Brightness improvement in a graphene inserted GaN/ZnO heterojunction light emitting diode

Heat dissipation is a crucial issue for heterojunction light emitting diodes (LEDs) because the requirement of high brightness necessitates higher current densities that would trigger more joule heating. We demonstrate that the embedded graphene in a ZnO/MgO/GaN LED alleviates self-heating issues by virtue of its heat-spreading ability and improves the brightness of the device. The effect of graphene was studied by optical characteristics, energy band structure and thermal field simulation of the devices. The optimized device acts as an LED with ultraviolet emission at 397.4nm. Compared with the one without graphene, a 6.2-fold improvement in intensity and a 16.8 nm blue shift in central wavelength were obtained. The graphene induced heat sinking on the junction area was proposed to explain this optical improvement. Followed by thermal simulation, the joule heat related photoluminescence suppression of individual ZnO microrods further proves the mechanism.