 cm2/Vs for homogeneous IGZO111 and high-In IGZO channels, respectively. In addition, threshold voltage stability (ΔVth) of the TFTs showed big a difference between homogeneous IGZO111 and high-In IGZO channels under positive bias and temperature stress (PBTS). The IGZO111 TFT exhibited good Vth stability (ΔVth of +0.4 V) after the PBTS of +20 V for 104 sec at 60 °C. In contrast, although the homogeneous high-In IGZO TFT exhibited a higher μFE than the IGZO111 TFT, the PBTS stability noticeably degraded (ΔVth of +7.0 V) from the IGZO111 TFT.

For the heterojunction channel TFTs, when the high-In IGZO layer was deposited on the IGZO layer, μFE increased from the IGZO111 TFT especially in low gate voltage (VGS) region. In addition, the PBTS stability of the heterojunction channel TFT was clearly improved from the high-In IGZO TFT by inserting IGZO111 layer at the interface between HI-IGZO and the GI. A maximum μFE of 24.7 cm2/Vs and improved PBTS stability (ΔVth of +0.3 V) were achieved by the heterojunction channel TFT with a high-In IGZO/IGZO111 thicknesses of 10/5 nm.

Device simulation results revealed that quantum confinement effect in the heterojunction channel played an important role in determining carrier transport properties in the TFT, result in improving μFE and PBTS stability. A channel engineering approach will provide a method of overcoming the trade-off between μFE and the PBTS stability of oxide TFTs.
(Invited) Amorphous Zinc Oxysulfide Thin Films: Synthesis, Physical Properties, and TFT Application
Authors: Hirose Yasushi , Chen Zhen , Hasegawa Tetsuya
Published: December 2020

Amorphous oxide semiconductors (AOSs) have been under extensive research during recent years. Because of their high electron mobility even under amorphous state, they have been widely used as key materials for flat panel displays and flexible electronics devices, especially as channel layer of thin film transistor (TFT). Recently, it has been reported that an amorphous mixed-anion semiconductor consisting of only earth-abundant elements, zinc oxynitride (a-ZnON), shows high electron mobility and capability to TFT application [1]. However, a-ZnON is unstable in air due to weak chemical bonds between Zn and N [2]. To overcome this drawback, we synthesized another earth-abundant amorphous mixed-anion semiconductor, amorphous zinc oxysulfide (a-ZnOS) thin films and found that their electron mobility is comparable to those of conventional AOSs (~15 cm2V-1s-1), in addition to good chemical stability under ambient conditions [3]. Successively, a-ZnOS based TFTs were fabricated with bottom-gate and top contact configuration. a-ZnOS thin films with S/(S+O) = ~0.30 shows obvious TFT performance in the pristine states, although their field effect mobility (μ
FE) was moderate (μ
FE <1 cm2V−1s−1). μ
FE increased with the decrease of S/(S+O), but the carrier density became too large for TFT operation. By annealing these films in vacuum at 150 °C for 10 min, their TFT performance was significantly improved; on/off ration over 104 and μ
FE over 10 cm2V−1s−1.

[1] Kim et al., Sci. Rep. 3, 1459 (2013).

[2] Lee et al. Appl. Phys. Lett. 107, 122105 (2015)

[3] Y.Zhu et al., Adv. Electron. Mater. 6, 1900602 (2019).
High Mobility and Air-Stable Zinc Oxynitride Thin-Film Transistors Via ZnF2 Interlayer Insertion
Authors: Kim Hyoung-Do , Kim Hyun-Suk
Published: December 2020

Increasing demands for high-performance thin-film transistors (TFT) in the display application have led to the development of amorphous oxide semiconductors (AOS) such as In-Ga-Zn-O (IGZO), In-Zn-O (IZO), etc. The AOS based TFTs show high field-effect mobility as high as 10 cm2/Vs, and are suitable for the fabrication of large size liquid crystal display (LCD) with high resolution. However, the displays based on organic light-emitting diodes (OLEDs) or micro light-emitting diodes (micro-LED) with very high resolution (super-high vision, 8000 X 4000) require relatively high driving currents compared to the LCD display. Therefore, the AOS based TFTs with higher field-effect mobility (> 50 cm2/Vs) are strongly required into the display backplane array.

Recently, zinc oxynitride (ZnON) have researched intensively as an active material for high-performance TFTs due to its high field-effect mobility (> 50 cm2/Vs), excellent stability under bias or light irradiation, and easily tunable bandgap energy. However, some studies reported that the nitrogen-related defects such as nitrogen-deficient site (VN) in ZnON act as carrier trap sites, so that degrade the electrical characteristics of ZnON TFTs. Moreover, the zinc nitride (Zn3N2) is unstable to air due to its low heat of formation, thus the Zn3N2 into ZnON is easily converted to zinc oxide. Therefore, reducing VNs and preventing the degradation of Zn3N2 is necessary for obtaining high-performance ZnON TFTs.

In this study, the effects of a thin ZnF2 interlayer between source/drain electrode and ZnON active layer are investigated. The properties of ZnON TFTs were evaluated by the different thicknesses of ZnF2 and the change of deposition conditions. The inserted ZnF2 interlayer acts as i) carrier modulation between source/drain and active layer due to high resistive ZnF2, and ii) passivation layer which prevents Zn3N2 volatilization. Furthermore, in our previous study demonstrated that the incorporated fluorine in ZnON acts as a structural stabilizer, so that reduces VN sites by increasing the effective coordination number of zinc. Moreover, incorporated fluorine which substitutes nitrogen also shown acceptor-like behavior rather than carrier donor. Thus, the VNs near the interface between ZnF2 and ZnON would be reduced, therefore the net density of VNs is decreased.

Experimental results showed that an optimized ZnON/ZnF2 TFTs showed high field-effect mobility (> 50 cm2/Vs) and good transfer characteristics (high on/off ratio and low subthreshold swing), whereas ZnON TFTs without ZnF2 interlayer showed completely conductive behavior. In addition, the air stability of ZnON TFTs was improved via the ZnF2 interlayer, the transfer characteristics were almost unchanged even a few months later. Further analysis such as bias and illumination stability and charge transport mechanisms were discussed in detail.
Effects of Tantalum Doping on Electrical Characteristics of Indium-Gallium-Zinc Oxide Thin-Film Transistors
Authors: Baek Seung-Ryum , Seong Tae-Yeon
Published: December 2020

Thin-film transistors (TFTs) that utilize oxide semiconductors as channel materials have been widely used in various electronic device applications, such as displays, sensors, and memory devices. Among the oxide semiconductors, transparent amorphous indium-gallium-zinc oxides (a-IGZO) have superior characteristics, namely, high field-effect mobility (~10cm2/Vs), good uniformity, low processing temperatures, optical transparency, and low-cost fabrication processability compared with conventional amorphous/poly-silicon TFTs. However, oxide TFTs including a-IGZO TFTs have bias stress-induced instabilities, which are still critical issues in launching commercial oxide TFT products. These issues can be attributed to the oxygen vacancy-related defects, which are known to act as a major source of electrons and as carrier traps. To suppress such oxygen vacancy-related defects, many researchers reported various techniques, such as ozone treatment, oxygen annealing on oxide TFTs, passivation, and metal-doped oxide semiconductors.

In this study, we investigated the device performance of tantalum (Ta)-doped IGZO TFTs as a function of Ta content. Ta was used as a dopant because of its bond-dissociation-energy (BDE, 805kJ/mol) with oxygen higher than those of In, Ga, and Zn. The Ta-doped IGZO, which was adopted as a channel layer of bottom-gate TFTs, was fabricated using a magnetron co-sputtering method. Heavily doped p-type Si wafer with thermally grown SiO2 (300nm) was used as substrates. The RF power for the a-IGZO (In2O3 :Ga2O3 : ZnO = 1:1:1)target was fixed at 100 W while the power for the Ta target increased from 0 to 50 W. Aluminum (Al) was deposited as source/drain electrodes using an electron beam evaporator. With increasing Ta content in the IGZO films, the field-effect mobility (μFE) of the Ta-doped IGZO TFTs decreased, the threshold voltage (Vth) increased from negative to positive values, and the subthreshold swing (SS) became smaller with higher on/off ratio. Especially, Ta (10W)-doped IGZO TFTs exhibited μFE of 7.11 cm2/Vs, a SS of 0.195V/decade, and an on/off ratio ~1x108. These results show that the Ta-doping improves the switching characteristics of the Ta-IGZO TFTs. Furthermore, to evaluate the bias-stress stability, positive bias stress (PBS), negative bias stress (NBS) tests were conducted.
Photoconductive Solution Processed ZnO Quasi-superlattice Films
Authors: Buckley Darragh , Inguva Saikumar , McNulty David , Zubialevich Vitaly Z. , Parbrook Peter , Gity Farzan , Hurley P. K. , O'Dwyer Colm
Published: December 2020

Zinc oxide (ZnO) and Al-doped ZnO are important optoelectronic materials. ZnO in particular has a wide band gap (Eg
~ 3.3 eV at 300 K), large exciton binding energy (~66 meV) and especially for the variety of methods by which it can be processed. Moreover, ZnO is readily able to alloy with other metals in the oxide form and has a lattice that can facilitate interstitial doping using several metals, including Al and Sn. This gives ZnO a key role in optoelectronics, metal oxide thin films and thin film transistor (TFT) technologies.

We demonstrate that crystalline, epitaxial-like and highly ordered ZnO and Al:ZnO (AZO) quasisuperlattice thin films can be achieved from a precursor liquid at relatively low temperature via spin-coating, which crystallize with near epitaxy with a pronounced c-plane texture. We also show the visible and near-infra red (VIS-NIR) light spectroscopy of ZnO and Al:ZnO multi-layered thin film structures grown on oxidized silicon substrates.

We show measurements demonstrating sub-band optical pumping of AZO QSLs that enable significant photoconductivity. In AZO QSLs, conduction band electrons from valence band pumping at incident irradiation > Eg, are not required to initiate or enhance photoconductivity, and PL data indicate a donor level that enable enhance sub-band photoconductivity even up to bias voltages of 200 V. Photoexcitation with a 532 nm source efficiently pumps the AZO conduction band without increasing the density of electron-holes in the valence band, minimizing field-driven recombination and enabling significant photoconductance over wide voltage ranges. Density functional theory analysis on ZnO systems with Al-doping configurations of ~2% indicate that interstitial doping is required to generate a density of states that corroborates the proposed donor level to enable the photoconductive properties seen in this work.

References

[1] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano and H. Hosono, Nature 432, 488 (2004).

[2] T. Kamiya, K. Nomura and H. Hosono, Sci. Tech. Adv. Mater. 11, 044305 (2010).

[3] R. A. Street, Adv. Mater. 21, 2007 (2009).

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(Invited) Percolation Carbon Nanotube Thin Film Transistors
Authors: Shur Michael , Park Junsung , Zhang Yuhui , Liu Xueqing , Ytterdal Trond
Published: December 2020

The decrease of the gate voltage swing switching a field effect transistor from on to off state and, consequently, the decrease of the power supply voltage is the key challenge of the transistor design. Gate voltage dependent tunneling has been used to achieve this goal by decreasing the slope of the exponential current decay in the subthreshold regime below 60 mV per decade. We describe a new Carbon Nanotube (CNT) Percolating Thin Film Transistor (PTFT) that should allow achieving a steep subthreshold slope. CNT TFTs use mats of CNTs deposited on a substrate and forming a random percolating network. The conduction contacts between the individual CNTs is determined by tunneling and, therefore, could be strongly affected by external agents, such as gases or biological fluids. The asymmetry of the contacts to each CNT enables the rectification of electromagnetic radiation impacted on the CNT mat changing the drain-to-source conduction, with giant relative changes near the percolation point. Our experimental data show that sub-THz radiation shifts the percolation point at high intensity, when the rectified radiation changes the shape of the potential barrier between the CNT in a proximity contact. The CNT PTFT operates near the percolation point. In this regime, the gate bias shifts the percolation point by (a) depleting the CNTs in the subthreshold regime and (b) changing the shape of the tunneling barrier. This ensures the metal-insulator transition resulting in a sharp decrease of the subthreshold current slope. We present a compact model of the percolated CNT PTFT based on our Unified SPICE/ADS model that shows that this effect could reduce the subthreshold slope of the CNT TFs from 340 meV per decade to about 190 meV per decade.

Acknowledgments

This work at RPI was supported by the U.S. Army Research Laboratory under the Cooperative Research Agreement (Project Monitor Dr. Meredith Reed) and by the US ONR (Project Monitor Dr. Paul Maki).
Phase Control of MoTe2 Synthesized Via Laser Annealing Process: A Non-Transfer, Fast and Patternable Approach
Authors: Kuo Yao-Zen , Medina Henry , Chueh Yu-Lun , Chen Yu-Ze
Published: December 2020

Layared materials such as graphite and transition metal dichalcogenides have attracted lots of attention owing to their unusal nature of reacing atomic thickness. These so-called two-dimensional materials reveal outstanding physical properties when their thickness reduce to mono layer, such as indirect to direct bandgap transition for TMDs, which is ideal for different kinds of potential applications in optoelectronics, energy harvesting, Li-ion batteries and supercapacitors. Among the numorous TMDs, MoTe2 is the only TMD which can be synthesized in two phases because of the small energy difference between them. However, the synthesis approach to control these two phases is not refined enough. Most reliable strategy is CVD process, but its require high temperature annealing for a long time while control the Te atomphere at the same time. These complicated process is hard to applied and high temperature also restrict the use of substrates. Therefore, further improvement of the synthesis methods is an important issue.

Here, we use a laser approach to induce the MoTe2 growth directly on different substrates such as Quartz and sapphire and so on. We control the two phases by tuning the laser power and irradiation time. TEM supported by Raman and X-ray Photoelectron Spectroscopies confirm the existence and quality of the synthesized films. Furtheremore, this approach can be extended to the synthesis of other TMDs. The laser annealing assisted method develops a new approach that is fast, cheap, patternable and does not require transfer giving a step forward on the technology development for practical applications.
Porous Metal-Organic-Framework (MOF) Based Hybrid Materials for Thermoelectric Applications
Authors: Redel Engelbert , Baumgart Helmut -
Published: December 2020

Thermoelectric materials based on porous hybrid and MOFs constitute a very recent development, with many new and undiscovered phenomena for the research field. These porous Hybrid materials and MOF (Metal-Organic-Framework) films represent modern designer materials that exhibit many requirements of a near ideal and tunable future thermoelectric (TE) material. It is anticipated that especially the inherent porosity can be used advantageously in the design and simulation predictions of future thermoelectric materials. In principle, porous Hybrid and MOFs materials can comply with most of the requirements of an ideal and tunable future thermoelectric (TE) material. In contrast to traditional semiconducting bulk thermoelectric materials, porous hybrid MOF templates can be used to overcome some of the constraints of physics in bulk thermoelectric materials. These porous hybrid systems are amenable for simulation and modeling to design novel optimized electron-crystal phonon-glass materials with potentially very high Figure of Merit (ZT) numbers. Porous MOF and Hybrid materials possess an ultra-low thermal conductivity, which can be further modulated by phonon engineering within their complex porous and hierarchical architecture to advance the thermoelectric figure of merit ZT. This class of novel materials offers new approaches to the design of complex and hierarchical porous structures, possessing ultra-low thermal conductivity, which are able to trap, and localize phonons, thus resulting in a new generation of thermoelectric materials with a high ZT number. This work is demonstrating recent results of MOF thermoelectric Materials and provides a future outlook to the search for the next generation thermoelectric porous Hybrid and MOF materials, which could be part of a green renewable energy revolution with novel materials of sustainable high ZT values.
Quasi-2D Organic–Inorganic Hybrid Perovskite for High Performance Rechargeable Aluminon-Ion Battery
Authors: Wu Shu-Chi , Tang Shin-Yi , Yang Tzu-Yi , Ai Yuanfei , Chen Yu-Ze , Chueh Yu-Lun
Published: December 2020

Recent advances in the use of organic–inorganic hybrid perovskites have been investigated in a variety of applications, such as solar cells, photodetector, light emitting devices (LEDs), and lasers because of their outstanding semiconductor properties. Furthermore, the perovskite structure has the ability to host extrinsic elements, making it a promising candidate for battery field. Previous studies have shown that organic–inorganic hybrid perovskites can be a suitable anode material for both lithium- and sodium-ion batteries. However, the multivalent rechargeable batteries with perovskite material have not yet been realized. Herein, we studied the electrochemical performance of three-dimensional (3D) CH3NH3PbI3 and quasi-two dimensional (C4H9NH3)2(CH3NH3)3Pb4I13 thin films as electrode materials for rechargeable Al-ion batteries. In this work, these electrodes were successfully synthesis on carbon cloth through a feasible solution process. The (C4H9NH3)2(CH3NH3)3Pb4I13 electrode yield a specific capacity of 210 mAh g–1 at the current density of 50mA g−1 . It still delivered 81 mAh g–1 after 250 cycles at the current density of 200mA g−1 with a retention of as high as 95%, indicating a long cycling stability. Compared with the CH3NH3PbI3, the (C4H9NH3)2(CH3NH3)3Pb4I13 presented higher initial capacities, better reversibility, and more excellent high-rate capabilities, all demonstrating the vitally prominent role of isobutyl amine (C4H9NH3). which can be attributed to the unique hydrogen-bonding interaction of isobutyl amine could effectively hinder the shuttle effect of polyiodide. We anticipate that these results open a new direction for the use of organic–inorganic hybrid perovskites for new secondary aluminum ion batteries.
GaN Single Crystalline Domain Growth on Graphene Substrate
Authors: Park Jonghyurk , Lee H. , Kim D. , Jang D. , Kim C , Yoon S
Published: December 2020

Graphene is very well known 2D nano-material which have novel physical and chemical properties even in a few layer thick form. Recently, there have been extensive studies on hetero-structures based on these Van-der-Waals 2D crystals like graphene, transition metal dichalcogenide (TMD), boron nitride (BN) and so on. In the case of graphene, this 2D layer can be stable and can be transferred to other target substrate with ease. Therefore, graphene can be a good candidate materials for growing other active materials on it. In this study, we tried to grow GaN micro-domain on graphene substrate using hydride vapor phase epitaxy (HVPE) method. GaN epitaxial behavior can be affected by the condition of graphene substrate and we compared the growth behavior of GaN micro-domain on graphene changing the preparation condition. And, several experimental parameters could be controlled like flow rate of Ga and N source with carrier gas, temperature and time to get the proper morphology of GaN micro-crystals. Despite of lattice mis-match of hexagonal GaN on graphene, we could grow single crystalline GaN micro-domain having the lateral size of a few or lager microns. We characterized these micro-crystalline GaN domains using optical microscopy, secondary electron microscope (SEM), micro-Raman spectroscopy and x-ray diffraction (XRD) which confirmed the crystalline phase of each domain. As a typical Van-der-Waals crystal, pristine non-defective graphene may have lacking dangling bonds leading to very low nucleation density for GaN growth and can be used even as a mask layer. When grown on the transferred graphene, however, we expect to have enough nucleation sites originating from the physical defects like grain boundary, vacancy and ripples of poly-crystalline graphene layer. This experimental finding is very interesting to further studies of graphene applications for hetero-structures of graphene and other complementary active materials because graphene has disadvantage in the applications of switching devices, optical elements and can be a potential candidate to overcome these weak points by utilizing very efficiently active GaN together.

[1] Y. Kim et al., Nature, 544, p.340 (2017)

[2] V. Kumaresan et al,, Nano Letters, 16, p.4895 (2016)
Interfaceof Electrogenic Bacteria and Reduced Grapheneoxide: Energetics and Electron Transport
Authors: Cotts Sheldon , Berry Vikas , Keisham Bijentimala
Published: December 2020

A synergistic, nanoscale electrical-interface with the membranes of exoelectrogenic microbes will have transformative impact on biological cell based electronic-devices. Here, we report that a conformal graphenic interface on biocatalytic Geobacter sulfurreducens membrane results in quantum-capacitance induced n-doping in reduced graphene oxide (rGO) that further enhances electron shuttling from the membrane to improve electron harvesting from the electrogenic organism. The quantum coupling of rGO with the connected protein-membrane channels leads to an additional electron density of 3.91 x 1012cm-2 and an increase in the in-plane phonon vibration energies (G) of rGO by ~5 cm-1. This n-doping enhances the electron transfer-rate from the cell membrane into the rGO via a net driving potential of 158 meV with a 3-fold increase in the power density.The synergistic electron-harvesting and conformal membrane-interfacing of flexible 2D nanomaterials can lead to an evolution in the design of microbe-circuitry to power stand-alone nanodevices.
(Invited) Ion-Conductive Metal-Organic Frameworks
Authors: Sadakiyo Masaaki
Published: December 2020

Proton conductivity in solids is of importance not only for useful applications such as fuel cells but also for better understanding of the nature of proton-transport phenomena. Recently, metal–organic frameworks (MOFs) have been emerged as a novel class of proton-materials because the ability to rationally design and chemically tune their architecture allows chemists to establish various methods to control the proton conductivity. We have proposed three types (types I–III) of concepts to give high proton conductivity to MOFs. In type I, proton carriers are introduced as counterions into the pores (e.g., H3O+). In type II, acidic groups are placed on the framework (e.g., –COOH). In type III, charge-neutral proton-conducting species are incorporated within the pores (e.g., H3PO4).1 We have synthesized (NH4)2(adp)[Zn2(ox)3]·3H2O (adp = adipic acid; ox = oxalate), having both type I and type III features; (NH4)2(adp)[Zn2(ox)3]·3H2O shows high proton conductivity because of the existence of two-dimensional (2-D) hydrogen-bonding networks which act as a crystalline proton-conducting pathways.2 Intentional control of proton conductivity and the proton dynamics in this MOF has been also studied.

On another front, hydroxide-ion conductors have received a great deal of interest as electrolytes for alkaline fuel cells that can operate without precious metal catalysts such as Pt. We have also focused on creating novel hydroxide ion conductors using the MOFs. We proposed a new strategy to introduce hydroxide ions into MOFs, i.e., which is “hydroxide salt inclusion into alkaline-stable MOFs”. We succeeded in synthesizing a novel MOF including alkylammonium hydroxide salt by employing an alkaline-stable ZIF-85 framework (NBu4-ZIF-8-OH) (Figure 1).6
,7 Ionic conductivity of NBu4-ZIF-8-OH was found to be 2.3 × 10–8 S cm–1 at maximum, which is four orders of magnitude higher than that of blank ZIF-8. Considering that the framework structure of NBu4-ZIF-8-OH is the same as that of ZIF-8, the enhancement in the ionic conductivity can be attributed to the included salt.

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Figure 1