The achievements of Professor Theodore Moustakas (ECE), associate head of the Division of Materials Science & Engineering, are legion. He is perhaps best known for pioneering the nucleation steps for the growth of gallium nitride on sapphire and other substrates, an essential process for the manufacture of blue LEDs, which are widely used in solid state lighting applications; and for developing highly-efficient, deep ultraviolet (UV) LEDs, which are expected to provide environmentally friendly water and air purification.
On March 3, Moustakas discussed the primary focus of his research—the fabrication of nitride semiconductors for high-performance visible and UV LEDs—in the 2011 College of Engineering Distinguished Scholar Lecture, “Nitride Semiconductors and their Applications to Solid State Lighting and Water/Air Purification.” Speaking at the Trustee Center Ballroom, he addressed students, faculty and researchers from throughout the Boston University academic community and other Boston-area research institutions.
A professor in the ECE Department for more than 20 years, Moustakas has had a significant impact on his field, through 25 patents, hundreds of invited talks and journal papers, eight co-edited books and 7,000 citations in research literature. Recently selected as the 2010 Molecular Beam Epitaxy (MBE) Innovator Award, he has been named a Fellow of the American Physical Society and Electrochemical Society.
“What an extraordinary volume of incredible and creative work by Ted,” said Dean Kenneth R. Lutchen, acknowledging not only Moustakas’ significant research achievements but also his leading role in propelling the ECE Department’s PhD program into the nation’s top-ranked programs, putting the MSE Division on the national map and helping establish BU as a national center of photonics research. “Ted is really an icon of excellence and impact, and incredible dedication to Boston University.”
Nitride Semiconductors and Their Applications
“I am humbled to come here and talk to you about solid state lighting,” said Moustakas. “I was born in a small village in Greece, and I would study my school books using a lantern that burned oil.”
Moustakas observed that nitride semiconductors such as indium, gallium and aluminum nitride cover the entire range of the electromagnetic spectrum, from the infrared to the deep UV; and exhibit high thermal conductivity, chemical resistance, radiation-hardness, and other properties that make them suitable for a wide range of applications.
These include existing devices and technologies such as photovoltaic solar cells, biological and chemical detectors, full-color displays, optical recording lasers, high-temperature and high-power electronics, visible and UV lasers—as well as emerging LED-based applications such as solid state lighting for general illumination and water, air and surface sterilization.
White-Light LEDs for General Illumination
Providing the same light for less than half the energy required by a compact fluorescent bulb and lasting up to 100,000 hours, a high-quality white-light LED would reduce U.S. energy costs by up to $20 billion and carbon dioxide emissions by 150 million tons annually, but today’s white-light LEDs are inadequate for use in general lighting applications, Moustakas noted.
To produce white light that you can read by, blue, green and red LEDs must be combined—and making green LEDs is very inefficient and costly. Moustakas’s group has made significant progress in resolving this “green gap” by developing semiconductor particles called quantum dots that exhibit unique properties.
“The Department of Energy projects that by 2020 LEDs will produce approximately 150-200 lumens per watt and replace all other light sources for general illumination,” said Moustakas.
UV LEDs for Water/Air Purification
Dividing the ultraviolet spectrum, which extends from 10 to 400 nanometers of radiation frequency, into four domains, Moustakas called special attention to LEDs that emit light in the UV-C range (200-290 nm).
“UV-C radiation can damage microorganisms’ DNA, and we can use this radiation for water, air and surface decontamination, for example, in hospitals,” said Moustakas. “This radiation can also be used to detect chemical and biological substances, which has both medical and security implications.”
Nucleic acids in DNA and RNA absorb UV radiation from the 240-290 nm range, with peak absorption at 266 nm, he explained. A UV light source at 266 nm would prevent a microorganism’s DNA and RNA from replicating, thereby killing it.
“Recently, the U.S. Environmental Protection Agency has recommended UV-radiation as the most sound technology to inactivate pathogenic microorganisms—instead of chlorination—in public water supplies,” said Moustakas, noting that approximately 2,000 UV drinking water treatment systems exist in Europe, and 1,000 in the U.S.
Current UV-LEDs are energy-inefficient, but Moustakas’s group has produced aluminum gallium nitride alloys that promise to significantly improve UV-LED performance.
Moustakas also described some of his research group’s many scientific contributions to the development of high-performance nitride semiconductors, including progress in growing nitride semiconductors using sophisticated methods such as an atom-by-atom assembly technique called molecular beam epitaxy.
Initiated in 2008, the annual Distinguished Scholar Lecture Series honors a senior faculty member engaged in outstanding, high-impact research at the College of Engineering. The previous three recipients are Professors Irving Bigio (ECE, BME), John Baillieul (ECE, ME) and Malvin Teich (ECE).