Category Archives: LED Packaging and Testing

LED Taiwan will be held at TWTC Nangang Exhibition Hall in Taipei on April 13-16. As the LED market stabilizes, companies in the industry continue to invest in technology R&D as part of their efforts to stand out amid a pricing war of end products. In line with current key issues in the industry, this year’s LED Taiwan will feature five theme pavilions, several industry forums and the TechSTAGE. The Taiwan International Lighting Show (TiLS) will be co-located; with 700 booths, the exhibitions and conferences expect to attract over 20,000 visitors.

Research firm LEDinside estimated that the value of the global high-brightness LED market will increase three percent year-over-year in 2016. Despite the modest outlook, prospects still look good for niche applications in IR LED or UV LED, and may even become the main growth driver in the market. In LED lighting, the market reached US$25.7 billion of revenue in 2015 with a penetration rate at 31 percent. The numbers are expected to increase to $30.5 billion and 36 percent, respectively, in 2016.

LED Taiwan is made possible with collaboration and resources from SEMI, TAITRA, the Taiwan Lighting Fixture Export Association and the Taiwan Optoelectronic Semiconductor Industry Association. Each year, foreign buyers and leading manufacturers are invited to the exposition where various business matching events, forums and meetings are arranged to help Taiwan vendors expand connections and secure business opportunities by interacting with the elite members of foreign industrial and academic circles.

In addition to the existing pavilions (High-Brightness LED and Sapphire), LED Taiwan 2016 expands three more pavilions (LED Components, Smart Lighting Technology and Power Devices) and also invited international leading companies: Aurora Optoelectronics, Cree, Epileds, Epistar, Lextar, MLS, and Rubicon to demonstrate on show floor to help visitors explore the latest moves and trends in the market to increase their global competitiveness.

To enable innovation and bring more energy to the local LED industry, TechSTAGE will be held as part of this year’s LED Taiwan event, showcasing the Taiwan LED R&D capability in the areas of LED Manufacturing Equipment & Materials, Power Device Technology, Sapphire Processing Technology & Application, LED Advanced Technologies, and Smart Lighting & Automobile Lighting. For more information on LED Taiwan, please visit: www.ledtaiwan.org/en/ (English) or www.ledtaiwan.org/zh/.

Veeco Instruments Inc., a supplier of metal organic chemical vapor deposition (MOCVD) systems, announced today that it has signed a joint development project (JDP) agreement with imec, the Belgium-based nano-electronics research center. The collaboration is expected to accelerate the development of highly-efficient, Gallium Nitride (GaN) based, power electronic devices using GaN Epi wafers created using Veeco’s Propel Power GaN MOCVD system.

Imec has already demonstrated significant gains in GaN layer uniformity and run-to-run repeatability with Veeco’s Propel system, resulting in significantly improved power device yields. The single wafer reactor incorporates Veeco’s proprietary TurboDisc technology that delivers superior film uniformity, run-to-run control and defect levels compared to batch reactors.

“Within the framework of our industrial affiliation program on GaN-on-Si, Veeco and imec have collaborated over the last four years to improve the Epi quality of GaN layers deposited on silicon wafer substrates,” said Rudi Cartuyvels, Senior Vice President Smart Systems and Energy Technologies at imec. “The ultimate goal is to produce the next generation of highly efficient power switching devices. We have set very high GaN device yield and reliability targets for 2016 and we look forward to partnering with Veeco to achieve these targets.”

According to IHS research, industry requirements are growing and requiring smaller, more energy efficient power ICs. This, in turn, is driving the need for improved power devices using advanced materials. GaN-on-Si coupled with improved process solutions, such as single-wafer GaN MOCVD, are critical to the development of these improved power devices.

“We are very pleased with our imec collaboration,” said Jim Jenson, Senior Vice President and General Manager, Veeco MOCVD Operations. “Global demand for advanced power electronics with greater energy efficiency, a smaller form factor and greater reliability is rapidly accelerating. We believe that the technology in our Propel single wafer system will enable imec to achieve their power device targets and help to bring these advanced devices to market faster.”

SEMI announced today the launch of the European Semiconductor integrated Packaging and Test (ESiPAT) Special Interest Group.  The Special Interest Group (SIG) represents SEMI members who have semiconductor packaging, assembly, test manufacturing, or design activities in Europe. The purpose of the SIG is to foster collaboration among companies and to collectively raise the profile and reinforce the semiconductor back-end industry in Europe. Activities will include:

  • Maintaining a strong back-end network in Europe
  • Increasing awareness between European suppliers and device/packaging manufacturers
  • Mapping and reporting capabilities and capacities of European SiPAT members
  • Identifying gaps in the European back-end supply chain relative to other regions
  • Advocating for the  Packaging, Assembly, and Test industry in Europe
  • Building project consortia and bidding for European funding

The newly formed executive committee of the SIG includes representatives from AEMTec, First Sensor, NANIUM, RoodMicrotec, Sencio, STMicroelectronics, and Swissbit. More than 20 additional companies from the European back-end supply chain have already expressed interest to join.

Companies meeting the requirements can apply to join the ESiPAT group. SEMI membership and ESiPAT SIG membership dues are required. Additional information, including the charter and by-laws, is available online.  Within SEMI, Europe is pioneering the SiPAT SIG. Additional chapters in North America and Japan are currently under development.

Ultratech, Inc., a supplier of lithography, laser processing and inspection systems used to manufacture semiconductor devices and high­brightness LEDs (HB­ LEDs), as well as atomic layer deposition (ALD) systems, announced the promotion of two of its executives. Tammy D. Landon, Senior Vice President of Operations, and Dave Ghosh, Senior Vice President, Global Sales and Service, have been promoted to be executive officers at Ultratech. These promotions are an example of the company’s ongoing leadership succession process and efforts to cultivate top industry talent at Ultratech.

Ultratech Chairman and CEO Arthur W. Zafiropoulo, who remains the company’s principal operating officer said, “I congratulate both Tammy and Dave as they are both deserving of their respective promotions.  Tammy joined Ultratech in 2000, and her level of leadership and expertise have earned her the role of executive officer.  For this executive officer position, Dave will be leveraging his experience from the various responsibilities he has had at Ultratech since 1989.  Healthy companies both retain top talent and implement leadership plans as a means to remain competitive. Tammy and Dave each have over 30 years of industry experience, and these promotions are a part of the management process for Ultratech.  I have every confidence that Tammy and Dave will be successful in their new roles as executive officers, and I look forward to their continued contributions to Ultratech.”

Tammy D. Landon, Senior Vice President of Operations, Ultratech, Inc.
Landon joined Ultratech in 2000.  During this time, she had multiple responsibilities that included manufacturing, operations, materials, engineering, quality, training, technical support and installations. More recently, Landon has led the human resources, information technology and corporate services within the company. Her background includes more than 30 years of manufacturing, project management and engineering positions in the semiconductor and defense industries. Landon has a bachelor’s degree in biochemistry as well as a bachelor’s degree in industrial technology from California Polytechnic State University, San Luis Obispo.

Dave Ghosh, Senior Vice President Global Sales and Service, Ultratech, Inc.
Since 1989, Ghosh has served Ultratech in various capacities and has been responsible for risk management, corporate services, real estate, facilities, environment, health and safety, human resources, information technology systems and worldwide service. In addition, he works with the CEO on special projects that include M&A activities, initiating and negotiating with foreign governments for business development and risk management. His experience spans over 30 years in a variety of operations and service positions. Ghosh earned his bachelor’s degree in industrial technology from San Jose State University.

The global value of quantum dot markets was $306 million USD in 2014 and is expected at $4.6 billion USD over the forecast period due to the subsequent generation device, display, and system activated by quantum dot, according to a new report released this week by Radiant Insights. Semiconductor revolution is represented by quantum dots which provide complicated functions on the bases of nanoparticles shape. A verity of devices can be made with low-cost due to easy manipulation of the material.

Quantum Dot & Quantum Dot LED market sectors are solar, HDTV 7 displays, ID tags, LED lighting, cancer imaging, telco lasers, and personalized medicine. All sectors are expected to attain amazing expansion, with solar market and TV display technology getting more than $1 billion USD in profits annually by 2021. Qdot cancer imaging attains $750 million USD & quantum dot ID Tags reach $700 million USD over the forecast period.

Quantum dot market is growing rapidly. Technology maturity force is the key drive to the market. Solar quantum dots, fuel cell catalysts, TV displays, and a variety of applications depend on the aptitude to quantum dot time to time in enough amount needed for commercial purpose. One of the foremost applications of quantum dots commercially was the display of large screens and is proven to be a very good market.

SEMICON Korea 2016 at COEX in Seoul opens tomorrow with more than 540 exhibiting companies and an expected 40,000 attendees. Today’s SEMICON Korea press conference expressed a positive lookout, for both 2016 and for longer-term growth drivers, like the Internet of Things (IoT).

Denny McGuirk, president and CEO of SEMI, reported at the Press Conference that even with slightly decreased annual spending, Korea is expected to remain the second largest equipment market for the second year in a row. In 2014, the materials market in Korea surpassed Japan to become the second largest materials market after Taiwan. This year, we expect Korea to represent about a $7.3 billion market, representing 16 percent of the world materials market.

Much of the semiconductor manufacturing capacity in Korea is targeted towards both advanced NAND Flash and DRAM. Korea represents the largest region of installed 300mm fab capacity in the world. Korean semiconductor manufacturers represent about 60 percent of the worldwide Memory output, and is the market leader for installed Memory fab capacity.  According to the SEMI World Fab Forecast, memory was a significant driver for semiconductor equipment spending in 2015 and is expected to remain the largest spending segment 2016, driven mainly by investments for 3D NAND. The primary driver for the Memory market continues to be mobility, keeping the pressure on scaling and added functionality.

Korea fab equipment spending (front-end) in 2016 is forecast to be US$ 8.1 billion. The combined equipment and materials spending outlook for Korea in 2016 will likely top $15.3 billion. The semiconductor, semiconductor equipment, and materials supply chain in Korea is increasingly deep and broad and filling out as a complete ecosystem.

In addition, the LED market will experience strong double-digit growth in lighting applications over the next several years. Overall LED fab capacity continues to expand, and many manufacturers are transitioning to manufacturing with 4-inch diameter sapphire wafers. Korean manufacturers are prominently positioned in the global LED rankings.

Tomorrow’s keynotes at SEMICON Korea will be presented by AUDI, Synopsys, and Texas Instruments. Highlights include: Semiconductor Technology Symposium which addresses the global trends and new technologies of the semiconductor manufacturing process; Market Seminar; Supplier Search Program; OEM Supplier Search Meeting; Presidents Reception; and International Standards meetings.

SEMICON Korea 2016 is a semiconductor technology event for market trends and breaking technology developments, featuring deep technical forums, business programs and standards activities.

Sponsors of SEMICON Korea 2016 include: Special sponsors Samsung, SK Hynix, and Dongbu HiTek; Platinum sponsors Lam Research, Applied Materials, Wonik, Exicon, ASE Group, Advantest, EO Technics, and TEL; and Gold sponsors Hitachi High-Tech and PSK.

The event is co-located with LED Korea 2016.  For more information on the events, visit SEMICON Korea: www.semiconkorea.org/en/  and LED Korea: www.led-korea.org/en/.

Scientists from Germany and Spain have discovered a way to create a BioLED by packaging luminescent proteins in the form of rubber. This innovative device gives off a white light which is created by equal parts of blue, green and red rubber layers covering one LED, thus rendering the same effect as with traditional inorganic LEDs but at a lower cost.

Increasingly popular LEDs, or light-emitting diodes, are the light of choice for the European Union and the United States when it comes to creating lighting devices of the future. This preference can be attributed to the fact that LEDs are more efficient than traditional incandescent bulbs and more stable than energy-efficient light bulbs.

Despite their advantages, however, LEDs are manufactured using inorganic materials that are in short supply -such as cerium and yttrium-, thus meaning that they are more expensive and difficult to sustain in the long run. Additionally, white LEDs produce a colour that is not optimal for eyesight since they lack a red component that can psychologically affect individuals exposed to them for long periods of time.

Now, however, a German-Spanish team of scientists has drawn inspiration from nature’s biomolecules in search of a solution. Their technique consists in introducing luminescent proteins into a polymer matrix to produce luminescent rubber. This technique involves a new way of packaging proteins which could end up substituting the technique used to create LEDs today.

“We have developed a technology and a hybrid device called BioLED that uses luminescent proteins to convert the blue light emitted by a ‘normal’ LED into pure white light”, explains Rubén D. Costa to Sinc, a researcher at the University of Erlangen-Nürnberg (Germany) and co-author of the study.

It is always necessary to have either a blue or an ultraviolet LED to excite the rubbers that are put over the LED in order to make it white. In other words, we can combine blue LED/green rubber/red rubber, or ultraviolet LED/blue rubber/green rubber/red rubber. The result is the first BioLED that gives off a pure white light created by similar parts of the colours blue, green and red, all while maintaining the efficiency offered by inorganic LEDs.

The authors clear up that the blue or ultraviolet LEDs are much cheaper than white ones, which are made of an expensive and scarce material known as YAG:Ce (Cerium-doped Yttrium Aluminium Garnet). The idea is replace it by proteins.

“The Bio-LEDs are simple to manufacture and their materials are low-cost and biodegradable, meaning that they can easily be recycled and replaced”, points out Costa, while also highlighting the high stability of these proteins that have “luminescent properties that remain intact during the months of storage under different environmental conditions of light, temperature and humidity”.

In fact, with this technique “we have been able to achieve a sustained use of proteins in optoelectronic devices with an excellent stability for the first time, something that had not happened in the last 50 years. This thus represents a major breakthrough in this field,” stresses Pedro B. Coto, another one of the authors who also conducts research at this German university.

Scientists are already working on optimising this new elastic material in order to achieve greater thermal stability and an even longer operating lifetime. They are addressing how to optimise the chemical composition of the polymer matrix in addition to using proteins that are increasingly more resistant to device operating conditions. The goal is to make this new BioLED more accessible on an industrial scale in the not too distant future.

Use of copper as a fluorescent material allows for the manufacture of inexpensive and environmentally compatible organic light-emitting diodes (OLEDs). Thermally activated delayed fuorescence (TADF) ensures high light yield. Scientists of Karlsruhe Institute of Technology (KIT), CYNORA, and the University of St Andrews have now measured the underlying quantum mechanics phenomenon of intersystem crossing in a copper complex. The results of this fundamental work are reported in the Science Advances journal and contribute to enhancing the energy efficiency of OLEDs.

Organic light-emitting diodes are deemed tomorrow’s source of light. They homogeneously emit light in all observation directions and produce brilliant colors and high contrasts. As it is also possible to manufacture transparent and flexible OLEDs, new application and design options result, such as flat light sources on window panes or displays that can be rolled up. OLEDs consist of ultra-thin layers of organic materials, which serve as emitter and are located between two electrodes. When voltage is applied, electrons from the cathode and holes (positive charges) from the anode are injected into the emitter, where they form electron-hole pairs. These so-called excitons are quasiparticles in the excited state. When they decay into their initial state again, they release energy.

Excitons may assume two different states: Singlet excitons decay immediately and emit light, whereas triplet excitons release their energy in the form of heat. Usually, 25 percent singlets and 75 percent triplets are encountered in OLEDs. To enhance energy efficiency of an OLED, also triplet excitons have to be used to generate light. In conventional light-emitting diodes heavy metals, such as iridium and platinum, are added for this purpose. But these materials are expensive, have a limited availability, and require complex OLED production methods.

It is cheaper and environmentally more compatible to use copper complexes as emitter materials. Thermally activated delayed fluorescence (TADF) ensures high light yields and, hence, high efficiency: Triplet excitons are transformed into singlet excitons which then emit photons. TADF is based on the quantum mechanics phenomenon of intersystem crossing (ISC), a transition from one electronic excitation state to another one of changed multiplicity, i.e. from singlet to triplet or vice versa. In organic molecules, this process is determined by spin-orbit coupling. This is the interaction of the orbital angular momentum of an electron in an atom with the spin of the electron. In this way, all excitons, triplets and singlets, can be used for the generation of light. With TADF, copper luminescent material reaches an efficiency of 100 percent.

Stefan Bräse and Larissa Bergmann of KIT’s Institute of Organic Chemistry (IOC), in cooperation with researchers of the OLED technology company CYNORA and the University of St Andrews, United Kingdom, for the first time measured the speed of intersystem crossing in a highly luminescent, thermally activated delayed fluorescence copper(I) complex in the solid state. The results are reported in the Science Advances journal. The scientists determined a time constant of intersystem crossing from singlet to triplet of 27 picoseconds (27 trillionths of a second). The reverse process – reverse intersystem crossing – from triplet to singlet is slower and leads to a TADF lasting for an average of 11.5 microseconds. These measurements improve the understanding of mechanisms leading to TADF and facilitate the specific development of TADF materials for energy-efficient OLEDs.

Oxygen is indispensable to animal and plant life, but its presence in the wrong places can feed a fire and cause iron to rust.

In the fabrication of solid state lighting devices, scientists are learning, oxygen also plays a two-edged role. While oxygen can impede the effectiveness of gallium nitride (GaN), an enabling material for LEDs, small amounts of oxygen in some cases are needed to enhance the devices’ optical properties. GaN doped with europium (Eu), which could provide the red color in LEDs and other displays, is one such case.

Last week, an international group of researchers shed light on this seeming contradiction and reported that the quantity and location of oxygen in GaN can be fine-tuned to improve the optical performance of Eu-doped GaN devices. The group includes researchers from Lehigh, Osaka University in Japan, the Instituto Superior Técnico in Portugal, the University of Mount Union in Ohio, and Oak Ridge National Laboratory in Tennessee.

Writing in Scientific Reports, a Nature publication, the group said that small quantities of oxygen promote the uniform incorporation of Eu into the crystal lattices of GaN. The group also demonstrated a method of incorporating Eu uniformly that utilizes only the oxygen levels that are inevitably present in the GaN anyway. Eu, a rare earth (RE) element, is added to GaN as a “dopant” to provide highly efficient red color emission, which is still a challenge for GaN-based optoelectronic devices.

The devices’ ability to emit light is dependent on the relative homogeneity of Eu incorporation, said Volkmar Dierolf, professor and chair of Lehigh’s physics department.

“Some details, such as why the oxygen is needed for Eu incorporation, are still unclear,” said Dierolf, “but we have determined that the amount required is roughly 2 percent of the amount of Eu ions. For every 100 Eu ions, you need two oxygen atoms to facilitate the incorporation of Eu to GaN.

“If the oxygen is not there, the Eu clusters up and does not incorporate. When the oxygen is present at about 2 percent, oxygen passivation takes place, allowing the Eu to incorporate into the GaN without clustering.”

The article is titled “Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications.” The lead author, Brandon Mitchell, received his Ph.D. from Lehigh in 2014 and is now an assistant professor of physics and astronomy at the University of Mount Union and a visiting professor at Osaka University.

 

A comprehensive study

Gallium nitride, a hard and durable semiconductor, is valued in solid state lighting because it emits light in the visible spectrum and because its wide band gap makes GaN electronic devices more powerful and energy-efficient than devices made of silicon and other semiconductors.

The adverse effect of oxygen on GaN’s properties has been much discussed in the scientific literature, the researchers wrote in Scientific Reports, but oxygen’s influence on, and interaction with, RE dopants in GaN is less well understood.

“The presence of oxygen in GaN,” the group wrote in their article, which was published online Jan. 4, “…is normally discussed with a purely negative connotation, where possible positive aspects of its influence are not considered.

“For the continued optimization of this material, the positive and negative roles of critical defects, such as oxygen, need to be explored.”

The group used several imaging techniques, including Rutherford Backscattering, Atomic Probe Tomography and Combined Excitation Emission Spectroscopy, to obtain an atomic-level view of the diffusion and local concentrations of oxygen and Eu in the GaN crystal lattice.

Its investigation, the group wrote, represented the “first comprehensive study of the critical role that oxygen has on Eu in GaN.” The group chose to experiment with Eu-doped GaN (GaN:Eu), said Dierolf, because europium emits bright light in the red portion of the electromagnetic spectrum, a promising quality given the difficulty scientists have encountered in realizing red LED light.

The group said its results “strongly indicate that for single layers of GaN:Eu, significant concentrations of oxygen are required to ensure uniform Eu incorporation and favorable optical properties.

“However, for the high performance and reliability of GaN-based devices, the minimization of oxygen is essential. It is clear that these two requirements are not mutually compatible.”

Preliminary LED devices containing a single 300-nanometer active GaN:Eu layer have been demonstrated in recent years, the group reported, but have not yet achieved commercial viability, in part because of the incompatibility of oxygen with GaN.

To overcome that hurdle, said Dierolf, the researchers decided that instead of growing one thick, homogeneous layer of GaN:Eu they would grow several thinner layers of alternating doped and undoped regions. This approach, they found, utilizes the relatively small amount of oxygen that is naturally present in GaN grown with organo-metallic vapor phase epitaxy (OMVPE), the common method of preparing GaN.

“Instead of growing a thick layer of Eu-doped GaN,” said Dierolf, “we grew a layer that alternated doped and undoped regions. Through the diffusion of the europium ion, oxygen from the undoped regions was utilized to incorporate the Eu into the GaN. The europium then diffused into the undoped regions.”

To determine the optimal amount of oxygen needed to circumvent the oxygen-GaN incompatibility, the researchers also conducted experiments on GaN grown with an Eu “precursor” containing oxygen and on GaN intentionally doped with argon-diluted oxygen.

They found that the OMVPE- grown GaN contained significantly less oxygen than the other samples.

“The concentration of this oxygen [in the OMVPE- grown GaN] is over two orders of magnitude lower than those [concentrations] found in the samples grown with the oxygen-containing Eu…precursor,” the group wrote, “rendering the material compatible with current GaN-based devices.

“We have demonstrated that the oxygen concentration in GaN:Eu materials can be reduced to a device-compatible level. Periodic optimization of the concentration ratio between the normally occurring oxygen found in GaN and the Eu ions resulted in uniform Eu incorporation, without sacrificing emission intensity.

“These results appear to coincide with observations in other RE-doped GaN materials. Adoption of the methods discussed in this article could have a profound influence on the future optimization of these systems as well as GaN:Eu.”

The group plans next to grow GaN quantum well structures and determine if they enable Eu to incorporate even more favorably and effectively into GaN. Toward that end, Dierolf and Nelson Tansu, professor of electrical and computer engineering and director of Lehigh’s Center for Photonics and Nanoelectronics, have been awarded a Collaborative Research Opportunity (CORE) grant from Lehigh.

Light and electricity dance a complicated tango in devices like LEDs, solar cells and sensors. A new anti-reflection coating developed by engineers at the University of Illinois at Urbana Champaign, in collaboration with researchers at the University of Massachusetts at Lowell, lets light through without hampering the flow of electricity, a step that could increase efficiency in such devices.

An array of nanopillars etched by thin layer of grate-patterned metal creates a nonreflective surface that could improve electronic device performance. Credit: Image courtesy of Daniel Wasserman

The coating is a specially engraved, nanostructured thin film that allows more light through than a flat surface, yet also provides electrical access to the underlying material – a crucial combination for optoelectronics, devices that convert electricity to light or vice versa. The researchers, led by U. of I. electrical and computer engineering professor Daniel Wasserman, published their findings in the journal Advanced Materials.

“The ability to improve both electrical and optical access to a material is an important step towards higher-efficiency optoelectronic devices,” said Wasserman, a member of the Micro and Nano Technology Laboratory at Illinois.

At the interface between two materials, such as a semiconductor and air, some light is always reflected, Wasserman said. This limits the efficiency of optoelectronic devices. If light is emitted in a semiconductor, some fraction of this light will never escape the semiconductor material. Alternatively, for a sensor or solar cell, some fraction of light will never make it to the detector to be collected and turned into an electrical signal. Researchers use a model called Fresnel’s equations to describe the reflection and transmission at the interface between two materials.

“It has been long known that structuring the surface of a material can increase light transmission,” said study co-author Viktor Podolskiy, a professor at the University of Massachusetts at Lowell. “Among such structures, one of the more interesting is similar to structures found in nature, and is referred to as a ‘moth-eye’ pattern: tiny nanopillars which can ‘beat’ the Fresnel equations at certain wavelengths and angles.”

Although such patterned surfaces aid in light transmission, they hinder electrical transmission, creating a barrier to the underlying electrical material.

“In most cases, the addition of a conducting material to the surface results in absorption and reflection, both of which will degrade device performance,” Wasserman said.

The Illinois and Massachusetts team used a patented method of metal-assisted chemical etching, MacEtch, developed at Illinois by Xiuling Li, U. of I. professor of electrical and computer engineering and co-author of the new paper. The researchers used MacEtch to engrave a patterned metal film into a semiconductor to create an array of tiny nanopillars rising above the metal film. The combination of these “moth-eye” nanopillars and the metal film created a partially coated material that outperformed the untreated semiconductor.

“The nanopillars enhance the optical transmission while the metal film offers electrical contact. Remarkably, we can improve our optical transmission and electrical access simultaneously,” said Runyu Liu, a graduate researcher at Illinois and a co-lead author of the work along with Illinois graduate researcher Xiang Zhao and Massachusetts graduate researcher Christopher Roberts.

The researchers demonstrated that their technique, which results in metal covering roughly half of the surface, can transmit about 90 percent of light to or from the surface. For comparison, the bare, unpatterned surface with no metal can only transmit 70 percent of the light and has no electrical contact.

The researchers also demonstrated their ability to tune the material’s optical properties by adjusting the metal film’s dimensions and how deeply it etches into the semiconductor.

“We are looking to integrate these nanostructured films with optoelectronic devices to demonstrate that we can simultaneously improve both the optical and electronic properties of devices operating at wavelengths from the visible all the way to the far infrared,” Wasserman said.