Category Archives: LED Manufacturing

The case is made for delivering liquid precursors from a central delivery system to the epi/dep tool as a vapor of precisely-controlled composition. 

By EGBERT WOELK, Ph.D., Dow Electronic Materials, North Andover, MA, USA and ROGER LOO, Ph.D., imec, Leuven, Belgium 

The epi and deposition processes for silicon-based semiconductor devices have used gaseous and liquid precursors. Gaseous precursors are compounds whose vapor pressure at room temperature is higher than 1500 torr (2000 mbar), which is sufficient to drive a mass flow controller (MFC). Using only one MFC, gaseous precursors can conveniently be metered to the process. Silane and dichlorosilane (DCS) have been used with that method. The industry has also used Trichloro silane (TCS) that boils at around 33°C and can be directly metered to a low pressure epi process using an appropriate MFC. For the epi of SiGe, germane, which is a gas, has been used.

Tetraethylorthosilicate (TEOS) has long been used for the deposition of SiO2 and has mostly been delivered using direct liquid injection (DLI). DLI meters the flow of the liquid precursor to a flash evaporator and provides good control, but flash evaporation requires high temperatures and care must be taken that the precursor compound does not break up prematurely. This can be a challenge for precursors that work at lower deposition temperatures.

More recently, trisilane (Si3H8) has been used for low temperature Si epi and deposition. The delivery of trisilane to the process uses the carrier-gas-assisted delivery method. In the most common implementation, it employs an on-board evaporation ampoule dedicated to one reactor. The same setup has been used for III-V compound semiconductor and LED epi with good success. Driven by cost pressure, however, the LED epi industry is moving from dedicated onboard ampoules to a central delivery system for high-volume precursors like trimethylgallium (TMGa). One part of the cost reduction simply comes from the economies of scale. Another aspect comes from the elimination of excessive hardware, such as thermal baths and pressure controllers, and their maintenance. Most importantly, a substantial part of the cost reduction comes from yield increases due to improved process control. The same central delivery system can be used for trisilane and other liquid CVD precursors for silicon-based CVD for similar cost reduction.

Carrier-gas-assisted precursor delivery

Liquid compounds with an RT vapor pressure between 1 and 400 mbar require carrier-gas-assisted delivery. Many liquid compounds within that vapor pressure range are excellent precursors for CVD and epi processes. For such compounds, the difference between the vapor pressure and the process pressure is too small to drive an MFC for straight metering. Adding a carrier gas increases the pressure to between approximately 760 and 1500 torr (1000 and 2000 mbar). The selection of a good delivery pressure depends primarily on the desired concentration.

The carrier-gas-assisted delivery method has long been used for trimethylgallium (TMGa) and trimethylaluminium (TMAl) for the growth of GaAs and GaN. For the growth of GaAlN and GaInN for LEDs, the composition ratio of the two group III precursors is extremely critical for the performance of the final product. Therefore, the precision of the evaporation and the metering has always been a concern.

FIGURE 1a shows the setup for a straight gas delivery and FIGURE 1b shows the setup for a carrier-gas-assisted delivery. The design shown in Figure 1b requires no modification of the epi/dep tool in order to accept a normally liquid precursor. From an epi/ dep tool perspective, the design shown in Figure 1b behaves just like the straight gas delivery of Figure 1a. As such, it allows the use of the gas mixture from one delivery system at several points of use, i.e. the output of the delivery system can be subdivided. In Figure 1b the precursor vapor is made on demand. While the output (mol flux of precursor per time) is theoretically unlimited, there are practical limits that restrict the output to approximately 20 standard liters per minute (slm). The main limitation is the dynamic range of the metering valve: the best units have a dynamic range of 1 in 104, which means that they can reliably control a flow between 0.002 and 20 slm. This is important for the mol flux precision at smaller flows, i.e. when only one or two tools draw precursor.

FIGURE 1a. High vapor pressure precursor, straight vapor delivery. S: pressure sensor, V: metering valve. S and V are normally integrated into a pressure regulator. MFC meters neat vapor.

FIGURE 1a. High vapor pressure precursor, straight vapor delivery. S: pressure sensor, V: metering valve. S and V are normally integrated into a pressure regulator. MFC meters neat vapor.

FIGURE 1b. Low vapor pressure precursor, carrier gas assisted delivery in Dow's VAPORSTATIONTM Central Delivery System. S: pressure sensor, V: metering valve. MFC meters diluted precursor vapor. Pressure and temperature control guarantee high precision concentration.

FIGURE 1b. Low vapor pressure precursor, carrier gas assisted delivery in Dow’s VAPORSTATIONTM Central Delivery System. S: pressure sensor, V: metering valve. MFC meters diluted precursor vapor. Pressure and temperature control guarantee high precision concentration.

On-board ampoules and central delivery system

There are several designs of carrier-gas-assisted delivery sources. The traditional design meters carrier gas into the ampoule rather than the mixture into the process chamber. Such a delivery system is dedicated to one reactor because the mass flow is metered upstream of the evaporation vessel and the associated MFC is controlled by the epi/dep tool. The ampoule serves two functions: (1) as the transport vessel and (2) as an evaporation device. For cost reasons, the ampoule should be of simple design. This means that trade-offs for the evaporation performance have to be made. The trade-offs result in line-to-line delivery rate variations and a noticeable change of delivery rate over the life of the ampoule. For some products, such changes require run-to-run recipe adjustments. In some cases the on-board ampoule is connected to a central dispense unit that transfers liquid precursor into the on-board ampoule. The result is a complex system that is still subject to delivery rate shifts requiring recipe adjustments.

A new central delivery system design is shown in Figure 1b. The task-optimized evaporator is fitted with temperature, pressure and level sensors that hold the precursor output variation at less than +/-0.4% by use of special stability algorithms. The evaporator is a permanently-installed part of the central delivery system. It is fed from a supply canister and features two precision thermometers inside the precursor liquid and gas distribution baffles and strainers for entrained droplets. Once calibrated, the system delivers a precisely known rate to a number of epi/dep reactors in the fab.

FIGURE 2 shows the output concentration of two calibrated central delivery units under various loads [1]. The curve that is alternately dotted and solid represents the signal of the binary gas sensor, which was alternately connected to one or the other unit. The other curves represent the output of the two units in standard liters per minute. The results show that proper calibration of the temperature and pressure sensors results in error of the delivery of less than +/- 0.4%. This precision cannot be achieved with ordinary on-board ampoules.

FIGURE 2. Output and concentration of two calibrated VAPORSTATIONTM Central Delivery Systems. Concentration remains within +/- 0.4% of set point regardless of load.

FIGURE 2. Output and concentration of two calibrated VAPORSTATIONTM Central Delivery Systems. Concentration remains within +/- 0.4% of set point regardless of load.

Recently, the application of the VAPORSTATION Central Delivery system has been expanded to deliver SnCl4 to a new process for the deposition of GeSn. It was fitted to a gas delivery line that was available on a mainstream silicon epi tool.

GeSn epi using a SnCl4 as new precursor

There has been increasing interest in GeSn and SiGeSn as alternative Group IV semiconductor material for electrical and optical device applications. The continuing expansion of traditional silicon with Sn and Ge offers additional design options for band gap and stress engineering. Over the past years, stress engineering using Ge made a major contribution to the improvement in Si-CMOS device performance. More recently the use of GeSn as a stressor for Ge-CMOS and relaxed GeSn as a virtual substrate, which is used to create tensile strain in a Ge epitaxial film, have been considered. The creation of tensile strain in an epitaxial Ge film is expected to result in germanium with a direct band gap [5] for photonic devices. Epitaxial Ge1-xSnx itself has also been considered as a promising candidate material for lasers and photodetectors. It has been predicted that, for sufficiently high Sn content, relaxed Ge1-xSnx turns into a direct band gap semiconductor [6,7]. Recent work of imec and its partners describe the active functionality based on the heterogeneous integration of strained GeSn/Ge on a Si platform providing photo-detection in the mid-infrared [8].

Due to the poor solubility of Sn in the Ge matrix of less than 1%, the epitaxial growth of (Si)GeSn is very challenging. Low solubility demands out-of- equilibrium growth conditions and, from epitaxial growth point of view, extremely low growth temperatures. Until recently, GeSn was grown by molecular beam epitaxy — a technique that is not suited for mass production. More recently, deuterated stannane, SnD4 has been used as Sn precursor for a CVD process, but the practical application is questionable due to the instability of SnD4.

To eliminate the problems posed by SnD4, imec chose to investigate stannic chloride SnCl4 , a stable, benign, abundant and commercially-available liquid Sn compound. Currently though, most of the CVD reactors for SiGeSn epi are not designed to use liquid precursor sources. In order to facilitate the use of liquid CVD precursors at imec, Dow Electronic Materials provided an R&D version of the central delivery system. It features the output stability and other benefits described above. The use of one of these units enabled imec to use SnCl4 and develop a groundbreaking new CVD process using digermane (Ge2H6) and SnCl4 to grow GeSn epitaxial films in a production-compatible CVD reactor. The films are metastable GeSn alloys with up to 13% substitutional Sn [10,11].

FIGURE 3 shows a typical cross section transmission electron microscope (TEM) picture with associated (224) x-ray diffraction reciprocal space mapping (XRD RSM) of a fully strained GeSn layer, grown on top of a relaxed Ge virtual substrate. The deposition temperature for the GeSn growth was kept low (320°C) in order to allow Sn incorporation in Ge lattice without Sn precipitation or agglomeration.

FIGURE 3. (a) Cross-section TEM of a 40 nm fully strained defect free GeSn layer on 1 lm Ge/Si buffer substrate with 8% Sn grown with AP- CVD using combination of Ge2H6 and SnCl4. (b) RHEED diagram of the Ge0.92Sn0.08 surface after deoxidation in UHV at 420°C. The pattern exhibits a strong (2x1) surface reconstruction along the [110]Ge direction. (c) (224) XRD-RSM of the 40 nm Ge0.92Sn0.08/Ge bilayer showing that GeSn is fully strained on Ge.

FIGURE 3. (a) Cross-section TEM of a 40 nm fully strained defect free GeSn layer on 1 lm Ge/Si buffer substrate with 8% Sn grown with AP- CVD using combination of Ge2H6 and SnCl4. (b) RHEED diagram of the Ge0.92Sn0.08 surface after deoxidation in UHV at 420°C. The pattern exhibits a strong (2×1) surface reconstruction along the [110]Ge direction. (c) (224) XRD-RSM of the 40 nm Ge0.92Sn0.08/Ge bilayer showing that GeSn is fully strained on Ge.

The TEM picture in Fig. 3(a) exhibits a defect-free and high crystalline quality for the 40-nm-thick GeSn layer. Furthermore, the surface quality of the as-grown Ge0.92Sn0.08/Ge/Si heterostructure was investigated by reflection high-energy electron diffraction (RHEED) analysis after ex-situ transfer to a MBE system. An annealing in ultra-high vacuum up to 420°C resulted in an oxide-free GeSn surface showing a strong (2×1) surface reconstruction as seen on RHEED pattern along the [110] azimuth (Fig. 3(b)). Finally, the XRDRSM around the (2 2 4) Bragg reflections (Fig. 3(c)) demonstrates that the grown GeSn layer is fully strained on Ge/Si (001) substrate.

Conclusion

The use of an improved delivery system for liquid CVD precursors allowed the
use of stannic chloride for the growth of GeSn. The new process developed by imec produces metastable GeSn with concentrations of substitutional tin of 13%.
TM Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

References

1. Control of vapor feed from liquid precursors to the OMVPE process, E. Woelk, R. DiCarlo, Journal of Crystal Growth, Available online 29 October 2013, In Press, Corrected Proof.
2. p and n-type germanium layers grown using iso-butyl germane in a III-V metal-organic vapor phase epitaxy reactor, R. Jakomin, G. Beaudoin, N. Gogneau, B. Lamare, L. Largeau, O. Mauguin, I. Sagnes, Thin Solid Films, 519, (2011), 4186–4191.
3. Crystalline Properties and Strain Relaxation Mechanism of CVD Grown GeSn, F. Gencarelli, B. Vincent, J. Demeule- meester, A. Vantomme, A. Moussa, A. Franquet, A. Kumar, H. Bender, J. Meersschaut, W. Vandervorst, R. Loo, M. Caymax, K. Temst, M. Heyns, ECS Trans. 50, (2013), 875-883.
4. Antimony surfactant for epitaxial growth of SiGe buffer layers at high deposition temperatures. Storck, P.; Vorder- westner, M.; Kondratyev, A.; Talalaev, R.; Amamchyan, A.; Woelk, E. Thin Solid Films vol. 518 issue 6 January 1, 2010. p. S23-S29.
5. M. V. Fischetti and S. E. Laux, Journal of Applied Physics 80, 2234 (1996).
6. D. W. Jenkins and J. D. Dow, Physical Review B, 36, 7994 (1987).
7. M. R. Bauer, J. Tolle, C. Bungay, A. V. G. Chizmeshya, D. J. Smith, J. Menéndez and J. Kouvetakis, Solid State Communication 127, 355 (2003).
8. A. Gassenq, F. Gencarelli, J. Van Campenhout, Y. Shimura, R. Loo, G. Narcy, B. Vincent, and G. Roelkens, OPTICS EXPRESS 20 (25) , 27297 (2012).
9. R. F. Spohn and C. B. Richenburg, ECS Transactions 50 (9), 921 (2012).
10. B. Vincent, F. Gencarelli, H. Bender, C. Merckling, B. Douhard, D. H. Petersen, O. Hansen, H. H. Henrichsen, J. Meersschaut, W. Vandervorst, M. Heyns, R. Loo, and M. Caymax, Appl. Phys. Lett., 99, 152103 (2011).
11. F. Gencarelli, B. Vincent, J. Demeulemeester, A. Vantomme, A. Moussa, A. Franquet, A. Kumar, H. Bender, J. Meerss- chaut, W. Vandervorst, R. Loo, M. Caymax, K. Temst, and M. Heyns ECS Journal of Solid State Science and Technology 2 (4), 134 (2013).
12. S. Gupta, B. Vincent, B. Yang, D. Lin, F. Gencarelli, J. Lin, R. Chen, O. Richard, H. Bender, B. Magyari-Koepe, M. Caymax, J. Dekoster, Y.; Nishi, and K. Saraswat, K. Extended Abstracts of the 2013 International Electronic Device Meeting (IEDM) (2012) p. 375.

EGBERT WOELK, PH.D., is director of marketing at Dow Electronic Materials, North Andover, MA. ROGER LOO, PH.D., is a principal scientist at imec, Leuven, Belgium.

The use of a semi-aqueous organic film stripper and residue remover that does not contain N-Methyl-2 pyrrolidone (NMP) is compared with current NMP-based chemistry.

By NIK MUSTAPHA and DR. GLENN WESTWOOD, Avantor Performance Materials, Inc. MARKUS TAN, JOACHIM NG, and YANG MING CHIEH, Philips Lumileds Singapore

Philips Lumileds collaborated with Avantor Performance Materials, a global manufacturer of high-performance chemistries, to evaluate one of Avantor’s post-etch residue remover and photoresist stripper products as a replacement for a current chemistry. Avantor’s J.T. Baker ALEGTM-368 organic film stripper and residue remover is an engineered blend of organic solvents and semi-aqueous compo-nents suitable for bulk photoresist removal and post-etch/ash residue and sidewall polymer removal. Designed to provide broad process latitude in terms of processing times and temperatures, ALEGTM-368 organic film stripper and residue remover is completely water soluble, requires no intermediate solvent rinse, and contains no hydroxylamine (HA), NMP, or fluoride elements.

The authors worked together to assess whether a change to Philips Lumileds’ process of record (POR), using this product, could be accomplished without impacting yield or device quality, and with the desired cost savings.

NMP replacement challenges

Pending changes in environmental, health, and safety regulations in key manufacturing locations around the world may prohibit the use of NMP-based post-etch residue and photoresist removal products in LED manufacturing. The shift can already be observed in Europe and in some parts of Asia and the United States, where companies are moving toward NMP-free manufacturing environments. In today’s competitive environment, it is vital for companies to find alternative chemistries that are not only effective and emphasize good performance, but also provide better cost of ownership. Philips Lumileds is taking a significant step to be part of this change.

Initial verification tests of NMP-free product

As part of the process verification, several wafers were used to check etch rate on critical substrates such as III/V Nitride, Al, Ag, and Au. These wafers were also used to verify the effectiveness of the ALEGTM-368 product to remove photoresist. Data were then compared with the current POR (TABLE 1).

TABLE 1. Comparable etch rate data (A/min) shown by baseline and ALEGTM-368 product on critical substrates.

TABLE 1. Comparable etch rate data (A/min) shown by baseline and ALEGTM-368 product on critical substrates.

It was important to confirm the effectiveness of the ALEGTM-368 product in stripping capability of negative photoresist. A wafer with 5μm thickness was used as an experiment. The wafer was dipped in the ALEGTM-368 product at 75°C followed by a water rinse step. To ensure uniformity of chemical performance, five locations were inspected by a scanning electron microscope (SEM) before and after treatment with the NMP-free product (FIGURE 1). Post-treatment images after dipping the wafer in the ALEGTM-368 product indicated that no resist remained on top of the metal surface (FIGURE 2). This supports the effectiveness of the ALEGTM-368 product; it is capable of stripping photoresist completely, without visible damage to the metal surface.

FIGURE 1. Cross-sectioning images showing resist on top of III/V metal surface before ALEGTM-368 process step.

FIGURE 1. Cross-sectioning images showing resist on top of III/V metal surface before ALEGTM-368 process step.

FIGURE 2. Cross-sectioning images showed no resist on top of III/V metal surface after processing in ALEGTM-368.

FIGURE 2. Cross-sectioning images showed no resist on top of III/V metal surface after processing in ALEGTM-368.

Resist stripping and residue remover verification test on pattern wafers

Further tests were conducted on pattern wafers comparing POR and the ALEGTM-368 product at 75 °C, for 30 minutes. Wafers were then cleaved and subjected to SEM inspection.

LEDs Fig 3a LEDs Fig 3b

 

FIGURE 3. Post-treatment for POR material. No photoresist remained under high-magnification confocal microscope inspection. POR material showed good stripping capability on patterned wafers.

LEDs Fig 4a LEDs Fig 4b

 

FIGURE 4. Post-treatment using the ALEGTM-368 product. No resist remained under high-magnification confocal microscope inspection. POR material showed good stripping capability on patterned wafers. 

 

High-magnification images were obtained to verify cleaning performance and stripping capability of the ALEGTM-368 product and POR wafers. For top-view inspection, a high-magnification confocal microscope was used to verify complete removal of photoresist. Results are shown in FIGURES 3 and 4. Both the POR and the ALEGTM-368 product showed equal performance in terms of cleaning polymer residues and stripping photo resist on patterned wafers (FIGURES 5 and 6). The next critical step was to verify electrical performance for both the POR and the ALEGTM-368 product.

LEDs Fig 5a LEDs Fig 5b

 

FIGURE 5. SEM images showing post-treatment for POR. 

LEDs Fig 6a LEDs Fig 6b

 

FIGURE 6. SEM images showing post-treatment for the ALEGTM-368 product. 

Electrical performance for engineering lots

Wafers were sampled from several production lots before being split into two groups, one group using the baseline and the other using the ALEGTM-368 product. Both groups were processed in an automated tool following the recommended process condition at an operating temperature of 75°C and a processing time of 30 minutes. To achieve wafer uniformity, the tool was equipped with a mega-sonic function and recirculation to ensure effective cleaning of post-etch residues and stripping of negative photoresist.

After chemical treatment, the wafers were given an intermediate rinse using an IPA solvent to remove any remaining traces of the ALEGTM-368 product from the surface of the wafer. Without this step, chemical left on the surface of the wafer could cause corrosion, water marks, or other device defects. Wafers were then subjected to a QDR (quick dump rinse) to remove all remaining solvent on the wafers. This step normally takes five to ten minutes, with noticeable CO2 bubbling to serve as extra protection from corrosion of exposed metal. Finally, all wafers were subjected to a nitrogen dry for five minutes, a vital process since any remaining moisture could cause severe corrosion and impact electrical performance and final yield.

Once all process steps were performed, both groups were subjected to electrical tests to ensure the chips on the wafers were functioning well and within specifications. Results, as indicated in FIGURE 7, showed no significant differences in term of electrical performance for both the baseline and the ALEGTM-368 product. All wafers met specification and were subject to final yield probe.

FIGURE 7. Electrical performance comparing ALEGTM-380 and ALEGTM-368 products for real production wafers.

FIGURE 7. Electrical performance comparing ALEGTM-380 and ALEGTM-368 products for real production wafers.

Comparable Performance in Final Yield

The same production wafers which were processed using the ALEGTM-368 product at 75 °C were then subjected to final yield analysis and compared to current POR. There was slight improvement in the standard deviation for the ALEGTM-368 product when compared to baseline chemistry. Overall, both products showed comparable final yield at 98 percent (FIGURE 8).

FIGURE 8. Yield distribution for ALEGTM-380 and ALEGTM-368 products on real production wafers.

FIGURE 8. Yield distribution for ALEGTM-380 and ALEGTM-368 products on real production wafers.

Reduced Cost of Ownership

It is undeniable that operating cost is a major consideration in LED manufacturing. Prior to adopting the current POR chemistry, Philips Lumileds tried both HA-based and NMP-based chemistries. Using the HA-based chemistry, a pre-treatment process was needed to soften the photoresist prior to stripping, followed by a solvent intermediate rinse. A strip process with the ALEGTM-368 product eliminated this step and resulted in significant cost savings and increased throughput due to process simplification (TABLE 2).

TABLE 2. Higher throughput and better cost of ownership due to a reduction in process steps.

TABLE 2. Higher throughput and better cost of ownership due to a reduction in process steps.

Summary

The NMP-free ALEGTM-368 product was comparable to POR when tested in various steps of the LED manufacturing process, including: substrate compatibility on critical layers, electrical performance on actual device, and final yield. In terms of process simplification, use of the ALEGTM-368 product also showed similar technical benefits as POR, in which a significant reduction of the number of steps and chemicals used in the process leads to improved cost of ownership.

This collaboration demonstrates how a manufacturer can translate its commitment to environmental, health, and safety improvements and reduction of cost of ownership into the commercialization of a new cleaning process which can bolster its competitive position in the global LED manufacturing industry.

NIK MUSTAPHA is a Principal Applications Engineer, AvantorTM Performance Materials, Inc. MARKUS TAN is Chief Process Engineer, JOACHIM NG is Senior Manager-Process Engineering, and YANG MING CHIEH is a Process Engineer at Philips Lumileds Singapore. DR. GLENN WESTWOOD, Senior Research Scientist, AvantorTM Performance Materials, Inc.

Daintree Networks has been named by CIO Review Magazine as one of the ’50 Most Promising Internet of Things (IoT) Companies 2014.’ The list features the best vendors and consultants providing technologies and services related to IoT. In the same issue, Daintree Networks CEO Danny Yu was featured as the ‘Entrepreneur of the Month,’ which highlights his career path and leadership of Daintree Networks to becoming a prominent player in the Enterprise-IoT market and top provider of wireless mesh networking solutions for smart buildings.

A distinguished panel comprised of CEOs, CIOs, CTOs, and analysts including the CIO Review editorial board determined the list of top companies at the forefront of tackling challenges in the Internet of Things market in the U.S. “We are happy to showcase Daintree Networks as a top IoT company due to the success of its ControlScope solution in advancing the IoT landscape for commercial entities,” said Harvi Sachar, publisher and founder, CIO Review. “Daintree’s dedication to true open standards-based solutions continues to break down adoption barriers and provides significant cost advantages to its customers. We’re excited to have them on our top IoT companies list, and to feature Daintree’s leadership, CEO Danny Yu, as the ‘Entrepreneur of the Month.'”

“We are honored to be recognized by CIO Review Magazine as one of the top ’50 Most Promising IoT Companies for 2014,'” said Danny Yu, Daintree Networks CEO. “This distinction reinforces the success of our Enterprise Internet of Things,(E-IoT) approach, which leverages our true open standards-based solutions to provide cost-effective wireless mesh networking for smart buildings. In addition, as ‘Entrepreneur of the Month,’ I appreciate the recognition, but the credit goes to the dedicated, forward-thinking employees of the company who are driving our explosive growth.”

A team of researchers led by North Carolina State University has found that  stacking materials that are only one atom thick can create semiconductor junctions that transfer charge efficiently, regardless of whether the crystalline structure of the materials is mismatched – lowering the manufacturing cost for a wide variety of semiconductor devices such as solar cells, lasers and LEDs.

“This work demonstrates that by stacking multiple two-dimensional (2-D) materials in random ways we can create semiconductor junctions that are as functional as those with perfect alignment” says Dr. Linyou Cao, senior author of a paper on the work and an assistant professor of materials science and engineering at NC State.

“This could make the manufacture of semiconductor devices an order of magnitude less expensive.”

Schematic illustration of monolayer MoS2 and WS2 stacked vertically. Image: Linyou Cao.

Schematic illustration of monolayer MoS2 and WS2 stacked vertically. Image: Linyou Cao.

For most semiconductor electronic or photonic devices to work, they need to have a junction, which is where two semiconductor materials are bound together. For example, in photonic devices like solar cells, lasers and LEDs, the junction is where photons are converted into electrons, or vice versa.

All semiconductor junctions rely on efficient charge transfer between materials, to ensure that current flows smoothly and that a minimum of energy is lost during the transfer. To do that in conventional semiconductor junctions, the crystalline structures of both materials need to match. However, that limits the materials that can be used, because you need to make sure the crystalline structures are compatible. And that limited number of material matches restricts the complexity and range of possible functions for semiconductor junctions.

“But we found that the crystalline structure doesn’t matter if you use atomically thin, 2-D materials,” Cao says. “We used molybdenum sulfide and tungsten sulfide for this experiment, but this is a fundamental discovery that we think applies to any 2-D semiconductor material. That means you can use any combination of two or more semiconductor materials, and you can stack them randomly but still get efficient charge transfer between the materials.”

Currently, creating semiconductor junctions means perfectly matching crystalline structures between materials – which requires expensive equipment, sophisticated processing methods and user expertise. This manufacturing cost is a major reason why semiconductor devices such as solar cells, lasers and LEDs remain very expensive. But stacking 2-D materials doesn’t require the crystalline structures to match.

“It’s as simple as stacking pieces of paper on top of each other – it doesn’t even matter if the edges of the paper line up,” Cao says.

The paper, “Equally Efficient Interlayer Exciton Relaxation and Improved Absorption in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures,” was published as a “just-accepted” manuscript in Nano Letters Dec. 3.

Lead authors of the paper are Yifei Yu, a Ph.D. student at NC State; Dr. Shi Hu, a former postdoctoral researcher at NC State; and Liqin Su, a Ph.D. student at the University of North Carolina at Charlotte. The paper was co-authored by Lujun Huang, Yi Liu, Zhenghe Jin, and Dr. Ki Wook Kim of NC State; Drs. Alexander Puretzky and David Geohegan of Oak Ridge National Laboratory; and Dr. Yong Zhang of UNC Charlotte. The research was funded by the U.S. Army Research Office under grant number W911NF-13-1-0201 and the National Science Foundation under grant number DMR-1352028.

Pixelligent Technologies, producer of PixClear, nanocrystal dispersions for demanding applications in the Solid State Lighting and Optical Coatings & Films markets, announced today that it closed $5.5 million in new equity funding. The funds will be used to support its accelerating customer growth in Asia, the EU and the U.S., and also to hire application engineers, product managers, manufacturing engineers, and staff scientists.

“During the past 12 months Pixelligent has seen a tremendous increase in demand for its nanocrystal dispersions, predominantly driven by the leading LED package manufacturers and the emerging OLED panel makers. Pixelligent’s high-index and transparent nanocrystals are becoming increasingly important in delivering more lumens per watt while also delivering cost efficiencies. This demand is coming from LED and OLED customers around the globe with the fastest growth being realized in Asia,” commented Craig Bandes, President & CEO, Pixelligent Technologies.

To support the growth coming out of the Asian market, Pixelligent appointed distributors and agents throughout Asia in 2014 and expects to do the same in the EU in 2015. Part of the proceeds from this round are being used to support the global expansion of Pixelligent’s marketing and distribution footprint.

This round included support from both a number of new family offices and existing investors. To date, Pixelligent has raised more than $23.0M in equity funding and has been awarded more than $10.0M in U.S. government grant programs.

Gallium nitride (GaN) based devices are attractive for harsh environment electronics because of their high chemical and the mechanical stability of GaN itself that has a higher atomic displacement energy than other semiconductor materials.

However, degradation mechanisms of GaN device under radiation environments is not clear mainly because devices consist of many different types of semiconductors, such as p-type and n-type layers in light emitting diode (LED), and each layer has different hardness to radiation.

Now, researchers at the Electronics-Inspired Interdisciplinary Research Institute (EIIRIS) and Department of Electrical and Electronic Information Engineering at Toyohashi University of Technology, and the Japan Atomic Energy Agency (JAEA) describe the physical mechanism of an observed increase in the resistance of p-type GaN irradiated with 380 keV protons compared with n-type GaN.

This image depicts two-terminal resistance of p- and n-type GaN as a function of proton fluence. This inset shows schematic of sample, and lines are guide for eyes. Credit: Copyright (c) 2014 Toyohashi University of Technology.

This image depicts two-terminal resistance of p- and n-type GaN as a function of proton fluence. This inset shows schematic of sample, and lines are guide for eyes.
Credit: Copyright (c) 2014 Toyohashi University of Technology.

The GaN-based LED structure shown in Fig.1 was irradiated with protons and the resulting electrical properties measured. Notably, the electrodes to measure the resistance of the p-type and n-type layers were produced independently using the clean room facilities at EIIRIS and the ion implanter in JAEA.

The two terminal resistance of the n-type GaN did not vary from its initial value after 1×1014 cm-2 proton irradiation, and remained of the same order after 1×1015 cm-2 protons. However, a clear increase of the resistance was found in the p-type GaN after 1×1014 cm-2 irradiation. The resistance increased further by six orders of magnitude after 1×1015 cm-2.

The observed increase of the resistance in p-type GaN is explained as being due to the lower initial carrier density than in n-type GaN due to a lack of efficient p-type doping technology for GaN, which is a key for the realization of novel devices operable in harsh environments.

Samsung Electronics Co. today introduced new chip-on-board (COB) LED package products, the LC006B and LC008B, with six and eight watts of power respectively. The new packages join five others in Samsung’s popular LC series (LC013B, LC019B, LC026B, LC033B and LC040B), to complete its COB package line-up.

“With the introduction of our new under-10 watt COB packages, we are signaling our intent to aggressively target the indoor LED lighting market,” said Bangwon Oh, Senior Vice President, Strategic Marketing Team, LED Business, Samsung Electronics. “Samsung will continue to advance its LED technology and business objectives by providing lighting manufacturers with the best in LED lighting components, delivering exceptionally high-quality LED package and engine products and services that reliably meet customer needs,” he added. “We remain dedicated to increasing our breadth of market solutions, to further grow our LED lighting component business.”

A chip-on-board LED package provides a single light source that combines multiple LED chips to achieve higher light intensity and uniformity, while simplifying luminaire design.

The LC006B and LC008B offer high-efficacy levels of 140lm/W and 142lm/W at 5000K CCT, respectively. The new packages will support a wide range of CCT (Correlated Color Temperature) specifications from 2700K to 5000K with a CRI (Color Rendering Index) over 80. They also feature a compact package size with an 8mm LES (Light Emitting Surface) and a package structure that can be easily connected with holders or screw mounts for greater installation convenience.

Samsung’s LC series has gained widespread attention for delivering high luminance from a small LES, as well as low heat resistance and outstanding light efficacy. The LC packages also feature high color uniformity with 3-step MacAdam ellipses and consistently superior light quality.

Samsung COB LED lighting solutions now can be used in a significantly wider range of applications, including downlight for home lighting, flood light for industrial lighting, and spotlight and downlight for commercial lighting.

Soraa announced today that it has introduced a perfectly compatible version of its award-winning MR16 LED lamp. Featuring the company’s signature elements of full-visible-spectrum light, Soraa’s constant current MR16 LED lamp is the ideal lighting solution for restaurants, retail, high-end residential, and office environments where superior light quality and dimming are essential.

Equipped with a standard GU5.3 two-pin base, Soraa’s constant current MR16 LED lamp fits into any MR16 fixture and fully conforms to the ANSI/ IECE compatible form factor. Unlike other MR16 LED lamps, the constant current LED lamp is designed to accept an external driver which supplies the lamp with low voltage DC input current, eliminating the need to fit a transformer in limited space.

Providing enormous dimming and control flexibility, light output can now be programmed to the desired level when using a programmable or remote driver. The lamp also achieves zero flicker when used with a DC driver and is available in 10 degree, 25 degree and 36 degree versions.

“Incompatibility issues between LED lamps, fixtures, dimmers and transformers continue to hinder the advancement and adoption of LED technology,” explained George Stringer, Senior VP of North America Sales at Soraa. “Our new constant current MR16 LED lamp overcomes these hurdles, enabling flexibility and choice without compromising on performance and quality.”

Soraa’s constant current MR16 LED lamp features the company’s Point Source Optics for beautiful, high intensity, and uniform beams; and unique Violet-Emission 3-Phosphor (VP3) LED technology for perfect rendering of colors and whiteness. Utilizing every color in the rainbow, especially deep red emission, Soraa’s VP3 Vivid Color renders warm tones beautifully and accurately, and achieves a color-rendering index (CRI) of 95 and deep red (R9) rendering of 95 at color temperatures ranging from 2700K to 4000K. And unlike blue-based white LEDs without any violet/ ultra-violet emission, the company’s VP3 Natural White is achieved by engineering the violet emission to properly excite fluorescing agents including natural objects like human eyes and teeth, as well as manufactured white materials such as clothing, paper and cosmetics.

Related news: Soraa founder wins Nobel Prize in physics

By Daniel QI, SEMI China

General Lighting is a Key Growth Driver

As a result of cost reduction and performance improvements, LED lighting is becoming more and more competitive in general lighting market. Energy-efficient fluorescent lamps (like CFL) productions have experienced growing and stabilizing stages in recent years; however, energy-efficient fluorescent lamp production is now facing a significant decline in 2014 as LED lighting products represent a faster growing segment of this market. SEMI China believes that the general lighting market will replace the LCD TV backlight market as the largest application market for LEDs in 2014, and general lighting market will continue to drive the LED industry over the next several years.

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China’s LED Fab Industry Is Consolidating and Recovering

Due to overly optimistic expectations for future market growth and opportunities, coupled with many local governments providing subsidies for MOCVD equipment procurement, China’s LED fab industry entered into a hyper-growth period between 2010 and 2011, resulting in 76 LED fabs being established by the end of 2011. Many of these companies struggled given challenges in ramping up and with over-supply in the market. Fab capacity utilization lagged for many companies.

Following this post hyper growth period, fab utilization eventually recovered and improved throughout 2013, reaching about 90% by first quarter in 2014 (see next figure). Two key reasons are evident for improved capacity utilization. First, as previously mentioned, demand in general lighting application has increased. Second, China’s LED fabs have undergone consolidation since 2012. Consolidation occurred as some of LED fabs went bankrupt or exited the industry entirely, thus mitigating oversupply in the China market. These bankrupted or former LED fabs are not included in the utilization statistics shown in the figure below.

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China LED Fab Industry Expansion Plan

There has been very limited news of LED fab expansions over the previous two years, but the situation has changed as a number of China’s LED companies have announced new fab projects and/or expansion plans in 2014. SEMI believes that over the next three to four years upstream LED manufacturers in China will enter robust era of growth. Unlike 2010 and 2011, this expansion round will be dominated by leading manufacturers, not new entrants. Also, the total increase in MOCVD tool quantity in 2014 and 2015 will be from just six companies  and will account 74% of the total quantity of MOCVD tools installed in China. It is expected that the number of new MOCVD tools installed will exceed 1,000 from 2014 to 2018.

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The New Edition of China LED Fab Industry Report

SEMI China has recently published a new report of China’s LED Fab Industry in October 2014.This report covers: the LED lighting market, global LED fab capacity forecast, China’s LED fab industry utilization statistics, a listing of all of China’s LED fabs, LED fab expansion plans by supplier, China MOCVD tool market analysis and forecast, China GaN epitaxial wafer capacity statistics, and LED forecast by wafer size.

For more information, please contact Daniel QI: [email protected]

Intematix Corporation, a manufacturer of phosphor solutions for LED lighting, today announced Jerry Turin as the company’s Chief Financial Officer.  Most recently, Mr. Turin served as Chief Financial Officer of Oclaro, Inc., which scaled to a peak of $600M revenue run-rate from $250M during his tenure.  Mr. Turin will direct the company’s financial strategy and finance team.

“Jerry Turin’s experience and financial expertise will promote the strategic growth objectives of Intematix,” said Mark Swoboda, CEO of Intematix. “His understanding of the financial ecosystem, and his rapport with the investment community, will contribute to the financial foundation supporting the execution of our plans.”

“I am excited to step into this role at Intematix,” stated Mr. Turin. “The core competencies of Intematix are impressive, and the market opportunities are significant. I look forward to working with the talented team at Intematix.”

Prior to his appointment as Chief Financial Officer at Intematix, Mr. Jerry Turin was the Chief Financial Officer of Oclaro, Inc. from 2008 through 2013. Mr. Turin served as the Vice President of Finance, Corporate Controller and Treasury from July 2005 to 2008. Before his tenure at Oclaro, Mr. Turin worked at executive level financial positions in Silicon Valley and has more than 20 years of combined accounting and corporate finance experience in the technology industry. He also served at Deloitte & Touche as Senior Manager of Audit Services. Mr. Turin holds a Bachelor’s in Business Administration and Commerce from the University of Alberta. He is also a member of the Canadian Institute of Chartered Accountants and the Institute of Chartered Accountants of Alberta.