PLAYA DEL CARMEN, México — April 1, 2014 — Hot on the heels of Cree's revelation of a world record 303 lm/W white LED, GaNgle Optronix Ltd., a Herzliya, Israel, startup funded by a Who's Who cadre of Sand Hill Rd. venture capitalists, is coming out of stealth mode at this week's IEEE International Caribbean Conference on Devices, Circuits, and Systems (ICCDCS 2014) by presenting a paper on the details of its super-high-efficacy, high-power, white LED product line.
The paper's lead author, GaNgle's CTO and former Bell Labs Fellow, Dr. Hyam Kydding, disclosed in an exclusive to UBM All Led Lighting's Ron Amok:
We're elated to be announcing our new LED product line today, which will have guaranteed efficacies of 300 lumens/Watt, with us seeing typical numbers in pilot production of over 333 lumens/Watt, unlike those cherry-picking lab rats over at Cree. And we're not talking about a coddled 25°C monster die at 350mA, but hot lumens, and I mean really hot lumens, at an unprecedented production wafer test of TJ = 600°C.
The difficulties in attaining high efficacies on low-cost silicon substrates, as GaNgle Optronix is using, are well known, and many a brave Seoul has tried to overcome the very serious barrier of growing mismatched GaN crystal films on monocrystalline silicon. Compounding the problem is silicon's low bandgap, which absorbs light produced by the GaN layer.
No buffers
Not relying upon proprietary "buffer" layers to ease slowly into the growth of a "low" dislocation density GaN epitaxial layer, GaNgle has taking a rather innovative "angle" on the problem. While most companies like Bridgelux/Toshiba take up to 8 hours to grow GaN in extremely expensive MOCVD reactors, and though some startups like Plessey have claimed to speed up to a couple of hours but have had difficulties in demonstrating efficacies much more than about 60 lumens/watt, GaNgle Optronix has cut the epi growth cycle times to 30 minutes while boosting white LED efficacies by a factor of up to six times.
Figure 1. The napkin drawing that launched GaNgle Optronix Ltd.
(an All LED Lighting exclusive)
How do they do this? While the devil is in the details, it all boils down to nothing more than high-school geometry, really. All LED Lighting was able to talk the CTO into showing off his prized possession, the commissary napkin sketch, shown here as a world exclusive, from which the company was born and which initiated a stampede of investor money that was willing to get into the company with nothing more than non-voting common stock -- completely unheard-of, to date in Silicon Valley.
The lattice constants of silicon and GaN are mismatched by 17 percent (see Figure 2). By presenting the silicon substrate at a tilt of 33.9° to the epi source, GaN is grown at a 33.9° angle to the Si lattice. Using simple cosine calculations, we can see that the silicon, in projection, will have its lattice shrunk by a factor of cos(33.9°) or 0.8300122, or by approximately 16.9987714%. With the extremely low crystalline defects in modern-day silicon, GaNgle (the origin of the corporate name now becomes obvious) Optronix is able to grow completely dislocation-free (in theory) GaN in unprecedentedly thin layers, completely eliminating cracking (see photomicrograph), and with most of the 30 minutes in the MOCVD reactor being spent in simply pumping down a vacuum in the chamber.
(Source: Institute of Microelectronics, Agency for Science, Technology, and Research)
Grooves
Dr. Kydding told us:
In addition to our low-defect density, which we expect to improve quickly with our perfect lattice-matching to yield 500 lumen/watt devices in about a year, we get some added benefits on the optical side as well. By virtually tilting the substrate, using a very shallow MEMS v-groove micro-machining technique (see Figure 3), we can not only use standard 8" wafer reactor tooling, we also affect the way light rays are reflected in the epi layers. By bringing the silicon closer to its critical angle of reflection, the backside silicon substrate is no longer an in-plane absorber of light, but becomes a dielectric mirror. The mirror, coupled with the 19.3564193Å-thin GaN layers, means we achieve optical extraction ratios exceeding 98.7341775%. Not only that, we get 20.4801444% more GaN surface area projecting upwards from the die, or that many more die per wafer, offsetting the grooving cost.
All LED Lighting was also able to speak briefly on the phone with the paper's co-author and Dr. Kydding's wife, Ling-Mei "Fing" Kydding-Meh. Also a Bell Labs alum, Kydding-Meh, a leading expert on ohmic metals, told us, "In addition to what my darling Hyam has told you, we were also able to completely eliminate the need for lossy transparent ITO metals on our diode, and we were able to use the much lower work-function metal, tungsten, as our ohmic contact, evaporating it onto the groove vertices."
Ohmic metals
Kydding-Meh continued:
GaNgle Optronix Ltd's SiliGaN(TM) LEDs, available in CCT bins of 1900K, 2400K, 2700K, 3000K, 4000K, and 5000K, are expected to begin sampling to non-Chinese customers next month, with production planned for 2Q 2014. Budgetary pricing for the SiliGaN™ 1900K, 300 lumen at 350mA, 1-Watt device, in 100M quantities is $0.1342 each, with flip-chip POD die formats available for about 40% less. For more information about today's announcement, click here.
Reported live by Ron Amok, All LED Lighting Technical Contributor, from Playa del Carmen.
