Virtual and CREOL: CROL-103

Title: The development of AlGaN ultrawide bandgap (UWBG) semiconductors on native AlN substrates for UVC and far UVC device applications

Abstract: Ultrawide bandgap semiconductors (bandgaps greater than 4.5 eV) have attracted recent attention for new applications in high power switches (EV and smart grid) and high-power rf. UWBG semiconductors are also being used to make novel light emitters at wavelengths shorter than 280nm. However, the UWBG semiconductors still present big challenges in growth and doping. One of the best examples are the pseudomorphic AlGaN alloys gown on high quality AlN substrates where 2-inch diameter is now widely available and 100mm are being sampled. These single-crystal AlN substrates have enabled growth of high quality Al1-xGaxN alloys that are pseudomorphically strained to match the lattice of the underlying AlN substrate. The low extended defect density has made it possible to take advantage of a new kind of conductivity (distributed polarization doping) made possible in materials that have a spontaneous polarization. Most significantly, p-type Al1-xGaxN has now been demonstrated in Al1-xGaxN without the use of impurity doping. This breakthrough solved the critical problem of unacceptable resistivities in the doped layers with increasing band gap (particularly for p-type dopants).

Pseudomorphic growth and distributed polarization doping have made the achievement of new devices possible, such as the UVC laser diode. These laser diodes open new possibilities for optical instruments which will benefit from very compact sources of radiation which are coherent and nearly monochromatic. It is also possible to precisely direct laser radiation in ways that simply are not possible for LEDs. As this technology develops, it may even be possible to achieve higher wall plug efficiencies than are achievable with UVC LEDs due to improved photon extraction efficiencies. However, the lifetime of these diodes (which operate at much higher current densities than LEDs) is still an important issue that needs to be addressed.

In this talk, I will give an introduction to the societal issues that can be addressed by UWBG semiconductors as well as explaining why there are still issues with these special materials. I will explain so-called "distributed polarization doping" and how we used this phenomena to make the world's first UVC laser diode. I will also introduce our new effort at the Visium UltraLabs in the Cornell Tech Park to develop far UVC (shorter than 235nm) LEDs.

About the Speaker: Leo Schowalter was employed by the GE Global Research Center after receiving his Ph.D. in Physics from the University of Illinois in 1981. He was a professor in the Rensselaer Polytechnic Institute Physics Department from 1987 until 2006 and was Department Chair from 1997 to 2000. In 1997, he co-founded Crystal IS where he was the first CEO and later CTO until he retired in 2021. Schowalter continues the collaboration with Prof. Amano as a Visiting Professor but has also now joined the Florida-based startup company Lit Thinking which is developing cost-effective far UVC for safe disinfection of shared spaces. Schowalter is also leading the effort to found the Visium Ultralabs in the Cornell Tech Park, with support from Lit Thinking, to develop the AlGaN ultrawide bandgap semiconductors including for far-UVC light emitters for human safe disinfection.

Virtual Location URL: https://ucf.zoom.us/j/96065292638#success