| With the development of semiconductor technologies and micro manufacturing technologies,the size of light-emitting diodes has gradually decreased from the millimeter level used in traditional lighting to the micrometer level which is called micro light-emitting diode（Micro-LED）.Because of the advantages of low power consumption,long life,high brightness,strong stability,and fast response speed,it is widely used in full-color display and visible light communication.In Ga N-based green light Micro-LEDs can provide one of the three primary color light sources for full-color display that become an important research object in the field of Micro-LEDs.However,there are still many problems in In Ga N-based green Micro-LEDs:First,traditional In Ga N-based green Micro-LEDs are fabricated on polar Ga N,which is not only affected by spontaneous polarization,but also affected by piezoelectric polarization due to the lattice mismatch of the internal structure of In Ga N/Ga N multiple quantum wells The polarization will cause the energy band of the multiple quantum wells to bend and tilt,make the overlap of the wave functions of electrons and holes smaller,cause the emission wavelength to redshift,which is called quantum confinement stark effect.The internal quantum efficiency of Micro-LEDs will be reduced by quantum confinement stark effect,so that the luminous efficiency of the device reduced too.Second,as the device size decreases,the performance of Micro-LEDs will change due to a few factors such as reduced mesa area,current expansion,and non-radiative recombination.Third,because the mesa etching damaged the sidewall of the Micro-LEDs to form sidewall defects,the defects will introduce electron and hole traps,increase the SRH recombination,reduce the probability of radiation recombination,and also form a leakage current channel.The performance of Micro-LEDs will be affected by such problems.In order to solve the above problems,this paper studies In Ga N-based green Micro-LEDs,and the main conclusions are these followings from points 1-3:1.By using APSYS simulation software to simulate and analyze the different structures which is based on Ga polar,N polar,non-polar a-plane and different sizes（10μm×10μm、50μm×50μm、100μm×100μm）of In Ga N-based green Micro-LEDs,the results show that the non-polar a-plane structure can suppress electron leakage,weaken the influence of the polarization effect,thereby improve the optoelectronic properties of Micro-LEDs,and the effect of the non-polar a-plane structure is the best.Also,it is proved the influence of the sidewall defects on the device become bigger as the sizes get smaller,which will lead to the surface non-radiative recombination occupying a more dominant position,making the internal quantum efficiency lower in the lower current density,but the smaller sizes of the Micro-LEDs can make the current spread more uniform.2.The crystal quality of In Ga N-based green light multiple quantum wells with four different n-type layers were characterized by atomic force microscopy,high resolution X-ray diffraction and photoluminescence,and the luminescence properties of each sample were characterized by electroluminescence.The results show that for the multiple quantum wells of the n-type layer sample without Al composition,it has low surface roughness,more flat and smooth surface,less precipitation and aggregation of indium,low screw dislocation density and high crystal quality.Besides,the optical output power and the wall plug efficiency is higher,and the luminescence performance of the device is better.But,for the multiple quantum wells of the n-type layer sample with uniform Al composition,it makes In composition bigger,so that the emission wavelength is longer,which can be applied to long-wavelength In Ga N-based Micro-LEDs.3.Four kinds of In Ga N-based green Micro-LEDs with different passivation layer structures were obtained by the metal organic chemical vapor deposition and device preparation process.By analyzing their current-voltage characteristics,optical output power,electroluminescence and other optoelectronic characteristics,it was found that using the chemical vapor deposition to deposit Si O2 as the passivation layer on In Ga N-based green Micro-LEDs will be better compared with other passivation layers,and the results show it gets higher optical output power,stronger luminous intensity and higher electro-optical conversion efficiency.The above passivation methods can better repair the sidewall damage of the In Ga N-based green Micro-LEDs so that improve the luminous performance of it. |
