MSE Ph.D. Seminar: Brelon May, Investigation and Engineering of the Homogeneity and Current Injection of Molecular Beam Epitaxy Grown III-Nitride Nanowire Ultraviolet LEDs

This presentation is not part of MSE 7895, though MSE graduate students are welcome to attend.

Abstract

The III-Nitride material system has found applications in sensors, photovoltaics, lasers and LEDs. The versatility is in large part to the wide range of direct bandgaps spanning form the infrared to the deep ultraviolet. Typical devices are thin-films, three-dimensional structures where the formation of strain related defects limits the choice of substrate and restricts the device engineering opportunities. Conversely, nanowires are one-dimensional structures which effectively relieve strain without the creation of defects, enabling the use of innovative substrates and increasing engineering flexibility. However, self-assembled nanowires have inherent nonuniformities that inhibit macroscopic device efficiency. The work presented here will be focused on nanowire LEDs with emission in the ultraviolet grown via molecular beam epitaxy. The differences between individual nanowires and how these disparities manifest in macroscopic devices are examined. The use of a short-term-overload bias will be established as a way to reduce the presence of some nonuniformities, increasing the efficiency of ensemble devices. The use of metal substrates for III-Nitride nanowires is also investigated; and the grain-dependent nonuniformities that arise due to growth on polycrystalline foils will be discussed. These “large-scale” uniformity issues are shown to be addressed through the use of nanocrystalline films and amorphous metallic glass. Various types of metal are shown to be suitable substrates for high-quality GaN nanowires. The growth and fabrication of nanowire UV LEDs and their characteristics on these new materials will be discussed. Finally a different nanowire LED structure is introduced, in which the upper portion of the nanowires is coalesced, giving a 35× increase in efficiency.

Bio

Brelon May received his B.S in 2013 from Clarkson University in Potsdam, New York in Chemical Engineering. He is currently a PhD candidate in the materials science and engineering department at the Ohio State University, where he has worked with Prof. Roberto Myers on the epitaxial growth of various material systems. His focus has been on nanowire based ultraviolet LEDs and he created the first UV LED on metal. This lead to a top story in NSF Science360 News and a feature in Semiconductor Today. He has won numerous student talk awards at international conferences and was the winner of the 3 Minute Thesis at Ohio State in 2018. In 2016 he was runner-up for the Ohio State University Student Innovator of the Year award and was awarded the Presidential Fellowship for his final year of research.