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- ItemImproving AlN Crystal Quality and Strain Management on Nanopatterned Sapphire Substrates by High-Temperature Annealing for UVC Light-Emitting Diodes(Weinheim : Wiley-VCH, 2020) Hagedorn, Sylvia; Walde, Sebastian; Susilo, Norman; Netzel, Carsten; Tillner, Nadine; Unger, Ralph-Stephan; Manley, Phillip; Ziffer, Eviathar; Wernicke, Tim; Becker, Christiane; Lugauer, Hans-Jürgen; Kneissl, Michael; Weyers, MarkusHerein, AlN growth by metalorganic vapor-phase epitaxy on hole-type nanopatterned sapphire substrates is investigated. Cracking occurs for an unexpectedly thin-layer thickness, which is associated to altered nucleation conditions caused by the sapphire pattern. To overcome the obstacle of cracking and at the same time to decrease the threading dislocation density by an order of magnitude, high-temperature annealing (HTA) of a 300 nm-thick AlN starting layer is successfully introduced. By this method, 800 nm-thick, fully coalesced and crack-free AlN is grown on 2 in. nanopatterned sapphire wafers. The usability of such templates as basis for UVC light-emitting diodes (LEDs) is furthermore proved by subsequent growth of an UVC-LED heterostructure with single peak emission at 265 nm. Prerequisites for the enhancement of the light extraction efficiency by hole-type nanopatterned sapphire substrates are discussed. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemStatus and Prospects of AlN Templates on Sapphire for Ultraviolet Light-Emitting Diodes(Weinheim : Wiley-VCH, 2020) Hagedorn, Sylvia; Walde, Sebastian; Knauer, Arne; Susilo, Norman; Pacak, Daniel; Cancellara, Leonardo; Netzel, Carsten; Mogilatenko, Anna; Hartmann, Carsten; Wernicke, Tim; Kneissl, Michael; Weyers, MarkusHerein, the scope is to provide an overview on the current status of AlN/sapphire templates for ultraviolet B (UVB) and ultraviolet C (UVC) light-emitting diodes (LEDs) with focus on the work done previously. Furthermore, approaches to improve the properties of such AlN/sapphire templates by the combination of high-temperature annealing (HTA) and patterned AlN/sapphire interfaces are discussed. While the beneficial effect of HTA is demonstrated for UVC LEDs, the growth of relaxed AlGaN buffer layers on HTA AlN is a challenge. To achieve relaxed AlGaN with a low dislocation density, the applicability of HTA for AlGaN is investigated. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemThe 2020 UV emitter roadmap(Bristol : IOP Publ., 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, YueweiSolid 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.