2021, Hjort, Filip, Enslin, Johannes, Cobet, Munise, Bergmann, Michael A., Gustavsson, Johan, Kolbe, Tim, Knauer, Arne, Nippert, Felix, Häusler, Ines, Wagner, Markus R., Wernicke, Tim, Kneissl, Michael, Haglund, Åsa

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm). © 2020 American Chemical Society. All rights reserved.

2017, Kolbe, Tim, Knauer, Arne, Rass, Jens, Cho, Hyun Kyong, Hagedorn, Sylvia, Einfeldt, Sven, Kneissl, Michael, Weyers, Markus

The effects of composition and p-doping profile of the AlGaN:Mg electron blocking layer (EBL) in 310 nm ultraviolet B (UV-B) light emitting diodes (LEDs) have been investigated. The carrier injection and internal quantum efficiency of the LEDs were simulated and compared to electroluminescence measurements. The light output power depends strongly on the temporal biscyclopentadienylmagnesium (Cp 2 Mg) carrier gas flow profile during growth as well as on the aluminum profile of the AlGaN:Mg EBL. The highest emission power has been found for an EBL with the highest Cp 2 Mg carrier gas flow and a gradually decreasing aluminum content in direction to the p-side of the LED. This effect is attributed to an improved carrier injection and confinement that prevents electron leakage into the p-doped region of the LED with a simultaneously enhanced carrier injection into the active region.

2020, Amano, Hiroshi, Collazo, Ramón, De Santi, Carlo, Einfeldt, Sven, Funato, Mitsuru, Glaab, Johannes, Hagedorn, Sylvia, Hirano, Akira, Hirayama, Hideki, Ishii, Ryota, Kashima, Yukio, Kawakami, Yoichi, Kirste, Ronny, Kneissl, Michael, Martin, Robert, Mehnke, Frank, Meneghini, Matteo, Ougazzaden, Abdallah, Parbrook, Peter J., Rajan, Siddharth, Reddy, Pramod, Römer, Friedhard, Friedhard, Jan, Sarkar, Biplab, Scholz, Ferdinand, Schowalter, Leo J, Shields, Philip, Sitar, Zlatko, Sulmoni, Luca, Wang, Tao, Wernicke, Tim, Weyers, Markus, Witzigmann, Bernd, Wu, Yuh-Renn, Wunderer, Thomas, Zhang, Yuewei

Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm - due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments. © 2020 IOP Publishing Ltd.