Special Materials Science & Engineering Seminar
IBM Research, Thomas J. Watson Research Center
"Gallium Nitride Compound Semiconductors for Ultraviolet, Visible, and Terahertz Photonics"
Gallium Nitride (GaN)-based compound semiconductors, throughout their entire composition (tuned by varying the Aluminum (Al), Gallium (Ga), and Indium (In) elemental content), possess direct bandgap and their bulk-layer-spectrum can be tuned from deep ultraviolet (~200 nm) to near-infrared (~1700 nm). Furthermore, subband-energy engineering of AlGaN/GaN superlattice quantum structures enable the spectral response be pushed up to terahertz (~300 um). As such, GaN-based photonic technology can be used in everyday to biotech and scientific applications including solid state lighting; detection of bio-agents/drugs/explosives; and optogenetics.
In the first part of my talk, I will be focusing on ultraviolet and visible spectrum light emitting diodes (LEDs). Ultraviolet (UV) spectrum is very important as many biological agents (e.g. anthrax) and biological tissues (e.g. cells) are responsive only in UV but yet UV LEDs lack of desired performance. Visible spectrum LEDs are most critical in general lighting thanks to supreme energy conversion efficiency but yet cost-effectiveness pose a threat for reaping the global energy-savings benefits. After a brief review, I will be discussing integration of such LED technologies with silicon as a means of bringing affordability and further functionality.
In the second part of my talk, I will be focusing on infrared to terahertz quantum devices. Terahertz (THz) spectrum offers promising scientific (e.g. cancer detection), industrial (e.g. product defect detection), and military (e.g. explosives detection) applications. Thus yet, generation of THz frequency is rather challenging as it lies at the cusp of electronic and photonic frequencies - creating the so-called "THz gap". Large conduction bandoffset (~1.8 eV), large longitudinal optical phonon energy (~90 meV), and fast carrier dynamics (~ fs) of GaN compound semiconductors motivate for THz emitters. I will summarize recent intersubband device results (i.e. optical modulators and resonant tunneling diodes) and then move to discussing promising THz emitter schemes.
In conclusion, with continuous developments from materials to devices, GaN-based compound semiconductors extend their unique photonic solutions from ultraviolet and visible wavelengths towards THz spectrum.
Dr. Can Bayram is currently working as a Postdoctoral Research Scientist at IBM Thomas J. Watson Research Center, Yorktown Heights, NY. As a part of his current postdoctoral work, he is part of the Advanced Substrate Research group in the Silicon Technologies Division and working with Dr. Devendra Sadana. He received the Ph.D. degree in 2011 from Electrical Engineering and Computer Science Department of Northwestern University, IL with a focus on Solid State and Photonics. During his doctoral work, he worked with Prof. Manijeh Razeghi and was part of the Center for Quantum Devices research center.
His research interests focus on GaN technology and novel photonic devices. He is an expert in the development of InGaN-based visible light emitting diodes and high efficiency III-V solar cells, and interested in novel growth and fabrication technologies. He has (co-)authored 29 high-impact journal papers with more than 50 ISI-indexed scientific contributions (h-index ≥ 14). He is an active reviewer for journals and agencies, and regularly serves on the conference program and fellowship committees.
Dr. Bayram is the recipient of most distinguished world-wide awards including 2012 Best Paper Award in MIOMD-XI, 2010 IBM PhD Fellowship, 2010 Link Foundation Energy Fellowship, 2010 IEEE Electron Devices Society PhD Fellowship, 2009 Boeing Engineering Student of the Year, 2009 IEEE Photonics Society Graduate Student Fellowship, 2009 SPIE Laser Technology, Engineering and Applications Scholarship, 2009 Ludo Frevel Crystallography Scholarship, and 2008 Dow Sustainability Innovation Award.
Host: Prof. I.C. Noyan