bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Spatially Resolved Study of the EQE Droop in InGaN QW LEDs: Interplay of Point Defects, Extended Defects, and Carrier Localization
Authors: Lin Yue , Zhang Yong , Liu Zhiqiang , Wei Tongbo , Chen Zhong
Published: February 2020

Spatially-resolved electroluminescence (as a function of injection current) and spatially-resolved photoluminescence (as a function of excitation power) are used to investigate the external quantum efficiency (EQE) droop in InGaN QWs based blue LEDs. The spatially-resolved EL mapping allows us to study two most commonly observed but distinctly different droop behaviors on a single device, minimizing the ambiguity trying to compare independently fabricated devices. We conclude that the EQE ~ current curve reflects the interplay of three effects: nonradiative recombination through point defects, carrier localization due to either In composition or well width fluctuation, and nonradiative recombination of the extended defects, which is in fact common to various optoelectronic devices.[1] By comparing EL and PL mapping data, we show that individual singular sites exhibiting either particularly strong or weak emission in PL do not usually play any significant and direct role in the EQE droop. We introduce a two-level model that can capture the basic physical processes that dictate the EQE ~ current dependence and describe the whole operating range of the device from 0.01 – 100 A/cm2.

[1] Y. Lin, Y. Zhang, Z. Q. Liu, L. Q. Su, J. H. Zhang, T. B. Wei, and Z. Chen, Appl. Phys. Lett. 101, 252103 (2012).

In collaboration with Yue Lin, Zhiqiang Liu, Liqin Su, Jihong Zhang, Tongbo Wei, and Zhong Chen.
Analysis of InGaN/GaN Multiple Quantum Well Heterostructures by Means of Photoconductivity Measurements
Authors: Krause John Robert , Stokes E. B. , Deguzman Panfilo C , Mizuyama Yosuke , Kolli Rajesh
Published: February 2020

A novel method for the characterization of multiple quantum well(MQW) light emitting diodes(LEDs) is investigated. This method involves the measurement of photocurrent generation in an LED when irradiated with photons of energy near the absorption edge of the quantum wells. In this situation the I-V curve of the LED reveals a number of photocurrent oscillation zones corresponding to spatial variations in the heterostructure (Figure 1).

The mechanism leading to the voltage-bias dependence of these features is hypothesized to be the expansion of the depletion (space-charge) region. Electrons and holes, from the N and P regions respectively, are drawn to the P-N junction as the reverse bias-voltage is increased. The area occupied by the ionized dopant atoms left behind by these charges is referred to as the ‘depletion region’. As the magnitude of the bias increases this area of depleted atoms becomes larger, engulfing the quantum wells in series. An electric field forms between the charges gathered at the P-N junction and the ionized atoms, giving rise to a potential gradient across the depletion region. The I-V features are then caused by the dynamics of the excited electrons as the potential gradient traverses each quantum well.

A preliminary model is constructed by using the SIMS data (Figure 2) for the LED heterostructure supplied by Veeco. The spatial extent of the depleted region is calculated as a function of the applied bias using a doping profile derived from the SIMS data. This allows the estimation of the voltage at which each quantum well will become depleted and thus when a feature will be expected. The resulting curve is compared to the experimentally determined I-V feature spacing.

The wavelength and temperature dependencies of this phenomenon are discussed, citing examples from existing literature. The benefits of this method of analysis are examined in terms of acquisition speed, measurement resolution and hardware cost with respect to current techniques such as capacitance-voltage measurement.

Further research into this effect would involve the spectral transmission of the MQW devices as a function of voltage bias and the possible applications in spectrometry or optical filtering. A more complete picture of the quantum mechanical interaction between the incident photons, quantum wells, and potential gradient would also be valuable for the interpretation of the I-V curves and possible engineering applications.
Ti/Al/Ni/Cu Ohmic Contact with Low Contact Resistance and Smooth Surface Morphology for AlGaN/GaN HEMT
Authors: Wong Yuen-Yee , Chang Edward Yi , Chen Yu-Kong , Liu Shih Chien , Lin Yueh-Chin , Maa Jer-Shen
Published: February 2020

The feasibility of replacing the Au layer in Ti/Al/Ni/Au ohmic contact for AlGaN/GaN structure with Cu has been investigated. In this study, the thicknesses of Ti, Al and Cu layers were fixed at 200 Å, 1200 Å and 1000 Å, respectively. On the other hand, Ni layer with different thicknesses were used to examine its influence on the Cu-based ohmic contacts. The results showed that the Ni layer played an important role in the Ti/Al/Ni/Cu metallization for achieving low contact resistance, smooth morphology and excellent edge acuity. With a 50-Å Ni layer, a low specific contact resistance of 1.35x10-6 ohm-cm2 has been realized. This result is comparable with the conventional ohmic contact of Ti/Al/Ni/Au (1.19 x 10-6 ohm-cm2). Furthermore, in the absence of Au, the surface roughening caused by Au-Al alloy in the conventional ohmic contact was also prevented. As a result, the root-mean-square roughness of the optimized Cu-based contact was only 7.62 nm as compared to 134 nm for the conventional structure.

The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results suggest that the formation of TiN at the Ti/semiconductor interface has played an important role in achieving low contact resistance similar to the case for the Ti/Al/Ni/Au structure. In addition, the formation of more stable Ti-Al-Cu based alloys in the Cu-based ohmic contact had successfully confined the Cu within the ohmic contact. Both TEM and Auger electron spectroscopy (AES) results confirmed that no Cu was detected in the semiconductor layers. Finally, high electron mobility transistors (HEMTs) were fabricated using the Cu- and Au-based ohmic contacts. Both devices showed the similar DC characteristics suggesting that the Ti/Al/Ni/Au metallization has a great potential to be used as the ohmic contact for AlGaN/GaN devices.
(Invited) Novel Luminescent Materials Based on Semiconductor Nanowires
Authors: LaPierre Ray R , Gustafsson Anders , Kuyanov Paul , Haapamaki Chris
Published: February 2020

We report novel luminescent materials based on group III-V compound semiconductor nanowires. Semiconductor nanowires are essentially one-dimensional rods with length of several microns and diameter below 100 nm. Hence, nanowires exhibit interesting quantum confinement and carrier transport properties. Nanowires are grown using metal seed particles by the vapor-liquid-solid (VLS) process in a molecular beam epitaxy or metalorganic chemical vapor deposition system. By varying the material deposition during growth, axial or radial nanowire heterostructures and p-n junctions may be formed for various device applications including light emitting diodes, lasers, and photodetectors. Due to the large surface area to volume ratio of a nanowire, lattice mismatch strain may be accommodated by elastic distortion of the nanowire without detrimental misfit dislocations, which gives a much greater ability to perform bandgap engineering in nanowires as compared to thin films. Hence, unique heterostructures are possible in nanowires that would be impossible in thin films, opening up new device applications and possibilities in condensed matter physics.

We will report our recent work on the photoluminescence properties of InAsP/InP nanowires. InP nanowires were grown on <111> Si substrates by the Au-assisted vapor-liquid-solid process in a gas source molecular beam epitaxy system. InAsyP1-y segments were grown in the middle of the InP nanowires, creating a multiple quantum dot structure or superlattice. The quantum dot dimensions and composition were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX). Photoluminescence (PL) from the quantum dot structure could be tuned by the InAsyP1-y composition (y), or by the size of the quantum dot via the quantum confinement effect. Cathodoluminescence (CL) measurements confirmed localized emission from the quantum dots. To reduce detrimental surface states, the nanowires were passivated with an AlInP shell, which resulted in strong PL emission.

The growth mechanism of the quantum dots were inferred from the InAsP and InP segment lengths as a function of nanowire diameter. Short InAsP segment lengths were found to grow by depletion of In from the Au particle as well as by direct impingement, while longer segments of InAsP and InP grew by diffusive transport of adatoms from the nanowire sidewalls. The present study offers a manner to engineer the lengths of InAsP quantum dots embedded in InP barriers to better control the PL or CL emission. A novel group III and V gas switching sequence is presented to improve compositional control of the QD.
Green Emission of Terbium Doped Silicon Rich Silicon Oxide Films Obtained By Chemical Vapor Deposition
Authors: Podhorodecki Artur , Zatryb Grzegorz , Golacki Lukasz W , Misiewicz Jan , Wojcik Jacek , Willson Patric R.J. , Masher Peter , Wang J , Jadwisienczak Wojciech
Published: February 2020

The effect of silicon concentration, annealing temperature and influence of post-growth hydrogen incorporation on terbium (Tb3+) luminescence was investigated for thin silicon rich silicon oxide films (SRSO). The structures were deposited by means of plasma enhanced chemical vapor deposition (ECR-PECVD). The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy, FTIR and Raman scattering. The optical properties were investigated by means of photoluminescence, cathodoluminescence and photoluminescence decay spectroscopy.

In this poster, we present a detailed discussion of these issues and determine the optimal conditions of the SRSO films from the point of view of Tb3+ emission properties.

An increase in the Si concentration in SRSO influences the emission properties in two ways. First of all, the refractive index of the film increases which enhances the oscillator strength of the optical transitions. On the other hand, the non-radiative recombination also increases, limiting the PL intensity. Therefore, from the point of view of emission efficiency, the optimal Si concentration in the film is about 35 at.% Si. Besides the Si concentration, another effect investigated in this work was the influence of the annealing temperature on Tb3+ emission. It was found that the PL intensity increases as a function of the annealing temperature. This effect was ascribed to the structural changes of the SRSO matrix. At early stages of the annealing (up to annealing temperature equal to 900oC) the most important factor enhancing the Tb3 emission intensity is a reduction in the number of non-radiative recombination centers. However, as shown by Raman measurements, starting from Ta =1100oC structural changes occur in the matrix (crystallization and formation of the Si nanocrystals) and the Tb environment significantly changes. Therefore, the further increase in the PL intensity obtained for high annealing temperatures (temperatures in the 1100–1200 oC range) can be ascribed to the increasing oscillator strength of the intra-4f transitions, induced by the change of the crystal field around the ions.
Influence of Size Purification and Self-Assembly on the Photoluminescence of Silicon Nanocrystal Ensembles
Authors: Miller Joseph , Van Sickle Austin , Anthony Rebecca , Kortshagen Uwe , Kroll Daniel , Hobbie Erik
Published: February 2020

Silicon nanocrystals (SiNCs) synthesized through a nonthermal plasma reaction are purified through density-gradient ultracentrifugation in mixed organic solvents to achieve highly monodisperse fractions. These fractions show a reduction in photoluminescent (PL) linewidth, increased band alignment, and the emergence of short-range crystalline order in dried films. The films display a significant PL enhancement that we suggest arises from nanocrystal interactions in densely packed arrays and we exploit this to achieve photostable emission. We also explore how this PL enhancement emerges, from the scale of individual nanocrystals up to clusters of more than a thousand, and we examine the influence of different polymers on the self-assembly and PL stability of ensemble structures.
Fluorinated Graphene-Based High Performance Electrodes for Primary Lithium Batteries
Authors: Damien Dijo , Sudeep Parambath M , Narayanan Tharangattu , Anantharaman Maleimadam R , Ajayan Pulickel M , Shaijumon Manikoth M
Published: February 2020

Though rechargeable Li ion battery has become the dominant power source for portable electronics applications, primary batteries are used in applications like military and defense tools, medical implants, long time spatial exploratory missions, cameras etc.1 By virtue of the low molecular weight and high redox potential of the constituting elements, Li/CFx primary battery has clear dominance over any other competing primary battery technologies like Li/MnO2 or Li/SOCl2 in terms of its energy density, exceptionally long shelf life and a wide operating temperature window.2, 3 However, with its poor rate capability, owing to low electrical conductivity and diffusion limited kinetics, Li/CFx battery system is less preferred compared to other battery chemistry like MnO2 based systems.2 Different strategies have been developed specifically for improving energy density, power density and faradic yield of Li/CFx batteries.1 However, a single step strategy capable of improving all the electrochemical parameters still remains to be challenge. Here, we demonstrate the use of fluorinated graphene (FG) as high performance cathode for Li primary battery. FG, obtained through chemical exfoliation of fluorinated graphite polymer (CF0.25)n using improved method,4 exhibited enhancements in energy density and power capability along with exceptional faradaic yield, all in a single step. The obtained specific capacity for FG derived from (CF0.25)n in the present work, is comparable to the theoretical capacity of (CF0.75)n. Further improvements in electrochemical performance could be achieved by optimizing the fluorine content in the starting material. The excellent electrochemical performance achieved here using fluorinated graphene with a very low fluorine content (x= 0.22) could lead to the development of highly efficient primary battery systems with low cost and minimum environmental impact.

Figure 1. Comparison of specific capacities of (CF0.25)nand FG electrodes when galvanostatically discharged against lithium at different current rates.

References

1 K. Guérin, M. Dubois, A. Houdayer and A. Hamwi, J. Fluorine Chem., 134 (2012), 11

2 P. Lam and R. Yazami, J. Power Sources, 153 (2006), 354

3 Z. Sheng , D. Foster and J. Read, J. Power Sources, 188 (2009), 601

4 A. Mathkar, T. N. Narayanan, L. B. Alemany, P. Cox, P. Nguyen, G. Gao, P. Chang, R. Romero-Aburto, S. A. Mani and P. M. Ajayan, Part. Part. Syst. Charact., 30 (2013), 266
Thin and Flexible Solid State Electrolytes for Ambient and Middle Temperature Storage Systems
Authors: Ahlbrecht Katharina , Hupbauer Cornelius , Tübke Jens , Hoffmann Michael J
Published: February 2020

Solid state electrolytes are generally used in high-temperature systems such as fuel cells or sodium/sulfur batteries. They are common in stationary energy storage applications. The benefit of the solid state electrolytes is their high ion selective conductivity, even exceeding the value of most liquid electrolytes at elevated temperatures. But a widespread use is hindered by their brittleness and fragility. To use the solid state electrolyte in next generation systems, such as in Li/S, Li/Air or sodium-based systems at ambient or middle temperature, the solid state electrolyte is embedded in a flexible, ductile and non-metallic material by using a recently developed manufacturing process. The advantage of those composite materials is the possibility of their plastic deformation under stress. The connection between the solid state electrolyte and the ductile material can be established for example by surface bonding.

By using adjusted and optimized electrolytes for each electrode in the Li/S battery, intrinsic parasitic effects like the polysulfide shuttle mechanism or electrolyte degradation at the side of the alkaline metal anode could be prevented. As an alternative to commercialized lithium-based batteries sodium-based systems become more and more popular. Due to the low melting temperature of sodium (about 100 °C), it is conceivable to use molten sodium as an anode separated with a thin, flexible and stable solid state electrolyte from a cathode. With this design a formation of dendrites and a reaction with the liquid electrolyte could be reduced and improved cycling stability can be obtained.
Multi-Electrode Configurations for Electrochemical Measurements
Authors: Moss Eugene Newton , Nelson Ruben , Moss Pedro L. , Weatherspoon Mark H.
Published: February 2020

Multiple electrodes for standard electrochemical measurements can provide appropriate results depending on the system. Two electrode measurements are common in such systems where the interactions between the anode and the cathode are of interest, such as in batteries. It is beneficial to understand the capability of three electrode measurements, since this configuration can provide accurate data on a single electrode of interest with respect to a third reference electrode in any system, like in aqueous solution.

The cyclic voltammetry (CV) measurements were performed by the Solartron 1287 at a scan rate of 50 mV/s on a system where a platinum metal counter electrode and a Teflon rod with a circular, planar glassy carbon surface working electrode were immersed in a solution of 0.5 M sodium sulfate (Na2SO4). The EIS measurements were performed by the VersaStat 4 potentiostat on an identical system.

The two electrode CV in Figure 1 show various potentials where anodic and cathodic peaks occur, indicating the presence of oxidation and reduction reactions [1]. The fact that there appears to be two peaks on the voltammogram at about -0.4 V during the forward scan and -0.5 V during the reverse scan suggests that this process is reversible or quasi-reversible [2].

For comparison, a third electrode, a silver/silver chloride (Ag/AgCl) reference electrode, is introduced to the system and a CV is performed, with the results shown in Figure 2. During the forward scan, the peak at -0.4 V in Figure 1 is hardly visible in the Figure 2 measurement, potentially indicating that there is no significant reaction at the working electrode, although it must be considered that the peak in Figure 1 is a much smaller current density scale. The -0.5 V peak on the reverse scan remains, albeit resulting in a different current density. Hence, a possible conclusion can be made in that a change in the rate of reaction at the working electrode is present.

The EIS measurements in Figure 3 show the comparison of the impedance of two different electrodes using a three electrode system. The impedance measurements were performed using the same electrode setup that was used in the three electrode CV measurements. As expected, the impedance of the carbon electrode was much greater than that of the platinum electrode across the spectrum, especially away from the high frequency end.

Acknowledgment

This work was supported by the FREEDM ERC program of the National Science Foundation under award number EEC-08212121.

References

1. Linden, David, and Thomas B. Reddy. Handbook of Batteries. New York: McGraw-Hill, 2002. Print

2. Jan C. Myland, Keith B. Oldham. Quasi-reversible Cyclic voltammetry of a surface confined redox system: a mathematical treatment. Ont. Canada. 2005
Chitosan-Based Polymer Electrolyte Containing an Ionic Liquid and Inorganic Salt
Authors: Chupp Jeremy , Shellikari Annadanesh , Chatterjee Jhunu
Published: February 2020

Abstract:

Electrochemical energy storage systems (e.g. batteries and supercapacitors) have a vital role in the applications of many portable electronics, medical equipment, electric vehicles, military devices, and renewable energy [1]. The advancements in these technologies, increase the demand for electrochemical energy systems to achieve higher levels of performance [2]. The development of these high-performance systems have proven extremely difficult because of the need to simultaneously satisfy multiple battery performance requirements such as high energy, high power, long cycle life, low-cost, wide temperature range, safety, minimal impact to the environment, and flexibility to meet various design needs [3,4].

Currently, conventional electrochemical storage systems suffer from serious problems such as leakage, toxicity, and high-cost disposal, resulting in unsuitable long-term sustainability [1]. Solid polymer electrolytes have attracted considerable attention for their potential in electrochemical devices due to their light weight, thermal stability, reduced risk of leakage, and flexibility [4]. These systems are mainly comprised of a crosslinked network between a polymer, an organic liquid (e.g. ethylene carbonate, propylene carbonate, diethyl carbonate, etc.), and lithium based salt [5].

In this study, a gel electrolyte consisting of the host polymer, chitosan, has been synthesized to compare the crosslinking components, acetic acid and adipic acid. The films were incorporated with an ionic liquid and inorganic salt (LiCl) to increase ionic conductivity. FT-IR plots were compared to determine possible cross-linking mechanisms. Thermal analysis and AC impedeance data were obtained to determine the effect of the crosslinker, as well as the concentration of salt on the thermal stability and ionic conductivity of the gel samples.

References:

[1] N.K. Idris, N.A. Nik Aziz, M.S.M. Zambri, N.A. Zakaria, M.I.N. Isa, Ionic conductivity studies of chitosan-based polymer electrolytes doped with adipic acid. Springer Ionics 2009, 15:643-646

[2] (article in press, main paper I have been following, I couldn’t find it online) M. Yamagata, et. al., Chitosan-based electrolyte containing an ionic liquid for high-performance non-aqueous supercapacitors. Electrochim. Acta (2012)

[3] Edited by Claus Daniel, Jurgen O. Besenhard. Handbook of Battery Materials 2e. Wiley-VCH Verlag GmbH & Co. KGaG (2011)

[4] G P Pandey, Yogesh Kumar, S A Hashm, Ionic Liquid incorporated polymer electrolytes for supercapacitor application. Indian Journal of Chemistry (2012), 49:743-751

[5] Jhunu Chatterjee, Tao Liu, Ben Wang, Jim P. Zhang, Highly conductive PVA organogel electrolytes for applications of lithium batteries and electrochemical capacitors. Solid State Ionics (2010), 181:11-12:531-535
Characteristics of Graphene Oxide /Al2O3 Films on Flexible Substrate
Authors: Fang Te-Hua , Kang Shao-Hui , Chen Ming-Yuan
Published: February 2020

The mechanical and electrical properties of graphene oxide (GO)/ Al2O3 have been investigated. Al2O3 nanoparticles were doped on graphene oxide (GO) films using water-electrophoretic deposition method. The direct synthesis of large-scale GO/Al2O3 films using transfer imprinting processes on a flexible polydimethylsiloxane (PDMS) substrate was conducted. The effect of the GO/ Al2O3 film layers on the optical, electrical, and mechanical properties were discussed.
Enhanced Areal Capacitance of Solid-State Supercapacitors Based on Graphene Mixed Gel Electrolyte
Authors: Wang Jun-Yi , Liao Chiang-Sheng , Luo Yi-Hsiang , Huang Kuo-Yen , Huang Jin-Hua
Published: February 2020

To meet the widely used portable and wearable electronic devices with improved funtionalities, developing flexible energy storage devices with larger energy density is an important issue. To this end, fabricating electrodes with materials that can act well while bending or twisting is necessary. Reduced graphene oxide is a promising candidate because of its outstanding mechanical and chemical properties, easily accessed surface area, and potential to be manufacturable [1]. In this research, we proposed a facile method to fabricate a graphene-based, flexible all solid-state supercapacitors. Briefly in fabrication, reduced graphene oxide (rGO) solution derived from modified Hummers method and hydrazine reduction [2] was directly drop cast on a flexible Au-coated polyimide substrate to form a porous electrode. Then the rGO solution mixed with PVA/H3PO4 was poured onto the electrode and air dried for 12 hours until solidified. Two as-made electrodes were pressed face to face to finish the device encapsulation.

SEM images of drop cast rGO electrode show a layered morphology with pores enable the gel electrolyte to inject in. The electrochemical characteristic of the as-made device is investigated by CV measurement. For the device using PVA/H3PO4 as electrolyte, only 41 mF/cm2
is obtained at the scan rate of 100 mV/s, whereas the device with rGO/PVA/H3PO4 as electrolyte shows 130 mF/cm2, about two times larger. We believe that a suitable mass ratio of rGO dispersed in the gel electrolyte forms a continuous 3D network that can contribute to electric double layer capacitance. The CV result shown in figure 2 comes from the sample using PVA/H3PO4 with 0.1 wt% rGO mixed. And the optimization of varied rGO mass ratio is investigated.

Reference

[1] M. Segal, Nat. Nanotechnol. 2009, 4, 611-613.

[2] D. Li, M. B. Muller, S. Gilje, R. B. Kaner, G. G. Wallace, Nat. Nanotechnol. 2008, 3, 101-105
Sige Selective Epitaxial Growth Process for 22 Nm Node CMOS and Beyond
Authors: Wang Guilei , Tianchun Ye , Luo Jun , Qin Changliang , Xu Yefeng , Chen Tao , Xu Qiang , Hong Peizhen , Yang Tao , Li Chunlong , Xu Gaobo , Yu Jiahan , Yin Haizhou , Li Junfeng , Yan Jiang , Zhu Huilong , Zhao Chao , Radamson Henry H
Published: February 2020

As CMOS technology downscales into 22nm and beyond nodes, strain engineering technologies are widely used to improve the short channel effect and enhance MOS mobility to make high performance devices. During these technology developments, SiGe selective epitaxial growth has been used as stressor material in source and drain (S/D) region to induce uniaxial strain in channel region [1].

In order to further enhance the MOS channel mobility, the recess shape has to be designed to create maximum strain from the grown SiGe layers. To achieve this goal the etch step has been modified to elaborate a sigma (∑) shape recess and a high Ge content film is deposited in S/D regions [2]. Then SiGe epitaxy process becomes sensitive to surface quality of the recess where a careful etching and in- and ex-situ cleaning are demanded.

In this study, selective Si1-xGex growth (0.25≤x≤0.35) with boron concentration of 1-3×1020 cm-3for 22nm node CMOS process has been investigated (see Fig.1). The selectivity issue has examined/tuned around the gate region where both nitride and oxide layers were presented and the thermal budget was decreased to 800 °C to preserve the sigma shape in the S/D regions (see Fig.2).

The structures contained two Si1-xGex layers; where the recess was filled first with Si0.65Ge0.35 and then a cap Si0.75Ge0.25layer to elevate the S/D regions. The purpose for having the elevated SiGe cap layer was to avoid strain relaxation in the SiGe bottom layer during the Ni-silicidation process.

The Ge content in epi-layers on the chips was measured directly by rocking curves (RCs) using high-resolution x-ray diffraction (HRXRD). RC were done at (113) reflection where the incident beam is as low as 2.6° and a large area of sample containing an enormous of number of transistors could be covered by x-ray beam. These RCs were simulated by the Takagi-Taupin equations and compared to the experimental curves in order to obtain the high precision data analysis[3]. In these measurements, the boron concentration was estimated by the strain compensation in SiGe layers. The shift of B-doped SiGe peak was compared to the intrinsic ones and interpreted into the substitutional dopant concentration. In these SiGe layers, the B dopant concentration was quite high and the strain compensation could easily be measured.

Cross-section images where provided by high-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (HRTEM) to measure the layer thickness, epi-quality, and integrity of the whole transistor structures. In the latter analysis, energy dispersive spectroscopy (EDS) technique was also employed to measure the Ge profile in parallel and perpendicular directions in the S/D regions of the transistors.
Finfet Gate Etch Towards 16nm Node CMOS Technology
Authors: Hong Peizhen , Zhao Zhiguo , Li Chunlong , Meng Lingkuan , He Xiaobin , Han Jianghao , Lu Yihong , Xiong WenJuan , Zhang Yongkui , Yin Huaxiang , Zhu Huilong , Li Junfeng , Yan Jiang , Zhao Chao
Published: February 2020

The 3D tri-gate FinFET device architecture is a key transistor scaling to 22nm node and beyond for its excellent short-channel performance[1]. However, compared with planar transistors, it poses greater challenge in the finFET gate etch.[2] As shown in fig.1, the etch needs to stop on top of the fin while etching further down to the STI oxide layer. Therefore, the top of fin needs to endure long time over etch without any structural damage which would adversely affect device performance. What’s more, the gate profile must be vertical and there should not be residual in the corner of gate and fin. It is not an easy task to achieve, at the same time, the three goals of vertical gate profile, no residual in the corner of fin and gate, as well as no structure damage on the top of fin, due to an unavoidable tradeoff. More specifically, vertical gate profile and no residual in the corner of fin demand strong etch function and light polymer, while no structure damage in the top of fin requires weak etch function and heavy polymer, which points to high etch selectivity of silicon to oxide layer.

To achieve good etch results, one often falls into this dilemma. As far as we know, few publicly available papers have provided satisfactory solutions to the above- mentioned problem. In this work, we deal with it.

The process of gate stack with CD below 30nm is illustrated in fig.2. Then, a HBr/O2 process in transformer coupled plasma is applied to finFET gate etch. As shown in fig.3, gate profile is vertical, fin is well protected and no residual appears in the corner fin.

In conclusion, an HBr/O2 plasma etch process of finFET gate with CD below 30nm is investigated.Through appropriate tradeoff , an etch result of vertical gate profile, no residual in the sidewall and corner of fin, no structure damage on the top of fin is achieved.
Real Time Isothermal Raman Spectroscopy of Solid-State Kinetics: Goethite Dehydration in N2 Atmosphere
Authors: Sendova Mariana , Hosterman Brian , Grebe Anthony
Published: February 2020

A novel, real-time, in-situ, micro-Raman technique was developed for the monitoring and physicochemical kinetics characterization of solid-state reactions. The technique comprises the acquisition and analysis of a set of time-dependent, isothermal Raman spectra. The pertinence of the technique is demonstrated by the contributions to the study of the dehydration of synthetic goethite (FeOOH) to hematite (Fe2O3). The process was monitored for up to 16 hrs in N2 atmosphere at temperatures of 220, 230 and 240 oC. The Raman spectral range of 200 to 700 cm-1 was deconvoluted using an iterative fitting algorithm. The isothermal, time-dependent mode analysis yields values for the reaction rates, which exhibit first-order kinetic behavior. The energy barriers of a two-step dehydration process are estimated to be 105 ± 19 kJ/mol and 74 ± 7 kJ/mol in agreement with molecular dynamic simulations (Wen-Juan Zhang et al, J. Mol. Struct.: THEOCHEM, 950 (2010) 20–26). Our study concurs with other reports on the activation energy of the same process in air, employing infrared spectroscopy, thermogravimetry, and differential scanning calorimetry (Walter D., Thermochim. Acta 445 (2006) 195 -199; Prasad et al., J. Asian Earth Sci. 27 (2006) 503-511). This in-situ, Raman spectroscopic experiment is a promising, non-destructive, real-time analysis technique with applications to various kinetic solid-state processes such as oxidation, dehydration, and phase transformations.
Electrical Properties of Alkali/Alkaline-Earth Borosilicate Glass Composite Sealants for Solid Oxide Fuel Cells
Authors: Lee Jae Chun , Kim Kwang-Joong , Kim Bong-Soo , Park Sung
Published: February 2020

Development of a reliable sealant or sealing system remains one of the top priorities in planar solid oxide fuel cells (SOFCs) technology. Recently, a compliant glass seal such as an alkali silicate glass was proposed for SOFCs. In contrast to the conventional glass–ceramic sealant which develops a rigid or semi-rigid microstructure after sealing, the compliant glass shows so called “self-healing” behavior and will remain vitreous without substantial crystallization after sealing and during operation at elevated temperatures. The objective of this study was to investigate the relationship between sealant structure and high temperature electrical conductivities of glass composite sealants for SOFCs. Alkali/alkaline-earth borosilicate glass-based sealants, both with and without Al2O3 or ZrO2 fillers, were heat treated at various temperatures for periods of up to 48 h. The effects of filler type, densification of glass and alkali/alkali-earth oxide content in sealants on the electrical conductivities of the sealants were investigated. The results showed that the electrical conductivity of a glass composite sealant containing ZrO2 filler increased ten times after 48 hours of heat treatment. The electrical conductivity of a ZrO2 filler-containing glass after heat treatment was similar to that of an Al2O3 filler-containing glass. This was attributed to the densification of sealing glass by heat treatment.
Photovoltaic Effect in 0.9BiFeO3-0.1YCrO3 Composite Thin Film Fabricated Using Sequential Pulsed Laser Deposition
Authors: Sharma Yogesh , Misra Pankaj , Katiyar Ram S.
Published: February 2020

We report on photovoltaic properties of 0.9BiFeO3-0.1YCrO3 composite thin film deposited on Pt/TiO2/SiO2/Si substrate by sequential ablation of BiFeO3 and YCrO3 ceramic target using pulsed laser deposition. The desired composition of composite was achieved by controlling ablation time of respective targets. As confirmed by X-ray diffraction pattern the resultant films were found to be polycrystalline in nature, and composed of a mixture of both rhombohedral BiFeO3 and orthorhombic YCrO3 phases. The surface morphology of the as grown films was confirmed by atomic force microscope and found to be smooth and free from particulates. Under the light illumination, the short circuit currents (ISC) = 2.42 μC/cm2, and 0.74 μC/cm2, and open circuit voltages (VOC) = 0.4 V, and 0.32 V were observed in top-bottom and lateral electrode configurations, respectively. Beside this, large ON and OFF photo current ratio and fast decay time have been observed in both the type of electrode configurations. In addition, the interesting multiferroic properties in terms of saturation magnetization of ~ 15 emu/cm3 and the remnant polarization of ~ 7μC/cm2 have been observed.
A Nitrogen Doped Graphene Oxide-Immobilized Glassy Carbon Electrode for the Simultaneous Detection of Dopamine, Uric Acid and Ascorbic Acid
Authors: Chih Yi-Kai , Hsieh YI-Yun , Yang Ming-Chang
Published: February 2020

Nitrogen-doped graphene oxide (NGO) was prepared by rapid thermal pyrolysis of polyvinylpyrrolidone (PVP) in a graphite oxide mixture. The NGO was immobilized on a glassy carbon electrode (GCE) by dispersion of NGO in a Nafion solution, and coating of the mixture on the GCE for drying. This modified electrode, GCE/NGO-Nafion, was applied to simultaneously determine small biomolecules of dopamine (DA), uric acid (UA) and ascorbic acid (AA). Due to its unique surface structure and properties originating from NGO showed highly electrocatalytic activity toward the oxidation of DA, UA and AA. When NGO was immobilized onto the GCE, the sensitivity of DA was found to be 5.621 µA µM-1cm-2 in the concentration range of 0.4-4.0 µM and 2.047 µA µM-1cm-2 in the concentration range of 4.0-20 µM. Similarly, in the UA concentration range of 6.0-48 µM and 48-330 µM, the sensitivity of UA was found to be 0.433 and 0.119 µA µM-1cm-2, respectively. Similarly, in the AA concentration range of 150-400 µM and 400-2000 µM, the sensitivity of AA was found to be 0.038 and 0.009 µA µM-1cm-2, respectively. These results demonstrate that NGO is a promising candidate of advanced electrode material in electrochemical sensing and other electrocatalytic applications.

Acknowledgement

The authors gratefully acknowledge the National Science Council of Taiwan for the financial support (102-2221-E-006-223).
Interdigitated Nanoelectrode Arrays for Enhanced Sensitivity
Authors: Rohan James F. , Moore Michael , Barry Sean , Wahl Amelie , O' Riordan Alan
Published: February 2020

Nanoelectrode arrays offer the potential for enhanced performance due to the improved mass transport characteristics offering the potential for faster and more sensitive electroanalysis. The inter-electrode distance can be tailored to optimise the electrochemical response depending upon the requirements.

Diffusion profiles for nanowire electrode arrays with various inter-electrode distances have shown that nanowires sufficiently spatially resolved and diffusionally independent in potential sweep experiments demonstrate superior electrochemical performance by comparison with nanowires that are relatively close to each other (overlapping diffusion profiles). Alternatively, arrays with diffusionally overlapping profiles exhibit enhanced performance (current amplification) when employing step voltammetric techniques such as square wave voltammetry. This has been attributed to operation in the generator-collector (GC) mode.

In this work we demonstrate that interdigitated gold nanowire arrays fabricated on silicon can also operate in the GC mode in simple potential sweep experiments. Collection efficiencies above 90% are achieved for the nanoelectrode designs employed. The use of nanowire arrays in the GC mode led to a 25 times current amplification over that for single nanowires thereby permitting significantly lower detection limits for electroanalysis.

Figure shows a CV of 2 mM FcCOOH in 10 mM PBS solution produced when the second side of the array is held at -0.15V (red), +0.45V (green), and +0.15V (purple).
Large Sensitivity Enhancement: Incorporation of Ultra-Fine Metal Nanoparticles into Organic Field Effect Transistor and Single Electron Transistor Based Sensors
Authors: Zheng Haisheng , Asbabhi Mohamed , Ramalingam Balavinayagam , Yang Joel Kwang Wei , Gangopadhyay Shubhra
Published: February 2020

We report pentacene-based field effect transistor devices with remarkable improvement in sensitivity towards trace nitroaromatic vapors through the incorporation of high density, sub-2 nm metal nanoparticles (NPs). Exploiting the unique electrical properties of these NPs, we have demonstrated a detection limit of 2,4-dinitrotoluene (DNT) vapor to be 56.6 parts per billion while control samples (without any embedded NPs) showed no observable DNT sensitivity. We attribute this remarkable enhancement in sensitivity to the ability of these NPs to function as discrete nodes, participating in charge transfer with adsorbed nitroaromatic molecules. To further improve sensor performance, we reduced the feature size of the channel down to sub-10 nm level by electron beam lithography. A pentacene nanoflower structure with average size of 300 nm was deposited on top of the sub-2nm Au NPs between the nanogap as the tunneling barrier to reduce the tunneling resistance. With this device configuration, the size-dependent Coulomb charging energies of 0.48 eV (for 0.5 nm size of Au NPs) to 0.11 eV (for 1.93 nm of Au NPs) are much larger than thermal energy under 300 K (0.0259 eV), allowing us to observe single electron tunneling behaviors by simple current-voltage (I-V) measurements at room temperature. The single electron interaction between the SET and the target molecules as well as the sensor performance have also been investigated.
Citrus Limon Peel As a Component of Modified Carbon Paste Electrode for Electrochemical Stripping Analysis of Pb (II)
Authors: Rajawat Deepak Singh , Satsangee Soami Piara
Published: February 2020

The present work deals with the modification of Carbon paste electrode (CPE) with Citrus limon peel to enhance its activity toward metal determination in aqueous samples. Differential pulse anodic stripping voltammetry was utilized to characterize the electrochemical parameters and the performance of this new metal sensor under different preparation and operation conditions. Metal ions were pre-concentrated on the modified electrode surface at open circuit and determination of these metal ions was carried out by stripping voltammetry in anodic direction. Different operational conditions were optimized for determination of lead. The effect of surface active macro molecules was also studied. Enhancement in metal detection and determination has been observed with the modified electrode for Pb (II) as compared to the bare CPE. The LOD values are 59.5 ppb for Pb (II).
Novel Carbon Based Electrochemical C-Reactive Protein Biosensor
Authors: Papa Henry , Chatterjee Jhunu
Published: February 2020

Abstract:

C-Reactive Protein (CRP), found in blood serum has been proven to show a direct correlation to the inflammation of arteries and likelihood of myocardial infarction (MOI) and cardiovascular disease (CVD). Conventionally, CRP is quantified at a third-party laboratory using Enzyme-Linked Immunosorbent Assay (ELISA). A point-of-care, accurate, and cheaper diagnosis technique could allow for rapid CRP detection and reduce health care cost.

Biosensors have been fabricated in attempts to meet diagnoses requirements. Biosensors belong to a class of diagnostic devices that play a significant role in unique detection and measurement of various biomarkers. In order to obtain a CRP biosensor with the necessary sensitivity and selectivity, a nanohybride material with unique catalyst system has been proposed.

The nanohybride material integrates carbon nanotubes (CNT) and metallic nano-particle catalysts. The carbon based material has an enhanced surface area that allows for excellent electrochemical biosensor performance. Immobilization of a CRP reactive enzyme provides for the needed CRP selectivity. These engineered CNT based electrodes have shown excellent sensitivity and detection of CRP as low as 0.025 mg/L.
Synthesis of γ-WO3 By Reactive Spray Deposition Technology for NOx and H2 Sensing
Authors: Jain Rishabh , Liu Yixin , Wang Yang , Lei Yu , Maric Radenka
Published: February 2020

Metal oxide semiconductors such as n-type WO3 has remarkable sensing properties for NOx, NH3, acetone, ethanol, H2 and O3. Sensor response (S) is a function of the conductivity of the WO3 film on interdigited Pt or Au electrodes in given by the following equation:

S = Canalyte/Cair -1

where Canalyte is the conductivity of the film in presence of testing analyte and Cair is the conductivity of the film in air.

The gas detection occurs because of the reaction on the WO3 surface in presence of these gases causing a change in electron concentration and hence fluctuation in electrical conductivity.

In this work Reactive Spray Deposition Technology (RSDT) has been employed as a single step flame based open atmosphere direct deposition process for synthesizing 5-10 nm WO3 particles of primarily γ phase. RSDT is able to synthesize some unique phases of WO3 nano particles by rapidly quenching the particles by a ring of cold air flowing at 28 L/min as soon as they are produced in the hot zone of the flame at temperature around 700 ˚C. The particles reside in the hot zone for 6 milli sec and are quenched immediately. This causes the formation of some very unique phases and incorporation of defects which are otherwise not stable at room temperature.

The RSDT process with optimization of conditions such as temperature of the flame, flow rate of quench air and residence time of the particles in flame is able to synthesize materials with different structures and varying concentration of dopants. The influence of crystal structures on sensing activities will be largely explored.

The structure and morphology of the WO3 films prepared by RSDT has been probed by XRD, Raman Spectroscopy, BET, mercury porosimetry, profilometry, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Fig 1 shows the WO3 nano particles synthesized by RSDT.

Fig 2 shows the sensors used for depositing WO3. The as-prepared WO3 sensors will be applied for the detection of NOx and H2 sensitivities in the range of 30-400 ˚C, and characteristics such as sensitivity, limit of detection, reproducibility, stability will be reported. The selectivity for the interfering analytes such as CO2, NO2, SO2 and humidity will also be investigated. Finally the sensing mechanism will be discussed.
Business Principles in Sensor Development and Commercialization
Authors: Carter Michael T , Stetter Joseph R , Stetter Edward F
Published: February 2020

The overarching goal of sensor development is to provide information and knowledge that can be used beneficially in decision making for individual and societal well being. Additionally, businesses must be profitable in pursuit of this goal or they do not survive. Business development and commercialization of technology involves a set of unique and challenging circumstances and problems. We are familiar with the problems encountered in making basic research a success, but many of us have not been exposed to the practical concepts and issues involved in business development and successful technology commercialization. This presentation will address some of the basic ideas of business, as well as many of the issues that one encounters in taking a sensor technology from the lab to the market. We will explore markets and market fragmentation, the nature of demand, barriers to market entry, supply and distribution chains, competition, intellectual property protection, competitive advantage, the product lifecycle, market analysis and other concepts relevant to sensor development. Understanding these concepts is important for conceiving and executing a commercial strategy.

During these discussions, various sensors, customers and markets will be used as illustrative examples. In particular we will discuss new printed sensors developed at KWJ Engineering and introduced in 2013, where relevant to the discussion. We will examine how regulation, codes and standards drive sensor markets and opportunities and will discuss some key considerations when embarking on invention and practical development of new sensors. Everyone involved in basic or applied sensor R&D should understand the basic realities of marketplaces to have a clear vision of where and how their technology can be implemented in the world.