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China IC industry outlook


October 17, 2017

SEMI, the global industry association and provider of independent electronics market research, today announced its new China IC Industry Outlook Report, a comprehensive report for the electronics manufacturing supply chain. With an increasing presence in the global semiconductor manufacturing supply chain, the market opportunities in China are expanding dramatically.

China is the largest consumer of semiconductors in the world, but it currently relies mainly on semiconductor imports to drive its growth. Policies and investment funds are now in place to further advance the progress of indigenous suppliers in China throughout the entire semiconductor supply chain. This shift in policy and related initiatives have created widespread interest in the challenges and opportunities in China.

With at least 15 new fab projects underway or announced in China since 2017, spending on semiconductor fab equipment is forecast to surge to more than $12 billion, annually, by 2018. As a result, China is projected to be the top spending region in fab equipment by 2019, and is likely to approach record all-time levels for annual spending for a single region.

Figure 1

Figure 1

This report covers the full spectrum of the China IC industry within the context of the global semiconductor industry. With more than 60 charts, data tables, and industry maps from SEMI sources, the report reveals the history and the latest industry developments in China across vast geographical areas ranging from coastline cities to the less developed though emerging mid-western regions.

The China IC industry ecosystem outlook covers central and local government policies, public and private funding, the industry value chain from design to manufacturing and equipment to materials suppliers. Key players in each industry sector are highlighted and discussed, along with insights into China domestic companies with respect to their international peers, and potential supply implications from local equipment and material suppliers. The report specifically details semiconductor fab investment in China, as well as the supply chain for domestic equipment and material suppliers.

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Figure 2

Using a simple layer-by-layer coating technique, researchers from the U.S. and Korea have developed a paper-based flexible supercapacitor that could be used to help power wearable devices. The device uses metallic nanoparticles to coat cellulose fibers in the paper, creating supercapacitor electrodes with high energy and power densities – and the best performance so far in a textile-based supercapacitor.

By implanting conductive and charge storage materials in the paper, the technique creates large surface areas that function as current collectors and nanoparticle reservoirs for the electrodes. Testing shows that devices fabricated with the technique can be folded thousands of times without affecting conductivity.

“This type of flexible energy storage device could provide unique opportunities for connectivity among wearable and internet of things devices,” said Seung Woo Lee, an assistant professor in the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. “We could support an evolution of the most advanced portable electronics. We also have an opportunity to combine this supercapacitor with energy-harvesting devices that could power biomedical sensors, consumer and military electronics, and similar applications.”

The research, done with collaborators at Korea University, was supported by the National Research Foundation of Korea and reported September 14 in the journal Nature Communications.

Yongmin Ko, Minseong Kwon, Wan Ki Bae, Byeongyong Lee, Seung Woo Lee & Jinhan Cho, “Flexible supercapacitor electrodes based on real metal-like cellulose papers,” (Nature Communications, 2017) http://dx.doi.org/10.1038/s41467-017-00550-3

Yongmin Ko, Minseong Kwon, Wan Ki Bae, Byeongyong Lee, Seung Woo Lee & Jinhan Cho, “Flexible supercapacitor electrodes based on real metal-like cellulose papers,” (Nature Communications, 2017) http://dx.doi.org/10.1038/s41467-017-00550-3

Energy storage devices are generally judged on three properties: their energy density, power density and cycling stability. Supercapacitors often have high power density, but low energy density – the amount of energy that can be stored – compared to batteries, which often have the opposite attributes. In developing their new technique, Lee and collaborator Jinhan Cho from the Department of Chemical and Biological Engineering at Korea University set out to boost energy density of the supercapacitors while maintaining their high power output.

They began by dipping paper samples into a beaker of solution containing an amine surfactant material designed to bind the gold nanoparticles to the paper. Next they dipped the paper into a solution containing gold nanoparticles. Because the fibers are porous, the surfactants and nanoparticles enter the fibers and become strongly attached, creating a conformal coating on each fiber.

By repeating the dipping steps, the researchers created a conductive paper on which they added alternating layers of metal oxide energy storage materials such as manganese oxide. The ligand-mediated layer-by-layer approach helped minimize the contact resistance between neighboring metal and/or metal oxide nanoparticles. Using the simple process done at room temperatures, the layers can be built up to provide the desired electrical properties.

“It’s basically a very simple process,” Lee said. “The layer-by-layer process, which we did in alternating beakers, provides a good conformal coating on the cellulose fibers. We can fold the resulting metallized paper and otherwise flex it without damage to the conductivity.”

Though the research involved small samples of paper, the solution-based technique could likely be scaled up using larger tanks or even a spray-on technique. “There should be no limitation on the size of the samples that we could produce,” Lee said. “We just need to establish the optimal layer thickness that provides good conductivity while minimizing the use of the nanoparticles to optimize the tradeoff between cost and performance.”

The researchers demonstrated that their self-assembly technique improves several aspects of the paper supercapacitor, including its areal performance, an important factor for measuring flexible energy-storage electrodes. The maximum power and energy density of the metallic paper-based supercapacitors are estimated to be 15.1 mW/cm2 and 267.3 uW/cm2, respectively, substantially outperforming conventional paper or textile supercapacitors.

The next steps will include testing the technique on flexible fabrics, and developing flexible batteries that could work with the supercapacitors. The researchers used gold nanoparticles because they are easy to work with, but plan to test less expensive metals such as silver and copper to reduce the cost.

During his Ph.D. work, Lee developed the layer-by-layer self-assembly process for energy storage using different materials. With his Korean collaborators, he saw a new opportunity to apply that to flexible and wearable devices with nanoparticles.

“We have nanoscale control over the coating applied to the paper,” he added. “If we increase the number of layers, the performance continues to increase. And it’s all based on ordinary paper.”

In addition to those already mentioned, the research team included Yongmin Ko and Minseong Kwon from Korea University, Wan Ki Bae from the Photoelectronic Hybrids Research Center at the Korea Institute of Science and Technology, and Byeongyong Lee from Georgia Tech.

As microchips become ever smaller and therefore faster, the shrinking size of their copper interconnects leads to increased electrical resistivity at the nanoscale. Finding a solution to this impending technical bottleneck is a major problem for the semiconductor industry.

One promising possibility involves reducing the resistivity size effect by altering the crystalline orientation of interconnect materials. A pair of researchers from Rensselaer Polytechnic Institute conducted electron transport measurements in epitaxial single-crystal layers of tungsten (W) as one such potential interconnect solution. They performed first-principles simulations, finding a definite orientation-dependent effect. The anisotropic resistivity effect they found was most marked between layers with two particular orientations of the lattice structure, namely W(001) and W(110). The work is published this week in the Journal of Applied Physics, from AIP Publishing.

The measured resistivity of epitaxial tungsten layers with (001) and (011) crystal orientation vs thickness d. The tungsten Fermi surface is color coded according to the wave vector dependent Fermi velocity vf. At small thickness, where surface scattering dominates, W(011) is nearly twice as conductive as W(001). Transport simulations indicate that this is due to the anisotropy in the Fermi surface. These results indicate how narrow wires in future computer chips can be made two times more conductive, effectively reducing the required electric power by 50 percent. Credit: Daniel Gall, Rensselaer Polytechnic Institute

The measured resistivity of epitaxial tungsten layers with (001) and (011) crystal orientation vs thickness d. The tungsten Fermi surface is color coded according to the wave vector dependent Fermi velocity vf. At small thickness, where surface scattering dominates, W(011) is nearly twice as conductive as W(001). Transport simulations indicate that this is due to the anisotropy in the Fermi surface. These results indicate how narrow wires in future computer chips can be made two times more conductive, effectively reducing the required electric power by 50 percent. Credit: Daniel Gall, Rensselaer Polytechnic Institute

Author Pengyuan Zheng noted that both the 2013 and 2015 International Technology Roadmap for Semiconductors (ITRS) called for new materials to replace copper as interconnect material to limit resistance increase at reduced scale and minimize both power consumption and signal delay.

In their study, Zheng and co-author Daniel Gall chose tungsten because of its asymmetric Fermi surface — its electron energy structure. This made it a good candidate to demonstrate the anisotropic resistivity effect at the small scales of interest. “The bulk material is completely isotropic, so the resistivity is the same in all directions,” Gall said. “But if we have thin films, then the resistivity varies considerably.”

To test the most promising orientations, the researchers grew epitaxial W(001) and W(110) films on substrates and conducted resistivity measurements of both while immersed in liquid nitrogen at 77 Kelvin (about -196 degrees Celsius) and at room temperature, or 295 Kelvin. “We had roughly a factor of 2 difference in the resistivity between the 001 oriented tungsten and 110 oriented tungsten,” Gall said, but they found considerably smaller resistivity in the W(011) layers.

Although the measured anisotropic resistance effect was in good agreement with what they expected from calculations, the effective mean free path — the average distance electrons can move before scattering against a boundary — in the thin film experiments was much larger than the theoretical value for bulk tungsten.

“An electron travels through a wire on a diagonal, it hits a surface, gets scattered, and then continues traveling until it hits something else, maybe the other side of the wire or a lattice vibration,” Gall said. “But this model looks wrong for small wires.”

The experimenters believe this may be explained by quantum mechanical processes of the electrons that arise at these limited scales. Electrons may be simultaneously touching both sides of the wire or experiencing increased electron-phonon (lattice vibrations) coupling as the layer thickness decreases, phenomena that could affect the search for another metal to replace copper interconnects.

“The envisioned conductivity advantages of rhodium, iridium, and nickel may be smaller than predicted,” said Zheng. Findings like these will prove increasingly important as quantum mechanical scales become more commonplace for the demands of interconnects.

The research team is continuing to explore the anisotropic size effect in other metals with nonspherical Fermi surfaces, such as molybdenum. They found that the orientation of the surface relative to the layer orientation and transport direction is vital, as it determines the actual increase in resistivity at these reduced dimensions.

“The results presented in this paper clearly demonstrate that the correct choice of crystalline orientation has the potential to reduce nanowire resistance,” said Zheng. The importance of the work extends beyond current nanoelectronics to new and developing technologies, including transparent flexible conductors, thermoelectrics and memristors that can potentially store information. “It’s the problem that defines what you can do in the next technology,” Gall said.

A team of University of Wisconsin–Madison engineers has created the most functional flexible transistor in the world — and with it, a fast, simple and inexpensive fabrication process that’s easily scalable to the commercial level.

It’s an advance that could open the door to an increasingly interconnected world, enabling manufacturers to add “smart,” wireless capabilities to any number of large or small products or objects — like wearable sensors and computers for people and animals — that curve, bend, stretch and move.

Literal flexibility may bring the power of a new transistor developed at UW–Madison to digital devices that bend and move. PHOTO COURTESY OF JUNG-HUN SEO, UNIVERSITY AT BUFFALO, STATE UNIVERSITY OF NEW YORK

Literal flexibility may bring the power of a new transistor developed at UW–Madison to digital devices that bend and move. PHOTO COURTESY OF JUNG-HUN SEO, UNIVERSITY AT BUFFALO, STATE UNIVERSITY OF NEW YORK

Transistors are ubiquitous building blocks of modern electronics. The UW–Madison group’s advance is a twist on a two-decade-old industry standard: a BiCMOS (bipolar complementary metal oxide semiconductor) thin-film transistor, which combines two very different technologies — and speed, high current and low power dissipation in the form of heat and wasted energy — all on one surface.

As a result, these “mixed-signal” devices (with both analog and digital capabilities) deliver both brains and brawn and are the chip of choice for many of today’s portable electronic devices, including cellphones.

“The industry standard is very good,” says Zhenqiang (Jack) Ma, the Lynn H. Matthias Professor and Vilas Distinguished Achievement Professor in electrical and computer engineering at UW–Madison. “Now we can do the same things with our transistor — but it can bend.”

Ma is a world leader in high-frequency flexible electronics. He and his collaborators described their advance in the inaugural issue of the journal npj Flexible Electronics, published Sept. 27.

Making traditional BiCMOS flexible electronics is difficult, in part because the process takes several months and requires a multitude of delicate, high-temperature steps. Even a minor variation in temperature at any point could ruin all of the previous steps.

Ma and his collaborators fabricated their flexible electronics on a single-crystal silicon nanomembrane on a single bendable piece of plastic. The secret to their success is their unique process, which eliminates many steps and slashes both the time and cost of fabricating the transistors.

“In industry, they need to finish these in three months,” he says. “We finished it in a week.”

He says his group’s much simpler high-temperature process can scale to industry-level production right away.

“The key is that parameters are important,” he says. “One high-temperature step fixes everything — like glue. Now, we have more powerful mixed-signal tools. Basically, the idea is for flexible electronics to expand with this. The platform is getting bigger.”

His collaborators include Jung-Hun Seo of the University at Buffalo, State University of New York; Kan Zhang of UW–Madison; and Weidong Zhou of the University of Texas at Arlington.

Band gaps, made to order


September 28, 2017

Control is a constant challenge for materials scientists, who are always seeking the perfect material — and the perfect way of treating it — to induce exactly the right electronic or optical activity required for a given application.

One key challenge to modulating activity in a semiconductor is controlling its band gap. When a material is excited with energy, say, a light pulse, the wider its band gap, the shorter the wavelength of the light it emits. The narrower the band gap, the longer the wavelength.

As electronics and the devices that incorporate them — smartphones, laptops and the like — have become smaller and smaller, the semiconductor transistors that power them have shrunk to the point of being not much larger than an atom. They can’t get much smaller. To overcome this limitation, researchers are seeking ways to harness the unique characteristics of nanoscale atomic cluster arrays — known as quantum dot superlattices — for building next generation electronics such as large-scale quantum information systems. In the quantum realm, precision is even more important.

New research conducted by UC Santa Barbara’s Department of Electrical and Computer Engineering reveals a major advance in precision superlattices materials. The findings by Professor Kaustav Banerjee, his Ph.D. students Xuejun Xie, Jiahao Kang and Wei Cao, postdoctoral fellow Jae Hwan Chu and collaborators at Rice University appear in the journal Nature Scientific Reports.

Their team’s research uses a focused electron beam to fabricate a large-scale quantum dot superlattice on which each quantum dot has a specific pre-determined size positioned at a precise location on an atomically thin sheet of two-dimensional (2-D) semiconductor molybdenum disulphide (MoS2). When the focused electron beam interacts with the MoS2 monolayer, it turns that area — which is on the order of a nanometer in diameter — from semiconducting to metallic. The quantum dots can be placed less than four nanometers apart, so that they become an artificial crystal — essentially a new 2-D material where the band gap can be specified to order, from 1.8 to 1.4 electron volts (eV).

This is the first time that scientists have created a large-area 2-D superlattice — nanoscale atomic clusters in an ordered grid — on an atomically thin material on which both the size and location of quantum dots are precisely controlled. The process not only creates several quantum dots, but can also be applied directly to large-scale fabrication of 2-D quantum dot superlattices. “We can, therefore, change the overall properties of the 2-D crystal,” Banerjee said.

Each quantum dot acts as a quantum well, where electron-hole activity occurs, and all of the dots in the grid are close enough to each other to ensure interactions. The researchers can vary the spacing and size of the dots to vary the band gap, which determines the wavelength of light it emits.

“Using this technique, we can engineer the band gap to match the application,” Banerjee said. Quantum dot superlattices have been widely investigated for creating materials with tunable band gaps but all were made using “bottom-up” methods in which atoms naturally and spontaneously combine to form a macro-object. But those methods make it inherently difficult to design the lattice structure as desired and, thus, to achieve optimal performance.

As an example, depending on conditions, combining carbon atoms yields only two results in the bulk (or 3-D) form: graphite or diamond. These cannot be ‘tuned’ and so cannot make anything in between. But when atoms can be precisely positioned, the material can be designed with desired characteristics.

“Our approach overcomes the problems of randomness and proximity, enabling control of the band gap and all the other characteristics you might want the material to have — with a high level of precision,” Xie said. “This is a new way to make materials, and it will have many uses, particularly in quantum computing and communication applications. The dots on the superlattice are so close to each other that the electrons are coupled, an important requirement for quantum computing.”

The quantum dot is theoretically an artificial “atom.” The developed technique makes such design and “tuning” possible by enabling top-down control of the size and the position of the artificial atoms at large scale.

To demonstrate the level of control achieved, the authors produced an image of “UCSB” spelled out in a grid of quantum dots. By using different doses from the electron beam, they were able to cause different areas of the university’s initials to light up at different wavelengths.

“When you change the dose of the electron beam, you can change the size of the quantum dot in the local region, and once you do that, you can control the band gap of the 2-D material,” Banerjee explained. “If you say you want a band gap of 1.6 eV, I can give it to you. If you want 1.5 eV, I can do that, too, starting with the same material.”

This demonstration of tunable direct band gap could usher a new generation of light-emitting devices for photonics applications.

Researchers from the National University of Singapore (NUS) have established new findings on the properties of two-dimensional molybdenum disulfide (MoS2), a widely studied semiconductor of the future.

In two separate studies led by Professor Andrew Wee and Assistant Professor Andrivo Rusydi from the Department of Physics at the NUS Faculty of Science, the researchers uncovered the role of oxygen in MoS2, and a novel technique to create multiple tunable, inverted optical band gaps in the material. These novel insights deepen the understanding of the intrinsic properties of MoS2 which could potentially transform its applications in the semiconductor industry.

The studies were published in prestigious scientific journals Physical Review Letters and Nature Communications respectively.

MoS2 – An alternative to graphene

MoS2 is a semiconductor-like material that exhibits desirable electronic and optical properties for the development and enhancement of transistors, photodetectors and solar cells.

Prof Wee explained, “MoS2 holds great industrial importance. With an atomically thin two-dimensional structure and the presence of a 1.8eV energy band gap, MoS2 is a semiconductor that can offer broader applications than graphene which lacks a band gap.”

Presence of oxygen alters the electronic and optical properties of MoS2

In the first study published in Physical Review Letters on 16 August 2017, NUS researchers conducted an in-depth analysis which revealed that the energy storage capacity or dielectric function of MoS2 can be altered using oxygen.

The team observed that MoS2 displayed a higher dielectric function when exposed to oxygen. This new knowledge shed light on how adsorption and desorption of oxygen by MoS2 can be employed to modify its electronic and optical properties to suit different applications. The study also highlights the need for adequate consideration of extrinsic factors that may affect the properties of the material in future research.

The first author of this paper is Dr Pranjal Kumar Gogoi from the Department of Physics at NUS Faculty of Science.

MoS2 can possess two tunable optical band gaps

In the second study published in Nature Communications on 7 September 2017, the team of NUS researchers discovered that as opposed to conventional semiconductors which typically have only one optical band gap, electron doping of MoS2 on gold can create two unusual optical band gaps in the material. In addition, the two optical bandgaps in MoS2 are tunable via a simple, straight forward annealing process.

The research team also identified that the tunable optical band gaps are induced by strong-charge lattice coupling as a result of the electron doping.

The first author of this second paper is Dr Xinmao Yin from the Department of Physics at NUS Faculty of Science.

The research findings from the two studies lend insights to other materials that possess similar structure with MoS2.

“MoS2 falls under a group of material known as the two-dimensional transitional metal dihalcogenides (2D-TMDs) which are of great research interest because of their potential industrial applications. The new knowledge from our studies will assist us in unlocking the possibilities of 2D-TMD-based applications such as the fabrication of 2D-TMD-based field effect transistors,” said Asst Prof Rusydi.

Leveraging the findings of these studies, the researchers will apply similar studies to other 2D-TMDs and to explore different possibilities of generating new, valuable properties in 2D-TMDs that do not exist in nature.

 Yole Développement (Yole) expects the IGBT market to go over US$ 5 billion by 2022 with a major growth coming from IGBT power module. The high performance that SiC and GaN materials can afford is already creating a battlefield with Silicon based IGBT. To overcome this thread, Si IGBT manufacturers need to look for prompt solutions as technologically update their systems for better efficiency or to increase their IGBT portfolio offer.

How is the IGBT market evolving for different applications? How will the IGBT market face the adoption of high performance WBG based devices?… Yole’s power electronics team proposes you today a new technology & market report titled IGBT market and technology trends 2017 report. Yole’s report presents an overview of the IGBT market including detailed forecasts and a new application section focused on energy storage systems. This analysis is also showing the status of the competitive landscape.

Figure 1

Figure 1

The IGBT market represents a very promising bet for the next few years, announces the “More than Moore” market research and strategy consulting company: its analysts invite you to discover the latest IGBT technology trends and market challenges.

“The IGBT industry will follow power electronics’ growth pattern, mainly caused by the high volume automotive market, especially for the electrification of powertrains in EV/HEV ”, asserts Dr Ana Villamor, Technology & Market Analyst, Power Electronics at Yole Développement.

The EV/HEV sector has great growth prospects because it is still an emerging market with tremendous volume potential.

Another big sector for IGBT is clearly motor drives, which keep on growing, thanks to aggressive regulation targets. Yole Développement forecasts a 4.6% CAGR for motor drives from 2016 to 2022. Photovoltaics and wind are very dynamic markets with growth from huge installations being installed during the last few years. It is worth to say that China led the solar panel implementation in 2016, with an impressive 35 GW installed.

“There will be applications for SiC which will impact the IGBT market, for example it is highly possible that it will take over the automotive market”, comments Dr Ana Villamor. “However, we forecast that IGBTs will keep a significant market share in the power electronics industry and will not be replaced completely.”

In fact, even if the IGBT has almost reached its technological limit, new designs and new materials can still be used to improve system performance to overcome the WBG devices arrival. In coming years, there will be new IGBT designs from Infineon, Fuji or ABB coming into the market. Packages are being improved by different manufacturers to decrease parasitics and improve system efficiency. A clear example is the introduction of the embedded techniques for discrete IGBTs and overmolded solutions for IGBT modules to reduce size or increase functional density.

Currently, IGBT manufacturers can have wide voltage ranges in their portfolios, going from 400 V to 6.5k V. The 400 V IGBTs will directly compete with MOSFETs, whereas IGBTs with voltages higher than 600 V will compete with SJ MOSFETs and WBG devices, which exhibit advantages over IGBTs. Lower voltage IGBTs will not be developed since they do not show any advantage compared with MOSFETs.

As IGBTs is a mature technology, the supply chain is well established, with strong partnerships and companies well positioned in each level.

“Therefore, the main IGBT manufacturers that we included in our 2015 report are still in the IGBT best sellers, except ON Semiconductor, which has become one of the top five IGBT vendors after the acquisition of Fairchild at the end of 2016”, explains Dr Ana Villamor. “However, more companies are entering the IGBT market in order to capture added value, like Littelfuse, who just announced the agreement on the acquisition of IXYS Corporation.”

A group of international physicists, jointly with NUST MISIS researchers, have conducted a series of experiments on graphene bombardment by swift heavy ions. The experimental results show that such a bombardment allows for the creation of nanopores in graphene. The diameter of these nanopores can be adjusted in a range of 1 to 4 nanometers.

The experimental results on graphen bombardment by swift heavy ions, conducted by NUST MISIS scientists together with colleagues from the University of Helsinki and Aalto University (Finland), the University of Nottingham (the United Kingdom), the University of Duisburg-Essen (Germany), the University of Vienna (Austria), the Center of Research on Ions, Materials and Photonics CIMAP (France), Ruder Boskovic Institute (Croatia), and the Institute of Ion Beam Physics & Materials Research (Germany) have been published in Carbon journal.

The experimental results on grapheme bombardment with a large amount of ions of different masses of C, O, Si, I, Au, Ta, Xe with high-energy  (up to 91 MeV) have shown that it is possible to create nanopores with a diameter from 1 to 4 nm when changing the energy of ions. Information on the dependence of nanopores on the energy of ions brings scientists closer to a controlled obtainment of such structures.

“We have experimentally and theoretically studied the process of nanopores occurrence (pores) in graphene after interaction between graphene with ions, as well as studying the dependence of pores` sizes on the type and ions` energy, and the nature of the appearance of these defects in grapheme have been explained,” said Arkady Krasheninikov, visiting Professor at NUST MISIS, Candidate of Physical and Mathematical Sciences, research author, and head of the ‘Minimization of degradation of two-dimensional inorganic materials with the use of atomistic calculations’ project.

According to Krasheninikov, “The current development of grapheme research is connected with studies of the possibility of controlled changes of its properties, for example by introduction of defects in its structure. The creation of defects in graphene can significantly change its electronic and conductive properties, and even lead to the induction of magnetism. One of the possible ways of introducing defects into a graphene structure is a bombardment of ions of different elements.”

Krasheninikov also added that scientists have been interested in nanoporous graphene for quite a while. He believes that the obtained nanostructures can be widely used in various fields of science and technology, in particular in the capacity of materials for the purification of liquids, DNA sequencing, etc.

“One expects that with a regular arrangement of pores in graphene, its spectrum would be readjusted into a semiconductive state and that would allow us to use it in electronics,” added Krasheninikov.

 

A discovery by two scientists at the Energy Department’s National Renewable Energy Laboratory (NREL) could aid the development of next-generation semiconductor devices.

The researchers, Kwangwook Park and Kirstin Alberi, experimented with integrating two dissimilar semiconductors into a heterostructure by using light to modify the interface between them. Typically, the semiconductor materials used in electronic devices are chosen based on such factors as having a similar crystal structure, lattice constant, and thermal expansion coefficients. The close match creates a flawless interface between layers and results in a high-performance device. The ability to use different classes of semiconductors could create additional possibilities for designing new, highly efficient devices, but only if the interfaces between them can be formed properly.

Park and Alberi determined that ultraviolet (UV) light applied directly to the semiconductor surface during heterostructure growth can modify the interface between two layers. Their paper, “Tailoring Heterovalent Interface Formation with Light,” appears in Scientific Reports.

“The real value of this work is that we now understand how light affects interface formation, which can guide researchers in integrating a variety of different semiconductors in the future,” Park said.

The researchers explored this approach in a model system consisting of a layer of zinc selenide (ZnSe) grown on top of a layer of gallium arsenide (GaAs). Using a 150-watt xenon lamp to illuminate the growth surface, they determined the mechanisms of light-stimulated interface formation by varying the light intensity and interface initiation conditions. Park and Alberi found the UV light altered the mixture of chemical bonds at the interface through photo-induced desorption of arsenic atoms on the GaAs surface, resulting in a greater percentage of bonds between gallium and selenium, which help to passivate the underlying GaAs layer. The illumination also allowed the ZnSe to be grown at lower temperatures to better regulate elemental intermixing at the interface. The NREL scientists suggested careful application of UV illumination may be used to improve the optical properties of both layers.

Many next-generation electronic and electro-mechanical device technologies hinge on the development of ferroelectric materials. The unusual crystal structures of these materials have regions in their lattice, or domains, that behave like molecular switches. The alignment of a domain can be toggled by an electric field, which changes the position of atoms in the crystal and switches the polarization direction. These crystals are typically grown on supporting substrates that help to define and organize the behavior of domains. Control over the switching of domains when making crystals of ferroelectric materials is essential for any future applications.

Now an international team by Nagoya University has developed a new way of controlling the domain structure of ferroelectric materials, which could accelerate development of future electronic and electro-mechanical devices.

“We grew lead zirconate titanate films on different substrate types to induce different kinds of physical strain, and then selectively etched parts of the films to create nanorods,” says lead author Tomoaki Yamada. “The domain structure of the nanorods was almost completely flipped compared with [that of] the thin film.”

Lead zirconate titanate is a common type of ferroelectric material, which switches based on the movement of trapped lead atoms between two stable positions in the crystal lattice. Parts of the film were deliberately removed to leave freestanding rods on the substrates. The team then used synchrotron X-ray radiation to probe the domain structure of individual rods.

The contact area of the rods with the substrate was greatly reduced and the domain properties were influenced more by the surrounding environment, which mixed up the domain structure. The team found that coating the rods with a metal could screen the effects of the air and they tended to recover the original domain structure, as determined by the substrate.

“There are few effective ways of manipulating the domain structure of ferroelectric materials, and this becomes more difficult when the material is nanostructured and the contact area with the substrate is small.” says collaborator Nava Setter. “We have learned that it’s possible to nanostructure these materials with control over their domains, which is an essential step towards the new functional nanoscale devices promised by these materials.”

The article, “Charge screening strategy for domain pattern control in nanoscale ferroelectric systems,” was published in Scientific Reports at DOI:10.1038/s41598-017-05475-x