Ultraviolet Materials and Devices
The UV community for the fourth time took part in the International Workshop on Ultraviolet Materials and Devices (IWUMD4), which was organized in September 2019 by the Ioffe Institute, St. Petersburg, Russia. This event, following the successful meetings in Beijing, China (2016), Fukuoka, Japan (2017), Kunming, China (2018), was intended to show new horizons beyond the UV-blue LEDs based on wide-bandgap III-Nitrides. Material science, modeling and technology for the “UV gap” (200-300 nm) are at the frontier of applied physics. The studies are aimed at developing devices for such areas as medicine – for human-safely disinfection and rapid detection of viral threats, communication – for noise-protected and solar- blind UV-optical communication, nanotechnology – for high- resolution photolithography and for many other applications in the field of biology, pharmaceuticals and forensics.The Workshop was attended by 125 scientists from 15 coun- tries, including half from Asia and half from Europe and theDOI: 10.1002/pssa.202000378USA. The Program was very eventful and included 2 plenary talks by Prof. Chris G. Van de Walle (UCSB) and Prof. Michael Kneissl (TU Berlin&FBH), 4 keynotes, and 25 invited papers, as well as 35 oral presentations and 36 poster contributions displayed during two poster sessions. Prior to Workshop, the Tutorials on the basic properties of wide-gap semiconductor materials and nanostructures with lectures of outstanding experts in this field were held for one and a half days. The scope of the presentations at the Workshop was quite wide. Besides the fundamental properties of wide-gap semiconductor materials and nanostructures, their optical and structural characterization and applications, it highlighted new trends, such as the growth, basic properties and applications of Ga2O3 and physics of BN from bulk to 2D materials.This issue features selected reports from the Workshop participants. Recent results on the manufacture of high-quality templates of the nitrides and oxides by using differenttechnological approaches are presented. The fundamental problems of low-dimensional heterostructures and the techno- logical challenges of various epitaxial growth methods, such as molecular beam epitaxy and metalorganic chemical vapor deposition, are examined in detail to further improve the quan- tum efficiency and output power of UV light-emitting devices. A study of the optical properties of AlGaN layers and laser diode heterostructures are presented, which elucidate the nature and characteristics of spontaneous and stimulated emis- sions in AlGaN laser structures. In addition, the fabrication and radiation of GaN hexagonal microcavities are discussed. A variety of topics reflects the wide range of interests of the Workshop.The Editors would like to thank all the members of the International Advisory and Program Committees for their encouragement and great help during the Workshoporganization. We are grateful to the referees for their efforts and time devoted to the paper review process. We owe our best thanks to the official partners and sponsors of the workshop, as well as all participants at the symposium exhibition. Finally, we would like to express our sincere gratitude to Dr. Stefan Hildebrandt and the production team of physica status solidi for their friendly assistance and collaboration in the editorial process.The next 5th International Workshop on Ultraviolet Materials and Devices (IWUMD5) is planned to be held in November 2020 in Jeju, Korea. We wish the organizers a gorgeous and successful meeting.