| AlGaN-based deep ultraviolet(DUV)light-emitting diodes(LEDs)have received widespread attention for their long operating life,small size,controllable wavelength,and low power consumption,making them an ideal new generation of solid-state UV light sources.High-efficiency DUV LEDs have been used in air/water purification and sterilization,and have great potential for applications in confidential communications,optical medicine,and anti-counterfeit detection.However,the luminous efficiency of AlGaN-based DUV LEDs is currently at a low level,and the main reasons include the TM-mode dominated light polarization in high Al component AlGaN materials,severe total internal reflection due to the high refractive index difference at the semiconductor/air interface,and the absorption of deep UV light by GaN layers and metal electrodes,which keeps the light extraction efficiency at a low level.The use of metal localized surface plasmonic excitations(LSPs)resonance to improve the light extraction efficiency is a proven method and has become a research hotspot for improving the light extraction efficiency of DUV LEDs.In this paper,we focus on the resonance properties of Al nanocomposite structured LSPs,and through simulation and device preparation,we deeply investigate the effect of the coupling effect between LSPs and excitons on the luminescence efficiency of deep UV LED quantum wells,and obtain the following conclusions:(1)This thesis innovatively proposes the use of graphene/Al nanoparticles/graphene(Gr/Al-NPs/Gr)composite structure to achieve the resonance enhancement of LSPs in the deep UV band.Based on the finite element analysis,the electric field distribution characteristics of the hemispherical Al-NPs in single and composite structures are simulated and the effects of metal particle size and period variation on the LSPs resonance characteristics of hemispherical Al-NPs are systematically analyzed.Compared with Al-NPs,the surface electric field intensity of hemispherical Al-NPs at resonant excitation is increased by a factor of 3.1 by introducing graphene dielectric layer at the bottom and top of metal nanoparticles,and the distribution range of local electric field at the metal-substrate end is further expanded.(2)Based on the simulation results,the composite structure of Gr/Al-NPs/Gr sandwich type LSPs was prepared.The parameters such as the period of metal nanoparticles can be adjusted by a high-temperature rapid thermal annealing process,and an optimized annealing temperature of 500℃ was obtained experimentally.Based on the dehumidification effect,the introduction of graphene layer makes the high-temperature annealed Al-NPs have a periodic distribution and more uniform particle size,in which the nanoparticle diameter is～54 nm and the standard deviation is only 4.8 nm.in the static absorption spectroscopy test,the resonance absorption intensity of the composite structure LSPs is significantly increased and the resonance wavelength is red-shifted.Meanwhile,the increase in the number of graphene layers leads to an increase in resonance absorption intensity and absorption red-shift.(3)Gr/Al-NPs/Gr sandwich-type and other composite structure-enhanced AlGaN-based deep-ultraviolet quantum wells were prepared experimentally.The photoluminescence(PL)test results show that the addition of graphene layers all increase the luminescence intensity of the quantum wells,in which the luminescence intensity of the sandwich-type composite structure-enhanced AlGaN quantum well structure is nearly three times that of the original structure.The graphene insertion layer greatly increases the intensity of the local electric field around the Al-NPs,which makes the resonance intensity of the LSPs increase;meanwhile,the increase of the skinning depth further increases the proportion of excitons involved in the coupling out of the LSPs in the active region.Therefore,the Gr/Al-NPs/Gr composite structure can significantly improve the light extraction efficiency. |
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