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Speaker: Ronny Kirste, Adroit Materials, Cary, N.C.
November 1, 2019 @ 11:00 am - 12:00 pm
Speaker: Ronny Kirste, Development of the AlGaN Material System for Next-Generation UV-Optoelectronic Devices
Affiliation: Adroit Materials, Cary, N.C.
Development of the AlGaN Material System for Next-Generation UV-Optoelectronic Devices
The AlGaN material system is currently the only ultra-wide-bandgap semiconductor with demonstrated potential for implementation in UV-emitters and next generation high power devices. AlGaN epitaxial device structures are typically grown on non-native substrates such as sapphire, Si, or SiC resulting in a threading dislocation density greater than 109 cm-2. Threading dislocations and associated point defects are detrimental to the performance and reliability of devices since they allow for unwanted recombination/compensation centers and current leakage paths. This eventually leads to lower efficiency, unnecessary heating, and shortened operational lifetime. In order to overcome these limitations, the use of native GaN and AlN substrates has been proposed and established over the last few years, leading to significant performance improvements and operational breakthroughs. In this presentation, the growth of AlGaN films on such native substrates is discussed and the advancement towards novel UV optoelectronic devices is discussed. For Al-rich films grown on AlN substrates, we show that the surface morphology is a function of the miscut and growth conditions with bilayer step growth determined by the particular surface kinetics involved in the growth process. Doping of such films is challenging, but both n- and p-type doping can be achieved in such UWBG material, allowing for the technical doping needed for device applications. For Ga-rich films grown on native GaN substrates tensile strain management is necessary to avoid cracking or any other unwanted relaxation mechanism that would be detrimental for device performance. It is shown that when an appropriate relaxation scheme is applied, UVA and UVB emitters are possible. Finally, a short outlook on future challenges and the next research ideas are presented.
Dr. Ronny Kirste is the Chief Operating Officer at Adroit Materials, which develops optoelectronic devices for the UV-range including lasers, LEDs, and detectors. Prior, he served as a postdoc in the Wide Bandgaps Laboratory at NCSU developing epitaxy processes for the growth of AlGaN on native substrates. He received his PhD (2012) and Master degree (2008) in Applied Physics from the Technical University in Berlin (Germany) for his work on the optical characterization of wide bandgap materials, which included photoluminescence and Raman spectroscopy studies. Other research interests include the development of novel plasmonic materials, control of point defects, and doping of oxides and nitrides. Dr. Kirste has authored and co-authored more than 90 articles and book chapters, in addition to giving many presentations at domestic and international conferences and meetings.