Graphene serves as both substrate and transparent electrode in ultraviolet LEDs

Researchers at the Norwegian University of Science and Technology (NTNU) in Norway, Sophia University in Japan and SINTEF Industry, Norway have demonstrated the use of graphene as both a growth substrate and transparent conductive electrode for an ultraviolet light-emitting diode.

Top- and bird-view SEM images of nanocolumns grown on DLG transferred onto amorphous silica glass

The team focused on a flip-chip configuration, where GaN/AlGaN nanocolumns were grown as the light-emitting structure using plasma-assisted molecular beam epitaxy. Although the sheet resistance increased after nanocolumn growth compared with pristine double-layer graphene, the experiments showed that the double-layer graphene functioned adequately as an electrode. The GaN/AlGaN nanocolumns were found to exhibit a high crystal quality with no observable defects or stacking faults.

The team has shown that graphene can be used as a substrate for the growth of GaN/AlGaN nanocolumns, and subsequently as the transparent electrode in a fabricated UV-A LED device. Although graphene gets damaged by plasma-activated nitrogen during the nanocolumn growth, it retains its prominent characteristics and functions as a transparent electrode.

These results indicate that graphene can be used as a functional substrate and electrode for III-nitride-based device technology. Furthermore, this work indicated several possible steps for growth and device design optimization to improve the EQE now that this platform has been established.