bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Latest Progress on B-III-N Alloy Research and Working Principle of TMA Preflow on AlN MOVPE
Authors: Li Xiaohang 
Published: February 2020

The B-III-N alloys have not been studied extensively as compared to conventional III-nitride AlGaInN alloys. However, due to the large and tunable bandgap, tunable lattice constant, and many other electronic properties, this emerging material system has enormous potentials for DUV-IR optoelectronics and power electronics devices. In this presentation, some of the latest research progress of the B-III-N alloys will be discussed, covering from epitaxial growth, microscopic characterization to electronic properties.
The TMA and NH3 preflow processes have been critical for the AlN MOVPE process on sapphire, in that they pre-condition the sapphire substrates for the Al-polar epitaxy. Although the mechanism of the NH3 preflow has been thoroughly studied and clear, that of the TMA preflow has been a bit mysterious. Some MOVPE scientists have hypothesized that the TMA preflow resulted one or more than one layers of Al or Al-rich layers on sapphire surface, which further leads to the growth of Al-polar AlN. I will present our model of the TMA preflow based on systematic electron microscopy studies.
Thermal Stability of Quasi-Two-Dimensional β-Ga2O3 and Its Device Application
Authors: Kim Suhyun , Kim Janghyuk , Kim JiHyun 
Published: February 2020

An ultra-wide bandgap of around 4.8-4.9 eV (at room temperature), high thermal and chemical stabilities are some of the attractive properties of β-gallium oxide (β-Ga2O3) for fabricating (opto)electronics. Its noticeably high dielectric breakdown field (Ebr) also has drawn attention; the theoretical value was calculated to be ~8 MV/cm and a recent report reached an experimental value of 3.8 MV/cm, which is higher than those of GaN and SiC. These advantages obviously led to various applications on power devices including metal-semiconductor field-effect transistors (MESFETs), metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes.
Mechanically exfoliated β-Ga2O3 flakes were studied in our investigation. The mechanical exfoliation of β-Ga2O3 is possible although it is not formed by van der Waals interaction as its monoclinic structure allows cleavage into thin flakes along [100] direction. This new possibility of preparing β-Ga2O3 samples not only suggests that β-Ga2O3 can possess two-dimensional (2D) properties, but also offer a solution for low thermal conductivity of β-Ga2O3, which is a critical limitation when fabricating high power devices. Since it is only recently that mechanically exfoliated β-Ga2O3 gained attention, there still exists several characteristics to be investigated. Unlike bulk substrates, quasi-2D β-Ga2O3 needs more research on stability to be applied to devices such as sensors and high-power electronics that operate at high temperature. In this study, the thermal stability of β-Ga2O3 flakes was observed over time and the means to improve the stability were investigated. The optical and structural changes with time were measured as the samples were exposed to higher temperature (200 – 400 °C). MESFETs were also fabricated using β-Ga2O3 flake as the channel material to investigate the thermal effects on the device, especially the Schottky barrier between the channel and the gate metal. Different metals and an additional thermally conductive 2D layer was used to enhance the thermal stability of the device. This study shows the potential of quasi-2D material (β-Ga2O3) devices with long term stability at high temperature. Further results and discussion will be presented in detail.
Anomalous Electron Accumulation at Al2O3/in2O3 Interface Via Short-Range Ordered Two-Dimensional Electron Gas
Authors: Lee Sang Yeon , Seo Hyungtak 
Published: February 2020

Transparent conducting oxide (TCO) films, which is one of the widely used as window electrodes at the various devices, fulfil high electrical conductivity and optical transparency in the visible region of spectrum. Conventional TCO films are formed by the tuning charge transport of wide band gap oxides like indium gallium zinc oxide (IGZO), zinc oxide (ZnO), tin dioxide (SnO2), and indium oxide (In2O3). Among the various TCO candidates, In2O3 is an attractive TCO candidate since In2O3 can satisfied the visible transparency and high carrier density via doping processes. To achieve the high mobility In2O3 films, doping processes with metal dopants such as Ti, Zr, Mo, and W have been suggested by many previous study. Intrinsic In2O3, however, has n-type semiconductor due to its native oxygen vacancy act as n-type donor and indium interstitial. As another approach to gain highly conductivity TCOs, two-dimensional electron gas (2DEG) channel can be suggested since 2DEG channel can be applied to increase the electrical conductivity of oxide semiconductors up to the metallic conduction level. The tuning of electrical and optical properties in oxides via surface and interfacial 2DEG channels is of great interest, as they reveal the extraordinary transition from insulating or semiconducting characteristics to metallic conduction or superconductivity enabled by the ballistic transport of spatially-confined electrons. Although most previous studies have been carried out in crystalline phase like single crystal SrTiO3 or III-V compound semiconductor, realizing practical aspects of this exotic phenomenon toward short-range ordered and air-stable 2DEG channels remains a great challenge.
In this study, we fabricated Al2O3/In2O3 heterojunction system on soda-lime glass consisting of In2O3 deposited by RF reactive sputter with a thickness from 8 to 100 nm and Al2O3 deposited by ALD with a thickness below 100 nm. We suggest that Al2O3/In2O3 heterojunction acts as short-range ordered 2DEG channel with a low temperature (~200 ℃). After deposition of Al2O3 layer, the heterojunction two-dimensional metallic channel was fabricated between Al2O3 and In2O3 interface as showing the metallic conduction with sheet charge density > 10 14/cm2, sheet resistance of 850 Ω/cm2, room temperature Hall mobility of 20.5cm2 V-1 sec-1 depending on the In2O3 thickness. To prove existence of 2DEG channel at the interface, we performed the I-V measurement, time of flight secondary ion mass spectrometry, ultraviolet-visible spectrophotometer, tunneling electron microscope–electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and Hall measurement.
Towards InGaAs MS-DRAM Memory Cells
Authors: Navarro Carlos , Navarro Santiago , Marquez Carlos , Sampedro Carlos , Donetti Luca , Karg Siegfried , Riel Heike , Gamiz Francisco 
Published: February 2020

The need of a low-power, fast and low-cost CMOS compatible embedded DRAM cell is rising incessantly with the upcoming Internet of Things (IoT) era [1]. Capacitor-less DRAM cells [2, 3] have emerged as a promising solution since they do not require dedicated fabrication steps to deal with the storage node. Among this breeze of cells, the MSDRAM [4] can be highlighted due to the simpler manufacturing process.
The MSDRAM (Meta-Stable-Dip RAM) memory operation is based on inter-gate coupling [5] and non-equilibrium state [6]. The back gate (ground-plane) is biased positively to induce a virtual n-type back-channel while the front-gate voltage is negative to retain any available hole in the body. By modulating the hole population at the front-channel, the vertical top-gate induced electric field is screened (or not) so that the back electron-channel is maintained (or depleted). Depending upon the back-channel depletion degree different conductance values are achieved defining the logic ‘1’ and ‘0’ memory states. State programming is carried out by injecting holes by band-to-band tunneling at the drain edge (W1) or evacuating holes by top-gate capacitive coupling (W0)
In this work, a III-V InGaAs MSDRAM cell is built and its memory operation is demonstrated by TCAD numerical simulations in Synopsys [7, 8]. The detailed structure and the doping are shown in Fig.1. The basic memory operation is depicted in Fig. 2a for a W0-R-W1-R-W0-R sequence with W1/0 being the ‘1’/’0’ state programming and R the reading. The current after any W0 operation remains much lower than after W1. Figure 2b represents the body electron and hole densities after the first W0 and W1, respectively. Following W0, the hole density is limited underneath the top dielectric allowing a strong vertical field that depletes the back-channel from electrons leading to a drastic drop in the conductance and thus in the drain current. On the contrary, after generating holes by band-to-band tunneling during W1, the electron back-channel is reinforced enabling a larger current level while reading afterward.
In conclusion, preliminary TCAD results demonstrate the feasibility of implementing the MSDRAM concept on III-V materials.
REMINDER project (No 687931) is thanked for support.

Figure 1
(Invited) All-Solid Hybrid Energy Fabric for Wearable Electronics
Authors: Fan Xing 
Published: February 2020

The demand for wearable power sources has been growing rapidly in the modern era of portable electronics. It is essential to make these power sources more comfortable and fit for the human body, especially for some medical applications in which case we need to wear it day and night. Energy harvesting and storage devices in the form of a common-looking fabric is thus of a great interests in recent years. Herein, we have successfully woven out a type of micro-cable power textile for simultaneously harvesting energy from ambient sunshine and mechanical movement. Solar cells fabricated from lightweight polymer fibers into micro cables are then woven via a scalable shuttle-flying process with fiber-based triboelectric nanogenerators to create a hybrid energy harvesting fabric. The hybrid power fabric is just 320 µm thick, fabricated with a size of 4 cm by 5 cm, was demonstrated to charge a 2 mF commercial capacitor up to 2 V in 1 min under ambient sunlight in the presence of mechanical excitation, such as human motion and wind blowing. Based on the similar strategy, a novel solid solar energy harvesting and storage hybrid textile combining both photovoltaic cells and super-capacitors were also designed and realized, in order to provide power at dark condition within a single textile. With such features as low-cost, thinness, light-weight, being flexible and wearable, as well as colorful appearance, this work represents a significant step towards the development of large scale energy harvesting and storage for wearable electronics and self-powered home technology. Some recent publications were selected as “Research Highlights” by Nature and the “9 most impressive social innovation goods from October” of Yahoo News in 2016.

References

[1] J. Chen#, Y. Huang#, N. Zhang, H. Zou, R. Liu, C. Tao, X. Fan*, Z. L. Wang*, Nature Energy. 2016, 1, 16138.
[2] N. Zhang#, J. Chen#, Y. Huang, W. Guo, J. Yang, J. Du, X. Fan*, C. Tao*, A Wearable All‐Solid Photovoltaic Textile, Advanced Materials, 2016, 28 (2), 263-269
[3] Z. Chai#, N. Zhang#, P. Sun, Y. Huang, C. Zhao, H. Fan, X. Fan*, W. Mai*, ACS Nano. 10 (2016) 9201–9207.
(Invited) Charge Carriers, Defects and Interfaces in Two-Dimensional Materials and Devices
Authors: Liu Yuanyue 
Published: February 2020

Two-dimensional semiconductors show great promise for next-generation electronics and optoelectronics, yet they still face significant challenges to realize their potential. Here I will discuss our recent theoretical/computational studies on the charges carriers, defects and interfaces in two-dimensional materials and devices. Specifically, I will show (i) how to estimate the electron/hole mobility with reasonable accuracy; (ii) the role of defects and how to passivate the harmful ones [1,2]; and (ii) how to lower the metal-semiconductor resistance [3,4].
[1] Y. Liu, P. Stradins, S. Wei, Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201508828
[2] Y. Liu, H. Xiao, W. A. Goddard III, Nano Lett. 2016, 16, 3335
[3] Y. Liu, P. Stradins, S. Wei, Science Advances 2016, 2, e1600069
[4] Y. Liu, H. Xiao, W. A. Goddard III, JACS, 2016, 138, 15853
(Invited) Indium Gallium Phosphide Photodiode with 50% Increased External Quantum Efficiency and Higher Signal to Noise Ratio for Blood Pressure Measurement
Authors: Kao Yung-Hua , Chao Chang-Po , Kumar Amarendra , Lin Yi-Chieh , Hsu Chia-Liang 
Published: February 2020

Measurement of blood pressure is one of the most important parameters for personal healthcare. Arteries are responsible for carrying blood from the heart to all parts of the body and the pressure of blood in arteries is measured in many abnormalities. The blood pressure is explained by two parameters. The highest blood pressure during heart pumping is measured by systolic pressure whereas the diastolic pressure measures the lowest blood pressure when the heart is not pumping the blood. For current work, the principle of light absorption is used to measure blood pressure in arteries. Light is more strongly absorbed by blood compared to skin or tissues and therefore, blood flow change can be detected by the change in intensity of light. This blood flow change is proportional to blood pressure and hence the blood pressure can be measured by measurement of change in light intensity.
In this work, we have developed the InGaP photodiode module with higher signal to noise ratio for blood pressure measurement. The InGaP photodiode External Quantum Efficiency (EQE) is 50% higher than Silicon (Si) photodiode. The EQE is ever higher than Si photodiode equipped with the filter as shown in Fig. 1(a). The newly developed InGaP photodiode has the advantage of selective EQE at different wavelength. The photodiode has almost zero EQE outside the desired region of wavelength (300 nm- 700 nm) where the Si photodiode EQE is spread in the longer wavelength region (300 nm - 1200 m). This higher region of EQE can lower the signal to noise ratio. The InGaP photodiode has an increased signal to noise ratio (24.8) compared to other photodiodes (24.0) due to the smaller wavelength region of EQE. Both systolic blood pressure and diastolic blood pressure measurement was compared for actual value and predicted value. The R2 correlation value for systolic and diastolic blood pressure is measured to be 0.86 and 0.91 respectively as shown in Fig. 1(b) and Fig. 1(c).
This works explore new doorway for LED and photodiode application in the field of biomedical sensors. The application of our new photodiode with enhanced EQE and the wide range of LED has numerous possibilities. The higher possibility of multichip design with Flip chip packaging technique can provide a single module for measurement of blood pressure, blood glucose, blood lipid and other parameters using LED of different wavelength.

Figure 1
Sensitivity Enhancement Techniques for Black Phosphorus-Based Gas Sensors
Authors: Lee Geonyeop , Kim Suhyun , Jung Sunwoo , Jang Soohwan , Kim JiHyun 
Published: February 2020

Two-dimensional materials (2DMs) have been widely studied as sensing materials because their distinct 2D structure allows their entire volume to adsorb gas molecules. Black phosphorus (BP) has received much attention in recent years as one of the promising 2DMs. BP has direct band gap (0.3-2.0 eV), high carrier mobility (~1,000 cm2/V∙s) and high current on/off ratio (104-105). In addition, the unique properties of BP such as puckered structure, lone pair electrons on the surface and high charge transfer rate results in high sensitivity toward gas molecules. It is reported that BP shows higher sensitivity compared to graphene and MoS2. However, the sensitivity of BP-based gas sensor still requires better performance for the practical use.
In our study, we have tried to enhance the sensing properties of BP-based gas sensors toward NO2, NH3, and H2. BP-based gas sensors were fabricated by using a dry-transfer technique. BP flakes mechanically exfoliated from the bulk sample were transferred on to source-drain electrodes; the electrodes (Ti/Au) were pre-patterned on a SiO2/Si substrate. We performed two different approaches to improve the sensitivity of the sensors. First, we altered the supported structure to suspended structure to use both sides as the sensing area and eliminate the substrate effect such as charge scattering. We also functionalized BP sensors with Pt nanoparticles to improve its hydrogen sensing ability. We measured the resistive sensitivity and confirmed that sensing performance of treated sensors was higher than that of the untreated samples. The details of our experiment conditions and results will be presented at the meeting.
(Invited) Triboelectric Nanogenerator for Self-Powered Flexible Electronics and Internet of Things
Authors: Wang Zhong Lin , Wang Aurelia Chi 
Published: February 2020

Triboelectrification is an effect known to society ever since the ancient Greek era, but it is usually considered a negative effect and avoided in many technologies. We have recently invented a triboelectric nanogenerator (TENG) that is used to convert mechanical energy into electricity by a conjunction of triboelectrification and electrostatic induction. As for this power generation unit, in the inner circuit, a potential is created by the triboelectric effect due to the charge transfer between two thin organic/inorganic films that exhibit opposite tribo-polarity; in the outer circuit, electrons are driven to flow between two electrodes attached on the back sides of the films in order to balance the potential. Ever since the first report of the TENG in January 2012, the output power density of TENG has been improved for five orders of magnitude within 12 months. The area power density reaches 500 W/m2 , and a conversion efficiency of ~50-85% has been demonstrated. The TENG can be applied to harvest all kind mechanical energy that is available but wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water and more. Alternatively, TENG can also be used as a self-powered sensor for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage and current output signals of the TENG, respectively, with potential applications for touch pad and smart skin technologies. The TENG is possible not only for self-powered portable electronics, but also as a new energy technology with a potential of contributing to the world energy in the near future.
[1] Z.L. Wang, Materials Today, 20 (2017) 74-82.
[2] “Nanogenerators for Self-Powered Devices and Systems”, by Z.L. Wang, published by Georgia Institute of Technology (first book for free online download): http://smartech.gatech.edu/handle/1853/39262
[3] Z.L. Wang, L. Lin, J. Chen. S.M. Niu, Y.L. Zi “Triboelectric Nanogenerators”, Springer, 2016. http://www.springer.com/us/book/9783319400389
[4] Z.L. Wang “Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors”, ACS Nano 7 (2013) 9533-9557.
[5] Z.L. Wang, J. Chen, L. Lin “Progress in triboelectric nanogenerators as new energy technology and self-powered sensors”, Energy &amp; Environmental Sci, 8 (2015) 2250-2282.
(Invited) Flexible Organic Sensors for Biomechanical Measurements
Authors: Amit Moran , Zhai Yichen , Wu Zhenghui , Ng Tse Nga 
Published: February 2020

This presentation shows an example of an instrumented glove for augmenting movement disorder assessments. The system is based on capacitive pressure sensing, and the validation allows an objective, repeatable metric that improve resolution over the current best practices. The glove measures the power required to move a patient’s arm and shows reduced inter- and intra-rater variability. Our approach using wearable sensors offers an objective route for the characterization of movement patterns, which would permit the effective evaluation of intervention outcomes, as well as provide a platform for novel motor interventions in the future.
In addition, another type of biomechanical measurements involving blood pulsations is being developed using photosensors responsive to the short wavelength infrared (SWIR) spectra. Currently conventional SWIR sensors are limited by complex die transfer and bonding processing. Here we are advancing SWIR photodiodes by using a new generation of narrow bandgap conjugated polymers that are processed by solution processing techniques and allow simple direct deposition. The polymers are processed into bulk heterojunction photodiodes with photoresponse up to wavelength of 1.7 micron. The performances of devices with different polymer structures were compared through metrics including detectivity, quantum efficiency, response time and rectification ratio. Example applications including blood pulse measurements and spectroscopic identification will be demonstrated.
(Invited) Printable Two-Dimensional Nanomaterial Inks for Flexible Electronics and Photonics
Authors: Hersam Mark C. 
Published: February 2020

Layered two-dimensional nanomaterials interact primarily via van der Waals bonding, which has created new opportunities for heterostructures that are not constrained by epitaxial growth [1]. In order to efficiently explore the vast phase space for van der Waals heterostructures, our laboratory employs solution-based additive assembly [2]. In particular, constituent two-dimensional nanomaterials (e.g., graphene, boron nitride, transition metal dichalcogenides, and black phosphorus) are isolated in solution, and then deposited into thin films with scalable additive manufacturing methods (e.g., aerosol, inkjet, gravure, and screen printing) [3]. By achieving high levels of nanomaterial monodispersity and printing fidelity, a variety of electronic, electrochemical, and photonic applications can be enhanced including digital logic circuits [4], lithium-ion batteries [5], and photodetectors [6]. Furthermore, by integrating multiple nanomaterial inks into heterostructures, unprecedented device function is realized including anti-ambipolar transistors [7], gate-tunable photovoltaics [8], and neuromorphic memristors [9]. In addition to technological implications for electronic and photonic technologies, this talk will explore several fundamental issues including band alignment, doping, trap states, and charge/energy transfer across two-dimensional van der Waals heterointerfaces [10].
[1] D. Jariwala, et al., Nature Materials, 16, 170 (2017).
[2] J. Zhu, et al., Advanced Materials, 29, 1603895 (2017).
[3] J. Kang, et al., Accounts of Chemical Research, 50, 943 (2017).
[4] M. Geier, et al., Nature Nanotechnology, 10, 944 (2015).
[5] K.-S. Chen, et al., Nano Letters, 17, 2539 (2017).
[6] J. Kang, et al., Nano Letters, 16, 7216 (2016).
[7] D. Jariwala, et al., Nano Letters, 15, 416 (2015).
[8] D. Jariwala, et al., Nano Letters, 16, 497 (2016).
[9] V. K. Sangwan, et al., Nature Nanotechnology, 10, 403 (2015).
[10] S. B. Homan, et al., Nano Letters, 17, 164 (2017).