Enhancement Of Internal Quantum Efficiency In AlGaN-based Deep Ultraviolet LEDs Via Local Surface Plasmons Resonance

As a novel kind of solid-state UV light source,AlGaN based deep ultraviolet emitting diodes?DUV-LEDs?have many advantages,such as small volume,low power consumption,long lifetime and continuous wavelength adjustment.High-performance DUV-LEDs are of great application value in the civilian and military fields,such as disinfection,medical health and confidential communications.At present,heteroepitaxy growth on sapphire substrate is the prevailing method to manufacture AlGaN based DUV-LEDs.There is a large lattice mismatch and thermal mismatch between AlGaN and sapphire substrate,and in the MOCVD epitaxy process,the high-Al-component AlGaN material has a strong gas-phase pre-reaction,which results in a high defect density(10⁹ cm^-2)in the AlGaN material.These dislocations reach the active region of the quantum well would form numerous non-radiative recombination centers,leading to a low internal quantum efficiency?IQE?.It is widely concerned for enhancing the internal quantum efficiency of DUV-LED using resonant coupling of local surface plasmons?LSPs?on metal nanostructures.In this paper,we carried out research on enhancement of internal quantum efficiency in AlGaN-based deep ultraviolet LEDs via LSPs of Al nanostructure.we proposed a novel Al/SiO₂ composite structure to achieve the LSPs resonance in DUV region.By FDTD simulation,the extinction characteristics of triangular Al nanoparticle in half-space surrounded by AlGaN or SiO₂/AlGaN dielectrics were simulated and the influence of the dielectric on the LSPs resonance mode of triangular Al nanoparticle was systematically analyzed.Compared to AlGaN space semi-enveloping environment,by introducing SiO₂ interlayer between the triangular Al nanoparticle and AlGaN,the main peak of LSPs resonance undergoes a significant blue shift.Moreover SiO₂ interlayer greatly increases the distribution of the localized electric field at the metal-substrate side under the DUV incident light.An optimized structure corresponding to a triangular Al nanoparticle with the width of 60 nm and SiO₂ thickness of 20 nm by the simulation results.Based on the simulation,LSPs enhanced AlGaN-based MQWs was prepared via Al/SiO₂ composite structure.the photoluminescence?PL?intensity of the AlGaN-based MQWs structure was increased by 2.6 times,and the IQE obtained by the temperature-dependent PL measurement was correspondingly increased by 2.3 times.The SiO₂ insertlayer enhanced the depth of resonance penetration of the LSPs,so that the excitons in active region and the Al/SiO₂ composite structure could achieve effective LSPs resonance coupling,and the proportion of excitons involved in radiation recombination in MQWs was increased.The activation energy of non-radiative recombination obtained by fitting the temperature-dependent PL results indicated the LSPs resonance effectively inhibits the non-radiative recombination of excitons in MQWs,which resulted in the improvement of IQE for AlGaN based MQWs.