Ida Marie Høiaas (1), Andreas Liudi Mulyo (1,2), Dong-Chul Kim (1), Bjørn-Ove Fimland (1), Katsumi Kishino (2), Helge Weman (1)
(1) Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway 
(2) Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-Ku, 102-8554 Tokyo, Japan

Ultraviolet light sources are used for water and air disinfection, but traditional thin film AlGaN-based LEDs in the deep UV spectrum (200-300 nm) suffer from low internal and external quantum efficiencies. AlGaN nanocolumn-based LEDs show promise of mitigating these shortcomings as they have efficient lattice relaxation and can be grown on foreign substrates in a heteroepitaxial manner. This also allows for more freedom in the device design. Graphene is an especially promising growth substrate, as it is transparent in the deep UV region. We have investigated the growth of GaN/AlGaN nanocolumns by molecular beam epitaxy (MBE) on single- and double-layer graphene transferred onto fused silica. A fabrication process for flip-chip GaN/AlGaN nanocolumn LED devices has been developed where graphene on silica is a transparent top-contact for the UV light emission.  Van der Pauw and Raman measurements were used to check the sheet resistance and material quality of the graphene electrode before and after processing the combined graphene/nanocolumn device. Partial and complete LED devices were grown on single- and double-layer graphene and optoelectrical measurements were carried out. 

Ida Marie Høiaas is currently a PhD student at the Norwegian University of Technology and Science (NTNU), at the Department of Electronics and Telecommunications. Her research is mainly focused at developing optoelectronic devices combining 1D- and 2D-materials. She received her MSc. degree in Nanotechnology from NTNU in 2014.