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Stephen D. Hersee, Ph.D. — 2012 STC.UNM Innovation Fellow

2012
This year’s recipient of the 2012 Innovation Fellow Award, Dr. Stephen Hersee, is a shining example of distinguished innovation—and not only because he is an expert in light-emitting devices (LEDs)! His technologies have led to many commercialization opportunities that have branched out to established companies in the semiconductor and electronics industries, a home-grown start-up company and ones beyond our borders, and spurred the pace of research and development for the nascent field of smart lighting. His nanowire technologies, the culmination of ten years of research at UNM, represent the foundation for developing LEDs for solid-state lighting applications and the next generation of high-quality, low-cost semiconductor wafers for LCD backlighting of cell phones, laptops and televisions.

In his more than twenty years as a University of New Mexico researcher and inventor, Dr. Hersee has pioneered the way in which gallium nitride (GaN) crystals, called nanowires for their microscopic size, are grown for use as semiconductors and light-emitting diodes (LEDs). Gallium nitride is considered superior to silicon as a semiconductor material because it can facilitate a much higher flow of energy in a smaller space. In addition, GaN LEDs convert electrical current to visible light very efficiently, are strong and stable, and defect free. But current technology can’t grow the nanowires with the same uniformity and orientation that is needed for greater efficiency, quality, and mass production—that is, until Dr. Hersee created his process. He has been searching for a way to control the growth of the wires. The method he created involves using a growth mask that has been patterned with an ordered arrangement of tiny holes. The nanowires are grown through the holes using metalorganic chemical vapor deposition (MOCVD). The MOCVD is pulsed after the nanowires start to grow above the mask. This technique prevents the wires from spreading outward over the surface of the mask into a tangle of wires of different sizes and shapes and pointing in different directions—what’s amusingly but accurately referred to as “nanonoodles.” The pulsed deposition lays down the gallium (Ga) and nitrogen (N) growth precursors in alternate layers, which allows the gallium and nitrogen atoms to settle into the best position to produce uniform, defect-free crystals. The method is capable of producing billions of nanowires in the area of a typical semiconductor wafer.

Here’s what Dr. Steve Brueck, Director of UNM’s Center for High Technology Materials, has to say about Dr. Hersee’s achievement: “Steve Hersee has been an outstanding innovator in developing nanoscale growth techniques for GaN and related materials that are important for solid-state lighting because there is no naturally available substrate for GaN. The commonly used materials—silicon carbide and sapphire—have large lattice mismatches with GaN leading to large numbers of crystal defects that impact the light-emitting efficiency and lifetime of today’s GaN light-emitting devices. Steve has pioneered the growth of GaN from nanoscale seed areas that leads to perfect crystals without the threading faults that bedevil other approaches. Over time this technology will have a major commercial impact.”

The impact is already being seen in the New Mexico-based start-up company formed around this new process. Nanocrystal Corporation President Petros Varangis explained that Dr. Hersee’s “defect-free gallium nitride nanowires will be used for the manufacturing of lower-cost and higher-performance and quality GaN substrates and InGaN light-emitting diodes. It is the most viable method for the commercialization of cost-efficient and high brightness LEDs required for applications such as general white lighting for residential, industrial, street, and automotive lighting and back-lighting for electronic components and outdoor displays. This technology has the potential to enable the rapid growth of all these high-volume markets. So far, high-brightness LEDs are too expensive to be adopted in large volumes.”

His efforts to fund and build an engineering research center devoted to advancing LED technologies and creating smart lighting systems, and training the young engineers who will be ready, as future inventors and entrepreneurs, to lead this new industry is yet another impressive accomplishment. The Smart Lighting Engineering Research Center (ERC), an interdisciplinary, multi-institutional group of faculty researchers from Rensselaer Polytechnic Institute, Boston University and the University of New Mexico, and industry partners, was created and funded by the National Science Foundation in 2008, one of only 17 ERC’s across the nation. Dr. Robert Karlicek, Director of the Smart Lighting ERC, provides this analysis: [As the former Associate Director of the Center], “Steve was heavily involved in the formulation of the Smart Lighting ERC from the very beginning, and played a key role in securing the Smart Lighting ERC award in 2008. His work on innovative LED device design was a key part of securing that award. As the center matured and moved to develop a top-down, systems-level view of how solid state lighting would evolve, Steve also played a critical role in bringing other UNM talent to the ERC mix. Steve had the grasp of the diverse skills needed to create the technical foundation for lighting systems (LEDs, sensors and controls architectures) and proactively recruited new UNM talent which, today, is making valuable contributions to the ERC team. Steve brings a calm, experienced and open view to technical discussions and is always open to new possibilities. Unlike many researchers who are narrowly focused on their own interests, Steve fits the model of the ERC professor very well: one who is interdisciplinary, collaborative, and a pleasure to work with. His passion for education was clearly evident in his work with students and educational outreach.” Indeed, the ERC’s educational outreach program aims to bring the science behind the new technology into middle and high school classrooms to spark an interest in the field early on. At the university level, Center researchers are engaging undergraduate and graduate students in smart lighting research, and they are focusing on attracting more female and minority students to this new field of engineering.

The possibilities are exciting. Dr. Hersee’s innovations have so many applications across so many disciplines. Imagine dime- sized solid-state microscopes that have no lenses or moving parts but have the power to magnify just as well as conventional optical microscopes by using nanowire LEDs to produce high-resolution digital images. Imagine optical access to the internet through your room lights. Or a full-spectrum lighting system that will be able to sense changes to the environment and automatically and continuously make adjustments for energy efficiency and healthy indoor lighting. How about lighting systems with biosensors that will be able to scan for biological and biochemical contamination. All of these radical technologies are currently being developed thanks to Dr. Stephen Hersee. The wonders of the innovative mind—celebration imagination!