Category Archives: LED Manufacturing

The Semiconductor Industry Association (SIA), representing U.S. leadership in semiconductor manufacturing, design, and research, today announced the global semiconductor industry posted sales totaling $412.2 billion in 2017, the industry’s highest-ever annual sales and an increase of 21.6 percent compared to the 2016 total. Global sales for the month of December 2017 reached $38.0 billion, an increase of 22.5 percent over the December 2016 total and 0.8 percent more than the previous month’s total. Fourth-quarter sales of $114.0 billion were 22.5 percent higher than the total from the fourth quarter of 2016 and 5.7 percent more than the third quarter of 2017. Global sales during the fourth quarter of 2017 and during December 2017 were the industry’s highest-ever quarterly and monthly sales, respectively. All monthly sales numbers are compiled by the World Semiconductor Trade Statistics (WSTS) organization and represent a three-month moving average.

Worldwide semiconductor revenues, year-to-year percent change

Worldwide semiconductor revenues, year-to-year percent change

“As semiconductors have become more heavily embedded in an ever-increasing number of products – from cars to coffee makers – and nascent technologies like artificial intelligence, virtual reality, and the Internet of Things have emerged, global demand for semiconductors has increased, leading to landmark sales in 2017 and a bright outlook for the long term,” said John Neuffer, SIA president and CEO. “The global market experienced across-the-board growth in 2017, with double-digit sales increases in every regional market and nearly all major product categories. We expect the market to grow more modestly in 2018.”

Several semiconductor product segments stood out in 2017. Memory was the largest semiconductor category by sales with $124.0 billion in 2017, and the fastest growing, with sales increasing 61.5 percent. Within the memory category, sales of DRAM products increased 76.8 percent and sales of NAND flash products increased 47.5 percent. Logic ($102.2 billion) and micro-ICs ($63.9 billion) – a category that includes microprocessors – rounded out the top three product categories in terms of total sales. Other fast-growing product categories in 2017 included rectifiers (18.3 percent), diodes (16.4 percent), and sensors and actuators (16.2 percent). Even without sales of memory products, sales of all other products combined increased by nearly 10 percent in 2017.

Annual sales increased substantially across all regions: the Americas (35.0 percent), China (22.2 percent), Europe (17.1 percent), Asia Pacific/All Other (16.4 percent), and Japan (13.3 percent). The Americas market also led the way in growth for the month of December 2017, with sales up 41.4 percent year-to-year and 2.1 percent month-to-month. Next were Europe (20.2 percent/-1.6 percent), China (18.1 percent/1.0 percent), Asia Pacific/All Other (17.4 percent/0.2 percent), and Japan (14.0 percent/0.9 percent).

“A strong semiconductor industry is foundational to America’s economic strength, national security, and global technology leadership,” said Neuffer. “We urge Congress and the Trump Administration to enact polices in 2018 that promote U.S. innovation and allow American businesses to compete on a more level playing field with our counterparts overseas. We look forward to working with policymakers in the year ahead to further strengthen the semiconductor industry, the broader tech sector, and our economy.”

A crystal method


January 31, 2018

From Mother Nature to our must-have devices, we’re surrounded by crystals. Those courtesy of the former, such as ice and snow, can form spontaneously and symmetrically. But the silicon-based or gallium nitride crystals found in LEDs and other electronics require a bit of coaxing to attain their ideal shapes and alignments.

At UC Santa Barbara, researchers have now unlocked another piece of the theoretical puzzle that governs the growth of crystals — a development that may save time and energy in the many processes that require crystal formation.

“The way most industrial processes are designed today is by doing an exhaustively large number of experiments to find out how crystals grow and at what rate they grow under different conditions,” said UCSB chemical engineer Michael Doherty, an author of a paper that appears in the Proceedings of the National Academy of Sciences. Snowflakes, for instance, form differently as they fall, depending on variable conditions such as temperature and humidity, hence the widely held belief that no two are alike. After determining the optimal conditions for the growth of the crystal of choice, Doherty added equipment must be designed and calibrated to provide a consistent growing environment.

However, by pooling decades of expertise, Doherty, along with UCSB colleague Baron Peters and former graduate student Mark Joswiak (now at Dow Chemical) have developed a computational method to help predict growth rates for ionic crystals under different circumstances. Using a relatively simple crystal — sodium chloride (NaCl, more familiarly known as table salt) — in water, the researchers laid the groundwork for the analysis of more complex crystals.

Ionic crystals may appear to the naked eye — and even under some magnification — to consist of perfectly smooth and even faces. But look more closely and you’ll often find they actually contain surface features that influence their ability to grow, and the larger shapes that they take.

“There are dislocations and around the dislocations there are spirals, and around the spirals there are edges, and around the edges there are kinks,” Peters said, “and every level requires a theory to describe the number of those features and the rates at which they change.” At the smallest scale, ions in solution cannot readily attach to the growing crystal because water molecules that solvate (interact with) the ions are not readily dislodged, he said. With so many processes occurring at so many scales, it’s easy to see how difficult it can be to predict a crystal’s growth.

“The largest challenge was applying the various techniques and methods to a new problem — examining ion attachment and detachment at surface kink sites, where there is a lack of symmetry coupled with strong ion-water interactions,” Joswiak said. “However, as we encountered problems and found solutions, we gained additional insight on the processes, the role of water molecules and differences between sodium and chloride ions.”

Among their insights: Ion size matters. The researchers found that due to its size, the larger chloride ion (Cl-) prevents water from accessing kink sites during detachment, limiting the overall rate of sodium chloride dissolution in water.

“You have to find a special coordinate system that can reveal those special solvent rearrangements that create an opening for the ion to slip through the solvent cage and lock onto the kink site,” Peters said. “We demonstrated that at least for sodium chloride we can finally give a concrete answer.”

This proof-of-concept development is the result of the Doherty Group’s expertise with crystallization processes coupled with the Peters Group’s expertise in “rare events” — relatively infrequent and short-lived but highly significant phenomena (such as reactions) that fundamentally change the state of the system. Using a method called transition path sampling, the researchers were able to understand the events leading up to the transition state. The strategy and mechanistic insights from the work on sodium chloride provides a blueprint for predicting growth rates in materials synthesis, pharmaceuticals and biomineralization.

Seoul Semiconductor Co., Ltd. (KOSDAQ 046890), a developer of LED (light emitting diode) design and manufacturing, today announced 2017 fiscal year consolidated revenues of US$ 1.04 billion. The 16% rise in consolidated revenues far exceeds the industry average, which grew 2% during the same period. The growth of revenue is contributed to improvements in both general lighting sales and IT product related sales growing in the mid-teens as well as the automotive lighting business which grew more than 20%.

The rise in revenue for the general lighting segment was largely due to an increase in sales of 220V and 370V Acrich MJT products for household and industrial applications. Other notable revenue increases were reported for WICOP, an innovative product line of package-less LEDs, as well as for the Acrich NanoDriver, which incorporates step drive methods that achieve results greater than those of conventional SMPS technology. In addition to offering these differentiated technologies, Seoul expects its SunLike natural spectrum LED technology, which may offer health benefits for human eyes, to lead the future of LED lighting and become a large contributor to the future sales and profit for the company.

Researchers who won the Nobel Prize in 2017 were recognized for their new findings of the impact of light on circadian rhythm in humans. This has proven to be an important topic in our society and generated great attention for Dr. Charles Czeisler, the Harvard professor that has dedicated his research to this particular area. He is now conducting research study with NASA on how light affects the circadian rhythms of astronauts.

According to new research, myopia (near-sightedness) increased from 20% in the 1950s to 80% in 2010 among populations in Asia. Fluorescent lights and conventional LED light sources emit a strong blue light that is known to cause eye fatigue, which may later result in retinal damage. Seoul Semiconductor, together with Toshiba Materials of Japan, has jointly developed SunLike natural spectrum LED technology, which provides lighting conditions most similar to actual sun light and can be seen as a solution that helps to protect human eyes from this potential damage.

The company provided a revenue guidance of KrW 270 to 290 billion for the first quarter of 2018. This figure is in range of 5% to 13% on a year-over-year basis. Although first quarter is normally considered to be an off-season, the company is showing a positive outlook for growth from last year for this 2018 fiscal year.

Sangbum Kim, the company’s Chief Financial Officer, has stated that fiscal year 2017 sales were a result of the company’s relentless efforts to stay ahead of competition by continuously investing in R&D and strengthening global sales organizations. In order to further accelerate revenue growth into the double digit range for 2018, the company plans to further drive sales of differentiated products such as SunLike while also shifting more focus to its rapidly growing automotive lighting business.

Advanced Micro-Fabrication Equipment Inc. (AMEC) today announced that the Patent Re-examination Board (PRB) of the State Intellectual Property Office (SIPO) in China, ruled on Jan. 23 that all patent claims relating to patent number ZL 01822507.1 held by Veeco Instruments Inc. (Veeco U.S.), and titled “Susceptorless reactor for growing epitaxial layers on wafers by chemical vapor deposition”, are invalid. The court cited “lack of novelty and non-obviousness” for its decision.

The patent ruled invalid is the Chinese counterpart of the patents (U.S. 6506252 and U.S. 6726769) asserted by Veeco U.S. in an infringement action taken last year against AMEC’s wafer carrier supplier, and filed in the U.S. District Court for the Eastern District of New York.

AMEC thoroughly analyzed the patent when first developing its MOCVD technology. The company found that the technology covered by the patent was preceded by substantial prior art dating back to the 1960s. As such, the patent should be invalid. AMEC had earlier filed petitions to invalidate the counterpart patents in the Intellectual Property (IP) offices of China, South Korea and the U.S.

“We are pleased that based on our compelling evidence, the Chinese Patent Re-examination Board has ruled Veeco’s patent invalid,” said Dr. Zhiyou Du, senior vice president, COO & general manager of AMEC’s MOCVD product division. “We are confident that the same decision will be reached by the Patent Trial and Appeal Boards of the U.S. Patent & Trademark Office and the Korean IP office.”

Dr. Du continued: “To be enforceable, a patent must meet the requirements of patent law. It is intolerable to us that Veeco U.S. would attempt to stifle competition by leveraging an obviously invalid patent to file a lawsuit against AMEC’s wafer carrier supplier.”

In a separate development that occurred on Jan. 12, 2018, Chinese customs temporarily detained two EPIK700 MOCVD tools upon their arrival in China. The tools, shipped by Veeco Asia, are suspected of infringing AMEC’s patent (CN 202492576). The detention was consistent with Chinese law. AMEC is contemplating further legal action, which may include filing a patent infringement lawsuit with the Chinese court.

The enforcement action by Chinese customs on Jan. 12 followed a ruling last Dec. by the Fujian High Court in Chinawhen it granted AMEC’s motion for an injunction against Veeco Shanghai. The injunction prohibits Veeco Shanghai from importing, manufacturing, selling or offering for sale to any third party any MOCVD systems and wafer carriers used in the MOCVD systems that would infringe AMEC’s patent in China.

Dr. Gerald Yin, chairman and CEO of AMEC stated: “AMEC will never tolerate infringement of its IP rights. We will vigorously defend against violations and will always proactively protect our IP investment. Of course, we prefer to concentrate on innovating high-value products and providing quality services to customers instead of wasting time and resources on lawsuits.”

Dr. Yin concluded: “The Chinese LED industry should not be distracted or harmed by litigation involving Veeco U.S., our wafer carrier supplier, and AMEC. Therefore, we are open to reaching a solution that is beneficial for all three parties.”

By Jay Chittooran, Manager, Public Policy, SEMI

International trade is one of the best tools to spur growth and create high-skill and high-paying jobs. Over 40 million American jobs rely on trade, and this is particularly true in the semiconductor supply chain. Over the past three decades, the semiconductor industry has averaged nearly double-digit growth rates in revenue and, by 2030, the semiconductor supply chain is forecast to reach $1 trillion. Trade paves the way for this growth.

Unfortunately, despite its importance to the industry, trade has been transformed from an economic issue into a political one, raising many new trade challenges to companies throughout the semiconductor industry.

GHz-ChinaChina’s investments in the industry will continue to anchor the country as a major force in the semiconductor supply chain. China’s outsized spending has spawned concern among other countries about the implications of these investments. According to SEMI’s World Fab Forecast, 20 fabs are being built in China – and construction on 14 more is rumored to begin in the near term – compared to the 10 fabs under construction in the rest of the world. China is clearly outpacing the pack.

The Trump Administration has levied intense criticism of China, citing unfair trade practices, especially related to intellectual property issues. The U.S. Trade Representative has launched a Section 301 investigation into whether China’s practice of forced technology transfer has discriminated against U.S. consumers. Even as the probe unfolds, expectations are growing that the United States will take action against China, raising fears of not only possible retaliation in time but rising animosity between two trading partners that rely deeply on each other.

A number of other open investigations also cloud the future. The Administration launched two separate Section 232 investigations into steel and aluminum industry practices by China, claiming Chinese overproduction of both items are a threat to national security. The findings from these investigations will be submitted to the President, who, in the coming weeks, will decide an appropriate response, which could include imposing tariffs and quotas.

Another high priority area is Korea. While U.S. threats to withdraw from the U.S.-Korea Free Trade Agreement (KORUS) reached a fever pitch in August, rhetoric has since tempered. Informal discussions between the countries on how best to amend the trade deal are ongoing. The number of KORUS implementation issues aside, continued engagement with Korea – instead of scrapping a comprehensive, bilateral trade deal – will be critically important for the industry.

Lastly, negotiations to modernize the North American Free Trade Agreement (NAFTA) will continue this year. The United States wants to conclude talks by the end of March, but with the deadline fast approaching and the promise of resolution waning, tensions are running high. Notably, the outcome of the NAFTA talks will inform and set the tone for other trade action.

What’s more, a number of other actions on trade will take place this year. As we wrote recently, Congress has moved to reform the Committee on Foreign Investment in the United States (CFIUS), a government body designed to review sales and transfer of ownership of U.S. companies to foreign entities. Efforts have also started to revise the export control regime – a key component to improving global market access and making international trade more equitable.

SEMI will continue its work on behalf of its members around the globe to open up new markets and lessen the burden of regulations on cross-border trade and commerce. In addition, SEMI will continue to educate policymakers on the critical importance of unobstructed trade in continuing to push the rapid advance of semiconductors and the emerging technologies they enable into the future. If you are interested in more information on trade, or how to be involved in SEMI’s public policy program, please contact Jay Chittooran, Manager, Public Policy, at [email protected].

For the first time an international research group has revealed the core mechanism that limits the indium (In) content in indium gallium nitride ((In, Ga)N) thin films – the key material for blue light emitting diodes (LED). Increasing the In content in InGaN quantum wells is the common approach to shift the emission of III-Nitride based LEDs towards the green and, in particular, red part of the optical spectrum, necessary for the modern RGB devices. The new findings answer the long-standing research question: why does this classical approach fail, when we try to obtain efficient InGaN-based green and red LEDs?

This is a scanning transmission electron microscopy image of the atomic ordering in (In, Ga)N monolayer: single atomic column, containing only indium (In) atoms (shown by higher intensity on the image), followed by two, containing only gallium (Ga) atoms. Credit: IKZ Berlin

This is a scanning transmission electron microscopy image of the atomic ordering in (In, Ga)N monolayer: single atomic column, containing only indium (In) atoms (shown by higher intensity on the image), followed by two, containing only gallium (Ga) atoms. Credit: IKZ Berlin

Despite the progress in the field of green LEDs and lasers, the researchers could not overcome the limit of 30% of indium content in the films. The reason for that was unclear up to now: is it a problem of finding the right growth conditions or rather a fundamental effect that cannot be overcome? Now, an international team from Germany, Poland and China has shed new light on this question and revealed the mechanism responsible for that limitation.

In their work the scientists tried to push the indium content to the limit by growing single atomic layers of InN on GaN. However, independent on growth conditions, indium concentrations have never exceeded 25% – 30% – a clear sign of a fundamentally limiting mechanism. The researchers used advanced characterization methods, such as atomic resolution transmission electron microscope (TEM) and in-situ reflection high-energy electron diffraction (RHEED), and discovered that, as soon as the indium content reaches around 25 %, the atoms within the (In, Ga)N monolayer arrange in a regular pattern – single atomic column of In alternates with two atomic columns of Ga atoms. Comprehensive theoretical calculations revealed that the atomic ordering is induced by a particular surface reconstruction: indium atoms are bonded with four neighboring atoms, instead of expected three. This creates stronger bonds between indium and nitrogen atoms, which, on one hand, allows to use higher temperatures during the growth and provides material with better quality. On the other hand, the ordering sets the limit of the In content of 25%, which cannot be overcome under realistic growth conditions.

“Apparently, a technological bottleneck hampers all the attempts to shift the emission from the green towards the yellow and the red regions of the spectra. Therefore, new original pathways are urgently required to overcome these fundamental limitations,” states Dr. Tobias Schulz, scientist at the Leibniz-Institut fuer Kristallzuechtung; “for example, growth of InGaN films on high quality InGaN pseudo-substrates that would reduce the strain in the growing layer.”

However, the discovery of ordering may help to overcome well known limitations of the InGaN material system: localization of charge carriers due to fluctuations in the chemical composition of the alloy. Growing stable ordered (In, Ga)N alloys with the fixed composition at high temperatures could thus improve the optical properties of devices.

The historic flood of merger and acquisition agreements that swept through the semiconductor industry in 2015 and 2016 slowed significantly in 2017, but the total value of M&A deals reached in the year was still more than twice the annual average in the first half of this decade, according to IC Insights’ new 2018 McClean Report, which becomes available this month.  Subscribers to The McClean Report can attend one of the upcoming half-day seminars (January 23 in Scottsdale, AZ; January 25 in Sunnyvale, CA; and January 30 in Boston, MA) that discuss the highlights of the report free of charge.

In 2017, about two dozen acquisition agreements were reached for semiconductor companies, business units, product lines, and related assets with a combined value of $27.7 billion compared to the record-high $107.3 billion set in 2015 and the $99.8 billion total in 2016 (Figure 1).  Prior to the explosion of semiconductor acquisitions that erupted several years ago, M&A agreements in the chip industry had a total annual average value of about $12.6 billion between 2010 and 2015.

Figure 1

Figure 1

Two large acquisition agreements accounted for 87% of the M&A total in 2017, and without them, the year would have been subpar in terms of the typical annual value of announced transactions.  The falloff in the value of semiconductor acquisition agreements in 2017 suggests that the feverish pace of M&A deals is finally cooling off.  M&A mania erupted in 2015 when semiconductor acquisitions accelerated because a growing number of companies began buying other chip businesses to offset slow growth rates in major end-use applications (such as smartphones, PCs, and tablets) and to expand their reach into huge new market opportunities, like the Internet of Things (IoT), wearable systems, and highly “intelligent” embedded electronics, including the growing amount of automated driver-assist capabilities in new cars and fully autonomous vehicles in the not-so-distant future.

With the number of acquisition targets shrinking and the task of merging operations together growing, industry consolidation through M&A transactions decelerated in 2017.  Regulatory reviews of planned mergers by government agencies in Europe, the U.S., and China have also slowed the pace of large semiconductor acquisitions.

One of the big differences between semiconductor M&A in 2017 and the two prior years was that far fewer megadeals were announced.  In 2017, only two acquisition agreements exceeded $1 billion in value (the $18 billion deal for Toshiba’s memory business and Marvell’s planned $6 billion purchase of Cavium).  Ten semiconductor acquisition agreements in 2015 exceeded $1 billion and seven in 2016 were valued over $1 billion.  The two large acquisition agreements in 2017 pushed the average value of semiconductor M&A pacts to $1.3 billion.  Without those megadeals, the average would have been just $185 million last year. The average value of 22 semiconductor acquisition agreements struck in 2015 was $4.9 billion.  In 2016, the average for 29 M&A agreements was $3.4 billion, based on data compiled by IC Insights.

A recent paper published in NANO showed the gas-solid reaction method provides a full coverage of the perovskite film and avoids damage from the organic solvent, which is beneficial for light capture and electrons transportation, resulting in a faster response time and stability for perovskite photodetectors.

A schematic illustration of hybrid perovskite photoconductivity visible region detector with high speed and high stability. The gas-solid reaction in replace of the traditional solution methods provides a non-solvent environment during the reaction process, constructs a high crystallization and a full coverage film to increase the light capture and transportation, as well as enhance a good stability in the humidity condition, leading to a high response performance for the photodetector. Credit: Dr. Guoqing Tong

A schematic illustration of hybrid perovskite photoconductivity visible region detector with high speed and high stability. The gas-solid reaction in replace of the traditional solution methods provides a non-solvent environment during the reaction process, constructs a high crystallization and a full coverage film to increase the light capture and transportation, as well as enhance a good stability in the humidity condition, leading to a high response performance for the photodetector. Credit: Dr. Guoqing Tong

Pervoskite materials have long been considered candidates in the semiconductor manufacturing due to their characteristics of high light absorption, carrier mobility and wider light spectrum. They are widely applied in solar cells, light-emitted devices and photodetectors. However, the organic solvent in the traditional solution method will damage the perovskite film and form unstable phases during the synthesis process, which makes the perovskite film decompose quickly in wet conditions, limiting the practical application of perovskite devices. Considering the significant influence of the solvent, a team of researchers from Dongchang college of Liaocheng University and Hefei University of Technology proposed a new gas-solid process to fabricate the perovskite film. This non-solvent approach provides high crystallization and full coverage film in lower vacuum and low temperature systems.

The researchers investigated the morphology, light absorption and the crystal phases of the perovskite film at the different annealing temperature after gas-reaction to obtain the high-quality perovskite film. The devices exhibited high responsivity and detectivity of 5.87AW-1 and 1012 Jones. The response time of the device is estimated to be 248 μs/207 μs, which is faster than most previous reports via the solution method. Remarkably, the responsivity and detectivity are estimated to be 0.26 AW-1, 2.13×1010 Jones after lasting exposure in air (25oC, RH~40%) for up to two months. This improvement of the stability of the devices demonstrates that the well-controlled vapor deposition method allows a thorough removal of the residual solvents (i.e. DMF, DMSO et. al) and thus effectively promotes a high-quality crystallization of perovskite grains, reducing the metastable phases among the thin films.

This work was financed by Science and Technology Plan Project of Shandong Higher Education Institutions, NSFC and Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology of China.

Littelfuse, Inc. today introduced four new series of 1200V silicon carbide (SiC) Schottky Diodes from its GEN2 product family, which was originally released in May 2017.

The LSIC2SD120A08 Series, LSIC2SD120A15 Series, and LSIC2SD120A20 Series offer current ratings of 8A, 15A ,20A, respectively and are provided in the popular TO-220-2L package. Additionally, the LSIC2SD120C08 Series offers a current rating of 8A in a TO-252-2L package. The merged p-n Schottky (MPS) device architecture of the GEN2 SiC Schottky Diodes enhances surge capability and reduces leakage current. Replacing standard silicon bipolar power diodes with the new GEN2 SiC Schottky Diodes allows circuit designers to reduce switching losses dramatically, accommodate large surge currents without thermal runaway, and operate at junction temperatures as high as 175°C. This allows for substantial increases in power electronics system efficiency and robustness.

Typical applications for these new GEN2 SiC Schottky Diodes include:

  • Active power factor correction (PFC).
  • Buck or boost stages in DC-DC converters.
  • Free-wheeling diodes in inverter stages.
  • High-frequency output rectification.

The markets they can serve include industrial power supplies, solar energy, industrial motor drives, welding and plasma cutting, EV charging stations, inductive cooking fields and many others.

“The latest GEN2 SiC Schottky Diodes are ideal solutions for circuit designers who need to reduce switching losses, accommodate large surge currents without thermal runaway, and operate at higher junction temperatures,” said Michael Ketterer, Global Product Marketing Manager, Power Semiconductors at Littelfuse. “They expand the component options available to circuit designers striving to improve the efficiency, reliability, and thermal management of the latest power electronics systems.”

LSIC2SD120A08 Series, LSIC2SD120A15 Series, and LSIC2SD120A20 Series GEN2 1200V SiC Schottky Diodes are available in TO-220-2L packages in tubes in quantities of 1,000. Meanwhile,LSIC2SD120C08 Series GEN2 1200V SiC Schottky Diodes are available in TO-252-2L package in tape and reel in quantities of 2,500.  Sample requests may be placed through authorized Littelfuse distributors worldwide.

An international team of researchers from ETH Zurich, IBM Research Zurich, Empa and four American research institutions have found the explanation for why a class of nanocrystals that has been intensively studied in recent years shines in such incredibly bright colours. The nanocrystals contain caesium lead halide compounds that are arranged in a perovskite lattice structure.

Three years ago, Maksym Kovalenko, a professor at ETH Zurich and Empa, succeeded in creating nanocrystals – or quantum dots, as they are also known – from this semiconductor material. “These tiny crystals have proved to be extremely bright and fast emitting light sources, brighter and faster than any other type of quantum dot studied so far,” says Kovalenko. By varying the composition of the chemical elements and the size of the nanoparticles, he also succeeded in producing a variety of nanocrystals that light up in the colours of the whole visible spectrum. These quantum dots are thus also being treated as components for future light-emitting diodes and displays.

In a study published in the most recent edition of the scientific journal Nature, the international research team examined these nanocrystals individually and in great detail. The scientists were able to confirm that the nanocrystals emit light extremely quickly. Previously-studied quantum dots typically emit light around 20 nanoseconds after being excited when at room temperature, which is already very quick. “However, caesium lead halide quantum dots emit light at room temperature after just one nanosecond,” explains Michael Becker, first author of the study. He is a doctoral student at ETH Zurich and is carrying out his doctoral project at IBM Research.

A cesium lead bromide nanocrystal under the electron microscope (crystal width: 14 nanometer). Individual atoms are visible as points. Credit: ETH Zurich / Empa / Maksym Kovalenko

A cesium lead bromide nanocrystal under the electron microscope (crystal width: 14 nanometer). Individual atoms are visible as points. Credit: ETH Zurich / Empa / Maksym Kovalenko

Electron-hole pair in an excited energy state

Understanding why caesium lead halide quantum dots are not only fast but also very bright entails diving into the world of individual atoms, light particles (photons) and electrons. “You can use a photon to excite semiconductor nanocrystals so that an electron leaves its original place in the crystal lattice, leaving behind a hole,” explains David Norris, Professor of Materials Engineering at ETH Zurich. The result is an electron-hole pair in an excited energy state. If the electron-hole pair reverts to its energy ground state, light is emitted.

Under certain conditions, different excited energy states are possible; in many materials, the most likely of these states is called a dark one. “In such a dark state, the electron hole pair cannot revert to its energy ground state immediately and therefore the light emission is suppressed and occurs delayed. This limits the brightness”, says Rainer Mahrt, a scientist at IBM Research.

No dark state

The researchers were able to show that the caesium lead halide quantum dots differ from other quantum dots: their most likely excited energy state is not a dark state. Excited electron-hole pairs are much more likely to find themselves in a state in which they can emit light immediately. “This is the reason that they shine so brightly,” says Norris.

The researchers came to this conclusion using their new experimental data and with the help of theoretical work led by Alexander Efros, a theoretical physicist at the Naval Research Laboratory in Washington. He is a pioneer in quantum dot research and, 35 years ago, was among the first scientists to explain how traditional semiconductor quantum dots function.

Great news for data transmission

As the examined caesium lead halide quantum dots are not only bright but also inexpensive to produce they could be applied in television displays, with efforts being undertaken by several companies, in Switzerland and world-wide. “Also, as these quantum dots can rapidly emit photons, they are of particular interest for use in optical communication within data centres and supercomputers, where fast, small and efficient components are central,” says Mahrt. Another future application could be the optical simulation of quantum systems which is of great importance to fundamental research and materials science.

ETH professor Norris is also interested in using the new knowledge for the development of new materials. “As we now understand why these quantum dots are so bright, we can also think about engineering other materials with similar or even better properties,” he says.