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Engineers at the University of California San Diego have developed a material that could reduce signal losses in photonic devices. The advance has the potential to boost the efficiency of various light-based technologies including fiber optic communication systems, lasers and photovoltaics.

The discovery addresses one of the biggest challenges in the field of photonics: minimizing loss of optical (light-based) signals in devices known as plasmonic metamaterials.

SEM images of a 'lossless' metamaterial that behaves simultaneously as a metal and a semiconductor. Credit: Ultrafast and Nanoscale Optics Group at UC San Diego

SEM images of a ‘lossless’ metamaterial that behaves simultaneously as a metal and a semiconductor. Credit: Ultrafast and Nanoscale Optics Group at UC San Diego

Plasmonic metamaterials are materials engineered at the nanoscale to control light in unusual ways. They can be used to develop exotic devices ranging from invisibility cloaks to quantum computers. But a problem with metamaterials is that they typically contain metals that absorb energy from light and convert it into heat. As a result, part of the optical signal gets wasted, lowering the efficiency.

In a recent study published in Nature Communications, a team of photonics researchers led by electrical engineering professor Shaya Fainman at the UC San Diego Jacobs School of Engineering demonstrated a way to make up for these losses by incorporating into the metamaterial something that emits light — a semiconductor.

“We’re offsetting the loss introduced by the metal with gain from the semiconductor. This combination theoretically could result in zero net absorption of the signal — a ‘lossless’ metamaterial,” said Joseph Smalley, an electrical engineering postdoctoral scholar in Fainman’s group and the first author of the study.

In their experiments, the researchers shined light from an infrared laser onto the metamaterial. They found that depending on which way the light is polarized — which plane or direction (up and down, side to side) all the light waves are set to vibrate — the metamaterial either reflects or emits light.

“This is the first material that behaves simultaneously as a metal and a semiconductor. If light is polarized one way, the metamaterial reflects light like a metal, and when light is polarized the other way, the metamaterial absorbs and emits light of a different ‘color’ like a semiconductor,” Smalley said.

Researchers created the new metamaterial by first growing a crystal of the semiconductor material, called indium gallium arsenide phosphide, on a substrate. They then used high-energy ions from plasma to etch narrow trenches into the semiconductor, creating 40-nanometer-wide rows of semiconductor spaced 40 nanometers apart. Finally, they filled the trenches with silver to create a pattern of alternating nano-sized stripes of semiconductor and silver.

“This is a unique way to fabricate this kind of metamaterial,” Smalley said. Nanostructures with different layers are often made by depositing each layer separately one on top of another, “like a stack of papers on a desk,” Smalley explained. But the semiconductor material used in this study (indium gallium arsenide phosphide) can’t just be grown on top of any substrate (like silver), otherwise it will have defects. “Rather than creating a stack of alternating layers, we figured out a way to arrange the materials side by side, like folders in a filing cabinet, keeping the semiconductor material defect-free.”

As a next step, the team plans to investigate how much this metamaterial and other versions of it could improve photonic applications that currently suffer from signal losses.

Gadgets are set to become flexible, highly efficient and much smaller, following a breakthrough in measuring two-dimensional ‘wonder’ materials by the University of Warwick.

This is a heterostructure of two-dimensional 'wonder' materials. Credit: Gabriel Constantinescu

This is a heterostructure of two-dimensional ‘wonder’ materials. Credit: Gabriel Constantinescu

Dr Neil Wilson in the Department of Physics has developed a new technique to measure the electronic structures of stacks of two-dimensional materials — flat, atomically thin, highly conductive, and extremely strong materials – for the first time.

Multiple stacked layers of 2D materials — known as heterostructures — create highly efficient optoelectronic devices with ultrafast electrical charge, which can be used in nano-circuits, and are stronger than materials used in traditional circuits.

Various heterostructures have been created using different 2D materials — and stacking different combinations of 2D materials creates new materials with new properties.

Dr Wilson’s technique measures the electronic properties of each layer in a stack, allowing researchers to establish the optimal structure for the fastest, most efficient transfer of electrical energy.

The technique uses the photoelectric effect to directly measure the momentum of electrons within each layer and shows how this changes when the layers are combined.

The ability to understand and quantify how 2D material heterostructures work – and to create optimal semiconductor structures — paves the way for the development of highly efficient nano-circuitry, and smaller, flexible, more wearable gadgets.

Solar power could also be revolutionised with heterostructures, as the atomically thin layers allow for strong absorption and efficient power conversion with a minimal amount of photovoltaic material.

Dr. Wilson comments on the work:

“It is extremely exciting to be able to see, for the first time, how interactions between atomically thin layers change their electronic structure. This work also demonstrates the importance of an international approach to research; we would not have been able to achieve this outcome without our colleagues in the USA and Italy.”

Dr Wilson worked formulated the technique in collaboration with colleagues in the theory groups at the University of Warwick and University of Cambridge, at the University of Washington in Seattle, and the Elettra Light Source, near Trieste in Italy.

Understanding how interactions between the atomic layers change their electronic structure required the help of computational models developed by Dr Nick Hine, also from Warwick’s Department of Physics.

A new spin on electronics


February 15, 2017

Modern computer technology is based on the transport of electric charge in semiconductors. But this technology’s potential will be reaching its limits in the near future, since the components deployed cannot be miniaturized further. But, there is another option: using an electron’s spin, instead of its charge, to transmit information. A team of scientists from Munich and Kyoto is now demonstrating how this works.

The extremely thin, electrically conducting layer between the materials lanthanum-aluminate (LaAlO2) and strontium-titanate (SrTiO3) transports spin-information from the point of injection to a detector. Credit: Christoph Hohmann / Nanosystems Initiative Munich

The extremely thin, electrically conducting layer between the materials lanthanum-aluminate (LaAlO2) and strontium-titanate (SrTiO3) transports spin-information from the point of injection to a detector. Credit: Christoph Hohmann / Nanosystems Initiative Munich

Computers and mobile devices continue providing ever more functionality. The basis for this surge in performance has been progressively extended miniaturization. However, there are fundamental limits to the degree of miniaturization possible, meaning that arbitrary size reductions will not be possible with semiconductor technology.

Researchers around the world are thus working on alternatives. A particularly promising approach involves so-called spin electronics. This takes advantage of the fact that electrons possess, in addition to charge, angular momentum – the spin. The experts hope to use this property to increase the information density and at the same time the functionality of future electronics.

Together with colleagues at the Kyoto University in Japan scientists at the Walther-Meißner-Institute (WMI) and the Technical University of Munich (TUM) in Garching have now demonstrated the transport of spin information at room temperature in a remarkable material system.

A unique boundary layer

In their experiment, they demonstrated the production, transport and detection of electronic spins in the boundary layer between the materials lanthanum-aluminate (LaAlO2) and strontium-titanate (SrTiO3). What makes this material system unique is that an extremely thin, electrically conducting layer forms at the interface between the two non-conducting materials: a so-called two-dimensional electron gas.

The German-Japanese team has now shown that this two-dimensional electron gas transports not only charge, but also spin. “To achieve this we first had to surmount several technical hurdles,” says Dr Hans Hübl, scientist at the Chair for Technical Physics at TUM and Deputy Director of the Walther-Meißner-Institute. “The two key questions were: How can spin be transferred to the two-dimensional electron gas and how can the transport be proven?”

Information transport via spin

The scientists solved the problem of spin transfer using a magnetic contact. Microwave radiation forces its electrons into a precession movement, analogous to the wobbling motion of a top. Just as in a top, this motion does not last forever, but rather, weakens in time – in this case by imparting its spin onto the two-dimensional electron gas.

The electron gas then transports the spin information to a non-magnetic contact located one micrometer next to the contact. The non-magnetic contact detects the spin transport by absorbing the spin, building up an electric potential in the process. Measuring this potential allowed the researchers to systematically investigate the transport of spin and demonstrate the feasibility of bridging distances up to one hundred times larger than the distance of today’s transistors.

Based on these results, the team of scientists is now researching to what extent spin electronic components with novel functionality can be implemented using this system of materials.

University of Pennsylvania researchers are now among the first to produce a single, three-atom-thick layer of a unique two-dimensional material called tungsten ditelluride. Their findings have been published in 2-D Materials.

Unlike other two-dimensional materials, scientists believe tungsten ditelluride has what are called topological electronic states. This means that it can have many different properties not just one.

When one thinks about two-dimensional materials, graphene is probably the first that comes to mind.

The tightly packed, atomically thin sheet of carbon first produced in 2004 has inspired countless avenues in research that could revolutionize everything from technology to drinking water.

One of the most important properties of graphene is that it’s what’s called a zero bandgap semiconductor in that it can behave as both a metal and a semiconductor.

But there are tons of other properties that 2-D materials can have. Some can insulate, others can emit light and still others can be spintronic, meaning they have magnetic properties.

“Graphene is just graphene,” said A.T. Charlie Johnson, a physics professor in Penn’s School of Arts & Sciences. “It just does what graphene does. If you want to have functioning systems that are based on 2-D materials, then you want 2-D materials that have all of the different physical properties that we know about.”

The ability of 2-D materials to have topological electronic states is a phenomenon that was pioneered by Charles Kane, the Christopher H. Browne Distinguished Professor of Physics at Penn.

In this new research, Johnson, physics professor James Kikkawa and graduate students Carl Naylor and William Parkin were able to produce and measure the properties of a single layer of tungsten ditelluride.

“Because tungsten ditelluride is three atoms thick, the atoms can be arranged in different ways,” Johnson said. “These three atoms can take on slightly different configurations with respect to each other. One configuration is predicted to give these topological properties.”

Marija Drndi?, the Fay R. and Eugene L. Langberg Professor of Physics; Andrew Rappe, the Blanchard Professor of Chemistry and a professor of materials science and engineering in the School of Engineering and Applied Science, and Robert Carpick, the John Henry Towne Professor and chair of the Department of Mechanical Engineering and Applied Mechanics, also contributed to the research.

“It’s very much a Penn product,” Johnson said. “We’re collaborating with multiple other faculty members who investigate the material in their own ways, and we brought it all together to put a paper out there. Everybody comes along for the ride.”

The researchers were able to grow this material using a process called chemical vapor deposition. Using a hot-tube furnace, they heated a chip containing tungsten to the right temperature and then introduced a vapor containing tellurium.

“Through good fortune and finding exactly the right conditions, these elements will chemically react and combine to form a monolayer, or three-atom-thick regions of this material,” Johnson said.

Although this material degrades extremely rapidly in air, Naylor, the paper’s first author, figured out ways to protect the material so that it could be studied before it was destroyed.

One thing the researchers found is that the material grows in little rectangular crystallites, rather than the triangles that other materials grow in.

“This reflects the rectangular symmetry in the material,” Johnson said. “They have a different structure so they tend to grow in different shapes.”

Although the research is still in its beginning stages and the researchers haven’t yet been able to produce a continuous film, they hope to conduct experiments to show that it has the topological electronic properties that are predicted.

One property of these topological systems is that any current traveling through the material would only be carried on the edges, and no current would travel through the center of the material. If researchers were able to produce single-layer-thick materials with this property, they may be able to route an electrical signal to go off into different locations.

The ability of this material to have multiple properties could also have implications in quantum computing, which taps into the power of atoms and subatomic phenomena to perform calculations significantly faster than current computers. These 2-D materials might allow for an intrinsically error-tolerant form of quantum computing called topologically protected quantum computing, which requires both semiconducting and superconducting materials.

“With these 2-D materials, you want to realize as many physical properties as possible,” Johnson said. “Topological electronic states are interesting and they’re new and so a lot of people have been trying to realize them in a 2-D material. We created the material where these are predicted to occur, so in that sense we’ve moved towards this very big goal in the field.”

Worldwide silicon wafer area shipments increased 3 percent in 2016 when compared to 2015 area shipments according to the SEMI Silicon Manufacturers Group (SMG) in its year-end analysis of the silicon wafer industry, while worldwide silicon revenues increased by 1 percent in 2016 compared to 2015.

Silicon wafer area shipments in 2016 totaled 10,738 million square inches (MSI), up from the previous market high of 10,434 million square inches shipped during 2015. Revenues totaled $7.21 billion, one percent higher from the $7.15 billion posted in 2015. “Annual semiconductor silicon volume shipments reached record levels for the third year in a row,” said Chungwei (C.W.) Lee, chairman SEMI SMG and Corporate Development VP of GlobalWafers. “However, despite historical shipment highs, the same cannot be said about silicon revenue. The market remains well below pre-downturn levels.”

Annual Silicon* Industry Trends

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016
Area Shipments (MSI)

8,661

8,137

6,707

9,370

9,043

9,031

9,067

10,098

10,434

10,738
Revenues ($B)

12.1

11.4

6.7

9.7

9.9

8.7

7.5

7.6

7.2

7.2

*Shipments are for semiconductor applications only and do not include solar applications

Silicon wafers are the fundamental building material for semiconductors, which in turn, are vital components of virtually all electronics goods, including computers, telecommunications products, and consumer electronics. The highly engineered thin round disks are produced in various diameters (from one inch to 12 inches) and serve as the substrate material on which most semiconductor devices or “chips” are fabricated.

All data cited in this release is inclusive of polished silicon wafers, including virgin test wafers and epitaxial silicon wafers, as well as non-polished silicon wafers shipped by the wafer manufacturers to the end-users.

A team of scientists from the Nanoelectronic Materials Laboratory (NaMLab gGmbH) and the Cluster of Excellence Center for Advancing Electronics Dresden (cfaed) at the Dresden University of Technology have demonstrated the world-wide first transistor based on germanium that can be programmed between electron- (n) and hole- (p) conduction. Transistors based on germanium can be operated at low supply voltages and reduced power consumption, due to the low band gap compared to silicon. Additionally, the realized germanium based transistors can be reconfigured between electron and hole conduction based on the voltage applied to one of the gate electrodes. This enables to realize circuits with lower transistor count compared to state-of-the-art CMOS technologies.

Energy-efficient germanium nanowire transistor with programmable p- and n- conduction is shown. Transmission electron microscope image of cross section. Credit: NaMLab gGmbH

Energy-efficient germanium nanowire transistor with programmable p- and n- conduction is shown. Transmission electron microscope image of cross section. Credit: NaMLab gGmbH

Today´s digital electronics are dominated by integrated circuits built by transistors. For more than four decades transistors have been miniaturized to enhance computational power and speed. Recent developments aim to maintain this trend by employing materials having higher mobility than silicon in the transistor channel, like germanium and indium-arsenide. One of the limitations in using those materials is the higher static power loss in the transistor´s off-state, also originating from their small band gaps. The scientist team around Jens Trommer and Dr. Walter Weber from NaMLab in cooperation with cfaed succeeded in solving this issue by conceiving the germanium-nanowire transistor with independent gating regions. Dr. Weber who leads cfaed’s Nanowire Research Group points out: “For the first time the results demonstrate the combination of low operation voltages with reduced off-state leakage. The results are a key enabler for novel energy efficient circuits.”

The work has been published in the journal ACS Nano.

By Denny McGuirk, SEMI president and CEO

“Do not go where the path may lead, go instead where there is no path and leave a trail.”  Attributed to Ralph Waldo Emerson, this could be the credo of our industry.  Moore’s Law has created $13 trillion of market value and we’ve been pioneering the way forward – since even before Gordon Moore made the famous “observation” that became Moore’s Law more than 50 years ago.  Our industry paved the road forward with advancements in design, materials, processing, equipment, and integration, traveling at the speed of exponential growth number in transistors per chip (doubling approximately every two years).

Today, globally, we’re shipping more than one trillion ICs per year!  Leading-edge chips boast more than 10 billion transistors at the advanced 10nm (gate length) technology node and are made with 3D FinFET architectures formed by 193nm wavelength immersion multi-patterning lithography.  It’s become a very challenging – and very expensive – road (a single lithography tool alone costs in the tens of millions of dollars).  The companies building the road ahead are bigger and fewer as massive bets now need to be placed on new fabs costing more than $5 billion and even $10 billion and where a new single chip design alone costs more than $150 million to bring into production.

What follows, in Part 1 of this two-part article, is a quick look back at the industry in 2016 and the road ahead in 2017 followed by what SEMI achieved in 2016 and where SEMI’s road will lead in 2017 to keep pace our industry charging forward where there is no path. Part 2 (next week’s Global Update) will focus on SEMI 2020 initiatives.

A look back at 2016: “Straight roads do not make skillful drivers”

2016 was definitely not a straight road; truly it was a wild ride – so, SEMI members have become extremely skilled drivers. The semiconductor manufacturing industry had a slow first half with pessimism building throughout the first quarter, but by April semiconductors bottomed and NAND investment and a slate of new China projects drove a strong second half.  For semiconductor equipment, SEMI’s statistics indicate global sales in 2015 were $36.5 billion and 2016 came in at $39.7 billion, ultimately ending up about 9 percent.  For reference semiconductor materials in 2015 was $24.0 billion and 2016 came in at $24.6 billion, up nearly 2.6 percent year-over year (YoY).

But, it turns out, that’s not half the story.  2016 was full of surprises.  At the geopolitical level, Brexit, an impeachment in South Korea, and a Trump win were wholly unanticipated and leave a lot of questions as to how that road ahead might look.  In technology, the Galaxy Note 7 mobile phone became an airline hazard announcement and stalwarts like Yahoo! faded into the background (now part of Verizon).  In part due to challenges of the road ahead (and because the cost of capital remained low) M&A fever continued in semiconductors with more than $100B in deals announced in 2016.

It was an astonishing year for combinations with huge deal announcements such as Qualcomm buying NXP for $47 billion and SoftBank buying ARM for $32 billion.  Meanwhile, mergers in the equipment and materials space continued, to name a few notables ASML’s acquisition of Hermes Microvision, DuPont and Dow announcing the intent to merge (announced December 2015, but still in the works), and Lam Research and KLA-Tencor ultimately calling off their deal due to complications of regulatory pushback.  The extended supply chain was mixing things up, too, with acquisitions like the announcement by Siemens to acquire Mentor Graphics.  It has been very active, overall.  This was the second year of semiconductor M&A deals valued at more than $100 billion, a signal that size and scale is critical to build the road ahead.

A look ahead: “Difficult roads often lead to beautiful destinations”

With all the talk about roads, it’s no surprise that the automotive segment is gathering momentum as a strong growth driver for the electronics supply chain.  Not only is there increasing electronics content in cars for comfort and infotainment, but also for assisted and autonomous driving and electric vehicles which are ushering in a new era of electronics consumption.

Along with automotive, IoT (Internet of Things), 5G, AR/VR (Augmented Reality and Virtual Reality), and AI (Artificial Intelligence) round out a set of powerful IC and electronics applications drivers (see figure).  Per an IHS Study, 5G alone may enable as much as $12.3 trillion in goods and services in 2035. Gartner’s most recent forecast is cause for optimism further down the electronics manufacturing supply chain.  Gartner see IC revenue growing from 2016’s $339.7 billion to 2017’s $364.1 billion up 7.2 percent and growing further in 2018 at $377.9 billion up 3.8 percent.  For semiconductor equipment, SEMI’s forecast indicates 2015 was $36.5 billion, 2016 will come in at $39.7 billion, and 2017 is projected to be $43.4 billion, pointing to both 2016 and 2017 experiencing approximately 9 percent YoY growth.

In 2017, China investment is projected to continue as a major driver, likely consuming over 16 percent of the total global equipment investment (second only to South Korea).  SEMI is currently tracking 20 new fab projects.  Investments come from both multinationals and local Chinese ventures.  A sign of the rise of China is China’s upward production share trend of its own IC consumption market (IC Insights): 8 percent in 2009, 13 percent in 2015, and 21 percent in 2020. Further down in the electronics supply chain, fab equipment related spending in China will rise to more than $10 billion per year by 2018 and remain at that level or above for subsequent years.

NAND will continue to be a major driver with 3D NAND investment leading the way.  Silicon in Package (SiP) and heterogeneous integration will increasingly be solutions to augment traditional feature scaling to fit more transistors into less space at lower costs.  Materials innovations will be relied upon to solve front-end and packaging challenges while standard materials will be the focus of increased efficiencies and cost reduction. 200mm fab capacity will grow and stimulate new 200mm investment with upside driven by power devices and MEMS segments.  Investment in foundry MEMS will grow by an estimated 285 percent (2015 to 2017).

“There are far better things ahead than any we leave behind”

SEMI, the global non-profit association connecting and representing the worldwide electronics manufacturing supply chain, has been growing with the industry for 47 years.  SEMI has evolved over the years, but it has remained as the central point to connect.  Whether connecting for business, connecting for collective action, or connecting to synchronize technology, SEMI connects for member growth and prosperity.

As a reminder, here are SEMI’s mission, vision, and 2020 strategic focus areas.

  • Mission — our focus for the next five years
    • SEMI provides industry stewardship and engages our members to advance the interests of the global electronics manufacturing supply chain.
  • Vision — what we stand for
    • SEMI promotes the development of the global electronics manufacturing supply chain and positively influences the growth and prosperity of its members.  SEMI advances the mutual business interests of its membership and promotes a free and open global marketplace.
  • Members’ Growth — 2020 strategic focus
    • SEMI enables member growth opportunities by evolving SEMI communities and building new communities across the global electronics manufacturing supply chain via cooperation, partnerships, and integration.
  • Members’ Prosperity — 2020 strategic focus
    • SEMI enables members to prosper by building extended supply chain collaboration forums providing opportunities to increase value while optimizing the supply chain for SEMI members.

Our industry is in the midst of a vast change.  To deal with the escalating complexity (making a semiconductor chip now uses the great majority of the periodic table of the elements) and capital cost, many companies have had to combine, consolidate, and increasingly collaborate along the length of the electronics manufacturing supply chain.

Some companies have broadened their businesses by investing in adjacent segments such as Flexible Hybrid Electronics (FHE), MEMS, Sensors, LEDs, PV, and Display.  Lines are blurring between segments – PCBs have morphed into flexible substrates, SiP is both a device and a system.  Electronics integrators are rapidly innovating and driving new form factors, new requirements, and new technologies which require wide cooperation across the length of the electronics manufacturing supply chain and across a breadth of segments.

The business is changing and SEMI’s members are changing.  When SEMI’s members change, SEMI must change, too – and SEMI has, and is.  SEMI developed a transformation plan, SEMI 2020, which I wrote about at the beginning of 2016.  We’re well on our way on this path and in next week’s e-newsletter Global Update, I’d like to update you on what we’ve accomplished and what’s to come.

Research managed by SUNY Polytechnic Institute (SUNY Poly) and conducted by a number of collaborating institutions has led to findings that have been named a top ten 2016 breakthrough in physics by Physics World. The publication recently named the SUNY Poly-led Institute for Nanoelectronics Discovery and Exploration’s (INDEX) “Theme I” work on the negative refraction of electrons in graphene p-n junctions as “a top ten breakthrough,” as it supports the physics for p-n junctions in graphene, which could lead to more powerful and energy efficient computing capabilities in the future.

“SUNY Poly’s position as a world class research institution is unmatched, and our faculty and students should be proud to be a part of that success,” said Dr. Bahgat Sammakia, Interim President of SUNY Polytechnic Institute. “It’s an incredible honor to have research managed by the talented people here at SUNY Poly recognized among the top ten physics breakthroughs of this past year, and I salute the SUNY Poly INDEX team and the researchers at partnering institutions who, collectively, enabled this fascinating research.”

As part of the research, scientists created a p-n junction, a building block of many modern day semiconductor-based electronic devices, in graphene, a two-dimensional honeycomb-shaped form of carbon that is incredibly strong and conductive. By ensuring that the p-n junction interface was smooth, the researchers minimized reflections, which enabled them to measure the negative refraction of electrons, an accomplishment that could one day form the basis of a new type of electronic switch, potentially replacing the transistor, which is currently the basis of computers worldwide. While this research shows that this new type of switch is possible, it could still take many years for any practical applications to result.

“We are excited that this great work of physics has been recognized by Physics World, and as part of the SUNY Poly team, we are thrilled to have solidified INDEX’s funding and look forward to continuing this important work, ” said SUNY Poly Vice President for Research Dr. Michael Liehr. “This acknowledgement is a testament not only to SUNY Poly’s ability to lead collaborations that can have significant research impact, but also to working collaboratively as research partners with other leading institutions such as Columbia University.”

The research that led to the notable findings was specifically conducted at Columbia University, the University of Virginia, and Harvard University, and was managed by SUNY Poly; Cornell University, the National Institute for Materials Science in Japan, and IBM were also recognized by Physics World for their teams’ contributions.

“This work is significant for proving the fundamental physics of the graphene p-n junction, and we are excited that the research of ‘Theme I’ of INDEX has resulted in this recognition,” SUNY Poly Interim Dean of the College of Nanoscale Science and Empire Innovation Professor of Nanoscale Science Dr. Alain Diebold said. “This is a credit to researchers Cory Dean and Jim Hone of Columbia University, who fabricated and measured the test structures using a method called magnetic steering, as well as Avik Ghosh of the University of Virginia, who modeled and simulated the data enabling the interpretation and helping to design new test structures. SUNY Poly was proud to play an enabling role.”

The research was conducted under the SUNY Poly-led umbrella of INDEX, which is one of three active centers in the Semiconductor Research Corporation’s Nanoelectronics Initiative leveraging faculty and students across ten universities. INDEX has three research areas, or themes: graphene p-n junction devices, spintronic devices, and fabrication – with a goal to develop a new switch to replace the transistor. Currently, Dr. Alain Diebold serves as INDEX’s Director, following the tenure of Dr. Michael Liehr, who had previously served as director at the Nanoelectronics Research Institute-funded center. In addition, INDEX is a Semiconductor Research Corporation (SRC) program sponsored by the Nano-Electronics Research Corporation (NERC) and the National Institute of Standards and Technology (NIST).

A team of researchers at the University of Illinois at Urbana-Champaign has advanced gallium nitride (GaN)-on-silicon transistor technology by optimizing the composition of the semiconductor layers that make up the device. Working with industry partners Veeco and IBM, the team created the high electron mobility transistor (HEMT) structure on a 200 mm silicon substrate with a process that will scale to larger industry-standard wafer sizes.

Can Bayram, an assistant professor of electrical and computer engineering (ECE), and his team have created the GaN HEMT structure on a silicon platform because it is compatible with existing CMOS manufacturing processes and is less expensive than other substrate options like sapphire and silicon carbide.

However, silicon does have its challenges. Namely, the lattice constant, or space between silicon atoms, doesn’t match up with the atomic structure of the GaN grown on top of it.

“When you grow the GaN on top, there’s a lot of strain between the layers, so we grew buffer layers [between the silicon and GaN] to help change the lattice constant into the proper size,” explained ECE undergraduate researcher Josh Perozek, lead author of the group’s paper, “Investigation of structural, optical, and electrical characteristics of an AlGaN/GaN high electron mobility transistor structure across a 200mm Si(1 1 1) substrate,” in the Journal of Physics D: Applied Physics.

Without these buffer layers, cracks or other defects will form in the GaN material, which would prevent the transistor from operating properly. Specifically, these defects — threading dislocations or holes where atoms should be–ruin the properties of the 2-dimensional electron gas channel in the device. This channel is critical to the HEMTs ability to conduct current and function at high frequencies.

“The single most important thing for these GaN [HEMT] devices is to have high 2D electron gas concentration,” said Bayram, about the accumulation of electrons in a channel at the interface between the silicon and the various GaN-based layers above it.

“The problem is you have to control the strain balance among all those layers–from substrate all the way up to the channel — so as to maximize the density of the of the conducting electrons in order to get the fastest transistor with the highest possible power density.”

After studying three different buffer layer configurations, Bayram’s team discovered that thicker buffer layers made of graded AlGaN reduce threading dislocation, and stacking those layers reduces stress. With this type of configuration, the team achieved an electron mobility of 1,800 cm2/V-sec.

“The less strain there is on the GaN layer, the higher the mobility will be, which ultimately corresponds to higher transistor operating frequencies,” said Hsuan-Ping Lee, an ECE graduate student researcher leading the scaling of these devices for 5G applications.

According to Bayram, the next step for his team is to fabricate fully functional high-frequency GaN HEMTs on a silicon platform for use in the 5G wireless data networks.

When it’s fully deployed, the 5G network will enable faster data rates for the world’s 8 billion mobile phones, and will provide better connectivity and performance for Internet of Things (IoT) devices and driverless cars.

Germanium may not be a household name like silicon, its group-mate on the periodic table, but it has great potential for use in next-generation electronics and energy technology.

Of particular interest are forms of germanium that can be synthesized in the lab under extreme pressure conditions. However, one of the most-promising forms of germanium for practical applications, called ST12, has only been created in tiny sample sizes–too small to definitively confirm its properties.

“Attempts to experimentally or theoretically pin down ST12-germanium’s characteristics produced extremely varied results, especially in terms of its electrical conductivity,” said Carnegie’s Zhisheng Zhao, the first author on a new paper about this form of germanium.

The study’s research team, led by Carnegie’s Timothy Strobel, was able to create ST12-germanium in a large enough sample size to confirm its characteristics and useful properties. Their work is published by Nature Communications.

“This work will be of interest to a broad range of readers in the field of materials science, physics, chemistry, and engineering,” explained Carnegie’s Haidong Zhang, the co-leading author.

ST12-germanium has a tetragonal structure–the nameST12 means “simple tetragonal with 12 atoms.”(See illustration below.) It was created by putting germanium under about 138 times normal atmospheric pressure (14 gigapascals) and then decompressing it slowly at room temperature.

The millimeter-sized samples of ST12-germanium that the team created were large enough that they could be studied using a variety of spectroscopic techniques in order to confirm its long-debated characteristics.

Like the most common, diamond-cubic form of germanium, they found that ST12 is a semiconductor with a so-called indirect band gap. Metallic substances conduct electrical current easily, whereas insulating materials conduct no current at all. Semiconducting materials exhibit mid-range electrical conductivity. When semiconducting materials are subjected to an input of a specific energy, bound electrons can be moved to higher-energy, conducting states. The specific energy required to make this jump to the conducting state is defined as the “band gap.” While direct band gap materials can effectively absorb and emit light, indirect band gap materials cannot.

“Our team was able to quantify ST12’s optical band gap–where visible light energy can be absorbed by the material–as well as its electrical and thermal properties, which will help define its potential for practical applications,” Strobel said. “Our findings indicate that due to the size of its band gap, ST12-germanium may be a better material for infrared detection and imaging technology than the diamond-cubic form of the element already being used for these purposes.”