bluuebunny/crossref_metadata_2025 huggingface dataset:
Fast and Accurate in-Line Monitor of Boron Implantation Energy and Dose by Spectroscopic Ellipsometry
Authors: Wen Tsai-Yu , Lu Tsuo-Wen , Wang Yu-Ren , Lin Chin-Fu , Wu J Y , Chang Shao-Ju , Chiu Sheng-Min , Huang Chien-Jen , Cheng Chao-Yu , Cheng Juli , Raphael Getin , Jiang Zhiming , Tan Zhengquan
Published: February 2020

Ion implantation is a key process for front end of line semiconductor manufacturing and directly correlates to device performance. Inability to rework mandates precise control. As of today, there is still limited production worthy solution for in-line boron implanted energy and dose monitor on product wafer. This paper describes a fast and accurate in-line method for monitoring Boron (B) implantation energy and dose measurement, simultaneously, in a production environment using spectroscopic ellipsometry (SE) after the source-drain PMOS implant process step. The implanted species damage the silicon substrate lattice, producing amorphous-Si like characteristics and a different refractive and absorption indexes compared to crystalline silicon substrate. Furthermore, the damaged depth is a function of implant energy. SE spectra are very sensitive to measure the optical properties variation of these materials (Figure 1).

In this work, a single look-up optical model is created to monitor the damaged layer. The look-up components relate to implanted dose behavior, the thickness of the damage layer to the implanted depth (energy) behavior.

Secondary Ion Mass Spectrometer (SIMS) is used as a reference tool. Excellent correlation (R2> 0.99) can be achieved between SE results and SIMS (Figure 2). The damaged layer thickness correlates to SIMS depth (Rp); and the look-up model components correlate to SIMS dose.

Q-time limitation must be considered to achieve stable implantation monitoring before annealing. The implanted surface is unstable and damaged depth and implanted dose decay rapidly within a few hours. Q-time correlation formula is used to compensate the implanted decay behavior (Figure 3).

As a result, 1.64% depth and 0.43% dose range variation can be achieved after Q-time correlation is applied. This research also shows that SE metrology is sensitive to other species used for source-drain implantation and can be extended to control NMOS implant process using Arsenic (As) species.
(Invited) Si Waveguide-Integrated High-Speed Ge Photodetector
Authors: Fujikata Junichi , Miura Makoto , Noguchi Masataka , Arakawa Yasuhiko
Published: February 2020

Silicon photonics has recently become a subject of intense interest because it offers an opportunity for low cost, low power consumption, and high bandwidth of optoelectronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects. By the integration of germanium into silicon photonics circuit, very efficient photodetection has been demonstrated for the past several years. However, higher performance with low drive voltage and small footprint has not been achieved.

In this paper, we present a Si waveguide (WG)-integrated PIN-type Ge-PD (photodetector), which shows high speed of 50 GHz bandwidth with small footprint. We also compare Si waveguide-integrated PIN and Schottky Ge PDs, which showed very low dark current density with high efficiency.

We fabricated two types of PIN Ge-PDs, which were evanescently coupled and butt-joint coupled with the Si WGs. The optimized evanescently coupling type of a PIN Ge-PD showed good photoresponsivity of 0.8 to 1.0 A/W and low dark current density of 0.6 nA/um2. It showed 50 GHz bandwidth at Vdc more than 3 V, and 30 GHz at 0 Vdc in case of 10 um optical coupling length. Furthermore, we developed a butt-joint type PIN Ge-PD and achieved 46 GHz bandwidth and high-efficiency with only 5 um optical coupling length.

We also studied PIN and Schottky type Ge PDs. Both PIN and Schottky type Ge PDs showed good photoresponsivity of about 1.0A/W, and a low enough dark current density of 0.4 nA/um2 for the PIN Ge PD and 0.8 nA/mm2 for the Schottky Ge PD. The frequency of the 3 dB bandwidth was 40 GHz for the PIN Ge PD and 30 GHz for the Schottky Ge PD in case of 1 um-thick Ge layer. At lower dc bias voltage (Vdc), a much larger bandwidth was obtained for the PIN Ge PD. From the equivalent circuit model fitting, the Schottky Ge PD showed much larger capacitance around the zero bias voltage.

The PIN Ge PD showed a larger bandwidth with decreasing Ge thickness. About 50 GHz bandwidth was obtained with a voltage more than 3 Vdc, and at even zero bias, 30 GHz bandwidth was obtained.

Finally, we studied a PIN Ge PD with a small footprint and low consumption CMOS TIA circuit. To achieve a smaller footprint and larger impedance gain, we used an inverter-type TIA circuit. We demonstrated large sensitivity and high-speed response of 12.5 Gbps.
Virtual Substrate Technology for Ge1-XSnX Heteroepitaxy on Si Substrates
Authors: Kostecki Konrad , Oehme Michael , Koerner Roman , Widmann Daniel , Gollhofer Martin , Bechler Stefan , Mussler Gregor , Buca Dan , Kasper Erich , Schulze Joerg
Published: February 2020

The fabrication of GeSn layers is one of the worldwide current areas of research in material science. The driving force behind it, is the possibility to realize a group IV direct bandgap semiconductor. Theoretical calculations show values between 10 % for relaxed GeSn crystals and 6 % for tensile-strained GeSn crystals. However, only its synthesis on Si substrates is of interest for the photonic components applications. For the manufacture of GeSn based components on Si substrates, a specific Ge VS (virtual substrate) has to be first realized in order to overcome the large lattice mismatch (≥ 4.2 %). This method has been developed by Kasper et al. for SiGe heterostructures on Si and its here used to provide, without epitaxial break, the desired lattice constant for the grow of Sn based alloys. The use of such VS minimize the number of the threading dislocations as required for high performance optical devices.

The significant progress made in recent years allowed the demonstration of GeSn based electro-optical components integrated on Si.

A compressively strained heterostructure can by relaxed by various methods. These are, for example, special annealing steps, increasing the layer thickness over the critical thickness tcrit or by means of point defects introduced during low temperature growth. If a Ge or GeSn film is deposited directly on Si it relaxes very quickly since the critical thickness is only a few nanometer thick. At the same time the threading dislocation density is extremely high. An alternative is an ultra-thin Ge VS developed in the last few years. The threading dislocation density is significantly reduced by high temperature annealing steps close to the melting point of Ge. This technology is used here as a basis for GeSn structure growth.

The optical properties of the GeSn layers with 2 % and 4 % Sn content are addressed via pin photodetectors fabrication (see Fig. 1). As a reference the GeSn pin detectors were manufactured without VS directly on Si. An overview of the layer structures are shown in figure 2.

The strain statuses of the individual samples were analyzed by RSM (reciprocal space mapping). These show that the samples on Si are 100 % strain relaxed and the samples on Ge VS are still under 50 % rest compressive strain.

The dark current of the individual samples are shown in the figure 3. The GeSn samples grown directly on Si show a much higher dark current due to the significantly higher threading dislocation densities compared to the samples on Ge-VS. At a bias of -1 V, the dark current is increased by more than one order of magnitude. In Figure 4, the optical responsivity of each sample is shown as a function of wavelength.
Phonon Transport and Scattering in Rough and Porous Silicon Nanowires
Authors: Glynn Colm , Jones Kim , McSweeney William , Lotty Olan , Geaney Hugh , Sotomayor Torres Clivia M , Holmes Justin D , O'Dwyer Colm
Published: February 2020

Silicon nanostructures and methods to grow them and influence their structure and morphology has recently been demonstrated to offering a useful strategy to control thermal conductivity and light-matter interactions. The transport and scattering of phonons in Si has demonstrated effective thermoelectric performance largely due to effects caused by surface roughening and nanoscale irregularities in the crystal structure that contribute to diffuse boundary scattering mechanisms. When confinement effects are introduced in crystalline materials the electron and phonon transport can be significantly due to three discrete effects: increased boundary scattering, changes in phonon dispersion, and quantization of phonon transport. Using both room-temperature and in-situ thermal Raman scattering spectroscopy the transport of phonons within Si and its nanostructures can be probed quickly and with little sample preparation. Both ambient and high temperature characteristics of the Si are examined and phonon transport changes between the b-Si and the SiNWs can be linked to scattering effects due to the different morphologies possible using metal-assisted chemical etching to form NWs with tunable porosity and surface roughness. This work demonstrates that by increasing the number of available scattering sites in nanostructured Si within the structure (not just boundary scattering at rough surfaces), the role of four phonon processes on the phonon transport within Si can be optimised. This study is important for providing information on the phonon transport within Si and its nanostructures allowing morphologies that affect phonon transport to be exploited for engineering the thermoelectric properties of future Si devices.

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Ge-Si based Nanowire Thermoelectric Materials in the Phonon Confinement Regime
Authors: Xiang Jie
Published: February 2020

For over a decade, nanotechnology has allowed rational synthesis of nanodot, nanowire and nanotube materials with different structure, composition, and with size control at the atomic precision. These nanoscale building blocks make it possible to explore electronic and energy harvesting devices with completely new operating principles. Similar to photonic and electronic confinement regimes where the device size approaches the wavelength of photon and electron wavefunctions, nanoscale semiconductor materials have enabled a new era of phononic engineering to turn waste heat into power and to explore the greener side of silicon. In particular, we have devised a highly sensitive differential bridge thermometry method to characterize thermal transport properties of individual Ge and heterostructure core-shell Ge/Si nanowires with diameters < 20 nm[1]. The resulting drastically suppressed thermal conductance beyond the diffusive boundary scattering limit is the first experimental evidence for the role of confinement effect on acoustic phonon dispersions in nanowires[2]. Lately we have also explored the high carrier mobility and concentration modulation in the semiconductor Ge/Si nanowires using gate modulation, and presented the first field-effect modulated thermoelectric power factor measurement on nanowires with diameters down to 11 nm[3]. The power factor was found to strongly correlate with carrier mobility and can exceed that of bulk Ge in nanowires with high hole mobility. Taken together, the well-established tunable electronic property, excellent thermoelectric power in Ge/Si nanowire materials, combined with thermal transport in the phonic confinement regime, are expected to open up a new level of thermoelectric performance beyond classical avenues.

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3. J. Moon, J-H. Kim, Z.C.Y. Chen, J. Xiang, and R. Chen, Nano Lett. 2013, 13 (3), 1196–1202.
Nanoengineering Pure Polymers with High Thermal Conductivity
Authors: Cola Baratunde
Published: February 2020

Several researchers are pursuing a better understanding of thermal conductivity in polymers. Significant progress has been made; but the interplay of structure and thermal transport is still not well understood in polymers. Polymers with high thermal conductivity typically have a high degree of crystallinity. Such polymers are usually stretched to align their chains, which is a process that is known to enhance thermal conductivity. But it is difficult to achieve enhanced thermal conductivity with current approaches while retaining the tough, amorphous structure of bulk polymers because aligned, long chains have a thermodynamic preference to fold into crystals. Using electropolymerization in nanoscale templates, in contrast, we found that the thermal conductivity of amorphous polythiophene nanofibers can be over 20 times the bulk value. This enhancement results from significant molecular chain re-orientation in the direction of heat conduction and from high thermal conductivity in individual polythiophene chains. Surface interactions during the templated electropolymerization align polymer chains and prevent them from folding into crystals, demonstrating a unique approach to tailoring macromolecular structure and thermal transport properties. Using vertical arrays of the nanofibers, we demonstrate effective heat transfer at critical contacts in high-power, high-temperature electronics, and in a new class of thermally-conductive flexible substrates. In addition to these results, I will discuss the unique thermal metrology used to extract the thermal conductivity of large area polymer nanofiber arrays.
Thermoelectric Performance of Nanostructured Bismuth-Tellurium and Bismuth-Antimony-Tellurium Powders Fabricated by Galvanic Displacement Reaction Process
Authors: An Chang Yong , Park Jun Young , Chung Chan-Hwa
Published: February 2020

Thermoelectric devices are of promising interest for applications as heat pumps and power generators. The efficiency of thermoelectric devices can be intended by figure of merit (ZT=(S2σT/κ), where S, σ, κ, T are the seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively [2]. In this study, by utilizing the nanosize powder, it is intended to enhance the figure of merit to obtain a low thermal conductivity.

The powder of bismuth-tellurium and bismuth-antimony-tellurium was fabricated using alumina substrate in acid aqueous solution by galvanic displacement reaction process [3]. The advantage of this process is that it can be relatively simple and easy to produce powders from few micrometer to hundreds nanometer in size, and the mass production is facile.

The morphologies of bismuth-tellurium and bismuth-antimony-tellurium powders were characterized using field emission scanning electron microscope (FESEM, JEOL JSM 7000F). X-ray diffraction (XRD) patterns have been investigated with a Bruker Coporation (Cu kα). The composition ratio of powders was confirmed using ICP (PerkinElmer, Optima-4300 DV).

These nanocrystalline bulk materials were prepared by hot pressing nanopowders at 350 °C for 30min with a uni-axial pressure of approximately 40 MPa to form pellets. The measurements of electrical resistivity and seebeck coefficient of the pellet samples have been carried out by using a equipment ULVAC ZEM-3 for operating temperature range of 30 to163 °C. The thermal conductivities have been measured by using a laser flash (ULVAC-RICO).

Fig 1. SEM images of a) Bi2Te3, and b)Bi0.5Sb1.5Te3powders fabricated by galvanic displacement reaction process.

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[2] Z. Lu, L.P. Tan, X. Zhao, and H.H. Hng, J. Mater. chem. C, 1, 6271, (2013)

[3] K. Zhuo, M.G. Jeong, and C-H. Chung, RSC Advances, 3, 12611, (2013)
ALD Synthesis of PbSe Thin Films inside Porous Si Templates for Innovative Thermoelectric Applications
Authors: Zhang Kai , Ramalingom Pillai Arun Deepak , Chen Xin , Baumgart Helmut , Kochergin Vladimir
Published: February 2020

The IV-VI lead chalcogenides are considered as prospective thermoelectric materials which have their potential applications in green renewable energy by waste heat recovery and infrared devices. Among these materials, PbSe demonstrates a remarkable thermoelectric performance, The thermoelectric figure of merit ZT exceeds 1 for both n-type and p-type PbSe at high temperature. ZT is defined as ZT=σS2T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity, respectively. In addition, Se element is more abandant and less costly than Te which is a scarce element [1].

PbSe thin films on Si substrates have been synthesized by various methods. However, a careful literature search reveals, there are few if any reports on the synthesis of PbSe thin films by atomic layer deposition (ALD). The ALD technique exhibits self-limiting surface reactions in each ALD cycle which consequently results in precise layer thickness control, stoichiometry, composition, uniformity of large area on the substrate. ALD also can be used to deposit conformal film onto very complex substrates or nano-porous template surfaces. This is the one advantageous property of ALD which renders it more competitive and promising in porous template nano-structures. In contrast, magnetron sputtering and PLD cannot be used to coat complex 3D structures with PbSe. Furthermore, the growth temperature of ALD is rather low in comparison with other fabrication processes.

In this work we report on the successful synthesis of multiple PbSe thin films on silicon substrates and inside microporous Si templates by thermal ALD, using lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2) and (trimethylsilyl) selenide ((Me3Si)2Se) as the chemical ALD precursors for lead and selenide, respectively. The repetitive structure of nano-porous Si templates offers an additional degree of periodicity in the quest for high ZT thermoelectric films.

The XRD and FE-SEM results reveal that the Lead selenide thin films are polycrystalline at deposition temperatures of 170 °C based on Volmer Weber Island growth mode and have characteristic FCC rock-salt crystal structure as shown in Figure (1), (2) and (3).

References:

H. Wang, Z. M. Gibbs, Y. Takigawa, G. J. Snyder, Energy Environ. Sci., 7, 804 (2014).
Transparent Electrodes Based on Three-Dimensional Nanohelixes Light Harvesting Applications
Authors: Kim Jong Kyu , Choi Ilyong , Kwon Hyunah , Lee Seung Hee , Oh Seung Jae
Published: February 2020

We present transparent electrodes based on 3-dimensional nanohelix array for light harvesting applications. Arrays of nanohelixes fabricated by electron-beam oblique-angle deposition (OAD) of various metal oxides including TiO2, WO3 and ITO have been used for improving the performance of dye-sensitized solar cells (DSSCs), Photoelectrochemical (PEC) cells for water splitting, and organic photovoltaics (OPVs), respectively. Such light harvesting devices with transparent electrodes based on metal-oxides nanohelixes array show enhanced performances such as higher light absorption and power conversion efficiency than devices with conventional thin-film and sintered nanoparticle electrodes. This is attributed to the unique optical, microstructural, and electrical properties of metal-oxides nanohelixes such as enhanced light scattering and large specific area enabled by 3-dimensional geometry, and improved separation and transportation of photo-generated carriers by the near-single-crystallinity of metal-oxides nanohelixes. In addition, a number of applications including dichroic filters for high efficiency white light-emitting diodes, near-perfect anti-reflection coatings for solar cells, and high performance chemical sensors will be discussed.

References

[1] Hyunah Kwon and Jong Kyu Kim et al., Advanced Energy Materials, Accepted (2014).

[2] Seung Hee Lee and Jong Kyu Kim et al., Optics Express (2014).

[3] Xing Yan et al., Advanced Functional Materials 23, 583 (2013).
Transparent Conductive Vanadium Oxide-Based Thin Films from Liquid Precursors
Authors: Glynn Colm , Aureau Damien , Collins Gillian , Etcheberry Arnaud , O'Dwyer Colm
Published: February 2020

New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photovoltaics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. In thin film oxide deposition, where non-uniformities and porosity are not ideal, diffusion from glass substrates into oxide thin films during thermal treatment has previously been considered detrimental and was suppressed using diffusion barriers such as thick coatings of SiO2. In this work, we show how the transparency and conductivity of a dip-coated thin film of vanadium oxide can be markedly improved by substrate diffusion during thermal treatment, resulting in a completely transparent thin film of vanadium oxide-based material with an order of magnitude increase in electrical conductivity. The phase change and stoichiometry variation during thermal annealing of the vanadium oxide dip-coated from liquid precursors is elucidated using X-Ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Angle-resolved transmission spectra correlated the transparency to the changes in optical properties of the thin films and electron microscopy confirms no formal structural change contributes to the change in transparency. Hall probe measurements demonstrate improved conductivity with transparency due to diffusion of cations from the substrate into the host material lattice.

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Invited: From Graphene to Transition-Metal Dichalcogenide (TMDs) Semiconductors: Probing at Atomic Scale
Authors: Pan Minghu
Published: February 2020

Doping is an efficient way to tailor the electronic, chemical, optical and magnetic properties of two-dimensional materials. Although some attention has been paid to the synthesis and potential applications of doped graphene, the nature of the dopants, e.g. the bonding type, the dopant location and the induced perturbation in the graphene lattice, are important to both basic research and practical applications, have not been fully understood. Here, we explored the synthesis of large-area, highly-crystalline monolayer doped graphene sheets via an atmospheric-pressure chemical vapor deposition (AP-CVD) method, and yielding unique types of dopants. Scanning tunneling microscopy/spectroscopy (STM/S) is presently used to explore in-depth intertwined electronic and structural phenomena on doped graphene. Furthermore, with the rising of the transition-metal dichalcogenide (TMDs) materials, we extend our STM/S technique to study the layered TMDs materials by highly resolved STM/S. These microscopic investigations, combining with theoretical calculation, transport and optical measurements of devices, lead to a wide variety of choices with different physico-chemical properties that could be used as components in electronic and sensing devices.
Simulation on the Microelectrode of Cell Electrofusion Chip
Authors: Xianwei Han
Published: February 2020

The process of cell electrofusion including cell alignment, cell electroporation cell electrofusion. Cell manipulation mainly related to the electric field gradient and electroporation is concerned with the intensity of the electric field. The first thing to consider in the design of Cell electrofusion chip is the control of the cell capacity , which depends on the intensity and distribution of the electric field, and this is associated with the applied voltage and the shape and distribution of the microelectrode. In the experiment, we can change the applied voltage, but the shape and distribution of the microelectrodes is hard to change. In order to improve the efficiency of the experiment, the optimum distribution and the size of the microelectrode in the chip should be determined before the experiment. Using COMSOL Multiphysics software to model and simulate the cell electrofusion chip to provide theoretical guidance for optimum chip design and experimental study late.

In this study, five different cell electrofusion chip are simulated. Using the finite element analysis method, combined with COMSOL simulation software, the electric field around the chip microelectrode is simulated and analyzed. Through the establishment of simulation model, to explore the influence on the internal electric field of the cell electrofusion chip be different parameters, including the distribution and spacing of microelectrode, , microelectrode length, width, and the size of the microstructure. Thus, best design parameters of chip microelectrode are achieved.
Simulation and Experimental Studies of the Impact of EOF on the Electroformation of GUVs
Authors: Wang Qiong , Yang Jun , Hu Ning , Liao Yan-jian , Luo Hong-yan
Published: February 2020

Electroformation is widely used to prepare giant unilamellar vesicles (GUVs) because of its simplicity and high-efficiency. As mentioned by many previous studies, electroosmotic flow (EOF) is an important influence factor in the lipid vesicle electroformation, which may induce the peeling off, rearranging, breaking, and self-assembling of deposited amphiphilic molecules (lipid film) to form vesicles finally. However, the influencing mechanism of EOF is not really clear.

In this study, numerical simulation and experimental methods have been used to study the impact of EOF on lipid vesicle electroformation. Simulation results show that EOF can generate vortex near the walls, which will act on the lipid film and induce the formation of lipid vesicles. These results are matched with some previous studies well, and can give some reasonable explanations of those experimental observations. For example, failure to carry out electroformation of GUVs in buffers with high ionic strength is because zeta potential z decreases with increased ionic strengths and then weakens EOF significantly.

According to the simulation results, the electric field within the traditional electroformation method is optimized by applying electric field coplanar with the deposited lipid film. It can solve the terrible vesicle electroformation in high ionic strength buffers and increase the yield, because the strongest EOF appears near the plane in parallel with the electric field in a closed chamber. On-chip experiments show that attached vesicles on the bottom were pulled by EOF and tilted to its direction, so transverse EOF helps the electrofomation. Furthermore, production of GUVs was demonstrated to be several orders of magnitude higher than those of traditional methods.

Figure. Lipid film was deposited on the substrate of the chamber. A 2D modeling of the vertical chamber was numerically studied. A) and B) Velocity profile and streamlines of EOF formed when applying a non-coplanar electric field and a coplanar one, respectively. Arrows illustrate the electric field applied. C) Velocity distributed on the bottom under the effect of different field, which demonstrated the advantage of coplanar electric filed apparently. D) Vesicles generated under the coplanar field. The production proved to be several orders of magnitude higher than those under non-coplanar filed. Vesicles under the arrow were pulled by EOF and tilted to its direction.
GaN Based Optoelectronic Devices: From Ultraviolet Detectors and Visible Emitters Towards THz Intersubband Devices
Authors: McClintock Ryan , Razeghi Manijeh
Published: February 2020

III-Nitride material system (AlGaInN) possesses unique optical, electrical and structural properties such as a wide tunable direct bandgap, large longitudinal optical phonon energy, inherit fast carrier dynamics; good carrier transport properties, high breakdown fields; and high robustness and chemical stability. Thanks to these inherit advantages, they are investigated for everyday to military and scientific applications such as illumination sources; bio-agent detection, concealed weapons/drugs detection; and space exploration.

In the first part of the talk, we will be focusing on ultraviolet (UV) spectrum. Ultraviolet region is very important as many biological agents (such as anthrax) are luminescent in UV. Scattering of short-wavelengths in atmosphere enables non-line-of-sight secure communications in rugged terrains whereas strong reflection/absorption of UV at ionosphere promises secure space-to-space communications. Where photomultiplier tubes are found to be bulky and fragile, and Si(C)-based photodiodes require external filter elements, compact high performance UV (Al)GaN avalanche photodiodes (APDs) can be employed. Via Geiger-mode operation of these APDs, single UV photons can be counted that could enable quantum computing and data encryption in near future.

In the second part of the talk, we will be focusing on visible spectrum. The total annual energy consumption in the United States for lighting is approximately 800 Terawatt-hours and costs $80 billion to the public. The energy consumed for lighting throughout the world entails to greenhouse gas emission equivalent to 70% of the emissions from all the cars in the world. InGaN-based novel light emitting diodes are the key components of an affordable, durable and environmentally benign lighting solution that can achieve unique spectral quality and promise superior energy conversion efficiency than current lighting sources.

In the third part of the talk, we will be focusing towards Terahertz (THz) spectrum. Terahertz spectral range offers promising applications for science (such as cancer detection), industry (such as product defect detection), and military (such as drug, concealed weapon or explosives detection), and III-Nitrides are the integral part of unique quantum cascade laser designs that are theoretically capable of THz lasing at room temperature (RT). Recently, AlN/GaN and AlGaN/GaN superlattices are employed to show intersubband absorption in near- and mid-infrared spectra, respectively. Moreover, AlN/GaN resonant tunneling diodes have been shown to possess negative differential resistance at RT. These recent demonstrations motivate THz emitters at RT.

In conclusion, with continuous developments in material growth/characterization and device processing/measurement technologies, gap engineered III-Nitride materials extend their unique solutions from ultraviolet and visible regime towards THz spectra.
Progress on Large Diameter Single Crystal Growth of SiC
Authors: Ruland Gary , Wu Ping , Xu Xueping , Rengarajan Varatharajan , Zwieback Ilya , Gupta Avi , Ramm Mark
Published: February 2020

Large-diameter SiC single crystals are grown at II-VI by physical vapor transport (PVT). II-VI manufactures up to 150 mm diameter substrates of two types: vanadium doped semi-insulating and nitrogen doped n-type. We have previously discussed in some detail the practice of SiC crystal growth at II-VI [1], and reported on the properties of the grown crystals, including dominating defects and their evolution during growth [2]. This paper is an update on the progress of the growth of high quality large diameter substrates over the past 18 months.

SiC single crystals grown by sublimation exhibit relatively high dislocation densities and may contain slightly misoriented grains. Defect data will be presented on wafers that have been characterized by etch pit density and X-ray rocking curves and topography. Resistivity was characterized by an eddy current measurement for conducting and capacitive based measurement for semi-insulating substrates. Using these methods a comparison of progress will be provided.

We have achieved stacking fault and micro pipe free wafers with a typical total dislocation density of 6x103 cm-2, TSD density of ~1.2x103 cm-2, and typical BPD density of 5x102 cm-2 in 150mm substrates and 3x102 cm-2 in 100mm substrates. For semi-insulating wafers we have achieved resistivities in excess of 1E11ohms*cm.

[1] A. Gupta et al., “Status of Large Diameter SiC Single Crystals”, Materials Science Forum, 2012, vol. 717-720, pp. 3-8.

[2] P. Wu et al., “Defect Evolution during Growth of SiC Crystals”, J. Cryst. Growth, Vol. 310, 7-9 (2008), pp. 1804-1809.
The Materials and Reliability of Power Electronics Devices
Authors: Christou Aris , McCluskey P
Published: February 2020

Small signal commercial electronics have traditionally been designed to operate at temperatures from 0°C to 70°C. Increased temperature often compromises performance and when combined with the higher voltages, current densities, and heat dissipations associated with power electronics can result in an increased susceptibility to oxide breakdown, electromigration, and other catastrophic on-chip failure mechanisms. Furthermore, the large temperature swings of extreme environments and the rapid temperature cycles resulting from turning on and off large amounts of power can cause fatigue of the die, wires, die attach, and substrate in the package. The course sequence focuses on understanding the device technologies, and developing packaging and thermal management strategies that mitigate risks related to the operating temperatures and large temperature cycles common in extreme temperature and power electronics.

Included will be issues related to the effect of high and low operating temperatures on device and packaging reliability, power device (IGBT, MOSFET, BJT) and material (Si, SiC, GaN) selection, passive component and packaging materials selection, thermal management, and assembly of reliable high power and extreme temperature electronic systems. Finally, failure mechanism models for high temperature and power electronics will be presented together with a discussion of design options to mitigate failure.

Topics covered : Reliable design and manufacture of power semiconductor components;Reliable design of power inverters and converters;Effects of temperature on device performance and reliability;Reliable packaging of power modules and assemblies.

The development of robust and reliable power electronic systems for sustainable energy systems requires an understanding of the fundamental degradation processes that can cause failure at the device, interconnection, and packaging level in the environments encountered in a wide range of energy systems applications. The course sequence will present the dominant failure mechanisms at each of these levels, along with selected models and reliability assessment methodologies. Mechanisms to be covered include degradation in GaN and SiC devices; fatigue and fracture of wirebonds, die attach, and substrates in power electronic modules; corrosion and conductive filament formation in boards; and fatigue of solder joints.

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor has been developed and has reached the market. While GaN device and circuit technology is poised to break out in the commercial arena, certain risks or barriers to entry in the market should not be overlooked. The relative technology immaturity of GaN with respect to Silicon and GaAs leave issues like long-term reliability unanswered. The courses also present the main degradation mechanisms of GaN-based HEMTs devices.
New Material Technologies in AlGaN/GaN Based Electronic Devices
Authors: Leszczynski Mike
Published: February 2020

We will show a number of new material technologies which can be applied for the AlGaN/GaN electronic devices. These technologies are as follows:

i) Application of GaN bulk crystals with dislocation density as low as 104 cm-2as substrates to construct HEMTs and power devices. Schottky diodes with an ultra low leakage and high breakdown voltage (above 700 V) will be demonstrated. Fig. 1

shows the I-V characteristics for such diode.

ii) Lateral patterning of SiC substrates to modify locally the offcut. This approach has an advantage of paving the way to monolithically integrated GaN-based and SiC-based devices, as they deserve a different substrate off-cut (0.3 and 4 degrees, respectively).

iii) Lateral patterning of SiC and GaN substrates to get atomically smooth areas, as well as much higher concentration of Al in AlGaN layers avoiding cracking and other defect generation.

For all materials, we will show results of XRD, TEM and AFM studies, as well as electrical characteristics.
Nanomaterial-Based Macroscale Printable Flexible Sensors
Authors: Takei Kuniharu , Harada Shingo , Honda Wataru , Arie Takayuki , Akita Seiji
Published: February 2020

Printable electronics are of great interests for flexible and wearable devices as next generation electronics. In fact, printable electrodes and transistors have been widely studied by using organic and inorganic materials on plastic substrates1-3. To realize the practical, flexible device systems, many components such as transistors, sensors, and displays need to be integrated by using printing methods or compatible macroscale and low-cost fabrication methods.

In this study, we propose printable sensor sheets using nanomaterial-based inorganic and organic solutions4,5. Especially here printable strain and temperature sensors for different kinds of applications are demonstrated on flexible substrates such as silicone rubber, PET, etc. by using a screen printer and a laser patterning technique. As a proof-of-concept, macroscale, low-cost sensor sheet in order to monitor the strain and cracking information from infrastructures and vehicles were fabricated on a silicone rubber using the screen printing method. The results exhibited that high sensitivity (~59%/Pa) strain sensor detected <10 µm displacement on a wall. This suggests that high sensitive low-cost sensor sheet can be used for the infrastructure monitoring system as an example.

Furthermore, we will also talk about our recent results of a self-cleaning passivation layer for the flexible devices and more sensor applications such as an artificial electronic whiskers4 and smart bandage5.

Our proposed printable flexible sensors may be applied to a variety of applications such as human interfaces, infrastructures, and vehicles.

References:

Z. Fan et al., Advanced Materials, 21, 3730, 2009.

K. Takei et al., Nature Materials, 9, 821, 2010.

P. H. Lau et al., Nano Letters, 13, 3864, 2013.

S. Harada et al., ACS Nano, 2014 (DOI:10.1021/nn500845a).

W. Honda et al., Advanced Functional Materials, 2014 (DOI:10.1002/adfm.201303874)
Solar Water Splitting Photoelectrodes Utilizing Oxide 2-Dimensional Electron Gas and Plasmonic Nanoparticles
Authors: Jang Ho Won
Published: February 2020

The solar water splitting is the third generation of solar energy utilizing technology for future energy problem. Through the past years, the technology has been amazingly meliorated, and theoretical basis has been enormously progressed. In recent days, much endeavor has been dedicated to enhancing solar water splitting efficiency. For further improvement, we need to deeply reflect a perspective of charge generation and transport in photoelectrodes and at interfaces between the electrodes and water. One of the most appropriate strategy for this concept would be grafting plasmonics to the photoelectrodes gernally based on oxide semiconductors. If we put plasmonic nanoparticles onto the surface of oxide semiconductors, the photoactivity of the electrodes can be improved by the three mechanisms ; direct electron transfer of hot electrons (DET), local electromagnetic field enhancement (LEMF), and resonant energy transfer (RET). In this reason, revealing the interaction of plasmonic nanoparticles with 2-dimensional electron gas (2DEG) interface which has huge amount of charge in the interface and extremely high mobility would be very interesting. In this talk, we present photoelectrochemical properties of LaAlO3/SrTiO3 2DEG system with plasmonic nanoparticles. Our results clearly reveal the substantial enhancement of photoactivity in SrTiO3 by incorporating 2DEG interface and plasmonic nanoparticles, suggesting the synergetic effect of 2DEG and plasmon for enhaced photoactivity of oxide-based solar water splitting photoelectrodes.
Voltage Control of Magnetization and Its Chemical Properties
Authors: Suzuki Yoshishige , Bonell Frederic , Shiota Youichi , Miwa Shinji , Nozaki Takayuki , Shinjo Teruya
Published: February 2020

Magnetization control using an electric field [1] will be useful because of its expected ultra-low power consumption and coherent behavior. Several experimental approaches to realize it have been done using ferromagnetic semiconductors [2], materials with magnetostriction together with piezo-driver [3], multiferroic materials [4], ferromagnetic metal films sintered in a liquid electrolyte [5], and ultra-thin ferromagnetic layer in solid-state junctions[6-8].

One of the critical issues in the electric field switching is a realization of bi-stable switching. Since the electric field does not break time reversal symmetry, it does not remove degeneracy of two magnetic states with opposite magnetization. Therefore, a selection of an arbitral magnetic state is not straightforward [9]. Here, we demonstrate a realization of the bi-stable switching using a coherent precessional magnetization toggle switching in nanoscale magnetic cells with a few atomic FeCo (001) epitaxial layers adjacent to MgO barrier [10].

The control of the magnetization by voltage requires well controlled interface structure. We have investigated chemical states of the ferromagnetic atoms at interface with MgO using XAS and XMCD, and found several problems that may happen at the interfaces in voltage devices, i.e. segregation [11] and voltage controlled reversible oxidization/reduction [12]. We discuss the significance of those effects and the intrinsic effect.

References:

[1] Curie, P., J. Phys. 3, 393 (1894).

[2] Ohno, H. et al., Nature 408, 944-946 (2000), Chiba, D., et al, Science 301, 943-945 (2003).

[3] Novosad, V. et al., Journal of Applied Physics 87, 6400-6402 (2000), Lee, J.-W., et al., Applied Physics Letters 82, 2458-2460 (2003).

[4] Eerenstein, W., et al., Nature 442, 759-765 (2006), Chu, Y.-H. et al., Nature Materal 7, 478-482 (2008).

[5] Weisheit, M. et al., Science 315, 349-351 (2007).

[6] Maruyama, T. et al., Nature Nanotechnology 4, 158-161 (2009).

[7] M. Endo, et al., Appl. Phys. Lett. 96, 212503 (2010).

[8] D. Chiba, et al., Nat. Mat. 10, 853 (2011) .

[9] Shiota, Y. et al. Applied Physics Express 2, 063001 (2009).

[10] Shiota, Y. et al., Nature Materials, 11, 39-43 (2012).

[11] Bonell, F. et al., Surface Science 616, 125-130 (2013).

[12] Bonell, F. et al., Appl. Phys. Lett. 102, 152401 (2013).
Non-Equilibrium Transport Theory Applied to Nano Electronics Problems
Authors: Asai Yoshihiro , Nakamura Hisao
Published: February 2020

Atomistic non-equilibrium transport theory has been developed a lot in a bit different community than the nano-electronics, i.e., the atomic and molecular junctions community.[1] The NEGF (non-equilibrium Green function) method has been combined with first principle electronic structure methods, which has become a standard tool in nano-electronics, too, nowadays. After making a brief overview of the latest progresses obtained in non-equilibrium transport theory including the heat problem and the noise problem, we will discuss some results obtained in our nano-electronics research. The subject of our discussions includes channel and electrode materials dependence of transport properties of some resistive RAM junctions. [2]

Ref.)

[1] Yoshihiro Asai, “Nonequilibrium phonon effects on transport properties through atomic and molecular bridge junctions”, Phys. Rev. B 78, 045434 (2008).

[2] Takehide Miyazaki, Hisao Nakamura, Kengo Nishio, Hisashi Shima, Hiroyuki Akinaga, and Yoshihiro Asai, ”First-Principles Transport Modeling for Metal/Insulator/Metal Structures”, JPS Conf. Proc. , 012075 (2014).

ACKNOWLEDGMENTS

The authors would like to thank to Drs. Takehide MIYAZAKI, Kengo NISHIO, Hisashi SHIMA, and Hiroyuki AKINAGA for their collaborations and discussions.
Effect of Valence State of Doping Materials on Resistance Switching Characteristics of Doped HfO2 Films
Authors: Lee Kyumin , Kim Young jae , Kim Jong il , Kim Tae ho , Sohn Hyunchul
Published: February 2020

In this work, the effect of valence state of doping materials on the resistance switching characteristics of HfO2 films was investigated in conjunction with an analysis of the film chemical bonding states. TiN/as-grown and doped HfO2/Pt metal-insulator-metal (MIM) stacks were fabricated using HfO2 films with Mg, Al, and Nb doping materials sputtered by reactive dc magnetron co-sputtering. From XPS analysis, the doping concentration of Mg, Al, and Nb doped HfO2 films was 2.2%, 2.9%, and 2.6%, respectively. The resistance switching characteristics of the MIM stacks were examined with a study on the physical properties such as the microstructure and chemical bonding of doped HfO2 films. The microstructure of as-grown HfO2 film and Mg, Al, Nb doped HfO2 films shows the monoclinic and tetragonal structure. And the concentration of non-lattice oxygen of as-grown and doped HfO2 films was related to resistance switching characteristics. TiN/as-grown and doped HfO2/Pt stacks showed typical bipolar resistance switching characteristics after electro-forming. In general, a large number of grain boundaries and high concentration of non-lattice oxygen lead to high conductivity of the metal oxides. The resistance switching characteristics was influenced on change of grain boundaries and the concentration of non-lattice oxygen. From these findings, we estimated that the controlling of microstructure and the chemical bonding states influenced the resistance switching characteristics of doped HfO2.