Improve The Emission And Color Conversion Efficiency Of Micro-LED With Nano-materials And-structures

Micro-light-emitting diodes(Micro-LEDs,μLEDs)are regarded as the core technology of the new generation of displays.Therefore,it has been widely concerned and studied in recent years.Different from LED with traditional size,the size of Micro-LED is often reduced to less than 100 Microns.The smaller size makes Micro-LED has more obvious advantages and characteristics,which means its application scenarios will be more multidimensional and diversified.At present,the application scenarios of Micro-LED include display panels,VR/AR,optical communication,biomedicine and flexible wearable devices,et al.Due to the smaller size of Micro-LED,the proportion of the side wall is significantly increased and the effect of sidewall defects introduced by sidewall etching will be more significant.The non-radiative recombination center mainly composed of sidewall defects leads to the loss of a large amount of energy through the non-radiative recombination process,resulting in the low emission efficiency of Micro-LED.The low emission efficiency limits the application of Micro-LED in various fields.Therefore,studying how to improve the emission efficiency of Micro-LED is still the basic task and main goal at this stage.Besides,the difficulty of colorization also limits its application.There are two main schemes for Micro-LED colorization at the moment.One way is using three primary pixels(red,green and blue Micro-LED)transferred and spliced to a new substrate to form full-color emitting.The other way is to realize colorization by absorbing and transforming the light from the light source through quantum dots(QDs).The scheme of three primary pixels splicing needs to mass transfer pixels from one substrate to another,which will consume a lot of time and resource costs.Meanwhile,the efficiency and yield problems caused by the mass transfer process are still the bottlenecks in engineering.Therefore,this is still not an ideal way to achieve colorization at this stage.In recent years,the rapid development of QDs research has given the bright prospect for the Micro-LED color conversion application and become the main way to realize Micro-LED colorization.Even so,this scheme to achieve full color still faces many challenges,such as limited by the light extraction of Micro-LED itself and the absorption and conversion efficiency of QDs.The final color conversion efficiency still needs to be greatly improved.This thesis mainly focuses on two topics: one is how to improve the emission efficiency of Micro LED,and the other is how to improve the color conversion efficiency of Micro LED.Firstly,how to directly and effectively improve the emission efficiency of Micro-LED is studied,which mainly using a localized surface plasmon(LSP)coupled with multiple quantum wells(MQW)to improve the energy utilization efficiency,thus enhance the final emission efficiency.In addition,in the aspect of color application of Micro-LED,the improvement of color conversion efficiency of quantum dots Micro-LED is emphatically studied.By optimizing the structure of Micro-LED and using a non-radiative energy transfer method,a higher color conversion efficiency was finally achieved.The main research contents of this thesis are as follows:1.A new method of LSP produced by noble metal nanoparticles(NPs)coupling with MQW is proposed to improve the emission efficiency of Micro-LED.This method provides an additional channel for energy transfer,allowing partial energy to be preferentially transferred to a LSP system before reaching the non-radiative recombination center,achieving maximum energy utilization.Due to the field generated by the LSP is a evanescent field,and the range of field is limited to tens of nanometers,the closer the metal nanoparticles are to the multiple quantum wells,the stronger the coupling effect.With the continuous reduction of the size of Micro-LED,the proportion of side wall emission in the total light emission area will gradually increase.The advantages of LSP coupling will be more prominent in Micro-LED devices with high sidewall ratio.In this thesis,the above conjectures are verified firstly.Metal nanoparticles are added to Micro-LED of different sizes.It is found that the smaller the size of Micro-LED,the more obvious the final light output increase,and with the increase of current density,the more obvious the enhancement,which effectively confirms the feasibility of the application of the LSP coupling in Micro-LED;Furthermore,in order to increase the effect of LSP coupling,Micro-LED structure was optimized,and array nanoholes and nanorods structures were proposed,which provided more sidewall area for metal nanoparticles to contact,and played a role in increasing light extraction.In the nanohole structure,by etching the nanohole to the active area,a large amount of multiple quantum wells region is exposed,which can be directly contacted by the filled nanoparticles,greatly increasing the coupling efficiency of the LSP.In addition,graphene is used to replace ITO as a transparent conductive layer in the structure of nanorod array Micro-LED structure,which reduces the material cost and connects the independent nanorod structure.The final results of the experiments confirm that the emission efficiency of Micro-LED structure assisted by LSP has been improved in different degrees.2.The non-radiative energy transfer(NRET)method was used to improve the color conversion efficiency(CCE)of QDs based Micro-LED.By optimizing the structure of Micro-LED,a kind of Micro-LED with array nanohole structure was designed.The nanohole was etched to the N-Ga N layer to make QDs and MQW have no distance contact,greatly improved the efficiency of NRET,and finally achieved a large improvement in CCE.Through the TR-PL analysis of this system,the energy transmission path in the system is further understood.In comparison with the typical planar spin-coated QDs-based Micro-LED,we found that the CCE of this new type of nano-hole Micro-LED has increased by about 118% compared with the former,which effectively accelerated the industrialization of color conversion Micro-LED.3.Nanosized n LED was designed and fabricated.By using NRET method to increase the color conversion efficiency,compared to the above work,the color conversion efficiency of this n LED is much higher.Through theoretical analysis,as the size of LED continues to decrease,the proportion of LED sidewall emission gradually increases,and the application of NRET method can more intuitively and effectively increase Micro-LED color conversion efficiency.In addition,during the process of studying n LEDs,due to size constraints,traditional DC injection schemes are no longer applicable.Therefore,in this work,a single ended contact AC injection method is proposed to light n LEDs,and the principle of this method is also analyzed,demonstrating the feasibility of AC injection lighting LEDs.