Technology Team
Professor Steve Hersee
Dr. Hersee is Professor of Electrical Engineering at the Center for High Technology Materials at the University of New Mexico and IEEE Fellow. Dr. Hersee is the inventor of the defect-free GaN nanowire LED technology. He has numerous technical publications and patents and more than twenty five years of experience in advanced materials and devices both in academia and industry (Plessey Research, Thompson CSF, General Electric).
Dr. Lei Zhang
Dr. Zhang is the Chief Technology Officer of Nanocrystal Group. Dr. Zhang received his B.Sc. from Beijing University, China, and Ph.D. in electrical engineering from the University of New Mexico. Dr. Zhang has more than fifteen years experience in the design and development of optoelectronic devices (lasers, solar cells, LEDs) in the industry (Emcore, Zia Laser Inc) and R&D institutions (Sandia National Laboratory, and University of New Mexico).
Technology Innovation: Defect-Free Core-Shell Nanowire-Array LEDs
Gallium Nitride (GaN) is the most important semiconductor market for optoelectronics and will remain so for the next 20+ years. The total available market for visible LED and Laser Diode products will grow to approximately $100 billion annually within the next 10-15 years when the Solid State Lighting, Liquid Crystal Display (LCD) back-lighting and ultra high density digital video markets fully develop. High brightness GaN-based LEDs can revolutionize a host of emerging high volume markets for lighting applications by offering devices with a more compact and aesthetic design, longer operating lifetime and a rich optical spectrum. In addition, the adoption of GaN LEDs in general white light illumination can result in 50% lower energy consumption and significant energy savings (hundreds of TWhs annually by 2020) worldwide.
Despite their superior lighting performance characteristics, the manufacturing cost of high brightness LEDs is currently approximately 10 times higher than that of compact fluorescent lamps. The high manufacturing cost of LEDs is related to the poor GaN wafer material quality. Thus, bulkier and lower efficiency existing lighting technologies, such as incandescent and fluorescent lamps, prevail in the marketplace.
Nanocrystal’s approach is a patented and manufacturable technology that grows uniform defect-free GaN nanostructures, essentially eliminating the materials issues that have plagued the GaN industry since its inception. Nanocrystal’s pulsed MOCVD growth method results in GaN nanowires for use as epitaxial material for LEDs with approximately 100,000-times lower defect density than what can be achieved currently. This novel epitaxial growth technique, coupled with the improved chip design of nanowire-array LEDs, will lead to LED devices of higher performance, reliability, lifetime and several times lower manufacturing cost compared to conventional technologies for high power LEDs.
At a high level the advantages of the defect-free core-shell nanowire-array LED technology can be summarized as follows:
- (i) A simpler epitaxial growth method (compared to more complicated epitaxial growth techniques used in the industry for high quality GaN material, such as multi-step Epitaxial Lateral Overgrowth) which will result in lower cost and higher yield epitaxial wafers.
- (ii) Uniform and Defect-Free GaN nanostructures, which will result in LEDs of improved internal quantum efficiency and operating lifetime / reliability.
- (iii) Improved Design of LED chip (i.e., vertical waveguide geometry instead of planar LEDs used in the industry), which will result in improved wall-plug efficiency ηwd (or equivalently luminous efficacy ηL) and higher output power per chip.
The wall-plug efficiency of an LED is equal to the product of the voltage efficiency (ηv), internal quantum efficiency (ηint), and light extraction efficiency (ηext); ηwd = ηv ηint ηext. The main problem with conventional high-power planar LEDs developed by manufacturers is that the voltage efficiency decreases fast at higher values of the operating current (that is, as you drive the LED harder), since ηv varies inversely proportional with the operating current I, and the LED series resistance R. This is due to the high series resistance of conventional LEDs. As a result the luminous efficacy also decreases at high operating currents. Figure 1b in White Paper No.4 shows this trend.
Nanocrystal’s defect-free core-shell nanowire-array LEDs because of their vertical waveguide geometry can in principle reduce significantly (by 4-5 times) the series resistance of the LED chip of same footprint, therefore nanowire-array LEDs can be operated at a much higher operating current (4-5 times higher) without sacrificing voltage efficiency or luminous efficacy. Our objective is to leverage this advantage and develop nanowire-array LEDs that can correspondingly emit 4-5 times higher luminous flux per chip than conventional LEDs developed by major manufacturers. This would allow us to replace 4 or 5 conventional LED chips by a single higher power nanowire-array LED chip and therefore reduce correspondingly (4-5 times) the cost of solid state white lighting at the luminaire level through this development alone.
Over the next 18 months, following joint R&D collaboration with major LED manufacturers in Taiwan, Nanocrystal Group will be in position to provide samples of the Alpha-version of the nanowire-array LED chips for independent testing and evaluation.
White Papers
White Paper No.1 and White Paper No.2 provide a description of the epitaxial MOCVD growth process of the defect-free GaN nanostructures, and characterization results from the first prototype of a nanowire-array LED device (GaN p-n homojunction nanowire-array), which proves the feasibility of developing an LED device based on the defect-free nanowire technology.
White Paper No.3 provides an overview of the fundamental advantages of the defect-free nanowire-array LED technology versus conventional LEDs developed by the industry so far.
White Paper No.4 provides a cost model which describes at a high level how the advantages of the GaN core-shell nanowire-array LEDs, in terms of a manufacturable and lower cost epitaxial growth process, improved LED chip design (vertical geometry) and defect-free GaN nanostructures, will translate in significantly lower manufacturing cost for high power LEDs.