Study On Luminous Efficiency Lifting Method Of GaN-based Yellow-green LED

Recent years,light-emitting diodes(LED)have attracted more and more attention due to its advantages of small size,high efficiency,energy saving,eco-friendly and long lifetime.It is widely used in varies solid state lighting and display devices.The ?-? family materials,represented by GaN,has the characteristics of wide bandgap,large carrier mobility,high stability and strong radiation resistance.It has became the basis for the fabrication of light-emitting diodes.With the development of science and technology,the research of GaN based light-emitting diodes has made great progress.However,there are still some problems that restrict the development of LED industry,such as the lattice mismatch caused by heteroepitaxy,the quantum-confined Stark effect caused by polarized electric field,and the efficiency droop with high-power.In this paper,a series of research work has been carried out in the yellow green light emitting diodes.The possibility of improving the device performance is explored by optimizing the structure and growth conditions.Firstly,according to the characteristics of InGaN materials,the low-temperature p-GaN transition layer and superlattice electron barrier structure were designed.The influence of the low temperature p-GaN transition layer and the superlattice electron barrier layer on the photoelectric performance and efficiency degradation of LED was studied.The simulation results of the simulation software APSYS show that compared with the traditional LED structure,the new structure can alleviate the polarization electric field inside the crystal,especially nearby the active region,enhance the hole injection efficiency,prevent the electron leakage more effectively,improve the electronic hole recombination efficiency,thus strengthening the luminous performance.The simulation results of the simulation software APSYS show that,compared with the traditional LED structure,the new structure can alleviate the polarization electric field inside the crystal especially nearby the active region,enhance the hole injection efficiency,block the electron leakage better,improve the electronic hole recombination efficiency,and strengthen the luminous performance.At the same time,according to the experimental results,after inserting LT p-GaN transition layer,the quantum well active region is well protected,and the epitaxial wafer has better crystalline quality,and the number of dislocations inside the crystal is reduced.Also,the use of superlattice electron barrier can further enhance the photoelectric properties of the device.Finally,compared with the traditional LED,the enhanced output power about 41.9% was achieved at the injection current of 100 mA and efficiency droop problem can be significantly improved.Considering the influence of quantum well on device performance,we further design an optimal scheme to explore how to grow quantum well better.We designed three sets of experiments to investigate the effect of barrier growth temperature,barrier growth thickness and well layer thickness on device performance.The growth temperature of the barrier layer directly affects the performance of the well barrier interface.The barrier layer grown at a certain temperature can well protect the well layer and mitigate component fluctuations.The well layer is related to the polarization electric field inside the crystal and the limiting effect of the quantum well on the carrier.Therefore,the thickness also has a great influence on the luminescence property.As the well layer becomes thinner,the quantum-confined Stark effect can be alleviated and the risk of electron leakage is increasing.When the thickness of the well layer is a certain value,the overall luminescence performance and pressure resistance characteristics of the sample are relatively good,and the overall characteristics are optimal.The thickness of the barrier layer also affects the crystal quality of the crystal.Sample grown at specific barrier thicknesses has relatively small screw dislocations and edge dislocation densities inside the crystals,better crystal quality,fewer non-radiative recombination centers,higher electron-hole recombination efficiency,and higher luminous efficiency.We analyzed the effects of quantum well growth factors on the overall performance of LED devices from the aspects of well barrier interface properties,crystal crystallization quality,limitation of carriers by quantum wells,and internal composition fluctuations,and found the optimal quantum well growth scheme,thereby obtaining the LED with best device performance.Through software simulation and experiments,this paper gives effective measures to improve the efficiency of hole injection in quantum wells and improve the quality of crystallization,improve the luminous efficiency of LED devices,alleviate the phenomenon of efficiency degradation,and give a certain direction for further improving the performance of yellow-green LEDs.