Study On Temperature And Radiation Characteristics Of Thermal Electron Light Emission From Graphene

Benefit from the unique two-dimensional honeycomb-like lattice structure,graphene has superior electrical,optical and thermal properties,electrically biased graphene has recently demonstrated excellent performance in high-frequency circuit,ultra-fast photoelectric detection and thermal emitter.In recent years,the thermal radiation in nanometer scale has attracted great interest,especially for the thermal transport properties of two-dimensional materials.Graphene has only one layer of carbon atoms,excellent thermal conductivity,low heat capacity and it can withstand extremely high current densities,making it a perfect platform for studying micro-nano scale thermal radiation.In this thesis,We studied the influence of narrow constrictions and different substrates on thermal radiation characteristics of graphene.The main conclusions are listed as following:1.The lattice temperature distribution of graphene is determined by an integrated system of self-assembled electronics and spatially resolved Raman spectroscopy.Most of the heat in graphene dissipated through the substrate and the metallic contacts.Because of the oxidation,the highest temperature is 500K at the middle of silicone-based graphene without constrictions in air.In contrast,due to the greatly enhanced Joule heating effect,for graphene devices with constriction exposed in air,the highest temperature approaches 900K and 1300K for Gr-C-1.5?m and Gr-C-1.0?m,respectively,which clearly showed a localized“hot spot”.2.With the effective combination of constriction and h BN encapsulated graphene,the graphene is isolated from the oxygen.We observed bright visible light emission from h BN encapsulated graphene constriction device at a smaller V_b in air.Strikingly,we found that the light emission is perfectly confined at the constriction,and the power density are less,compared with previous h BN encapsulated graphene emitters without constrictions(?400 k W·cm^-2).The resonance effect from a photonic cavity formed by the h BN/air and SiO₂/Si interfaces,dramatically tailors the emission spectrum of graphene to visible range.Since the higher the temperature is,the more energy the electron gains.The intensity of emission spectra monotonically increases as increased V_b.3.A 4×4 graphene emitters array is realized using chemical vapor deposited graphene and atomic layer deposited Al₂O₃ capping layer.The 16 emitter units have different constriction sizes.They demonstrate stable and size-dependent electrical illumination in air,normal devices without constriction cannot shine light,while all graphene constrictions emit visible photons under the same voltage.The measured intensity of thermal emission from graphene constrictions is highly size-dependent,the narrower the constrictions are,the stronger the light illuminate.In our study,we provides an effective approach for large-scale fabrication of graphene emitters array.4.With simulation calculation,we have got the temperature distribution for 3cases.They are electrically biased graphene supported by SiO₂,encapsulated by h BN,supported by SiO₂ and covered by Al₂O₃ respectively.We found that the calculation results agree very well with the experimental results.5.We demonstrate a simple device structure of silicon-based graphene device by doping effect of photo excitation.They have high responsivity of 500 A/W for 450 nm light and 4 A/W for 1064 nm light at room temperature.The light absorption in the silicon/silicon oxide(Si/SiO₂)substrate generates an additional photovoltage which effectively modulates the conductance of graphene.The generated photocurrent changes with applied gate voltage and shows a strongly nonlinear power dependence.