Applications Of Graphene In LEDs And Plasmonic Devices

Graphene,a two-dimensional honeycomb lattice of carbon,possesses intriguing mechanical,thermal,electrical and optical properties that make it attractive for a broad range of applications in optoelectronic devices in future.Theoretically,the sheet resistance and transmittance of the pristine graphene film are about 31?/sq and 97.5%,respectively,and its electron mobility can reach 21000 cm2/(V·s)at room temperature.Therefore,graphene is considered as the next generation transparent conductive electrode in place of Indium tin oxide(ITO)for applications in light emitting diodes(LEDs).Researches show that the highly confined plasmonic wave for a wide wavelength range from mid-infrared to THz can propagate many micrometers in a continuous graphene layer.Thus,graphene is also used as the platform to fabricate highly integrated active plasmonic devices such as optical modulator,modulator,filter.The main conclusions in this paper are listed as follows:1.Through the researches on the properties of the CVD-synthesised graphene,which is transferred to SiO2,gallium nitride(GaN)bulk material and GaN nanopillar,by using the optical microscope,Raman scattering,atomic force microscopy(AFM)and scanning electron microscopy(SEM),it is confirmed that the monolayer graphene with a low defect density can closely contact with the substrate material.Besides,the tensile strain exists in the graphene suported by GaN nanopillar and its ability to transfer heat declines.2.Through the researches on the opto-electrical properties of the graphene-electrode LEDs without and with a NiOx inter-layer,it is confirmed that graphene can succeed in providing efficient current spreading and hole injection into the active layers of the LED for light emission.Moreover,the EL performance of the device is enhanced by 1.5 times by introducing a 3nm-thick NiOx inter-layer between graphene and p-GaN and its overall performance can compare favourably with that of the conventional ITO-electrode LEDs.The enhancement is due to the reduced ohmic contact resistance between graphene and p-GaN deriving from the impact of the NiOx inter-layer with a large work function and high hole concentration.3.Through the study on the material properties of graphene film such as the conductivity,the transmittance and the dielectric function,it is confirmed that the continuous graphene can support the propagation of the TE-mode and TM-mode surface plasmonic wave.Two-dimensional periodic nanopillar array can compensate the momentum mismatch between the incident light and surface plasmonic wave in graphene,so the surface plasmonic wave can be excited,which lay a theoretical foundation for the preparation of graphene-based active plasmonic devices.