Substrates & Materials Award
Production of Sapphire using CHES
Semi Insulating SiC Substrate Manufacturing
6-inch sapphire substrates
High-transparency n-type substrates
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Integrated multifunctional endpoint capability with EndpointWorks
Palomar TechnologiesAutomated Precision Assembly for High-Volume HB LEDs
Palomar Technologies Assembly Services™ (“Assembly Services”) is the on-shore contract assembly process development prototyping and test division of Palomar Technologies providing a low-cost alternative to purchasing capital equipment. The majority of light engines are currently assembled offshore—for the purpose of this submission “offshore” indicates production outside of the United States—which depending on the supplier can pose the threat of loosely regulated process flows and an increased risk of rejected products. Shifting assembly to on-shore production (in the U.S directly addresses these concerns among others. Depending on the chosen supplier on-shore contract assembly ensures but is not limited to the following points many of which are important during product development where cycle times are critical:
Each validation and certification checkpoint can take between 2 to 10 minutes depending on the process. The Palomar Technologies die attach and wire bond equipment used in the contract assembly of HB LEDs perform diagnostic tests that evaluate the performance of each motion and servo system. Palomar Technologies’ motion validation test takes only about 20 seconds and scans hundreds of data points grading them green yellow or red. This process consistently catches degrading performance and therefore reduces future production downtime and allows scheduled correction before the process or machine fails. Not all LED assemblies require the level of detail and strict regulation employed by Assembly Services however the division abides by this process flow to ensure high quality for LED applications.
Challenge: Today die bonders can perform epoxy die attach at a rate of 1.5 to 4 thousand die per hour and wire bonders can interconnect complex packages at speeds of more than 10 wires per second. The advantage of automation is speed and consistency. However having a tightly regulated assembly processes helps avoid the risk of building a large batch of rejected product. To ensure time-to-market success in high-volume production specific methods to achieve throughput and quality are required to achieve the ultimate goal of an automated precision HB LED assembly—to blend the requirements of high-reliability and high-throughput to support high-volume commercial production.
Assembly Services begins LED assembly by validating all materials at incoming inspection. Material validation is based on standard guidelines usually including standards for automated processes where the recipe is static to eliminate varying process parameters. All equipment is verified against minimum performance guidelines. Off-line visual and in-process inspections are conducted to ensure the assembly process does not drift. This also offers an instant indication of any material or equipment issues before beginning production. Assembly Services uses a 2” x 2” gold-plated test coupon for material validation which is defined per a material specification or drawing. Since key decisions are made based on this coupon’s performance the coupon’s quality must be known.
Noteworthy: Outsourcing to an offshore production can no longer be assumed as the best choice. There are cases where on-shore (production in the U.S. assembly is nearly as competitive on price and will outperform offshore options in terms of lead-time response time IP control and traceability. Assembly Services has developed a reliable paperless manufacturing software system called Automated Data Management and Analysis (ADMA which directly communicates with Palomar Technologies die attach and wire bond machines. ADMA begins by kitting parts to a traveler and ends when parts are shipped. Palomar Technologies developed Bond Data Miner™ (BDM to track trend and machine calibrations aggregate run data and timestamp data sets. BDM is used to export test die placement analysis details to an Excel™ database in the ADMA program. BDM works in concert with ADMA to provide a more comprehensive and centralized data management and analysis system.
The TurboDisc® MaxBright™ GaN MOCVD Multi-Reactor System is an MOCVD system designed to manufacture high quality, high brightness light emitting diodes (LEDs). MaxBright leverages Veeco's production-proven Uniform FlowFlange® technology and automation expertise by combining multiple high throughput MOCVD reactors in a modular 2- or 4-reactor cluster architecture. The improved reactors, based on Veeco's highly-successful K465i design, feature both expanded wafer capacity and advanced, proprietary, closed-loop thermal control technology to achieve a 25% throughput improvement over the standard K465i. In addition, recipes can be transferred from the K465i to MaxBright seamlessly for rapid production start.
Ming Jiunn Jou, Ph.D., President of Epistar, commented, "Veeco's MaxBright Multi-Chamber System enables us to ramp production quickly on the industry's most productive platform. We will continue to rely on Veeco for technological innovation and process expertise as a strong strategic partner. Veeco's commitment to providing best-in-class MOCVD equipment, as well as enhanced local support with their new technology center in Hsinchu, will help Epistar to achieve our future expansion goals and success."
The Candela® 8620 substrate and epitaxy (epi wafer inspection system is designed for the inspection needs of the light-emitting diode (LED industry to capture a wide variety of mission-critical substrate and epitaxial defects. For LED device manufacturers the Candela offers automated defect inspection for LED materials such as gallium nitride sapphire and silicon carbide—enabling enhanced quality control of both opaque and transparent substrates faster time-to-root cause and improved metal Organic Chemical Vapor Deposition (MOCVD reactor uptime and yield. With its proprietary optical design and detection technology the Candela 8620 LED substrate and epi wafer inspection system detects and classifies sub-micron defects that are not consistently identified by current inspection methods—thereby enabling for the first time a production line monitor for these yield-limiting defects. As LED manufacturers transition production to larger wafer sizes and introduce new patterned sapphire substrate (PSS processes there is significant economic impact of resulting process-induced defects. Defects from substrate and epi processes impact device performance yield and field reliability. The Candela 8620 LED substrate and epi wafer inspection system can detect:
LED substrate and epitaxy layers pose significant inspection challenges due to high levels of background signal and nuisance defects. To date detecting and classifying sub-micron defects have been difficult challenges on gallium nitride epitaxy layers due to high levels of background scatter signal from back surface of the transparent material.
The Candela 8620’s revolutionary optics imaging and detection methodology effectively separates front surface and backside signals allowing superior sensitivity and improved classification. The enhanced inspection capability offers full wafer surface coverage and production-level throughput thereby enabling comprehensive statistical process control of critical MOCVD processes.
When using the Candela 8620 inspection is performed at production-grade throughputs enabling for the first time a true production line monitor of classes of wafers used to produce LED devices. The automated defect classifica¬tion capability allows customers to filter out nuisance defects and quickly zero in on mission-critical defects of interest. As a result LED manufacturers are equipped to conduct rapid root cause analysis to speed process development quickly fine-tune produc¬tion processes to optimize yields and minimize process excursions and achieve higher revenues per wafer. GaN epitaxial layer defects in particular can account for as much as 50 percent of the total wafer level yield budget per industry estimates. Many of these yield-impacting defects have been shown to origi¬nate at substrate level. Industry leaders utilizing automated inspection to monitor defect densities—within wafer wafer-to-wafer and batch-to-batch—estimate that optimal inspection practices can reduce the yield impact of material defects by 50 percent.
The QC3 High-Resolution X-Ray Diffractometer (HRXRD) from Jordan Valley is a true leapfrog technology over the existing HRXRD technology within the market. The QC3 boasts more than an order-of-magnitude improvement in performance compared to other HRXRD systems, with scans taking seconds rather than minutes or even hours. This provides LED manufacturers a dramatic improvement in quality control of LED devices, with more wafers and higher sampling within wafers possible.
The development and market launch of QC3 demonstrates the success of JVS’ 2008 acquisition of Bede’s HRXRD and compound semi technology. Furthermore, it reinforces JVS management’s ability to apply its business model and expertise in providing the semiconductor market with enabling, high-throughput systems with low cost-of-ownership, achieving market dominance with a valued, customer-preferred product.
Features and benefits:
Productivity and Precision: The QC3 has a dedicated and optimized HRXRD system for LED quality control. As a result of its high intensity, the system gives higher precision and throughput compared to other HRXRD systems.
Automation: The system operates with fully-automated alignment, measurement and analysis of wafers, conducting batch wafer measurements with optional robot or multi-sample plates. The multi-sample plates allow up to 20 wafers to be loaded into the system for measurement without requiring a robot. For the automated analysis of the data spectra, the QC3 uses tried and trusted, industry-leading RADS software for automated analysis. This will automatically analyse the collected data and report the results for specific wafers, batches, chambers. This reporting can be extended to host reporting if required.
Economy: QC3 incorporates XRGProtect™, to ensure the tube lifetime is maximized. It also has an Eco-mode, ensuring system power consumption is reduced when there is no measurement being performed.
Simplicity and Reliability: The system is so reliable and easy to use, that no expert is required to operate the system.
LEDs are entering the consumer market for solid state lighting. However costs still have to drop significantly to end-up in a broad LED market acceptance. Enhancing the production capacity by using larger wafers is one of the currently paced ways to reduce production cost. Besides process yield enhancement is a top priority goal for cost reduction. To use larger wafers and to increase the yield at the same time however is a big challenge for LED producers. This is because wafer bowing effects become much more pronounced with increasing wafer size. This leads to larger temperature variations across the wafer and thereby to larger emission wavelength inhomogeneities.
LayTec has recently developed a new method for in-situ measurement of the GaN surface temperature. This method has proven to give a direct correlation of the surface temperature line-scans across the wafers during quantum well growth and the later on-wafer emission wavelength distribution measured by Photoluminescence. This GaN surface temperature measurement is now being used at first customer sites to individually control the surface temperature of the wafers during GaN LED epitaxy and has proven to be the only direct method to increase at once both wafer size and yield
Conventional in-situ pyrometry can only detect the temperature of the susceptor under the sapphire or SiC wafers because at infrared wavelengths the wafers and layers are transparent. Although the temperature differences between susceptor surface and wafer surface are often small for 2 wafers bowing effects of larger wafers cause dramatic during-growth temperature deviations across the diameter of the wafer. Temperature decreases in direct relation to the increase of the distance between pocket and wafer. With a conventional infrared pyrometer all these deviations remain undetected since the temperature of the pocket stays constant.
At around 400 nm wavelengths GaN absorbs and thermally emits light becoming visible to pyrometric measurement. This is the underlying principle of the LayTec Pyro 400 metrology system. It directly measures the surface temperature of the GaN layers with high accuracy at quantum well growth temperatures. Simply put the Pyro 400 is the first tool in GaN based LED production on sapphire that gives the surface temperature with the necessary resolution at quantum well growth temperature and the adequate data repetition rate to regulate the temperature individually for each wafer in a multi-wafer production environment.
To perform uv-pyrometry measurements insight of a hot MOCVD chamber with a lot of IR stray-light overlaying the few 400nm photons coming out of a few µm thick GaN layer was an extraordinary challenge. Small optical access accompanied with deposition effects on view-ports further enhanced the measurement challenge. Combining novel optical filter approaches advanced ultra low-noise electronics and sophisticated software-filtering LayTec is the first company to offer a reliable wafer surface temperature measurement solution for industrial production-line equipment.
Recently first industrial customers started to equip their complete production lines with the new metrology technique. The combination of Pyro 400 with EpiCurve® TT in-situ monitoring systems offers deepest insight into surface temperature changes caused by carrier gas rotation speed and reactor pressure variations as well as wafer bowing effects.
Cree XLamp® MT-G EasyWhite® LED is the first LED in the industry that is optimized for a 50W MR16 halogen replacement bulb. It is also the industry's first LED to be binned for luminous flux and chromaticity at 85°C which can simplify luminaire design calculations and speed time-to-market. Featuring Cree's EasyWhite technology the MT-G LED delivers the industry's tightest LED-to-LED color consistency that matches the color consistency of incandescent light bulbs. Prior to the MT-G LED LED-based MR16 lamps have been a tremendous challenge for the lighting design community in terms of both light output and color consistency due to their small size and limited capacity for thermal management. Optimized for high-output small form-factor directional-lighting applications such as MR retrofit bulbs accent and down lighting the MT-G LED can be driven to higher currents in less constrained designs achieving up to 1670 lumens at 25 W 85°C. Unlike competitor products the MT-G LED is available in a wide range of color temperatures CRI and binning options both in 6V and 36V options. Its minimum 90- CRI option enables customers to address applications such as retail and restaurant lighting where high CRI and lighting uniformity is required. The MT-G LED has over 6000 hours of IESNA LM-80 published lifetime data which can assist lighting manufacturers with ENERGY STAR® qualification. With its unparalleled performance Cree XLamp MT-G truly enables applications traditionally supported by halogen light sources.
What is a High Power Laser Diode?
A high power laser diode is made when an intrinsic semiconductor's electrical properties are altered by introducing impurities to the surface of a crystal wafer. When semiconductor layers meet, charge carriers combine and the electrical current in the laser's energy is released as light. High power diode lasers are small and light and require very little power. The laser's power output is what defines it as "high power." Most commercially available lasers have power outputs of milliwatts, whereas a high power laser diode has a power output of WATTs, generally above 10 watts. SemiNex supplies laser diodes with power outputs between 3 watts and 25 watts.
Market Demands for High Power Laser Diodes
High gain, high energy solid state lasers operating in the eye safe region (wavelength > 1.5 microns) are in demand for military and commercial applications. These lasers, which are based on crystals doped with erbium (Er) atoms, are expected to be more compact and efficient with improvements in laser diode design, cooling techniques, and component packaging. Since these diodes are currently unavailable with sufficient performance and cost, many system designs use short-wavelength diodes at 800 – 980 nm, which are readily available at high power and efficiencies. However, these short-wavelength diodes are not eye safe and do not meet the needs of many of the stated applications compared to 14xx-15xx wavelengths. Thus, there is an acute need for high energy, high power laser diodes.
SemiNex Corporation has taken on a slightly different business model by providing better high-power semiconductor laser performance and efficiency with higher wall plug efficiency (~35%), while drastically reducing laser size, power consumption, and cost than other sources in the market place today. SemiNex's unconventional approach towards laser manufacturing utilizes a doping profile and unique application of quantum physics, exclusive to SemiNex, which has produced high power diode lasers available for extremely high volume production. SemiNex is positioned to provide high power laser diodes in a variety of systems and powers to meet the demands for both the defense and consumer markets.
Cree’s Z-Fet MOSFETs are the industry’s first fully qualified commercial silicon carbide (SiC power MOSFETs. The family of devices is comprised of 80mohm and 160mohm versions in TO-247 packaged and bare die form. Z-FETs establish a new benchmark for energy-efficient power switches and can enable design engineers to develop high-voltage circuits with extremely fast switching speeds and ultra-low switching losses. The SiC MOSFETs provide critical energy savings in solar inverters 3-phase power supplies electric vehicle battery chargers emerging DC based data center power distribution motor drives and power conditioning in many industrial applications. Z-FET MOSFETs used with Cree’s world-class SiCSchottky diode family enables power electronics design engineers to develop “all-SiC” implementations of critical high power switching circuits and systems. The result is levels of energy efficiency that are not achievable with any commercially available silicon power devices of comparable DC ratings. Z-FET achieves low on resistance in a fraction of the die area required for silicon IGBT or MOSFETs. Stable performance across operating temperature and ultra-low leakage currents assure ease of design and ultra-high system reliability. Z-FET’s switching loss reductions can also enable higher system switching speeds that reduce the size weight and cost of magnetic and capacitive elements. Size and weight reductions of greater than 50% are achievable reducing system bill-of-material shipping and installation costs.
Cree’s Z-FETs reduce energy loss in power electronics that today go to producing wasted heat inside the system. That heat must be dissipated by large heavy expensive heatsinks fans and even liquid cooling schemes. The lost system energy must be paid for in utility bills or goes unutilized in alternative energy generation systems. In either case wasted energy is wasted money. In large power consuming applications such as data centers there is the added cost of air conditioning the facility. Finally heat generated in power electronic contributes to poor system reliability and expense from maintenance and repair.
Z-Fet MOSFETs solves the problem by employing the nearly ideal power semiconductor characteristics of SiC. Combining silicon carbide’s intrinsic power density and ultra-fast switching capability with a well understood easy to use MOSFET device architecture Cree has created a high speed power switch with both low on-resistance per unit area and uni-polar switching characteristics. Small die size for the required power handling low capacitance from the small die size and no bipolar tail currents (the performance limiter in commonly used silicon IGBTs produce a switch that is fast and very highly efficient.
The innovation is in the development refinement and application of silicon carbide to build familiar easy to use power semiconductors. The Z-FET MOSFET reduces switching losses in many applications by up to 50 percent increasing overall system efficiencies up to 2 percent while operating at 2 – 3 times the switching frequencies when compared to the best silicon IGBTs. As a result of this improved efficiency SiC devices have lower operating temperatures and fewer thermal management requirements which combine with their ultra-low leakage current (1µA to reduce system size and weight and increase reliability. Z-Fets will enable delivery and conversion of power in space weight and cost unheard of in silicon implementations and save tremendous amounts of precious expensive energy. Z-FET MOSFETs represent a revolutionary new era in high power semiconductor devices.
LUXEON A LEDs incorporates thin film flip chip technology and unique Lumiramic phosphor technology to target white color point performance. Then by hot testing each LED we deliver Freedom From Binning – all parts within a 3-step MacAdam ellipse - and unmatched uniform and quality of light from every LUXEON A LED.
The innovation of hot testing and Freedom From Binning addresses the longstanding problem of color binning for white LEDs that too often results in visible variations in luminaires when they are in use.
For the first time the manufacturing process is managed to eliminate the potential significant differences between color bins. Because the distribution is so small every LUXEON A falls within a 3-step MacAdam ellipse – supportability is ensured design is simplified and time to market is faster.
We are the only company to offer and release a single white die emitter with a single bin selection. The entire production has the same color so when a customer specifies a CCT of 2700K that’s what they get. There are no other color selections to be made.
Solar Junction is commercializing their proprietary Adjustable Spectrum Lattice Matched (A-SLAM™) multi-junction solar cell architecture. The A-SLAM™ architecture provides material bandgap tunability – particularly from 0.8 to 1.42 eV - to maximize the absorbed sunlight within CPV modules, thereby increasing the efficiency and energy harvested. This unique and proprietary adjustable spectrum technology is the basis of performance leadership throughout the next decade of increasingly efficient and industry leading cells. The technology's capability to adapt to customer's optics and deployment location ensures the most efficient CPV systems are installed around the world. While simultaneously enabling the industry-leading roadmap, the A-SLAM™ architecture maintains the lattice-matched paradigm, in which interatomic spacing is constant throughout the entire crystalline material stack, and has been the foundation of semiconductor and multi-junction solar cell reliability for decades. Furthermore, Solar Junction has achieved breakthroughs with ultra-concentration tunnel junctions, allowing cells to perform optimally at 1000-1300 sun concentrations and far beyond. Solar Junction's A-SLAM™ uniquely provides CPV system manufacturers the foundation to deliver the most efficient conversion of solar to electrical energy over 25 to 30 year project lifetimes.
Solar Junction, took another giant leap forward in cell efficiency earlier this year. Just one month after achieving 40.9 percent efficiency, the Company reached 41.4 percent on a production cell, and quickly followed this up with a world record breaking 43.5% production cell; all milestones have been validated by the National Renewable Energy Laboratory (NREL). The significance of the advancement belies the speed at which the Company is hitting efficiency milestones for a standard commercial-ready production cell, moving the industry beyond champion cell gains. Concurrently, the Company is on a short list of finalists chosen for post-selection due diligence within the Department of Energy's (DOE) Loan Guarantee Program (LGP). The grant would support the commissioning of Solar Junction's high-volume, 250-MW capacity manufacturing facility co-located with its headquarters in San Jose, California. Solar Junction expects to begin shipping commercial cells this year.
The $12.3 million Microscale Power Conversion (MPC) program [Technical Area I] funded by the Defense Advanced Research Projects Agency (DARPA) seeks to develop compact, innovative RF power amplifier designs that incorporate DC-DC supply modulation and control that far exceeds the capabilities of solid-state products now available for commercial or defense applications. Achieving this goal will be facilitated by TriQuint's new power switch (modulator) technology created by the company using its E-Mode gallium nitride (GaN) semiconductor fabrication processes. The variable-voltage, high-power GaN switch created in this endeavor will be integrated with transmitter architectures and PA circuits designed by Technical Area II contract leader, Northrop-Grumman. The overall goal for the MPC GaN switch R&D program is to achieve composite 75% power added efficiency (PAE) with 200 volts of blocking voltage, ultra-low dynamic on resistance of 1 ohm-mm and a slew rate of 500 volts per nanosecond.
What challenge does this product / process or innovation address?
The key challenge facing the MPC program is to develop solid-state DC-DC switch (modulator) circuits that deliver composite efficiency of 75% (PAE) with 200 volts blocking voltage and ultra-low dynamic resistance, while at the same time achieving a nearly-instantaneous, high-power switching speed of 500 V/nanosecond. This performance will be achieved through innovative physical circuit designs that will utilize an InAlN/AlN/GaN epitaxial structure.
How does the product / process or innovation solve the problem?
Gallium nitride (GaN)-based semiconductors are capable of substantially greater power density, efficiency and ruggedness compared to GaAs and silicon-based devices. GaN is uniquely able to solve complex challenges like delivering high efficiency combined with very high power handling and ultra-fast speeds, while retaining small form factors with high reliability for aerospace and defense applications. TriQuint's achievements supporting the DARPA-funded 'NEXT' program developing mixed-signal, very high frequency devices have led to advances in enhancement-depletion (E/D) mode circuits with InAlN/AlN/GaN epitaxial structures. TriQuint's standard-setting R&D achievements will enable the break-throughs required by MPC.
What is particularly novel or noteworthy about the product /process or innovation?
TriQuint is the only company developing the ultra-high efficiency / high power, ultra-fast variable voltage solid-state (DC-DC) switch technology needed for solving the challenges posed by MPC requirements. TriQuint R&D innovation will enable new compact, high-efficiency semiconductor applications that do not exist at this time, but are needed to solve the aerospace, defense and commercial needs for future high-speed, wide bandwidth and high-power applications. This technology will create an opportunity for new generations of products that are orders of magnitude smaller and/or more efficient, faster and lighter compared to similar devices constructed utilizing today's power amplifier and switch technologies.
Bridgelux, a trailblazer of white LEDs grown on 200 mm silicon, has made tremendous progress in improving device efficacy.
1.5 mm by 1.5 mm cool-white LEDs produced in the labs of the Californian outfit can now deliver 160 lm/W at 350 mA, a gain of 25 lm/W compared to the company's best devices reported this March. What's more, warm-white LEDs of the same size show an even bigger improvement at the same drive current – efficacy is now 125 lm/W, compared to 85 lm/W five months ago.
"The performance levels that we have announced are the highest lumen-per-Watt values yet published for GaN-on-silicon, and rival the best commercial LEDs grown on sapphire or silicon carbide," claims Steve Lester, chief technology officer for Bridgelux.
Although the company is not giving much away regarding the secrets of its recent success, vice-president of marketing, Jason Posselt, told Compoundsemiconductor.net that improvements in the epitaxial process have helped to deliver gains in efficacy.
"We are no longer taking a sapphire recipe and trying to figure out how to grow it on silicon," says Posselt. "We're optimising for the silicon wafer process." Some slight changes to packaging also led to efficacy improvements.
Thanks in part to these efforts, that latest blue LEDs - which are the foundation of making white emitters - have a forward voltage of just 2.85 V at 350 mA . "The bandgap to emit light is around 2.75 V," says Long Yang, Vice-President of Chip Technology, "[So we are] we are only about 0.1 V above the bandgap."
Driven at 350 mA, these blue LEDs deliver 591 mW at a wall-plug efficiency of 59 percent, and when the current is cranked up to 1 A, they produce 1.52 W at a wall plug efficiency of 47 percent. Although this indicates that the devices do suffer from LED droop, the decline in efficiency as current is increased may not be as high as it is for sapphire-based devices.
Other details of Bridgelux's white LEDs made from these blue-emitting chips include a colour temperature of 4350K for the 160 lm/W, cool-white LED, and a colour temperature of 2940K and a colour rendering index of 80 for the 125 lm/W, warm-white emitter.
In terms of where Bridgelux's technology stands today, the efficacy of these LEDs exceeds the company's next-generation of warm-white LEDs on sapphire, which will deliver 120 lm/W and be released within the next 12 months. "We are seeing equivalent to - and some cases even better performance now – on silicon compared to sapphire," says Posselt.
A substantial reduction in manufacturing cost is Bridgelux's primary motivation for developing LEDs on silicon. The company believes switching substrates could reduce costs by up to 75 percent. The benefit of silicon is not just a cheaper substrate –processing is also far less expensive, because the epiwafers can be churned into chips at under-utilised high-throughput 200 mm fabs.
In order to tap in to this spare fab capacity, Bridgelux has to ship incredibly flat wafers to these processing partners – the bow cannot exceed 60 microns. Realising this is a challenge, because there are considerable differences in both the thermal expansion and the lattice constant of silicon and the III-Ns. To eliminate stress in the wafers, the company has developed a proprietary buffer layer.
One of the company's latest goals is to improve the peak emission wavelength uniformity of its wafers. Engineers have fabricated wafers with a wavelength uniformity, in terms of the standard deviation, of 6.8 nm. "Our target is 3 nanometers," says Yang.
The number of LEDs that the company is making in its R&D labs is rising fast. "Now we make these LEDs in thousands; a few months ago we made them in hundreds," says Yang.
Sampling of products will follow, but potential customers should not expect to get their hands on Bridgelux's silicon-based LEDs in the next month or so. "We are building prototypes of products, but this is not a tomorrow technology," says Posselt.
According to Yang, pilot production of the GaN-on-silicon LEDs should begin within a year. Once any processing issues related to this are ironed out, Bridgelux will invest in capital equipment for the growth of the wafers in high volume. According to the company, large-scale commercial production is still two years' away.
The performance gap between conventional LEDs and those built on silicon is closing fast thanks to the efforts of Bridgelux
RESEARCHERS from the University of California, Santa Barbara, have shown that increasing the number of quantum wells in an LED can slash its droop, the decline in device efficiency as current is cranked up. The team, which includes Stephen DenBaars and Shuji Nakamura, fabricated two high-power blue LEDs that differed only in the number of quantum wells. The version with six quantum wells had an external quantum efficiency (EQE) of 50.7 percent at 20 mA, falling to 38.4 percent at 60 mA. In comparison, the chip with nine quantum wells had an EQE of 49.7 percent at 20 mA and 49.5 percent at 60 mA. Both devices had mesa sizes of 526 μm x 315 μm and a peak emission wavelength of 447 nm. One of the noteworthy features of this study is that it uses high-power LED structures. In this case, the devices are grown on patterned sapphire.
The LEDs fabricated by the researchers featured 20 nm-thick barriers, 4 nm-thick quantum wells and a 10 nm-thick undoped Al0.15Ga0.85N electron-blocking layer. "Though our wells may be a little thicker [than those used in many commercial LEDs], it is the best structure for a high output power LED at UCSB," revealed Tanaka.
He believes that LEDs with more quantum wells suffers from less droop because the current density in these structures are lower, reducing nonradiative Auger recombination. In addition, he argues that more quantum wells can reduce the overflow of carriers – particularly electrons – through the active region.
|Nominations open||25th November 2016|
|Nominations close||9th January 2017|
|Shortlist announced||16th January 2017|
|Voting opens||16th January 2017|
|Voting closes||21st February 2017|
|Winners informed||21st February 2017|
|Awards ceremony||7th March 2017|
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