The development of efficient (In)AlGaN light emitting diodes (LEDs) in the ultraviolet B (UVB) spectral region (280nm-320nm) is essential due to their vast commercial potential. UVB LEDs are expected to not only replace traditional mercury lamps in applications such as curing of materials and phototherapy but also to establish new applications in the fields of plant growth and sensing. Although a lot of progress has been made on the performance of the UVB LEDs, the efficiency of the devices as well as the lifetime still needs to be improved. In this study the influence of the heterostructure design and package on the efficiency of UVB LEDs, grown by metalorganic vapor phase epitaxy on c-plane sapphire substrates, will be presented. Firstly, the performance of UVB AlGaN and InAlGaN multiple quantum well LEDs were studied and the influence of the material composition on the emission characteristics was analyzed. Secondly, the performance of LEDs with different electron blocking layer (EBL) designs and doping concentrations was compared. The highest internal quantum efficiency and emission power were obtained for LEDs with a gradient-like EBL, with decreasing aluminum content, because of the improved carrier injection. Additionally, the output power of the LEDs was found to increase with the p-doping level in the EBL. Finally, investigations on the influence of the metal contacts and insulator as well as the device packaging on the performance of UVB LEDs will be presented. Based on these optimizations, 315nm LEDs with output powers up to 10mW at 100mA were realized
Neysha Lobo Ploch, Tim Kolbe, Arne Knauer, Jens Rass, Hyun Kyong Cho, Johannes Glaab, Jan Ruschel, Anna Andrle, Sylvia Hagedorn, Katrin Hilbrich, Christoph Stoelmacker, Steffen Knigge, Maria Reiner, Ina Ostermay, Andreas Thies, Deepak Prasai, Olaf Krueger, Sven Einfeldt, Markus Weyers, and Michael Kneissl, "From heterostructure design to package: development of efficient and reliable UVB LEDs (Conference Presentation)," Proc. SPIE 10532, Gallium Nitride Materials and Devices XIII, 1053220 (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287131.5751516188001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon